The problem: Near surface residual stresses on ground cam lobes
A manufacturer of camshafts needed to frequently verify the near surface residual stresses on ground cam lobes in a non-destructive manner. Their only current means of achieving this was in a less frequent and destructive manner using X-Ray Diffraction.
The testing method: A Correlation Between Barkhausen Noise and X-Ray Diffraction
Barkhausen Noise (BN) testing was implemented, as it is non-destructive and is able to look beyond the surface of the ground lobes.
In order to correlate the two methods, select spots on the lobe were chosen and the BN results and X-Ray diffraction stress depth profiles were compared.
Barkhausen noise measurements:
The spots shown below are the areas where XRD Depth profiles were performed. On lobe 1, spots were chosen at the ramps (blue & green), nose (yellow), and the center of the base circle (pink). On Lobe 2, the nose (orange) was chosen.
The residual stresses measured at a subsurface depth approximately 0.020mm below the finished surface were seen to have a linear relationship with the Barkhausen noise values. This is shown in the following correlation results.
The favorable correlation enables the BN testing to be used at a much more frequent interval to supplement the XRD testing, all while not having to destroy any of the camshafts.
Instruments used for this application:
CamScan 100 is a semi-automated grinding burn and heat treatment defect detection system for low-volume applications. It is designed for quality control needs of small to medium sized circular symmetrical parts like passenger car shafts.
X-ray diffractometer Xstress G2R represents advances in design and construction, which provide enhanced reliability and function in a truly portable residual stress and retained austenite analyzer. Bi-axial and tri-axial stress state analysis is effortless and automated with rotating diffractometer.