Integrated design of automated material handling systems in assembly production systems

Abstract

In manufacturing, material movement is often a fundamental part of the transformation process, and contributes to a significant portion of the final product````s cost. Thus, material handling systems usually become a basis for the infrastructure of manufacturing system. Inventory related issues need to be considered at the design stage of automated material handling systems. Although shop floor inventory control and material handling decisions are closely interrelated, they are rarely considered together. The purpose of this thesis is to develop design methodologies for automated material handling systems in assembly production systems with an emphasis on shop floor inventory control policies. The first part of the thesis deals with the problem of determining unit load sizes of an AGV in an assembly production system with multiple lines. A defining characteristic of the problem is that the length of assembly cycle time, the product type, and the production quantity are allowed to be different among assembly lines. We propose an operating policy of the AGV and then develop a mathematical formulation for the problem. To solve the model, an appropriate sequence of the vehicle trips is determined. And then, based on the characteristics of the objective function and constraints, an iterative heuristic algorithm is developed through alternative formulations of the model. Also, for comparison purpose, a genetic algorithm and a lower bound for the problem are developed. The performances of these proposed algorithms are examined. The second part addresses the problem of determining unit load sizes of an AGV in a job-shop-type assembly production system. At each workstation, a continuous review policy is assumed for inventory control policy. Treating the AGV system as an M/G/1 queueing system, a nonlinear mathematical formulation is developed. To solve the formulation, we present a heuristic algorithm which is based on the mathematical properties of the objective functio...