Question

The Ace Machine Company is considering using a priority scheduling rule in its fabrication shop and must decide whether to use: the critical rule, the order slack rule, the shortest operation next rule or the slack per operation rule.

 

The table below shows the company’s current inventory and shop status.

 

Exhibit 1

 

Order number	Manufacturing Lead Time Remaining	Time   Remaining Until Due Date	Current Operation Processing Time	Number   of Operations Remaining	Total   Processing Time Remaining
1	15	7	2	3	8
2	15	11	3	4	8
3	20	-2	5	2	8
4	15	-5	4	3	8
5	15	3	1	12	8

Note: Time is measured in days. Manufacturing lead time remaining includes both the machine processing time and the length of time orders spend moving and waiting to be processed in a machine queue. Current operating processing time (as well as total processing time remaining) includes no move or queue times

Compute the scheduling priority index for each order in Exhibit 1 for the four sequencing rules

Answer 1

Answer 2

Critical
Ratio	Job	Start	Days*	Done	Due
Order 4	-0.33	0	15	15	-5
Order 3	-0.1	15	20	35	-3
Order 5	0.2	35	15	50	2
Order 1	0.47	50	15	65	7
Order 2	0.73	65	15	80	11

Order Slack

Critical
Ratio	Job	Start	Days*	Done	Due
Order 3	-22	0	20	20	-3
Order   4	-20	20	15	35	-5
Order 5	-12	35	15	50	2
Order 1	-8	50	15	65	7
Order 2	-4	65	15	80	11

Shortest Operation Next

Critical
Ratio	Job	Start	Days*	Done	Due
Order 5	1	0	15	15	2
Order 1	2	15	15	30	7
Order 2	3	30	15	45	11
Order 4	4	45	15	60	-5
Order 3	5	60	20	80	-3