ASSESSMENT OF THE DESCRIPTION FORMAT OF TOOL TRAJECTORIES IN 3-AXIS HSM

摘要

In this paper, our main objective is to assess polynomial interpolation formats in 3 axis milling of sculptured surfaces. So, we point out the interest of calculating tool path in Bspline format comparatively to the linear format, in terms of surface quality and machining time. Moreover, the assessment of the polynomial interpolation on line, now proposed by numerical controllers, is also performed. As expected, machining time is optimal when using polynomial formats (native or on line). Although the speed during machining rarely conserves the maximum value, speed variations are better managed when the polynomial format is used. Nevertheless, for profiles presenting succession of sharp edges, maintaining the highest feedrate value requires the acceleration to be too high. The management of discontinuity points turns out to be a limiting factor. Whatever the description format used, the precision obtained is satisfactory. No significant difference can be highlighted, even for the discontinuity points. Here again, the precision is worse near those points. It is interesting to notice that the polynomial interpolation on line provides a machining time similar to that obtained with the B-spline interpolation while respecting the expected precision. To conclude, the polynomial description of tool trajectory seems well adapted for the machining of sculptured surfaces. But, to be efficient the tool trajectory must integrate constraints linked to the control unit behaviour. For example, the partitioning of the tool trajectory in portions free of C~2 discontinuities is an essential step, as maximization of segment length is.