INTEGRATING FEATURE-BASED SURFACE DESIGN WITH FREEFORM DEFORMATION

A feature-based procedural method has been presented for designing a s mooth surface that can be explicitly described as the graph of a singl e-valued bivariate function z = f(x,y). Such surfaces often occur in p ractice in manufacturing involving stamping or injection moulding oper ations (for example in car inner panels, brackets, beer cans, and elec tronic consumer products). Operationally, the design approach entails modifying the shape of an existing surface by sequentially adding arbi trarily shaped protrusions and pockets to it. Sederberg and Parry prop osed a versatile technique for deforming existing geometric objects in a freeform manner. Their technique turned on the use of trivariate, p arametric Bernstein polynomials, and it can be applied either locally or globally. Unlike the author's feature-based method, in which the de sign process is carried out by direct manipulation of the surface mode l, freeform deformation is independent of the geometric model being de formed. The paper presents results that combine the feature-based and freeform deformation design techniques into one 2-stage CAD design app roach. Although nothing that is technically new is offered in either o f the individual stages, the paper illustrates how this integration pr oduces significant value in practical industrial surface design by com bining the advantages offered by each method. These include the intuit ive, fast, easily modifiable feature-based design of complicated surfa ces (that need not be graphs of a function), and the ability to make s ubstantial, predictable and physically meaningful changes in surface g eometry by the manipulation of shaping parameters (feature parameters and control points). The author's experience with the design of multif eature automotive sheet metal panels indicates that combining the two CAD methods allows parts to be designed that cannot be designed using either method alone.