Scheduling of die casting operations including high-mix low-volume and line-type production

Abstract

This article addresses the scheduling problem of a real die casting shop. The problem is of practical importance and yet complicated, especially for a modern casting environment where a variety of cast products made of different alloys are simultaneously manufactured in relatively small lot sizes. As a simple and robust scheduling methodology, a Linear Programming (LP) model is proposed so as to determine the quantity of each product in a casting shift. The solution of the LP model maximises the average efficiency of melting furnaces, i.e., the percentage use of molten alloys throughout the shifts. Our model can represent a most general casting environment to the extent that some die casting machines carry out frequent in-process die exchanges for flexible manufacturing. At the same time, we employ line-type casting as well as a combination die with multi-cavities which can cast dissimilar shapes concurrently. In the high-mix low-volume manufacturing world, the proposed LP model can assist the die casting industry to strengthen its competence by providing an optimal schedule that satisfies practical constraints on casting processes.

A scheme of supplementary production in linear programming scheduling of die casting processes

“…In spite of the optimized die casting scheduling devised by either GA 6,7 or LP [2][3][4][5] and its flawless execution, they do not automatically guarantee successful production quality wise and thus quantity wise in a real foundry. Nonconforming castings or defectives with one or multiple defects are sometimes manufactured inevitably in a die casting shop.…”

“…Elegantly designed as their GA operators may be, the main purpose of using GA in the studies by Deb and coworkers 6,7 is just to provide faster solving procedures than an LP model, which for itself generates the optimal solution. As proved in the studies by Yang and Park, [2][3][4][5] the LP model can represent general die casting environment with frequent inprocess die exchanges, while the computation burden is reasonably managed. Based on these facts, we assert that LP models are more suitable than GA to die casting scheduling.…”

“…As a deterministic scheme, linear programming (LP) models have been widely used, especially in the authors' works. [2][3][4][5] LP models are fit for representing die casting processes because the properties of major die casting parameters are described in linear forms. They achieve the maximum efficiency either in raw material utilization 2,3,5 or production time and cost 4 of die casting processes.…”

“…For further qualitative comparison between LP models and GA in die casting scheduling, the readers are referred to the studies by Yang and Park. 2,5 The objective of this article is to propose a scheme of supplementary production in LP scheduling of die casting processes. Our study follows the setting of Yang and Park, 2,5 that is, the LP model that searches for the solution that maximizes the percentage use of molten alloys throughout the entire shifts.…”

“…2,5 The objective of this article is to propose a scheme of supplementary production in LP scheduling of die casting processes. Our study follows the setting of Yang and Park, 2,5 that is, the LP model that searches for the solution that maximizes the percentage use of molten alloys throughout the entire shifts. Like the scheme of recycling scrap, 3 our scheme is classified into a postoptimization method.…”