Study On Volatility Safety Stock For Kanban Controlled Manufacturing System

In reducing WIP inventory, domestic and international research mostly has focused on exploring WIP inventory strategy in the push&pull production system. A typical representative of push production system is MRP Ⅱ. And JIT is the typical pull production system. JIT emphasizes production timely and suitably without waste, and also the need for small batch size production and transmission, as well as synchronized production by takt time.Small batch size production means a smaller amount of WIP stock, shorter production cycles, and fewer warehouses stock and workshops buffer stock area. However, once the batch size is too small high transportation costs will increase the total production costs. Therefore, the reasonable batch size must be based on specific conditions, a comprehensive analysis and consideration of various factors. It is helpful for reducing WIP costs to determine the optimal batch size. Kanban controlled lean production system requires moving only enough parts from the preceding workstation to the succeeding workstation issued in withdrawal kanban. This paper explores the minimum amount of safety stock on each workstation under the condition that batch size is given. This safety stock includes semi-finished stock between the workstations, line-side parts stock, and the safety stock needed to cover the unsteady production.In the dual-kanban pull production system, safety stock is not a minimum stock which is theoretically calculated by considering the batch size, cycle time of each station, and the takt time only. In the circumstances of unbalanced production line, the material handling system broken unexpectedly, or unreasonable high defect rate, the additional safety stock will be needed. Further, the emergent production caused by adding a production for an unplanned order from an important customer, or by catching up a due date, also calls an extra safety stock. Overlooking these factors will probably result in kanban operation failure, shortages, due date delay, and so on.In this paper, a volatility model is established to adjust safety stock dynamically with considering the emergent production. Finally, an engine assembly line example is presented to illustrate a realistic safety stock determination for the kanban controlled workstation with the help of ExtendSim simulation software.