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Aggregate Planning

Aggregate Planning. Chapter 12. Learning Objectives. Review of forecasting Forecast errors Aggregate planning. Phases of Decisions. Strategy or design: Forecast Planning: Forecast Operation Actual demand

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Aggregate Planning

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  1. Aggregate Planning Chapter 12

  2. Learning Objectives • Review of forecasting • Forecast errors • Aggregate planning

  3. Phases of Decisions • Strategy or design: Forecast • Planning: Forecast • Operation Actual demand • Since actual demands differs from forecasts so does the execution from the plans. • E.g. Supply Chain concentration plans 40 students per year whereas the actual is ??.

  4. Characteristics of forecasts • Forecasts are always wrong. Should include expected value and measure of error. • Long-term forecasts are less accurate than short-term forecasts. Too long term forecasts are useless: Forecast horizon • Forecasting to determine • Raw material purchases for the next week • Annual electricity generation capacity in TX for the next 30 years • Aggregate forecasts are more accurate than disaggregate forecasts • Variance of aggregate is smaller because extremes cancel out • Two samples: {3,5} and {2,6}. Averages of samples: 4 and 4. • Variance of sample averages=0 • Variance of {3,5,2,6}=5/2 • Several ways to aggregate • Products into product groups • Demand by location • Demand by time

  5. Forecast Variability implies time zones Frozen and Flexible zones

  6. Time Fences in MPS Period “frozen”(firm orfixed) “liquid”(open) “slushy”somewhatfirm Time Fences divide a scheduling time horizon into three sections or phases, referred as frozen, slushy, and liquid. Strict adherence to time fence policies and rules.

  7. Long range Intermediate range Short range Now 2 months 1 Year Planning Horizon Aggregate planning: Intermediate-range capacity planning, usually covering 2 to 12 months. In other words, it is matching the capacity and the demand.

  8. Overview of Planning Levels • Short-range plans (Detailed plans) • Machine loading • Job assignments • Intermediate plans (General levels) • Employment • Output • Long-range plans • Long term capacity • Location / layout • Product/Process design

  9. Listen to Tom Thumb’s manager • Need more space in 2005 to expand the store • Allocate 25% of the floor space to fresh produce • During the winter months employ 6 cashiers during rush hours • On Wed before Thanksgiving, employ 12 cashiers throughout the day • In the next two weeks, no Italian parsley will be delivered. Shelve Dill instead of parsley

  10. Why aggregate planning • Details are hard to gather for longer horizons • Demand for Christmas turkeys at Tom Thumb’s vs Thanksgiving turkeys • Details carry a lot of uncertainty: aggregation reduces variability • Demand for meat during Christmas has less variability than the total variability in the demand for chicken, turkey, beef, etc. • If there is variability why bother making detailed plans, inputs will change anyway • Instead make plans that carry a lot of flexibility • Flexibility and aggregation go hand in hand

  11. Aggregate Planning • Aggregate planning: General plan • Combined products = aggregate product • Short and long sleeve shirts = shirt • Single product • Pooled capacities = aggregated capacity • Dedicated machine and general machine = machine • Single capacity • Time periods = time buckets • Consider all the demand and production of a given month together • Quite a few time buckets • When does the demand or production take place in a time bucket?

  12. Economic, competitive, and political conditions Corporate strategies and policies Aggregate demand forecasts Establishes production and capacity strategies Business Plan Establishes production capacity Production plan Establishes schedules for specific products Master schedule Planning Sequence

  13. Resources Workforce Facilities Demand forecast Policy statements Subcontracting Overtime Inventory levels Back orders Costs Inventory carrying Back orders Hiring/firing Overtime Inventory changes subcontracting Aggregate Planning Inputs

  14. Aggregate Planning Outputs • Total cost of a plan • Projected levels of inventory • Inventory • Output • Employment • Subcontracting • Backordering

  15. Strategies • Proactive • Alter demand to match capacity • Reactive • Alter capacity to match demand • Mixed • Some of each

  16. Demand Options to Match Demand and Capacity • Pricing • Price reduction leads to higher demand • Promotion • Not necessarily via pricing • Free delivery, free after sale service • Some Puerto Rico hotels pay for your flight • Back orders • Short selling: Sell now, deliver later • New demand • Finding alternative uses for the product

  17. Capacity Options to Match demand and Capacity • Hire and layoff workers, unions are pivotal • Layoff: Emotional stress • Fired Moulinex (appliances producer in France) workers start fire at the plant • Hire: Availability of qualified work force • Operators at semiconductor plants • Overtime/slack time • How too use slack time constructively? Training. • Overtime is expensive, low quality, prone to accidents • Part-time workers • 35 hour work week of Europe • Inventories, To smooth demands • Subcontracting. Low quality. Reveals technological secrets

  18. Fundamental tradeoffs in Aggregate Planning • Capacity (regular time, over time, subcontract) • Inventory • Backlog / lost sales: Customer patience? Basic Strategies • Chase (the demand) strategy; Matching capacity to demand; the planned output for a period is the expected demand for that period • fast food restaurants • Time flexibility from high levels of workforce or capacity; • machining shops, army • Level strategy; Maintaining a steady rate of regular-time output while meeting variations in demand by a combination of options. • swim wear

  19. Matching the Demand with Level or Time flexibility strategies Use inventory Demand Use delivery time Demand Use capacity Demand

  20. Chase vs. Level Level Approach • Advantages • Stable output rates and workforce • Disadvantages • Greater inventory costs • Increased overtime and idle time • Resource utilizations vary over time Chase Approach • Advantages • Investment in inventory is low • Labor utilization in high • Disadvantages • The cost of adjusting output rates and/or workforce levels

  21. Techniques for Aggregate Planning • Inputs: • Determine demand for each period • Determine capacities for each period • Identify policies that are pertinent • Determine units costs • Analysis • Develop alternative plans and costs • Select the best plan that satisfies objectives

  22. Technique 1: Cumulative Graph Cumulative output/demand Cumulative production Cumulative demand 6 7 1 2 3 4 5 8 9 10

  23. Technique 2: Mathematical Techniques Linear programming: Methods for obtaining optimal solutions to problems involving allocation of scarce resources in terms of cost minimization. Minimize Costs Subject to: Demand, capacity, initial inventory requirements

  24. Summary of Planning Techniques Linear decision rule???

  25. Example - Relationships

  26. Technique 3: Simulation ExampleLevel Output Average Inventory= (Beginning Inventory + Ending Inventory)/2

  27. Technique 3: Simulation ExampleLevel Output + Overtime

  28. Aggregate Planning in Services • Services occur when they are rendered • Limited time-wise aggregation • Services occur where they are rendered • Limited location-wise aggregation • Demand for service can be difficult to predict • Personalization of service • Capacity availability can be difficult to predict • Labor flexibility can be an advantage in services • Human is more flexible than a machine, well at the expense of low efficiency.

  29. AggregatePlanning Disaggregation MasterSchedule Aggregate Plan to Master Schedule For a short planning range 2-4 months: • Master schedule: The result of disaggregating an aggregate plan; shows quantity and timing of specific end items for a scheduled horizon. • Rough-cut capacity planning: Approximate balancing of capacity and demand to test the feasibility of a master schedule.

  30. Master Scheduling Master Scheduler • Evaluates impact of new orders • Provides delivery dates for orders • Deals with problems • Production delays • Revising master schedule • Insufficient capacity Master schedule • Determines quantities needed to meet demand • Interfaces with • Marketing • Capacity planning • Production planning • Distribution planning

  31. Inputs Outputs Beginning inventory Projected inventory Master Scheduling Forecast Master production schedule Committed Customer orders ATP: Uncommitted inventory Master Scheduling Process

  32. Preview of Materials Requirement Planning Terminology Net Inventory After Production Requirements=Forecast Assuming that the forecasts include committed orders Net inventory before production= Projected on hand inventory in the previous period - Requirements Produce in lots if Net inventory is less than zero Net inventory after production= Net inventory before production+ Production

  33. Projected On-hand Inventory Beginning Inventory

  34. Example: Find ATP with lot size of 70

  35. Summary • Aggregate planning: conception, demand and capacity option • Basic strategy: level capacity strategy, chase demand strategy • Techniques: Trial and Error, mathematical techniques • Master scheduling

  36. Practice Questions • 1. The goal of aggregate planning is to achieve a production plan that attempts to balance the organization's resources and meet expected demand. Answer: True Page: 541 • 2. A “chase” strategy in aggregate planning would attempt to match capacity and demand. Answer: True Page: 548 • 3. Ultimately the overriding factor in choosing a strategy in aggregate planning is overall cost. Answer: True Page: 550

  37. Practice Questions 1. Which of the following best describes aggregate planning? A) the link between intermediate term planning and short term operating decisions B) a collection of objective planning tools C) make or buy decisions D) an attempt to respond to predicted demand within the constraints set by product, process and location decisions E) manpower planning Answer: D Page: 541

  38. Practice Questions 2.Which of the following is an input to aggregate planning? A) beginning inventory B) forecasts for each period of the schedule C) customer orders D) all of the above E) none of the above Answer: D Page: 561

  39. Practice Questions 3.Which of the following is not an input to the aggregate planning process: A) resources B) demand forecast C) policies on work force changes D) master production schedules E) cost information Answer: D Page: 545

  40. Practice Questions 4. Which one of the following is not a basic option for altering demand? A) promotion B) backordering C) pricing D) subcontracting E) All are demand options. Answer: D Page: 545

  41. Practice Questions 5. Which of the following would not be a strategy associated with adjusting aggregate capacity to meet expected demand? A) subcontract B) vary the size of the workforce C) vary the intensity of workforce utilization D) allow inventory levels to vary E) use backorders Answer: E Page: 546-547

  42. Practice Questions 6. Moving from the aggregate plan to a master production schedule requires: A) rough cut capacity planning B) disaggregation C) sub-optimization D) strategy formulation E) chase strategies Answer: B Page: 559

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