Question

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ABC's machine shop is considering the use of priority scheduling rule in the fabrication shop and must decide whether to use: a. Critical ratio (CR) Earliest due date (EDD) C. Shortest operation next (SON)/Shortest processing time 9SPT) d. Order Slack Order No. Total Remaining Time Remaining Current operation Manufacturing until Due Date Processing time Time (days) (days) (days) А 12 15 10 14 D 18 15 19 Using the four sequencing rules, compute the scheduling priority for each order given in the table above. What order should be run first under each of these scheduling rules? Hint: time remaining Due date - Present time CR = work remaning Lead time remaning (including setup,run, and queue) CR = 1 → the job is on time CR< 1.0 — the job is behind-schedule CR>1.0 → a head-of-schedule condition Rule: process that job with the smallest critical ratio next. Order slack: time remaining until due date - sum the setup times and run/processing time for all remaining operations. Rule: work on the job with the least slack.

Answer 1

order NO Page 1 Total Remaining Time Remaining Manufacturing until Due time (days) Date current operation processing time 00 15 12 D 15 J 10 915 LE I 20 @ Critical Ratio (CR) for order A, CR = Due date Time Remaining until total Remaining time = 12 =0.8</ For order B, CR - 15 = 1.25 > 1 For order C, CR : 4 =1.4 For order D,CR - = 1.2 > 1 for order E ,CR : 19 = 0.95</ ūlo oli rolü

Page 2 smallest CR comes ist so sequence will be A → →D → B C © Earliest Due date (EPD) • Sequencing will be based on earliest I due date given • Smallest Due date come first so sequence will be A —— — B-→ D-LE (12) (14) (15) (18) (19) © shortest processing time CSPT) · smallest processing time required for order comes first so sequence will be D B > E - A (3) (4) (5) (6) (8)

Page 3 @ order slack = Time remaining for Due date - Processing time 0.5 For Order A - 12 - 8 = 4 OS For Order B= 15-5 = 10 os For order c = 14-4 = 10 os for order o = 18-3 = 15 Os For Order E = 19-6 = 13 · Job with least slack comes first so sequence will be A < B >C -E D