Some tasks and the order in which they must be performed according to their asse
ID: 467949 • Letter: S
Question
Some tasks and the order in which they must be performed according to their assembly requirements are shown in the following table. These are to be combined into workstations to create an assembly line. The assembly line operates 9.5 hours per day. The output requirement is 1,710 units per day.
Balance the line using the longest task time based on the 1,710-unit forecast, stating which tasks would be done in each workstation. (Leave no cells blank - be certain to enter "0" wherever required.)
After production was started, Marketing realized that they understated demand and must increase output to 1,800 units. What action would you take? Be specific in quantitative terms, if appropriate.(Input all amounts as positive values. Round down "cycle time" value to the next smallest integer and "overtime" to nearest whole number.)
Some tasks and the order in which they must be performed according to their assembly requirements are shown in the following table. These are to be combined into workstations to create an assembly line. The assembly line operates 9.5 hours per day. The output requirement is 1,710 units per day.
Explanation / Answer
Activity
Predecessor
Duration (week)
A
None
17
B
A
14
C
A
6
D
B
11
E
B
5
F
C
13
G
C
15
H
D
6
I
E
2
J
F, G
6
K
H, I
10
L
J, K
8
Total Work Time
113
Demand = D =1710 units per day
Available hours = 9.5 hours per day
Available time (seconds) = 9.5 x 60 x 60 = 34,200 seconds
Total Work time = 113 seconds
a.
Determine Cycle Time
Cycle time of the Line = Available time (seconds)/Demand
Ct = 34200/1710 = 20 seconds
So assembly must be capable of processing units once every 20 seconds.
Cycle time gives idea of how frequently the products are processed by assembly line.
b.
Determine number of workstation required:
Number of workstation required in assembly line depends on the cycle time and total work content that is total amount of time required to produce the product.
So for assembly line number of workstation required is as follows:
Number of workstation = (total work content)/(required cycle time)
Number of workstation required = 113/20 = 5.65
Actual numbers of workstations required are 6 workstations.
Arrange the tasks according to longest tasks first as shown below:
Activity
Predecessor
Duration (week)
A
None
17
G
C
15
B
A
14
F
C
13
D
B
11
K
H, I
10
L
J, K
8
C
A
6
H
D
6
J
F, G
6
E
B
5
I
E
2
Applying largest candidate rule to balance the line:
Work Elements Assigned to Stations According to the Largest Candidate Rule
First largest duration activity is A(17). As the activities B or C, if combined with A have cycle time above 20 seconds, thus, workstation #1 will include only activity A only.
Next largest duration activity is G(15) but required C to be completed. Next activity is B(14), next activity which requires B and/or A to be completed is C(6). Combined task time of activity B and C is 19, which is less than 20 seconds. Workstation #2 consists of activities B and C.
Next largest duration activity is G(15) which requires C to be completed. So workstation #3 will consists of G. Next activity which requires A, B, C, or G to be complete is E(5). Combined duration of Workstation #3 – G+E = 15 + 5 = 20 seconds.
Next largest duration activity is F(13) requires C to be completed. Next activity is J(6) requires F and G to be completed. Combined duration of workstation #4 – F+G = 13 + 6 = 19 seconds.
Similarly, other workstations are determined as follows:
Workstation #
Tasks
workstation, Work Time (CW)
Cycle Time (Ct)
Idle = Ct + CW
1
A
17 = 17
20
3
2
B, C
14+6 = 20
20
0
3
G, E
15+5 = 20
20
0
4
F, J
13+6 = 19
20
1
5
D, H, I
11+6+2 = 19
20
1
6
K, L
10+8 = 18
20
2
C.
Efficiency of assembly line = Total work time/(no. of workstation x Cycle time)
Efficiency = 113/(6 x 20)
Efficiency = 94.17%
D
Revised Demand = 1800 units
Revised Cycle Time = 34200/1800 = 19 seconds
As there is no idle time for Workstations #2 and #3, do not reduce the cycle time, instead work overtime.
Overtime production units = Revised demand - Production per day as per CT = 20 sec
Overtime production units = 1800 – 1710 = 90 units
Overtime (seconds) = 90 units x CT = 90 x 20 = 1800 seconds
Overtime in minutes = 1800/60 = 30 minutes.
Thus, work 30 minutes of overtime
Activity
Predecessor
Duration (week)
A
None
17
B
A
14
C
A
6
D
B
11
E
B
5
F
C
13
G
C
15
H
D
6
I
E
2
J
F, G
6
K
H, I
10
L
J, K
8
Total Work Time
113
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