Modélisation de l’influence de la profondeur de coupe en micro-coupe orthogonale

Bien que les principes de base du micro-fraisage soient identiques à ceux du macro-fraisage, le phénomène de microcoupe n’est pas une réduction directe de celui rencontré en macro-coupe. La formation du copeau implique le phénomène d’épaisseur minimale de copeau et la structure granulaire du matériau ne peut plus être négligée. Dans le but d’investiguer le phénomène d’épaisseur minimale de copeau, l’influence de la profondeur de coupe sur la formation du copeau en micro-coupe est étudiée dans cet article à l’aide d’un modèle développé avec la méthode aux éléments finis. Ce modèle de coupe orthogonale a été mis au point à l’aide du logiciel commercial ABAQUS/Explicit v6.7. et est basé sur une formulation lagrangienne classique. Les résultats obtenus avec ce modèle sont ensuite présentés et comparés à des résultats issus de la littérature, avant d’aborder les perspectives d’évolution du modèle

Green Ceramic Machining: Influence of the Cutting Speed and the Binder Percentage on the Y-TZP Behavior

The demand for inert bioceramics is always increasing in the dental field. Yttrium oxide tetragonal zirconia polycrystals (Y-TZP) are oxide ceramics which are currently used because of their interesting mechanical properties due to a toughening transformation. Industrially speaking, machining of the ceramic before sintering (green body) is very common because it allows a better productivity and it reduces crack probability during the sintering process. The goal of this paper is to determine the behavior of green ceramic during the machining operation. This study is carried out on several blanks with different binder percentages. The specific cutting energy (SCE) and the surface quality (Ra and Rz) are determined for several cutting speeds. The SCE follows a logarithmic evolution when the cutting speed increases. Despite this increase, the Ra are relatively stable whatever the cutting speed and the binder percentage. At a low cutting speed, a higher Rz value is observed caused by pullout of material. The increase of cutting speed allows to stabilize the Rz value whatever the binder percentage. This study shows that the green ceramic has a pseudo-plastic behavior whose machinability depends mainly on the interaction between the material and the cutting edge of the tool, so unlike pre-sintered ceramic or metallic part cutting speed has a low influence on the quality of the machined part

An Analytic Approach to the Cox Proportional Hazards Model for Estimating the Lifespan of Cutting Tools

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Influence of Constitutive Models and the Choice of the Parameters on FE Simulation of Ti6Al4V Orthogonal Cutting Process for Different Uncut Chip Thicknesses

The constitutive model and its pertinent set of parameters are important input data in finite element modeling to define the behavior of Ti6Al4V during machining process. The present work focusses on comparing different constitutive models and the parameters sets available in literatures and investigating the quality of the predictions when varying uncut chip thickness (40 µm, 60 µm, 100 µm and 280 µm). In addition, temperature-dependent strain hardening factor along with strain softening phenomenon based reconstructed material model is proposed. The results from the numerical simulations are compared with experimental results available in literature. The comparison shows that the force values are highly influenced by constitutive models and the choice of parameters sets, whereas the chip morphologies are mainly influenced by the uncut chip thickness and constitutive models. This work justifies the need for an appropriate set of parameters and constitutive model that replicate the machining behavior of Ti6Al4V alloy for different cutting conditions

Comparison of residual stresses obtained by the crack compliance method for parts produced by different metal additive manufacturing techniques and after friction stir processing

Metal additive manufacturing (AM) techniques are promising to build complex components in automotive, aerospace and biomedical industries. However, as built AM parts generally present residual stresses which may degrade the fatigue resistance of the material. Although the AM techniques have been substantially studied, few data about the residual stress level and distribution are available in literature. This paper presents residual stress measurements and analysis on the metal powder bed AM parts using the crack compliance method. Both electron beam melting (EBM) and selective laser melting (SLM) processes are investigated for two manufactured alloys, i.e., Ti6Al4V and AlSi10Mg. It is found that: (i) the EBM process results in negligible residual stresses; (ii) the SLM leads to compressive stresses in the middle, accompanied by tensile stresses at the bottom and the top of the built part; (iii) preheating the build platform in the SLM process significantly reduces the residual stresses and effectively mitigates the porosity. Moreover, we show that post-treatment by friction stir processing inverts the residual stress distribution compared to the SLM process while significantly reducing the porosity

A Systematic Method for Assessing the Machine Performance of Material Extrusion Printers

The performance assessment of additive manufacturing (AM) printers is still a challenge since no dedicated standard exists. This paper proposes a systematic method for evaluating the dimensional and geometrical performance of such machines using the concept of machine performance. The method was applied to an Ultimaker 2+ printer producing parts with polylactic acid (PLA). The X and Y axes of the printer were the most performant and led to narrower potential and real tolerance intervals than the Z axis. The proposed systematic framework can be used to assess the performance of any material extrusion printer and its achievable tolerance intervals