Material handling improvement in warehouses for the assembly line parts feeding in case of kitting and in case of different parts categories

The assembly line parts feeding is a complex problem that strongly involves the logistic activities at the warehouse. In case of kitting the handling activities within the warehouse are related to the collection of parts for each kit composition, which is called the Order Picking Problem. Improving the order picking means to minimize the total travel distance and to minimize the time spent to pick the single part once reach its position. Typically to a certain kit belong different parts categories: small parts (SP), large parts but pickable by an operator (PLP), large parts not pickable by an operator but only using a proper equipment (NPLP) typically stored in different warehouse facilities (i.e. racks, shelves, ground). A two-level approach is proposed that determines the locations of parts in the warehouse. Once assigned to each part a proper stock keeping unit in the warehouse and the related SP, PLP, NPLP attribute the first step clusters parts into part families depending on in which zone/kit of the assembly line they are used. The general output of this phase is a different dimension of each SP, PLP, NPLP families are generated for each cluster. In the second step an optimization model is proposed to determine the optimal location of parts minimizing the total picking distance with the aim of storing the same cluster in the same aisle, considering the typical constrain that in the warehouse each isle is composed by all the three warehouse facilities to store SP, PLP, NPLP with a fixed dimension for each one and equal for all the isles. The applied algorithm can easily be modified to be used with different configurations and for parts with different categorization. A case study from a harvesting producer company is detailed reported demonstrating the applicability and the practical implication of the research.