<i>In Situ</i> 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. Based on an industrial robot and quickchange systems, the process integration of hightemperature grippers and an endoscopic 3D-measurement sensor for the in-situ inspection of hot forging dies is carried out. 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 die and take high-precision 3D-measurements inside. The ambient air heated by the forming process creates an inhomogeneous refractive index field around the measuring system and the hot die, so that the straight beam path required for optical measuring systems cannot be ensured. This can lead to strong deviations in the reconstructed point clouds and the functional geometries derived from them. By means of a compressed air actuator, the measuring system can be protected from the hot tool and dirt as well as the effect of inhomogeneous refractive index can be 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 relevance, as the thermalstress is high and large material flow takes place. For the wear measurement, 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.