I. Mirisidis

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.

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.

Fatigue Induced Alteration of the Superficial Strength Properties of 2024 Aluminum Alloy

Aircraft aluminum alloy 2024 T3 specimens have been subjected to constant amplitude fatigue loading at R =0.1. During fatigue, an appreciable increase of the surface hardness of the material at the meso-scale can be observed and captured by means of nanoindentations. Surface hardness increases with increasing fatigue stress amplitude and advancing number of applied fatigue cycles. Observed increase of specimen surface hardening degree during fatigue causes an evolution of superficial mechanical strength properties of the alloy. Stress-strain curves associated with the evoluting superficial mechanical properties are derived, employing a developed finite element method (FEM)-supported evaluation procedure of nanoindentation experimental results.

Superficial Strength Properties Modification of 2024 Aluminum Specimens Subjected to Cyclic Loading, Detected by Nanoindentations

Structural elements and components of planes are mainly manufactured by aluminum alloys due to weight restrictions. According to experimental results, it has been observed that specimen regions of aluminum alloys which have been stressed at various loads, potentially leading to fatigue damages, have higher hardness compared to regions in which no fatigue mechanisms have been activated. With the aid of nanoindentations, the material hardness increase due to fatigue was captured, especially when a fatigue fracture approaches and the remaining safe operational time of structural components can be estimated. Moreover, stress-strain curves associated with the superficial mechanical properties of the examined materials are determined, employing a developed FEM-supported evaluation procedure of nanoindentation experimental results. The procedure was applied to obtain the superficial strength properties of the alloy during fatigue loading. By means of these techniques, valuable conclusions on the fatigue mechanism development of various plane structural elements and components can be drawn.