Topics

1. Detailed Scheduling (DS) EGN 5623 Enterprise Systems Optimization(Professional MSEM)Fall, 2011

2. Detailed Scheduling (DS)Theories & Concepts EGN 5623 Enterprise Systems Optimization(Professional MSEM)Fall, 2011

3. DS concepts • Finite and infinite loading • Scheduling directions • Sequencing rules • Criteria for evaluation of sequencing rules • Example for comparison of sequencing rules • Controlling changeover costs • Minimize total production time • Assignment problems • DS in SAP APO Topics

4. 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. Process-Focused Operations

5. Master Production Schedule (MPS) Product Design and Process Plans Material Requirements Plan (MRP) Capacity Requirements Plan (CRP) Order- Processing or Routing Plans Planned Order Releases Report Work Center Loading and Overtime Plan Assignment of Orders to Work Centers Scheduling and Shop-Floor Decisions Day-to-Day Scheduling and Shop-Floor Decisions

6. Design the product in customer order • Plan the operations the product must pass through ..... this is the routing plan • Work moves between operations on a move ticket Pre-production Planning

7. The production control department controls and monitors order progress through the shop. • 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 Common Shop Floor Control Activities

8. Input-Output Control • Gantt Chart • Finite and Infinite Loading • Forward and Backward Scheduling Shop Floor Planning and Control

9. Input-output control identifies problems such as insufficient or excessive capacity or any issues that prevents the order from being completed on time. • Input-output control report compares planned and actual input, planned and actual output, and planned and actual WIP in each time period Input-Output Control

10. Gantt charts are useful tools to coordinate jobs through shop; graphical summary of job status and loading of operations Gantt Charts

11. Work Centers Wed. Sat. Mon. Tue. Fri. Thu. Machining Fabrication Assembly Test E F G D E F C H C D E D H C Gantt Charts Scheduled Progress Setup, Maint.

12. Infinite loading • Assigns jobs to work centers without regard to capacity • Unless excessive capacity exists, long queues occur • Finite loading • Uses work center capacity to schedule orders • Popular scheduling approach • Integral part of CRP Assigning Jobs to Work Centers:How Many Jobs/Day/Work Center

13. Forward scheduling • Jobs are given earliest available time slot in operation • excessive WIP usually results • Backward scheduling • Start with promise date and work backward through operations reviewing lead times to determine when a job has to pass through each operation • Less WIP but must have accurate lead times Assigning Jobs to Work Centers:Which Job Gets Built First?

14. Sequencing Rules • Criteria for Evaluating Sequencing Rules • Comparison of Sequencing Rules • Controlling Changeover Costs • Minimizing Total Production Time Order-Sequencing Problems

15. 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. Order-Sequencing Problems

16. First-Come First-Served (FCFS) Next job to process is the one that arrived first among the waiting jobs • Shortest Processing Time (SPT) Next job to process is the one with the shortest processing time among the waiting jobs • Earliest Due Date (EDD) Next job to process is the one with the earliest due (promised finished) date among the waiting jobs Order-Sequencing Rules

17. Least Slack (LS) Next job to process is the one with the least [time to due date minus total remaining processing time] among the waiting jobs • Critical Ratio (CR) Next job to process is the one with the least [time to due date divided by total remaining processing time] among the waiting jobs • Least Changeover Cost (LCC) Sequence the waiting jobs such that total machine changeover cost is minimized Order-Sequencing Rules

18. Average flow time - average amount of time jobs spend in shop • Average number of jobs in system - • Average job lateness - average amount of time job’s completion date exceeds its promised delivery date • Changeover cost - total cost of making machine changeovers for group of jobs Evaluating the Effectivenessof Sequencing Rules

19. First-come-first-served • Performs poorly on most evaluation criteria • Does give customers a sense of fair play • Shortest processing time • Performs well on most evaluation criteria • But have to watch out for long-processing-time orders getting continuously pushed back • Critical ratio • Works well on average job lateness criterion • May focus too much on jobs that cannot be completed on time, causing others to be late too. Experience Says:

20. Use the FCFS, SPT, and Critical Ratio rules to sequence the five jobs below. Evaluate the rules on the bases of average flow time, average number of jobs in the system, and average job lateness. JobProcessing TimeTime to Promised Completion A 6 hours 10 hours B 12 16 C 9 8 D 14 14 E 8 7 Example: Sequencing Rules

21. FCFS Rule A > B > C > D > E Processing Promised Flow JobTimeCompletionTimeLateness A 6 10 6 0 B 12 16 18 2 C 9 8 27 19 D 14 14 41 27 E 8 7 4942 49 141 90 Example: Sequencing Rules

22. FCFS Rule Performance • Average flow time: 141/5 = 28.2 hours • Average number of jobs in the system: 141/49 = 2.88 jobs • Average job lateness: 90/5 = 18.0 hours Example: Sequencing Rules

23. SPT Rule A > E > C > B > D Processing Promised Flow JobTimeCompletionTimeLateness A 6 10 6 0 B 8 7 14 7 C 9 8 23 15 D 12 16 35 19 E 14 14 4935 49 127 76 Example: Sequencing Rules

24. SPT Rule Performance • Average flow time: 127/5 = 25.4 hours • Average number of jobs in the system: 127/49 = 2.59 jobs • Average job lateness: 76/5 = 15.2 hours Example: Sequencing Rules

25. Critical Ratio Rule E > C > D > B > A Processing Promised Flow JobTimeCompletionTimeLateness E (.875) 8 7 8 1 C (.889) 9 8 17 9 D (1.00) 14 14 31 17 B (1.33) 12 16 43 27 A (1.67) 6 10 4939 49 148 93 Example: Sequencing Rules

26. Critical Ratio Rule Performance • Average flow time: 148/5 = 29.6 hours • Average number of jobs in the system: 148/49 = 3.02 jobs • Average job lateness: 93/5 = 18.6 hours Example: Sequencing Rules

27. Comparison of Rule Performance Average Average Average Flow Number of Jobs Job Rule Time in System Lateness FCFS 28.2 2.88 18.0 SPT 25.4 2.59 15.2 CR 29.6 3.02 18.6 SPT rule was superior for all 3 performance criteria. Example: Sequencing Rules

28. Changeover costs - costs of changing a processing step in a production system over from one job to another • Changing machine settings • Getting job instructions • Changing material • Changing tools • Usually, jobs should be processed in a sequence that minimizes changeover costs Controlling Changeover Costs

29. Job Sequencing Heuristic • First, select the lowest changeover cost among all changeovers (this establishes the first two jobs in the sequence) • The next job to be selected will have the lowest changeover cost among the remaining jobs that follow the previously selected job Controlling Changeover Costs

30. Hardtimes Heat Treating Service has 5 jobs waiting to be processed at work center #11. The job-to-job changeover costs are listed below. What should the job sequence be? Jobs That Precede A B C D E A -- 65 80 50 62 B 95 -- 69 67 65 C 92 71 -- 67 75 D 85 105 65 -- 95 E 125 75 95 105 -- Jobs That Follow Example: Minimizing Changeover Costs

31. Develop a job sequence: A follows D ($50 is the least c.o. cost) C follows A ($92 is the least following c.o. cost) B follows C ($69 is the least following c.o. cost) E follows B (E is the only remaining job) Job sequence is D – A – C – B – E Total changeover cost = $50 + 92 + 69 + 75 = $286 Example: Minimizing Changeover Costs

32. Sequencing n Jobs through Two Work Centers • When several jobs must be sequenced through two work centers, we may want to select a sequence that must hold for both work centers • Johnson’s rule can be used to find the sequence that minimizes the total production time through both work centers Minimizing Total Production Time

33. 1. Select the shortest processing time in either work center 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job in the last unassigned slot in the schedule. 3. Eliminate the job assigned in step 2. 4. Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot. Johnson’s Rule

34. It is early Saturday morning and The Finest Detail has five automobiles waiting for detailing service. Each vehicle goes through a thorough exterior wash/wax process and then an interior vacuum/shampoo/polish process. The entire detailing crew must stay until the last vehicle is completed. If the five vehicles are sequenced so that the total processing time is minimized, when can the crew go home. They will start the first vehicle at 7:30 a.m. Time estimates are shown on the next slide. Example: Minimizing Total Production Time

35. Exterior Interior Job Time (hrs.) Time (hrs.) Cadillac 2.0 2.5 Bentley 2.1 2.4 Lexus 1.9 2.2 Porsche 1.8 1.6 Infiniti 1.5 1.4 Example: Minimizing Total Production Time

36. Johnson’s Rule Least Work Schedule Time Job Center Slot 1.4 Infiniti Interior 5th 1.6 Porsche Interior 4th 1.9 Lexus Exterior 1st 2.0 Cadillac Exterior 2nd 2.1 Bentley Exterior 3rd Example: Minimizing Total Production Time

37. 0 1.9 3.9 6.0 7.8 9.3 12.0 L C B P I Idle Exterior Interior Idle L C B P I 0 1.9 4.1 6.6 9.0 10.6 12.0 It will take from 7:30 a.m. until 7:30 p.m. (not allowing for breaks) to complete the five vehicles. Example: Minimizing Total Production Time

38. Minimize Total Production Time

39. Minimize Total Production Time

40. Minimize Total Production Time

41. Minimize Total Production Time

42. Tasks and activities of detailed scheduling • Controlling Detailed Scheduling • Dates/Times and Planning Directions • Resource Availability • Selection of Resources • Time Relationships • Pegging Relationships • Automatic Propagation of Changes • Determining the Setup Time for Sequence-Dependent Setup Activities • Synchronizing Activities on Multi-resources • Block planning • Scheduling Log • Terminating Scheduling • Detailed Scheduling Heuristics DS in SAP APO

43. Detailed scheduling is used to:  Determine the resources and dates/times for carrying out operations, taking resource and product availability into consideration. Support the scheduler in scheduling resources when creating an optimal processing sequence for operations Tasks of Detailed Scheduling

44. Basic DS Activities: • Scheduling • dispatching operations to resources at a specific date/time • Rescheduling • dispatching already scheduled operations to a different date/time or to different resources • De-allocating • removing scheduled operations from the resource schedule • Adjusting • a new date/time or new resources are assigned to a de-allocated operation. • Fixing • the resource and date/time for the operation is fixed. Activities of Detailed Scheduling

45. Schedule: • For an operation of a newly created order or for a de-allocated operation • The resources are determined on which the operation should be processed • The date/time is determined when the operation should be processed on the resources • With scheduling, the operation is dispatched to the resources. Scheduling an order means scheduling all the operations of the order. Activities of DS: Schedule

46. Reschedule: • A new date/time or new resources are specified for a scheduled operation. • With rescheduling, the operation remains loaded on resources. • After rescheduling, it loads either the previous resources or the new resources. • Rescheduling an order means rescheduling all the operations of the order. Activities of DS: Reschedule

47. Remove an operation from the resource schedule. • With de-allocation, an operation is given the status de-allocated. The operation no longer loads any resources. • De-allocating an order means de-allocating all the operations of the order. • An operation in the SAP APO system is either scheduled  with no separate status  or de-allocated (in this case it has the status de-allocated). Activities of DS: De-allocate

48. A new date/time or new resource is assigned to a de-allocated operation. • In the case of an adjustment, the operation retains the status de-allocated. The operation does not load the resources to which it is assigned. Adjusting does not change any resources schedules. • Adjusting is a detailed scheduling activity that is carried out automatically by the system for dependent objects (for example, if relationships or pegging relationships have to be adhered to). You cannot adjust de-allocated operations manually. Activities of DS: Adjust

49. The resource and date/time for the operation is fixed. • Through the fixing process, a scheduled or de-allocated operation is assigned the status fixed. • A fixed scheduled operation cannot be rescheduled or de-allocated, and a fixed de-allocated operation cannot be scheduled or adjusted. Activities of DS: Fix

50. Integrated Distribution & Production Planning SAP Implementation EGN 5623 Enterprise Systems Optimization(Professional MSEM)Fall, 2011