Automated process planning for CNC machining of spherical space-frame nodes

Abstract

Space-frame nodes are joints connecting linear members in complex space frames. Each spherical node has a particular hole configuration that defines the orientation of the bolt holes used to connect the space-frame members. The hole configurations are determined by CAD software for space-frame design. Nodes with the same hole configuration vary in number depending on the design of the space frame. A computer-automated machining cell has been implemented to batch manufacture the spherical nodes. The machining cell consists of a three-axis vertical machining center interfaced with a two-axis CNC rotary table. To reduce changeover time between the machining of batches, produce consistent and reliable NC programs, and minimize manpower required to run the cell, a PC-based computer-automated process planning system has been developed to directly translate geometric data from the CAD software to NC programs, without intervention by the operator. An important consideration in the process plan for the machining of the space-frame node is the transformation of the CAD-defined bolt hole configuration to a mounting-hole-referenced configuration that minimizes setup and mounting hole requirements. Based on the optimal mounting-hole-referenced configuration, NC toolpaths are derived and corresponding NC programs are generated. This paper presents the approach to determine the optimal mounting-hole-referenced configuration and the operation of the automated process planning system that is suitable for the machining of spherical parts. © 1995.