Evaluation of the application of job shop scheduling decision rules to plastic injection molding operations

Includes bibliographical references (page 24)Job shop scheduling research has been done mostly on sequencing of machining operations in which each machine is treated as a work center, performing one of many operations necessary to complete a job. Many mathematical decision rules have been evaluated on a simulated condition of machine-limited operations, yielding some definite\ud performance superiority of some rules over the others with respect to different criteria. Of these decision rules the two that were chosen to be applied in this project to scheduling of job shop operations of plastic injection molding were the shortest operating time ("SOT'') and the "COVERT??? rules. These were chosen since the "SOT??? has been shown to be superior for almost 99% of orders and is simple to apply. The "COVERT' rule was chosen due to its systematic approach and its retention of the superiority of the "SOT" while minimizing the lateness of a few jobs (which was the only disadvantage of the "SOT").\ud A sample of one month orders scheduling by the existing decision rule of Medical Plastics was compared with scheduling same data by the "SOT'' and "COVERT" rules. The results were a great improvement over the existing rule with respect to percent jobs completed on time. Hence, improved decision rules were suggested for scheduling production at Medical Plastics for better achieving management objectives.\ud An attempt was made to compare the trade off of stopping running jobs in order to achieve a better percent of jobs completed on time, but due to lack of sufficient data no\ud definite conclusion was reached