Mohammed Nouari

Active vibration control of composite plate with optimal placement of piezoelectric patches

ABSTRACT The active vibration control of a composite plate using discrete piezoelectric patches has been investigated. Based on first order shear deformation theory, a finite element model with the contributions of piezoelectric sensor and actuator patches to the mass and stiffness of the plate was used to derive the state space equation. A global optimization based on LQR performance is developed to find the optimal location of the piezoelectric patches. Genetic algorithm is adopted and implemented to evaluate the optimal configuration. The piezoelectric actuator provides a damping effect on the composite plate by means of LQR control algorithm. A correlation between the patches number and the closed loop damping coefficient is established.

Mechanistic approach applied to the gear hobbing process

Abstract This paper proposes a new approach to simulate 3D cutting force components generated during the finishing hobbing process of larger spur gear parts. This new approach combines three modelling steps. In the first step, the profile of the undeformed chip created for every hob’s tooth is calculated using the geometrical simulation of the gear hobbing process. In the second step, the calibration of the specific force coefficients (cutting and edge effects) is obtained from a 2D numerical model. In the final step, a mechanistic model is applied to the hobbing process. The results of this investigation are presented in terms of the analysis of the undeformed chip characteristics and the evolution of the hobbing cutting forces.

A study of the BTA deep drilling process through a quantitative and qualitative analysis of the chip formation process

This paper deals with the analysis of the cutting process in the BTA (Boring Trepanning Association) deep hole drilling. The process is a major technique of drilling when the machining with a conventional tool is not possible. Poor training and/or poor chips evacuation often cause a temperature rise and excessive wear detrimental to the tool life and the dimensional stability of machined parts. The process is relatively not explored enough, because it is difficult to instrument experimental tests (measurement of forces acting at each insert of the BTA drilling tool, temperature at each cutting edge…). Moreover, the thermomechanical phenomena related to the cut are localized at the end of the BTA drilling head and confined in a zone inaccessible to the observation. Hence, a study of this process based on a scientific approach has been proposed. The evaluation of the chips morphology has been performed. Indeed, it is a good indicator of the stability of the cutting process and it can therefore be a serious help in the selection of optimal cutting parameters. Adequate parameters are proposed to highlight the impact of cutting conditions on the cutting process. Macro and microscopic observations of generated chips under several cutting conditions are performed. Fragmentation and segmentation of chips are some examples of analysed phenomena. In this sense, experimental tests have been conducted. The chips have been sorted according to their morphology and identified according to their origin and then proposed physical parameters are assessed. The quantitative and qualitative analysis of chips allowed identifying the impact of the cutting speed and feed rate on the cutting process.

Numerical Simulation of Incremental Sheet Forming by Simplified Approach

The Incremental Sheet Forming (ISF) is a process, which can transform a flat metal sheet in a 3D complex part using a hemispherical tool. The final geometry of the product is obtained by the relative movement between this tool and the blank. The main advantage of that process is that the cost of the tool is very low compared to deep drawing with rigid tools. The main disadvantage is the very low velocity of the tool and thus the large amount of time to form the part. Classical contact algorithms give good agreement with experimental results, but are time consuming. A Simplified Approach for the contact management between the tool and the blank in ISF is presented here. The general principle of this approach is to imposed displacement of the nodes in contact with the tool at a given position. On a benchmark part, the CPU time of the present Simplified Approach is significantly reduced compared with a classical simulation performed with Abaqus implicit.

Analysis of coating performances in machining titanium alloys for aerospace applications

The current study emphasises the role of coating materials in enhancing the wear resistance of the cutting tool and improving the tool-chip contact. The wear mechanisms have been investigated through a series of cutting experiments performed on an instrumented planer machine. Machining tests were conducted on the usual Ti-6Al-4V alloy (workpiece) and cemented carbide tools. Four new coatings were especially designed for the study: 1diamond (thin layer, about 2 to 3 μm) 2diamond+TiB2+CrN/DLC (diamond like carbon, about 3, 5 μm) 3diamond (thick layer, 6 μm) 4TiB2+CrN/DLC (3 μm). The performance of each coating material was analysed and compared in one hand to the uncoated carbide tools and on the other hand to the CBN reinforced carbide tools in terms of cutting forces and tool wear mechanisms.

Some cases of machining large-scale parts: Characterization and modelling of heavy turning, deep drilling and broaching

Machining large-scale parts involves extreme loading at the cutting zone. This paper presents an overview of some cases of machining large-scale parts: heavy turning, deep drilling and broaching processes. It focuses on experimental characterization and modelling methods of these processes. Observed phenomena and/or measured cutting forces are reported. The paper also discusses the predictive ability of the proposed models to reproduce experimental data.

A thermomechanical analysis of sticking-sliding zones at the tool-chip interface in dry high-speed machining of aluminium alloy A2024–T351: A hybrid Analytical-Fe model

In high speed dry machining of aluminium alloy (A2024-T351), the tribological conditions at the tool-chip interface strongly affect the thermomechanical process of chip formation, the tool wear and the surface integrity. In order to contribute to the understanding of the effect of friction conditions, a hybrid Analytical-FE model is presented. The transient nonlinear thermal problem in the tool-chip-workpiece system is solved by using a Petrov-Galerkin finite element model. To illustrate the model results, the relationship between the local friction coefficient, in the sliding zone, and the apparent friction coefficient, which takes into account the whole tool-chip contact, is presented.

New stochastic wear law to predict the abrasive flank wear and tool life in machining process

Tool wear and tool failure are some of the main critical problems in industrial manufacturing fields since they affect the quality of the machined part and raise production costs. Improving our knowledge of wear mechanisms and capabilities of wear prediction are therefore of great importance in the machining process. Abrasion, adhesion and diffusion are usually identified as the three main wear modes at the tool–chip and the tool–workpiece interfaces. From an experimental point of view, the analysis of mechanisms that govern the wear process is still difficult to conduct. The objective of this research work is then to develop a wear modeling focusing on the abrasive wear mode at the tool–workpiece interface. This wear phenomenon is assumed to be closely linked to the microstructure’s material workpiece and caused by hard conical particles trapped into the contact between the cutting tool and the workpiece. The proposed model is based on an analytical approach including a statistical description governing the distribution of particles with conical shape embedded in the contact area. The volume of the removed material per unit time was chosen in this study as the main parameter to describe abrasive flank wear mode. A parameter V b 0 was introduced as the sudden flank wear which occurs in the former few cutting instants. A parametric study has been conducted that highlights the slight effect of the adopted value. The effect of the cutting conditions (cutting speed, pressure) at the tool flank that has a major influence on the wear rate, was deduced from a numerical study on the 42CrMo4/WC-Co tool–workpiece combination. Finally, a wear criterion has been proposed to estimate the tool life in order to address the concerns of industries.

Analysis of Physical Cutting Mechanisms and Their Effects on the Tool Wear and Chip Formation Process When Machining Aeronautical Titanium Alloys: Ti-6Al-4V and Ti-55531

The current research deals with the analysis of physical cutting mechanisms involved during the machining process of titanium alloys: Ti-6Al-4V and Ti-55531. The objective is to understand the effect of all cutting parameters on the tool wear behavior and stability of the cutting process. The investigations have been focused on the mechanisms of chip formation and their interaction with tool wear. At the microstructure scale, the analysis confirms the intense deformation of the machined surface and shows a texture modification. As the cutting speed increases, cutting forces and temperature show different progressions depending on the considered microstructure Ti-6Al-4V or Ti-55531 alloy. Results show for both materials that the wear process is facilitated by the high cutting temperature and the generation of high stresses. The analysis at the chip-tool interface of friction and contact nature (sliding or sticking contact) shows that the machining Ti-55531 often exhibits an abrasion wear process on the tool surface, while the adhesion and diffusion modes followed by coating delamination process are the main wear modes when machining the usual Ti-6Al-4V alloy. Moreover, the proposed study describe the real effect on machining of the tool geometry, coating and lubrication. Finally, the investigations allow to identify some ways to improve the machinability of these alloys, particularly the Ti-55531 alloy.

Experimental Study on Tool Wear when Machining Super Titanium Alloys: Ti6Al4V and Ti-555

To understand the effect of the workpiece microstructure on the tool wear behavior, anexperimental investigation was conducted on machining two different microstructures of supertitanium alloys: Ti-6Al-4V and Ti-555. The analysis of tool-chip interface parameters such asfriction, heat flux and temperature rise and the evolution of the workpiece microstructure underdifferent cutting conditions have been discussed. As cutting speed and feed rate increase, the meancutting forces and temperature show different progressions depending on the consideredmicrostructure. Results show that wear modes for cutting tools used in machining the Ti-555 alloyshow contrast from those exhibited by tools used in machining the Ti6AI4V alloy. In fact, onlyabrasion wear was observed for cutting tools in the case of machining the near-β titanium Ti-555alloy. The last alloy is characterized by a fine-sized microstructure (order of 1 μm). For the usualTi6Al4V alloy, adhesion and diffusion modes followed by coating delamination process on the toolsubstrate have been clearly identified. Moreover, a deformed layer was observed under secondaryelectron microscope (SEM) from the sub-surface of the chip with β-grains orientation along thechip flow direction. The analysis of the microstructure confirms the intense deformation of themachined surface and shows a texture modification, without phase transformation. For the Ti-555β-alloy, β grains experiences more plastic deformation and increases the microhardness of theworkpiece inducing then an abrasion wear process for cemented carbide tools. For the Ti6Al4Vmicrostructure, the temperature rise induces a thermal softening process of the workpiece andgenerates adhesive wear modes for cutting tools. The observed worn tool surfaces confirm theeffect of the microstructure on tool wear under different cutting conditions for the two studiedtitanium alloys.