Production Activity Control in Manufacturing Settings

1. Production Activity Control

2. When the plan has been developed, the next step is execution of the plan • Production Activity Control (or often called Shop Floor Control) is to have activities performed as planned • Techniques for scheduling different for various manufacturing systems: • Project • Job shop • Batch • Flow shop

3. Scheduling Batch Flow Line • A group of similar items is manufactured on the batch line • The focus is to minimize changeover time • The smaller the changeover time, the greater the scheduling flexibility • It is becoming very complicated when you have sequence-dependent setup

4. How much to produce? Or How long the run time will be? • Depends on: • Available on hand • Demand rate • The changeover time • Production rate • The sequence, if any, in which items should be run • When the setup times are relatively small and independent of the sequence  produce first the item with smallest runout time • Runout time is the period existing inventory will last given forecast usage (= units in inventory / demand rate)

5. Example

6. Another Example Do you see any problem here? What would be the solution?

7. Job Shop Scheduling • Job shop production is characterized by: • Process layout • Many orders with different sequence of processes • Scheduling is assigning of starting and completion times to orders (jobs) and frequently includes the time when orders are to arrive and leave each department. • Sequencing is the assigning of the sequence in which orders are to be processed.

8. Priority Control • To determine the sequence in which orders should be processed • Common Priority Rules: • First come first served (FCFS) • Short processing time (SPT) : results in lowest WIP, lowest MLT, and lowest average job lateness • EDD (Earliest due date): works well when processing times are approximately the same • Slack time (ST): supports the achievement of due date objectives • Critical ratio (CR)

9. Example Day 125 (all times are in days) ST = Due Date – Present Date – Total Operations Time Remaining Due Date – Present Date CR = ------------------------------------------- CR = 1 means the order is on schedule MLT Remaining

10. Sequencing Results • EDD : A – B – C – D • SPT : B – A – C – D • ST : A – B – D – C • CR : B – A – C – D • Observation: • A and B always scheduled earlier than C and D • Important: • The status of WC to which each order goes next should be considered. (If A will go to a work center overloaded with high priority orders, there is little point of scheduling it first in the current WC)

11. Queue Length Management • Affect WIP and manufacturing lead times • Queues are planned to compensate uneven flow of incoming work and the variations in work center processing times • The objective of QLM: • To reduce WIP • To shorten MLT • To better utilize bottleneck resources

12. Operations Overlapping • Dividing a lot into two or more batches • Used to reduce MLT To avoid idle of operation B, SU2+TAB+Q1PB>=Q2PA+TAB Where Q = Q1+Q2

13. Savings in Lead Time Without overlapping With overlapping Lead time savings

14. INPUT/OUTPUT CONTROL • Short-range control technique (normally daily) • Compare scheduled input and output to actual input and output • Effective for controlling queue, WIP, and MLT • Enable the planner to determine the actions necessary to achieve the desired output , WIP, and MLT

15. Single Work Center Processes

16. Input / Output Control

17. Normal Situation (Under Control) • PWIP is less than 3 or 4 times of std of the ending WIP • Acceptable deviation is about twice the standard deviation • Typical out of control situations: • Queues exceed upper limit due to equipment failure, inefficient processing, and excessive input. Solution: decreasing input or increasing process output. • Output is below the lower limit due to equipment failure, inefficient processing, inadequate input, or wrong input at assembly work centers.

18. WIP Reduction

19. Inadequate Input