Evaluating the interaction between material substitution and part sharing in product design : a case study of automotive lightweighting

Abstract

Firms seek to create a product that are both desired by consumers, and also minimize costs. These goals come into conflict, as minimizing costs leads firms toward mass production, and meeting consumer needs leads firms toward product differentiation. One strategy to resolve these conflicting goals is to share component parts across distinct product variants allowing firms to maintain differentiated products while obtaining some of the economies of scale. In this way, part sharing reduces the cost burden of maintaining multiple product variants. However, part sharing also reduces product differentiation by resulting in some feature sharing, as the requirements of component parts differ across different product variants. Though some sharing may add desirable features, there may also be negative impacts, such as unnecessary mass from overdesign, referred to as "scar mass." In products where low mass is an important feature, this scar mass may deter designers from implementing part sharing. A common way of reducing mass in products is to exchange the material used for a lighter-weight alternative. However, lighter materials may be more expensive to use due to higher unit price or more complicated forming. This research investigates combined part sharing and material substitution strategies and their implications on cost and product weight. Specifically, it seeks to evaluate whether there exist situations in which 1) the cost savings from part sharing outweigh the increased cost from material substitution, while simultaneously 2) the mass savings from material substitution outweigh the scar mass penalty from sharing. To address this problem, this research develops a framework for modeling the implementation of different part sharing and material substitution strategies. In this framework, design changes to products from material substitution and part sharing are estimated using equivalent structural performance. The cost implications of these design changes are then calculated using a Process-Based Cost Modeling approach. This framework is then used to address a case of a hypothetical generic product and finally is applied to a real case. The real case is based on three real vehicle bodies that share a common platform. The research findings identify situations in which material substitution and part sharing strategies can be combined to produce lower mass and lower cost products. Automotive manufacturers may benefit from using these findings to implement cost-effective lightweighting policies to help them meet fuel efficiency standards.