Generation of Alternative Feature-Based Models and Precedence Orderings for Machining Applications

Abstract

For machining purposes, a part is often considered to be a feature-based model (FBM), i.e., a collection of machining features. However, often there can be several different FBM's of the same part. These models correspond to different sets of machining operations, with different precedence constraints. Which of these sets of machining operations is best depends on several factors, including dimensions, tolerances, surface finishes, availability of machine tools and cutting tools, fixturability, and optimization criteria. Thus, these alternatives should be generated and evaluated.In this paper we present the following results: 1. We give general mathematical definitions of machining features and FBMs.2. We present a systematic way to generate the alternative FBMs for a part, given an initial FBM for the part.3. For each FBM, interactions among the features will impose precedence constraints on the possible orderings in which these features can be machined. We show how to generate these precedence constraints automatically for each interpretation.4. We show how to organize the above precedence constraints into a time-order graph that represents all feasible orderings in which the features can be machined, and examine the time-order graph to see if it is consistent. If it is not consistent, then there is no way to machine this particular interpretation.This work represents a step toward our overall approach of developing ways for automatically generating the alternative ways in which a part can be machined, and evaluating them to see how well they can do at creating the desired part. We anticipate that the information provided by this analysis will be useful both for process planning and concurrent design.