PROCESS MEASUREMENT IMPACT ON THE VERIFICATION UNCERTAINTY

Coordinate measuring machines are now widely used to qualify industrial pieces. Nevertheless, the actual CMM software’s usually restrict to the determination of mean values. This is the case for both the characterization of individual surfaces and for the determination of geometrical errors. However, in accordance with quality standards, the uncertainty of each measurement should also be defined. At last CIRP seminar, a new non linear least squares method has been proposed for that purpose to define the error bars of the parameters estimated for each measured surface. These values are deduced from the gap between the measured coordinates and the associated optimized surface. Our new presentation now extends to the propagation of such uncertainties to the determination of ISO1101 tolerances (dimensions and geometrical errors). To illustrate this approach, a specification was inspected on a true real industrial piece, with respect to the ISO 1101 standard. For this industrial application, different measurement procedures were proposed and carried out. The uncertainties of the estimated geometrical errors were then evaluated, showing the influence of the experimental method onto the reliability of the measurement. This example thus demonstrates the need to optimize the inspection process. To conclude our presentation, different aspects of the inspection are finally discussed to improve the verification of ISO 1101 specifications.