Generating CT-TH-PM surfaces using EPT-based aggregate modelling

Cycle Time-Throughput-Product mix (CT-TH-PM) surfaces give the mean cycle time as a function of throughput and product mix for manufacturing workstations. To generate the CT-TH-PM surface, detailed simulation models may be used. However, detailed models require much development time, and it may not be possible to estimate all model parameters. Instead, we propose an aggregate simulation model to generate a workstation's CT-TH-PM surface. In the aggregate model, the various workstation details are lumped into an ‘effective process time’ (EPT) distribution. The EPT distribution in the aggregate simulation model is estimated from arrival and departure data measured at the workstation in operation. We validate the proposed method using a simulation example representing a semiconductor workstation. We find that the method can accurately predict the mean cycle time in a region around the workstations’ operational product mix. We also present an industry test case; the applicability of the method is demonstrated for a workstation in the Crolles2 wafer factory.