In-process workpiece based temperature measurement in cylindrical grinding

Abstract

In conventional grinding processes a huge partition of the machining energy is received by the workpiece. Damage due to high thermal load might happen on the surface as well as in sublayers of the workpiece where favourable process parameters and optimized coolant supply are stringent to avoid them. To detect thermal damage known as grinding burn various established techniques like barkhausen noise measurement for ferromagnetic materials or the NITAL-etching test are available for measurement after the workpiece is machined. In this work the development and influencing factors of grinding burn are studied by a continuously in-process and workpiece based measurement of the temperatures in cylindrical grinding. A two-color pyrometer is used with a rotary joint between the rotating and stationary fibre from the workpiece to the sensor element. The radial and circumferential temperature profiles below the workpiece surface are measured to determine the thermal limits and temperature gradients. Due to the high temporal resolution the temperature gradient for single workpiece revolutions can be shown and evaluated. The heating and cooling rates are calculated and compared for different depths in the workpiece, where the heating rates are up to 50 times higher than the cooling rates depending on the distance to the surface. The knowledge can help to model grind hardening processes which rely on finite element simulations of the temperature distribution in the workpiece.