1. 3 Assembly Line Balancing CHAPTER Arranged by
Dr Sh Salleh bin Sh Ahmad
Originated from: Operations Management, Eighth Edition, by William J. Stevenson
Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

2. Line Balancing Green Grass, Inc. Big Broadcaster
The final section of the presentation deals with line balancing (Examples 10.4, 10.5, and 10.6) as presented in the Chapter. We will follow the Big Broadcaster example. This slide advances automatically. 63

3. Line Balancing Big Broadcaster
This slide advances automatically and clears the screen for the data. 64

4. Line Balancing Big Broadcaster Work Time Immediate
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)
The first data is the list of the work elements, the time they require, and the required precedent elements. This is from Example 10.4.
Example 7.3 65

5. Line Balancing Big Broadcaster DRAWING THE PRECEDENCE DIAGRAM
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
DRAWING THE PRECEDENCE DIAGRAM
Work Time Immediate
Element Description (sec) Predecessor(s)
We move the table to the upper left to allow room for the network diagram as shown in Figure This slide advances automatically.
Example 7.3 66

6. Line Balancing A 40 Big Broadcaster Example 7.3 Work Time Immediate
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) A 40
The first node assigned is element A as it is the only one with no required precedent tasks.
Example 7.3 67

7. Line Balancing B 30 A 40 Big Broadcaster Example 7.3
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) 40 30 B A
The second element added is B. It would be equally as ‘correct’ a decision to add element C at this point since both have their precedent requirement satisfied by element A.
Example 7.3 68

8. Line Balancing B 30 A 40 C 50 Big Broadcaster Example 7.3
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) 40 50 B C A 30
Following in alpha order, we add element C. This slide advances automatically as do the remaining slides in this sequence to build the network. In each case the appropriate row in the task list is highlighted to show the information used for the decision.
Example 7.3 69

9. Line Balancing D B 30 A 40 C 50 Big Broadcaster Example 7.3
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) 40 50 30 D B C A
This slide advances automatically.
Example 7.3 70

10. Line Balancing D B 30 E 6 A 40 C 50 Big Broadcaster Example 7.3
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) 40 6 50 E 30 D B C A
This slide advances automatically.
Example 7.3 71

11. Line Balancing D B 30 E 6 A F 40 C 25 50 Big Broadcaster Example 7.3
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) 40 6 50 E 30 25 D B F C A
This slide advances automatically.
Example 7.3 72

12. Line Balancing D B 30 E 6 A F 40 C 25 50 G 15 Big Broadcaster
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) 40 6 50 15 E 30 25 D B F C A G
This slide advances automatically.
Example 7.3 73

13. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 G 15 Big Broadcaster
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) 40 6 20 50 15 E 30 25 H D B F C A G
This slide advances automatically.
Example 7.3 74

14. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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) 40 6 20 50 15 18 E 30 25 H I D B F C A G
This slide completes the network and advances automatically.
Example 7.3 75

15. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster 40 6 20 50 15 18 E 30 25 H I D B F C A G
It might be a good time to stress that developing a network such as this is often a messy and iterative process with the final ‘nice’ version of the network emerging only after some experimentation with alternative design options.
Figure 7.12 76

16. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
We add in a worksheet for the basic calculations necessary for line balancing.
Example 7.4 77

17. r = desired output rate (units/hr)
Line Balancing
Big Broadcaster 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
r = 2400/40 = 60 units/hour
r = desired output rate (units/hr)
We first calculate r which we will use in other equations.
Example 7.4 78

18. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
We can now find the value of c, an important component of the analysis.
r = 2400/40 = 60 units/hour
Line cycle time c
= 60 min/hr / 60 units/hr = 1 minute/unit
= 60 seconds/unit
Example 7.4 79

19. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
c = 60 seconds/unit 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
This slide clears the calculations and adds the value for c to the upper left of the slide.
Example 7.4 80

20. TM = Theoretical minimum for the
Line Balancing
Big Broadcaster
c = 60 seconds/unit 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
TM = 244 seconds/60 seconds
= or 5 stations
TM = Theoretical minimum for the
number of stations
We can now calculate the theoretical minimum number of workstations required for this line.
Example 7.4 81

21. Theoretical Maximum Efficiency
Line Balancing
Big Broadcaster
c = 60 seconds/unit 40 6 20 50 15 18 E 30 25 H I D B F C A G
Desired output rate = 2400/week
Plant operates 40 hours/week
TM = 244 seconds/60 seconds
= or 5 stations
Theoretical Maximum Efficiency
= [244\5(60)]100 = 81.3%
Once we know the theoretical minimum (TM), we can determine the efficiency of a line operating at the TM.
Example 7.4 82

22. Theoretical Maximum Efficiency
Line Balancing
Big Broadcaster
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
Desired output rate = 2400/week
Plant operates 40 hours/week
TM = 244 seconds/60 seconds
= or 5 stations
Theoretical Maximum Efficiency
= [244\5(60)]100 = 81.3%
The values for TM and efficiency are added to the upper left of the slide and the worksheet is cleared. This slide advances automatically.
Example 7.4 83

23. Line Balancing 40 6 20 50 15 18 E 30 25 H I D B F C A G
Big Broadcaster
Computing Ranked Positional Weight
The positional weight of task i is defined as the time required to perform task i plus the times required to perform all tasks having task i as a predecessor. 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.
As Task A must precede all other tasks, its positional weight =
40 (from Task A) + all other tasks = 244 84

24. Line Balancing 40 6 20 50 15 18 E 30 25 H I D B F C A G
Big Broadcaster
Computing Ranked Positional Weight
The positional weight of task B=
= 96
The positional weight of task E=
= 26 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. 84

25. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
Computing Ranked Positional Weight
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18 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. 84

26. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
We can now start the assignment of work elements to work stations.
Example 7.5 84

27. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
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.
Example 7.5 85

28. Line Balancing D H B 20 30 E 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
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.
Example 7.5 86

29. Line Balancing D H B 20 30 E S1 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
Work station S1 contains only element A.
Example 7.5 87

30. Line Balancing D H B 20 30 E 6 S1 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
S2 B,C C 50 10
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
The next work station has two possible choices, of which C meets the decision criteria. 88

31. Line Balancing D H B 20 30 E S1 6 A F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
S2 B,C C 50 10
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
We assign C to a work station and there are only 10 seconds left allowing no other assignments. This slide advances automatically.
Example 7.5 89

32. Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15
Big Broadcaster
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
Cumm Idle
Station Candidate Choice Time Time
S1 A A 40 20
S2 B,C C 50 10 S2
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
This completes work station S2.
Example 7.5 90

33. Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15
Big Broadcaster
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
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 S2
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
The next work station has three possible elements, of which B is the appropriate choice.
Example 7.5 91

34. Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15
Cumm Idle
Station Candidate Choice Time Time
Line Balancing
Big Broadcaster
S1 A A
S2 B,C C
S3 B,F,G B
E,F,G
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 S2
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
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. 94

35. Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15
Cumm Idle
Station Candidate Choice Time Time
Line Balancing
Big Broadcaster
S1 A A
S2 B,C C
S3 B,F,G B
E,F,G F
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 S2
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
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. 94

36. Line Balancing D H B 20 30 E S1 6 A S2 F 40 C 25 50 I 18 G 15
Big Broadcaster S1 S2 40 6 20 50 15 18 E 30 25 H I D B F C A G
We add F to the work station. This slide advances automatically. 95

37. Line Balancing S1 S2 40 6 20 50 15 18 E 30 25 H I D B F C A G S3
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18 S1 S2 40 6 20 50 15 18 E 30 25 H I D B F C A G S3
Line Balancing
S1 A A 40 20
S2 B,C C 50 10
S3 B,F,G B 30 30
E,F,G F 55 5
S D,E,G D
E,G G
Cumm Idle
Station Candidate Choice Time Time
And this completes work station S3. 96

38. Line Balancing D H B 20 30 E S1 S3 6 S4 A S2 F 40 C 25 50 I 18 G 15
Big Broadcaster S1 S2 S3 S4 40 6 20 50 15 18 E 30 25 H I D B F C A G
And following the same decision rules, assign the remaining work elements to work stations.
In this case it was possible to balance the line without exceeding the TM value of 5 work stations. This is not always the case and this point should probably be stressed for the student's benefit. It might also be a good idea to comment that, in general, the more (and shorter) work elements you have, the easier it is to achieve a well balanced line.
Figure 7.13 98

39. S1 S2 S3 S4 40 6 20 50 15 18 E 30 25 H I D B F C A G
Task
Pos. weight A
244 B 96 C
108 D 60 E 26 F 43 G 33 H 20 I 18
S1 A A 40 20
S2 B,C C 50 10
S3 B,F,G B 30 30
E,F,G F 55 5
S D,E,G D
E,G G
S E,I E
H,I H
I I
Cumm Idle
Station Candidate Choice Time Time
And following the same decision rules, assign the remaining work elements to work stations.
In this case it was possible to balance the line without exceeding the TM value of 5 work stations. This is not always the case and this point should probably be stressed for the student's benefit. It might also be a good idea to comment that, in general, the more (and shorter) work elements you have, the easier it is to achieve a well balanced line.
Figure 7.13 98

40. Line Balancing D H B 20 30 E S1 S3 6 S4 A S2 F S5 40 C 25 50 I 18 G 15
Big Broadcaster
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 S4 S2 S5
And following the same decision rules, assign the remaining work elements to work stations.
In this case it was possible to balance the line without exceeding the TM value of 5 work stations. This is not always the case and this point should probably be stressed for the student's benefit. It might also be a good idea to comment that, in general, the more (and shorter) work elements you have, the easier it is to achieve a well balanced line.
As n = TM = 5, we can do no better than
this with a 60 second cycle time. 98

41. What are the efficiency and balance delay of the solution found?
Tutorial 2
A company is setting up an assembly line to produce 192 units per eight-hour shift using the information in the table below.
Work Element
Time (sec)
Immediate predecessors A 40
None B 80 C 30
D,E,F D 25 E 20 F 15 G
120 H
145 I
130 J
115
C,I
Total = 720
This slide supports Solved Problem 1.
What is the desired cycle time and theoretical minimum number of work stations?
Use the ranked positional weight technique to generate a balance solution, and show your solution on a precedence diagram.
What are the efficiency and balance delay of the solution found? 64

42. b. Theoretical minimum number of work stations: TM = ∑t / c =
Tutorial 2: Answer
a. Desired cycle time
c = 1 / r =
b. Theoretical minimum number of work stations:
TM = ∑t / c =
This slide supports Solved Problem 1. 64

43. c. Tutorial 2 : Ask student to draw the precedence diagram
This slide supports Solved Problem 3. 64

44. c. Tutorial 2 compute the positional weights
Task
Pos. weight A B C D E F G H I J
This slide supports Solved Problem 3. 64

45. Efficiency = (∑t / nc ) 100 = %
c. Tutorial 2: Balance the line using ranked positional weight technique
Station
Candidates
Choice
Work element time (sec)
Cumulative time (sec)
Idle time (c = 150 sec)
This slide supports Solved Problem 1.
Efficiency = (∑t / nc ) = %
Thus, the balance delay = % 64

46. Parallel Workstations
1 min.
2 min.
30/hr.
60/hr.
Bottleneck
Parallel Workstations

47. Process Layout - work travels to dedicated process centers
Milling
Assembly & Test
Grinding
Drilling
Plating

48. Functional Layout Gear cutting Mill Drill Lathes Grind Heat treat
Assembly
111
333
222
444
1111
2222
3333
44444
333333
22222

49. Cellular Manufacturing Layout
-1111
- 2222
Assembly
- 3333
- 4444
Lathe
Mill
Drill
Heat
treat
Gear
cut
Grind