A material microstructure-level (MML) cutting model based on the crystal plasticity theory is ado... more A material microstructure-level (MML) cutting model based on the crystal plasticity theory is adopted for modeling the material removal by orthogonal cutting of the Titanium alloy Ti-6Al-4V. In this model, the grains are explicitly taken into account, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the machined material. To obtain the material degradation process, the continuum intra-granular damage model and the discrete cohesive zone intergranular damage model have been implemented. Zero thickness cohesive elements are introduced to simulate the bond between grain interfaces. The material model is validated by the simulation of a compression test and results are compared with experimental data from the literature. Simulation results demonstrate the ability of the MML cutting model to capture the influence of the material microstructure, in terms of initial grain orientation angles (GOA), on chip formation and machined surface integrity.
International Journal of Machine Tools and Manufacture, 2010
The quantification of friction coefficient along the tool–workmaterial interface in machining rem... more The quantification of friction coefficient along the tool–workmaterial interface in machining remains an issue in tribology. This paper aims identifying the evolution of friction coefficient for a large range of sliding velocity during the machining of a AISI4140 steel (290HB) with a TiN coated carbide tool. The influence of a straight oil is investigated compared to a dry sliding situation
ABSTRACT This paper overviews some typical tribo-contact characteristics obtained in the turning ... more ABSTRACT This paper overviews some typical tribo-contact characteristics obtained in the turning of the pearlitic-ferritic nodular iron (EN-GJS-500-7 grade with UTS=500 MPa) when using carbide tools coated with single TiAlN and multiple TiC/Ti(C,N)/Al 2 O 3 /TiN layers, as well as silicon nitride Si 3 N 4 based ceramic tools. As a competitor, a P20 uncoated carbide grade was selected. The fundamental process readings include the tool-chip interface temperature, Peclet number, friction coefficient and the tool-chip contact length as functions of cutting parameters. In particular, the measurements of cutting temperature were carried out using conventional tool-work thermocouple method and IR mapping technique. It is concluded based on many process characteristics that multilayer coated and ceramic tools can substantially improve the performance of nodular iron machining.
The positive effect of an appropriate cutting edge geometry on the cutting performance of coated ... more The positive effect of an appropriate cutting edge geometry on the cutting performance of coated tools, has been recorded in several publications . In this context, the tool wedge rounding affects significantly the developed mechanical and thermal loads during the material removal and thus, the cutting performance of the applied tools.
According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutt... more According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutting, leading to material removal (grinding), and on the other hand as micro-ploughing, leading to plastic deformation and lower material removal (abrasive wear). Understanding various flowing transitions around an abrasive particle, under well-established conditions, makes it possible to better control these processes. The aim of the present study is to understand plastic deformation and failure local phenomena induced by an abrasive process. Experimental studies have been carried out on an abrasive process which consists in scratching a soft flat surface (AISI4140 steel) by mean of a turning tool fixed on the periphery of a disc. Regulating angular and feed speeds, successive scratches are expected to study phenomena generated by a single pass of the cutting tool. Scratch topography and forces are measured in order to highlight the influence of the depth of cut and the cutting speed on these parameters and on specific energy.
CIRP Journal of Manufacturing Science and Technology, 2008
A better understanding of friction modeling is required to lead to more realistic finite element ... more A better understanding of friction modeling is required to lead to more realistic finite element models (FEMs) of machining process. This work proposes to evaluate the performance of a new friction model depending on the local sliding velocity, compared to a standard approach considering a constant Coulomb friction coefficient. A finite element model, based on the Arbitrary Lagrangian–Eulerian (ALE) approach,
Most of superfinishing processes are based on the action of abrasive grains scratching the surfac... more Most of superfinishing processes are based on the action of abrasive grains scratching the surface of a workpiece. These processes are known to improve the surface texture but they also modify the surface integrity, and thus the durability of engineering parts. In this paper, the residual stress field induced by the scratch of a single round abrasive grain is investigated by means of an implicit finite element analysis. First, it is shown that the residual stress profile is always modified over a depth of two or three times the contact radius, whatever the mechanical and physical properties. Second, key-parameters having a high influence on the tensile and compressive zone have been identified. They are the contact severity, the friction coefficient and the workpiece hardness. Third, it appears that the residual stress profile is not really affected by the presence of initial homogeneous residual stress field in the material. These results are then used to explain the experimental residual stress fields induced by a belt finishing process and a honing process on a AISI52100 hardened steel. Finally the possibility to design appropriate abrasive tools to improve both surface texture and surface integrity of manufactured parts is discussed.
This chapter presents an analysis of workpiece surface integrity. The definition and material and... more This chapter presents an analysis of workpiece surface integrity. The definition and material and mechanical aspects of surface integrity are discussed.
Chip formation is a high strain rate process studied with analytical and numerical models. Analyt... more Chip formation is a high strain rate process studied with analytical and numerical models. Analytical models have the advantage of a small calculation time, however, they are often based on some assumptions which are difficult to verify. Finite element modelling (FEM) of chip formation process provides more details on the chip process formation, such as plastic strain, strain rate or stress fields. FEM can be used to improve the analytical models' assumptions. There is still a wide dispersion of formulations and numerical parameters adopted in order to obtain accurate results in numerical models. In the Lagrangian approach, it is of crucial importance to establish realistic criteria for element deletion, allowing chip separation from original workpiece. In the arbitrary Lagrangian Eulerian (ALE) formulation no element deletion is needed. This work is focused in modelization of orthogonal cutting. A comparison between both numerical approaches, Lagrangian and ALE is shown. The effects of geometrical parameters, erosion criterion and cutting speed are evaluated. Comparisons between numerical and theoretical results are performed, and the results obtained from the numerical approach are used as an input of analytical model, improving its accuracy.
International Journal of Machining and Machinability of Materials, 2008
Several phenomena are involved in residual stresses generation: mechanical effects, thermal effec... more Several phenomena are involved in residual stresses generation: mechanical effects, thermal effects, microstructure modifications and/or a combination of the previous mechanisms. A lot of experimental investigations have shown the influence of machining parameters on the distribution of residual stresses but only few works have tried to model the fundamental phenomena. Past works tried to model the chip removal process by means of finite element software. Such models are very limited to predict accurately the residual stresses profiles in very narrow affected layers (some micrometers). The idea presented in this paper consists in disconnecting the chip formation process and the modelling of the mechanisms leading to the residual stresses. This approach needs to quantify the thermomechanical loads induced by the cutting tool onto the machined surface. Secondly, a finite-element model simulates the application and the movement of this thermomechanical load on to the machined surface so as to predict the residual stresses induced.
The rolling contact fatigue is a major problem in mechanical systems submitted to very high conta... more The rolling contact fatigue is a major problem in mechanical systems submitted to very high contact pressure. Sintered steels are often used to build camshaft so as to save weight and decrease cost production. However, the porosity of sintered steels may worsen the resistance to rolling contact fatigue. Previous investigations have already shown the importance of the surface hardness and its density in the fatigue resistance of sintered steel. The objective of this paper is to investigate, by a numerical approach, the influence of various material parameters, such as work-hardening nature, yield stress, on the stress near porosities during a rolling contact. Residual tensile stresses due to plastic strain near porosities have been particularly revealed after a sliding sequence, which could explain the crack's propagation observed experimentally on camshafts. It is shown that the crack initiation can be explained using Dang Van fatigue criterion. The opening and the propagation of the crack are then discussed with the help of the fracture mechanics of brittle material. The crack's propagation observed experimentally is then discussed.
We built an experimental device able to record both luminance and temperature of a sample surface... more We built an experimental device able to record both luminance and temperature of a sample surface without oxidation. We used this device to extract an emissivity curve depending on temperature for the 316L. We used the emissivity curve to calculate temperature fields during turning. We found interesting temperature levels closed to the tool edge.
A material microstructure-level (MML) cutting model based on the crystal plasticity theory is ado... more A material microstructure-level (MML) cutting model based on the crystal plasticity theory is adopted for modeling the material removal by orthogonal cutting of the Titanium alloy Ti-6Al-4V. In this model, the grains are explicitly taken into account, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the machined material. To obtain the material degradation process, the continuum intra-granular damage model and the discrete cohesive zone intergranular damage model have been implemented. Zero thickness cohesive elements are introduced to simulate the bond between grain interfaces. The material model is validated by the simulation of a compression test and results are compared with experimental data from the literature. Simulation results demonstrate the ability of the MML cutting model to capture the influence of the material microstructure, in terms of initial grain orientation angles (GOA), on chip formation and machined surface integrity.
International Journal of Machine Tools and Manufacture, 2010
The quantification of friction coefficient along the tool–workmaterial interface in machining rem... more The quantification of friction coefficient along the tool–workmaterial interface in machining remains an issue in tribology. This paper aims identifying the evolution of friction coefficient for a large range of sliding velocity during the machining of a AISI4140 steel (290HB) with a TiN coated carbide tool. The influence of a straight oil is investigated compared to a dry sliding situation
ABSTRACT This paper overviews some typical tribo-contact characteristics obtained in the turning ... more ABSTRACT This paper overviews some typical tribo-contact characteristics obtained in the turning of the pearlitic-ferritic nodular iron (EN-GJS-500-7 grade with UTS=500 MPa) when using carbide tools coated with single TiAlN and multiple TiC/Ti(C,N)/Al 2 O 3 /TiN layers, as well as silicon nitride Si 3 N 4 based ceramic tools. As a competitor, a P20 uncoated carbide grade was selected. The fundamental process readings include the tool-chip interface temperature, Peclet number, friction coefficient and the tool-chip contact length as functions of cutting parameters. In particular, the measurements of cutting temperature were carried out using conventional tool-work thermocouple method and IR mapping technique. It is concluded based on many process characteristics that multilayer coated and ceramic tools can substantially improve the performance of nodular iron machining.
The positive effect of an appropriate cutting edge geometry on the cutting performance of coated ... more The positive effect of an appropriate cutting edge geometry on the cutting performance of coated tools, has been recorded in several publications . In this context, the tool wedge rounding affects significantly the developed mechanical and thermal loads during the material removal and thus, the cutting performance of the applied tools.
According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutt... more According to most studies dealing with wear, abrasion can be considered on one hand as micro-cutting, leading to material removal (grinding), and on the other hand as micro-ploughing, leading to plastic deformation and lower material removal (abrasive wear). Understanding various flowing transitions around an abrasive particle, under well-established conditions, makes it possible to better control these processes. The aim of the present study is to understand plastic deformation and failure local phenomena induced by an abrasive process. Experimental studies have been carried out on an abrasive process which consists in scratching a soft flat surface (AISI4140 steel) by mean of a turning tool fixed on the periphery of a disc. Regulating angular and feed speeds, successive scratches are expected to study phenomena generated by a single pass of the cutting tool. Scratch topography and forces are measured in order to highlight the influence of the depth of cut and the cutting speed on these parameters and on specific energy.
CIRP Journal of Manufacturing Science and Technology, 2008
A better understanding of friction modeling is required to lead to more realistic finite element ... more A better understanding of friction modeling is required to lead to more realistic finite element models (FEMs) of machining process. This work proposes to evaluate the performance of a new friction model depending on the local sliding velocity, compared to a standard approach considering a constant Coulomb friction coefficient. A finite element model, based on the Arbitrary Lagrangian–Eulerian (ALE) approach,
Most of superfinishing processes are based on the action of abrasive grains scratching the surfac... more Most of superfinishing processes are based on the action of abrasive grains scratching the surface of a workpiece. These processes are known to improve the surface texture but they also modify the surface integrity, and thus the durability of engineering parts. In this paper, the residual stress field induced by the scratch of a single round abrasive grain is investigated by means of an implicit finite element analysis. First, it is shown that the residual stress profile is always modified over a depth of two or three times the contact radius, whatever the mechanical and physical properties. Second, key-parameters having a high influence on the tensile and compressive zone have been identified. They are the contact severity, the friction coefficient and the workpiece hardness. Third, it appears that the residual stress profile is not really affected by the presence of initial homogeneous residual stress field in the material. These results are then used to explain the experimental residual stress fields induced by a belt finishing process and a honing process on a AISI52100 hardened steel. Finally the possibility to design appropriate abrasive tools to improve both surface texture and surface integrity of manufactured parts is discussed.
This chapter presents an analysis of workpiece surface integrity. The definition and material and... more This chapter presents an analysis of workpiece surface integrity. The definition and material and mechanical aspects of surface integrity are discussed.
Chip formation is a high strain rate process studied with analytical and numerical models. Analyt... more Chip formation is a high strain rate process studied with analytical and numerical models. Analytical models have the advantage of a small calculation time, however, they are often based on some assumptions which are difficult to verify. Finite element modelling (FEM) of chip formation process provides more details on the chip process formation, such as plastic strain, strain rate or stress fields. FEM can be used to improve the analytical models' assumptions. There is still a wide dispersion of formulations and numerical parameters adopted in order to obtain accurate results in numerical models. In the Lagrangian approach, it is of crucial importance to establish realistic criteria for element deletion, allowing chip separation from original workpiece. In the arbitrary Lagrangian Eulerian (ALE) formulation no element deletion is needed. This work is focused in modelization of orthogonal cutting. A comparison between both numerical approaches, Lagrangian and ALE is shown. The effects of geometrical parameters, erosion criterion and cutting speed are evaluated. Comparisons between numerical and theoretical results are performed, and the results obtained from the numerical approach are used as an input of analytical model, improving its accuracy.
International Journal of Machining and Machinability of Materials, 2008
Several phenomena are involved in residual stresses generation: mechanical effects, thermal effec... more Several phenomena are involved in residual stresses generation: mechanical effects, thermal effects, microstructure modifications and/or a combination of the previous mechanisms. A lot of experimental investigations have shown the influence of machining parameters on the distribution of residual stresses but only few works have tried to model the fundamental phenomena. Past works tried to model the chip removal process by means of finite element software. Such models are very limited to predict accurately the residual stresses profiles in very narrow affected layers (some micrometers). The idea presented in this paper consists in disconnecting the chip formation process and the modelling of the mechanisms leading to the residual stresses. This approach needs to quantify the thermomechanical loads induced by the cutting tool onto the machined surface. Secondly, a finite-element model simulates the application and the movement of this thermomechanical load on to the machined surface so as to predict the residual stresses induced.
The rolling contact fatigue is a major problem in mechanical systems submitted to very high conta... more The rolling contact fatigue is a major problem in mechanical systems submitted to very high contact pressure. Sintered steels are often used to build camshaft so as to save weight and decrease cost production. However, the porosity of sintered steels may worsen the resistance to rolling contact fatigue. Previous investigations have already shown the importance of the surface hardness and its density in the fatigue resistance of sintered steel. The objective of this paper is to investigate, by a numerical approach, the influence of various material parameters, such as work-hardening nature, yield stress, on the stress near porosities during a rolling contact. Residual tensile stresses due to plastic strain near porosities have been particularly revealed after a sliding sequence, which could explain the crack's propagation observed experimentally on camshafts. It is shown that the crack initiation can be explained using Dang Van fatigue criterion. The opening and the propagation of the crack are then discussed with the help of the fracture mechanics of brittle material. The crack's propagation observed experimentally is then discussed.
We built an experimental device able to record both luminance and temperature of a sample surface... more We built an experimental device able to record both luminance and temperature of a sample surface without oxidation. We used this device to extract an emissivity curve depending on temperature for the 316L. We used the emissivity curve to calculate temperature fields during turning. We found interesting temperature levels closed to the tool edge.
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Papers by Joel RECH