Abstract
Mold-dies are important tools for producing various types of press and injection products. They generally consist of dozens of parts, each of which is machined in various fabrication stages, and are assembled through many subassembly stages. So, in order to manufacture them efficiently it is important to complete assembly parts nearly at the same time just before sub-assemblies start. Furthermore, in order to increase orders from customers and capture the customer's confidence it is necessary to manufacture mold-dies in a short time and reduce tardy mold-dies. In this paper, we study a scheduling method for a manufacturing system which manufactures various mold-dies requiring subassemblies under dynamic manufacturing conditions. First, we consider three types of dispatching rules which can be applied to the system and may reduce assembly time losses, and present the rule which minimizes the mean of make span using an evaluation scale α; α is the ratio of a make span to an ideal minimum make span. Next, we propose a new method to estimate the minimum due date coefficient which yields an Lp smaller than a given value; Lp is the ratio of the number of tardy mold-dies to the number of completed mold-dies. Finally, we present the usefulness of the proposed method and effects of due date coefficient and load on mold-die tardiness. The main results are as follows : (1) MMO dispatching rules, which use the mold due date revised according to the tardiness of machining stage, minimize the mean of make span. (2) The proposed method can approximately estimate the minimum due date coefficient which yields an Lp smaller than a given value. (3) MMO dispatching rules minimize Lp and the mean tardiness, and MO and DDATE dispatching rules, which use mold and stage due dates calculated from a given due date, minimize the maximum tardiness.
