Question

Question 1:

Sequence the jobs shown below by using a Gantt chart. Assume that the move time between machines is one hour. Sequence the jobs in priority order 1, 2, 3, 4.

Job Work Center/Machine Hours                                  Due Date (days)
1	A/3, B/2, C/2	3
2	C/2, A/4	2
3	B/6, A/1, C/3	4
4	C/4, A/1, B/2	3

1. Using finite capacity scheduling, draw a Gantt chart for the schedule (Marks 0.5)
2. What is the make span? (Marks 0.5)
3. How much machine idle time is there? (Marks 0.5)
4. How much idle time (waiting time) is there for each job? (Marks 0.5)
5. When is each job delivered? (Marks 0.5)
6. Which department is the bottleneck? (Marks 0.5)
7. Calculate the machine utilization? (Marks 0.5)

Answer 1

(a)

Gantt Chart is as follows:

The hatched portions ar the machine idle time.

The arrows are showing the job's waiting time.

(b)

The makespan, as shown in the Gantt chart is 18 hours

(c)

Idle time for machine-A, B, and C are 9, 8, and 6 hours respectively.

(d)

The Job's waiting time is shown using the red arrows, just find the gaps between the arrows.

Job	Waiting time (hours
1	0
2	0
3	6
4	4

(e)

Job-1 is delivered at the end of 9 hours

Job-2 is delivered at the end of 7 hours

Job-3 is delivered at the end of 18 hours

Job-4 is delivered at the end of 14 hours

(f)

Machine-C is the bottleneck because it has the least amount of idle time and hence the highest utilization.

(g)

Overall machine utilization = 1 - total idle time / (no. of machines * makespan) = 1 - (9+8+6) / (3*18) = 57.4%