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The effective application of laser machining for manufacturing the cutting edge roundness of cemented carbide inserts was investigated in a cooperative work of the Scientific Technical Committee (STC) “Cutting” of the International Academy for Production Engineering (CIRP). Machining with diverse laser beam pulsing duration and feed velocity as well as micro blasting were employed prior to the coating deposition for shaping the cutting tool’s edges. The wear behaviour of the coated inserts was tested in milling TiAl6V4 and Inconel 718. Considering the inserts’ surface micro-structure and mechanical properties developed after the laser treatment, the coated tools’ cutting performance deterioration or improvement compared to untreated substrates was explained. [ABSTRACT FROM AUTHOR]

The paper aims at clarifying whether thick HPPMS (High Power Pulsed Magnetron Sputtering) PVD coatings can be used more effectively in cutting processes compared to thin ones. In this context, nano-structured multilayer HPPMS PVD coatings with diverse thickness were deposited on cemented carbide inserts of the same specifications. The deposition of multilayer PVD coatings instead of mono-layer ones on cemented carbide tools contributes to a significant improvement of the coated tool life due to their capability to prevent the crack propagation. The coating's mechanical properties and their gradation versus the film thickness were determined by analytical results' evaluation of nanoindentations on annealed coated specimens. The films' brittleness was assessed by nano-impact tests. The strain rate-dependent fatigue endurance of the applied coatings was determined by means of impact tests with modulated force signals, resembling the developed ones during milling. The coated inserts were used in milling hardened steel. A Finite Elements Method (FEM) simulation of the contact between the coated tool and the workpiece provided information for elucidating the effect of the film thickness on the tool wear evolution. These investigations revealed that via increasing the film thickness the tool life is prolonged almost proportionally with the coating thickness augmentation, thus compensating for their higher cost compared to thin coatings. [ABSTRACT FROM AUTHOR]

The determination of the temperature dependent interface fatigue strength of Nano-Crystalline Diamond (NCD) coatings facilitates a thorough understanding of the NCD coated cutting tools wear mechanisms. In the present paper, the fatigue strength of the interface region between a NCD film and its hardmetal substrate was investigated by inclined impact tests at various temperatures. Depending upon the impact load and the applied temperature, after a certain number of impacts, damages in the film-substrate interface develop, resulting in coating detachment and lifting. These effects were attributed among others to the release of highly compressive residual stresses in the NCD coating structure. The attained inclined impact test's results contributed to the explanation of the wear-evolution of NCD-coated tools with diverse film-substrate adhesion qualities. The related milling experiments using as work material AA 7075 T6 verified the dominant effect of the film adhesion on the NCD coated tool life. [ABSTRACT FROM AUTHOR]

Abstract: Milling operations are associated with significant tool impact loads. In the present investigations, coated carbide inserts were employed in down and up milling hardened steel, at appropriate cutting conditions and tool diameters, for attaining various cutting edge entry impact durations (CEEID). The unexpected tool life improvement in up milling, when inserts with rake chamfer instead of sharper round ones were applied, was explained via FEM-determined tool loads and their duration during the material removal. The effect of CEEID on the film failure was quantified by impact tests at various force data. The tool life was effectively described dependent on CEEID. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: The knowledge of coated tool wear mechanisms in milling is crucial for explaining film failure and adjusting appropriately the cutting conditions. In the described research, coated cemented carbide inserts were applied in up- and down-milling stainless steel for monitoring the tool wear at repetitive cutting loads of various magnitudes and durations. The variable stress, strain and strain-rate fields developed in the tool during milling affect the film-substrate deformations, and thus the resulting cutting loads and the coating fatigue failure. For investigating the influence of cyclic impact load magnitude and duration on the film fatigue of coated specimens, an impact tester was employed which facilitates the modulation of the force signal. Using this device, repetitive impact loads with different duration and time profiles were applied on coated cutting inserts. These loads approximately simulate the developed ones in milling when the cutting edge penetrates the workpiece material. The attained coated tool life was associated with the developed maximum strain and its rate in the film during milling. The latter factors were correlated to the strain and strain rate dependent on coating fatigue endurance. In this way, the tool life in all examined milling kinematics and chip geometries was sufficiently explained. [Copyright &y& Elsevier]

The film deposition conditions on individual specimens in the vacuum chamber during a physical vapour deposition coating procedure cannot be considered as constant. Depending among others on the magnetic field distribution in the vacuum chamber as well as on the specimen fixture geometry and kinematics, the coating hardness and mechanical properties may vary. In order to investigate the effect of coating hardness and strength on the cutting performance in milling, (Ti46Al54)N films having thickness from 3 to 10 μm and varying hardness were deposited on cemented carbides inserts. The coating material properties and especially their stress–strain laws were determined from the nanoindentation measurement results using a finite elements method (FEM) based evaluation procedure. The initiation and progress of the coating and tool wear in milling were studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. The investigations revealed that as the coating grows thicker, its superficial hardness and strength decreases. For the thick coatings, however, this does not affect the cutting performance as much as for the thin coatings. In the case of thin coatings, a corresponding decrease of the film hardness and strength, diminishes significantly the cutting performance. A FEM simulation of the cutting process, whereas the coating mechanical properties vs. the film thickness are considered, elucidates the aforementioned results. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

The development of new materials is always associated with the requirements of low cost manufacturing of parts consisting of these materials. In order to meet the corresponding demands, a range of developments has been brought forward in the area of coating technology. One of the most promising state of the art coatings is the metastable solid solution phase (Ti,Al)N in cubic NaCl (B1) structure. These coatings offer a superior oxidation resistance and hardness as compared to the conventional TiN or TiCN. The oxidation resistance of these coatings increases with increasing Al content in the solution phase. Based on a unique plasma enhanced sputtering technology a novel generation of high performance hard coatings, the supernitrides was developed. Supernitrides comprise a whole family of sputtered films deposited by means of highly ionized plasmas, and they are characterized by a dense, nano-crystalline or nano-layered structure and a high content of oxide forming elements. They show an improved hot hardness, high thermal and chemical stability as well as oxidation resistance. They combine the properties of most modern hard coatings with the chemical and physical properties of typical oxides. In the present article, the frame of the investigations describes a characteristic (Ti,Al)N based supernitride variant, with an AlN content close to the conductivity limit of 65–67 mol.% AlN was deposited on the cemented carbide inserts. The mechanical properties of the film were extracted by means of nano-indentations and impact tests, and compared to the corresponding ones of an effective state of the art (Ti46Al54)N coating. Milling investigations, conducted with both previously mentioned coatings, demonstrated the enhanced cutting performance of the supernitride coating, especially at elevated cutting temperatures. [Copyright &y& Elsevier]