Relating CMM Data to Design Specification

Article

Roy, Uptal; Zhang, Xuzeng   (1992, ASQC)   Department of Mechanical and Aerospace Engineering, Syracuse University, Syracuse, NY 13244

Annual Quality Congress, Nashville TN    Vol. 46    No. 0
QICID: 9827    May 1992    pp. 116-123
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Article Abstract

This abstract is an edited version of the author's original.

The coordinate measuring technique used in coordinate measuring machines (CMMs) assess the geometric characteristics of manufactured parts; however, CMM techniques often lack unique and unambiguous definitions. This paper discusses techniques to: (1) determine unique and unambiguous definitions of the tolerance of any feature; (2) establish a definition of the measured sizes of all features, (3) determine the criteria for establishing datums from measured data points of the measured features, and (4) establish computational techniques for assessing the CMM data against the design specification.

A computer-aided design (CAD) database provides an unambiguous definition of parts' nominal shapes and information such as integrated dimensioning and tolerancing. A feature-based representational scheme based on the hybrid CSG/B-Rep (Constructive Solid Geometry/Boundary Representation) data structure was developed for the object modeling to support the tolerancing information. This scheme captures knowledge about the topological and geometrical relationships among different kinds of features and incorporates object attributes. Datums establish the reference frame on a part for manufacture, inspection, and assembly, and the author describes the steps required to establish the primary datum, secondary datum, and tertiary datum.

Geometric tolerance assessments established criteria for size tolerance and other tolerances (form, orientation, and location), and computational techniques established assessment criteria for tolerance variations. The extracted information on the shape errors of the manufactured parts are directly fed back to the "System Control" loop to improve the manufacturing process to produce precision parts.

Keywords

Statistical methods,Computer-Aided Design (CAD),Coordinate measuring machine (CMM),Electronic data systems,Inspection,Manufacturing,Tolerances


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