Simulation has been used to evaluate various aspects of manufacturing systems. However, building a simulation model of a manufacturing system is time-consuming and error-prone because of the complexity of the systems. This paper introduces a generic simulation modeling framework to reduce the simulation model build time. The framework consists of layout modeling software and a data-driven generic simulation model. The generic simulation model was developed considering the processing as well as the logistics aspects of assembly manufacturing systems. The framework can be used to quickly develop an integrated simulation model of the production schedule, operation processes and logistics of a system. The framework was validated by developing simulation models of cellular and conveyor manufacturing systems.

Formulating a schedule for unloading raw material from ships at the seaport of a steelworks is a difficult task. Even in its simplest possible form, finding an optimum solution for the problem is nondeterministic polynomial time (NP)-hard. The problem at a steelworks gets more complicated due to several factors, such as the difference in capacities of unloading equipment, the requirement of keeping ships balanced and the dynamic nature of berthing eligibility of each ship, as governed by the weight of the remaining payload. Moreover, the raw material must be transported through a network of belt conveyor units to designated storage yards while being discharged from ships. The combinatorial nature of this belt conveyor operation is analysed in this article. A heuristic approach to the raw-material unloading problem is proposed and its effectiveness was tested with real-world examples.

Simulation has drawn much attention as an analysis tool because it is often the only tool that has the capability of modeling the details of the semiconductor lines. However, building a simulation model of a semiconductor line is time-consuming and error-prone because of the complexity of the line. This paper proposes a generic simulation modeling framework to reduce the simulation model build time. The framework consists of a layout modeling software called AutoLay and a data-driven generic simulation model called AutoLogic. It can be used to develop an integrated simulation model of production processes and material handling processes in a short period of time. Early users of our framework reported that the initial model building time was reduced from two weeks to a half day.

This paper considers the vehicle dispatching problem in large-scale overhead hoist transport (OHT) systems of semiconductor fabrication lines. We propose a Hungarian algorithm based OHT reassignment approach named HABOR. HABOR attempts to take advantage of simultaneous vehicle reassignment based on up-to-date system status using the formulation of the assignment problem. The effectiveness of HABOR is demonstrated using a sample OHT system of a semiconductor fabrication line with more than 130 vehicles, where the flow path of the line allows direct delivery so that an inter-bay wafer movement can be accomplished by a single vehicle without an intermediate storage step at a stocker. HABOR compares favorably with the shortest travel distance first rule and with the reassignment-based rule recently proposed by the authors.

This paper proposes a simple blocking prevention method for a path-based automated material handling system (AMHS) such as a semiconductor fabrication line. Here, blocking means the situation in which a vehicle stands and waits without doing anything because the vehicle in front of it is in the process of loading or unloading. Since a typical bay type path-based AMHS has a single path in each bay and no sidetracks, the blocking issue is inevitable in a large complex system with many vehicles. The proposed method is based on the swapping of load assignments between retrieval vehicles on the same path. Our simulation study on an example semiconductor line shows that the proposed method improves the AMHS productivity under various vehicle dispatching rules.

This paper proposes an efficient vehicle reassignment dispatching rule and demonstrates the effectiveness of the rule using an overhead hoist transport (OHT) system for a semiconductor fabrication line. The OHT system has more than 150 OHT vehicles and its target vehicle utilization level is 70%. It allows direct delivery such that an inter-bay wafer movement can be accomplished by a single vehicle. Simulation analysis is used to compare the proposed rule with the shortest travel distance first (STDF) rule and existing reassignment-based rules. While STDF rule requires 170 vehicles for the target utilization level, the proposed vehicle reassignment rule requires only 161 vehicles. At the same time, the lead time and the variance of the lead time have been significantly reduced. The proposed rule also improves system performance compared to existing reassignment-based rules.