مقاله سال ۲۰۱۶

 مجله امگا – Omega

The warehouse layout problem is one of the key issues in warehouse management, which involves all stages of a supply chain. An effective warehouse layout can distinctly reduce the operation costs. The storage location assignment problem addressed in this paper is to determine the locations for different items in a warehouse; thus we consider warehouse layout and storage location assignment as interchangeable in this research. Production planning is the process of determining how to use and allocate the resources efficiently to satisfy the customer demands. The capacitated lot-sizing problem is a medium-term production planning, which decides how much to produce for each product so that the total cost of production, setup, and inventory is minimized. Usually, warehouse layout problems and production planning are analyzed separately. However, while warehouse space is one of the key resources for production, enhancing the utilization of the space can improve the production output and increase the manufacturer’s profit.

Our research is motivated by a real-world production warehousing problem. We perform the study at a food company that processes and packages rice products. The company always faces the challenges of finding available space for their products and managing the items in the warehouse. The lack of coordination between production planning and warehouse management leads to significant inefficiency in both departments. Thus we investigate a production planning that considers the warehouse space resource and a warehouse layout with new storage assignment. In essence, we propose an integrated strategy to combine the capacitated lot-sizing problem with warehouse layout problem so that production process and warehousing can be coordinated effectively.

The warehouse layout problem and the capacitated lot-sizing problem have been studied extensively in research. However, to our knowledge, these two problems have been addressed separately in the current literature and they have not been considered together in a mathematical model. Jans and Degraeve (2008) review the modeling for industrial lot-sizing problems and discuss the four extensions of lot-sizing models. It is indicated in their discussion on new research directions that the integration of lot-sizing, scheduling, and storage constraints affects the planning and scheduling. Buschkühl et al. (2010) presents a review of four decades of research on dynamic capacitated lot-sizing and focuses on modeling and algorithm for the problems. Although they highlight that production planning is strongly related to the layout type and organizational structure of a production system, the warehouse layout is not taken into account in their reviewed literature on the capacitated lot-sizing problem. Existing literature indicates that most of the lot-sizing problems are hard to solve. Zhang and Lai (2010) review the multi-level warehouse layout problem with a dedicated storage policy without considering the lot-sizing problem. Various researchers have combined the warehouse layout problem with different inventory models such as Economic Order Quantity (EOQ) models(e.g., Chu and Chu (2008), Wilson (1997), and Malmborg and Deutsch (1988)), and the replenishment policy models (e.g., Hassini (2008), and Kulturel et al. (1999)). It is noted that in existing research where the warehouse layout problem and inventory models are considered joinly, only static inventory models are utilized. The model presented in this paper not only combines a storage location assignment problem with dynamic inventory, but also takes into account production planning. To our knowledge, the dynamic joint multi-item storage location assignment combined with production planning has not been considered in the current literature.