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© 2007 Pearson Education DD DD GG GG GG MM MM MM AA AA L LL LL LL L Process Layout Chapter 8

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© 2007 Pearson Education Designing Line-Flow Layouts Line balancing is the assignment of work to stations in a line so as to achieve the desired output rate with the smallest number of workstations. Work elements are the smallest units of work that can be performed independently. Immediate predecessors are work elements that must be done before the next element can begin. Precedence diagram allows one to visualize immediate predecessors better; work elements are denoted by circles, with the time required to perform the work shown below each circle.

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© 2007 Pearson Education Example 8.3 Line Balancing Example 8.3 Green Grass, Inc., a manufacturer of lawn & garden equipment, is designing an assembly line to produce a new fertilizer spreader, the Big Broadcaster. Using the following information, construct a precedence diagram for the Big Broadcaster.

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© 2007 Pearson Education Green Grass, Inc. Line Balancing Green Grass, Inc. 6 E 20 H 18 I 40 D 30 B 25 F 50 C 40 A 15 G ABolt leg frame to hopper40None BInsert impeller shaft 30A CAttach axle50A DAttach agitator40B EAttach drive wheel6B FAttach free wheel25C GMount lower post15C HAttach controls20D, E IMount nameplate18F, G Total244 Work Time Immediate ElementDescription (sec) Predecessor(s)

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© 2007 Pearson Education Desired Output and Cycle Time Desired output rate, r must be matched to the staffing or production plan. Cycle time, c is the maximum time allowed for work on a unit at each station: 1r1r c =

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© 2007 Pearson Education Theoretical Minimum Theoretical minimum (TM ) is a benchmark or goal for the smallest number of stations possible, where total time required to assemble each unit (the sum of all work-element standard times) is divided by the cycle time. It must be rounded up Idle time is the total unproductive time for all stations in the assembly of each unit. Efficiency (%) is the ratio of productive time to total time. Balance Delay is the amount by which efficiency falls short of 100%.

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© 2007 Pearson Education Output Rate and Cycle Time Example 8.4 Green Grass, Inc. Desired output rate, r = 2400/week Plant operates 40 hours/week r = 2400/40 = 60 units/hour Cycle time, c = 1/60 = 1 minute/unit = 60 seconds/unit 1r1r

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© 2007 Pearson Education Calculations for Example 8.4 continued Theoretical minimum (TM ) - sum of all work-element standard times divided by the cycle time. TM = 244 seconds/60 seconds = 4.067 It must be rounded up to 5 stations Cycle time: c = 1/60 = 1 minute/unit = 60 seconds/unit Efficiency (%) - ratio of productive time to total time. Efficiency = [244/5(60)]100 = 81.3% Balance Delay - amount by which efficiency falls short of 100%. (100 − 81.3) = 18.7%

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© 2007 Pearson Education Line Balancing c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% S1 S2 S3 40 6 20 50 15 18 E 30 25 40 H I D B F C A G S1AA4020 S2B,CC5010 S3B,F,GB3030 D,E,F,GF555 S4D,E,GD4020 E,GG555 S5E,II1842 EE2436 HH4416 CummIdle StationCandidateChoiceTimeTime Green Grace, Inc.

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© 2007 Pearson Education S1 S2 S3 S5 S4 6 E 20 H 18 I 40 D 30 B 25 F 50 C 40 A 15 G Green Grass, Inc. Line Balancing Solution c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% The goal is to cluster the work elements into 5 workstations so that the number of work-stations is minimized, and the cycle time of 60 seconds is not violated. Here we use the trial-and-error method to find a solution, although commercial software packages are also available.

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© 2007 Pearson Education Line Balancing c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% Production = 2400 S2 S3 S1A4020 S2C5010 S3B,F555 S4D,G555 S5E,H,I4416 WorkWork StationWork station StationElementsTimeIdle Time Line Capacity Fastest cycle time = 55 seconds/unit Production = (40 hours x 60 minutes/hr x 60 seconds/hr)/55 = 2618 Efficiency at capacity = 244/(5x55) =.887 = 88.7% Green Grace, Inc.

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© 2007 Pearson Education Application 8.3

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© 2007 Pearson Education Application 8.3

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© 2007 Pearson Education Application 8.3

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© 2007 Pearson Education Application 8.4 Finding a Solution

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© 2007 Pearson Education Other Considerations In addition to balancing a line, managers must also consider four other options: 1. Pacing: The movement of product from one station to the next as soon as the cycle time has elapsed. 2. Behavioral factors of workers. 3. Number of models produced: A mixed-model line produces several items belonging to the same family. 4. Cycle times depend on the desired output rate, and efficiency varies considerably with the cycle time selected. Thus exploring a range of cycle times makes sense.

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© 2007 Pearson Education Solved Problem 2

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© 2007 Pearson Education Solved Problem 2 Precedence Diagram 20 E 145 H 130 I 25 D 80 B 15 F 50 C 40 A 120 G 115 J

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© 2007 Pearson Education Solved Problem 2 Line Balancing Process

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© 2007 Pearson Education Solved Problem 2 Line Balancing Solution 20 E 145 H 130 I 25 D 80 B 15 F 50 C 40 A 120 G 115 J S1 S4 S2 S5 S3

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