Mathematical Modeling of Industrial Products for Longer Physical Lifetime toward Eco-Design

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Remanufacturing is a new trend in the field of environmentally friendly products toward eco-design. A product undergoes functional failure or physical failure in a remanufacturing environment. A unit intended for reuse should be designed to be durable for a period equal to at least two functional lives through remanufacturing. Usage of excess materials can improve the strength of a reusable unit and give more than two physical lives ; however, such a method may increase the environmental impact due to the obsolescence of the reusable unit, which is an important factor to consider. This study aims to construct a mathematical model, which enables to evaluate environmental impact, and derive the optimal physical lifespan distribution of a reusable unit. In the first year, a mathematical model of a remanufacturing system has been constructed considering physical and functional failures. The incurred total environmental impact per unit time for a reusable unit is formulated as a minimization problem, by which the optimal design parameters of a reusable unit and the maximum number of times of reuse have been determined. In the second year, a mathematical model with consideration of the time series behavior of the value and demand of reusable units and sustainable products including reusable units has been developed. A discrete-event simulation model has been made for its purpose and statistical characteristics of the optimal physical life span distribution have been derived under various environmental conditions. In the last year, a method for setting the optimal physical life span of a reusable part has been proposed on the basis of the result obtained with life cycle simulation of environmentally-conscious products circulation and a nonlinear mathematical programming problem. The effectiveness of the proposed method has been examined by some numerical examples of actual mechanical element examples.