Abdelhakim Djebara

Machining and Machinability of Aluminum Alloys

The use of materials with low specific weight is an effective way of reducing the weight of structures. Aluminum alloys are among the most commonly used lightweight metallic materials as they offer a number of different interesting mechanical and thermal properties. In addition, they are relatively easy to shape metals, especially in material removal processes, such as machining. In fact, aluminum alloys as a class are considered as the family of materials offering the highest levels of machinability, as compared to other families of lightweight metals such as titanium and magnesium alloys. This machinability quantifies the machining performance, and may be defined for a specific application by various criteria, such as tool life, surface finish, chip evacuation, material removal rate and machine-tool power. It has been shown that chemical composition, structural defects and alloying elements significantly influence machinability [W Konig et al., 1983]. Thus, with similar chemical compositions, the machinability of alloys can be improved by different treatments. Heat treatments, which increase hardness, will reduce the built-up edge (BUE) tendency during machining [M. Tash et al., 2006]. In the case of dry machining, the major problems encountered are the BUE at low cutting speeds and sticking at high cutting speeds, hence the need for special tool geometries [P. Roy et al., 2008]. It has been shown that high levels of Magnesium (Mg) increase the cutting forces at the same level of hardness [M. Tash et al., 2006], while a low percentage of Copper (Cu) in aluminum alloy 319 decreases the cutting force. Similarly, it has been found that heat treatment of 6061, especially aging, influences the forces only at low cutting speeds, while at high speeds, the influence is negligible because of the low temperature rise seen in the cutting zone [Demir H et al., 2008]. Cutting force is just one among several parameters to be considered for a full assessment of the machinability of metallic alloys, with the others being the tool life, the surface finish, the cutting energy and the chip formation mode. Aluminum alloys are classified under two classes: cast alloys and wrought alloys. Furthermore, they can be classified according to the specification of the alloying elements involved, such as strain-hardenable alloys and heat-treatable alloys. Most wrought aluminum alloys have excellent machinability. While cast alloys containing copper, magnesium or zinc as the main alloying elements can cause some machining difficulties, the use of small tool rake angles can however improve machinability. Alloys having silicon as the main alloying element involve larger tool rake angles, lower speeds and feeds, making

Effect of Friction Testing of Metals on Particle Emission

Metallic particles emitted during manufacturing processes can represent a serious danger for occupational safety. The mechanisms responsible for these particle emissions include two- and three-body frictions; Moreover, such particles can also be emitted during several other processes, including mechanical braking. To be in a position to devise ways to reduce these particle emissions at the source, it is important to know their size, quantity, and distribution, as well as the relationships between operating conditions and particle emissions. This article investigates nanoparticle and microparticle emissions during two friction tests: one (setup 1: pin in rotation only) simulates the friction occurring during mechanical braking actions, and another (setup 2: pin in rotation and translation) simulates the friction taking place at the tool-workpiece interface during metal cutting processes. The materials tested were aluminum alloys (6061-T6 and 7075-T6), and the pin used was a carbide cylinder. Particle emission was monitored using the Scanning Mobility Particle Sizer (SMPS) for nanoparticles, and the Aerosol Particle Sizer (APS) for microparticles. It was found that friction produces more nanoparticles than microparticles, and that total particle emission can be reduced by operating at low or at high sliding speeds.

ON CHIP FORMATION DURING DRILLING OF CAST ALUMINUM ALLOYS

Aluminum alloys are widely used in several applications. Cast alloys are usually considered to be brittle materials leading to short chip formation during machining. Although they can be produced near net shapes, products made of these alloys very often require some machining. The purpose of this study is to evaluate the machinability of A319 and A356 under T0 and T6 conditions. The machinability was assessed during the dry drilling machining process, with the machinability indexes including the chip form, chip breakability, and the cutting forces. It was found that A319 and A356 exhibit different machinability behaviors, especially under the T6-condition in terms of force requirements, chip breakability, and chip segmentation. The chip grain size obtained by X-ray diffraction techniques was also studied and correlated to the machining conditions. It was also found that both the microstructure of the workpiece materials and the machining conditions significantly affect the chip formation mechanism, and so the machining parameters could therefore be selected to promote a chip form that is easily manageable in production.

Experimental Investigation on the Effect of Pre- holes on Drilling Process Performance of Aluminum Alloys: Forces, Surface Finish and Dust Emission

In most drilling applications, pre-holes are often performed prior to the final hole drilling in order to obtain holes with good quality (dimensional accuracy, surface finish, and reduced burr). While this operation can improve the process stability, it might however also have an impact on process performance indicators such as dust emission, energy required for the drilling process, cycle time and chip breakability. This work investigates the effects of pre-holes on cutting forces, chip formation, surface finish and dust emission. Aluminum alloys (6061-T6 and 7075-T6) were drilled at different cutting speeds using uncoated HSS drills and the thrust forces, dust emissions and surface finish were analysed. It was found that drilling with pre-holes reduced the cutting forces, improved hole surface finish and chip breakability, and increased the total amount of metallic particle emission.

Burr Size Minimization When Drilling 6061-T6 Aluminum Alloy

The burr formation mechanisms strongly depend on the machining methods as well as cutting conditions. Cutting fluids play significant roles in machining, including reduction of friction and temperature. Using a cutting fluid, however, degrades the quality of the environment and increases machining costs. In the present work, initially the effects of cutting fluid application (dry, mist and flood) and their interaction with cutting parameters on the burr size during drilling of 6061-T6 aluminum alloys were investigated using multi-level full factorial design. Second-order non-linear mathematical models were developed to predict burr height for various lubrication modes. The accuracy of the regression equations formulated to predict burr height when using different lubrication modes has been verified through carrying out random experiments in the range of variation of these variables. A procedure was developed to minimize burr size for drilling holes by presenting the optimal levels of process parameters. Taguchi optimization method based on L9 orthogonal array design of experiment was then used which has shown very accurate process parameters selection that leads to minimum burr height. According to experimental study, it was observed that dry and mist drilling can produce parts with quality comparable with those obtained in wet drilling when using the optimal cutting conditions. In addition, increase in cutting speed and feed rate exhibits a decrease in burr size.© 2012 ASME

A new sustainability model for machining processes

It is generally recognised that the sustainability concept integrates economic, environmental and social aspects. It would be interesting for manufacturers to be able to know which process, workpiece materials or machining condition is more sustainable than another. In this paper, a new model for the sustainability in the machining field is proposed with the goal to increase productivity, reduce power and energy used during cutting process and reduce the harmful impacts of the machining process on the environment and the occupational safety. Therefore, the evaluation method combines recyclability, energy, and particle and aerosol emission. Fuzzy logic helps to make decision on the evaluation of the sustainability of machining processes. The model is validated using test results from different cutting processes such as milling, drilling and turning.

CHARACTERIZATION OF NANOPARTICLES EMITTED DURING DRY CUTTING

This work has as main purpose to determine the levels of bioaccumulation (BAF) of metals present in the species Serrasalmus spp (Piranha) to evaluate the bioaccumulation of metals, especially heavy metals due to the damming of the Tocantins River to build the hydroelectric plant Tucurui - PA. The factor (BAF) was calculated: Cd (11625.00), Zn (10890.00), Ca (950.10), Al (935.34), Mg (613.81), Sr (461.89 ), Cr (383.72), Ag (275.36), Pb (104.84), Fe (69.67), Ba (63.72), Ni (52.86), Na (44.71). The metal that made the biggest factor was the accumulation of Cd, this finding shows that although the concentrations of Cd in tissue in the studied species, is on average below the limit set by ANVISA, this metal is bioaccumulative and can harm health the population that uses this species to be considered a carcinogenic metal. Index Terms - Fish, levels of bioaccumulation, Tucurui Dam

Comparison of the Capability of Peak Function in Describing Real Condensation Particle Counter Profiles

Accurate measurement of the aerosols concentration is important in many applications of aerosol science. Here we compare the adequacy of a peak function with the profiles distribution given by a particle counter (CPC) classified in the size range 5 to 500 nm, issued in a machine shop. The particle counter uses a laser source and an optical system for the detection of particles. Our experiments lead to some underestimation of the profile. This underestimation corresponds with the parasitic phenomena of air bubbles and water droplets which are recorded by default as particles. The results of this study underscore the compatibility of a function Gaussian modified by exponential with the distribution profile given by the particle counter (99%).