Combination of electromagnetic non-destructive testing methods and automated visual inspection for the estimation of grinding burn dimensions

Härtel, K.; imq Ingenieurbetrieb GmbH; Germany

Härtel, K.; imq Ingenieurbetrieb GmbH; Germany
Koch, F.; imq Ingenieurbetrieb GmbH; Germany
Seidel, M.; imq Ingenieurbetrieb GmbH; Germany
Zösch, A.; imq Ingenieurbetrieb GmbH; Germany

ID: ECNDT-0168-2018

Any form of mechanical processing of parts results in a change of near-surface areas. The term grinding burn is used, when the impact of heat is high enough to generate local tempered or re-hardened zones. Since the heat impact is on a low scale for grinding burn the resulting tempered zones have in general a marginal dimension. But in contrast to other microstructure irritations grinding burn occurs mainly on surfaces which are critical for the functionality of the parts. The existence of grinding burn in such areas results in a non-calculable reduction of the durability of the parts.
The most commonly used method for the detection of grinding burn is surface temper etching. Currently it is the only standardized grinding burn testing method. This method uses that the affected areas react differently than unaffected ones when etched with nital. A visual inspection of the etched parts is necessary. Non-destructive testing methods are easier to automate and free of human factors. Therefore they are already widely used in industrial applications for grinding burn testing.
Parts with defined defects are required for the correct interpretation of testing results and to ensure the reliability of non-destructive test methods as well as STE according to ISO 14104. The reproducible production of grinding burn-defects with defined dimension by mechanical processing is critical and in most applications not possible. An alternative is the usage of artificial defects.
It will be presented how the combination of electromagnetic testing methods, and automated visual inspection can be used to estimate the dimension of grinding burn. In future these method can be used to categorize different grinding burn and attain conclusions regarding their origin. Further it is possible to define a critical dimension for grinding burn and reduce the amount of scrap parts.