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Cutting tools coating failure prediction based on innovative film characterisation methods

: Bouzakis, K.-D.; Skordaris, G.; Maliaris, G.; Bouzakis, E.; Makrimallakis, S.; Katirtzoglou, G.; Gerardis, S.

Journal of the Balkan Tribological Association 18 (2012), No.1, pp.106-123
ISSN: 1310-4772
Journal Article
Fraunhofer IPT ()

The cutting performance of coated tools can be significantly improved by tailoring the coatings properties to application of specific requirements. For achieving this target, optimised PVD processes as well as appropriate substrate pre- and posttreatments of the coated surfaces have to be employed. To check the effectiveness of all these methods, innovative quality inspection tests should be applied. In the recent 3 years, various innovative methods for characterising the coatings properties towards explaining their performance in cutting applications have been developed. Characteristic related methods are presented in this paper and applications results are provided for demonstrating the effectiveness of these methods. In this context, nano-impact test is an effective tool for assessing the coatings strength and their brittleness as well. With the aid of its FEM simulation, a theoretical explanation of the nano-impact test results, concerning the film fracture initiati on and evolution, is attained. For investigating the effect of strain rate on the surface response and film fatigue fracture of coated specimens subjected to cyclic impact loads, an impact tester was developed, facilitating the impact force modulation concerning its signal pattern. The surface response depends, among others, on the substrate and coating strain, strain rate properties. Repetitive impact loads with variable duration are exercised on coated cutting edge in interrupted machining operations, depending on the applied kinematics and cutting conditions, as for example in milling. The coated tool life under certain cutting conditions was correlated to the film strain rate-dependent fatigue behaviour. In this way, the coated inserts cutting performance at various conditions was explained, considering the impact test results with modulated repetitive force. Finally, inclined impact test is a further procedure, which is analytically described appropriately by (FEM- based techniques, allowing the determination of films adhesion, in cases where the Rockwell indentation tests fail to deliver reliable results.