Olivier Calonne

Analysis of Residual Stress Induced by Hand Grinding Process

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.

Numerical Study of Hand Disc Grinding of Ni-Base Alloy 690

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®.

Influence of Hand Disc Grinding on Surface Integrity of Nickel-Based Alloys: Numerical Approach

For complex part geometry, hand grinding is one of finishing and super finishing process the most used in mechanical industry. Surface integrity is today one major concern for industrials. The surface integrity is defined by a set of important characteristics of ground surface as surface geometric parameters (roughness, …), mechanical behaviour of the subsurface (hardness, residual stress, …) and structural changes of the material in the near surface. High heat and pressure, high strain and strain rate observed during hand grinding process, strongly influence surface integrity. Therefore, the surface behaviour, in terms of resistance to corrosion and crack initiation depends on how the process was conducted. The purpose of this study is to understand the effects of thermal and mechanical plastic deformation induced on the surface of components. The action of the disc-grinding wheel on the workpiece is modelled by a moving heat flux on the surface. The challenge is to be able to find the shape and intensity of thermomechanical load entering the workpiece in accordance with the hand disc grinding process and taking into account specific parameters of the process. In a first part, a mechanical description of the action of the disc-wheel on the surface is proposed in order to develop an analytic formulation of the grinding power and the heat flux density. They are function of the disc-grinding wheel velocity, the feed speed and the applied forces. This expression is then used in a finite element modelling to perform thermomechanical simulations of the hand disc-grinding process. In a first stage, heating and cooling are computed. They give maximum temperature reached, temperature gradients and cooling kinematic. In a second stage, thermomechanical computation is conducted in order to compute residual stresses induced by this abrasion process. A discussion based on experimental results obtained by XRD method is then proposed and some local explanation are given on the way the material structure has changed leading to a structural hardening in the 50 first microns beneath the ground surface.Copyright