on two work centers or processes.
The primary objective is to minimizes the overall lead time (or, to reduce makespan).
( * Lead time = Makespan = The total amount of time it takes to complete all jobs )
Example:
A manufacturing department has five jobs, which must be processed on the sand process
and then on the varnish process. Determine the sequence that will allow the set of five jobs
to be completed in the minimum time.
----------------------------------------------------
Job Process Time (Minutes)
Sand Varnish
----------------------------------------------------
A 6 3
B 4 5
C 2 3
D 6 6
E 3 7
----------------------------------------------------
1. Smallest time is located in Job C (2min). Since the time is in Sand, schedule this job first.
Eliminate Job C from further consideration.
C - ? - ? - ? - ?
2. The next smallest time is Job A (3min) and Job E (3min).
Since Job A time is in Varnish, schedule this job as late as possible in job sequence.
Then, since Job E time is in Sand, schedule this job as early as can.
Eliminate Job A and Job E from further consideration.
C - E - ? - ? - A
3. The next smallest time is Job B (4min).
Since the time is in Sand, schedule this job as early as can.
Eliminate the Job B from further consideration.
C - E - B - ? - A
4. The only job remaining is Job D, therefore final sequence is as follows.
C - E - B - D - A
The Gantt Chart show as follows:
Thus, the total completion time is 26 minutes.
Read More: Expending Johnson's Rule (n-jobs,m-machines)
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