A facility is trying to set up an assembly line, and has identified the various tasks, and their relationship to each other, as shown in the following table. Managers wish to produce 600 units per day, working two 8-hour shifts

Question

Task Preceding Task Time to perform (sec.)
A -- 20
B -- 30
C -- 25
D -- 10
E A 55
F D, B, C 30
G E 25
H F, G 40

(a) Draw a network diagram of precedence relationships.
(b) Compute the required cycle time per unit in seconds.
(c) Compute the minimum number of workstations required to produce 600 units per day.
(d) Balance this line using the longest processing time heuristic.
(e) What is the efficiency of the line obtained in part (d)?

Answer 1

(a) The precedence diagram appears below.
(b) Required cycle time is 4802./600 = 1.6 minutes or 96 seconds.
(c) 235/96 = 2.45 or 3 workstations are needed.
(d) The computer output places tasks A-B-C-D in station 1, E-F in station 2, and G-H in station 3.
(e) Efficiency is about 82 percent.

Station Task Time (seconds) Time left (seconds) Ready tasks
A,B,C,D
1 B 30. 66. A,C,D
C 25. 41. A,D
A 20. 21. D,E
D 10. 11. E,F
2 E 55. 41. F,G
F 30. 11. G
3 G 25. 71. H
H 40. 31.
Summary Statistics
Cycle time 96 seconds
Time allocated (cycle time ∗ #) 288 seconds/cycle
Time needed (sum of task times) 235 seconds/unit
Idle time (allocated-needed) 53 seconds/cycle
Efficiency (needed/allocated) 81.59722%
Balance Delay (1-efficiency) 18.40278%
Min (theoretical) # of stations 3