신발 제조 공정의 생산성 및 품질 향상을 위한 설비 운영 전략에 관한 연구

Abstract

This study addresses managerial solution approaches for productivity improvement in footwear manufacturing systems. Our work focuses on two approaches, operational control strategies and facility optimization. The shoes are made by assembling bottom parts and upper parts on an assembly line. Before assembly processes, the upper parts of the shoes are manually sewed while bottom parts are produced by machines such as injection and molding machines. The manual operations for the upper parts lead to a large variability in processing times, resulting in higher work-in-process inventory. In most current footwear industries, production lines have been controlled by MRP-based push systems. Some industries attempt to introduce kanban-based pull systems. This dissertation identifies the characteristics of the footwear manufacturing processes, and discusses the problems of the current control systems. As an operational alternative, a CONWIP-based control strategy is presented. Simulation experiments are performed to examine the performance of the control strategies. For facility optimization approach, we take outsole rubber fabrication, a critical process in a bottom parts of the shoes, as our test bed. The outsole rubbers are made from the rubber pellets which are formed by metal cutters. Here, the shape of the cutter must be designed so as to reduce the maximum stress applied to the cutter. We design a variety of cutter shapes and use computer simulations to analyze the maximum stress in the rotary cutter for each design. A Taguchi method is used to identify the robust condition of the cutter. In L18 orthogonal array, the control factors such as knife width, twisted angle, number of knives, diameter, knife depth and supported angle are considered and noise factors like assembly tolerance and amount of antifriction are allocated in the outer array. It is found that the supported angle and diameter of the cutter are the most important factors to reduce maximum stress in the cutter. Productivity has been mainly dependent on workers’ experience in footwear manufacturing systems. This study will be able to identify the problem of the existing footwear factory operation method numerically through the academic background and make a scientific approach to the productivity improvement. In terms of operational control strategies, this study can help to choose proper method between pull and push systems according to the situation of the factory. When new equipment is developed, it will be possible to shorten R&D period and make more reliable machine.