CONTOUR MACHINING OF FREE-FORM SURFACES WITH REAL-TIME PH CURVE CNC INTERPOLATORS

Two strategies for contour milling of free-form surfaces, using real-t ime CNC interpolators for Pythagorean-hodograph (PH) curves, are descr ibed. The first method, applicable to convex surfaces, employs a hat-e nd mill and approximates the surface section curves by planar PH quint ics. The second approach, which employs a ball-end mill, approximates the tool-center trajectory by quintic PH space curves, and can accommo date nonconvex surfaces by choosing a sufficiently small tool radius. Both schemes generate compact part programs, in which numerous short l inear/circular G code motions are replaced by fewer analytic path segm ents, and eliminate the need for explicit offset curve or surface repr esentations to compensate for the tool radius. The surface sectioning and PH curve approximation algorithms required by these methods are pr esented, with appropriate tolerance analyses, and preliminary results from machining experiments performed on an open-architecture 3-axis CN C mill are described. (C) 1999 Elsevier Science B.V. All rights reserv ed.