A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1991

The present study concerns the development and implementation of production planning and scheduling models for injection moulding of pipe fittings in Thailand. The objective of the study is to minimize the total cost of production, inventory, and shortage. A Hierarchical Production Planning (HPP} approach with three stages is applied to solve this problem. Firstly, due to complexity of a large variety of product types and multi non-identical parallel machines, the product and machine classification are grouped by using technical characteristics, machine capability utilization, and load balancing. Then each group of products and machines is treated as a multi product and one machine subproblem. Secondly, goal programming models are formulated for the product-mix planning of each subproblem under a three month rolling plan period. Linear programming packages are used in the computations, utilizing both mainframe and personal computers. Thirdly, heuristic methods are developed to solve the parallel machine scheduling problem for the first planning month. The heuristic methods are written in Lotus Macro program for personal computer. Finally, the results obtained from the proposed procedure are compared with the existing intuitive procedure. Many aspects of sensitivity analysis are also presented. This study puts emphasis on how these models can be practically implemented.