In-Process Tool Deflection Measurement in Incremental Sheet Metal Forming

Incremental sheet forming is an economical alternative to deep drawing for forming large sheets in small quantities. However, the shape deviations resulting from a process-force-caused tool deflection limits the measuring accuracy. Therefore, an optical multi-sensor system is proposed to enable the contactless in-process measurement of the tool deflection independent of the machine kinematics for the first time. The presented design study of the sensor system aims to meet the requirement of a maximal measurement uncertainty of 15 µm at a measuring distance of up to 2 m. The multi-sensor system consists of a large number of inexpensive angulation sensors, each of which measures an angle to a light source on the tool. Based on the measured angles of all sensors calibrated to each other, the position of the tool in the three-dimensional manufacturing volume can be calculated by multi-angulation. Via experimental characterization of a realized angulation sensor as well as an uncertainty propagation, the measurement uncertainty achievable with the overall system is estimated. As a result, the multi-sensor concept fulfills all requirements for the measurement of the tool deflection in incremental sheet metal forming.