Determination of microstructure changes by eddy-current methods for cold and warm forming applications

Tangential profile ring rolling (Profiled Radial Ring Rolling, PRRR) enables the fast and compared to machining inexpensive production of bearing rings or similar ring-shaped parts with near net-shape geometry and advantageous material properties due to a high degree of work hardening at a high cadence. Conventionally, a specific heat treatment regime is required to achieve the desired microstructural and mechanical properties such as grain size, hardness or strength. Novel control strategies allow thermomechanical treatment during the forming operation itself. To monitor the evolution of properties during forming, a sensor system based on eddy current methods is presented and its ability to discriminate between various influences is demonstrated. It is shown that different process conditions result in different end-product microstructures, and that these differences both relate to application relevant properties and can be identified using non-destructive eddy current sensing, even in the presence of superposed disturbances such as local variations in electromagnetic properties.