Just in Time Inventories and Scheduling Procedures

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Just-in-Time and Lean Systems

Learning Objec�ves A�er comple�ng this chapter, you should be able to:

Understand the rela�onship among just-in-�me, lean systems, and the Toyota Produc�on System. Explain the basic concepts of just-in-�me (JIT). Describe the "pull" system. Explain how JIT simplifies a firm's opera�ons. Discuss the rela�onship between JIT and planning. Apply the concept of JIT to service opera�ons. Discuss strategic planning and JIT.

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11.1 Foundations of Just-in-Time and Lean

The Japanese automaker Toyota is o�en credited with the conceptual development of just-in-�me (JIT) produc�on, but the roots of this system can be found in the development and applica�on of the assembly line where work is organized in a con�nuous flow, and inventory and wasteful ac�vi�es are removed. Toyota claims that the original concept of JIT was used by Henry Ford, who applied these concepts to improve automobile assembly more than 100 years ago. While the United States grew lax in its applica�on of these concepts a�er World War II, the Japanese grasped these ideas, merged them with Deming's (1986) and Juran's (1988) quality management, and incorporated this approach into its supply chains. This was called the Toyota Produc�on System, and it is the basis for JIT. JIT is used by many organiza�ons throughout the world, including GM, Apple, and IBM. The basic techniques underlying JIT have now evolved into the concept known as lean systems, which was conceptualized by Womack and Jones (1990). It is reasonable to argue the development of JIT and lean stand on the shoulders of the Toyota Produc�on System and the Ford Motor Company. Today, JIT and lean systems are being implemented through the en�re supply chain, making these techniques powerful tools for cu�ng costs, reducing �me, and improving quality.

When the success of Japanese companies first brought a�en�on to JIT, many people outside of Japan immediately classified it as an inventory control system. JIT was o�en referred to under other names, including "stockless produc�on" and "zero inventories." Lowering levels of inventory is one possible approach to implementa�on, but JIT can also be much more than another system for controlling inventory. Some companies that are strong believers in the en�re JIT philosophy find it amounts to a philosophy of how an en�re company should operate. Thus, JIT is defined as a philosophy of opera�on that seeks to maximize efficiency and eliminate waste in any form. In its broadest sense, JIT influences all parts of a company, including purchasing, engineering, marke�ng, personnel, and quality control, and can determine the rela�onships among the company, its suppliers, and its customers. The benefits of JIT can carry far beyond cost savings due to reduced inventories, extending into a company's strategic planning. Today, this broader view of JIT is o�en referred to as lean manufacturing, lean thinking, lean systems, or, simply, lean.

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Oil refineries use a con�nuous flow process in which work-in-process inventories are kept to a minimum, and material flows smoothly from one processing step to the next.

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11.2 Fundamental Concepts of JIT

Experts disagree on the key components of JIT because implementa�on can range from a very narrow emphasis focusing on inventory control or shop floor scheduling to a broad organiza�onal philosophy. The following items are generally accepted components of JIT.

Generating Flow

Inventory represents a huge capital investment that �es up money a company could put to other uses. By decreasing inventory investments, a company could free up capital to purchase be�er equipment, develop new product lines, or give its employees raises. Any unnecessary inventory deprives a company of more beneficial ways to use the money.

For an automobile manufacturer, elimina�ng unnecessary inventory may mean that no inventory of �res would be kept in stock. Instead, the four �res for a car would arrive at the moment they must be mounted on the rims, just before being put on the car as it rolls down the assembly line. No inventory of �res is required. Further, there would be no inventory of any other parts for the car. Instead, parts would be delivered from suppliers or from the manufacturing opera�on for those parts only when needed and only in the quan�ty needed for that car. Throughout the en�re opera�on, there would be no unnecessary inventory—only work-in- process inventory des�ned for immediate use at the next processing opera�on.

How would this work in theory? A worker finishes a radiator part and immediately hands it to another worker, who combines that part with others to produce an assembled radiator. As soon as the radiator is finished, it gets handed to another worker, who puts it on an automobile rolling down the assembly line. All along the way, the same thing happens as parts and subassemblies are produced only when needed and only in the quan��es needed for immediate use.

JIT allows materials to flow in an assembly process similar to a con�nuous flow process, such as at an oil refinery. At a refinery, work-in-process inventories are kept to a minimum, and material flows smoothly from one processing step to the next. The difference is that a company's objec�ve with JIT is to make this smooth, uninterrupted flow move from the last �er in the supply chain to the final customers.

Figure 11.1 presents a useful analogy. In this figure, parts, materials, subassemblies, and final products are likened to water. If there are many pools in which this water can collect as inventory, then the flow will not be smooth and swi�, but will be like a series of quiet, stagnant ponds, as shown at the top of Figure 11.1. An objec�ve of JIT is to eliminate these ponds and produce a smooth, rapid flow—like the mountain stream shown at the bo�om of the figure.

Figure 11.1: Water analogy of JIT

This same concept applies to most service opera�ons. For example, when a university processes an applica�on to its graduate school, the paperwork, whether it is paper or electronic, follows a path for review and approval. In a poorly designed process, the paperwork suffers delays wai�ng for addi�onal informa�on orProcessing math: 0%

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decisions to be made. In a well-designed flow process, the parts of the organiza�on work together in a coordinated manner to make this decision quickly. There are only a few hours of real work to process, review, and approve or reject an applica�on. In a poorly designed process, this can o�en take months from the �me the applica�on is received un�l the decision is made.

Simplified Production Processes

Elimina�ng inventory is o�en much more difficult than it may seem. A certain machine may take five hours to readjust (set-up �me) whenever the company switches from making one part to making another. If only one unit is made at a �me, more �me will probably be spent readjus�ng the machine than making parts. The answer to this problem is to simplify—either by buying a more general-purpose machine that can easily be changed from making one part to making another, or by simplifying the readjustment process in some way. Companies that use JIT o�en have many general-purpose machines and have developed simple ways of switching them from making one part to making another. O�en, this set-up �me can be reduced to less than a minute. Some companies have eliminated set-up �me altogether by using one simple machine for each part, instead of trying to do all parts on one complex, mul�purpose machine.

Another problem encountered in JIT has to do with the movement of materials. In the previous sec�on, one worker handed a finished radiator part to another worker, who assembled the finished radiator. But, what if those workers are on opposite sides of the plant and an elaborate automated handling system has been used to move the radiator? A large amount of inventory builds up in the factory. Again, the answer is to simplify the process by moving the workers so they are in close proximity. This eliminates the need for an expensive material handling system and reduces the level of inventory. Many companies implemen�ng JIT have eliminated complex material-handling systems and rearranged the plant so that workers could simply move parts by hand from one opera�on to the next.

Most companies using tradi�onal purchasing methods will buy large quan��es from their suppliers once every month or every couple of months. These transac�ons usually involve much paperwork, such as purchase requisi�ons, packing slips, bills of lading, and invoices for each order. A company using JIT, which some�mes places orders with suppliers several �mes per day, would be deluged in paperwork under this tradi�onal approach to purchasing. Many companies have used blanket purchase requisi�ons, which authorize a vendor to supply a certain total quan�ty spread out over a certain �me to avoid such a problem. Individual orders may be ini�ated by phone calls, electronic data interchange, or by some other method.

Uncovering Problems Buried by Inventory

While inventory reduc�on is the most obvious aspect of JIT, its most valuable benefit is that it forces a company to uncover problems and inefficiencies in its opera�ons. To see why, consider the electric power supplied to a home. The flow of electricity occurs only in response to a need for power, such as turning on a light. There is no inventory of electricity anywhere between the house and the genera�ng plant; the electricity is supplied just in �me. Now suppose that something occurs between the genera�ng plant and the house—maybe a wire goes down or a transformer malfunc�ons. No ma�er what the problem, the homeowner becomes aware that something is wrong when there is no electricity. If this happens to enough people, the electric company will be deluged with calls; a crew will be dispatched immediately to find the problem and remedy it. The situa�on is very similar for a company opera�ng under JIT. With li�le or no inventory, any problem that disrupts the flow of work will become immediately obvious to everyone as work centers must shut down for lack of materials. A�en�on will immediately focus on the problem, and all effort will be devoted to solving that problem. In addi�on, because it is realized that produc�on will again be disrupted if the problem re-occurs, effort will be devoted to providing a long-term solu�on, not just a quick fix.

The water analogy used in Figure 11.1 also illustrates this point. As before, parts and materials are represented by water. But in this example, poten�al problems are the rocks below the water, as shown in Figure 11.2. Some of these rocks may be barely visible from the surface of the water. These are the problems that are present in the plant today. Other rocks may be totally obscured by the water. These rocks may represent quality problems, machine-breakdown problems, or any other problem that can disrupt produc�on. If the water level is lowered, that is if inventory is removed, the rocks become visible, which means that these problems surface, and disrupt the flow in the plant. It is best to iden�fy the problems first, remove them, and then decrease inventory.

Figure 11.2: Problems hidden by inventory

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An Emphasis on Quality

Quality is one problem that can be especially disrup�ve in a JIT system. Refer to the example of the radiator assembly opera�on in an automobile factory. Suppose the worker making radiator parts turns out a defec�ve part. When the next worker tries to assemble that part on the radiator, it won't fit. This immediately causes a problem because there will now be no assembled radiator to put on the next car. The assembly line will come to a halt because of one bad part.

If these parts were produced in large batches, then the worker assembling radiators could place the bad part in the defec�ve pile with other bad parts and reach into the batch for a good part. There would be no immediate signal that a problem exists and no incen�ve to change anything or to improve the process to avoid making defec�ve parts. Produc�on decisions that generate large amounts of work-in-process inventory allow a company to con�nue producing and never realize a quality problem exists. The company does not realize how much be�er and more efficiently it could be opera�ng.

Improvement as an Organizational Philosophy

The objec�ve of elimina�ng waste in any form is difficult to achieve. No company will ever reach the goal of elimina�ng all waste, but it remains a goal toward which companies should con�nuously pursue. A company opera�ng under JIT is constantly working to improve efficiency, reduce waste, and smooth the flow of materials. When working toward those ends, the company will uncover any problems and aim to find be�er ways to produce its products.

Companies that have been extremely successful with JIT have not stopped trying to improve. These companies extend some aspects of JIT to their suppliers—and to their customers—once their own systems have been put in place. Addi�onally, efforts have been undertaken to keep demand at the constant, uniform rate that is needed for a smooth flow from supplier to customer. Con�nuous improvement is also a component of total quality management.

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Instead of pushing materials through processing based on a preplanned schedule, JIT uses a "pull" system moving parts and materials based on actual needs at successive work centers.

©Tim Hawley/Photodisc/Ge�y Images

11.3 The JIT "Pull" System

Although the differences and similari�es between material requirements planning (MRP) and JIT are discussed in detail later in this chapter, there is one very important difference that is relevant here. Most tradi�onal produc�on systems, including MRP, use what is called a schedule "push" approach to move materials through the system. A push system moves materials through the processing opera�ons based on a schedule. An order to produce a part or product enters the system at a scheduled �me, and is pushed from one work center to another according to that schedule.

MRP is an improved push system in the sense that each order release is based on requirements generated by the master schedule. Thus, materials are pushed through the system in an effort to meet that schedule. With MRP, decisions are made to ensure that the outcomes on the master schedule, which occur at some future �me, are actually achieved.

JIT uses a "pull" system to move parts and materials. Instead of pushing materials through processing based on a preplanned schedule, a pull system moves materials based on actual needs at successive work centers. Thus, if work center A provides parts to work center B, work center A will produce only in response to an actual need for more parts at work center B. This pull system concept starts with customer demand, which pulls finished products from the company. As those finished products are made, they pull the appropriate materials through processing. Materials and parts are also pulled from vendors and suppliers.

One way of comparing a push system and a pull system is with the analogy of a rope. The material moving through the various produc�on processes is considered the rope. Under MRP, coils of rope (batches) are created at various machines and work centers throughout the plant. MRP is used to ensure that all coils of the rope are moved forward through the processes at the appropriate �me, preven�ng the coils from building up at any one spot. With JIT, the rope is not coiled, but remains as one long piece running through all processes. To move the rope forward, one simply has to pull on the end; there is no need to coordinate movement of coils because there are no coils, as shown in Figure 11.3. The key element of a pull system is some means for communica�ng backward through the produc�on process whenever more parts or materials are needed at "downstream" work centers. In some instances, workers can determine visually when the next work center needs to be supplied. Work centers, however, are o�en too far apart physically for direct visual communica�on.

Figure 11.3: Push systems vs. pull systems

Kanban Systems

Within a JIT system, there are several ways that pull signals can be communicated. One of the best known is a method developed by Toyota based on cards, or kanban (con-bon), as they are called in Japan. Kanban is a Japanese word that can refer to a sign or a marker and means "visible record." (Note that the word kanban is like the word "sheep" in that the plural has no le�er s on the end.) In the opera�ons context, the word kanban refers strictly to a card that is used to signal the need for more materials, parts, or subassemblies at downstream opera�ons (see Figure 11.4).

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Standard Containers of Parts

Theore�cally, the ideal situa�on with JIT is to produce one unit at a �me. However, this usually is not possible. For instance, the travel �me to and from a supplier may be much longer than the �me between requirements for the part from that supplier, or there may be an imbalance in the produc�on rate between a par�cular work center and the preceding work center that supplies it. In these and other cases, it is necessary to move containers of parts rather than single units. A kanban is most o�en associated either with the movement of a container of parts or with the produc�on of parts to fill an empty container. Accordingly, two types of kanban are generally used, the conveyance kanban and the produc�on kanban.

Conveyance Kanban

The conveyance kanban, or C-kanban, is an authoriza�on to move a container of parts or materials. Without it, nothing can be moved. The way a C-kanban works is depicted in Figure 11.5. As the figure shows, any container with parts in it cannot be moved without the C-kanban a�ached.

Figure 11.5: Single kanban system

Many companies, notably Kawasaki in the United States, use only the C-kanban. This single-card kanban system is s�ll an effec�ve way to control inventory. The number of full containers is limited by the number of C-kanban, and inventory at the using work center (work center 2 in Figure 11.5) can be replenished onlyProcessing math: 0%

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when a container is emp�ed. Thus, that center 2 cannot possibly hoard extra parts. The feeding work center (work center 1) usually produces a schedule, which may be generated through MRP. This schedule is generally based on the expected day's requirements for work center 2. However, limited storage space at work center 1 is used to shut off produc�on at that work center if parts are not being used at the expected rate (for example, if work center 2 is shut down for some reason). In order for the single-card kanban system to work, the following rules must be observed:

1. Containers holding parts can be moved only when a card is a�ached. 2. Standard containers must always be used.

Highlight: ProMedica Uses Kanban to Manage Inventory at its Hospitals

ProMedica manages approximately two dozen hospitals in the Midwest, and it uses a two-bin kanban system to manage much of its inventory. This system is used for everything from bedding to bandage to surgical gowns. Pharmaceu�cals and high-cost surgical items such as hip sockets are not part of this system, at least not yet.

The process works in the following way. Each item is stored at the hospital in two bins. A quick glance at the bins tells the order taker whenever one bin is empty and an order should be placed with Pro-Medica's medical supplier, Seneca. The barcode on the bin is scanned, and the order is placed. The larger hospitals in the system receive two shipments each day from its medical supplier. As a result, the amount of on-hand inventory at hospitals is kept low. This is an advantage not only because inventory investment is reduced, but also because space is at a premium and the available space has very high opportunity costs. ProMedica is a good example of how JIT works in service businesses.

Produc�on Kanban

Some companies use a two-kanban system that combines the conveyance kanban with a produc�on kanban. The produc�on kanban, or P-kanban, is used to authorize the produc�on of parts or subassemblies. The two-kanban system, which combines the C-kanban and the P-kanban, is known as a dual-card kanban system. Its major advantage over single-card kanban is that it allows greater control over produc�on, as well as over inventory, because both produc�on and withdrawal of inventory are directly connected to need. In contrast, a single-card system bases produc�on on a plan, which may lead to excess inventory if actual need does not match the plan.

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The flow within a plant can be compared to creeks that run into streams and eventually converge into rivers. Using this analogy, streams could be made up of processing opera�ons for individual parts that flow together into subassemblies, which are then joined together as finished products.

iStockphoto/Thinkstock

11.4 Effects of JIT on Production

The objec�ve of JIT is to eliminate the pools of inventory and obtain a smooth, steady flow of materials from supplier to customer. Within a plant, that flow is much like creeks and rivulets that converge into streams—and streams that eventually converge into rivers. In this analogy, the streams could be made up of processing opera�ons for individual parts. Those parts flow together into subassemblies, which are then eventually joined together as finished products. The objec�ve of JIT is to keep all those rivers and tributaries flowing smoothly without any pools of inventory. The following sec�ons describe some ways to achieve that objec�ve.

Facility Layout

The top of Figure 11.6 shows each part moving from one machine area to another. This requires a lot of material handling and also encourages the produc�on of each part in large batches. But when the machines are rearranged, as shown at the bo�om of Figure 11.6, each part can flow directly from one processing step to the next. This type of layout also allows the produc�on of small batches because each group of machines is dedicated to just one part. Also, there will not be interference between two parts that must both be processed on the same machine. It is this type of interference that leads to long queues of parts to be processed. McDonald's, Domino's Pizza, and many other fast-food restaurants are organized as shown in the "A�er" part of the diagram in Figure 11.6. The key ac�vi�es—shaping the crust, adding the toppings, baking the pizza, and removing and boxing it—flow smoothly with a minimum amount of set-up �me, handling, and movement. The process flows efficiently and without waste because of the layout.

Figure 11.6: Rearranging machine layout for smoother flow

Reducing Set-up Time

Set-up �me is the �me it takes to readjust a machine or group of machines a�er making one par�cular part un�l acceptable units of another part are produced. Set-up �me may involve changing the tooling, adjus�ng the equipment, checking that the new part is being made to specifica�ons, and then readjus�ng the equipment if it is not.

Set-up �me is an important considera�on in JIT because it may disrupt the smooth flow of materials. For example, a group technology (GT) produc�on system may be used to make several different, but related, parts. The idea behind GT is that each part follows the same essen�al processing sequence. However, each part may require different tooling in the machines or a different machine se�ng. By keeping similar parts together, set-up �me is reduced and the flow of materials is not interrupted. If excessive �me is taken for the set up, then the flow of materials will be stopped—causing downstream processing opera�ons to pause un�l the flow resumes. If "upstream" opera�ons con�nue unchecked, unnecessary inventory will build up in the system, much as water builds up when a dam is placed across a river.

Thus, another objec�ve in a JIT system is to reduce set-up �me as much as possible. Companies should:

Closely examine each set up to determine steps that can be eliminated or improved by changing the process. Prepare as much ahead of �me as possible. All tools and equipment needed for the set up should be readily available in predetermined loca�ons. Try to do as much set up as possible with the machine running. Stop the machine only when absolutely necessary. Use special equipment to shorten down�me whenever possible. Prac�ce and refine the set-up procedures.Processing math: 0%

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Many fast-food companies empower and engage employees by training them to do a variety of tasks in order to meet shi�ing demand pa�erns.

©Photodisc/Thinkstock

Mark machine se�ngs for quick adjustment.

Table 11.1 indicates the set-up �me reduc�ons that several companies have been able to achieve by using the procedures described above. These changes did not occur overnight, but their effects were drama�c. Some companies felt ini�ally that it was not possible to reduce set-up �mes by such a large amount, but Table 11.1 shows what can be achieved with hard work and dedica�on.

Table 11.1: Set-up �me reduc�ons

Company Machine Original Set-up Time Reduced Set-up Time

Toyo Kogyo Ring-gear cu�er 8 hrs. 10 min.

Hitachi Die-cas�ng machine 1.5 hrs. 5 min.

Omark Industries Punch press 4 hrs. 3 min.

General Electric Stamping press 50 min. 2 min.

Black & Decker Punch press 1 hr. 1 min.

As companies have sought ways to reduce set-up �mes, one area that is receiving more a�en�on is product design. In the past, design engineers tended to worry li�le about how the product was made. However, challenges concerning the ease of produc�on have begun to a�ract the a�en�on of designers, and set-up �me reduc�on is one of those challenges. It is may be possible to reduce set-up �me, or even eliminate set ups altogether. A company can reduce the number of different parts used to produce a piece of equipment by using the same parts in different final products. For example, Black & Decker might use the same electric motor in several different drills and power saws. A company can also reduce differen�a�on among parts so the set-up �me is greatly reduced.

Motorola and other companies that manufacture electronic products have found that set ups can be eliminated by using a common circuit board for different products. Previously, the automated equipment that inserts parts into the circuit boards needed an extensive set up every �me it processed the board for a different product. These companies need to change only the components and inser�on pa�ern, both of which are easy to modify, by using one common board with different components.

One ques�on that may be asked at this point is: "How short must set-up �me be?" The answer is that it depends. Some opera�ons may have enough slack that the exis�ng setup �me is not disrup�ng material flow. In those cases, nothing needs to change. In other opera�ons, set-up �me may cause problems. The goal is to try to understand what problems would surface if inventory is removed from the system. If those problems involve set-up �me on a machine, then that set-up �me should be reduced.

Total Preventive Maintenance

Equipment failure is another possible source of disrup�ons to the smooth flow in a JIT system. Machines that are not properly lubricated or maintained can produce defec�ve parts without breaking down. To prevent either of these results from occurring, companies have adopted total preven�ve maintenance (TPM), also called total produc�ve maintenance.

TPM involves three main components:

1. An emphasis on preven�ve maintenance: Efforts are undertaken to avoid equipment breakdowns by frequent inspec�on, lubrica�on, and the use of proper opera�ng techniques.

2. The alloca�on of �me each day for maintenance: Companies some�mes allow one en�re shi� for maintenance, or set aside specific �me during each shi�. 3. Operator responsibility for maintenance: Instead of assigning this responsibility to a maintenance department, operators are trained to perform all but the most

complicated maintenance on the machines they operate.

Employee Empowerment

Many companies, especially those that are highly unionized, find their workforce management procedures complicate the opera�ons func�on. Empowering employees to take more responsibility and exercise more authority in the workplace can eliminate many workforce management problems. For example, if employees are able to perform more than one job, resources can be shi�ed as needed or one employee can operate several machines. Many fast-food restaurants use this approach to meet shi�ing demand pa�erns.

Employee empowerment also means training employees to work in small problem-solving groups and allowing those groups to solve problems associated with the produc�on process. If the employees who must produce a good or service are the same employees who work to improve the produc�on process, then the process is greatly simplified and be�er solu�ons will result.

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11.5 Planning in JIT Systems

It may seem that JIT is a complete departure from the planning concepts introduced earlier in this text. Actually, companies that use JIT successfully follow most of the planning steps that were men�oned previously, from strategic planning to master scheduling. In addi�on, it is possible to combine JIT and MRP; but some changes must be made in the MRP planning and scheduling process under JIT.

Operations Planning and Master Scheduling

Planning and scheduling are easier with JIT because requirements for parts and materials can be �ed directly to each unit of the end item. If 50 units of the end item will be made during a given day, then enough parts and subassemblies must be ordered for that day to make the 50 units. Because JIT requires having only what is needed when it is needed, parts are usually not ordered in large batches. Instead, a steady stream of material in small batches is maintained at a rate that will match the produc�on of end items.

The Aggregate Plan

The aggregate produc�on plan for a company using JIT is nearly the same as that for any other company that doesn't use JIT, except that the JIT planning horizon may be somewhat shorter. Produc�on is generally planned by product families on a monthly basis for about one year into the future. This plan is used for determining general workforce requirements and overall capacity needs, as well as for ordering any parts or materials that have extremely long lead �mes.

The Master Schedule

The details of a master schedule for a company using JIT will be the same as that for most other companies that follow a master schedule. That is, planning is usually done in weekly �me buckets and by individual end items or product op�ons. The master schedule is usually developed with a 2- to 3-month planning horizon instead of the 6- to 12-month horizon used for MRP. The master schedule is also frozen for approximately one month into the future under MRP, whereas this �me period may be less with JIT due to the shorter lead �mes.

In an MRP environment, the master schedule is what drives the MRP deriva�on of planned order releases. However, in JIT, the pull system o�en eliminates this need for order release planning because parts and materials will be produced only in response to a downstream signal. The master schedule is used only when items with long lead �mes must be ordered. Thus, in a JIT system, the master schedule is primarily an intermediate step in reaching the final assembly schedule.

The Final Assembly Schedule

The final assembly schedule is an exact statement of the final products that are to be assembled. The final assembly schedule is stated on a daily basis, but most o�en goes only about a week into the future. The final assembly schedule indicates the quan��es of component parts that will be made each day, because lead �mes are usually short in a JIT environment. The JIT philosophy of elimina�ng unnecessary inventory has a major impact on the final assembly schedule. In addi�on to elimina�ng work-in-process inventory, it is important that any unnecessary finished-goods inventory be eliminated. However, this is hard to do when a company makes more than one finished product.

The approach that has been followed in tradi�onal manufacturing systems is to make a large number of one product before switching over to another. It means that the inventory of each finished product will increase when that item is being produced, but then decrease again when other products are being made, as shown in Figure 11.7.

Figure 11.7: Finished-goods inventory with long produc�on runs

This approach is inefficient because it leads to high levels of finished-goods inventory at some �mes and very low levels—with the possibility of being unable to sa�sfy customer demand—at other �mes. A be�er approach is to level the final assembly schedule. A level assembly schedule means that the number of units of each end product produced at a �me is as small as possible, and that total daily produc�on of each matches average daily demand during the scheduling horizon.

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If a company makes several end items such as Apple's different iPod models, it is desirable to distribute the produc�on of each model evenly throughout each day.

Peter Belanger/PR NEWSWIRE/AP Images

That is, if the scheduling horizon is 20 working days, and demand during that period is expected to be 300 units, a level schedule would require that 15 units (300/20) be produced each day.

A level assembly schedule requires that the smallest reasonable number of units of each end product should be produced at a �me. Thus, if 15 units of a product are to be made during a given day, those 15 units should be spread throughout the day. This even spread is achieved through mixed-model sequencing.

Mixed-Model Sequencing

Mixed-model sequencing is a procedure for maintaining the uniform produc�on required by a level assembly schedule. If a company makes several different end items (different products or different models of the same product), it is desirable to spread the produc�on of each evenly throughout each day. However, in order to keep the system running as smoothly as possible, there should be some con�nuity in the sequencing of those end items. For example, if four different products (A, B, C, and D) are produced, then the ideal schedule would produce them in some sequence such as A-B-C-D and to repeat that same sequence throughout the day for each day in the planning horizon. But some�mes demand for one product will be greater than for others. In that case, the sequence may need to be varied somewhat.

Problem

A company produces three products. Expected demand for each during the next 20 working days is as shown below:

Product Expected Demand Daily Requirements

A 420 420/20 = 21

B 280 280/20 = 14

C 140 140/20 = 7

The daily requirements are obtained by dividing expected demand over the planning horizon by the number of working days in the �me horizon. To maintain a level schedule, the company needs to plan so that each product's daily requirements will be produced every day, and evenly spread throughout the day, if possible. It is also desirable that a set sequence of products be made, and that this sequence be repeated throughout the day.

The trick in solving this problem is to find the largest integer that divides evenly into each product's daily requirements. In this example, the number is seven. Thus, the company should develop a sequence that will be repeated seven �mes each working day.

Product Daily Requirements/7

A 21/7 = 3

B 14/7 = 2

C 7/7 = 1

The result of dividing the daily requirements for each product by the largest integer that divides into each evenly is the number of �mes each product must be repeated in the sequence. Thus, product A should appear three �mes, product B twice, and product C once. Developing the sequence takes some trial and error, but the following is one possibility that would sa�sfy the company's objec�ves:

A-B-A-B-A-C

This sequence would be repeated seven �mes each day to produce the required 21 units of product A, 14 units of B, and seven units of C, while s�ll leveling the assembly schedule.

It should be noted in the above example that the mixed-model sequence produced is not the only one possible. Such a sequence would smooth out the produc�on, but could also cause problems due to excessive changeovers. When the cycle �me is short, it may be desirable to produce more than one unit of each end product at a �me. Thus, the following sequence would also be acceptable for short cycle �mes:

A-A-A-B-B-C

There may be restric�ons that jus�fy producing even more units of each product at a �me. For example, these products may be packed 10 per carton for final shipping. In such a case, it could be more efficient to produce 30 of A, 20 of B, and 10 of C at a �me, instead of allowing par�ally filled shipping cartons sit idle. Regardless, the objec�ve is to smooth out produc�on by producing each item in the smallest reasonable quan��es, given exis�ng constraints.Processing math: 0%

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Calcula�ng Cycle Times

The purpose of obtaining a level assembly schedule is to smooth out the produc�on of each end item so that it will closely match demand. A level schedule also smoothes out the requirements for component parts that go into each finished product. This smoothing makes the pull system work be�er because demand for each part will be fairly uniform throughout the day, instead of occurring in batches, as if each finished product were made in large batches.

The flow of component parts must be adjusted to match the rate at which finished products will be produced. For example, if one unit of product C is made every hour, it is not helpful to have a machine that makes parts for product C turning out one every two hours—or even one every half hour. The goal is to match the produc�on rate of all components to the final assembly schedule. This is done through cycle �mes. Cycle �me is a measure of how o�en a par�cular product is made. For example, automobile assembly lines usually have a cycle �me of approximately one minute. One new car rolls off the line every minute. The cycle �me of any product can be calculated as follows:

Cycle �me = working �me per day/units required per day

Problem

For the preceding example, the cycle �me is calculated by using the formula given above. Suppose the plant is in produc�on for seven hours (420 minutes) each day, and it must produce a total of 42 units each day (21 of A, 14 of B, and 7 of C) to match daily demand. The cycle �me will be:

420 minutes/42 units = 10 minutes/unit

This calcula�on can be extended to each of the individual products in order to determine how o�en each unit will be produced, based on a mixed-model sequence.

Product Daily Requirements Cycle Time

A 21 420/21 = 20 minutes

B 14 420/14 = 30 minutes

C 7 420/7 = 60 minutes

This means that one product A will be produced every 20 minutes, on the average, throughout the day by using the completely level sequence developed in the preceding example. In order to make this possible, the people and machines that supply parts and subassemblies for product A must also be balanced to produce with a cycle �me of 20 minutes. Likewise, the en�re system must be coordinated to produce one product—either A, B, or C—every 10 minutes. In some cases, this may mean that set-up �mes must be reduced, or that more machines must be added. It can also mean that some machines will not produce at their capacity. It is much more desirable in a JIT system for machines to sit idle than to produce inventory that is not needed. Ideally, all resources should be used as efficiently as possible, which may mean finding ways to use the same machine to make several different parts. This increases the efficiency of the machine.

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11.6 JIT in Service Operations

Although JIT originated in manufacturing, and most of the ini�al implementa�ons occurred there, service organiza�ons are now widely adop�ng many of its basic ideas. In fact, service organiza�ons may have an advantage because of their lack of work-in-process and finished goods inventories. For example, retailers are focusing on maintaining smaller inventories by being able to replenish their inventory more quickly and in smaller quan��es. Insurance companies are finding ways to eliminate unnecessary steps in their claims processing procedures so that customer claims are processed more quickly. Airlines are using yield management to level the demand for their flights. The JIT techniques that are most immediately relevant to services include elimina�on of waste in any form, such as unneeded steps in a process to review applica�ons for insurance or improving the produc�vity of people who are reviewing mortgage applica�ons.

Simplified Production Process

Service opera�ons o�en differ from manufacturing because customers are more directly involved, and are o�en ac�ve par�cipants, in the produc�on process. For example, ATMs allow customers to enter transac�on informa�on formerly entered by bank tellers. Because most customers are not trained employees, the process must be as simple and obvious as possible.

Uncovering Problems Buried by Inventory

Despite that services o�en have no finished-goods inventory, they s�ll may have inventories of supplies or even work-in-process, as with loan applica�ons in a bank. Those inventories can hide problems just as easily as inventory in a factory can. In fact, recent studies have shown that responding quickly to customer requests is becoming an important order winner for service opera�ons. Service organiza�ons can work toward providing the service when the customer wants it by uncovering problems through reduced inventory. Progressive Insurance has made great strides by reducing the �me it takes to apply and receive approval for insurance. Quickly responding to the customer with a decision means a higher yield from the total number of applica�ons because customers do not become disillusioned by the process and do not have as much �me to consider other op�ons. The forms, either paper or electronic, wai�ng to be processed are the service opera�ons equivalent to inventory.

Value Stream Mapping

Value stream mapping is a technique used to analyze the flow of materials, ideas, and informa�on to understand how processes func�on. Each ac�vity in the process is defined as value-added or non-value-added. For example, in health care, performing an ultrasound that is needed to diagnose an illness adds value, or in a restaurant, grilling the main course adds value. Alterna�vely, if the person performing the ultrasound or preparing the food must make a trip to the storage closet or the refrigerator to secure items that should be available, those ac�vi�es do not add value. That is, the pa�ent or customer is willing to pay for the tes�ng or the grilling because it has value for them. They see no value in taking the �me to find items that are needed to do the work. Value stream mapping allows the organiza�on to iden�fy the non-value-adding ac�vi�es or items and reduce or eliminate their impact on cost and �me required to deliver the service, thereby delivering greater value to the customer.

Value stream mapping is useful for both manufacturing and service opera�ons. In service opera�ons, it allows organiza�ons to understand how many different people and departments are involved, what their roles are, and how long tasks take to perform. The value stream map of the admissions process at a hospital could be an important tool for understanding the cost, efficiency, and customers' sa�sfac�on with this process. The basic steps are to:

1. Iden�fy the product or service that should be mapped. 2. Draw a rough, current state, value stream map, which shows the current steps, delays, and informa�on flows required to deliver the target product or service. 3. Es�mate the cost and �ming at each point, as well as the value added. 4. Assess the current-state value stream map to understand its flow and points where waste occurs to determine where processes can be improved. 5. Create a future-state value stream map using a team of people. 6. Prepare a plan to implement these improvements. 7. Work toward this future state.

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Strategic planning is based on a firm's strengths and weaknesses, the threats and opportuni�es in the external environment, and the type of product the company produces.

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11.7 Strategic Planning and JIT

Strategic planning is a vital element for any organiza�on. The strategy is based on the firm's strengths and weaknesses, the threats and opportuni�es in the external environment, and the type of product (goods and services) the company produces. The products are created by using the firm's strengths in ways to cope with the threats and take advantage of the opportuni�es present in the environment. However, JIT offers some very special compe��ve opportuni�es to the company that uses it. Within this process, the firm a�empts to mi�gate its weaknesses or to transform them into strengths. The implementa�on of JIT or lean thinking is a way to help an organiza�on build its capabili�es, in many cases transforming weaknesses into strengths. The following list notes some of the opportuni�es:

Elimina�on of waste People u�liza�on Cost reduc�on Quality and reliability Product flexibility Volume flexibility Delivery dependability

Elimination of Waste

Elimina�ng waste is a predecessor to JIT and lean thinking, and a fundamental component of JIT (as well as the Toyota Produc�on System). An important step when elimina�ng waste is to iden�fy which steps add value and which do not. One simple way to do this is to ask the customer which ac�vi�es are valuable. A customer may be willing to pay a lawn care company for an extra service such as edging the driveway, or a manufacturer that adds a power wash cycle to its dishwashers. Customers are not willing to pay for delays when an employee is late and the rest of the lawn crew must wait or for building and storing dishwasher inventory.

Waste can be categorized in two ways as necessary, but non-value-added or pure waste. It is always difficult to determine the exact amount of each. For example, with current technology some inventory is needed to make the system work. The dishwasher manufacturer will have some work-in- process inventory that is ac�ve in its assembly line because the dishwasher moves from sta�on to sta�on so that the line is filled with par�ally completed dishwashers. Also, some finished goods inventory is needed at the retail level so customers can evaluate the product and goods in transit between the manufacturer and the retailer. Companies

must determine how much inventory is needed to make the current system work, and how the system can be changed to reduce the amount of inventory even further.

The following list includes seven areas of waste to consider:

1. Over-Produc�on: producing more than customers demand. The most common cause is produc�on of large batches of products because set-up �me and costs are high. Rather than address the root cause and lower set-up �me and costs, firms produce more than they currently need and store the rest for future use. This leads to all of the costs associated with storing inventory. In addi�on, the firms run the risk of storing inventory that is defec�ve because the batch was not produced according to specifica�ons. Inventory may become obsolete when a part design changes before that inventory is consumed.

2. Wai�ng: occurs when a good is not being transported or processed. In manufacturing opera�ons prior to JIT, it was common for a part to be wai�ng for processing more than 90% of the �me. In service opera�ons, for example, pa�ents wait for treatment in a medical center or emergency room, or customers wait for paperwork to be processed at an insurance company.

3. Transporta�on: moving a product or a pa�ent from one point to another. Some part of transporta�on is essen�al, such as moving the par�ally completed dishwasher from one point in the assembly process to the next, or moving a pa�ent to a treatment center or surgery. While it does not make sense with current technology to complete surgery in a pa�ent's room, there are ways to bring some treatments to the pa�ent that lower costs and increase customer sa�sfac�on.

4. Over-Processing: occurs when more work is done than is required by the customer. This includes using tools that are more precise, complex, or expensive than required. Customers are unwilling to pay for this extra service so they are either forced to pay more or to accept more than they want. One example is cable services that offer groups of channels that are bundled. People are forced to pay for channels they do not watch. Why should customers who don't like or watch sports be required to pay for sports channels?

5. Inventory: represents items that are stored for future consump�on. Much has already been discussed about inventory in this chapter and throughout the book. 6. Mo�on or Movement: ac�vi�es that do not add value, such as excessive walking by a manufacturing employee or a service worker, or searching for items that are

lost, such as paperwork. The �me a machine operator wastes walking to the tool room or storage area for a fixture or a component could be far be�er u�lized. Keeping needed items nearby helps to reduce this form of waste.Processing math: 0%

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7. Defects: things such as scrap or rework that add cost, but no value. Defects can include goods or services that do not meet specifica�ons, such as a house entry door that does not close without s�cking, or a carpet cleaning company that must return because the job was not completed properly.

People Utilization

Companies using JIT depend heavily on their employees to solve problems, but u�liza�on of people extends even further. For instance, maintaining the smooth flow of materials o�en means that one employee may have to operate several different machines. This cross training leads to greater worker u�liza�on. Likewise, companies using JIT examine closely any areas where waste may be present. One such area in many companies is the office staff. Efforts are usually made to find ways that managerial jobs can be combined or even eliminated—something few companies have done in the past.

Cost Reduction

The JIT philosophy of avoiding waste leads logically to cost reduc�on. Although the cost savings associated with inventory reduc�on have o�en received the most no�ce, other savings may be more substan�al. For instance, total quality control can reduce material costs substan�ally and save on the labor costs that may have been used to make defec�ve products. A level schedule avoids costly over�me by evenly loading the plant. Likewise, extensive machine maintenance means that down�me will be eliminated, repair costs will be lower, and equipment will last longer. Overall, companies using JIT have been able to achieve much lower costs than their compe�tors.

Quality and Reliability

Total quality management is something that can have several payoffs. In a JIT system, the goal is to eliminate all defects, which means lower costs because scrap is nearly eliminated. At the same �me, customers will be happier because they will be ge�ng higher quality products that are likely to last longer. Producing higher quality products also means fewer returned items and fewer warranty repairs, which also will result in reduced costs. The goal of constant improvement will eventually lead to produc�on of a product that gives the customer greater value at a lower price.

Product Flexibility

JIT produc�on provides a company considerable flexibility in several ways. Producing to a level schedule means that each product is produced each day. Changes in customer demand can usually be accommodated quickly because the system is already designed to change from making one product to making another quite easily. Such is o�en not the case with companies that make long produc�on runs of each product. Low work-in-process inventories also provide added flexibility. With minimal inventories in the pipeline, companies can quickly switch to making different parts.

Volume Flexibility

It may seem contrary to the goal of using a level assembly schedule to smooth produc�on to argue that companies using JIT have more flexibility to change their volumes. Successful JIT implementa�on leads companies to a posi�on in which they have greater capability to respond to sudden surges or drops in demand. Part of this flexibility is related to low inventories. A company with very li�le work-in-process inventory can quickly stop its produc�on in response to a drop in demand. The ability to respond when demand increases is a result of the smooth material flows in a JIT system. Smooth flows generally mean that machines and people are being employed at a steady, uniform pace. When it is necessary to increase output, it is possible to quicken that pace.

Delivery Dependability

All of the strategic aspects of JIT men�oned in this text help contribute to delivery dependability. Improved quality will mean that shipments to customers are not delayed because of quality problems in the product or because of delays caused by defec�ve parts. Product and volume flexibility means that the company is be�er able to respond when customers suddenly change the size or product mix of their orders.

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11.8 Lean Systems

The term lean systems is o�en used to describe many of the aspects of JIT. In fact, many people view JIT and lean systems as interchangeable terms that mean the same thing. Others tend to view JIT as a component of lean systems. One reason for the la�er viewpoint is that JIT o�en is defined narrowly as consis�ng of only the pull (kanban) system described in this chapter. However, if one takes a broader view of JIT, then it is similar to lean systems.

Current trends tend to view lean systems as extending beyond JIT, and encompassing the en�re supply chain. While JIT was ini�ally applied to a company and its immediate suppliers, lean systems extended many of the basic concepts of JIT over the en�re supply chain. This is primarily a ma�er of perspec�ve and applica�on. Both lean systems and JIT can focus on elimina�ng non-value-added ac�vi�es from the en�re supply chain. The series of ac�vi�es that add value, through the en�re supply chain from raw materials to the final consumer, are referred to as the value stream. Lean systems focus on applying the basic ideas of JIT to this en�re value stream.

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Chapter Summary

JIT and lean are closely related ideas that were built on the Toyota Produc�on System and Ford Motor Company's efforts to apply the assembly line concepts to car produc�on more than 100 years ago. JIT is a philosophy of constant effort to eliminate waste and reduce costs. JIT is classified as a "pull" system because materials are pulled through processing opera�ons as they are needed. This includes standardizing containers and using kanban. The fundamental concepts of JIT include implemen�ng flow produc�on, simplifying processes, uncovering problems hidden by inventory, emphasizing quality, and con�nuous improvement. There are many ways to simplify the produc�on process using JIT including reorganizing the facility layout, reducing set-up �me, applying total preven�ve maintenance, and empowering employees. Planning the JIT system requires organiza�ons to produce each product frequently rather than to produce them in large batches and sa�sfy demand from inventory. JIT is very useful in service opera�ons. Some service opera�ons such as restaurant and wholesale and retail opera�ons have a great deal of inventory and can benefit from that facet of JIT. Other service providers have limited inventory, mostly as secondary items such as supplies. These firms can benefit from other aspects of process improvement. Value stream maps show the points where value is added. JIT is related to the strategic planning process because JIT can eliminate waste as well as improve produc�vity, people u�liza�on, cost compe��veness, quality and reliability, product flexibility, volume flexibility, and delivery dependability. These are important strengths that should be considered as the strategic plan is developed.

Case Studies

Southern Gear Company

The Southern Gear Company manufactures transmissions and speed reducers used in various farm machinery and industrial equipment. The company has been working on implemen�ng MRP for the past three years, but has not achieved the success for which it had hoped. It is now Monday morning as we join the company's execu�ve commi�ee during its weekly mee�ng.

Barry Renter (vice-president of manufacturing): "Look, I know we haven't achieved the results with MRP that we had expected. But, I think that's because we haven't been able to bring inventory under control. We s�ll don't have more than 90% accuracy in our inventory records, and that means that we've run out of parts when the MRP said we should have had enough. That's why I think JIT can help us. It's a way to eliminate the need to maintain accurate inventory records."

Dave Ashley (vice-president of marke�ng): "But Barry, how can we possibly change to JIT when our customer orders jump all over the place? You know as well as I do that one problem we've had in implemen�ng MRP is freezing the master schedule. Our customers expect us to meet their every whim, and they expect to be able to change their orders at the last minute. I just don't think we can achieve the level schedule that I understand JIT requires."

Al Simone (president and CEO): "Dave's got a point, Barry. I think one of our strong points has been that we're willing to respond quickly to customer demand even though we haven't always been able to do so because of parts shortages. In any case, with 20 different products and 200 possible varia�ons of those products, I think we're forced to s�ck with MRP. We're ge�ng some significant offshore compe��on that's offering lower prices than we are. I'm not sure I want to scrap a $1 million MRP system to try JIT."

Barry: "I don't think we have to scrap MRP. All I'm sugges�ng is that we con�nue using MRP for planning, but implement some aspects of JIT such as the kanban system. I also think we could benefit from changing to group technology. I've been looking at the bills of materials and rou�ngs. Even though we produce 200 different possible end items, we make those from only 50 different main parts, and many of those parts follow the same processing sequence. Part of our problem in controlling inventory has been tracking it through the long queues in the job shop. Group technology could simplify things for us."

1. Based on the informa�on given, would JIT be appropriate for Southern Gear? 2. Could JIT help to alleviate the problem of being unable to sa�sfy customer orders on short no�ce? 3. Is Barry Renter correct to suggest that MRP can be used in conjunc�on with JIT? If so, how would MRP func�on? 4. What addi�onal informa�on would you like to have before making a decision? 5. Which step should Southern Gear undertake first if it decides to implement JIT?

Steel Office Products

Steel Office Products makes four different types of steel filing cabinets: a 3-drawer le�er size, a 5-drawer le�er size, a 3-drawer legal size, and a 5-drawer legal size. The company currently uses the layout shown in the first illustra�on below to make these products. However, plans are under way to switch to JIT produc�on.

Each filing cabinet is assembled from three basic parts: cabinet, the drawers, and the guides on which the drawers slide, as shown in the second illustra�on below. All cabinets use the same guides. Both le�er-size cabinets use the same drawers, as do both legal-size cabinets. However, each product has its own cabinet.

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Basic Parts for Filing Cabinet

The guides (two per drawer) have rollers (two per guide) on which the drawers slide. These rollers are purchased from an outside supplier, but all other component parts are made internally, using sheet steel that is purchased from a supplier. The sequence of processing opera�ons for each part is listed below. There is no difference in produc�on �mes between legal-size and le�er-size, or between 3-drawer and 5-drawer cabinets, but a set up must be performed each �me the switch is made from one to the other. The following tables show the opera�on sequence and the processing �me for each part in minutes per unit.

CABINET

Opera�on Set up Run

Shear 5 0.5

Press 60 1

Weld 20 3

Paint 45 3

DRAWER

Opera�on Set up Run

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Press 50 0.8

Weld 10 2

Paint 45 1

GUIDES

Opera�on Set up Run

Shear 2 0.3

Press 20 0.5

Assemble 5 2

The plant operates five days per week, eight hours per day, and expects to con�nue this schedule. Weekly demand for the products is fairly constant at an average rate of 80 fivedrawer le�er-size units, 50 three-drawer le�er-size units, 40 five-drawer legal-size units, and 30 three-drawer legal-size units.

1. What mixed-model sequence should be used to con�nue this average? 2. What is the cycle �me for each product? 3. Based on these cycle �mes, will there be any problems with the processing �mes shown above? If so, what changes must be made? 4. Can you iden�fy any other changes that should be made to help implement JIT?

Discussion Ques�ons

Click on each ques�on to reveal the answer.

1. List the aspects of JIT that result from elimina�on of excess inventory. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

The elimina�on of excess inventory provides a situa�on where any problem that disrupts the flow of work will become obvious to everyone as work centers must shut down for lack of materials. A�en�on is focused on a problem and all effort is devoted to solving that problem. However, because it is realized that if the problem recurs produc�on will be disrupted again, effort is devoted to a long-term problem solu�on. Thus problem-solving by employees and preven�ve maintenance are necessary components of JIT. Quality control is another important aspect in a JIT system. With JIT, poor quality parts become immediately apparent. Without a backup of batched parts, a defect will result in stopped produc�on. The person making the part will immediately become aware of the problem so correc�ve measures can be taken.

2. Which aspects of a fast-food restaurant are done just-in-�me? Which are func�ons similar to batch produc�on? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

In many fast food restaurants sandwich prepara�on operates on a JIT system, preparing the sandwich as the customer orders it to their specifica�ons. Func�ons similar to batch produc�on include: chopping le�uce, slicing tomatoes, preparing salad bar items such as gra�ng cheese, cu�ng up cauliflower and green peppers.

3. In general, would you say that service organiza�ons operate in a just-in-�me mode? Why or why not? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

In general a service organiza�on does operate in a just-in-�me mode. A service organiza�on's primary func�on requires the presence of the customer before it can be accomplished. For example, a physician's office is able to prepare examining rooms ahead of �me by checking supplies and cleanliness, but the func�on of administering the doctor's services cannot be done un�l the pa�ent is present.

4. Define a pull system and a push system, and explain their differences. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

A push system is based on the idea that materials get pushed through the processing opera�ons based on a schedule. Under this system, an order to produce a part or product gets "launched" into the system at a scheduled �me and is pushed from one work center to another according to that schedule. Each successive work center usually has no idea whether the next work center really needs that order right away or not, but they keep pushing the material through anyway. In contrast, a pull system moves materials based on actual needs at successive work centers. The pull system concept actually starts with customer demand, which pulls finished products from the company. As those finished products are made, they pull the appropriate materials through processing. Materials and parts are also pulled from vendors and suppliers.

5. Develop a list of companies or industries that may best benefit from the results that JIT produces. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Those companies or industries that have repe��ve assembly opera�ons are generally most likely to benefit from JIT. Some examples are: automobile industry, electronics, furniture producers, motorcycle industry, power tool companies, and home appliance manufacturers. However, opera�ons that have a job shop process have started applying some of the JIT concepts with beneficial results. Elements of quality improvement and flexibility can be applied to service opera�ons such as healthcare.

6. Are there any companies or industries for which JIT would be totally inappropriate? Why? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

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Companies or industries that operate without any kind of repe��ve processing cycle, such as manufacturers of custom or specialized products, probably would not benefit fully from a JIT system. In par�cular the kanban system with p-cards and c-cards is designed for repe��ve produc�on. Without a produc�on process that is repe��ve, the company wouldn't know what materials are needed ahead of �me. However, some of the fundamental principles of just-in-�me including quality improvement efforts, system reliability, and opera�onal flexibility are valuable.

7. Explain the use of the C-kanban in a single-card system and the use of the C-kanban and the P-kanban in a dual-card system. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

In a single-card system the C-kanban is used as an authoriza�on to move material. Thus, the C-kanban limits inventory because new parts and materials cannot be obtained from suppliers (either internally or externally) without one.

The one weak link in the single-card system is that producing work centers may not have a clear-cut signal to produce more. Thus, in a dual-card system, the P-kanban is added to authorize produc�on while the C-kanban is s�ll used to authorize only conveyance.

8. What are some ways a produc�on process can be simplified? Explain each. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Plant Layout – Simple flow pa�erns and machines in close proximity to one another can simplify a process. This allows part to move short distances and workers to spend more �me doing value-added work rather than walking or wai�ng.

Group Technology – By making families of parts or products with similar processing opera�ons, it is possible to simplify opera�ons.

Reduced Setup Times – With very low setup �mes it is possible to easily switch from making one part or product to another with li�le disrup�on of flow.

Total Preven�ve Maintenance – Once again, a process is simplified if a smooth flow can be maintained. This is done by ensuring that machines will operate as expected. Preven�ve maintenance ensures that the machines are properly adjusted and lubricated and that parts are replaced before they become likely to break.

9. Describe at least two ways that quality control is important in JIT. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

The first way quality control is important is in elimina�ng waste. If defec�ve parts or products are produced then the labor and materials in them has been wasted. Second, defects disrupt the smooth flow of materials and, therefore, are to be avoided. A third aspect is that by collec�ng quality control data a company has informa�on it can use to constantly improve its produc�on process.

10. Find an ar�cle about a company outside Japan that uses JIT, and determine whether any modifica�ons have been made to fit local culture or business prac�ces. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

The answer to this ques�on will depend upon the ar�cle found. In many cases, U.S. companies have made modifica�ons in JIT to fit local circumstances.

11. Discuss how the lean manufacturing concept of a value stream may relate to the water analogies of JIT. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

There are similari�es. In both instances we are using the analogy of flowing water to represent undisrupted flow of materials and products. In both instances we also can think of pools (inventory) as being something that really does not contribute to a smooth flow. However, the value stream concept goes beyond the JIT water analogy to get us thinking about the fact that this stream can provide value for all those who are involved with it. Using this thinking we can begin focusing on how to maximize that value for everyone (suppliers, manufacturers, customer, etc.).

12. The term lean manufacturing appears to indicate that related ideas are not applicable to services. Is that true? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

No, that is not true. Because JIT was first developed for manufacturing, the lean system concept naturally was applied to manufacturing first. However, just as JIT use has now extended to services, lean systems concepts are also now being applied widely in service opera�ons.

13. What is the rela�onship between strategic planning and JIT? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

JIT offers some very special compe��ve opportuni�es to the company that uses it that allows the firm to improve its compe��ve posi�on. Within a well done strategic planning process, the firm a�empts to mi�gate its weaknesses or to transform them into strengths. The implementa�on of JIT or lean thinking is a way to help an organiza�on build its capabili�es, in many cases transforming weaknesses into strengths. Following are some of those opportuni�es: elimina�on of waste, produc�vity improvements, be�er people u�liza�on, cost reduc�on, quality and reliability improvements, product flexibility, volume flexibility, and delivery dependability.

14. Explain value stream mapping. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Value stream mapping is a technique used to analyze the flow of materials, ideas, and informa�on to understand how processes func�on. Each ac�vity is defined as value added or not value added. Value stream mapping is useful for both manufacturing and service opera�ons. In service opera�ons it allows organiza�ons to understand how many different people and departments are involved, what their roles are, and how long things take. The basic steps are to:

• Iden�fy the product or service that should be mapped.

• Draw a rough current state value stream map, which shows the current steps, delays, and informa�on flows required to deliver the target product or service.

• Es�mate the cost and �ming at each point as well as the value added. Processing math: 0%

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• Assess the current state value stream map to understand its flow and points where waste occurs to determine where the process can be improved.

• Create a future state value stream map using a team of people.

• Prepare a plan to implement these improvements.

• Work toward this future state.

Problems

1. A manufacturer of televisions produces three different models: X, Y, and Z. Demand over the next month is expected to be 400 units for model X, 200 units for model Y, and 100 for model Z. There will be 20 working days in the month. Develop a mixed-model sequence.

2. Refer to Problem One. Suppose that the company has eight working hours each day. Calculate cycle �mes for the three different television models. 3. An automobile manufacturer makes two-door sedans, four-door sedans, conver�bles, and sta�on wagons. Customer demand for the next 25 produc�on days is

expected to be 400 two-door sedans, 300 four-door sedans, 300 conver�bles, and 200 sta�on wagons. Develop a mixed-model sequence that will level the assembly schedule and sa�sfy daily demand.

4. Refer to Problem Two. If the automobile manufacturer runs the plant seven hours each day, calculate cycle �me for each type of car.

Click here to see solu�ons to the odd-numbered problems. (h�ps://media.thuze.com/MediaService/MediaService.svc/constella�on/book/AUBUS644.13.2/{pdf}bus644_ch11_odd_problem_solu�ons.pdf)

Key Terms

Click on each key term to see the defini�on.

conveyance kanban (C-kanban) (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A kanban that authorizes the movement of materials from one loca�on to another.

cycle �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A measure of how quickly a product is made. It is the amount of �me from the start of a task un�l the worker or machine is ready to start the next task. In an assembly, it is the �me between the nth vehicle being produced and the nth+1 vehicle.

dual-card kanban system (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A pull system that uses both C-kanban and P-kanban to carefully control WIP inventory.

just-in-�me (JIT) (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

Can be used as a basis for planning and scheduling, yet is more properly viewed as a strategy for designing manufacturing systems that are responsive to customer requirements. Applying JIT forces a re-examina�on of opera�ng philosophy. The JIT philosophy focuses on reducing lead �mes, reducing set-up �mes and improving product quality to minimize raw material, work-inprocess and finished goods inventory.

kanban (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A Japanese word meaning "visible record." In manufacturing, it is a card or marker that is used to indicate when more materials are needed in a pull system.

lean systems (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

Lean systems extends many of the basic concepts of JIT over the en�re supply chain. While both lean systems and JIT can focus on elimina�ng non-value-added ac�vi�es from the en�re supply chain, lean systems focuses on applying the basic ideas of JIT to the en�re value stream.

level assembly schedule (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A final assembly schedule that involves producing a specified sequence of products so that produc�on of each is matched with expected daily demand.

mixed-model sequencing (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The produc�on of different products in small batches on the same equipment following a repea�ng cycle.

produc�on kanban (P-kanban) (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/booProcessing math: 0%

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A kanban that authorizes the produc�on of more parts in a pull system.

pull system (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to manufacturing in which materials are pulled through processing based on actual requirements for those materials.

push system (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to manufacturing that forces materials through processing based on a schedule.

set-up �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The �me needed to prepare a machine to process a job.

single-card kanban system (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A pull system that uses only the C-kanban. Actual produc�on may be scheduled using MRP.

total preven�ve maintenance (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to equipment maintenance that emphasizes preven�on of breakdowns, maintenance each day, and operator responsibility for maintenance.

value stream mapping (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A technique used to analyze and design the flow of materials, ideas, and informa�on to understand how processes for making products func�on.

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12

©Greg Dale/Na�onal Geographic Society/Corbis

Scheduling

Learning Objec�ves A�er comple�ng this chapter, you should be able to:

List the six criteria for scheduling and discuss the trade-offs involved with each. Provide an overview of the scheduling process including data requirements, order informa�on, sequencing, and dispatching. Describe how scheduling for services differs from manufacturing. Discuss issues of concern that can occur when scheduling an assembly line. Use dispatching rules to schedule jobs and discuss each rule. Discuss how priori�es are determined in MRP systems. Understand forward and backward scheduling with finite and infinite capacity. Schedule employees for service opera�ons.

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12.1 Introduction to Scheduling

Scheduling is coordina�ng work tasks, people, materials, facili�es, and equipment needed to create goods and services at a specific point in �me. Scheduling is required for making goods and for providing services successfully. There are many different approaches to scheduling; some of the most common are discussed in this chapter.

Scheduling is the last step in the process that begins with strategic planning and proceeds through increasingly detailed stages. Each successive stage of the planning process builds on its preceding stage. Proper planning in the earlier stages increases the likelihood that a schedule can be created that will meet customer demand at a reasonable cost and without delays.

Scheduling can be one of the most challenging areas of opera�ons management. As many companies have found, scheduling presents many day-to-day problems because there may be changes in customer orders, equipment breakdowns, late deliveries from suppliers, and a myriad of other disrup�ons. Techniques are very sophis�cated mathema�cally because scheduling problems are o�en very detailed, have lots of informa�on to consider, and have many possible solu�ons. This chapter focuses on scheduling rules that can lead to good solu�ons as well as some rela�vely simple applica�on techniques.

To begin the discussion of scheduling, the master schedule in Figure 12.1 calls for the produc�on of two different products during a par�cular �me period. Using material requirements planning (MRP), it has been determined that certain parts for each of those finished products must be started in the produc�on process during week 20, as shown by the circled figures in Figure 12.1.The rou�ngs for these two parts are shown in Figure 12.2. Capacity requirements planning (CRP) has been used to determine that insufficient capacity will exist in week 20 on the lathe, which is the "gateway," or first work center, for both parts. Management inves�gated both short-run and long-run solu�ons to this capacity problem, but has decided that it will follow a short-run strategy and schedule over�me to alleviate the capacity problem in the lathe department.

Figure 12.1: Produc�on plan for two products

Figure 12.2: Rou�ng for two parts

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In this example, there are two scheduling problems. One involves scheduling employees, and the other with scheduling the two parts. It is necessary to schedule employees to work during the over�me used in the lathe department. The second scheduling problem, scheduling the parts, occurs because both parts will be released to the lathe department at the same �me. This second scheduling problem is one of sequencing—determining which part to produce first.

Scheduling is a complex process that involves many different steps. This sec�on summarizes those steps before describing scheduling techniques.

Data Collection

Collec�ng the data needed for scheduling begins with orders from the customer. These orders iden�fy which product the customer wants, special features, and the product due date, among other things. When data from order entry is combined with process data, the following informa�on about the jobs, ac�vi�es, employees, equipment, and facili�es are available to prepare a schedule.

Jobs Due dates, rou�ngs, material requirements, flexibility of due dates

Ac�vi�es Expected dura�on, required ac�vi�es that precede this ac�vity, desired �me of comple�on

Employees Availability, capability, efficiency, wage rates

Equipment Machine or work center capaci�es and capabili�es, cost of opera�on, availability

Facili�es Capaci�es, possible uses, cost of use, availability

Order Entry

Order entry drives the scheduling process. Orders may originate with the customer, but they may also be generated by internal or company orders that are given to create inventory. For a make-to-order company, one that produces only to customer orders or that provides services, this occurs when a customer places an order. Given exis�ng produc�on schedules, capacity available, and the customer's desired due date, the order can be scheduled. This order scheduling will be an es�mate based on capacity requirements to produce the customer's order. Producing the order will require further scheduling of the individual parts and components for a product or the employees and facili�es for a service.

In a make-to-stock company, one that produces for inventory and meets customer orders from inventory, produc�on orders are entered by the company based on the inventory level of each item in stock, and the expected future demand of that item. In general, a make-to-stock company has a somewhat easier job of scheduling because it has some control over which products will be made. However, unlike a make-to-order company, which must produce whatever is demanded by the customers, the make-to-stock company will have excess inventory if it produces something that customers do not want. This increases costs and may lead to discoun�ng to increase sales of an item.

In an MRP environment, the MRP system will generate planned order releases based on the master schedule. This is another form of order entry—in this case, for individual parts or subassemblies.

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Many car manufacturers use a make-to-stock inventory system. If a make-to-stock company produces something that customers do not want, it will have excess inventory of that item, which is one downside to this type of system.

iStockphoto/Thinkstock

The planning process involves a con�nual movement from strategic plans for the distant future toward more detailed plans for the less-distant future. As �me frames diminish, plans become more precise and detailed un�l each order is released for produc�on. At that point, the schedule is implemented.

Scheduling addresses the very near future because it is the last step in produc�on planning. Plans are made to schedule a par�cular job, ac�vity, or employee, but those plans are not converted into a detailed schedule un�l the last possible moment. The earlier planning stages determine what level of resources is needed to meet the produc�on plan. Scheduling allocates those resources.

When working with such minute details, such as individual machines, parts, or employees, it is always possible that changes will occur. An employee may become ill or quit, a machine may break down, or the raw materials for a part may not arrive on �me. Because of these possibili�es, scheduling must usually wait un�l the exis�ng condi�ons are known with rela�ve certainty. Even then, last minute changes must o�en be made, which is what makes scheduling so challenging.

As �me passes and the scheduled star�ng �me for a job or order is reached, that job or order is released for produc�on. That step starts the job on its way through the processing opera�ons. The final scheduling steps are the sequencing of ac�vi�es, jobs, or parts in the order they should flow through processing, and then the dispatching of those jobs. Dispatching is the assignment of priori�es and the selec�on of jobs for processing at a work center or facility. For example, a customer order for a made-to-order product must be sequenced with other orders. When the �me comes for work to begin on that order, it will be dispatched at the first work center according to its priority at that �me.

Managerial Considerations

Scheduling is an a�empt to allocate scarce resources efficiently. Machine �me may be a scarce resource that is allocated to different jobs, employee �me is allocated to different ac�vi�es, and facili�es are scheduled for a given ac�vity at a par�cular �me period. In all of these scheduling tasks, different criteria may be used when deciding which of several schedules will work best. Those criteria may relate to the amount of �me equipment may sit idle, the importance of a certain order or a certain customer, or the level at which a resource is u�lized.

The task of scheduling can be quite complex; what appears to be an op�mal schedule from one viewpoint may be far from op�mal from another. For example, a certain schedule may u�lize one machine very efficiently, but may mean idle �me for machines farther along in the processing opera�ons. Another schedule might mean that an important customer's order will not be delivered on �me. These six criteria may be used when evalua�ng possible schedules:

Provides the good or service when the customer wants it Length of �me it takes to produce that good or service (flow �me), which includes both processing and wai�ng �me Level of work-in-process (WIP) inventories Amount of �me that equipment is idle Amount of �me that employees are idle Overall costs

The rela�ve importance of each factor depends on the product or service being produced, a company's par�cular industry, and, especially, the organiza�on's compe��ve strategy. Different produc�on processes will also incur different problems, and certain criteria will, therefore, be more important. It may be impossible to sa�sfy all of the six criteria listed above at one �me. Instead, management must choose among the various trade-offs (see Table 12.1).

Table 12.1: Factors and trade-offs

Factor Trade-off

Providing the good or service when the customer wants it

Requires flexibility. Can lead to large inventories and excess capacity during periods of low demand.

Minimizing flow �me Requires flexibility, short set-up �mes, and fast produc�on rates. Can require having excess capacity available.

Minimizing WIP inventories May require excess capacity or the use of a pull system. Can lead to high machine or employee idle �me.

Minimizing machine idle �me O�en means keeping capacity low, producing product for inventory, or accep�ng any customer orders whether the order is profitable or not. Can result in high inventories, high costs, the overloading of equipment, and late orders.

Minimizing employee idle �me

O�en means keeping workforce size low, producing product for inventory, or accep�ng any orders. Can result in employee discontent, late orders, and high inventories.

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Minimizing costs O�en requires compromises on the preceding criteria. All relevant costs must be properly defined and measured. Can result in poor customer service—a cost that is difficult to measure.

When determining which criteria to use, a company must carefully consider its corporate objec�ves, compe��ve strategy, and capabili�es. The company's scheduling decisions will have a great impact on facility design, the type of equipment used, and the workforce requirements. Each of these will, in turn, influence its compe��veness in terms of cost, speed, and delivery reliability.

Highlight: Tim Horton's

Tim Horton's sells coffee, pastries, breakfast, sandwiches, and other items. It responds to customer demands quickly using a combina�on of make-to-order and make-to-stock. Their coffee is pre-made, that is, made-to-stock, but it has a �me limit. If not used within a certain �me, it must be thrown out. The donuts and bagels are make-to-stock, but sandwiches are make-to-order with components including bread, meat, and cheese, and prepared for further processing and assembly. Tim Horton's relies on fast delivery, low cost, and good quality. The store managers must an�cipate demand each day, even for each por�on of the day, in order to schedule the right people at the right �me and without idle employees, which increases costs. They must consider the wait �me at the drive up window. Cross training is important so that if there is slack at the front counter, employees can be shi�ed to other jobs where demand exceeds the restaurant's ability to serve its customers. Managers must order the materials, such as coffee, pastries, and sliced meat, so the shop has neither too li�le (so customers cannot get what they want), nor too much (so there is waste). Long term, managers should measure equipment use and iden�fy bo�lenecks to determine if the number of coffee machines, warming ovens, and other items are sufficient for demand. Should these be increased or possibly reduced? A manager would examine the facility to see how it might be altered to be�er serve customers. Scheduling is cri�cal to Tim Horton's success.

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An ice cream company must decide which flavors it should make, in what order, and how many gallons should be produced to op�mize profit and efficiency while reducing waste.

altrendo images/Stockbyte/Thinkstoc

12.2 Techniques for Successful Scheduling

When scheduling, two key ques�ons are:

1. When should a given job, order, or product be processed? 2. How many units should be processed at one �me?

The answers to these ques�ons impact the way a processing opera�on is run. For instance, a company that makes ice cream must decide which flavors should be made and when. If chocolate is made before vanilla, there may be extensive �me spent cleaning the equipment before switching to vanilla. Conversely, producing vanilla before vanilla-fudge marble may mean no cleanup between runs. In addi�on, the company must decide how many gallons of one flavor to make before it starts making another. The company does not want to produce so much of a given flavor that the ice cream deteriorates before it is sold. At the same �me, producing small quan��es at one �me will mean excessive �me spent cleaning and refilling the equipment between batches.

Different scheduling techniques are appropriate for different opera�on processes. Line flow, batch, and flexible manufacturing process have similari�es, and are discussed together in the next sec�on. The job shop process, which is quite different, is discussed in a later sec�on in this chapter.

Continuous Flow Processes

A con�nuous flow process is one in which materials flow in a con�nuous, or nearly con�nuous, stream from beginning to end. A good example of a con�nuous flow process is an oil refinery. Such produc�on processes are generally characterized by a few different finished products, only a few possible rou�ngs, and low work-in-process inventories.

Under such condi�ons, the relevant scheduling criteria become somewhat limited. For example, flow �me is determined by the produc�on process, rather than by a schedule because a con�nuous flow system operates with a defined sequence and that is difficult to interrupt. Generally, it is neither economical nor technically desirable to perform step one in the refining process, then place the output in inventory for a long period of �me. Work-in-process inventory is also not a major problem because it is generally quite low for con�nuous flow processes. Thus, the scheduling problem in a con�nuous flow process requires determining when to change from making one product to making another. The relevant criterion is usually minimizing cost, although minimizing the �me the facility is idle during changeover could also be important. When refining oil, a con�nuous flow process makes adjustments to make more hea�ng oil in

the fall for the coming winter, and adjus�ng again to make gasoline in the late spring for the summer driving season.

Balancing an Assembly Line

An assembly-line process is similar to con�nuous flow, but instead of the products flowing con�nuously, such as a stream of gasoline or a roll of paper, the products are discrete, individual items, such as automobiles.

One of the best examples of an assembly-line process is the automobile assembly line. In this example, the product follows a fixed path. Like the con�nuous flow process, an assembly-line process usually produces a limited number of products, and the rou�ngs are the same. Work-in-process inventory is also typically small. Thus, the same basic techniques used for scheduling in con�nuous flow can also be used for assembly-line process scheduling. There are, however, two par�cular problems unique to assembly-line scheduling that are described next.

It is cri�cal to assign the same amount of work to each sta�on because assembly lines are usually a series of worksta�ons with one worker assigned to each sta�on. If the line is unbalanced, meaning that one sta�on has more work than the others, then one worker will be rushed and unable to complete the work while the others will have idle �me, thereby genera�ng waste. Successful assembly line balancing depends on having the op�mal number of appropriate worksta�ons so that idle �me is zero or close to zero. The right number of worksta�ons is also important because it helps to determine the cycle �me. The cycle �me is the amount of work assigned to the sta�on with the most work and �me. Cycle �me controls the flow of product along the line, and therefore determines the capacity of the assembly. Mathema�cally, the cycle �me for the assembly in minutes per unit of product is the inverse of the produc�on rate, which determines capacity. Assembly-line balancing provides the framework for scheduling. Assigning tasks to worksta�ons allows the material flow and job assignments to be specified by the line balance.

Assembly-line balancing is not a perfect science because people with different abili�es will be assigned to the worksta�ons. The result may be that a perfect balance was achieved theore�cally, but it will not be perfect in prac�ce. Some employees will complete their tasks in less than the average �me. Others will take longer. The end result is that a theore�cally balanced line may be unbalanced in prac�ce.

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Assembly lines are comprised of a series of worksta�ons with one or more workers assigned to each sta�on. Successful assembly lines depend on balancing the line so that idle �me is minimized.

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Scheduling is one approach to overcoming this problem. A skillful supervisor will know which employees can work faster and will assign those to the sta�ons with more work. Tasks may also be shi�ed from one worksta�on to another as trouble spots appear. Thus, assigning employees to worksta�ons or tasks to employees is an integral part of fine-tuning the balance of a line through scheduling.

The details of assembly-line balancing involve complex mathema�cal problems that are beyond the scope of this book.

Sequencing

Sequencing an assembly is determining the order for making different products. In some cases, the differences are small, such as pain�ng a car red versus silver, or moun�ng 16-inch steel wheels versus 17-inch aluminum wheels. But, in other cases, the differences are very different, such as making a conver�ble versus a hardtop, or making different car models on a different pla�orm within the same produc�on line. In these cases, sequencing is very important. Assembling a conver�ble, for example, requires more �me at some worksta�ons, so it is be�er not to put those sta�ons back-to-back. This gives the workforce �me to catch up before the next conver�ble arrives.

Scheduling Batch Processes

In batch processes, the number of possible products is greater than can be produced in line-flow processes. As a result, each product is made in a group or batch. The process is stopped; the equipment is changed over, and the next product is made. The produc�on volume of each product is usually less than when made by a line-flow process. As a result, the same resources are used to produce at least several different products, producing a batch of each product at one �me. Because of this, determining the number of units to produce in one batch and the sequence of batches becomes important. The criterion of cost minimiza�on is usually used to determine produc�on quan�ty. Because each product is produced only intermi�ently, it must be produced o�en enough to avoid running out of inventory.

Note that many batch opera�ons use con�nuous flow or assembly-line processing. The difference is that a batch has a defined star�ng and ending �me with a setup or changeover between different batches. From a cost perspec�ve, it would be lower cost (lower set-up costs, less inventory, and higher equipment u�liza�on) to avoid batching by making the same or very similar product without an abrupt change. The problem with this approach is that customer demand requires a greater variety than the produc�on system can deliver without the abrupt change. The ideal, over �me, is to find a technology that can eliminate or greatly reduce the changeover so the opera�ons can make smaller batches and eventually run con�nuously.

The ice cream example described earlier is one example of a con�nuous flow process that has many op�ons and rela�vely small batches. There are hundreds of ice cream flavors available, and more are being developed every year. Determining the sequence and batch size for ice cream produc�on is cri�cal to effec�vely and efficiently schedule produc�on. Other examples of con�nuous flow process that are run in batches include paint, pharmaceu�cals, and breakfast cereals. Assembly lines can also operate in a batch mode. Appliance assembly lines that make air condi�oners and refrigerators are o�en batched to increase efficiency. Once demand is large enough for a par�cular model, or the changeover �me declines because of technology, the batch size can be greatly reduced or eliminated and the assembly lines can flow smoothly.

Run-Out Time

*Throughout this text, to enlarge the size of the math equa�ons, please right click on the equa�on and choose "se�ngs" then "scale all math" to increase the viewing percentage.

The ques�on of batch size only addresses how much to produce; it does not indicate which product should be produced next. One method that can be used to determine which product should be produced next is called run-out �me. This is simply a calcula�on of how long it will take for the company to run out of each product at current usage rates. Run-out �me is determined as follows:

Table 12.2 indicates current inventory and demand rates for five different products made by a process. Run-out �me calcula�ons are shown for each of the five different products. Based on those calcula�ons, product E should be produced next because it will run out first—in two weeks.

Table 12.2: Run-out �me calcula�ons

Product Current Inventory Demand Rate (Units per Week) Run-Out Time (Weeks)

A 1,000 200 1,000/200 = 5

B 500 150 500/150 = 3.3

C 2,000 500 2,000/500 = 4

D 2,500 500 2,500/500 = 5Processing math: 0%

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E 600 300 600/300 = 2

Flexible Manufacturing Systems

Chapter 10 discussed the trade-off between product changeover costs (or set-up costs) and inventory carrying costs. When the cost of changeover becomes extremely small, the ques�on of how many products to produce at one �me is less important. Flexible manufacturing systems (FMS) have been able to reduce changeover costs so much that it is economical to produce just one product or part at one �me. The challenge then becomes one of sequencing to keep the changeover �me—and consequently the cost—low enough.

Group technology is an important aspect of any FMS. By grouping similar products into families, a group technology cell within a FMS only makes products that have similar characteris�cs, which tends to reduce sequencing challenges. Because computerized control is an important part of a FMS, the computer can be used to evaluate different possible sequences and determine the best one for each cell.

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12.3 Job Shop Scheduling

There are few sa�sfactory scheduling techniques for job shop processing. Unlike con�nuous flow, assembly line, or batch processes, a job shop has many different and intersec�ng rou�ngs. A job shop is fundamentally different from these con�nuous flow processes because it is arranged with similar machines in one loca�on or work center. The part being produced or the pa�ent in a hospital, moves to the various work centers as needed. Each part or pa�ent may have a different path through the factory or hospital. This is called a process layout. Con�nuous flow and assembly lines are organized around a common sequence of steps, so that the path through the facility is the same. This is called a product layout.

What makes job shop scheduling more challenging is that different jobs are vying for �me on the same machines. Deciding which job to process first on a given machine or work center can have a major impact on what happens at other machines or work centers—possibly overloading some, while leaving others idle. The flow of product and the demands on the work centers in a job shop are different and uneven, which makes scheduling a challenge.

Dispatching Rules

One of the earliest approaches to job shop scheduling focused on the criteria for sequencing the jobs that are compe�ng for �me at the work center. Those criteria could be used to generate dispatching rules to be used at a machine or work center. A rule such as "first-come, first-served" is commonly used in retail opera�ons because it is perceived as fair. A rule like first-come, first-served with priority for pa�ents with severe problems is used in emergency rooms. This is called triage, where a medical professional makes an ini�al screening to see if a pa�ent's injuries are life threatening.

An important advantage of these rules is that they are easy to use. The informa�on is readily available, and it is not necessary to know what is happening at other work centers. As with many things that are simple, the rules can some�mes lead to poor performance. Five of the most common dispatching rules are described below.

Earliest Due Date

The earliest-due-date rule focuses on the criterion of providing the product when a customer wants it. The ra�onale is that whichever job is due first should be started first. The advantage of this approach is that some jobs may meet their due dates. This rule is popular with companies that are sensi�ve to due date changes. However, finishing one job on �me may make many others late. This method also does not consider how long it will take to process a job.

Shortest Processing Time

With the shortest-processing-�me rule, the ra�onale is to get the most work done as quickly as possible in order to minimize the level of WIP inventory. Unfortunately, jobs with long processing �mes may be made quite late as they wait for shorter jobs to be finished. Otherwise, this rule o�en works best on most measures. One way this rule has been modified is to make an adjustment for long-running jobs that have been wai�ng for a long �me by moving them to the front of the line.

Having determined that there are advantages to using the shortest-processing-�me rule, it is s�ll necessary to use good judgment before applying any rule. For example, the shortest- processing-�me, including adjustment for long wai�ng jobs, works poorly in an emergency room. A pa�ent with a severe problem that requires a long �me at a work center will be delayed while other pa�ents needing less care are serviced first. For example, using this rule, pa�ents with minor fractures would move ahead of a pa�ent with a severe compound fracture.

Longest Processing Time

The longest-processing-�me rule uses a different strategy—to get the jobs that will take longest done first, leaving �me at the end to do the short-processing-�me jobs. The ra�onale behind this rule is that jobs with long processing �mes may be more likely to miss their due dates than jobs with short processing �mes are. The great disadvantage of this approach is that many short jobs may also miss their due dates because of one long job. This rule also tends to result in an increase in WIP inventory. It may be used when a cri�cal job has a long lead-�me.

First-Come, First-Served

This rule is o�en used in service facili�es because customers usually see this as the fairest method. However, it ignores due date, processing �me, or the importance of one job over the other; therefore, it does not perform well on such measures. The emergency room example is only one place where this rule performs poorly. In manufacturing, machining a part that is needed to repair a city's water supply system should have a greater priority than making a part so that an amateur stock car racer can repair her car. A few years ago (despite that seats were pre-assigned) airplanes were loaded first-come, first-served for fairness; or from back-to-front for loading efficiency so that the planes could be loaded faster. Now, most airlines board their passengers based on some measure of customer importance. Airlines use priority status and zones to let passengers know when they can board.

Cri�cal Ra�o

The cri�cal-ra�o rule is an a�empt to combine aspects of the preceding rules into one that considers both due date and processing �me. It is based on calcula�ng the cri�cal ra�o (CR), which is

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Airline carriers have different boarding procedures; however, most board passengers based on some measure of customer importance, such as groups or priority status.

Creatas/Thinkstock

This rule is implemented by first scheduling those jobs that have the lowest cri�cal ra�o. Values of CR below one mean the job will be past due. A nega�ve value means it is already past due. Thus, an advantage is that those jobs scheduled first are the ones that have the lowest chance of missing their due dates.

It should be noted that the cri�cal-ra�o rule differs from the other dispatching rules in that it is dynamic. That is, a job's cri�cal ra�o will change over �me as the number of days un�l the due date changes and the processing �me remaining changes. Thus, the cri�cal ra�o must be updated constantly.

Highlight: Airlines Use Dispatching Rules to Load Passengers

Several years ago, most airlines boarded their airplanes by row. A�er the first-class passengers and those needing extra �me were boarded, the last few rows would be allowed to board. Next, the rows just prior to the last few rows were loaded. This boarding pa�ern was repeated from back to front of the airplane. This was done for efficiency, increasing the ability to rapidly load the airplane; if passengers in the front of the airplane load first, they would tend to block the aisles, slowing down boarding. Loading the airplane from back to front reduces this conges�on. This approach worked well. Today, airlines o�en board based on status. If passengers fly the airline o�en, they earn gold, silver, or other status, which allows them to board early. Remaining passengers use a "zone" boarding process, which is unrelated to the area of the airplane, and instead based on the passengers' frequent flier miles. This is important to passengers who want to carry on luggage for convenience, or to avoid checked baggage fees.

Problem

The Hillside Machine Corpora�on has four jobs wai�ng to be run on its lathe. Figure 12.3 shows the days un�l due date and the processing �me remaining for each job. Hillside wants to see which sequences will be generated by using each of the five dispatching rules. Figure 12.3 shows these sequences. It is interes�ng to note that in this example, the longest-processing-�me and cri�cal-ra�o rules produce the same sequence of jobs—although that result will not always occur.

Figure 12.3: Comparison of dispatching rules

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Sequencing Jobs on One Machine

Flow �me is the amount of �me it takes to produce a product. If the product spends a large amount of �me wai�ng to be processed, then its flow �me will be long. Average flow �me will be minimized by processing as many jobs as possible during a given period of �me. The way to achieve this result is by using the shortest-processing-�me rule, which has been proven to always minimize average flow �me.

Problem

Refer to the Hillside Machine Corpora�on data in the previous example. Suppose the company tracks the number of days each job requires un�l comple�on, using the cri�cal-ra�o and shortest-processing- �me rules. As the results in Figure 12.4 indicate, all four jobs are finished within 20 days, regardless of which rule is used. However, with the cri�cal-ra�o rule, the average �me each job spends before comple�on is 15.75 days. With the shortest-processing-�me rule, the average �me is only 9.25 days.

Figure 12.4: Comparison of average flow �mes for two sequencing rules

Johnson's Rule

When there are two successive machines or work centers through which a group of jobs must all be sequenced, Johnson's Rule can be used to minimize total processing �me for the group of jobs, which is called the makespan �me. The method u�lizes the following steps:

1. List the jobs and the �me each job requires at each work center. 2. From the list, select the job with the shortest �me at either work center (if two or more jobs in the list have the same �me, one is selected at random). If the �me is

for the first work center, proceed to step 2a. If it is for the second work center, proceed to step 2b. a. Place the job as close to the beginning of the sequence as possible without replacing other jobs. Go to step 3. b. Place the job as close to the end of the sequence as possible without replacing other jobs. Go to step 3.

3. Eliminate the job just scheduled from your list. Return to step 2.

Note that this rule requires all jobs to follow the same sequence through both work centers. The sequence cannot change at the second work center.

Problem

University Data Services has five computer payroll jobs wai�ng to be processed before Friday a�ernoon. Each job requires compu�ng and then prin�ng, in that order. Based on past experience, the company es�mates each job will take the following �me:

Processing Time (Hours)

Job Compu�ng Prin�ng

A 1.5 1.0

B 1.0 0.75

C 0.5 1.25

D 2.0 1.5

E 0.75 0.5

Using Johnson's Rule, proceed as follows. Processing math: 0%

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Two jobs, C and E, have the shortest processing �mes, 0.5 hours. Job C is selected arbitrarily. Because its shortest �me is for the first opera�on, Job C is scheduled at the beginning of the sequence.

Job C is eliminated from further considera�on, and the process returns to step 2. Now Job E has the shortest processing �me. Because that �me is for the second opera�on (prin�ng), Job E is scheduled at the end of the sequence.

Job E is now eliminated from the list. Therefore, Job B has the shortest processing �me, which is for the second opera�on. Job B is scheduled as close to the end of the sequence as possible.

A�er elimina�ng Job B, of the remaining two jobs, A has the shortest processing �me. Because that �me is for the second process, job A is scheduled as close to the end as possible, which, in this example, is the third posi�on.

The last remaining job, job D, is placed in the remaining slot in the schedule, producing the following sequence:

This sequence of jobs produces the processing sequence for each opera�on shown in Figure 12.5. This method completes all jobs within 6.25 hours and leaves only 0.5 hour of idle �me for the printer at the beginning of the sequence and 0.75 hour between Jobs C and D.

Figure 12.5: Processing of computer jobs based on sequencing by Johnson's Rule

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12.4 Dispatching in MRP

The rules men�oned above are limited because they only consider the condi�ons that exist for a given point in �me and a given work center. By and large, they ignore that a given part may be part of a subassembly that must be complete before the final product can be assembled.

MRP takes into account lead �mes. As long as the planning lead �mes used in MRP are valid, then the priority of each item should be based on the MRP lead �mes. Therefore, in an MRP system, priori�es are determined by referring to the planned order releases and lead �mes. Thus, the dispatching rules are irrelevant to MRP systems. Instead, MRP works from the order due dates, scheduling order releases far enough ahead of �me that the due dates should be met. Unfortunately, there s�ll may be conflicts at machines and work centers that need to be addressed.

Machine Loading

The dispatching rules previously described a�empt to determine a schedule based on the a�ributes, such as due date or processing �me, of each job. However, the �me it takes for a job to be processed consists of the following five components:

1. Wait �me 2. Move �me 3. Queue �me 4. Set-up �me 5. Run �me

Wait �me is the �me a job spends wai�ng before it is moved to the next work center. Move �me is the material-handling �me between work centers. Queue �me is the �me a job spends wai�ng to be processed at a work center. Set-up �me is the �me to prepare a machine to process that job, and run �me is actual processing �me.

In general, all of these components—except queue �me—will be nearly fixed. Queue �me really depends to a large extent on the workload that has been scheduled for each work center. If a machine's capacity is being used extensively, then it is more likely that many jobs will be wai�ng for processing at that machine. When the capacity of a work center is exceeded, lines of work (queues) will build up in front of that work center.

Loading is an approach to scheduling that a�empts to take capacity u�liza�on into account. There are several different approaches to loading, but loading begins with scheduling.

Forward Scheduling

Suppose scheduling begins immediately so that each job starts at the earliest possible moment. This is called forward scheduling. As jobs progress through a produc�on facility, each work center will have a certain workload placed on it from the jobs assigned to that work center. Figure 12.6 illustrates the schedule that could be generated by forward scheduling four jobs (A, B, C, and D) through three work centers (lathe, mill, and drill). This schedule assumes six hours for wait and move �me between machines. Note that the jobs use the same three work centers, but use them in different orders, so Opera�on l for Job A uses the lathe, but Opera�on l for Job D uses is the drill. Also note that Job B and Job D do not use the lathe and the mill, respec�vely.

Figure 12.6: Forward schedule for four jobs with finite loading

Work Center Sequence and Processing Time

(Number Is Sum of Set-up and Run Times in Hours)

Job Opera�on I Opera�on II Opera�on III

A Lathe 3 Drill 2 Mill 4 Processing math: 0%

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B Mill 4 Drill 3

C Lathe 2 Mill 3 Drill 4

D Drill 5 Lathe 4

In a forward schedule shown in Figure 12.6, each job begins as close to �me zero as possible, and each job is scheduled similarly through the successive opera�on, allowing six hours for wait and move �me between machines. Some jobs have been delayed (queue �me) at certain work centers because another job had already started at that work center. For example, Job C had to wait three hours before it could start on the lathe because Job A was s�ll being processed on that machine. This approach of making one job wait if another has been scheduled on the same machine is called finite loading because it takes into considera�on the limited capacity on each machine. Another approach uses infinite loading, which does not take capacity considera�ons into account. Infinite loading assumes that there is unlimited or infinite capacity.

Backward Scheduling

Backward scheduling starts from a desired due date and works backward. The informa�on for the four jobs and three work centers previously presented is used again, but the following due dates are added:

Job Due Date

A Hour 24

B Hour 16

C Hour 24

D Hour 16

In this case, infinite loading will be used, elimina�ng the problem of more than one job at the same work center at the same �me. The resul�ng schedule is shown in Figure 12.7. Backward scheduling begins by scheduling the last opera�on for each job so that it would end at the �me due, and then works backward through each opera�on. As a result of infinite loading, some work centers have been scheduled to do more than one job at one �me. This may not be a problem if more than one machine is available. Actually, either finite or infinite loading can be used with either forward or backward scheduling.

Figure 12.7: Backward schedule for four jobs with infinite loading

Either of the preceding schedules can also be used to generate a load profile for each work center. A load profile indicates the workload being placed on that work center. Figure 12.8 shows the load profiles for the backward schedule of Figure 12.7 at an hourly rate. These load profiles were obtained by adding up the number of jobs scheduled during each hour for each machine. No�ce that any hour in which more than one hour of machine �me is scheduled could present a problem if only one of each machine is available.

Figure 12.8: Load profiles for backward schedule

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Forward and backward scheduling are both widely used—and many companies use both. Forward scheduling is useful for jobs that need to start immediately. Backward scheduling works well when a desired due date is specified. Both finite and infinite loading can be used with forward and backward scheduling. Finite loading requires much more effort for companies to keep track of which jobs are scheduled for which machines and at what �me. Unforeseen problems, varia�ons in processing �me, and other factors can combine to make this a wasted effort. Therefore, most companies use infinite loading and then address over-loaded work centers a�er examining the load profile.

This approach to scheduling helps to point out the importance of capacity requirements planning and its �e-in with both the medium-range produc�on plan and the master schedule. While capacity requirements planning is only a rough es�ma�on, it s�ll helps to ensure that sufficient capacity will be available. If the master schedule indicates a realis�c capacity, then infinite loading does not o�en produce too many problems.

Sequencing

When using a forward schedule with finite loading, two jobs are not allowed to be in the same work center at the same �me. Thus, if Job 1 had been started at work center A, Job 3 had to wait. But, would it have been be�er to start Job 3 on work center A first and make Job 1 wait? To answer that ques�on, it is possible to use a tool to schedule each work center— the Gan� load chart.

Each work center can be indicated by one bar on the Gan� load chart. The job being processed at each work center and its processing �me can also be indicated. Figure 12.9 shows the Gan� load chart that corresponds to the forward finite load schedule of Figure 12.6. The primary difference between the forward schedule shown in Figure 12.6 and the Gan� load chart in Figure 12.9 is that the former is organized by job and �me, and the la�er is organized by opera�on and �me. The Gan� load chart is very useful for finite scheduling because it allows only one job to be run on each machine or work center at one �me. Any conflicts will immediately become apparent.

Figure 12.9: Gan� load chart for forward schedule

Input/Output Control

Input/output control is a simple method for managing work flow and queue lengths. If work is put into a work center faster than it comes out, a queue will build up. If work is put in at a slower rate than it comes out, the work center may run out of work.

Figure 12.10 shows the input/output report for a work center. The cumula�ve devia�on of actual input from planned input, and cumula�ve devia�on of actual output from planned output are recorded each week. Further, the cumula�ve change in backlog is determined each week by comparing actual input to actual output. For example, in week 43, actual output exceeds actual input by 30 hours. Therefore, the cumula�ve backlog decreases by that amount. In week 45, actual input exceeds actual output by 20 hours, therefore, backlog increases by 20 hours.

Figure 12.10: Input/output report in standard hours

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Simulation in Developing Schedules

Scheduling and sequencing can be rather difficult in some situa�ons. This is especially true in job shops where many different end products require different opera�ons. Unfortunately, manually developing schedules in such situa�ons can be extremely �me consuming and difficult because there are too many combina�ons to consider.

Computers help to address this difficulty. Using simula�on techniques, it is possible to develop a trial schedule on the computer and then test that schedule without actually processing the jobs. Through this simula�on, poten�al problems can be iden�fied and an improved schedule can be developed. Today, more companies are developing computer simula�on programs to help solve their scheduling problems.

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12.5 Special Problems in Scheduling Services

One major difference between scheduling the produc�on of goods and scheduling the produc�on of services is that a service cannot be inventoried. For example, a company that manufactures air condi�oners can build up its inventory during the winter months in prepara�on for peak summer demand. But a hospital cannot build up an inventory of emergency room services in advance. Unlike goods, services can be produced only at the �me of demand, which means that the strategies for mee�ng that demand are more limited than for goods. When scheduling some services, such as phone service or public transporta�on, there is less concern with sequencing and more concern with capacity and service delays or wai�ng �me. Because most service opera�ons cannot store finished goods, they try to resolve excess demand problems with extra capacity or by ra�oning capacity. These firms provide incen�ves for people to use services in off-peak �mes, such as traveling to Hawaii in the summer or offering discounts to seniors for shopping at non-peak �mes. These efforts to shi� demand are tools that service industries use to manage capacity.

Sequencing rules are usually applied to situa�ons in which parts or products are wai�ng to be processed. In the service industry it may be customers who are wai�ng. In general, companies o�en apply the first-come, first-served rule in such situa�ons. Of course, that can be frustra�ng for those of us who, for example, simply want to just cash a check at the bank and must wait for someone with a �me-consuming transac�on. Banks have adjusted by crea�ng a single wai�ng line to serve mul�ple tellers rather than a line for each teller; one person with a very long transac�on does not impact everyone wai�ng in line because that person is free to go to any of the other available tellers. ATMs are widely available so that a simple transac�on can be handled many places outside of the bank branch. Some banks have found ways to assuage those callers who must wait to speak with an employee. For example, frequent messages alert wai�ng customers that their calls will be answered shortly.

Services offer some unique challenges for scheduling. The following sec�ons discuss some of the more common approaches to scheduling for services.

Schedule for Peak Demand

One possible approach to scheduling for services is to schedule for peak demand. That means that sufficient capacity will be available at any �me to meet the peak expected demand. The advantage of this approach is that it allows for demand to be met at all �mes under normal condi�ons. Its greatest disadvantage is that a large por�on of capacity may be idle a large percentage of the �me.

U�lity companies like electricity providers face this problem because they are required by government regula�on to meet the demand of its consumers. Electrical power genera�on systems are very expensive, so idle equipment becomes very expensive. In response, some u�li�es have offered homeowners a free programmable thermostat with the caveat that the u�lity can turn up the thermostat by a couple of degrees on days when demand for air condi�oning is high in order to reduce usage during a power peak. The u�lity companies offer discounts to manufacturing companies who use power during low-demand �mes, like at night. Electric u�li�es can also buy power from another u�lity that is nearby when extra power is needed.

Chase Demand

There are two methods that companies can use to adjust produc�on rates to match demand—varying the workforce and using over�me. Either of these strategies can be very useful for service companies if they can es�mate expected demand with reasonable accuracy. For example, Burger King fast-food restaurants maintain extensive records of historical demand during various days of the week and hours of the day. Each restaurant uses this informa�on to determine how many employees it will need to schedule during each hour.

This approach works best if the employees are willing to work on a part-�me basis. Fast food is one industry that is able to schedule its employees in this way. The primary advantage of this approach is that it costs less than scheduling for peak demand, while it enables the organiza�on to meet its an�cipated demand. The disadvantages are that it requires an extremely flexible workforce, and demand forecasts must be accurate.

Other Approaches

Other methods for coping with uneven demand include scheduling appointments or reserva�ons for service, increasing consumer self-service, crea�ng adjustable capacity, sharing capacity, and cross-training employees.

The reserva�on strategy is commonly used by restaurants, hotels, and airlines. Reserva�ons allow an organiza�on to determine the advance demand for its service while also limi�ng access to that service. Airlines, in par�cular, have used reserva�ons to control access to their lowest fares. Those travelers who are willing to book their flights far in advance and sa�sfy certain length-of-stay criteria receive the best fares; those who book only hours before the flight, when space may be limited, must pay the highest fares. Conversely, when demand for a par�cular flight is light, late booking may pay dividends with a low-cost fare.

Fast-food restaurants have successfully used consumer par�cipa�on, such as allowing customers to serve themselves from the salad bar or pour their own drinks, as a way to reduce staffing requirements. This strategy considerably reduces workforce scheduling problems because fewer people are needed. Self-service gas sta�ons also use this technique. The single employee who takes the customers' money can usually handle any level of demand because the most labor-intensive part—pumping the gas—is done by the customers.

Adjustable capacity involves the ability to use only part of the facili�es or available employees at any given �me. For example, restaurants can close off sec�ons when demand is low. The wait staff who serve those sec�ons can fill saltshakers and perform other ac�vi�es to prepare for peak demand. As demand increases, those waiters and waitresses can be moved to wait on tables as sec�ons are opened.

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Reserva�ons allow an organiza�on to determine the advance demand for its service, while also limi�ng access to that service.

Tetra Images/Ge�y Images

Cross-training employees also provides similar advantages. If employees are trained to perform more than one ac�vity, then they can be shi�ed from one to another as demand changes, as when employees in a supermarket stock shelves when not working as checkers or baggers. Sharing capacity is a way that different organiza�ons, or different parts of the same organiza�on, with different demand pa�erns can use the same facili�es, and, possibly, the same employees. For example, many churches have found that their Sunday school facili�es, which are idle during the week, can be put to good use as day-care centers. On the weekend, when day care is not in session, the church will use those facili�es for other ac�vi�es. Airlines share gates, check-in facili�es, and even ground crews.

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Chapter Summary

There are a wide variety of criteria considered for scheduling, including due date, flow �me, WIP inventory, equipment idle �me, employee idle �me, and costs. Performing well on some criteria can mean performing poorly on others. Scheduling involves obtaining the right data about orders (jobs), ac�vi�es, employees, equipment, and facili�es. Scheduling a con�nuous flow process and an assembly line are based on knowing how that facility is organized and what work is assigned to each worksta�on or department. Scheduling a batch process, where different products with similar processing requirements share the same equipment, involves determining the load on the equipment and the sequence that provides the best outcome. Some of the most commonly used dispatching rules for scheduling job shops and some service opera�ons are the earliest due date; shortest processing �me; longest processing �me; first-come, first-served; and cri�cal ra�o. Johnson's rule is a way to schedule a set of jobs across two departments. This provides an op�mal result based on flow through �me. Forward and backward scheduling allows organiza�ons to assign tasks to machines to finish as early as possible to give maximum assurance that due dates will be met (forward scheduling), or as late as possible to avoid holding extra inventory (backward scheduling). These can be done with finite loading, which assumes limited capacity, or infinite loading, which assumes unlimited capacity. Priori�es are set in an MRP system by considering the due dates and lead �mes of jobs.

Case Study

Central Electronics Company

The Central Electronics Company makes electronic chassis that are used to hold the components of electronics such as televisions and microcomputers. Central has just received an order from a large microcomputer manufacturer with whom Central would like to develop a long-term rela�onship. If this order can be completed by the due date, such a rela�onship is almost assured. However, the chances of mee�ng that due date do not look good.

Each chassis in this order consists of four parts. Each part has the rou�ng and the run �mes given below. In addi�on, there is a one-hour set-up �me on each machine whenever it is changed from making one part to another, or from performing one opera�on to another on the same part. The following table shows the run �me in minutes per unit for each part.

Rail Bracket A Press—2 mins. Shear—1 min. Drill—1 min. Press—1 min. Press—2 mins. Press—3 mins. Shear—1 min. Drill—5 mins.

Bracket B Shield Shear—1 min. Shear—6 mins. Press—2 mins. Press—1 min. Drill—1 min. Drill—1 min.

Shear—2 mins. Drill—4 mins.

Central has only one press, one drill, and one shear, and each is available only eight hours per day. The order for 150 units must be completed within five days. Each machine must be set up at the start of processing, and again each �me a different opera�on or part is processed on it. There is no assembly �me, as the individual parts are shipped to the customer, which assembles them. However, 150 units of each part must be completed within five days for the order to be filled.

1. If the parts are made in batches of 150, will it be possible to meet the deadline? (Hint: Develop a Gan� load chart for each machine.) 2. Can you iden�fy one machine that has the heaviest load (the bo�leneck machine)? 3. What should your strategies be for scheduling produc�on on that bo�leneck machine? 4. How can you schedule other machines to be sure that the bo�leneck is not idle?

Discussion Ques�ons

Click on each ques�on to reveal the answer.

1. Discuss the ways in which flexible manufacturing systems may alter the ac�vi�es of produc�on scheduling. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

A flexible manufacturing system allows for a greater flexibility in scheduling because of the system's ability to change easily. In an FMS there is no backlog of parts wai�ng to be processed. The flow of materials in the flexible manufacturing system operates on an instantaneous movement basis, for example, through the use of conveyor belts. Thus, there may be less concern about sequencing in an FMS. At the same �me, there is also less flexibility in sequencing because a large backlog of jobs does not exist.

2. List the six criteria that can be used for scheduling. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/coveProcessing math: 0%

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The six criteria that can be used for scheduling are: 1) Providing the good or service when the customer wants it 2) Minimizing the length of �me it takes to produce that good or service (called flow �me) 3) Minimizing the level of work-in-process inventories 4) Minimizing the amount of �me that equipment is idle 5) Minimizing the amount of �me that employees are idle 6) Minimizing costs

3. Which scheduling criterion do you think is most relevant for a fast-food restaurant? For a physician's office? For a hospital emergency room? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

In a fast-food restaurant the most relevant scheduling criteria is that which will minimize the �me it takes to prepare a customer's order (flow �me). A physician's office will use scheduling criteria that will result in minimal idle �me for the doctor, keeping a steady stream of pa�ents throughout the day. An emergency room, however, is most concerned with scheduling so that those pa�ents with the most severe problems are seen first.

4. Which of the dispatching rules do you use to decide which homework assignment to do first? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

The answer to this may be unique for each student. However, the more likely choices will be either shortest processing �me, longest processing �me, or earliest due date.

5. Explain why scheduling a con�nuous flow produc�on process involves different methods than those used for scheduling a job shop process. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

In a high volume produc�on process there are a small number of products and usually only one or two possible rou�ngs. Thus, the scheduling problems in this process include when to change from making one product to another and assembly line balancing for smooth materials flow.

A job shop on the other hand has a large number of products with varying produc�on sequences. The scheduling problems become more complex with so many products vying for �me on the same machines. A decision on which job to process first will impact other machines or work centers with possible overload or idle �me.

6. Which service opera�ons may use the scheduling methods tradi�onally used for job shops? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Service opera�ons that might use job shop scheduling methods include: physicians, accoun�ng firms, hospitals, and print shops.

7. For each of the dispatching rules, indicate which scheduling criteria will be sa�sfied, as well as the advantages and disadvantages of that rule. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Click here to reveal the answer (h�ps://media.thuze.com/MediaService/MediaService.svc/constella�on/book/AUBUS644.13.2/{pdf}ch_12_ques�on_7.pdf)

8. List the data needed for scheduling, and indicate the usual sources. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Click here to reveal the answer (h�ps://media.thuze.com/MediaService/MediaService.svc/constella�on/book/AUBUS644.13.2/{pdf}ch_12_ques�on_8.pdf)

9. How does dispatching differ from sequencing? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Sequencing is determining the order in which jobs should be processed beforehand. Dispatching is the selec�on of jobs in real �me. This o�en involved a priority rule such as earliest due date.

10. How are priori�es set for jobs in an MRP system? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Priori�es in MRP are based ini�ally on the planned order releases and lead �mes. Thus, an order that is released earlier will have higher priority than one released later. If jobs get behind schedule then priori�es can be set again by referring to due dates and lead �mes.

However, there may s�ll be conflicts. In that case, either backward or forward scheduling can be used to determine job priori�es so due dates can be met.

11. Explain the purpose of using input/output control. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

The purpose of input/output control is to ensure that work centers are neither overloaded nor starved for work. The idea is simply to balance input and output so that work backlog does not become excessively long if input exceeds output or disappear if output exceeds input.

12. How can computer simula�on be used for scheduling? (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

Computer simula�on can be used to simulate various schedules. Thus, it is possible to es�mate rapidly the outcomes of many possible schedules and determine the one that best meets the company's objec�ves.

13. Discuss different scheduling procedures that might be used for various types of service opera�ons, such as a restaurant, a hospital, or an airline. (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cove

For service opera�ons there may be several different aspects that o�en must be scheduled. These may include scheduling the employees, scheduling the use of resources, and scheduling the customers. For example, in a restaurant, the restaurant's opera�ng hours will determine the availability of facili�es to customers. The pa�ern of demand at different �mes during the day and on different days of the week will determine the requirements for employees, who

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must be scheduled for their working �mes. If the restaurant takes reserva�ons, then customers are also scheduled into various �me periods. For a hospital, some parts of its services may resemble those of a restaurant. For example, elec�ve surgeries can be scheduled in advance when the facili�es are available, with each pa�ent having a reserved �me. However, emergencies may resemble a restaurant that does not accept reserva�ons, but must serve anyone who shows up. Airlines probably have the most fixed scheduling systems as flights are scheduled well in advance and each flight has a predetermined passenger limit. Flight crews are scheduled to match the flights.

Problems

1. A company produces four types of paper in batches. Based on the following informa�on, which product should be produced next according to the run-out �me criterion?

Product Demand Rate (1,000 �. per Month)

Current Inventory (1,000 �.)

Kra� paper 30,000 80,000 Duplicator bond 20,000 40,000 Regular bond 60,000 150,000 Carbon �ssue 10,000 40,000

2. The David-Harleyston Bicycle Company produces its two models of bicycles, the Avenger and the Hawk, in batches. Based on the following informa�on, which model should be produced next?

Model EOQ Current Inventory Monthly Sales Avenger 2,000 10,000 30,000 Hawk 5,000 6,000 20,000

3. A consultant must complete four reports. She es�mates that report A will take four hours, report B will take three hours, report C will take six hours, and report D will take two hours. In what sequence should she complete the reports, using the shortest-processing-�me rule?

4. A job shop has four jobs wai�ng to be processed on its computer numerically controlled (CNC) lathe. Determine the sequence of these jobs by using each of the five dispatching rules. Assume today is day 107, jobs arrived for processing in the order listed, and the following informa�on is given:

Job Due (Day) Process Time on CNC Lathe (Hours)

Total Processing Time Remaining (Days)

A 120 4 12 B 113 8 5 C 125 2 7 D 115 10 10

5. Late Wednesday a�ernoon, Data Processing Associates had four jobs wai�ng to be processed the next day. Each of these jobs requires keying in the data and then processing it on the company's computer. The DPNs data entry clerks, who work from 8:00 a.m. to 5:00 p.m., with an hour for lunch at noon, complete the data entry. The computer will be available con�nuously beginning at 9:00 a.m. on Thursday. Jobs may be processed immediately a�er being entered, or held for processing later.

Job Data Entry Time (Hours) Processing Times (Hours)

Time Due

A 1 1 3:00 p.m. B 1 2 12:00 noon C 2 0.5 2:00 p.m. D 2 2 5:00 p.m.

a. Develop schedules using the shortest-processing-�me, longest-processing-�me, and earliest-due-date rules, and draw Gan� load charts for data entry and processing, based on each rule.

b. Evaluate each of the schedules in part a to accommodate for customer service by calcula�ng average past due hours per job for each scheduling rule. 6. Bill Berry, the heat trea�ng department's second shi� foreman at Ace Machine Tool Company, wants to become foreman on the first shi�. To look good, Bill wants

to keep queues in his department to a minimum, so he has been using the shortest-processing-�me rule to schedule work. The assembly department, which usually receives jobs a�er they have been processed in Berry's department, is complaining they o�en do not get jobs early enough to meet the due dates.

The following jobs are currently in queue at the heat trea�ng department and must all be processed through the heat trea�ng department and then through the assembly department. Develop a schedule based on the shortest-processing-�me rule, and draw a Gan� chart for each department.

Processing Time (Days)

Job Heat Trea�ng Assembly Days Un�l Due 317 3 1 12 318 1 3 4 324 2 3 10 326 4 2 8

a. Determine whether there is a schedule that can meet all the due dates. b. Comment on the implica�ons of allowing each machine or work center to schedule its own work.

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7. Dr. Houseworth, an orthopedic surgeon, likes to be kept busy during his office hours. All pa�ents scheduled must first have X-rays before they see the doctor. On a certain Monday morning, Dr. Houseworth arrives at his office, and the following three pa�ents are wai�ng to be X-rayed before seeing him. Determine the sequence in which the pa�ents should be X-rayed to minimize the �me Dr. Houseworth is idle.

Pa�ent Time to X-Ray (Min.) Time with Doctor (Min.) Mrs. Green 5 10 Mr. White 15 20 Ms. Gray 10 20

8. The following jobs are wai�ng to be processed on one machine. Determine the sequence that will minimize average flow �me.

Job Processing Time (Days) A 4 B 2 C 6 D 3 E 5

9. The following jobs are wai�ng to be processed through two work centers. a. Use Johnson's Rule to determine a sequence. b. Draw a Gan� load chart for each work center.

Processing Time (Hours)

Job Work Center 1

Work Center 2

A 3.0 2.0 B 2.4 3.2 C 1.8 4.0 D 2.2 3.5

10. A printer has six prin�ng jobs. Each job requires typese�ng and prin�ng. a. Use Johnson's Rule to sequence the jobs based on the following expected processing �mes. b. Draw Gan� load charts for prin�ng and typese�ng.

Processing Time (Hours)

Job Typese�ng Prin�ng 1 2.00 3.00 2 3.00 4.00 3 2.50 1.75 4 1.25 2.00 5 3.50 2.50 6 2.25 3.00

11. A city government requires that all new construc�on projects be reviewed by an architect, a city planner, and an environmental engineer (in that order). Four different construc�on projects are wai�ng to be reviewed, and the review �me of each has been es�mated as shown in the following.

Project Architect City Planner

Environmental Engineer

A 3 hrs. 2 hrs. 4 hrs. B 2 hrs. 3 hrs. 2 hrs. C 4 hrs. 1 hr. 3 hrs. D 2 hrs. 1 hr. 3 hrs.

If the four projects must be processed in the order A, B, C, D by each person, use forward scheduling with finite loading to develop a Gan� load chart for each person.

12. Five parts must be processed through the following opera�ons, and each has the due date shown. The following table shows the �me required for each processing opera�on:

Part A Part B Part C Part D Part E Lathe (2 days) Lathe (1 day) Mill (1 day) Mill (3 days) Drill (1 day) Mill (3 days) Grind (1 day) Drill (1 day) Grind (1 day) Mill (3 days) Drill (1 day) Mill (2 days) Lathe (2 days) Grind (1 day)

Drill (1 day) Drill (1 day) Due at end of day 8 Due at end of day 6 Due at end of day 5 Due at end of day 10 Due at end of day 6

Use backward scheduling with infinite loading to develop a schedule for each part.

13. Develop a load profile for the city planner in Problem 11. Processing math: 0%

1/21/2020 Print

https://content.ashford.edu/print/AUBUS644.13.2?sections=cover,ch11,sec11.1,sec11.2,sec11.3,sec11.4,sec11.5,sec11.6,sec11.7,sec11.8,ch11sum… 48/49

14. Develop a load profile for the milling opera�on in Problem 12.

Click here to see solu�ons to the odd-numbered problems. (h�ps://media.thuze.com/MediaService/MediaService.svc/constella�on/book/AUBUS644.13.2/{pdf}bus644_ch12_odd_problem_solu�ons.pdf)

Key Terms

Click on each key term to see the defini�on

backward scheduling (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to scheduling that starts from a desired due date and works backward.

cri�cal-ra�o rule (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A measure of the ra�o between �me un�l an order is due and the processing �me remaining.

dispatching (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

Assigning priori�es and selec�on of jobs for processing at a work center.

dispatching rules (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

Rules used for assigning processing priori�es to jobs for scheduling.

finite loading (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to machine loading that considers available capacity.

forward scheduling (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to scheduling that starts from the present �me and schedules each job to start at the earliest possible moment.

Gan� load chart (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A graphic device for indica�ng the schedule of jobs on equipment or facili�es.

infinite loading (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to machine loading that does not take capacity considera�ons into account.

input/output control (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A method for managing work flow and queue lengths by comparing input to a machine with output from it.

load profile (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A diagram that indicates the work load being placed on each work center.

loading (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

An approach to scheduling that tries to take capacity u�liza�on into account.

makespan �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The total �me required to complete a set of jobs.

make-to-order company (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

Processing math: 0%

1/21/2020 Print

https://content.ashford.edu/print/AUBUS644.13.2?sections=cover,ch11,sec11.1,sec11.2,sec11.3,sec11.4,sec11.5,sec11.6,sec11.7,sec11.8,ch11sum… 49/49

A company that produces only to customer orders.

make-to-stock company (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A company that produces for inventory and meets customer orders from inventory.

move �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The material handling �me between work centers.

peak demand (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The highest level of demand that can be expected during a specific �me period.

queue �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The �me a job spends wai�ng to be processed at a work center.

run-out �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The period of �me before a company will run out of a par�cular product.

run �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The actual processing �me for a job.

scheduling (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A final, detailed determina�on of the �mes employees will work, the sequence in which goods or services will be provided, and the opera�ng �mes for machines.

sequencing (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

A step in the scheduling process in which the ordering of jobs or work is determined.

wait �me (h�p://content.thuzelearning.com/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/books/AUBUS644.13.2/sec�ons/cover/boo

The �me a job spends wai�ng before being moved to the next work center.

Processing math: 0%