Production planning and. Unit 3

Transcription

1 1 Production planning and scheduling Unit 3

2 2 Background Because the aircraft manufacturing industry is highly sensitive to fluctuating demands and to their corresponding impact on production costs, a thorough knowledge of scheduling systems is essential to our competitive position. A stable work force is a major goal of our aggregate planning process because of the added costs of erratic variations in the work force, Even minor changes, such as job transfers, multiple to many changes in a highly skilled and unionized environment.

3 3 McDonnell Douglas Canada Ltd. uses several methods to maintain the delicate balance between short-term flexibility, necessary to meet changing market demands, and long-term production planning necessary to keep costs competitive. The effective use of suitable long-term planning horizons, Inventories, reassigned employees, and level loading through finite capacity planning are some of the tools that help to temper the impact of change.

4 4 In an industry in which as many as different parts (some of them used in large multiple quantities) are incorporated into a single aircraft component that has relatively long flow times, a discipline approach to planning and scheduling systems is required. Garret G. Ackerson, President McDonnell Douglas Canada Ltd. Toronto, Ontario, Canada Adam and Ebert, Production and Operations Management

5 5 Success of Organization How would we use the potentially productive resources during the next six months, year, or even longer?

6 6 Production planning and scheduling concern The volume and timing of outputs. The utilization of operations capacity. Balancing outputs with capacity at desired levels for competitive effectiveness.

7 7 What do we want? Better customer service Lower inventory Shorten customer lead times Stabilize production rates For this BALANCING DEMAND AND SUPPLY is essential Production planning and scheduling

8 Overview: Business Plan 8 Output Planning Aggregate output planning Master production scheduling Material requirement planning Loading Operations Capacity Planning Aggregate capacity planning Rough-cut capacity planning Detailed capacity planning Sequencing Detailed Scheduling Expediting Shop floor control Short-term capacity control

9 9 The Business Plan A statement of an organization s overall level of business activity for the coming 6 to 18 months, usually expressed in terms of dollars / rupees volume of sales for its various product groups. BP Economic condition etc is an agreement between all functional areas is a general posture for competing Back

10 10 Aggregate Production (Output) Planning Production portion of Business plan Demand side of firm s activities The process of determining output levels (units) of product groups over the coming 6 to 18 months on a weekly or monthly basis; the plan identifies the overall level of outputs in support of the business plan. Back

11 11 Aggregate Capacity Planning The process of testing the feasibility of aggregate output plans and evaluating overall capacity utilization. Supply side of firm s ability to meet demand. Short term capacity manipulation Back

12 12 Master Production Scheduling (MPS) For meeting the demand of individual products in the product group disaggregating the product groups into individual products and indicates when they will be produced. A schedule showing week by week how many of each product must be produced according to customer orders and demand forecasts. Back

13 13 Rough-Cut Capacity Planning (Resource requirement planning) The process of testing the feasibility of master production schedules in terms of capacity. Ensuring a proposed MPS does not inadvertently overload any key department, work centre, or machine, making the MPS unworkable. Back

14 14 Shop floor Control Activities that execute and control shop operations; includes loading, sequencing, detailed scheduling, and expediting jobs in production. Loading: assigning individual jobs to machines and work centers Sequencing: determining the sequence of processing the jobs for priority control Detailed scheduling: deciding starts times and job assignments for each stage of processing expediting: monitoring and adjusting material and work flows from station to station Back

15 15 Short-term capacity control coordinating all of the activities into smooth flows, especially when unplanned delays and new priorities arise, often calls for last-minute adjustments of outputs and capacities. Back

16 Overview: Business Plan 16 Output Planning Aggregate output planning Master production scheduling Material requirement planning Loading Operations Capacity Planning Aggregate capacity planning Rough-cut capacity planning Detailed capacity planning Sequencing Detailed Scheduling Expediting Shop floor control Short-term capacity control

17 17 The Aggregate Planning Process Four basic considerations Concept of aggregation Meaningful measure of output produced Goals of aggregate planning Overall levels of output, inventory and backlogs dictated Using capacity in a manner consistent with the organization s strategy Consistent with the company s goals and policies regarding its employees.

18 18 The Aggregate Planning Process Forecasts of aggregate demand Benefits of aggregate planning depend on accurate forecasting The options for adjusting shortrun capacity

19 Example Source: Adam and Ebert (2007) 19 As manager of a refrigerator manufacturing facility, you want to plan the level of output for February. At the end of January you observe 100 refrigerators in inventory. Twenty assemblers were on the payroll in January, each earning a salary of $1600/month. On average, each assembler produces 10 refrigerators/month. You have just been informed that the demand for February is 200 refrigerators. Since you already have 100 in inventory, you decide to produce exactly 100 more during February so you can meet the February demand of 200 units. Since only 10 assemblers are required to produce February s planned output, you lay off 10 assemblers at an average layoff cost of $400/worker. One month later you face a similar decision. Demand for refrigerators in March is estimated to be 300 units for March must be produced during March. To accomplish this, you must hire 20 additional assembler at the beginning of March so that work force (30 assemblers) can produce the required 300 units. The cost of hiring and training assemblers averages $300/assembler.

20 One month planning horizon 20 Paid Employees Laid-off employees Hired Employees Mont h No. Output (10 units/ employe e) Wages ($1600/ employe e) N o. Cost ($400/ employe e) No. Cost ($300/ employee ) Total Cost Feb Mar Total

21 Two month planning horizon 21 Mont h No. Paid Employees Output (10 units/ employe e) Wages ($1600/ employe e) N o. Laid-off employees Cost ($400/ employe e) Hired Employees No. Cost ($300/ employee ) Total Cost Feb Mar Total # Short time horizons can be undesirable # By extending the planning horizon, we dramatically increase the number of alternatives

22 22 Strategies for developing Aggregate Planning AP translates the business plan into manufacturing terms (in units and labour hours) Vary the number of productive employees in response to varying output requirements Maintain a constant work force size but vary the utilization of work force Vary the size of inventory in response to varying demand

23 23 Master scheduling and rough cut capacity planning Disaggregation of aggregate plans

24 24 Master Production Schedule (MPS) Time-phased plan specifying how many and when the firm plans to build each end item Aggregate Plan (Product Groups) MPS (Specific End Items)

25 25 Rough Cut Capacity Planning Checking overall labour-hour requirements When discrepancies arise between When discrepancies arise between available and required capacities they must be reconciled by revising the MPS or by adjusting the capacity

26 26 Aggregate planning for Service organization

27 27 Aggregate planning for Service organization Service Organization Make-to-order rather than make-to-stock No finished goods for responding to demand fluctuation Backlogs of customer requests can be increased or decreased to utilize capacity at desired levels. Available options (Plans) for meeting excess demand Regular work force can work overtime Subcontracting to others. Supplemental labor Comparing plans lower cost alternative is to be accepted

28 28 Aggregate planning for Service organization OPTIMAL MODELS FOR AGGREGATE PLANNING Linear Programming: Optimal plans specifies the number of units of output to produce, how many shifts the manufacturing facility should operate, and.. Linear Decision Rules (LDRs): A set of equation for calculating optimal work force, aggregate output rate and inventory level A HEURISTIC APPROACH FOR AGGREGATE PLANNING Management coefficients model A set of equations that represent historical patterns of a company s aggregate planning decisions.

29 29 Implementing aggregate plans and master schedule

30 30 Implementing aggregate plans and master schedule Unplanned events Achieving developed aggregate plan is not always possible, Continually review to take account unexpected events Updated aggregate plan makes expectation of corresponding changes that needed in MPS Rolling through time

31 31 Implementing aggregate plans and master schedule Behavioural considerations In the planning process Do planners adopt a long enough horizon? Some experimental research reveals that they do not. Operating cost and difficult mental task In implementation It signals the need for actions by other parts of the organization Affect in organizational climate: lower the motivation and job satisfaction level

32 32 Intermittent scheduling: concepts & processes

33 33 Intermittent Systems Manufacturing Challenge is to manage flows of orders through shop Scheduling of intermittent systems poses a challenging problem for operation manager Services Similar systems in Restaurant, automobile repair service Workforce considerations in scheduling

34 34 Overview of the scheduling and control process Loading: The cumulative amount of work currently assigned to a work center for future processing Sequencing The stage establishes the priorities for jobs in the queues at the work centers Detailed scheduling Determining start times, finish times, and work assignments for all jobs at each work center. Expediting Tracking a job s progress and taking special actions to move it through the facility.

35 35 Loading Through MPS furthermore, particular work center s involvement to produce individual product. Imbalanced loads occurs even in best production schedule can be manipulated and manage (i.e. approaches for doing so infinite and finite loading) Discussion of loading distinguish between planned order and open order

36 36 infinite loading - assigning jobs to work centers without considering the work center s capacity constraints (assuming capacities are infinite). Help for evaluating the current loadings: Gantt Load Chart, Visual Load Profiles and assignment algorithm

37 37 infinite loading Work Centre Gantt Load Chart A B C Time

38 38 infinite loading Work Centre A Visual Load Profile rs Labor Hour Time

39 39 Gantt Load Chart: A graph showing work loads on a time scale Chart signals the need for reassigning resources when the load at one work centre becomes too large. Information about temporarily shifting employees from a low load centre to high one, or temporary employees can be hired. Multipurpose equipment can be shifted among work centers.

40 40 Visual Load Profiles: A graph comparing work loads and capacities on a time scale. Assignment algorithm: A linear program to assign jobs so that a specific criterion is optimized. Earlier loading problem can be solved. No. of jobs = No. of work centers Goodness and badness of assignments must be specifiable by some quantified criterion.

41 41 Sequencing (priority sequencing) Work Centre Priority Sequencing Rule A systematic procedure for assigning priorities to waiting jobs, thereby determining the sequence in which jobs will be processed. which rule should I use? what difference does it make? One s performance is not well according to all criterion (set-up cost, inventory cost, idle time)- Choice is to be made. Aim to minimizing these without jeopardizing service to customers.

42 42 Some of others are: First come first served (FCFS): Priority rule that gives top priority to the waiting job that arrived earliest in the production system. e.g. service industries such as banks, supermarkets Earliest due date (EDD): Priority rule that gives top priority to the waiting job whose due date is earliest.

43 43 Shortest processing time (SPT):A priority rule that gives top priority to the waiting job whose operation time at a work center is shortest. Truncated shortest processing time (TSPT): A priority rule that gives top priority to waiting job that has waited longer than a predetermined designated truncation time: if no job has waited that long, the SPT rule applies.

44 44 Detailed scheduling WHEN TO START WHICH JOB AND WHEN IT SHOULD BE FINISHED Gantt Scheduling Chart: A graph showing the time requirements of waiting jobs scheduled for production at machines and work centers.

45 45

46 46 finite loading A scheduling procedure that assigns jobs into work centers and determines their starting and completion dates by considering the work centers capacities. a detailed schedule for each job and each work center - - hour by hour and day by day in future.

47 Expediting 47 Disruptions in plan Rescheduling requirement Short-term capacity / input output control Process of controlling the actual and planned capacity utilization of work centers. If differences, adjustment should be done accordingly

48 48 Optimized Production Technology A production planning system that emphasizes identifying bottleneck work centers, and careful management of materials and resources related to those bottlenecks, to maximize output and reduce inventories.

49 49 BUILDNET SERVE SPLIT OPT BUILDNET It creates a model of the shop according to the data provided by the user: How each product is made? (buildup sequence, materials, and routing through shop) Product's time requirement. (set up time, schedule delay) The capacity availability of each resource (work centre, machine, worker) The order quantities and due dates of the work orders in the shop.

50 50 BUILDNET SERVE SPLIT SERVE Tentative schedules for the jobs waiting in the shop the more refined schedule Main function is an estimate of the percent utilization of the various shop resources. OPT

51 51 BUILDNET SERVE SPLIT SPLIT It distinguishes critical (bottleneck) resources from non critical resources. OPT

52 52 BUILDNET SERVE SPLIT OPT OPT It reschedules the critical part of the network using forward scheduling