The machine shop at Bycraft Enterprises operates 24 hours a day and uses a numerically controlled (NC) welding machine. The load on the machine is monitored, and no more than 24 hours of work is released to the welding operators in one day. The data for a typical set of jobs are shown in Table J.1. Management has been investigating scheduling procedures that would reduce inventory and increase customer service in the shop. Assume that at 9:00 a.m. on Monday the NC welding machine was idle. Also assume that job “arrival times” are the “release times” to the workstation.

a. Develop schedules for the SPT and EDD priority rules, and draw a Gantt machine chart for each schedule.
b. For each schedule in part (a), calculate the average flow time per job and the average past due hours per job.

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TABLE J.1 MANUFACTURING DATA Processing Setup Time (hr) Release Lot Time Job Time Size (hr/unit) Due Date 9:00 A.M. 9:00 P.M. 1 50 0.06 4 Monday Monday 10:00 A.M. 10:00 P.M. 2 120 0.05 3 Monday Monday 11:00 A.M. Monday 3 260 0.03 11:00 P.M. Monday 12:00 P.M. 200 0.04 2:00 A.M. Monday Tuesday 4+