A SIMULATION STUDY COMPARING GT VS JOB-SHOP MANUFACTURING SYSTEMS

Two discrete simulation models were developed, one representing a typi cal job shop (JS) manufacturing system (process layout) and the other representing group technology (GT) manufacturing system (cellular layo ut). Hypothetical data generated by FORTRAN program and MICRO-CRAFT la yout package were used to validate the two models. Simulation were per formed using SLAM II. The two layouts were compared with one another u nder controlled experimental conditions using various combinations of four operating variables: batch size, demand rate, ratio of setup time to process time, and transporter speed. Six indicators of systems per formance were used in the study. These were: average time in system, p roducts completed, jobs in process, average machine utilization, avera ge queue length, and average waiting time. The study found that for en vironment as set for the models, GT system outperformed JS system as e xpected. However, using large batch size (more than 75) in Experiment 1 changing batch size) allowed JS system to perform as well as GT syst em. Certain (specific changes in batch size also allowed to establish optimum results in both systems. No individual change of demand rate ( Experiment 2), ratio of setup time to process time (Experiment 3) , or transporter speed (Experiment 4) allowed JS system to outperform GT s ystem.