Elsevier

Computer-Aided Design

Volume 26, Issue 6, June 1994, Pages 490-496
Computer-Aided Design

Toolpath generation for freeform surface models

https://doi.org/10.1016/0010-4485(94)90070-1Get rights and content

Abstract

The generation of optimal NC code to drive milling machines for models defined by freeform trimmed surfaces is a difficult problem. In practice, two main approaches are used to generate toolpaths for surfaces, neither of which is optimal, in general. The first exploits the parametric representation, and generates isocurves that are uniformly distributed across the parametric domain. This approach is not optimal if the surface mapping into Euclidean space is not isometric. The second approach contours the models by intersecting the surfaces with planes equally spaced in Euclidean space, resulting in a piecewise-linear toolpath approximation which is nonadaptive to the local surface geometry. Further, the toolpath generated by contouring is suitable for 3-axis milling, but is inappropriate for 5-axis milling.

In the paper, an algorithm developed to extract isocurves for rendering adaptively is modified and enhanced to generate milling toolpaths for models consisting of trimmed surfaces, and it can be used in both -3 and 5-axis milling. The resulting toolpaths do not gouge locally, and they combine the advantages of both prior approaches. The output toolpath is appealing, since it is composed of isoparametric curves, and is therefore compact, exact, and easy to process. Further, it is more optimal than the previous methods in that the resulting toolpath is shorter, and it provides a direct quantitative bound on the resulting scallop height. This algorithm has been used to compute gouge-avoiding toolpaths for the automatic milling of freeform surfaces, without the introduction of auxiliary check and drive surfaces being required.

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Current address: Computer Science Department, Technion, haifa 32000, Israel.

1

Gershon Elber is a lecturer. His research interests span computer-aided geometric design, and computer graphics. He received a BS in computer engineering and an MS in computer science from the Technion, Israel, in 1986 and 1987, respectively, and a PhD in computer science from the University of Utah, USA, in 1993.

2

Elaine Cohen is a professor of computer science and a cohead of the Alpha_1 research project in geometric modelling and manufacturing. Current research interests include geometric representations, algorithms, modelling, computer-aided design, design and modelling operators, computer-aided manufacturing, visualization, and process planning. She received a BA from Vassar College, USA, and an MA and a PhD from Syracuse University, USA, all in mathematics.

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