In-Situ Wear Measurement of Hot Forging Dies Using Robot Aided Endoscopic Fringe Projection

Abstract

According to the current state of the art, wear conditions of forging dies are assessed visually in the dismantled state, as there is no measuring procedure available for inline wear measurement of hot forging dies. This paper introduces a handling concept for automated loading and in-situ tool inspection for a hot forging process. An industrial robot with a quick-change system mounted on its endeffector is utilized to integrate both, a high-temperature gripper and an endoscopic 3D-measurement sensor. By adapting the measuring method of fringe projection to an endoscopic design, the measuring system can be navigated into the difficult-to-access geometry of the forge and take high-precision 3D-measurements of the forging die. The ambient air heated by the forming process creates an inhomogeneous refractive index field around the measuring system and the hot die, which deflects the light during the measurement and deteriorates the overall accuracy of the reconstructed point cloud. This can lead to strong deviations in the reconstructed point clouds and the functional geometries calculated from them. Using a compressed air actuator, the measuring system can be protected from the heat effects of the measuring object, as well as from dirt. Furthermore, the effect of the inhomogeneous refractive index field can be significantly reduced. With this approach the in-situ wear measurement at highly stressed regions using the example of the mandrel radius and the flash radius will be demonstrated. These functional elements are of particular interest, as the thermal stress is high and large material flow takes place. For the wear determination, the functional elements of the tool are examined in detail by fitting geometrical features into the reconstructed point clouds and determining the deviations from a reference geometry. In addition, the measurement data is validated with the aid of a commercially available state-of-the-art measurement system.