Bài giảng Operations Management - Supplement 7 Learning Curves

Learning CurvesSupplement 7Copyright © 2015 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.Supplement 7: Learning ObjectivesYou should be able to:LO 7s.1 Explain the concept of a learning curveLO 7s.2 Make time estimates based on learning curvesLO 7s.3 List and briefly describe some of the main applications of learning curvesLO 7s.4 Outline some of the cautions and criticisms of learning curvesLO 7s.5 Estimate learning rates from data on job timesLearning curveThe time required to perform a task decreases with increasing repetitionsThe degree of improvement is a function of the task being doneShort, routine tasks will show modest improvement relatively quicklyLonger, more complex tasks will show improvement over a longer interval Learning CurvesLO 7s.1The learning effect is attributed to a variety of factors:Worker learningPreproduction factorsTooling and equipment selectionProduct designMethods analysisEffort expended prior to the start of workChanges made after production has begunChanges in work methodsChanges in tooling and equipmentManagerial factorsImprovements in planning, scheduling, motivation, and controlThe Learning EffectLO 7s.1The learning effect is predictableThe learning percentage is constantEvery doubling of repetitions results in a constant percentage decrease in the time per repetitionTypical decreases range from 10 to 20 percentInteresting Characteristics of LearningLO 7s.1Each time cumulative output doubles, the time per unit for that amount should be approximately equal to the previous time multiplied by the learning percentage.If the first unit of a process took 100 hours and the learning rate is 90%:Learning IllustratedUnitUnit Time (hours)1= 1002.90(100)= 904.90(90)= 818.90(81)= 72.916.90(72.9)= 65.6132.90(65.61)= 59.049LO 7s.2Unit Times: Formula ApproachLO 7s.2If the learning rate is 90, and the first unit took 100 hours to complete, how long would it take to complete the 25th unit?Example: Formula ApproachLO 7s.2The learning factor approach uses a table that shows two things for selected learning percentages:Unit value for the number of repetitions (unit number)Cumulative value, which enables us to compute the total time required to complete a given number of units.Unit Times: Learning Factor ApproachLO 7s.2If the learning rate is 90, and the first unit took 100 hours to complete, how long would it take to complete the 25th unit?How long would it take to complete the first 25 units?Example: Learning Factor ApproachLO 7s.2Learning Curve ApplicationsUseful application areas:Manpower planning and schedulingNegotiated purchasingPricing new productsBudgeting, purchasing, and inventory planningCapacity planningLO 7s.3Cautions and CriticismsLearning rates may differ from organization to organization and by type of workBase learning rates on empirical studies rather than assumptions where possibleProjections based on learning curves should be regarded as approximations of actual timesBecause time estimates are based on the first unit, care should be taken to ensure that the time is validIt is possible that at some point the curve might level off or even tip upwardLO 7s.4Cautions and CriticismsSome of the improvements may be more apparent than real: improvements in times may be caused by increases in indirect labor costsIn mass production situations, learning curves may be of initial use in predicting how long it will take before the process stabilizesThe concept does not usually apply because improvement in time per unit is almost imperceptibleLO 7s.4Cautions and CriticismsUsers of learning curves fail to include carryover effects from previous experiencesShorter product life cycles, flexible manufacturing, and cross-functional workers can affect the ways in which learning curves may be appliedLO 7s.4Estimating Learning RatesLO 7s.5UnitCompletion Time (hours)115.9212.0310.149.158.467.5A manager wants to determine an appropriate learning rate for a new type of work his firm will undertake. He has obtained completion times for the initial six repetitions of a job of this type. What learning rate is appropriate?According to theory, the time per unit decreases at a constant rate each time the output doubles (e.g., 1 to 2, 2 to 4, and 3 to 6). The ratios of these observed times will give us an approximate rate.Not surprisingly, there is some variability; the rate is usually a smoothed approximation. Even so, the ratios are fairly close – a rate of 75 percent in this case.