Improved Measurements of Case Depth by the Application of Signal Processing Algorithms to Barkhausen Effect Data

Industrial components such as cam shafts and ring gears often need to have a hard outer surface for wear resistance and a good internal toughness to resist deformation due to impact and loading. These two properties, however, are often mutually exclusive. Case hardening is one solution whereby carbon diffusion into steel results in hardened surface and near-surface layers. Wear resistance is improved while maintaining the bulk toughness of the component. As with many production processes, it is necessary to monitor the quality of the components being manufactured, with case hardening, it is the depth of treatment that is normally measured. Conventional case-depth measurements are destructive, time-consuming, and expensive. Although eddy-current techniques have been applied to the problem [1], the process is often cumbersome due to the need to use more than one frequency. In this paper we investigate how magnetic nondestructive measurement techniques can be used to form the basis of an NDE tool that can quickly and reliably determine case depth from surface measurements