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a
Interpretation: Tasks for each workstation, total time and idle time are to be calculated.
Concept Introduction:
Longest task time first rule:In this rule of line balancing, the task which has highest cycle time is assigned first to the workstation.
a
Explanation of Solution
Cycle Time:
It is the time between two consecutive outputs come out from a process.
Here CT = Cycle time; A = Available time to produce output; R = Demand
Assembly line:
It is a manufacturing process in which goods or services created in previous steps are joined together. Assembly line efficiency can be calculated by following formula:
Here t = Task time; N= Actual no. of workstations; CT = cycle time
Idle time:
It is time for which machines or employees do not work due to the stoppage or work for any causes.
Here N= Actual no. of work stations; CT= cycle time; t = task time
Assembly time per shift (A) = 480 min
No. of shifts each day = 1
Output forecasted per shift(R) = 60 units
The theoretical minimum no. of the workstation can be obtained as follows:
Here CT= Cycle time; t= Sum of tasks time;
Theoretically, minimum no. of the workstation is:
Line balancing by longest task time first rule can be calculated as follows:
Lines balanced by the assignable task are determined by longest task time first rule. It has following steps:
Task 2 has highest processing time and no prerequisite is required therefore it is assigned on station A.
Although task 1 has highest processing time after task 2 in that case, total time exceeds the cycle time, therefore, task 4 and 3 is assigned on station A along with task 2 as no prerequisite is required for these tasks.
Task 1 is assigned to station B and there is a tie between task 6 and 7 as both task time is same.
Task5 is assigned to station C as its preceding task 1, 2, 3 has already assigned.
Either task 6 or 7 is assigned to station D.
Finally, task 8 is assigned to station E.
In actual situation no. of workstation are 5 in order to follow precedence and cycle time rule.
| Station | Tasks | Total Time(min) | Idle Time(min) |
| A | 2,4,3 | 8 | 0 |
| B | 1,6 (or 7 tie) | 7 | 1 |
| C | 5 | 6 | 2 |
| D | 7 (or 6) | 3 | 5 |
| E | 8 | 8 | 0 |
| Total | 32 | 8 |
Total time at station A= Task Time of task 2+ Task Time of task 3+ Task Time of task 4
Total time at station A = 5+1+2
= 8 min
Idle time at station A= Cycle time-Total tasks at station A
= 8-8
= 0 min
Total time at station B = Task Time of task 1+ Task Time of task (6 or 7)
Total time at station B = 4+3
=7 min
Idle time at station B= Cycle time-Total tasks time at station B
=8-7
=1 min
Total time at station C = 6 min
Idle time at station C= Cycle time-Total tasks time at station c
= 8-6
= 2 min
Total time at station D= Task time of task 7 or 6
Total time at station D= 3 min
Idle time at station D= Cycle time-Total tasks time at station D
= 8-3
= 5 min
Total time at station E= Task Time of task D
Total time at station E= 8 min
Idle time at station E= Cycle time- Total tasks time at Station E
= 8-8
= 0 min
Total time
Total idle time:
It can be calculated as follows:
b
Interpretation:Assembly line efficiency is to be determined.
Concept Introduction:
Assembly line:It is a manufacturing process in which goods or services created in previous steps are joined together. Assembly line efficiency can be calculated by following formula:
Here t = Task time; N= Actual no. of workstations; CT = cycle time
b
Explanation of Solution
Assembly line efficiency can be calculated as follows:
c
Interpretation:Whether assembly line balance solution is good or bad and a criterion for assessment is to be explained.
Concept Introduction:
Idle time:It is time for which machines or employees do not work due to the stoppage or work for any causes.
c
Explanation of Solution
The assembly line balancing goodness is assessing its assembly line efficiency and idle time. In present case, although the assembly line efficiency is 80% the idle time is 8 min which is very high. It is highest for station D i.e. 5 min and at station B and C has 1 and 2 min idle time respectively. Therefore a fair chance that station B and C becomes bottleneck station for the assembly line. So it is not the very good balancing solution.
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