Medial axis extraction and thickness measurement of formed sheet metal parts

Optical scanning measuring systems enable probing of workpieces with a high point density and offer possibilities to create adequate evaluation solutions for different complex measurement tasks in the geometrical metrology. This work deals with the evaluation of scanned data in order to extract parameters which can contribute to improvement of sheet metal forming processes in the early production phase. These parameters are form of a medial surface and thickness values. An experimental measuring system for scanning formed sheet metal parts in certain areas of interests was developed. It consists of two fringe projection systems located opposite to each other. A solution for an accurate fusion of two independent measuring data in a unified coordinate system was found. Data obtained in a such manner reliably represent scanned sheet metal area. An innovative method for the extraction of medial surface points from the data and the calculation of large number of local thickness values in the direction orthogonal to the medial surface was designed and implemented. The extracted medial surface can be used for an assessment of the obtained sheet metal form by its comparison with a CAD model or with the form of a nominal sheet metal medial surface respectively. A visualization of the distribution of thickness values over the extracted medial surface enables localizing thinning and thickening places. Furthermore, the data obtained can be used for an evaluation of numerical simulations of thickness distributions offering possibility to compare simulated data with measuring data.

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