Jules Kouam

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.

Dry high-speed machining: a cost effective and green process

Dry machining and Minimum Quantity Lubrication (MQL) machining are two emerging technologies that can help metal cutting industries produce desired parts at lower costs while reducing the negative effects of the lubricant on environment and on machine-tool operator’s health. The introduction of these technologies into the industry has been however very slow. In order to accelerate the introduction of this new technology into the industries, there is a need to develop environmentally-friendly machining strategies that are also cost effective. This work presents the needs and the requirements of dry machining and its effect on productivity, part quality and metallic particles generation. Some strategies for limiting the particles generation while maintaining a competitive level of productivity are also presented.

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 part quality and metallic particle emission when milling 6061-T6 aluminium alloy

The quality of machining operations has a direct relationship with machined part quality and workshop air quality. The main characteristics that describe the machined part quality are burr size and surface finish, while fine particles are also considered as air quality characteristics in machining operations. In the present study, four main surface finish parameters (Ra, Rt, Rz and Rq), burrs size and mass concentration of metallic particles in milling of 6061-T6 aluminium alloy are investigated. The machining factors considered to build the experimental plan are cutting tool coating, insert nose radius, cutting speed and feed per tooth. The statistically significant responses to variation of process parameters and factors governing them are presented.

Effects of lubrication modes on part quality during drilling 6061-T6 aluminium alloy

The main objective of this research is to investigate the effects of the cutting fluid and application mode (dry, mist and flood drilling) and its interaction with cutting parameters on part quality during the drilling of 6061-T6 aluminium alloys. The part quality criteria include the burr form and sizes, and surface finish as well as the cutting forces generated. A multi-factorial design (DOE) is used to plan test and statistical analyses are used to determine the effects of lubrication and cutting parameters on part quality. The parameters governing the part quality are different from those governing the cutting force; the burr height and the surface roughness are mostly influence by cutting speed, cutting fluid modes and feed rate while the cutting force is mainly determined by the feed rate. It is found that dry machining and mist machining can produce parts whose quality is comparable to what is obtained in wet machining, when optimal cutting conditions are used.

Global Machinability of Al-Mg-Si Extrusions

Field performance, mechanical properties and workability usually sustain the develop‐ ment of new alloys. As far as the workability is concerned, most extrusions need not on‐ ly to meet good extrudability, but also good or acceptable machinability as some machining operations (eg. drilling or finishing machining) are usually required. Unfortu‐ nately, alloys with higher strength could have better machinability but lower extrudabili‐ ty; Aluminum alloys with excellent extrudability such as AA1060 or AA1100 (Figure 1) often exhibit low machinability, especially due to the chip formation and the workpiece material adhering to the cutting tool leading to the build-up-edge (BUE), modifying the cutting process, leading to tool breakage or deteriorating the surface finish when this BUE is broken. Al-Si-Mg alloys (6XXX series) usually exhibit good machinability and good extrudability; This is one of the reason why about 90% of most extruded alumi‐ num parts are in 6XXX family. The AA6262 which is recognized for its ease chip breaka‐ bility (a lot of second phase particles which help initiate fracture) generally leads to good machinability but poor extrudability because of its poor formability. Any new aluminum alloy with excellent machinability, extrudability and mechanical properties will therefore lead to considerable advantage compared to existing alloys.

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.

Dry, semi-dry and wet machining of 6061-T6 aluminium alloy

Sutherland et al. [3] showed in their study that the aerosol quantity produces in the lubrica‐ tion machining could be 12 to 80 times higher compared to the dry machining. Anselmo et al. [4] carried out a study in dry machining of steel 1045 using two different tools. They found that dry machining requires a very hard tool material that is resistant to high temper‐ ature. They also found that tool life in dry machining could be similar in lubricated machin‐ ing if the cutting depth is fewer with high cutting speed.

ÉquiNanos: innovative team for nanoparticle risk management

UNLABELLED Interactions between nanoparticles (NP), humans and the environment are not fully understood yet. Moreover, frameworks aiming at protecting human health have not been adapted to NP but are nonetheless applied to NP-related activities. Consequently, business organizations currently have to deal with NP-related risks despite the lack of a proven effective method of risk-management. To respond to these concerns and fulfill the needs of populations and industries, ÉquiNanos was created as a largely interdisciplinary provincial research team in Canada. ÉquiNanos consists of eight platforms with different areas of action, from adaptive decision-aid tool to public and legal governance, while including biological monitoring. ÉquiNanos resources aim at responding to the concerns of the Quebec nanotechnology industry and public health authorities. Our mandate is to understand the impact of NP on human health in order to protect the population against all potential risks emerging from these high-priority and rapidly expanding innovative technologies. FROM THE CLINICAL EDITOR In this paper by Canadian authors an important framework is discussed with the goal of acquiring more detailed information and establishing an infrastructure to evaluate the interaction between nanoparticles and living organisms, with the ultimate goal of safety and risk management of the rapidly growing fields of nanotechnology-based biological applications.