Wright Williams & Kelly
Factory Explorer® v2.2 Technical Alert #9
Summary: When calculating product-level raw process times in models with HoldTool, Factory Explorer® incorrectly double-counts the raw process time for steps contained in HoldTool regions. This error is corrected in Factory Explorer® v2.3 beta 6.
Details: To calculate product-level raw process times, Factory Explorer® sums the raw process times for individual steps in the process flow, and multiplies by the expected number of visits for each step (assuming no scrap, rework, etc.). In Factory Explorer® 2.2, in order to predict utilization of tools used by HoldTool steps, the capacity analysis engine calculated the raw process time for the HoldTool step as the sum of the raw process times for all steps in the HoldTool region. This method worked well enough when predicting utilization, but resulted in the raw process times for steps in the HoldTool region being double-counted when product-level raw process times were calculated. In Factory Explorer® v2.3 beta 6 and forward, a different method is used to predict utilization for tools used by HoldTool steps.
Workaround: To correctly estimate product-level raw process times, remove all HoldTool regions from process flows and perform capacity analysis (removal can be accomplished most easily in Excel models by deleting the FREESTEP keyword on all process flow worksheets). If you restore the HoldTool regions, be aware that the inflation in raw process times will cause a corresponding deflation in "cycle time divided by raw process time" estimates.