JOHNSON’S RULE. Five specialty jobs at a La Crosse, Wisconsin, tool and die shop must be processed through two work centers (drill press and lathe). The time for processing each job follows: Work (processing) Time for Jobs (hours) The owner, Niranjan Pati, wants to set the sequence to minimize his

Question

JOHNSON’S RULE. Five specialty jobs at a La Crosse, Wisconsin, tool and die shop must be processed through two work centers (drill press and lathe). The time for processing each job follows:

Work (processing) Time for Jobs (hours)

JOB	WORK CENTER 1 (DRILL PRESS)	WORK CENTER 2 (LATHE)
A	5	2
B	3	6
C	8	4
D	10	7
E	7	12

The owner, Niranjan Pati, wants to set the sequence to minimize his total time for the five jobs.

APPROACH [latex]\blacktriangleright[/latex] Pati applies the four steps of Johnson’s rule.

Accepted Answer

SOLUTION [latex]\blacktriangleright[/latex]
1. The job with the shortest processing time is A, in work center 2 (with a time of 2 hours). Because it is at the second center, schedule A last. Eliminate it from consideration.

JOB	WORK CENTER 1 (DRILL PRESS)	WORK CENTER 2 (LATHE)
A	5	2
B	3	6
C	8	4
D	10	7
E	7	12

2. Job B has the next shortest time (3 hours). Because that time is at the first work center, we schedule it first and eliminate it from consideration.

B

A

3. The next shortest time is job C (4 hours) on the second machine. Therefore, it is placed as late as possible.

B

C

A

4. There is a tie (at 7 hours) for the shortest remaining job. We can place E, which was on the first work center, first. Then D is placed in the last sequencing position:

B

E

D

C

A

The sequential times are:

Work center 1	3	7	10	8	5
Work center 2	6	12	7	4	2

The time-phased flow of this job sequence is best illustrated graphically in Figure 15.EX.7a.

Thus, the five jobs are completed in 35 hours.

INSIGHT [latex]\blacktriangleright[/latex] The second work center will wait 3 hours for its first job, and it will also wait 1 hour after completing job B.
LEARNING EXERCISE [latex]\blacktriangleright[/latex] If job C takes 8 hours in work center 2 (instead of 4 hours), what sequence is best? [Answer: B–E–C–D–A.]
RELATED PROBLEMS [latex]\blacktriangleright[/latex] 15.20, 15.22, 15.23 (15.25 is available in MyOMLab)
EXCEL OM Data File Ch15Ex7.xls can be found in MyOMLab.

Question 15.EX.7: JOHNSON’S RULE. Five specialty jobs at a La Crosse, Wisconsi...

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