Hédi Hamdi

Characterization of abrasive grain’s behavior and wear mechanisms

Abstract Grinding is a finishing process largely used in motor industry, aeronautics, space industry and precision cutting tool manufacturers. The grinding process can be summarized by the action of a grinding wheel on a workpiece. The wheel is constituted by abrasive grains. Thus grinding is in fact the action of grains on the workpiece. The grain behavior changes according to numerous parameters (geometry, mechanical characteristics, wear mechanisms). In some cases abrasive wear is observed while micro-cutting is obtained in some other cases. In this paper two useful and complementary experimental approaches for the interface physics understanding is presented. The study of the cutting power is carried out using a high-speed scratch test device in order to understand the grain behavior and the wear mechanisms for several wheel surface speeds. In this paper an approach for the specific abrasion energy computation is also presented.

OPTIMIZATION OF THE CUTTING EDGE GEOMETRY OF COATED CARBIDE TOOLS IN DRY TURNING OF STEELS USING A FINITE ELEMENT ANALYSIS

This paper investigates the effects of edge radius of a round-edge coated carbide tool on chip formation, cutting forces, and tool stresses in orthogonal cutting of an alloy steel 42CrMo4 (AISI 4142H). A comprehensive experimental study by end turning of thin-walled tubes is conducted, using advanced coated tools with well-defined cutting edge radii ranging from 5 to 68 microns. In parallel, 2-D finite element cutting simulations based on Lagrangian thermo-viscoplastic formulation are used to predict the cutting temperatures and tool-stress distributions within the tool coating and substrate. The results obtained from this study provide a fundamental understanding of the cutting mechanics for the coated carbide tool used, and can assist in the optimization of tool edge design for more complex geometries, such as chamfered edge. Specifically, the results obtained from the experiments and simulations of this study demonstrated that finite element analysis can significantly help in optimizing the design of coated cutting tools through the prediction of tool stresses and temperatures, especially within the coating layer.

Workpiece Surface Integrity

This chapter presents an analysis of workpiece surface integrity. The definition and material and mechanical aspects of surface integrity are discussed.

Numerical simulation and analytical modelling of ploughing and elastic phenomena during machining processes

The present work deals with the presentation of an analytical methodology allowing the modelling of chip formation. For that, a ‘phenomena split method’, based on assuming that the material removal is the contribution of three phenomena, ploughing, spring back and ‘pure cut’, is developed. In particular, the elaboration of analytical sub-model of ploughing and spring back is presented in detail. FEM simulations and experimental data concerning temperatures and forces evolution are exploited to calibrate and verify the proposed analytical model dealing with ‘ploughing and spring back’. It is possible with this model to understand the physics of chip formation, and model lateral burrs and elastic phenomena under the tool and at the rear (spring back). The cutting radius contribution is analysed, which is important to the understanding of the tool wear and the residual stresses in the finished work-piece.

A numerical study of phase transformation during grinding

Since grinding is often the last process of a manufactured part, caution has to be taken in order to ensure the integrity of the ground surface. Many authors have shown that in a few cases temperature can be very high and therefore can induce phase transformations. Thus, the best way to ensure the quality of the ground surfaces is to predict the apparition of these phases. This paper shows that numerical simulations of phases during grinding are possible and they gives good predictions of phases. An example using AISI 52100 bearing steel material for the workpiece and a triangular heat flux model is presented. The model of simulation is explained and results are detailed.

Emissivity calibration for temperature measurement using infrared thermography in orthogonal cutting of 316L and 100Cr6 grinding

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.

Influence of Cutting Edge Radius of Coated Tool in Orthogonal Cutting of Alloy Steel

This paper investigates the effects of edge radius of a round‐edge PVD coated tool upon chip formation, cutting forces, and tool stresses in orthogonal cutting of an alloy steel 42CrMo4 (AISI 4142H). A comprehensive experimental approach based on end turning of thin‐walled tubes is conducted using advanced coated tools with well‐defined cutting edge radii ranging from 9 to 28 microns. In parallel, 2‐D finite element cutting simulations based on Lagrangian thermo‐viscoplastic formulation are used to analyze cutting temperature and tool stress distributions within the coating layer and tool substrate. The results obtained from this study provide a fundamental understanding of the cutting mechanics for the coated tool used and can assist in the optimization of tool edge design for more complex geometries such as chamfered edge. Particularly, the results obtained from the experiments and simulations of this study have underlined that there exists an optimum cutting edge radius that minimizes tool stresses, es...

Tool design effect on microlubrication spray efficiency in milling using inner channels

This study consisted in investigating parameters that significantly influence the spray efficiency of minimum quantity lubrication in a milling tool with inner channels. An initial experimental approach was used to estimate the oil mist consumption and outlet particle velocities with different inlet pressures, for different shapes of inner channels, without rotation (static part). An experimental versus simulation comparison was undertaken between outlet velocities as a function of inlet pressure. The Reynolds-averaged Navier–Stokes model with the Lagrangian multiphase models was validated by comparing experimental and numerical outlet velocities for different inlet pressures. A numerical rotating tool with inner channels was used with the validated model in the second numerical simulation to analyze the influences of inlet conditions (inlet pressure) based on the tool shape and the rotation velocity, in a dynamic approach. The main objective of the oil mist is to reach the cutting edge (qualifying the minimum quantity lubrication spray efficiency) depending on the inlet conditions (inlet pressures) and the machining configurations (rotation velocities) by analyzing the streamlines of the oil mist particles. The study pointed out the tool design effect combined with its rotation velocity on the oil mist capability to reach the cutting edge. This study offered a trend of parameter sets to provide correct inlet parameters based on machining configurations. At high rotation speed, the inlet pressures needed to be high enough to counter the aerodynamic effects occurred by the tool design.

Numerical and experimental study of residual stress induced by machining process

Machining processes are widely used in different industries to cut different engineering parts. Usually, optimisation of these processes is made by experimental or numerical simulations. In particular, surface integrity modelling of the final piece is very important for the fatigue behaviour. In this paper modelling of the residual stresses in the fresh workpiece produced is studied. In particular finite element modelling using ABAQUS Explicit is employed in order to simulate chip formation and an implicit static calculation is made to have spring back in the workpiece after cooling. Orthogonal cutting process is chosen because it is simple and practice and different calculations method and numerical options are employed in order to replicate as well as possible physics during the process. In particular it is taken into account the cutting radius of the tool and the boundaries conditions of the workpiece. The setting of the numerical model is executed regarding the experimental conditions used. In the experimental section a complete study of the influence of the residual stresses by process variables (feed, cutting speed) is presented.

Analytical and numerical study of the separation line between chip and work-piece during cutting processes

In manufacturing industry, a high interest in analytical methods are usually researched because there are very practicable to use but those methods do not take into account all the aspects of the contact between the work material and the tool. In particular, ploughing and spring back are usually not considered, which is pertinent for small cutting edge radius but not for bigger ones (used tools). In reality, a part of the work-piece becomes chip and another part slides under the tool (elastic phenomena) and laterally (burrs). A separation line appears between those phenomena and the material under this surface stays in the work-piece during tool action. In this zone, elastic and plastic aspects induce temperature and spring back at the rear of the tool, which is important for residual stresses in the work-piece after cooling. In this paper, a simple analytical formulation is proposed in order to model the separation surface value. This analytical approach is fitted with 2D and 3D numerical simulations and verified with experimental forces and burr measurement.