Computer-aided generation of optimum chatter-free pockets

Abstract

This work outlines the development of NC programming subroutines for use in generating the tool path for pocket milling operations in such a way as to avoid the occurrence of chatter. While information is currently available to the programmer about acceptable feeds and speeds, choices of these parameters do not radically affect the part program structure by altering the number of passes or tool path required. For the purposes of chatter avoidance, however, the decisive parameters are the axial and the radial depth of cut, and these parameters are decisive in the program structure. There is almost no information currently available to the programmer about selecting these parameters, and he must use his experience or intuition. A substantial fraction of the productive time of a modern machine tool is therefore spent in verification cuts (the program must be written, tried, and then corrected several times). It is shown that the acceptable (chatter-free) axial and radial depths of cut change depending on the dynamics of the machine and particular tool, the direction of the cut, and the mode of milling (up- or down-milling). The subroutines outlined in this paper select from a database of acceptable cuts the tool path which will result in the maximum metal removal rate. The pockets may have complex 2 1/2 D geometries and may include multiple islands. Several examples are used to illustrate the resulting tool paths, and comparisons are made to tool paths resulting from other available software.