Manufacturing of calibration samples for barkhausen noise method: case studies on temperature controlled laser and hydrogen-oxygen flame

Non-destructive magnetic Barkhausen noise (BN) measurements are most widely used for studying the grinding burns from hardened and ground samples. The formation of the grinding burns occurs due to excess of heat generation and produces thus changes in the residual stresses and microstructure. The BN method can be used for quality control purposes because it is sensitive to changes both in stresses and microstructure. The important part of the BN inspection procedure is the verification that the sensor and the equipment are working properly. One option is to use calibration pieces to evaluate the operation of the sensor before the actual measurements. The best way is to use similar components and same measurement procedure as to be studied. The components should have artificially produced burn marks to mimic the damaged areas of grinding burns. To validate the BN measurement results properly, the BN sensor needs to be verified with both thermally damaged and thermally undamaged sample surfaces.

In this work, two different procedures to manufacture artificial burn marks were studied. A temperature controlled, robotic assisted, laser system was used to perform temperature controlled tempering marks to carburised gear wheel teeth surfaces. Also, hydrogen-oxygen flame with robotic control was used to produce artificial burn marks on the surfaces of carburised gear wheel teeth surfaces.

The aim was to analyse the suitability of thermal damages created by these two methods by comparing the BN readings of them to each other. The new, temperature controlled, laser system was found to produce uniform quality thermal damages. While the hydrogen-oxygen process was found to be more unpredictable and it needs to be controlled extremely carefully i.e. with robotic manipulation of the hydrogen-oxygen flame. The speed of the hydrogen-oxygen flame affected the RMS values greater than the other tested parameters.