Now showing 1 - 10 of 10
  • Publication
    Correlation between the wear behavior of coated cemented carbide tools and coatings properties assessed by nano-indentations, nanoand micro-impact tests
    ( 2016)
    Bouzakis, Konstantinos-Dionysios
    ;
    Charalampous, Panagiotis
    ;
    Bouzakis, Emmanouil
    ;
    Kotsanis, Tilemachos
    ;
    Skordaris, Georios
    ;
    Michailidis, Nikolaos
    ;
    Klocke, Fritz
    ;
    ;
    Ottersbach, Michael
    ;
    Busch, Marc
    The application of appropriate PVD coatings on cemented carbide tools plays an important role for achieving an enhanced milling performance. In the conducted investigations, two different PVD coatings with an overall thickness of about 3.5 mm were deposited on cemented carbide tools possessing a fine, or a normal grain size structure. The coated tools were applied in milling hardened steel and Ti-Al alloy. Nano-indentations supported by appropriate FEM-algorithms for the results evaluation were carried out for determining the stress-strain curves of the employed coatings and substrates. The films brittleness was assessed by conducting nano-impact tests. The fatigue behavior of the applied coatings under dynamic loads was evaluated via impact tests at various temperatures and impac t force durations similar to those developed during milling. Based on the determined coating properties, the attained tool wear results were sufficiently explained.
  • Publication
    Repetitive impact test near uncoated and coated cutting edges for assessing their fatigue behavior
    ( 2015)
    Bouzakis, K.-D.
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    Batsiolas, M.
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    Skordaris, G.
    ;
    Stergioudi, F.
    ;
    Michailidis, N.
    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.
  • Publication
    Brittleness and fatigue effect of mono- and multi-layer PVD films on the cutting performance of coated cemented carbide inserts
    ( 2014)
    Skordaris, G.
    ;
    Bouzakis, K.D.
    ;
    Charalampous, P.
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    Bouzakis, E.
    ;
    Paraskevopoulou, R.
    ;
    Lemmer, O.
    ;
    Bolz, S.
    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.
  • Publication
    Effect of cutting edge preparation of coated tools on their performance in milling various materials
    ( 2014)
    Bouzakis, K.D.
    ;
    Bouzakis, E.
    ;
    Kombogiannis, S.
    ;
    Makrimallakis, S.
    ;
    Skordaris, G.
    ;
    Michailidis, N.
    ;
    Charalampous, P.
    ;
    Paraskevopoulou, R.
    ;
    M'Saoubi, R.
    ;
    Aurich, J.C.
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    Barthelmä, F.
    ;
    Biermann, D.
    ;
    Denkena, B.
    ;
    Dimitrov, D.
    ;
    Engin, S.
    ;
    Karpuschewski, B.
    ;
    Klocke, F.
    ;
    Özel, T.
    ;
    Poulachon, G.
    ;
    Rech, J.
    ;
    Schulze, V.
    ;
    Settineri, L.
    ;
    Srivastava, A.
    ;
    Wegener, K.
    ;
    Uhlmann, E.
    ;
    Zeman, P.
    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.
  • Publication
    Coating's applications: Assessment of coatings' brittleness by nano-impact tests
    ( 2013)
    Bouzakis, K.-D.
    ;
    Skordaris, G.
    ;
    Gerardis, S.
    ;
    Bouzakis, E.
    In the described investigations, nano-impact tests were conducted on PVD film surfaces previously subjected to micro-blasting at different pressures for constant duration. Micro-blasting improves the film mechanical properties due to the induced residual compressive stresses into the coating structure. The film mechanical properties as well as the ratio of the film yield to rupture stress (SY/SM) grow up to a certain micro-blasting pressure. The augmentation of SY/SM ratio increases simultaneously the film brittleness. For analyzing the effect of the SY/SM ratio on the film brittleness, a multi-layer 3D-FEM model simulating the nano-impact test was developed, employing the LS-DYNA software package. The FEM calculated results converge sufficiently with the attained experimental ones. Based on these results, the film's failure initiation and evolution can be predicted depending on the SY/SM ratio of the individual film layers.
  • Publication
    Predictive model of tool wear in milling with coated tools integrated into a CAM system
    ( 2013)
    Bouzakis, K.D.
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    Paraskevopoulou, R.
    ;
    Katirtzoglou, G.
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    Makrimallakis, S.
    ;
    Bouzakis, E.
    ;
    Efstathiou, K.
    The coated tool wear evolution in milling at constant cutting conditions can be described analytically based among other factors on the cutting edge entry impact duration. A tool wear predictive mathematical model for milling parts of complicated geometry was created employing this methodology and a commercial CAM system. Parameters of the developed model were determined based on experimental results. In this way, the expected tool wear growth during numerically controlled milling can be estimated, considering the cutting penetrations along the tool paths, the process up or down kinematic and other factors. The application of the introduced model is demonstrated through appropriate examples. (C) 2013 CIRP.
  • Publication
    Nano-impact test on PVD-coatings with graded mechanical properties for assessing their brittleness
    ( 2013)
    Bouzakis, K.-D.
    ;
    Skordaris, G.
    ;
    Gerardis, S.
    ;
    Bouzakis, E.
    In the described investigations, nano-impact tests were conducted on PVD films with graded mechanical properties. The properties gradation was induced by micro-blasting at different pressures for constant duration. Micro-blasting improves the film mechanical properties due to the induced residual compressive stresses into the coating structure. The film mechanical properties as well as the ratio of the film yield to rupture stress (SY/SM) grow up to a certain micro-blasting pressure. The augmentation of S Y/SM ratio increases simultaneously the film brittleness. For analyzing the effect of the SY/SMratio on the film brittleness, a multi-layer 3D-FEM model simulating the nano-impact test was developed employing the LS-DYNA software package. The FEM calculated results converge sufficiently with the attained experimental ones. Based on these results, the film's failure initiation and evolution can be predicted depending on the SY/SMratio of the individual film layers.
  • Publication
    Grain size effect of pre- and post-coating treated cemented carbides on PVD films' adhesion and mechanical properties
    ( 2013)
    Bouzakis, K.-D.
    ;
    Michailidis, N.
    ;
    Skordaris, G.
    ;
    Tsouknidas, A.
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    Makrimallakis, S.
    ;
    Bouzakis, E.
    The grain size of coated cemented carbide tools may significantly affect the tool life by influencing either the coating adhesion to the substrate or the coating growth during deposition. In the present study three variously grained cemented carbides were coated with two different PVD films. Various pre- and post-treatments were applied, while their effect on the films' mechanical properties and adhesion was assessed by nanoindentations and inclined impact tests. The coatings deposited on ultra-fine-grained substrates exhibited the highest mechanical properties overall. The research revealed elevated adhesive properties for the fine-grained substrate compared to the normal and ultra-fine-grained one. The film adhesion of normal and fine-grained substrate can be further enhanced through micro-blasting. Post-treatments of the coatings were beneficial in all substrate cases, as brushing of the film surface removed droplets while at the same time inducing surface residual s tresses at the coating resulting in a hardness increase.
  • Publication
    Effect of tool diameter and cutting edge entry impact duration on coated tool wear in milling of various kinematics
    ( 2012)
    Bouzakis, K.-D.
    ;
    Katirtzoglou, G.
    ;
    Bouzakis, E.
    ;
    Makrimallakis, S.
    ;
    Maliaris, G.
    The die and mold industry registers nowadays a significant growth due to current developments among others in the sectors of energy and aerospace. The manufacturing procedure of dies and molds primarily includes milling operations, which are commonly linked to complicated chip geometry and contact conditions between tool and workpiece. Therefore, the optimisation of the cutting conditions and the description of the tool wear is a great challenge for production engineers. In the described experiments, cement-coated carbide inserts fixed on milling cutters with various diameters were applied in down and up milling for monitoring the wear behaviour at various cutting edge entry conditions. The corresponding developed strain rates cause different film-substrate deformations and resulting loads. These phenomena were investigated with the aid of a new impact tester with adjustable impact force characteristics. The effective tool life up to a certain flank wear land width vers us the cutting edge entry duration was explained and analytically described.
  • Publication
    Determination of PVD coating mechanical properties by nanoindentations and impact tests at ambient and elevated temperatures
    ( 2012)
    Bouzakis, K.-D.
    ;
    Pappa, M.
    ;
    Gerardis, S.
    ;
    Skordaris, G.
    The performance of physical vapour deposition (PVD) films depends on the operational mechanical and thermal loads of coated tools or components. To withstand these loads, sufficient film strength properties, at ambient and elevated temperatures are required. The present paper deals with the mechanical properties and the impact resistance of cemented carbides and high speed steel specimens, coated with various films, at temperatures up to 400 °C. Nanoindentations were conducted by a nanoindentation device, enabling measurements at room and elevated temperatures in an inert gas atmosphere. The obtained results were evaluated using appropriate FEM algorithms for determining the film stress-strain curves, at the temperatures of the conducted nanoindentations. The lesuits reveal a nonlinear temperature dependence of the coating properties. Moreover, perpendicular impact tests on the coated specimens were carried out up to 400°C, for investigating the film impact behaviour. T he developed impressions were recorded by scanning electron microscopy and white light confocal measurements. The attained results demonstrate a non-linear dependence of the film fatigue properties versus temperature, whereas a significant impact resistance improvement at approximately 150°C develops. Finally, a convergence between the yield and the fatigue endurance stress versus the temperature was revealed.