G. Skordaris

Effect of the Cutting Edge Radius and its Manufacturing Procedure, on the Milling Performance of PVD Coated Cemented Carbide Inserts

Abstract The fatigue and wear behaviour of PVD coatings on cemented carbide inserts with various cutting edge radii are investigated experimentally and analytically in milling. The inserts with cutting edge radii from 8 up to 35 μm were manufactured by honing and micro-blasting. The tool wear progress was depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) microspectral analysis. The Finite Elements Method (FEM) simulation of the contact between the tool and the workpiece highlights the effect of the cutting edge radius on the first coating fracture and the further wear development. The wear behaviour of the cutting edge radii manufactured by honing, in comparison to the corresponding ones by means of micro-blasting, is significantly enhanced, whereas the cutting edge radius increasing can lead to a higher tool life.

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.

Optimisation of the cutting edge roundness and its manufacturing procedures of cemented carbide inserts, to improve their milling performance after a PVD coating deposition

The fatigue and wear behaviour of PVD coatings on cemented carbide inserts with various cutting edge radii are investigated experimentally and analytically in milling. The inserts with cutting edge radii from 8 up to 35 μm were manufactured by honing and micro-blasting. The tool wear progress was depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) microspectral analysis. The Finite Elements Method (FEM) simulation of the contact between the tool and the workpiece highlights the effect of the cutting edge radius on the first coating fracture and the further wear development. The wear behaviour of the cutting edge radii manufactured by honing, in comparison to the corresponding ones by means of micro-blasting, is significantly enhanced, whereas the cutting edge radius increasing can lead to a higher tool life.

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.

Quantification of PVD Film Adhesion with Critical Shear Stress by Using Dynamic Simulation of the Inclined Impact Test

The film adhesion can be evaluated by the ratio of the tangential to normal film-substrate interface stiffness, as already described in recent publications. In the present paper, a new method is introduced for assessing the film adhesion based on the critical shear failure stress (SFLS). To predict SFLS in the coating-substrate region, a new 3D-FEM model was developed for the dynamic simulation of the inclined impact test, using the LS-DYNA software. This model enables the explicit determination of SFLS and also the relevant maximum equivalent stress developed in the film during the inclined impact test. The occurring SFLS in the coating-substrate interface affects the stresses resulting in the film during the operation of a coated component. In this way, they may lead to potential film material overloading and its cohesive failure.

New Methods for Characterizing Coating Properties at Ambient and Elevated Temperatures

In the paper, innovative methods for characterizing coatings’ properties at ambient and elevated temperatures are introduced based on various experimental procedures. Nanoindentation results, which were obtained at elevated temperatures, are evaluated by FEM algorithms, rendering possible the determination of temperature dependent coating mechanical properties. Impact tests conducted on coated specimens revealed a non-linear film impact resistance versus the temperature. The latter results were evaluated by appropriate FEM supported procedures, to predict the coating fatigue endurance stress versus the temperature. In these investigations, the impact load was induced electromagnetically for a duration of ca. 1ms, depending on the force amplitude. To change the impact load characteristics, such as frequency, impact duration etc., a new test device has been developed, employing a piezoelectric actuator. This device enables the investigation of the impact time effect on the dynamic response of coated surfaces and on the coating fatigue endurance stress. Finally, diffusion phenomena in coatings were examined by a developed convenient experimental setup. A specimen is pressed onto a coated surface at adjustable high temperature and pressure in an inert atmosphere. After this test, the diffusion of characteristic elements into the coating and vice versa is detected by EDX-microanalyses. These results contribute, among others, to the description of diffusion phenomena between coatings and various materials.

Micro-blasting of PVD Films, an Effective Way to Increase the Cutting Performance of Coated Cemented Carbide Tools

This paper investigates the feasibility of increasing the wear resistance of cemented carbide tools through micro-blasting of their PVD-coatings. The enhanced and graded film strength properties before and after micro-blasting are determined by means of a FEM-based evaluation of nanoindentation results. The coating topomorphy, induced by micro-blasting, was monitored and correlated to the substrate roughness and film adhesion. The cutting performance of inserts, coated with micro-blasted films, was investigated in milling and explained with the aid of a cutting process FEM simulation. The obtained results reveal a tool life growth through micro-blasting of coatings, deposited on substrates with appropriate roughness characteristics.

MILLING PERFORMANCE OF COATED INSERTS WITH VARIABLE COATING THICKNESS ON THEIR RAKE AND FLANK

During the Physical Vapour Deposition of coatings, the orientation of cemented carbides insert surfaces to the plasma flux direction affects the occurring film thickness distribution on the rake and flank, which in turn might influence the wear propagation in cutting processes. In the present paper the cutting performance in milling of PVD coated cemented carbides inserts with variable film thickness on the rake and flank is introduced and with the aid of FEM-supported calculations explained. The investigation results revealed that a thicker film on the tool rake in comparison to the existing one on the flank and moreover a thick and uniformly deposited film in the cutting wedge region significantly enhances the cutting performance in milling.