Cutter interference region detection in NC machining of free form surfaces.

Satisfactory handling of cutter interference in NC machining of free-form surfaces requires not only avoidance of cutter interference, but also detection of all the interference regions on the surfaces. This paper describes an algorithmic method for obtaining cutter interference regions due to self-intersections of an offset surface. In this method, the offset surface between a ball-endmill and a machining surface is composed of an offset surface of the machining surface and envelopes defined by a reversed tool shape with Z-direction along the circumference of the machining surface. Self-intersection curves are calculated efficiently by using the Powell-Zangwill method and the Runge-Kutta-Gill method, and cutter interference regions are represented on a machining surface. The numerical result is accurate and CPU memory is saved because all offset surface data including the envelopes are exactly generated from the original (machining) surface without offset approximation.