Triangulation Based Digitizing of Tooling and Sheet Metal Part Surfaces - Measuring Technique, Analysis of Deviation to CAD and Remarks on Use of 3D-Coordinate Fields for the Finite Element Analysis

Abstract

The dynamic development of highly accurate optical measuring machines within the last years pushed the introduction of digitizing techniques to many applications in the fields of quality control, reverse engineering and rapid prototyping. By projecting fringe patterns onto the object's surface and recording pictures of the curvature dependant deformation of the pattern, 3D coordinates for each camera pixel are calculated on the basis of the principle of triangulation. The generation of a polygon mesh can be used for the analysis of the deviation of a die or a formed part to the initial CAD data, i.e. by means of full field or section based comparison. This paper presents the application of the above mentioned techniques on a double sheet hydroforming process. The gathered 3D data of the clam-shell part as well as of the tooling dies served for the calculation of the deviation to the respective reference geometry. With respect to the utilization of digitized tooling data within the finite element analysis, further investigations were performed on the impact of data reduction strategies. Aiming on the minimization of the necessary number of elements, representing the tooling surface in a discrete state, and on the request for a sufficient degree of accuracy, these strategies have to be considered of high priority.

3-D metrology system with internal calibration

“…17 The dark and the bright image defines a minimal (min i ) and a maximal gray value (max i ) for each camera pixel i. After taking an image for measurement purposes, the detected gray value d i is corrected to gray value c i using Formula (1).…”

“…Another domain of 3-D shape measurement is reverse engineering. 1 In this process tooling data is generated directly from the object which has to be reproduced.…”

Fringe projection techniques: Whither we are?

“…Its applications range from measuring the 3D shape of MEMS components to the measurement of flatness of large panels (2.5 m × .45 m). The technique has found various applications in diverse fields: biomedical applications such as 3D intra-oral dental measurements [1], non-invasive 3D imaging and monitoring of vascular wall deformations [2], human body shape measurement for shape guided radiotherapy treatment [3,4], lower back deformation measurement [5], detection and monitoring of scoliosis [6], inspection of wounds [7,8] and skin topography measurement for use in cosmetology [9,10, 11]; industrial and scientific applications such as characterization of MEMS components [12,13], vibration analysis [14,15], refractometry [16], global measurement of free surface deformations [17,18], local wall thickness measurement of forced sheet metals [19], corrosion analysis [20,21], measurement of surface roughness [22,23], reverse engineering [24,25,26], quality control of printed circuit board manufacturing [27,28,29] and heat-flow visualization [30]; kinematics applications such as measuring the shape and position of a moving object/creature [31,32] and the study of kinematical parameters of dragonfly in free flight [33,34]; biometric identification applications such as 3D face reconstruction for the development of robust face recognition systems [35,36]; cultural heritage and preservation [37,38,39] etc.One of the outstanding featur...…”