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The softening of cemented carbide at the elevated temperature of MTCVD processes results in significant reduction of their strength, and thus, high coating deformation during cutting. In this way, at interrupted cutting loads, as during turning cast iron, the cutting performance of MTCVD coated cemented carbide inserts degrades due to premature coating fatigue fracture. To overcome this problem, appropriate heat treatments of MTCVD coated inserts were conducted. The related temperatures and durations for improving the substrate properties were optimized considering obtained strength data of uncoated inserts variously heat treated and the turning performance of coated ones correspondingly heat treated. [ABSTRACT FROM AUTHOR]

Micro-crystalline diamond (MCD) coatings were deposited on cemented carbide inserts at different temperatures using hot filament chemical vapor deposition technique. For investigating the effect of the developed diamond crystallinity on the fatigue strength and wear behaviour of the prepared MCD coated inserts, inclined impact tests and milling investigations were conducted correspondingly. Raman spectra were recorded for capturing the crystalline phases after the film deposition and their potential changes after the impact and milling experiments induced by the mechanical and thermal loads. Thus, the explanation of the cutting performance of the employed diamond coated inserts with various crystalline phases was enabled. [ABSTRACT FROM AUTHOR]

PVD coatings were deposited at various bias voltages on cemented carbide inserts. The coating’s mechanical properties, fatigue and adhesion were determined via FEM-supported evaluation of nanoindentation, perpendicular and inclined impact test results. The coated inserts were applied in milling hardened and normalized steel. For explaining the wear evolution based on the cutting loads and stress fields developed in the coating and its substrate, FEM calculations were performed considering among others the films’ strength and adhesion. According to the workpiece properties, certain coating’s parameters become prevailing for the tool life. These depend on the bias voltage and facilitate its optimum adjustment. [ABSTRACT FROM AUTHOR]

Coated cemented carbide inserts with diverse compressive residual stresses in the film structure were manufactured applying different substrate bias voltages. Moreover, a portion of the coated specimens was annealed for eliminating compressive residual stresses. Residual stress measurements, nanoindentations, nano- and inclined-impact tests, as well as FEM-supported calculations were performed for assessing the coating's mechanical properties, cohesion, brittleness and adhesion. Furthermore, the cutting performance of the coated inserts was investigated in turning AISI 1045. According to the attained results, coating residual stresses affect significantly the film properties and wear behavior. Hereupon, a certain residual stress level can be considered as optimum. [ABSTRACT FROM AUTHOR]

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 fatigue strength of the cutting edge affects dominantly the tool life, especially in the interrupted material removal processes. The cutting edge fatigue of uncoated and coated tools can be effectively assessed by the repetitive impact test. Cemented carbide inserts of various grain size, surface roughness, coating and heat treatment were investigated by applying repetitive impacts close to the cutting edge for detecting its fatigue strength. Complementary FEM simulations of the impact test, at various distances from the cutting edge, provided insights on the developed stress fields. The impact distance from the cutting edge was corroborated to have a dominant effect on the tool life, while a reduction of the roughness and the application of finer substrate grains led to an increase of the cutting edge fatigue strength. The proposed methodology facilitates an effective quality control of both coated and uncoated cutting inserts at loading conditions resembling those of interrupted cutting. [ABSTRACT FROM AUTHOR]

The cutting edges of coated tools are commonly treated in separate production steps during tool manufacturing. Various methods can be employed, focusing on the cutting edge strengthening by its rounding or by more complicated geometries including chamfer and optimized tool wedge radius and angles. The efficiency of diverse cutting edge preparations on the wear behaviour of coated tools, in milling different materials, was investigated in the framework of a cooperative project of the Scientific Committee "Cutting' of the International Academy for Production Engineering (CIRP). In this activity twenty academic and industrial partners were involved according to a predefined project plan. [ABSTRACT FROM AUTHOR]

Abstract: The effect of brittleness and fatigue of mono- and multi-layer PVD films on coated tools cutting performance is introduced. Cemented carbide inserts were coated to the same overall film thickness with various numbers of layers. Nanoindentations were conducted to evaluate the hardness of the diverse coating structures. The film brittleness and fatigue were characterized by nano- and macro-impact tests respectively. The coated inserts’ wear behaviour was investigated in milling hardened steel. The attained results revealed the coatings’ brittleness and fatigue endurance enhancement by increasing the number of film's layers. This increase leads simultaneously to the coated tool life improvement. [Copyright &y& Elsevier]

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]

If the film of a coated part deforms plastically due to operational loads, residual stresses (RS) develop in the coating after the load removal. In this way, the film mechanical properties change induced by endogenous reasons, i.e. by the coating crystalline structure plastic deformation. Moreover, if only the substrate deforms plastically, the coating remains elastically deformed during the relaxation, due to the substrate RS. In this case, the film residual RS-changes are caused by exogenous parameters, i.e by the permanent substrate deformation. In the paper, novel experimental-analytical methods, based on nanoindentation and FEM calculations are introduced to determine film RS-changes, when the coating is deformed plastically as for example after micro-blasting, or elastically due to substrate plastic deformation as for instance after the ball penetration into the coated specimen during the impact test. [ABSTRACT FROM AUTHOR]

Abstract: If the film of a coated part deforms plastically due to operational loads, residual stresses (RS) develop in the coating after the load removal. In this way, the film mechanical properties change induced by endogenous reasons, i.e. by the coating crystalline structure plastic deformation. Moreover, if only the substrate deforms plastically, the coating remains elastically deformed during the relaxation, due to the substrate RS. In this case, the film residual RS-changes are caused by exogenous parameters, i.e by the permanent substrate deformation. In the paper, novel experimental-analytical methods, based on nanoindentation and FEM calculations are introduced to determine film RS-changes, when the coating is deformed plastically as for example after micro-blasting, or elastically due to substrate plastic deformation as for instance after the ball penetration into the coated specimen during the impact test. [Copyright &y& Elsevier]

Abstract: The applied grains’ material in micro-blasting of Physical Vapour Deposition (PVD) films and the process conditions affect significantly the coated tools’ cutting performance. Through micro-blasting, compressive stresses are induced into the film, thus increasing the coating hardness, but its brittleness too. Simultaneously, abrasion phenomena are activated, which may lead to roughness augmentation, film thickness decrease and substrate revelation. The paper deals with the optimization of wet micro-blasting conditions for improving the coated tool''s wear resistance. The explanation of the grains’ penetration into the coated tool surface and of the film deformation mechanisms renders the achievement of this target possible. [Copyright &y& Elsevier]

Abstract: High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers can enhance tool life significantly. In the conducted research, TiAlN PVD-films and W-, Ti- or Cr-adhesive nanointerlayers were deposited by HPPMS on different superficially treated hardmetal inserts. The mechanical properties of the coatings were determined via nanoindentations and mathematical analysis. Additionally, inclined impact tests and milling investigations were performed to examine the substrate pretreatment and interlayer effects on film adhesion and wear behaviour. The results reveal that HPPMS jointly with an appropriate substrate pretreatment and a Cr-nanointerlayer lead to significant adhesion and cutting performance improvement. [Copyright &y& Elsevier]

Abstract: Impact tests were conducted on coated cutting inserts, revealing that a temperature increase at first enhances the coating impact resistance, and then leads to its non-linear deterioration. On the other hand, milling investigations with coated cemented carbide inserts demonstrated that the cutting speed increase, up to a certain level, causes initially a significant improvement of the cutting performance. FEM calculations of the developed temperature and stress fields during cutting provided additional insights. The joint study and the subsequent correlation of the aforementioned results, renders the impact test as a convenient and efficient methodological tool for the characterization of coated tools'' cutting performance. [Copyright &y& Elsevier]