The mixed-product assembly line sequencing problem of a door-lock company in Taiwan

This paper investigates the mixed-product assembly line sequencing problem in the door-lock manufacturing industry. Companies in the door-lock industries schedule their production processes to minimize their costs while meeting customer demand. The variances and diversities of each lock's components complicate the mixed-product assembly line sequencing problem and directly influence the material requirement planning and human resource costs. In the current research, we study one of the largest ironware manufacturing companies in Asia, company F. For this company, an export-oriented strategy makes its main products (such as door locks and door closers) available around the globe. The primary customers of company F are the largest home improvement co-op stores (such as Home Depot, Lowe's and True Value in the US) from the region of North America. The sales from this region account for over 80% of company F's total sales. The remaining company sales are geographically distributed around the world in areas such as Europe, Asia and Australia. However, as labor cost is the major concern, this company seeks supply sources in southeast Asia, China and Taiwan. In this paper, we analyze company F and formulate an integer programming mathematical model with constraints regarding production lines, labor, warehouse capacity and order fulfillment rates to minimize the total cost. The customer demand is derived from real data from company F. We use the branch and bound algorithm (CPLEX) to solve this problem and analyze the results. Salient results and practical issues involved in this unique problem are discussed in detail in this paper.