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FLEXIBLE DESIGN METHODOLOGY




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Proceedings of 5th Design for Manufacturing Conference: Design Engineering Technical Conferences Baltimore, Maryland; September 10-13, 2000 DETC2000/DFM-14016 FLEXIBLE DESIGN METHODOLOGY Christoph Roser Department of Mech. & Ind. Engineering University of Massachusetts Amherst David Kazmer Department of Mech. & Ind. Engineering University of Massachusetts Amherst ABSTRACT A flexible design methodology is developed to minimize the effect of uncontrolled variation by modeling potential design and manufacturing corrections in the product development process. Using this flexibility methodology, the different defect modes and the likelihood of these defects occurring is evaluated. For every defect mode, all design change options are investigated including the cost and probability of selection. The expected cost of the initial design including design changes is determined, thus allowing development of improved, more flexible designs. The theoretical method is demonstrated using an example. The results indicate that small changes in design variables may reduce the likelihood and cost of future design changes, yet provide opportunity for downstream cost minimization. KEYWORDS Flexible Design, Design Change Cost, Prediction Uncertainty, Robust Design INTRODUCTION The goal of robust design methodologies is to reduce the sensitivity of the design to variation. The robustness is typically evaluated using models, simulations or experiments. However, there is a possibility that the physical embodiment of the design might not satisfy the specifications due to uncertainties in the development process and lack of knowledge. Although the robust design prediction considers noise, it usually does not account for uncertainties and inaccuracies in the predictions of the design performance. Due to this lack of consideration for prediction inaccuracies, the finely tuned robust design might violate specifications because the underlying predictions lack the necessary accuracy. It is possible to model the uncertainty variation into the robust design evaluation to reduce the sensitivity to noise and uncertainty, yet this could increase the cost of the product while generating no value for the customer. The described methodology aims to minimize the expected cost of the design including development uncertainties. Figure 1 shows a predicted feasible design region within which a design is assumed to be feasible. From this predicted design region, a design is selected according to the objective function. The objective function is shown in the graph as the diagonal contour lines. However, the actual design window and the feasible design window might not coincide due to uncertainties in the system performance. If the selected design lies outside of the actual design window, a design change is necessary, even if the model predicted this design to be optimal. This required design change will result in unforeseen development costs, and may also alter the performance and cost of the product. De sire d Dir ect ion Design Variable x1 Predicted Design Window Original Selected Design Actual Design Window Pr edi cti on Er ror Changed Designs Design Cha nge D es ig n Va ria bl e x 2 Figure 1: Flexible Design Incentive Figure 2 provides an overview of the flexible design methodology. The method starts by selecting an initial investigated design, for which a ...





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