A lot sizing combined scheduling method for plastic molding process

Abstract

This paper considers the plastics molding process in a consumer appliance plant and proposes a lot sizing combined scheduling method, which is based on expert systems technique and derives a feasible plan while re-sizing the lots. The production planning for the plastic molding process has the properties of parallel-shop scheduling and necessitates the lot re-sizing, in order to arrive at a feasible plan satisfying multiple evaluation indices, which makes it difficult to apply operations research (OR) techniques. The proposed method has the following features. (1) Description of the planning strategy by means of parameters. (2) Automated heuristic support for scheduling and lot sizing. (3) Adjustment of the resulting plan via a user interface. (4) Iterative scheduling, flexibly iterating stages (1) to (3). Feature (2) in particular makes it possible to re-size lots and derive a feasible solution satisfying multiple evaluation indices by the subdivision and merging of lots based on planner heuristics. A production planning system was developed by the proposed method and was introduced into our company's electric iron plant. Its effectiveness is shown by the fact that it reduced planning time to 1/7 and lowered the stock of parts by 25%. Evaluation trials in other plants operated by our company demonstrate that the proposed method can be applied to a wide range of problems.