Topic-14

1. Topic-14 Production Activity Control

2. Production Activity Control (PAC) • Objectives of PAC: 1. Meeting job due-dates 2. Controlling work-in-process inventory level 3. Reducing shop congestion and leadtimes 4. Controlling the queues at each work center 5. Preventing bottleneck machines in advance. 6. Increasing shop utilization

3. Production Activity Control (II) • Five major data files in PAC: • Item master file • Job routing file • Work center master file • Shop order master file • Shop order status file

4. Data Requirements The Files generally required For a PAC System Are: Planning Files Control Files

5. Scheduling and Shop Floor Decisions in Job-Shop Operations

6. Function of Production Activity Control (I) The major function of an efficient productions activity control system consists of the following: • Releasing orders to the production on schedule having verified material, tool. Equipment and personnel available. • Preparing shop packet (shop order, drawing, pick list, route sheet, tool request form, labor ticket, move ticket, etc.) • Establishing scheduled start and completion dates of steps in the production process as well as the schedules completion date of the order, as milestones to measure progress

7. Function of Production Activity Control (II) • Comparing future workload with planned capacity to allow for a determination of appropriate action for balancing work • Ranking orders in desired priority sequence by work center and issuing a dispatch list • Tracking the current status of each order in process • Providing timely and accurate feedback on activities not proceeding according to plan • Revising order priorities on the basis of performance and changing conditions • Monitoring and controlling lead time, work center queue and work in process • Providing exception and performance evaluation reports (scrap, rework, late order, and work center efficiency analysis reports)

8. The large number of logs in the river at the same time creates a “log jam” which restricts the overall flow of the logs to their saw mill destination To increase the flow of the logs the saw mill down river, the number of logs placed in the river at one time must oftentimes be reduced.

9. Shop Work Load Control Load

10. Production Control Overview Four Major functions of production control:

11. Process-Focused Manufacturing • Process-focused factories are often called job shops • A job shop’s work centers are organized around similar types of equipment or operations • Workers and machines are flexible and can be assigned to and reassigned to many different orders • Job shops are complex to schedule

12. Process-Focused Manufacturing • The production department controls and monitors order progress through the shop by: • Assigns priority to orders • Issues dispatching lists • Tracks WIP and keeps systems updated • Controls input-output between work centers • Measures efficiency utilization and productivity of shop.

13. Job Dispatching (Sequencing) Rules • Dispatching rule: determine which job will be processed next among the jobs waiting in queue. • Common dispatching rules: • FCFS (first-come, first served) • SPT (shortest processing time—job first) • LPT ( longest processing time—job first) • EDD (earliest due-date—job first) • MRO ( most remaining operations—job first) • CR ( critical ratio: smallest CR job first)

14. Job Dispatching Rules (II) • CR=(due date – current time) / total remaining operation time If CR=1, this order is in critical If CR<1, this order is late already If CR>1, this order has some slack time • Most dispatching rules are heuristic in nature • Different rules perform differently under different measures.

15. Example of Evaluation Criteria for Production Scheduling • Minimize average lateness for completed jobs • Minimize average flow time for completed jobs • Minimize maximum lateness for completed jobs • Minimize maximum flow time for completed jobs • Maximize machine utilization in facility • Minimize average value of work-in-process • Maximize worker utilization • Balance workload assigned to each worker/machine • Maximize volume of work completed in each time period

16. Job Dispatching Example • There are three jobs waiting for machine 1. their processing time requirement and due-dates are given below: Dispatching jobs by SPT, LPT and EDD. Comparing the average job flow time and the the number of jobs late

17. Job Dispatching Example There are three jobs waiting for Machine 1. Their processing time requirement and due-dates are given below: Dispatching jobs by SPT, LPT, and EDD. Comparing the Average Job Flow Time and the Number of Jobs Late

18. Job Dispatching Example a) SPT 0 2 5 14 Average Job Flow Time = (2+5+14)/3=21/3=7 No. of Jobs Late = 1 (3)

19. Job Dispatching Example b) LPT 0 9 12 14 Average Job Flow Time = (9+12+14)/3=35/3=11.67 No. of Jobs Late = 1 (7)

20. Job Dispatching Example c) EDD 2 0 11 14 Average Job Flow Time = (2+11+14)/3=27/3=9 No. of Jobs Late = 0

21. Exercise: Job Dispatching Problem • There are eight jobs waiting in the queue for processing on machine 1. The jobs are arranged in order of their arrival with A, B, C,… G,H. • Use FCTS (First come first serve) dispatching rule. Compute Total Job Completion Time, Average Job Flow, and Average Job Lateness. • Use SPT (Shortest Processing Time) dispatching rule. Compute Total Job Completion Time, Average Job Flow Time, and Average Job Lateness.

22. Exercise: Job Dispatching Problem There are eight jobs waiting in the queue for processing on machine1. The jobs are arranged in the order of their arrival with A, B, C, … G, H. • Use FCFS (first-come-first-serve) dispatching rule. Compute total job completion time, average job flow time, and average job lateness. • Use SPT (shortest processing time) dispatching rule. Compute total job completion time, average job flow time, and average job lateness

23. By FCFS Rule A 27 27 32 -5 14 B 33 41 8 C 7 31 48 17 31 D 79 40 39 E 9 88 28 60 27 115 52 63 F 3 G 9 109 118 H 1 95 139 44 400 655 ( ) Total ( ) Average Job Flow Time= (Total Flow-Time)/Number of Jobs = 655/8=82 Average Lateness= (Total Lateness)/Number of Jobs = 400/8=50

24. By SPT Rule G 3 3 9 -6 17 C 7 10 -7 E -9 9 19 28 33 33 B 14 0 54 44 H 21 10 81 32 A 27 49 108 52 F 27 56 139 40 D 31 99 192 Total ( ) 447 ( ) Average Job Flow Time= (Total Flow-Time)/Number of Jobs = 447/8=56 < 82 Average Lateness= (Total Lateness)/Number of Jobs = 192/8=24 < 50

25. Using <POM-Windows> software to do Supplement Scheduling Problems on p. 14-9.

26. Operations Scheduling

27. Job-Sequencing Problems • We want to determine the sequence in which we will process a group of waiting orders at a work center. • Many different sequencing rules can be followed in setting the priorities among orders. • There are numerous criteria for evaluating the effectiveness of the sequencing rules.

28. Job-Sequencing Problems (II) General performance: 1.First come first served: poor performance and fair play. 2.Shortest processing time: good performance and may continuously push the long processing time orders back. 3.Critical ratio: good performance and focuses too much on jobs that cannot be completed on time.

29. Product-Focused (Production Line) Scheduling • Scheduling decisions: • If products are produced in batches on the same production lines: --how large should production lot size be for each product? --when should machine changeovers be scheduled? • If products are produced to a delivery schedule: --at any point in time how many products should have passed each operation if time deliveries are to be on schedule?

30. Product-Focused Scheduling • Computerized scheduling: • Develops detailed schedules for each work center indicating starting and ending times • Develops departmental schedules • Generates modified schedules as orders move • Many packages available select one most appropriate for your business

31. Scheduling in Service Operations • Major characteristics of scheduling in service operations: • Large demand fluctuation due to customer involvement • Intangible output can not be inventoried, capacity flexibility is critical • Capacity is labor-intensive in customer-contact operations

32. Scheduling in Service Operations (II) • Two major scheduling issues: • Worker shift construction: how many shifts per working day? • Staffing for each shift: how many workers will be assigned to each shift? • Major scheduling techniques in service operations: • Optimization analytical models • Practical-oriented scheduling heuristics • Queuing models • Computer simulation search algorithms • ………………

33. Scheduling in Service Operations- I • Scheduling customer demand • Appointments • Reservations • Backlogs • Scheduling the workforce • Translates the staffing plan into specific schedules of work for each employee • Must satisfy workforce requirements • Must reallocate employees if requirements change • Major Scheduling Constraints • Technical constraints • Legal and behavioral considerations • Schedule types fixed and rotating

34. Scheduling in Service Operations- II • Computerized workforce scheduling systems • Useful in coping with complex systems • 24/7 schedules and the need for great flexibility add significantly to the complexity of scheduling • Scheduling across the organization • Schedule involves an enormous amount of detail and affect every process in the firm • Product, services, and employees schedule determine specific cash flow requirements, trigger the billing process, and may initiate requirements for employee training processes • Good scheduling processes can decrease costs and improve responsiveness to supply-chain dynamics • The scheduling process, whether it is in manufacturing or services, can provide any firm with a capability useful in competing successfully

35. Service Operations: Planning and Scheduling • Service are operations with: • Intangible outputs that ordinarily cannot be inventoried • Close customer contact and short lead time • High labor costs relative to capital costs • Subjectively determined quality • Need better planning controlling and management to stay competitive

36. Service Operations: Planning and Scheduling (II) • Positioning strategies contain two elements: • Type of service design --Standard or custom --amount of customer contact --mix of physical goods and intangible services

37. Service Operations: Planning and Scheduling (III) • Type of production process: --quasi-manufacturing: production occurs much as manufacturing physical goods dominant over intangible services --customer as participant: high degree of customer involvement physical goods may or may not be significant service either standard or custom --customer as product: service performed on customer usually custom

38. Service Operations: Planning and Scheduling (IV) • Scheduling challenges in services: planning and controlling day-to-day activities difficult due to: --service produced and delivered by people --pattern of demand for services is non-uniform

39. Work Shift Scheduling in Service Operations • Three difficulties in scheduling services: --demand variability --service time variability --availability of personnel when needed • Managers use two tactics: --use full-time employees exclusively --use some full-time employees as base and fill in peak demand part-time employees

40. Work Shift Scheduling in Service Operations (II) • Scheduling customer-as-participant services • Must provide customer ease of use/access features lighting walkways, etc. • Layouts must focus on merchandising and attractive display of products • Employee performance crucial to customer satisfaction • Waiting times used extensively to level demand variation

41. Waiting Line in Service: Examples • Computer printing jobs waiting for printing • Workers waiting to punch a time clock • Customers in line at a driven-up window • Drivers waiting to pay a highway toll • Skiers waiting for chair lift • Airplanes waiting to take off

42. Waiting Line in Service (II) • Waiting line analysis: assists managers in determining: • How many servers to use • Likelihood a customer will have to wait • Average number of customer will wait • Waiting line space needed • Percentage of time all servers are idle

43. Waiting Line in Service (III) • Scheduling customer as product services • Wide range of complexity • Every facet designed around the customer • Highly trained motivated and effective workforce critical to success • Waiting-line analysis can be helpful in determining staffing levels • In more complex operations simulation is a helpful tool in scheduling resources.

44. Waiting Line in Service (IV) • Reasons for simulating operations • Experimentation with the real system is impossible impractical or uneconomical • System is so complex that mathematical formulas cannot be developed • Values of the system’s variables are not known with certainty