Algorithms for design and scheduling problems in parallel assembly systems

Abstract

This dissertation focuses on design and scheduling problems in a parallel-line assembly system producing multiple product types. Each line in this system can be regarded as an assembly system, in which a series of operations is processed while the products are moved on a conveyor system. These problems can be found in an air conditioner manufacturing system composed of parallel assembly lines that produce multiple product types. In this dissertation, we develop algorithms for a design problem in an assembly system and then, we develop scheduling algorithms for parallel assembly manufacturing systems with multiple product types. First, we focus on a design problem in an assembly system composed of parallel assembly lines that produce multiple product types. In the assembly system, different types of products can be assigned to the same line and each product type can be assigned to multiple lines. In the design problem, therefore, we consider decisions on the assignment of product types to the assembly lines including production quantities of each product type on each line. The cycle time of each line or the speed of the transport system of each line can be determined by the assignment. We formulate the problem to a non-liner mixed integer model and develop an algorithm based on Benders’ decomposition approach as well as heuristic algorithms for the problem with the objective of minimizing the weighed sum of workload imbalance of the lines. Here, the workload imbalance of a line is measured by the time differences between the cycle time and processing times of the operations of the product types on the line. Note that this weighted sum represents the sum of idle times of the assembly lines, or the time loss (loss of capacity) of the lines, which are caused by assigning product types requiring different processing time to the same line. Secondly, we focus on a scheduling problem in an air conditioner manufacturing system composed of multiple parallel assembl...