A Unified NURBS Interpolator for Five-Axes Machining

Abstract

NURBS interpolator has great advantages for machining complex part comparing to the simple linear and circular interpolator, such as reducing program size, smoothing tool motion and improving machining surface quality. However, the existing NURBS interpolators only deal with the case in which the NURBS trajectory is given in a customized NURBS G code. In addition, they are limited to three translation axes, which mean no rotation axes were considered so far. In this paper, a unified NURBS interpolator was developed to treat three kinds of situations so that NURBS interpolator can be thoroughly applied into five-axes machining. In first case, a NURBS curve converter was built to convert a series of linear and circular segments exactly to a NURBS trajectory. In second case, a series of linear and circular segments were fitted to a NURBS trajectory, which obtains the optimal smoothness instead of exactly representing. In third case, two kinds of NURBS G codes were proposed to represent NURBS trajectory directly, which includes both three translation axes and two rotation axes. Upon these three kinds of input NURBS trajectory, only one NURBS interpolator is designed, in which, most factors that influence the five-axes CNC machining performance are considered. Also, a three-steps NURBS interpolation algorithm was implemented inside the proposed interpolator. Two actual five-axes machining examples were used to evaluate the performance of the proposed interpolator.Copyright © 2005 by ASME