INTRODUCTION TO DESIGN FOR MANUFACTURING

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1. INTRODUCTION

The objective of design for manufacturability is to incorporate producibility issues early on in the product design stage so that the customers can be attracted and the needs of the customers can be satisfied in a short lead time and at a competitive cost. The customers’ needs include satisfaction in the product with respect to its performance capabilities, quality, reliability, serviceability, aesthetics, and time of delivery.

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Conventional engineering practice in the past has resulted in separate, and sometimes isolated, activities between design and manufacturing that have proven to be time consuming and costly. A study compared the cost of any change in design in three different stages, namely, in production, manufacturing engineering, and design. The cost of a change in the production stage may be ap-

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proximately an order of magnitude more than the cost of the change made early in the manufacturing engineering stage. Figure 1 shows comparative cost of an engineering change in different stages in the product cycle. To avoid the costly changes due to manufacturability problems, factors related to manufacturing must be considered in all phases of the design process, starting with the design- conception phase. Another study (Nevins and Whitney 1989) further confirmed the importance of making the right decision early. This study indicated that in the concept formulation stage 60% of the life-cycle cost of a product has already been determined. Before full-scale development 75% of the life-cycle cost has been determined. This is illustrated in Figure 2. It is clear from the figure that the DFM needs to be considered in the early conceptual design stage to yield the maximized benefits.

The major issues in competitiveness have moved from cost to productivity to quality. The current and future major issue is time. The other issue are not less important, but the new frontier is speed: studies have shown that over 80% of market share in a new product category goes to the first two companies that get their products to market. Further studies have shown that a 20% cost overrun in the design stage of the product cycle will result in about 8% reduced profits over the lifetime of the product. A six-month overrun in time during the design stage today will result in about 34% loss over the life of the product (Brazier and Leonard 1990).

Figure 3 compares Japanese and U.S. auto design and product cycles. The competitive advantage of the Japanese auto industry results from concurrent engineering and design for manufacture (Shina 1991).

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