Dry High Speed Orthogonal Turning of Titanium Alloy Wear Evolution and Chip Morphology

The present work is an experimental study on the dry high-speed turning of Ti-6Al-4 V titanium alloy. The objective of this study is to see for high cutting speeds, how wear occurs on the face of insert and how to evolve cutting forces and chip formation. Cutting speeds tested is 600, 800, 1000 and 1200 m/min in orthogonal turning with a carbide insert tool H13A uncoated and coated TiN on a cylindrical titanium alloy part. Investigation on the wear inserts with 3D microscope scanning revered the crater formation is instantaneous and a chip adhesion. Welded chip causes detachment of carbide particles. In these experiments the chip shape was systematically investigated at each cutting conditions using optical microscopy. The chips produced were collected and polished to measure the thicknesses t2max and t2min. The distance between each segments dch and ɸseg inclination angle as described in the introduction part, the shear angle ɸ and the inclination angle of a segment ɸseg are differentiated. ɸseg angle is actually measured on the collected chips while the shear angle ɸ cannot be. The angle ɸ represents the initial shear similar to the one that describes the formation of a continuous chip in the primary shear zone. Cutting forces increase and stabilize before removing the tool. The chip reaches a very high temperature

Etude des mécanismes d'endommagement des outils carbure WC-Co par la caractérisation de l'interface Outil-Copeau: application à l'usinage à sec de l'alliage d'aluminium aéronautique AA2024 T351

In the present study, carbide tool wear is analysed in the case of dry machining of an aeronautic aluminium alloy (AA2024 T351). The purpose is to determine the different tribological parameters at the tool-chip interface (friction, temperature, pressure) and to confront them with the wear mechanisms. A modelling of the contact between the chip and the tool, based on the viscoplastic properties of the material flow, is initially proposed. This allows to establish relationships existing between the chip geometry (shear angle), the stress applied on the tool, the friction coefficient and the sliding chip velocity in the neighbourhood of the cutting tool edge. The analytical model is then used to determine the nature of the contact (sticking, sliding) and to calculate the sliding speed. To determine the temperature and the contact pressure, a special device based on the experimental observation of the chip formation (high speed video camera, force measurement, heat flux calculation) and the finite element numerical simulation is also carried out. The surface analysis carried out using complementary techniques (MEB, EDS, AES, optical profilometry) allowed to clearly identify the different wear mechanisms. They result in the formation of built-up edges, in the formation of adherent layers (transfer layers formed by extrusion of precipitates) and in the tool embrittlement caused by the diffusion of chemical species from the chip towards the tool. Thanks to the study, it is possible to connect these various damage modes to the contact conditions existing at the tool-chip interface.L'étude proposée traite de la compréhension des mécanismes d'endommagement des outils carbure dans le cas de l'usinage à sec d'un alliage d'aluminium aéronautique (AA2024 T351). Elle a pour but de déterminer les différents paramètres tribologiques de l'interface outil-copeau (frottement, température, pression) et de les confronter aux différents modes d'usure. Une modélisation du contact entre le copeau et l'outil basée sur les propriétés viscoplastiques de l'écoulement du matériau est d'abord proposée. Elle permet d'établir les relations qui existent entre la géométrie du copeau (angle de cisaillement), les contraintes appliquées sur l'outil, le coefficient de frottement et la vitesse de glissement du copeau au voisinage de la pointe de l'outil. Le modèle analytique est alors employé pour déterminer la nature du contact (collant, glissant) et calculer la vitesse de glissement. Pour déterminer la température et la pression de contact, un dispositif d'étude basé sur l'observation expérimentale de la formation du copeau (caméra vidéo rapide, mesure des efforts, calcul de flux thermique) et la simulation numérique par la méthode des éléments finis est ensuite mis en place. La caractérisation physico-chimique réalisée à l'aide de techniques complémentaires d'analyse de surface (MEB, EDS, AES, profilométrie optique) a permis d'identifier clairement les différents types d'endommagement. Ils se traduisent par la formation d'arêtes rapportées et de couches adhérentes (couches de transfert formées par extrusion de précipités) ainsi que par la fragilisation de l'outil provoqué par la diffusion de certaines espèces chimiques du copeau vers l'outil. Grâce à la démarche proposée, il est possible de relier ces différents modes d'endommagement aux conditions de contact existant à l'interface outil-copeau

Etude des mécanismes d'endommagement des outils carbure WC-Co par la caractérisation de l'interface outil copeau (application à l'usinage à sec de l'alliage d'aluminium aéronautique AA2024 T351)

PARIS-Arts et Métiers (751132303) / SudocSudocFranceF

Very high speed cutting of Ti-6A1-4V titanium alloy - change in morphology and mechanism of chip formation

International audienceThe chip formation for a Ti-6A1-4V alloy was studied at high cutting speeds combined with large uncut chip thicknesses (0.1-0.25 mm). Orthogonal cutting tests were conducted by using uncoated carbide tools on a specific ballistic set-up with cutting speeds from 300 m/min to 4400 m/min (5-75 m/s). A hypothesis on the mechanism of chip generation is proposed for this speed range validated by highspeed imaging system enabled direct observation of cutting process. A transition, from serrated more or less regular with localized shearing and possible presence of cracking, to discontinuous at very high speed is observed. The inclination of the segment 0, is shown as resulting from the primary shear angle 0 that can be modified by compression between the tool and the uncut part. A maximum value of 60 for g is reached with increasing speed after which it decreases to 45 at very high speed. The cutting speed appears as the most important factor when compared with the uncut chip thickness, in determining the formation of chips by affecting the frequency of segmentation, the shear angles and the crack length. The significant reduction of cutting forces occurring with increases in cutting speed was firstly explained by the conflicting work hardening-thermal softening processes and then depended on whether the deformation phase of the chip segment is occurred

Prédiction de l’usure des outils en usinage à grande vitesse

Les modèles d’usure des outils en UVG nécessitent une bonne connaissance du profil de température de la pointe de l’outil jusqu’à la fin du contact avec le copeau. La formation du copeau et le profil de température sont observés en temps réel sur un dispositif balistique de coupe. Les résultats expérimentaux associés aux modèles d’usure, montrent l'importance de prendre en compte l'évolution du contact en plus des phénomènes de diffusion, afin de permettre une meilleure prédiction de l’usure

Analysis of adhered contacts and boundary conditions of the secondary shear zone

International audiencePrediction of the tribological parameters controlling the tool wear is one of the most complex research axes in the metal cutting literature. The nature of the friction on the tool-chip interface is the main process which influences the distribution of stresses and temperatures which in turn activates the thermomechanical process governing tool wear. Under extreme conditions of temperature, strain rates and pressure, occurring especially in high speed machining, the adhered contact phenomenon is highly localized especially near to the tool tip and extremely non-linear due to strong influence of the secondary shear zone (SSZ) and the nature of bonds between asperities of tool and chip. In addition, the analysis based on post-mortem examinations of chips and worn tools, especially in hard metal cutting alloy and high speed machining, show that the adhered friction with intimate contact and no relative motion of the material chip on the interface, are the principal cause of appearance of the plastic deformation layers (SSZ). This localized shear zone plays a role of intensive heat sources interacting with the tool side and, in turn, activates diffusive and abrasive wear. In this work, a hybrid model combining analytical and numerical approaches is performed in order to solve the non-linear thermomechanical problem on the chip and predicts the nature of friction contact, i.e. fully sliding, sticking/sliding or fully sticking contact, and these for a given distribution of asperities, characterizing the ratio between the real and apparent contact areas A(r)/A(n) on the interface, and a given global friction coefficient (mu) over bar, characterizing the ratio of the experimental cutting forces. The shear stress generated in the primary shear band, the energy produced in the secondary shear zone, the local friction coefficient and the friction energy produced on the sliding part of contact, the proportion of the sticking/sliding interfaces, and geometrical parameters of the chip, are obtained by analytical means. The analysis of this model is based on experimental data and applied for a large cutting speed (1 ms(-1) <= V <= 60 ms(-1)) and able to give some correlation about the distribution of adhesions marks on the contact with respect to the distribution of the tribological parameters at the interface. This model can be used in improving tool wear prediction and the estimation of tool-lif

Modeling of friction along the tool-chip interface in Ti6Al4V alloy cutting

International audienceThe aim of the paper is the modeling of chip formation in metal cutting in order to describe the thermomechanical interactions at the tool-chip interface (TCI). A particular attention is paid for the fully sticking case to complete previous modeling works which were more focused on the sliding regime or mixed sliding/sticking regime. The fully sticking contact is dominating due to the combined effects of high magnitudes of the normal stress, the average friction coefficient and the temperature. This case is also well adapted for cutting of titanium alloy. In the present model, these local parameters are macroscopically expressed through the average friction coefficient , and the velocity field on the secondary shear zone is modeled using a new approach. The ratio between real area of contact A (r) and the apparent area A (n) is taken into consideration. The developed approach is also fully thermomechanically coupled with heat transfer consideration. In this way, it was possible to predict normal and shear stress according to the variation of cutting velocities, feed and rake angle. The model was supported by the experimental trends from Ti6Al4V alloy cutting tests and worn tools analysis. It was shown that the distribution of the ratio A (r) /A (n) may be considered as a good indicator to describe the spreading of the adhesion marks on the contact. The model also highlights how the influence of the apparent friction coefficient, the rake angle, the feed and the cutting speed acts on the tool-chip contact length

Raman characterization of Ti–6Al–4V oxides and thermal history after kinetic friction

International audienc

Analysis of high friction conditions of Ti–6Al–4V alloy on tantalum by Raman spectroscopy and X-ray fluorescence

International audienceHigh friction conditions between tantalum and titanium alloy are analyzed. An experimental ballistic set-up was used to combine high sliding speed (34 m/s in this study) and high normal pressure (44.5 Mpa). Initial stages of friction were analyzed by a single friction pass. Raman spectroscopy and X-ray fluorescence analysis were used to examine the sliding surfaces. The presence of TiO2 in anatase form is detected over small localized zones in order of few microns. This observation confirms a rapid and very localized rise in temperature on the friction surface as soon as the friction phase begins. The tendency of titanium alloys to transfer material on the tantalum specimen (less than 10 mu m in thickness) is highlighted despite the high sliding velocity. The evolution of the surface roughness following tearing of micro weldings was quantified by a profilometer. (C) 2012 Elsevier Ltd. All rights reserved