Little’s Law Redux

Recently I had the opportunity to sit in on a desk top simulation of a manufacturing cell design.  The process is called HOCUS.  Hocus stands for Hand Operated Capacity Utilization Simulation.  Its purpose is to identify constraints and opportunities in the proposed new manufacturing cell layout.  With a group of workers and support people the flow and relationships between operations, and wip, throughput, queues, and flow days are studied in a virtual world.  Routing job sheets are created for each of the mix of products running through the cell.  In virtual fifteen minute increments work is ticked off and jobs moved around through the routing and process flow.  Once each virtual day work-in-process inventory at each work station is collected and total cell throughput is counted and recorded on a production chart hanging on the wall.  Operators and cell designers then discuss and tweak the model to address constraints with changes such as adding or removing work stations, adding shifts, changing equipment size or batching rules.  The process is very interactive and uncovers issues not brought out in the earlier design stages of process mapping and interviews. While running the recent event we noticed that throughput was as expected and wip was piling up at several operations.  OK so add more capacity, someone said, and we did and after several more iterations the backlog queues stopped growing but didn’t decrease.  We achieved steady state.  But start to finish throughput time was still too long, what to do? Well how about some selective overtime at the two bottleneck operations?