| Design For X Methodologies |
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The need for ‘design for’ methodologies was identified as Engineers became increasingly aware of a lack of appropriate detailed knowledge in important product Life-cycle processes. Design for X methodologies can be seen as tools to analyse designs for their Suitability for identified aspects of a Product’s Life Cycle . Of these manufacturability and assemblability were among the first to have been considered, since both were highly apparent cost reduction drivers (Benhabib, 2003). Similarly, following the example of DFA and DFM, other DFX methodologies have been proposed which consider alternative life-cycle values, assessing parameters like quality, maintainability, reliability, safety regulations and environmental issues earlier in the design process. DFX methodologies are tools to evaluate designs, typically at both concept and detail levels. As such, to provide meaningful comparative data, they typically quantify aspects of the design such as cost, quality and regulatory conformity (Reik et al., 2004). Thus they not only provide a benchmarking tool for designs but also provide an indication of the possible relative benefits of one design compared to another. By the simple expedient of the number of hits registered on an internet search engine the researchers determined that the most prominent and widely used DFX methodologies are probably Design for Assembly (DFA) and Design for Manufacture (DFM). DFA provides methods to evaluate ease of assembly, assembly times and costs. DFM helps the designer to enhance manufacturability, and again provides manufacturing cost data for a product and its components. Complex cost models have similarly been developed for different manufacturing processes and their respective process parameters (Boothroyd and Dewhurst, 1994; Swift and Booker, 1997). Boothroyd and Dewhurst (1994) have assessed DFA and DFM separately and explored possible trade-offs between assembly and manufacturing costs. Equipment set up times are considered in their work and are included in their cost models. These data are treated as constants in the calculations they undertake, where Boothroyd and Dewhurst fail to accurately determine differences in changeover times between various processes. In reality changeover times are strongly dependent on the product range and the manufacturing processes used (McIntosh et al., 2001). One objective of DFC is to allow more accurate estimates of the changeover capabilities of manufacturing equipment, and the influence that features of the final design will have. Design for Maintenance or Design for Service (DFS) considers how subassemblies can be exchanged as quickly and easily as possible. Depending on the relative likelihood of failure of a specified component or subassembly, greater effort can be made to improve its maintainability. Primarily this is achieved by enhancing ease of assembly and disassembly of these specified elements, where the additional cost incurred to achieve this enhanced capability is justified. |
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