Modular product design allows the designer to control the degree to which changes in requirements affect the product. By promoting interchangeability, modularity also gives designers more flexibility, with decreased cycle time, to meet changing requirements. Specific advantages associated with modular products include economies of scale, standardization of assemblies, minimization of assembly time, improved serviceability, and many more. Modular architecture is traditionally made up of functionally independent clusters of components. Past definitions of modularity have centered on a one-to-one correspondence between form and function. An expanded definition of product modularity has been used, which not only includes function, but also form and life-cycle process (manufacture, assembly, retirement, etc.) relationships. Modules contain a large number of components having very few similarities and dependencies on components not in the same module. This definition of product modularity differs from most, due to the inclusion of the similarity aspect. Modular products that are modular with respect to retirement are well designed for reuse, remanufacturing, recycling, and disposal.

Apart from addressing the incorporation of product retirement into product modularity, a comparison of retirement costs and product modularity has been shown in this paper. Comparing costs with modularity is essential since cost is a major factor in the success of a product. Any design change made to improve retirement modularity will be practical only if the benefits accrued from an environment-friendly design are coupled with decreased costs due to the design change. One question that remains to be addressed is — do improvements in product modularity always decrease retirement costs?

In this paper, an existing modular design method was focused on product retirement. Our initial study of the modularity-cost relationship is based upon the retirement of a consumer flashlight. We took a single flashlight and redesigned it, making it more modular, using a modular design method. The method has a set of guidelines helping in direct product development towards modular products. These are:

1. Eliminate the modules if they are not necessary.

2. Eliminate individual components of the modules.

3. Shift die components to other modules to increase the relative modularity of the product.

4. Redesign the attributes of the components to decrease or eliminate similarities or dependencies with outside components or increase similarities with components of the same module.

After completing the modular design method, we measured the product modularity and retirement cost of the product at each intermediate stage of redesign. Costs associated with retirement including, recycling, reuse, remanufacturing, and disposal were measured at each stage using the cost equations listed below. The result of the research in this paper is studying the relationship between measured retirement modularity and product retirement costs. Statistical analysis of the flashlight data was carried out to look at the relationships between relative modularity, number of design changes made, and retirement cost.

Our initial study of the relationship between product modularity and product retirement costs showed several trends. As was the hypothesis of this work, as product modularity and retirement modularity increase, product retirement costs tend to decrease. However, this trend is not as strong as previous literature has assumed. Our study of this hypothesis was complete but limited in scope. We have begun follow on research that expands this work to additional products and additional life-cycle stages.

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