Long-time survey of laser processed calibration samples for Barkhausen noise method

Abstract

Barkhausen noise (BN) measurements are commonly utilised in industrial quality control after machining processes such as grinding. Different power transmission components are ground to meet the final tolerances. The BN method enables to locate grinding burns which might arise during grinding and compromise the quality of the manufactured component. The proper, accurate and verified operation of the BN equipment is valuable. One tool to verify the operation of the BN equipment is the use of calibration samples with artificial damages. Artificial thermal damages will simulate the excess heat generation in the grinding process, and they have been processed with different heating systems for example: induction and laser processing [1], temperature-controlled laser processing [2] and hydrogen-oxygen flame burn processing [3]. Nowadays, the laser systems seem to be the most popular method for creating these artificial grinding burns which have been found suitable for BN calibration purposes.<br/>This study presents the results of long-term changes in residual stresses associated with the artificially laser-produced calibration samples. The two inspection methods are the magnetic Barkhausen noise and X-ray diffraction (XRD) based residual stress (RS) measurements. Two different sets of steel samples were measured with laser-processed thermal damages. Both materials were hardened steels, and the surface was normally ground prior the laser processing. The first set was laser processed with 4 kW Haas HL4006D laser and the detailed processing information can be found in [1]. The first set of samples were manufactured in 2010. This set was measured right after the manufacturing, 6 months and 12 months after the manufacturing and 14 years after the manufacturing. The second set of samples were manufactured with laser processing in 2022 with the similar type of temperature-controlled laser procedure as described in [3] and measured after the manufacturing and 2 years after the manufacturing. <br/>Studies concerning the time dependence of the laser-processed sample BN measurements indicated that no major changes were observed in the BN root-mean-square (RMS) values during up to one year for the first set of samples. However, the RS measurements revealed some changes. The longer survey times are still under characterization and are to be reported during the conference. The issue of time-dependent changes should be considered when determining the optimal utilization time for calibration samples. Temperature changes could be one contributing factor for RS changes so keeping calibration blocks at constant temperature may be beneficial. <br/>In addition, discussion is raised on the topics related to the calibration sample manufacturing. At the moment, there are no standards or guidelines for the calibration samples. The industries using the artificially produced calibration samples have their own internal guidelines and practices how to use them. The questions are how often the calibration samples should be changed and how to verify that the calibration sample needs to be replaced. Some issues are more related to the BN measurement system itself and others to the calibration samples.<br/>1. S. Santa-aho, M. Vippola, A. Sorsa, J. Latokartano, M. Lindgren, K. Leiviskä, T. Lepistö, J Mat Proc Tech, 212 (2012), pp. 293-298.<br/>2. S. Santa-aho, A. Sorsa, J. Latokartano, K. Leiviskä, L. Suominen, M. Vippola, 11th International Conference on Barkhausen Noise Measurements and Micromagnetic Testing ICBM11 (2015)<br/>3. S. Santa-aho, M. Deveci, S. Savolainen, M. Vippola, Proceedings of the 12th ECNDT (2018) <br/>Support of TEKES for NOVEBARK research project is gratefully acknowledged. Authors would like to thank Mr. Jyrki Latokartano and Mr. Pekka Ala-Mäyry for laser sample preparation. <br/>