Tarek Mabrouki

Mathematical modeling for turning on AISI 420 stainless steel using surface response methodology

In this study, an attempt has been made to statistically model the relationship between cutting parameters (speed, feed rate and depth of cut), cutting force components (Fx, Fy and Fz) and workpiece absolute surface roughness (Ra). The machining case of a martensitic stainless steel (AISI 420) is considered in a common turning process by means of a chemical vapor deposition–coated carbide tool. A full-factorial design (43) is adopted in order to analyze obtained experimental results via both analysis of variance and response surface methodology techniques. The optimum cutting conditions are achieved using mutually response surface methodology and desirability function approaches while the model adequacy is checked from residual values. The results indicated that the depth of cut is the dominant factor affecting (Fx: 86%, Fy: 58% and Fz: 81%), whereas feed rate is found to be the utmost factor influencing surface roughness behavior (Ra: 81%). In addition, a good agreement between the predicted and measured cutting force components and surface roughness was observed. The results are also validated experimentally by determining errors (Fx: 6.51%, Fy: 4.36%, Fz: 3.59% and Ra: 5.12%). Finally, the ranges for optimal cutting conditions are projected for serial industrial production.

EXPERIMENTAL INVESTIGATION AND PERFORMANCE ANALYSES OF CBN INSERT IN HARD TURNING OF COLD WORK TOOL STEEL (D3)

Long-term wear tests on the CBN tool behaviour during hard turning of AISI D3 (60 HRC) have been investigated. The evolution of surface roughness, cutting forces and temperature has been studied according to the cutting parameters and tool wear. Results show that CBN is resistant to wear despite of aggressiveness of AISI D3 steel. A great part of heat generated is mainly dissipated throughout the chip; at a cutting speed of 320 m/min the chip temperature is found to be 14 times higher than that recorded in the workpiece. The cutting speed range of 90 to 240 m/min has been found suitable to cut this material. The former speed range is appropriate to respect the cutting constraints, whereas beyond 240 m/min a drastic increase in tool wear occurs, causing a remarkable drop in tool life. Roughness measurements reveal a dependence on CBN tool wear. However, although the wear rises up to the allowable flank wear of value 0.3 mm, roughness Ra remains around 1.0 μm. The feed rate remains the most affecting factor on the roughness values. The proposed statistical models are based on the response surface methodology correlating the cutting parameters together with roughness, cutting forces and tool life.

Finite-element-based hybrid dynamic cutting model for aluminium alloy milling

Abstract The present contribution deals with milling tool vibration effects on chip morphology, cutting force, and cut surface topology. The study concerns an orthogonal down-cut peripheral milling case for aeronautic aluminium alloy A2024-T351. A finite-element-based hybrid dynamic cutting model (HDC model) is proposed to predict the chip morphology under dynamic cutting conditions. The latter is conceived with commercial software ABAQUS®/EXPLICIT and combines the stiffness of a high-speed milling spindle system (tool, toolholder, and rotor) with the chip formation process. A qualitative parametric study with various stiffness and damping coefficient values for a high-speed milling spindle system has been performed. The results concerning chip morphology and cutting force are compared with experimental data, while the surface profiles are compared with those obtained by considering a perfectly rigid spindle system. As expected, a less rigid undamped milling system generates higher-amplitude tool vibrations during milling. In this situation, the temperature rises at the tool—workpiece interface, enhancing material softening. This softening promotes chip segmentation and increases waviness of the machined surface profile. The numerical results show that higher values of cutting speed and uncut chip thickness are associated with higher vibration amplitudes.

Three-dimensional finite element modeling of rough to finish down-cut milling of an aluminum alloy

This contribution deals with a computational investigation highlighting the effects of cutting speed and depth of cut on chip morphology and surface finish for down-cut milling case. The global aim concerns the comprehension of multiphysical phenomena accompanying chip formation in rough, semifinish, and finish cutting operations, exploiting a three-dimensional finite element model. Numerical work has been performed in two phases. In the first phase, a three-dimensional model for rough cut operation has been validated with the experimental results, including chip morphology and cutting force evolution for an aerospace grade aluminum alloy A2024-T351. In the second phase, the model has been extended to semifinish and finish three-dimensional cutting operations. The numerical findings show that as depth of cut decreases (toward finish cutting), spatial displacement of workpiece nodes along the depth of cut increases. This represents an increase/extension in the percentage of volume undergoing shear deformation, resulting in higher dissipation of inelastic energy, hence contributing to size effect in finish cutting operation. The results also depict that material strain rate hardening enhances the material strength at higher cutting speeds. These material strengthening phenomena help to generate a smooth continuous chip morphology and better surface texture in high-speed finishing operations. The study highlights the significance of three-dimensional numerical modeling to better understand the chip formation process in semifinish and finish machining operations, regardless of the immense effort in computational time.

New Thermal Issues on the Modelling of Tool-Workpiece Interaction: Application to Dry Cutting of AISI 1045 Steel

The present work proposes to enhance the thermal interface denition in Finite Element (FE) simulations of machining. A user subroutine has been developed in Abaqus/Explicit

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.

RMS-based optimisation of surface roughness when turning AISI 420 stainless steel

The aim of this investigation is to determine the correlation between the cutting conditions such as cutting speed, feed rate, and depth of cut; and surface roughness parameters (Ra, Rq, Rt, Rp, and R3z). The case of turning operation of martensitic stainless steel AISI 420 using CVD coated carbide tool is studied. Full factorial design (43) was adopted. Statistical analysis ANOVA and response surface methodology (RSM) was used to develop quadratic regression models and to determine optimum cutting conditions. It was found that the feed rate (f) is the highest factor influenced the surface roughness parameters when compared with speed and depth of cut. Moreover, a good agreement was observed between the predicted and the experimental surface roughness criteria. The use of lower cutting speed, lower feed rate, and lower depth of cut ensures minimum surface roughness variations.

Turning modeling and simulation of an aerospace grade aluminum alloy using two-dimensional and three-dimensional finite element method

This article presents the development of two-dimensional and three-dimensional finite element–based turning models, for better prediction of chip morphology and machined surface topology. Capabilities of a commercial finite element code Abaqus®/Explicit have been exploited to perform coupled temperature–displacement simulations of an aerospace grade aluminum alloy A2024-T351 machining. The findings show that two-dimensional cutting models predict chip morphologies and machined surface textures on a plane section (with unit thickness) passing through the center of workpiece width, and not at the edges. The contribution highlights the importance of three-dimensional machining models for a close corroboration of experimental and numerical results. Three-dimensional cutting simulations show that a small percentage of material volume flows toward workpiece edges (out of plane deformation), augmenting the contact pressures at the edges of tool rake face–workpiece interface. This enhances the burr formation process. Computational results concerning chip morphologies and cutting forces were found in good correlation with experimental ones. In the final part of the article, numerical simulation results with a modified version of a particular turning tool have been discussed. It has been found that the proposed geometry of the tool is helpful in reducing burr formation as well as cutting force amplitude during initial contact of cutting tool with the workpiece material.

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.

Numerical investigations of optimum turning parameters—AA2024-T351 aluminum alloy

ABSTRACT Aerospace aluminum alloys have gained the prime significance due to their excellent machining characteristics. Numerous experimental and numerical studies have been conducted to establish the optimum cutting parameters of these alloys. In the numerical cutting models, the authenticity of computational results is suspected particularly because of the complex interaction at tool–chip interface, which involves a high material strain rate and thermal processes. The fidelity of cutting simulation results is appraised by a parametric sensitivity analysis and actual experimentation. In this research, the orthogonal turning of AA2024-T351 aluminum is simulated in Abaqus/Explicit by using a thermoviscoplastic damage model and Coulomb friction model for the contact interfaces. A parametric sensitivity analysis is performed to comprehend the chip morphology, tool–chip interface temperature, reaction force, and strain. Different simulations are performed with varied cutting speeds (200, 400, 600, and 800 m/min), rake angles (5°, 10°, 14.8°, 17.5°), feeds (0.3, 0.4 mm), and friction coefficients (0.1, 0.15). It is observed that an increased rake angle decreases the cutting force and increases tool–chip interface temperature. Similarly, the cutting depth has prominent effect on chip–tool interface temperature as compared to the friction. The computational results are found in close approximation with the published experimental data of AA2024-T351.