Linköping Studies in Science and Technology.
Dissertations No. 524

CAD Integrated Quality Control

Martin Helgoson

Akademisk avhandling

som för avläggande av teknologie doktorsexamen vid Linköpings Tekniska Högskola kommer att offentligt försvaras i sal C3, Linköpings Universitet, måndagen den 20 april 1998, kl 13.00. Fakultetsopponent är Professor John Corbett, Cranfield Institute of Technology, Storbritannien.


The thesis concludes the research work aimed at quality monitoring of parts associated with double twisted surfaces. Different CAD/CAM-based approaches and parameters for quality evaluation have been proposed.

The flexible research facility based on a co-ordinate measuring machine, CAD/CAM-system and CAD-based measuring/evaluation system has been made operational to analyse technology available today and to implement and test new routines. Links between the different components involving the local computer network have been set up in order to achieve efficient communication for monitoring and control. The effects of integration have been studied and results are briefly summarized. The functionality of links has been experimentally verified by tests, reverse engineering of turbine blade, as an example.

Traditional quality monitoring methods based on nominal-actual comparison at single points makes it difficult to estimate the missing volume of the part, as well as changes in mass and mass points etc. Thus new quality evaluation methods considering the entire surface also including functionality-related aspects, are explored in the thesis.

A volumetric concept for shape error evaluation of parts with complex surfaces has been proposed, facilitating the three-dimensional understanding of the shape error. Changes in volume, mass, mass point etc. can be evaluated and re-machining guided to the error-affected areas. Based on the concept the Surface Error Factor has been introduced as a new parameter for shape error evaluation. The principles of surface and solid modelling are briefly discussed in the thesis. During experiments limitations related to the solid modelling technology influencing the performance of quality monitoring have been experienced.

The effect of different point distributions and CAD-modelling strategies when reconstructing the measured surfaces has been experimentally analysed by means of the CAD-based evaluation tool developed. Errors of I nun when dealing with measuring accuracy of 0.001 mm can be introduced by improper strategies. Error sources related to the measurement process are discussed in the thesis in order to verify the used approach of simulation as a method for exploring the accuracy and the performance of CAD modelling.

Approaches based on adaptive algorithms integrated with CAD for measurement and reconstruction of known as well as unknown surfaces are proposed with the intention of increasing the level of automation.

By cooperation with participating companies the feasibility of implementing the proposed concepts and of possible benefits have been analysed as well as the need for further development.

Division of Production Engineering
Department of Mechanical Engineering
Linköping University, S-581 83 Linköping, Sweden

Linköping 1998

ISBN 91-7219-178-3 ISSN 0345-7524