Saint-Étienne, France


Saint-Étienne, France
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Pusavec F.,University of Ljubljana | Hamdi H.,LTDS ENISE | Kopac J.,University of Ljubljana | Jawahir I.S.,University of Kentucky
Journal of Materials Processing Technology | Year: 2011

In machining processes, a major quality related output is integrity of the machined part surface. In machining of difficult-to-cut materials, a drastic decrease in tool-life makes the machining process even more difficult. By considering the broader perspective of the machining system tailored towards sustainable operations, in this work an alternative - cryogenic machining is evaluated for machining performance. The surface integrity characteristics of machined surface as a function of depth have been analyzed for different combinations of cooling/lubrication machining conditions. The residual stresses on the machined surface and sub-surface, surface hardness, and surface roughness are among the significant characteristics studied in this work. The results show that cryogenic machining processes can be implemented to improve all major surface integrity characteristics, thus improving the final product quality level. © 2010 Elsevier B.V. All rights reserved.

Valiorgue F.,LTDS ENISE | Rech J.,LTDS ENISE | Hamdi H.,LTDS ENISE | Gilles P.,AREVA | Bergheau J.M.,LTDS ENISE
International Journal of Machine Tools and Manufacture | Year: 2012

This paper addresses the development of a new methodology predicting residual stresses induced in finish turning of a AISI304L stainless steel. A hybrid approach combining experimental results and a numerical model is applied. The model simulates the residual stresses generation by applying equivalent thermo-mechanical loadings onto the machined surface without modeling the chip removal process, which enables rapid calculation. The shape and the intensity of equivalent thermo-mechanical loadings are identified through experimental measurements. Friction tests enable to model the thermal and mechanical loadings along the toolworkmaterial interface. Orthogonal cutting tests provide thermal and mechanical loadings below the primary and third shear zone. This model has already been presented in several papers, but only in a 2D configuration. The objective of this paper is to transfer this hybrid approach into a 3D configuration, which is closer to a concrete longitudinal turning operation. Based on this new model, the paper aims at investigating the interactions between each revolution. It is shown that around five revolutions are necessary to reach a steady state. Finally numerical results are compared with experimental measurements obtained by X-Ray diffraction. It is shown that residual stresses cannot be considered as homogeneous over the surface due to tools feed. Additionally, the X-Ray beam is much too large to be able to quantify this heterogeneity. Based on average numerical values coherent with average values obtained by X-Ray diffraction, it is shown that the numerical model provides consistent results compared to experimental measurements for a large range of cutting speed and feed. © 2011 Elsevier Ltd All rights reserved.

Valiorgue F.,LTDS ENISE | Rech J.,LTDS ENISE | Hamdi H.,LTDS ENISE | Gilles Ph.,AREVA | Bergheau J.M.,LTDS ENISE
Advanced Materials Research | Year: 2010

Residual stresses are very important for the lifetime of pieces in their mechanisms. These kind of damages are mainly caused by mechanical, thermal, and metallurgical affectations of the machined material. To control these affectations, we need to link the cutting parameters to the residual stress state observed onto the workpiece surface and depth. These connections can be made with analytical works, experimental works or numerical works. In our case, it has been chosen to work with a numerical support in order to observe and understand precisely the phenomenon involved during cutting operation. While this way of study is really popular, we proposed to model the residual stress generation in a original way by keeping aside the chip formation. This new approach presented in a previous paper was simple and only use a 2D model. This first model moves thermo mechanical loadings onto the workpiece surface to recreate the relative motion between the tool and the workpiece. The new 3D model, presented in this paper, is now improved with an original friction law. It underlines the impact of each passage of the tool onto the others. The physical properties are thermo dependant and the flow stress model is based on a Johnson cook behaviour. © (2010) Trans Tech Publications.

Robin V.,AREVA | Gilles P.,AREVA | Bosco B.,AREVA | Mazuy L.,AREVA | Valiorgue F.,LTDS ENISE
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2015

Stress corrosion cracks have been observed on screws made of stainless steels grade 316 after some years of service in Pressurized Water Reactor (PWR) water environment. Grade 316 of stainless steel is not sensitive to corrosion unless it has been sensitized and/or subjected to a complex combination of factors including an important level cold work at the surface and in the bulk of the material. The tightening of the screw induces tensile stresses. This preload cannot explain the Stress Corrosion Cracking (SCC) defect appearing in the transition radius between the screw shank and its head. Thus, the question has been raised of the initial state of the screws after manufacturing. The simulation of the manufacturing processes has been carried out to have a better understanding of manufacturing process consequences on material degradation: solution annealing, cold drawing and machining. The dedicated "hybrid method", specifically set up to simulate finish turning has been applied to obtain stress and strain states close to the surface. This method is detailed in the paper. The manufacturing process of these bolts is likely to induce high strain hardening since they have been cold drawn and then machined. It is suspected that tensile residual stress and cold work play a major role in the initiation of stress corrosion cracking of austenitic stainless steel grade of 316 type in PWR water environment. Simulation chaining method and results are highlighted in the paper with comparison with experiments. The main achievements are: the smaller the screw the less the cold work, the residual stress on the surface is mainly due to machining and the location of crack in the transition radius is well explained. Copyright © 2015 by ASME.

Valiorgue F.,LTDS ENISE | Brosse A.,ESI France | Rech J.,LTDS ENISE | Hamdi H.,LTDS ENISE | Bergheau J.M.,LTDS ENISE
AIP Conference Proceedings | Year: 2010

Material removal operations such as turning or grinding are prone to generate very high temperatures at the tool/chip and tool/workpiece interfaces. These phenomena are involved in studies concerning tools or workpieces, and their estimation is a key point for predicting damages. Temperature elevation is the main cause in workpieces worsening because it generates residual stresses and metallurgical modifications. It is also linked to the tools wear because of the thermal fatigue phenomena and the thermally activated diffusion process. In this paper, a first attempt to measure the temperature fields during 316L orthogonal cutting and 100Cr6 grinding is presented and can be divided in three parts. In the first part the physics of temperature measurement using infrared thermography are presented. Then, the calibration of the infrared camera is realized and allows to obtain of the emissivity curves of 316L and 100Cr6 steels. To do so, an experimental device has been set up to reproduce the luminance recording conditions encountered during the machining operations. The last step is the computation of all the experimental data to obtain the temperature fields from the recorded luminance and the 316L and 100Cr6 emissivity curve. At last, temperature level measured is compared to those presented in the bibliography. © 2010 American Institute of Physics.

Valiorgue F.,LTDS ENISE | Rech J.,LTDS ENISE | Bergheau J.M.,LTDS ENISE
Materiaux et Techniques | Year: 2010

Research presented in this paper aims to link machining parameters to residual stress state and helps understanding mechanisms responsible of machined surface properties modifications. The first presented works are based on an experimental campaign. They reproduce the finishing turning operation of 304L and allow observing the residual stress state evolution at the work piece surface and for an affected depth of 0.2 mm for such processes. Then, the finishing turning operation is simulated numerically in order to realize the same sensitivity study to cutting parameters. This simulation is based on an hybrid approach mixing experimental data and numerical simulation. This method allows getting round the classical difficulties of turning simulation by applying equivalent thermo mechanical loadings onto the work piece surface without modeling the material separation phenomena. Moreover the numerical model uses an hardening law taking into account dynamic recrystallization phenomena. © 2010 EDP Sciences.

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