Synchronized tolerancing in growth design

Abstract

Competition in the global economy is increasing the demand for designing products right the first time. Tolerancing is an essential part of the design process of a product, but it is traditionally performed after the product structure has been determined. Therefore, the original information about precision requirements may not be fully utilized in early decision making for selecting the best structure from all the potential alternatives. To establish a solid foundation for integrating tolerancing in the conceptual design phase, growth design methodology has been proposed, in which the functional surface concept is first introduced to unify abstract function with visual structure; and second the generalized positioning principle is utilized to establish a theoretical relation between the product structure and all other factors in design; and third a logical and operable approach to evolving product structures is developed. Based on growth design, tolerancing has been integrated seamlessly into a synchronized design process in which a series of structure alternatives for a product are generated step by step and tolerancing is performed for each step to evaluate each new alternative structure at different levels. In the present paper a framework is proposed first to illustrate the relationship between growth design and tolerancing. Then the key models and algorithms for synchronized tolerancing are described in detail including the tolerance adaptation process, the automatic formation of a tolerance chain, and the product tolerance optimization. Finally, a prototype tolerancing system has been implemented and applied to a dedicated fixture design to verify the validity of the approach in engineering design.