Papers by Author: Hédi Hamdi

Abstract: Grinding is one of the important metal cutting processes used extensively in the finishing operation to get components of desired shape, size and accuracy. A perfect control of this process is thus necessary to ensure correct final part and limit damage. Lifetime of machined part depends on the surface integrity especially in terms of microstructure changes and residual stresses. The best way to control those factors is to study the way they appear. Thus, it is important to set up experimentation to get the maximum informations during the grinding process, with in situ measurements and after, on the final surface. On one side, forces and power were measured, on the other side temperature measurements were conducted using an infrared digital video camera. In fact the grinding temperature and the temperature gradients are the major factors which influence surface integrity. Experimentations show white layers in the near ground surface and the measured temperature is higher than the austenitizing temperature. The workpiece subsurface was then characterized by observing and measuring microstructural changes of surface layer. Numerical simulations, using SYSWELD software are performed to formalize what is modeled. Metallurgical transformation is then taken into account in the grinding FE model. The comparison showed that numerical model is capable to accurately predict the white layer thickness and residual stresses values.

Abstract: Grinding process is an energy intensive process in the sense that, it requires a larger amount of energy per unit of volume of material removal compared to other metal cutting processes. In this case, effects on the ground workpiece in terms of induced residual stresses and metallurgical changes due to heat generated play an important role on the lifetime of parts in their mechanism. In order to investigate effects on the workpiece during external cylindrical grinding process, a new analytical approach is firstly developed to model the action of the grinding wheel as a heat flux, which moves along the workpiece surface. The value and the shape of the heat flux entering the workpiece are directly identified. Based on the established model, numerical simulations are performed to predict temperature, cooling and its effects on residual stress distribution in the ground near surface.

Abstract: The state of the surface, whatever the metal or alloy used is of paramount importance. Hand disc grinding operation is difficult to master in terms of results on the surface due to its manual nature. From this, comes the great importance to the mastery of the consequences induced by this abrasive process. A previous experimental study on hand disc grinding revealed several consequences on the surface integrity in terms of residual stresses, micro-hardness, hardening of the material etc. Numerical simulation can be a good way to prevent manufacturers of very time consuming experiments for the prediction of residual stresses due to grinding. The purpose of this study is to predict the consequences in terms of induced temperature fields and the state of residual stresses. The action of the disk-grinding wheel on the Workpiece is modeled by a moving heat flux on top of the part surface. All the difficulties lie in the quantification of the heat flux and more precisely in the heat flux density that gives the way the thermal load is distributed in the contact disk grinding/workpiece area. In this paper, an original analytical model for the determination of the heat flux density has been developed. For each step, the thermo-mechanical calculation is performed. Finally, the distribution of temperature and residual stresses will be carried out with the FE software SYSWELD 2010®.

Abstract: The present work deals with the presentation of analytical methodology allowing the modeling of chip formation. For that a “decomposition approach”, based on assuming that the material removal is the summation of two contributions, ploughing and pure cut was adopted. Moreover, this analytical model was calibrated by a finite element model and experimental data in terms of temperature and applied forces evolutions. The global aim is to propose to the industrial community, an efficient rapid-execution analytical model concerning the material removal in the case of an orthogonal cutting process.

Abstract: Grinding cup wheel is often used in the case of hand grinding which allows an important material removal rate but with secondary concern of surface integrity. Integrity is strongly affected by the process and consequently influences the surface behaviour in terms of resistivity to stress corrosion and crack initiation. This operation is difficult to master in terms of results on the surface and subsurface due to its manual nature. The paper presents results of an experimental study to investigate the residual stresses induced by this hand grinding process.