| Cyclic, route-based material handling systems, known as (internal) "milk runs" in lean manufacturing, are typically used to deliver containerized parts, via tugger and carts, in small batches at a regular frequency from a central parts storage area to multiple customers or points of use. In this research, a single-tugger milk run system is analyzed. An approximation of the total number of container starts per tour is presented using a normal distribution. Simple "rule of thumb" metrics are presented utilizing the normal distribution. Further, the level of service provided to each customer, measured as the fraction of time parts are available for use at each customer location, is determined to be a function of the number of kanban in the system for each part type and the sequence customers are visited on the route. Finally, these results are applied to the classic facility "block layout problem." We consider the applicability of existing solution procedures to the block layout problem with milk run systems and present two alternate formulations. The first formulation, assumes customers are assigned to routes a priori while the second allows for a joint solution to the layout problem and customer assignments, using a linearized constraint based on the service level results. |
