Process Layout Chapter 8 L L M M D D D D L L M M L L M M G G L L G G A 1

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.

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. 63

Line Balancing Green Grass, Inc. © 2007 Pearson Education A Bolt leg frame to hopper 40 None B Insert impeller shaft 30 A C Attach axle 50 A D Attach agitator 40 B E Attach drive wheel 6 B F Attach free wheel 25 C G Mount lower post 15 C H Attach controls 20 D, E I Mount nameplate 18 F, G Total 244 Work Time Immediate Element Description (sec) Predecessor(s) Line Balancing Green Grass, Inc. 40 D 20 H 30 B 6 E 40 A 25 F 50 C 18 I 15 G 64

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: 1 r c =

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 i.e. St/C Idle time is the total unproductive time for all stations in the assembly of each unit. nC - St Efficiency (%) is the ratio of productive time to total time. St/nC x 100 % Balance Delay is the amount by which efficiency falls short of 100%.

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 1 r

Calculations for Example 8.4 continued Theoretical minimum (TM ) - sum of all work-element standard times divided by the cycle time. TM = St/C = 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%

Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G We can now start the assignment of work elements to work stations. Cumm Idle Station Candidate Choice Time Time 84

Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G The first element assigned is A since it is the only one with no precedent elements. We see that the 40 seconds required for A will leave 20 seconds left in the work station. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 85

Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G As there are no other elements with 20 seconds or less work required (that are available to us at this time), the work station is as complete as we can make it. This slide advances automatically. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 86

Line Balancing D H B 20 30 E S1 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 Work station S1 contains only element A. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 87

Line Balancing D H B 20 30 E S1 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 The next work station has two possible choices, of which C meets the decision criteria. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 88

Line Balancing D H B 20 30 E S1 6 A F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 We assign C to a work station and there are only 10 seconds left allowing no other assignments. This slide advances automatically. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 89

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 This completes work station S2. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S2 90

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 The next work station has three possible elements, of which B is the appropriate choice. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 S2 91

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 We add B to the work station and see that there are 30 seconds of time remaining. This slide advances automatically. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 S2 92

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 This slide advances automatically. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 S2 93

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 Of the three choices available to us at this point, F is the appropriate one given the decision criteria. This leaves us with only 5 seconds and no other tasks can be performed in that time. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S2 94

Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 We add F to the work station. This slide advances automatically. Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S2 95

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 And this completes work station S3. S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 Cumm Idle Station Candidate Choice Time Time S2 96

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 S2 Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S4 D,E,G D 40 20

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 S2 Cumm Idle Station Candidate Choice Time Time S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S4 D,E,G D 40 20 E,G G 55 5

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 Cumm Idle Station Candidate Choice Time Time S2 S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S4 D,E,G D 40 20 E,G G 55 5 S5 E,I I 18 42

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 Cumm Idle Station Candidate Choice Time Time S2 S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S4 D,E,G D 40 20 E,G G 55 5 S5 E,I I 18 42 E E 24 36

Line Balancing D H B 20 30 E S1 S3 6 A S2 F 40 C 25 50 I 18 G 15 Green Grace, Inc. c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% 40 6 20 50 15 18 E 30 25 H I D B F C A G S1 S3 Cumm Idle Station Candidate Choice Time Time S2 S1 A A 40 20 S2 B,C C 50 10 S3 B,F,G B 30 30 D,E,F,G F 55 5 S4 D,E,G D 40 20 E,G G 55 5 S5 E,I I 18 42 E E 24 36 H H 44 16

Green Grass, Inc. Line Balancing Solution © 2007 Pearson Education Green Grass, Inc. Line Balancing Solution 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. S5 S4 6 E 20 H 18 I 40 D 30 B 25 F 50 C A 15 G S3 S1 S2 c = 60 seconds/unit TM = 5 stations Efficiency = 81.3%

Line Balancing S3 S2 Green Grace, Inc. c = 60 seconds/unit S1 A 40 20 S2 C 50 10 S3 B,F 55 5 S4 D,G 55 5 S5 E,H,I 44 16 Work Work Station Work station Station Elements Time Idle Time c = 60 seconds/unit TM = 5 stations Efficiency = 81.3% Production = 2400 Line Capacity Fastest cycle time = 55 seconds/unit Production = (40 hours x 60 minutes/hr x 60 seconds/min.)/55 = 2618 Efficiency at capacity = 244/(5x55) = .887 = 88.7%

Application 8.3

Application 8.3

Application 8.3

Application 8.4 Finding a Solution

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.

Solved Problem 2

Solved Problem 2 Precedence Diagram 25 B E C 80 20 50 J A F 115 40 G 15 120 H I 145 130 64

Solved Problem 2 Line Balancing Process 64

Solved Problem 2 Line Balancing Solution 25 S5 B E C 80 20 50 S1 J A F 115 40 G 15 S2 120 H I S4 S3 145 130 64