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Strategies for Function-Oriented Optical Inspection of Formed Precision Workpieces

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Sheet Bulk Metal Forming (TCRC73 2020)


Shorter production times, associated with sheet-bulk metal forming (SBMF), require a demand-adapted monitoring and measurement of the formed geometries. In the present work, a multi-scale and multi-sensor setup was developed to meet these requirements. The difficulty in measuring workpieces formed during SBMF are highly reflective areas with varying demands on the measurement resolution of the functional elements. With the developed measurement setup and the integrated sensors used, the functional elements can be measured with sufficient resolution. The registration of the sensors is done with a specially constructed calibration plate. A parallel kinematic hexapod positioning unit provides six degrees of freedom to precisely position the workpiece in front of the individual measurement sensors. The hexapod is therefore registered in a global coordinate system with the new calibration plate. After the calibration, the measured datasets can be merged together automatically. The rigid connection of the calibration plate to the hexapod enables a more demand-oriented verification of the registration between the individual measurements of the sensors. For overexposure due to directly reflecting areas, it is possible to estimate the quality of each reconstructed data point. A deflectometry system, which is attached to the existing fringe projection sensor, makes it possible to detect strongly directionally reflecting areas and thus provide a holistic reconstruction of the workpiece. The influence of remaining lubricant on the workpiece is simulated by a developed thin film thickness standard. This is to adapt the measuring procedure for reconstructions under harsh conditions in industrial environment. This standard allows the measurement of thin films with the existing optical measurement systems in a range <100 µm. The effects of thin layers of lubricant on the result of the fringe projection measurements show an increasing impact on the measured dataset with increasing layer thickness. With the developed measurement setup, the investigations on the lubricant used and reflective properties, the formed workpieces can be measured at different scale ranges.

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This study was supported by the German Research Foundation (DFG) within the scope of the Transregional Collaborative Research Centre for sheet-bulk metal forming (TCRC 73, Subproject A06) under grant number 68237143. The authors are in addition grateful to all laboratory assistants and students who supported the realisation of this work.

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Correspondence to Sebastian Metzner .

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Metzner, S., Hausotte, T., Loderer, A. (2021). Strategies for Function-Oriented Optical Inspection of Formed Precision Workpieces. In: Merklein, M., Tekkaya, A.E., Behrens, BA. (eds) Sheet Bulk Metal Forming . TCRC73 2020. Lecture Notes in Production Engineering. Springer, Cham.

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