AGMA 17FTM07 PDF

The detection and prevention of grinding burn is critical to the production of ground gears of all types and sizes. Overheating during grinding, or grind temper, results in undesirable microstructure, hardness, and stress characteristics both on and below the surface. These characteristics result in failure modes on precision surfaces, which typically require high performance under load over a long lifetime. The traditional method for detection of grind temper, Nital Etch, is subjective, often destructive, and requires handling and disposal of hazardous chemicals. Additionally, the Nital Etch process requires a properly tailored process and a well-trained operator in order to prevent false-positives and/or false-negatives.

An alternative method, Magnetic Barkhausen Noise (MBN), is quantitative, repeatable, and non-destructive. Further, the MBN method is easily automated, thus removing operator influence as a variable. Using a sample set of carburized spur gears, ground to varying conditions of grind temper, the MBN method is demonstrated to match or exceed the detection effectiveness of traditional Nital Etch. Detection of various intensities of grind temper, including re-hardening burn, is demonstrated using fully automated MBN instrumentation. Residual Stress depth distributions measured with X-Ray Diffraction and electrochemical layer removal are utilized as a quantitative verification method.