Assembly Line Balancing and Sequencing

Abstract

Assembly line balancing (ALB) and sequencing is an active area of optimization research in operations management. The concept of an assembly line (AL) came to the fact when the finished product is inclined to the perception of product modularity. Usually interchangeable parts of the final product are assembled in sequence using best possibly designed logistics in an AL. The initial stage of configuring and designing an AL was focused on cost efficient mass production of standardized products. This resulted in high specialization of labour and the corresponding learning effects. However, the recent trend gained the insight of the manufacturers of shifting the AL configuration to low volume assembly of customized products, mass customization. The strategic shift took effect due to the diversified customer needs along with the individualization of products. This eventually triggered the research on AL balancing and sequencing for customized products on the same line in an intermix scenario, which is characterized as mixed-model assembly line balancing (MMALB) and sequencing. The configuration planning of such ALs has acquired an important concern as high initial investment is allied with designing, installing and redesigning an AL. The research carried out in this manuscript aims to contribute to the problem domain of MMALB and sequencing. Balancing refers to objective depended workload balance of the assembly jobs to different workstations. Sequencing refers to find an optimal routing/job dispatching queue considering the demand scenario, available time slots and resources. Primary factors associated to this problem domain includes different assembly plans (e.g. mixed/batch/single model production), variations in processing workstations (e.g. manual/robotic/hybrid stations), physical line layouts (e.g. straight/parallel/U-shaped lines) and varied work transporting methods (e.g. conveyor/pallet-based). These factors are mostly plant specific and must be considered as the design pre-requisites for line balancing and sequencing. The contribution of this work is twofold. Firstly, a brief review of the problem domain of ALB and sequencing is presented. This includes systematic design approach of an AL and different performance and workstation related indexes which helps the line designer to identify plant specific design factors for line balancing, re-balancing and sequencing. Different heuristics and meta-heuristics based ALB solution strategies, classification of ALB problems, MMALB and sequencing are also addressed (section 2). Secondly, a logic and mathematical formulation based methodology for solving ALB problem is proposed (section 3), addressed to low volume product customization in shop