Detection of surface damages in ground spur gears by non-destructive micromagnetic methods

Abstract

The analysis of the Barkhausen noise signal is a non-destructive micromagnetic method to detect grinding damages, such as grinding burn. This method is increasingly used in industrial production for quality control. However, there is still no scientifically validated knowledge about the influences and interactions of different material parameters resulting from the heat treatment on the Barkhausen noise signal. Therefore, no standardized guideline for interpretation of inspection results exists up to now; each company uses own test procedures. In this study, carburized spur gears made from 18CrNiMo7-6 steel were finished by discontinuous profile grinding and the influences of varying material and heat treatment parameters on the measured Barkhausen noise, such as case hardening depth, surface carbon content and tempering temperature were investigated. Thanks to extensive complementary characterizations, different grinding burn levels were defined and further analyzed to evaluate single effects and interactions on the Barkhausen noise signal. These findings provide a foundation for a more reliable detection of grinding damages for different heat treatment states. Additionally, the application of a Barkhausen multiparameter approach was investigated for a more reliable differentiation between different damage types such as type B (light tempering zone) and type D (strong tempering zone). A variation of the filter settings was furthermore used to get information out of different depths of the subsurface region. During these investigations differences in the signals of the multiparameter analysis were found for different types of damages with varying filter settings. Using this knowledge a clear classification of different damages due to grinding is possible and more reliable compared to current methods.