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Dan’s Machine Shop is considering the use of a priority scheduling rule in the fabrication shop and must decide whether to use: (1) critical ratio (CR), (2) earliest due date (EDD), (3) shortest operation next (SON), or (4) order slack. The current shop status of the company is given here:
| Order Number | Total Remaining | Time Remaining | Current Operation | |
| Manufacturing Time | until Due Date | Processing Time | ||
| 1 | 18 | 12 | 8 | |
| 2 | 12 | 15 | 5 | |
| 3 | 10 | 14 | 6 | |
| 4 | 15 | 18 | 7 | |
| 5 | 20 | 15 | 6 |
a. Using the four sequencing rules, compute the scheduling priority for each order given in the table above.
b. What order should be run first under each of these scheduling rules?
Expert Answer
The scheduling priority for each order:
- Critical ratio (CR) = Time until due date/ processing time
| Critical ratio (CR) Rule | |||
| Order number | Processing Time | Time until due date | Critical ratio (CR) |
| 1 | 8 | 12 | 12/8 = 1.5 |
| 2 | 5 | 15 | 15/5 = 3 |
| 3 | 6 | 14 | 14/6 = 2.33 |
| 4 | 7 | 18 | 18/7 = 2.57 |
| 5 | 6 | 15 | 15/6 = 2.5 |
| Total | 32 |
The order numbers will be scheduled as smallest critical ratio to largest critical ratio
| Critical ratio (CR) Rule | |||
| Order number | Processing Time | Time until due date | Critical ratio (CR) |
| 1 | 8 | 12 | 1.5 |
| 3 | 6 | 14 | 2.33 |
| 5 | 6 | 15 | 2.50 |
| 4 | 7 | 18 | 2.57 |
| 2 | 5 | 15 | 3 |
- Earliest due date (EDD)
The order numbers will be scheduled as earliest due date to latest due date
| EDD Rule | |||
| Order number | Processing Time | Completion of job | Time until due date |
| 1 | 8 | 8 | 12 |
| 3 | 6 | 14 | 14 |
| 2 | 5 | 19 | 15 |
| 5 | 6 | 25 | 15 |
| 4 | 7 | 32 | 18 |
- Shortest operation next (SON): it takes the next job which can be completed in shortest time.
| Shortest operation next (SON) Rule | ||
| Order number | Processing Time | Time until due date |
| 2 | 5 | 15 |
| 3 | 6 | 14 |
| 5 | 6 | 15 |
| 4 | 7 | 18 |
| 1 | 8 | 12 |
- Order slack = Time until due date – Processing Time
| Order slack Rule | |||
| Order number | Processing Time | Time until due date | Order slack |
| 1 | 8 | 12 | 12-8 = 4 |
| 2 | 5 | 15 | 15-5 = 10 |
| 3 | 6 | 14 | 14-6 = 8 |
| 4 | 7 | 18 | 18-7 = 11 |
| 5 | 6 | 15 | 15-6 = 9 |
Now arrange the order numbers as smallest slack to largest slack
| Order slack Rule | |||
| Order number | Processing Time | Time until due date | Order slack |
| 1 | 8 | 12 | 4 |
| 3 | 6 | 14 | 8 |
| 5 | 6 | 15 | 9 |
| 2 | 5 | 15 | 10 |
| 4 | 7 | 18 | 11 |
b. Order number 1 should be run first under each of these scheduling rules except shortest operation next (SON) rule where first order run is order no. 2.
