Question

RESTORE machine shop makes customized replacement parts for older equipment. All customer jobs listed must be machined first, then polished. Determine the optimal processing sequence of the six jobs listed below.

Jobs	Machining Hrs	Polishing Hrs
A	5	4
B	7	3
C	3	2
D	4	1
E	1	2
F	3	4

job A is finished at time

21

11

9

13

Answer 1

1. A IS FINISHED AT 13

USING JOHNSON’S RULE

RULES FOR SEQUENCING:

1. SHORTEST WORK TIME IS SELECTED

2. ACTIVITY WITH SHORTEST TIME IN B IS SEQUENCED LAST AND A IS SEQUENCED FIRST, ELIMINATING EACH ACTIVITY AND PROCEEDING FURTHER

ASSIGNMENT

JOB	CENTER 1	CENTER 2
E	1	2
F	3	4
A	5	4
B	7	3
C	3	2
D	4	1

CALCULATING FLOW TIME

MACHINE A	START TIME	FINISH TIME	MACHINE B	START TIME	FINISH TIME
E	0	1	E	1	3
F	1	4	F	4	8
A	4	9	A	9	13
B	9	16	B	16	19
C	16	19	C	19	21
D	19	23	D	23	24

TIME FOR COMPLETION OF A = 13

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