Tool path generation method for 5-axis NC machining with flat-end cutter.

摘要

By changing from 3-axis to 5-axis machining, cutting efficiency and machining quality could be enhanced a lot. The two more rotary axes make cutting flexible and efficient, but they also bring some troubles for controlling. More and more complex machining environment and complicated freeform surface challenge users to define more accurate and appropriate tool paths and tool orientations.;Traditionally, for the flat-end cutter, due to the intertwined dependence relationship between its axis and reference point, most 5-axis tool-path generation methods take a decoupled two-stage strategy: first, the so-called cutter contact (CC) curves are placed on the part surface; then, for each CC curve, tool orientations are decided that will accommodate local and/or global constraints such as minimum local gouging and global interference avoidance. For the former stage, usually simplistic "offset" methods are adopted to determine the cutter contact curves, such as the iso-parametric or iso-plane methods; whereas for the latter, the common practice is to assign fixed tilt and yaw angle to the tool axis regardless the local curvature information and, in the case of considering global interference, the tool orientation is decided solely based on avoiding global collision but ignoring important local machining efficiency issues. This independence between the placement of CC curves and the determination of tool orientations, as well as the rigid way in which the tilt and yaw angles get assigned, incurs many undesired problems, such as the abrupt change of tool orientations, the reduced efficiency in machining, the reduced finishing surface quality, the unnecessary dynamic loading on the machine, etc.;In our work, we present a system that aims at alleviating these problems and thus to improve the machining efficiency and accuracy. Iso-conic method and visibility map(VMap) are proposed to support the system. The former is to generate a series of tool paths on which the tool orientations have some special properties to guarantee large machining strip width and smooth changing in part coordinate system and machine coordinate system. And the later, VMap, is to collect all the information about the complex environments, including machining components and machining parts, to help to avoid global interference and guarantee the angular-velocity compliance. Delicate computation and manipulation of visibility maps and their derivative data ensure that the proposed algorithm is computationally feasible with acceptable computing time and memory requirement.;Finally, test examples are given to simulate experiments of the proposed algorithm. Comparisons with a leading commercial CAM software toolbox are also provided that demonstrate the claimed advantages.