Automatic Tool Path Generation from B-Rep Model of Sculptured Surfaces Using CAD Software API

Abstract

Conventional CNC machines have been used for machining complex geometries like dies for ergonomically designed parts or complex surfaces. The tool paths generated for these are extremely complex. The traditional paradigm of CAD to machined part uses a specialized CAD package along with an expert CAD designer. This expert gives output of geometry information in the form of 3-D model to a CAM software, which is operated by another expert in CAM. The CNC programmer then converts the tool paths that are generated in CAM software into codes using commands. An expert machinist different from the former experts does the machining which adds to the discontinuity in the flow of data and design requirements. This has inherent problem of multiple data types, multiple softwares, and multiple personnel causing problems in data transfer from one-step to other. The synchronization of these separate entities is a challenge. This thesis is an attempt to directly generate tool positions on a sculptured surface represented in CAD using B-rep and generate the tool path for a lathe mill, which can be used for tool positioning. This eliminates the CAD and CAM software, the experts required for CAD, CAM and machining in the conventional paradigm for machined part from CAD geometry. The past works use a neutral STL format to read the CAD geometry and generate a tool path for it. Use of STL, which contains faceted model data, has inherited errors like chordal error, which are minimized by increasing the density of triangles but that increases computations and processing time required for generating tool paths. This thesis makes an attempt at direct generation of the tool path using custom algorithm for pseudo-symmetric parts for the lathe mill directly in CAD software where B-rep geometric model is available. This eliminates STL file errors and subsequent processing of STL. The comparison of generation of the tool path using our developed method that uses B-rep model and the already published “Ball Drop method” [1] that uses STL model is done.