WHAT IS DESIGN FOR MANUFACTURE AND ASSEMBLY?

In this text we shall assume that "to manufacture" refers to the manufacturing of the individual component parts of a product or assembly and that "to assemble" refers to the addition or joining of parts to form the completed product. This means that for the purposes of this text, assembly will not be considered a manufacturing process in the same sense that machining, molding, etc., are manufacturing processes. Hence, the term "design for manufacture" (or DFM) means the design for ease of manufacture of the collection of parts that will form the product after assembly and "design for assembly" (or DFA) means the design of the product for ease of assembly. Thus, "design for manufacture and assembly" (DFMA) is a combination of DFA and DFM. DFMA is used for three main activities: 1. As the basis for concurrent engineering studies to provide guidance to the design team in simplifying the product structure, to reduce manufacturing and assembly costs, and to quantify the improvements. 2. As a benchmarking tool to study competitors' products and quantify manufacturing and assembly difficulties. 3. As a should-cost tool to help negotiate suppliers contracts. The development of the original DFA method stemmed from earlier work in the 1960s on automatic handling [1]. A group technology classification system was developed to catalogue automatic handling solutions for small parts [2]. It became apparent that the classification system could also help designers to design parts that would be easy to handle automatically. In the mid-1970s the U.S. National Science Foundation (NSF) awarded a substantial grant to extend this approach to the general areas of DFM and DFA. Essentially, this meant classifying product design features that significantly effect assembly times and manufacturing costs and quantifying these effects. At the same time, the University of Salford in England was awarded a government grant to study product design for automatic assembly. As part of the study, various designs of domestic gas flow meters were compared. These meters all worked on the same principal and had the same basic components. However, it was found that their manufacturability varied widely and that the least manufacturable design had six times the labor content of the best design. Figure 1.1 shows five different solutions for the same attachment problem taken from the gas flow meters studied. It can be seen that, on the left, the simplest method for securing the housing consisted of a simple snap fit. In the examples on the right, not only does the assembly time increase, but both the number and cost of parts increases. This illustrates the two basic principles of design for ease of assembly of a product: reduce the number of assembly operations by reducing the number of parts and make the assembly operations easier to perform. The DFA time standards for small mechanical products resulting from the NSF-supported research were first published in handbook form in the late 1970s, and the first successes resulting from the application of DFA in industry were reported in an article in Assembly Engineering [3] .In the article, Sidney Liebson, corporate director of manufacturing for Xerox and a long-time supporter of our research, suggested that "DFA would save his company hundreds of millions of dollars over the next ten years." The article generated intense interest in U.S. industry. 

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