Case Study 5-4
IET delivered a simulation model as a tool for evaluating the capacity, WIP requirements and scheduling mix of a new model year product on a new final assembly line.
Johnson Controls, Lakewood facility, supplies seating components to automotive manufacturers.
The client needed to add new sub-assembly equipment and new assembly lines to accommodate new model year products. In addition to space constraints, final assembly is tightly linked to sub-assembly of the components required at the final line. Sub-assembly of the components needed at the final line is fairly complex.
The challenge was to determine the capacity of the final lines, the WIP space required to keep the assembly lines running, identify bottleneck operations based on configuration changes, determine the effect of batch sizes and schedule changes on the final line output.
A simulation of the sub-assembly and final assembly lines based on FPV and CPV volumes was developed and analyzed with the JCI team members in order to identify capacity and WIP inventory issues associated with the addition of the new products.
IET built the simulation model using Witness Simulation Software. This model includes 63 sub-assembly and final assembly stations, associated labor, 14 final assembled parts and 28 sub-assembly components used at the final line. This model was based on a process flow document developed by IET with the JCI team.
Input variables and output reports are read from and written to an Excel file for ease of printing, analysis and distribution. Schedules, cycle times, changeover times and triggers, breakdowns, scrap, labor and batch sizes are some of the variables that can be changed by the client within the Excel spreadsheet interface.
Many scenarios were run and summarized to review with the team. The final assembly schedule of the 8 Way lines had a significant effect on both WIP inventory and final line output. By running smaller batch sizes more often, we can maintain a lower level of inventory, but this increases the number of changeovers on both the final line and the sub-assembly operations, decreasing our available time. By running larger batches of up to a one-week volume requirement, we can minimize the changeovers but will have to increase the inventory levels to up to a week’s worth of inventory on hand for those parts. By grouping the parts by vehicle types that utilize the same components, we can approach the best case scenario between these two options.
It was also determined that the amount of space allocated for WIP inventory was not sufficient for operating the final line near capacity. Additional space was located for this use. Additional racking requirements were also calculated based on the inventory requirements.