5. As part of a major plant renovation project, the industrial engineering depar
ID: 363310 • Letter: 5
Question
5. As part of a major plant renovation project, the industrial engineering department has been asked to balance a revised assembly operation to achieve an output rate of 240 units per eight- hour day. Task times and precedence relationships are as follows: ( Task Duration (minutes) Precedes Task .2 .2 .4 1.2 1.2 1.0 Do each of the following: a. Draw the precedence network. b. Determine the required cycle time. , c. Determine the minimum number of workstations needed. d. Assign the tasks to workstations using the heuristic rule "Assign the task with the most followers." Use the heuristic rule "Assign the task with the longest time" as a tiebreaker. If a tie still exists, choose randomly. e. Calculate the percentage idle time for the assignments in part d.Explanation / Answer
The precedence diagram as follows :
A
C
E
B
D
F
G
Since required output is 240 units per 8 hour day ,
Required cycle time = 480 minutes ( i.e. 8 hours ) / 240 = 2 minutes / unit
Total duration of all tasks( A to G ) = 0.2 + 0.4 + 0.2 +0.4 + 1.2 + 1.2 + 1 = 4.6 minutes
Minimum number of workstations needed
= Total duration of all tasks together/ Cycle time
= 4.6/ 2
= 2.3 ( 3 rounded to next higher whole number )
MINIMUM NUMBER OF WORKSTATIONS NEEDED = 3
The assignment of workstations using heuristic rule and ensuring that total duration of tasks in any workstation does not exceed 2 minutes of cycle time ,
WORKSTATION
TASKS
DURATION ( MINUTES)
IDLE TIME = 2 MINUTES - DURATION
1
E
1.2
0.8
2
A,B
0.2 + 0.4
1.4
3
C,D,G
0.2 + 0.4 + 1
0.4
4
F
1.2
0.8
Total idle time = 0.8 + 1.4 + 0.4 + 0.8 minutes = 3.4 minutes
Thus percentage idle time = Total idle time/ ( Actual number of workstations x Cycle time ) x 100
= 3.4/ ( 4 x 2) x 100
=42.5 %
PERCENTAGE IDLE TIME = 42.5%
A
C
E
B
D
F
G
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