Variational design for a structural family of CAD models

Computer-aided design (CAD) is an important industrial practice used in many applications, including automotive, shipbuilding, and aerospace. With the help of CAD tools, a large majority of part models are not constructed from scratch today but are modified versions of existing models, leading to what is commonly termed as variational design (or adaptive deign) [1– 3]. This CAD modeling means can reduce design time significantly. Given the competitive pressures in today’s market, variational design can make an important contribution towards shorter time-to-market and lower labor costs. Variational design is often carried out using a solid modeler, a field pioneered by Herb Voelcker [4–6]. Design variations are generated by varying parameters pre-defined in solid models [7]. Parametric solid modeling has proven effective in many engineering tasks, especially for those involving exact design requirements. It, however, restricts design variations to a parametric family of parts. This limitation manifests itself through dynamic design requirements that ask for, for example, adding new features and/or removing existing features [8]. Dynamic design requirements are not uncommon today due to the increasing popularity of product customization [9]. Although going beyond parametric variations, the desired new design is not likely to deviate from the design to be reused too much, otherwise we lose the advantages of variational design. Particularly, they often share main functions but have individually customized detail functions. There is thus a shared structural pattern between their CAD models. One typical example is the rotor discs of a jet engine; they are similar in their functions among frames but have different dovetail slots (i.e., detail functions) [10,11]. As product customization goes on, a company will accumulate a collection of structurally similar CAD models (to be called a structural family hereafter). The problem then arises: given a structural family of CAD models, how to easily and quickly carry out variational design when a new product customization order comes in. The above problem involves two essential tasks: (1) retrieving a base model fittest for the new purpose; and (2) modifying this model according to the new purpose. Without proper computer assistance, the user needs to manually thread through all models in the family to find the base model. Tedious model comparisons may also be needed to pick out detail features distributed in individual models and useful for the new design. Combining those detail features to the base model is, again, not trivial because of complex feature dependencies. To makes the situation even worse, such tedious manual work must be repeated whenever a new design is carried out. (Section 3 will give a more detailed discussion about these limitations.) This paper presents our attempts to address the above problem through reducing the manual effort involved. The idea is to construct automatically a master model for the family, which can be quickly modified to accommodate required design changes. The master model is a representative model for the Abstract