operational management

732

Solution

DISCUSSION AND REVIEW QUESTIONS

GhapterSixteen Scheduling

We assume that the processing sequence remains unchanged and proceed on that basis. The solution

from the previous problem is shown in the following chart. The next chart shows reduced idle time at

center B when splitting is used.

0 2.20 4.70 10.50 1 5.00 18.80

5.20 9.40 10.50 14.50 17.00 18.80 20.30

o 1.10 2.20 4.70 7.60 10.50 12.75 15.00 18.80

0 1.10 4.10 8.90 12.90 14.00 16.00 18.05 19.55

An inspection ofthese two figures reveals that throughput time has decreased from 20.30 hours

to 19.55 hours. In addition, the original idle time was 5.6 hours. After splitting certain jobs, it was reduced to 4.85 hours, so some improvement was achieved. Note that processing times at B are gen-

erally less than at A for jobs toward the end of the sequence. As a result, jobs such as e and b at B were scheduled so that they were centered around the finishing times of e and b, respectively, at A,

to avoid having to break the jobs due to waiting for the remainder of the split job from A. Thus, the

greatest advantage from job splitting generally comes from splitting earlier jobs when Johnson's rule

is used for sequencing.

1. Why is scheduling fairly simple for repetitive systems but fairly complex for job shops?

2. What are the main decision areas ofjob-shop scheduling? 3. What are Gantt charts? How are they used in scheduling? What are the advantages of using Gantt

pharts?

4. What are the basic assumptions of the assignment method of linear programming?

5. Briefly describe each ofthese priority rules: a. FCFS b. SPT c. EDD d. SiO e. Rush

6. Why are priority rules needed? 7. What problems not generally found in manufacturing systems do service systems present in terms

of scheduling the use of resources?

8. Explain forward and backward schedulings and each one's advantage.

9. How are scheduling and productivity related? 10. What factors would you take into account in deciding whether to split a job?

11. Explain the term makespan.

t . One approach that can be effective in reducing the impact of production bottlenecks in a job shop or batch operations setting is to use smaller lot sizes. a. What is the impact of a production bottleneck? b. Explain how small lot sizes can reduce the impact ofbottleneck operations.

TAKING STOCK &v,^" general trade-offs are involved in sequencing decisions? In scheduling decisions?

@ *o needs to be involved in setting schedules?

{"i}Ho* has technology had an impact on scheduling?

CRITICAL THINKING EXERCISES