The major task in the design process is to identify the optimal structural designs that would provide the best performance of the machine while minimizing the cost. It is known that eighty percent of the final cost and quality of a product are designed in during early stages of the design process. Design changes and optimization later in the design process can have only a limited impact on the final cost and quality. Thus it is critical that the right concept of the machine is selected in the early stages of the design. However, making informed decisions early in the design process is difficult because of time constraints and uncertainty. The analysis, which are performed during early stages of the design, typically have to work with information that is not clearly defined (sketches vs. drawings, all components or options are not included, developed duty cycles vs. actual cycles, unkown loads, etc.). Results of these preliminary analyses are rough and approximate but very effective where the level in precision required is less that the final design analysis. The timetable for these analysis is typically significantly shorter. The preliminary analyses of the machine concept and machine components have to provide sufficient data and criteria required to make sound decisions between concurrent designs. These considerations are important in the machine tool business, which have deal with large castings, expensive pattern costs and long lead-times. The machine tool specifications dictate the process of selection of the structural geometry, dimensions, and structural components. The selection process is constrained by geometrical limitations and functional requirements driven by the specifications. These constraints cannot be represented in all cases by obvious equality or inequality expressions and functions of a design stage. It is proposed to divide the early design process stage into three steps: - prepare sketches of acceptable conceptual designs with major components in place; - prepare sketches of major components and compare they as a individual parts to chose the bests for every concept; - implement these parts as simple conponents in the conceptual design and compare the conceptual designs by their major performance benefits. This approach allows comparing conceptual designs when the components for each design are prepared with the same knowledge of conditions and requirements, and are developed to similar level. The proposed conceptual approach is illustrated by design of nuemrical control machine tools.

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