Homework 2

  JUST-IN-TIME SYSTEMS

Basic Elements of JIT     JIT is a philosophy and integrated management system based on the concept of eliminating all waste. Just-in-time production is also known as lean production. The intention of just-in-time production is to produce only what is needed, when it is needed. Waste has a very comprehensive meaning in just-in-time systems. Some examples of waste are

· Watching a machine run

· Waiting for parts

· Counting parts

· Overproduction

· Moving parts over long distances

· Storing inventory

· Looking for tools

· Machine breakdowns

· Rework

Many techniques are used for eliminating waste in a just-in-time production system. Ideas come from employees working on continuous programs of improvement. There are also other common elements of just-in-time that define the philosophy and management system:

· Flexible resources

· Cellular layouts

· Pull production system

· Kanban production control

· Small-lot production

· Quick set-ups

· Uniform production

· Quality at the source

· Total productive maintenance

· Supplier networks

Flexible Resources

Flexibility is the key to eliminating waste, like excess or obsolete inventory and worker idle time. The following resources are the source of such flexibility:

· Multifunctional workers -- workers able to operate multiple machines or skilled at multiple tasks. They can be easily rotated as demand changes.

With workers operating several machines, an incentive is created to modify machines so that they require minimal human intervention.

· General purpose machines -- create flexibility by allowing various machining operations to be performed on a single machine.

· Improved operator movements and operations -- Time and motion studies lead to new ideas of how to minimize movement and travel.

Cellular Layouts

Intersecting flow patterns are a problem in process (functional) layouts where similar machines are grouped together. Cellular layouts eliminate the intersecting flow pattern by:

· Using group technology to group parts into families with similar processing requirements.

· Grouping dissimilar machines in a U-shape or manufacturing cell to produce a family of parts

· Laying out the cell so that work flows in one direction through the cell.

· Adjusting the cycle time by changing work paths. Workers in a cell may operate several machines. The workers do not necessarily operate in the same consecutive flow pattern as the product

The Pull System/Kanban Production System In a pull system, the system pace is determined by the slowest workstation in the system. A worker cannot pass on any work to the next station until the next station has passed its work on to its subsequent station   Pull production (Kanban System) is a process that aims to arrange an organization so that customer preference or orders are what cause materials to be "pulled" through a system.

Kanban is the Japanese word for card. It is the "visible record" used in a pull system. Kanbans provide the means for signaling when work needs to flow. The kanban system should always be kept as simple as possible.   Small-lot Production   Producing in small lots has many benefits, including

· Setup times -- can be reduced through a variety of techniques as described next.

Shigeo Shingo is well-known for his SMED (single-minute-exchange of dies) principles, which were developed to reduce setup times. For example, Shingo reduced the setup time on a 1,000 ton press from six hours to three minutes using the following principles:  

· Separate internal setup from external setup -- internal setups must be performed while the machine is stopped; external setups may be made while the machine is running.

· Convert internal setup to external setup

· Streamline all aspects of setup

· Perform setup activities in parallel or eliminate them entirely

  Total Productive Maintenance

Two basic types of maintenance are

· Breakdown maintenance -- repairs to make failed machine operational

· Preventive maintenance -- system of periodic inspection and maintenance to keep machines operating

Total productive maintenance (TPM) seeks a higher degree of maintenance than preventive maintenance. Total productive maintenance combines the practice of preventive maintenance with the concepts of total quality -- employee involvement, decisions based on data, zero defects, and a strategic focus. TPM requires management to

· Design products that can be easily produced on existing machines.

· Design machines for easier operations, changeover, and maintenance.

· Train and retrain workers to operate machines.

· Purchase machines that maximize productive potential

· Design preventive maintenance plan spanning life of machine

Uniform Production Levels

Uniform production levels help moderate the amount of inventory in the system and avoid the use of excess overtime. Production is leveled by the use of better forecasting techniques and the use of mixed model sequencing.

 A sequence of L-M-S-M-L repeated 40 times per day represents mixed model sequencing. Producing 80 L's, then 80 M's, then 40 S's is batch production and sequencing..

Quality at the Source   Quality must be extremely high in a JIT system because there is little inventory to buffer against quality mistakes. A JIT system should have a zero defect policy that seeks to identify quality problems at their source. Workers, not inspectors should be responsible for quality. Worker responsibility for quality requires the following components:

· Jidoka - the authority to stop the production line.

· Andon lights - to signal quality problems on the line.

· Undercapacity scheduling - allows for planning, problem-solving, and maintenance

· Visual control - makes problems visible (Figure 15.9)

· Poka Yoke - devices, processes, and designs to prevents defects

· Kaizen - Continuous improvement which requires total employment involvement

The essence of JIT is the willingness of workers to

· spot quality problems

· halt production when necessary

· generate ideas for improvement

· analyze problems

· perform different functions

Supplier Networks

Just-in-time purchasing and supply has developed rapidly. Trends in supplier policies include:

· Locate near to the customer

· Use small, side loaded trucks and ship mixed loads

· Consider establishing small warehouses near to the customer or consolidating warehouses with other suppliers

· Use standardized containers and make deliveries according to a precise delivery schedule

· Become a certified supplier and accept payment at regular intervals rather than upon delivery

Benefits of JIT     The benefits of JIT are similar to those of advanced manufacturing technology, but they are achieved through reduction of waste and productive management of human resources. In essence, JIT achieves the four strategic objectives of manufacturing simultaneously -- low cost, high quality, high flexibility, and quick delivery. These overall benefits come from

· Reduced inventory

· Reduced space requirements

· Shorter lead time

· Increased productivity

· Better relations with suppliers

· Simplified scheduling and control activities

· Increased capacity

· Better use of human resources

· More product variety

JIT Implementation

Just-in-time production began in Japan in the 1970’s and spread to the U. S. in the 1980’s. We can make these general observations about JIT:

· JIT is used to finely tune an operating system.

· JIT is somewhat different in U. S. than in Japan and goes by several names, including stockless production, material-as-needed, continuous-flow, zero inventory production system, and lean production.

· JIT is still evolving and meshing in new ways with advanced technology

· JIT isn’t for everyone -- mass production is still best for very high volume production; job shops are still necessary for highly specialized products