R. Cremer

The influence of the coating thickness on its strength properties and on the milling performance of PVD coated inserts

Abstract The evolution of the physical vapour deposition (PVD) process has contributed to the wide application of thin hard coatings on cutting tools. The film thickness can significantly affect the tool cutting performance. In the present paper, PVD (Ti46Al54)N coatings with thickness from 2 to 10 μm were deposited on cemented carbide inserts. The coating material properties and especially their stress–strain relationship for the various coating thicknesses were determined by means of a FEM-based evaluation procedure on nanohardness measurement results. An increasing of the coating thickness deteriorates the coating mechanical strength, however it can lead to higher effective cutting edge radii, thus inducing lower stresses on the cutting edge, as the related FEM simulation results of the cutting edge region during the material removal show. Moreover, the substrate is better protected against abrasive wear and thermal loads occurring during the cutting process. The tool wear investigations conducted in milling are depicted by the numerically extracted dependencies, explaining the increased cutting performance of thicker coatings which, on the other hand, cause higher PVD costs.

Determination of coating residual stress alterations demonstrated in the case of annealed films and based on a FEM supported continuous simulation of the nanoindentation

A method to determine coating residual stress alterations induced by various mechanical or heat treatments is introduced in the present paper. The developed procedure is based on a FEM supported continuous simulation of the nanoindentation, enabling the determination of stress distribution development in the coating during the indenter penetration. Herewith, the principal and equivalent stresses at various positions in the coating material at the moment of its plastic deformation beginning can be calculated. A thermal or mechanical coating treatment affects these stresses, which in turn can be defined in every case by means of nanoindentations and its aforementioned FEM supported simulation. The difference of the equivalent stresses associated with concrete coating treatments correspond to the related equivalent residual stress alterations. Heat-treated coated cutting inserts with different film thickness, annealed for various annealing times revealed considerable internal stress modifications.

Supernitrides: A novel generation of PVD hardcoatings to meet the requirements of high demanding cutting applications

Abstract Based on a unique sputtering technology using highly ionized plasmas a novel grade of high performance hard coatings, the Supernitrides with macro free morphology were developed. Within the scope of the investigations described, a characteristic (Ti, AI)N based Supernitride variant, with an AIN content doss to the conductivity limit of 65-67mol-% AIN was deposited on cemented carbide inserts. the films mechanical properties were extracted by means of nanoindentations and impact tests and compared to the corresponding ones of an effective state of the art (Ti46AI54)N coating. Milling investigations, conducted with both previous mentioned coatings, demonstrated the enhanced cutting performance of the applied Supernitride coating, especially at elevated cutting temperatures.

A nanoindentation based determination of internal stress alterations in PVD films and their cemented carbides substrates induced by recoating procedures and their effect on the cutting performance

Through the reconditioning of worn coated cutting tools by means of appropriate de-coating, micro-blasting and physical vapour deposition (PVD) recoating procedures, a production cost decreasing is intended. However, the cutting performance of recoated tools may be impaired compared to the corresponding one of new tools, due to the fact that during the reconditioning processes strength properties modifications in the substrates are induced, resulting in a potential wear behaviour deterioration. In this way, the cutting performance reliability and in general the tool cost management could be unfavourably affected. In the investigations described, a procedure based on nanoindentations and a finite elements method (FEM) supported evaluation of the corresponding measurement results is applied. This method enables an accurate determination of coatings and cemented carbides inserts mechanical surface strength properties and, moreover, of related internal stress alterations at every stage of reconditioning procedures. The occurring surface stress modifications in cemented carbides inserts during reconditioning procedures might affect the tool cutting performance. Investigations in milling and gear hobbing showed that the inferiority of the tool wear behaviour when using reconditioning cemented carbides tools, could be drastically reduced. The methodology introduced, contributes to the achievement of this target, since it facilitates the accurate assessment of the reconditioning procedures effect on the tool mechanical properties.

Erratum to “Application in milling of coated tools with rounded cutting edges after the film deposition”

In the above published article (b) Fraunhofer Project Center Coatings in Manufacturing, in Centre for Research andTechnology Hellas (CERTH), Thessaloniki, Greece and (c) Fraunhofer Institute for Production Technology (IPT), Aachen, Germany is one legal entity Fraunhofer Project Center Coatings inManufacturing, in Centre for Research and TechnologyHellas (CERTH), Thessaloniki, Greece and in Fraunhofer Institute for Production Technology (IPT), Aachen, Germany CIRP Annals Manufacturing Technology 58 (2009) 722