Effects of Speeds,Materials, and Tool Rake Angles on Metallic Particle Emission During Orthogonal Cutting

Dry high speed machining has been proposed as a viable and cost-effective process in metal cutting industries. However, it produces fine and ultra-fine metallic particles, also referred to as dust, which can be harmful to the machine-tool operator. The risk associated with exposure to metallic particles increases as the particle size decreases. For machining processes, little data exist on the size and distribution of dust generated during the shaping of materials. In order to reduce or eliminate the generation of these particles, it is necessary to understand how and under which conditions they are formed, as well as to be able to make predictions. In this study, the effects exerted by tool geometry, material, and machining parameters on dust emission were studied experimentally in order to understand the mechanisms of dust generation and to develop a predictive model. The particle sizes studied include the PM2.5 (particles with aerodynamique diameter below 2.5 μm) and a distribution of nanoparticles varying in size from 10 nm to 10 μm. Using dry machining and reducing the amount of dust generated should improve the air quality in machine shops in addition to helping protect the environment.     

Modeling of Particle Emission During Dry Orthogonal Cutting

Because of the risks associated with exposure to metallic particles, efforts are being put into controlling and reducing them during the metal working process. Recent studies by the authors involved in this project have presented the effects of cutting speeds, workpiece material, and tool geometry on particle emission during dry machining; the authors have also proposed a new parameter, named the dust unit (D _u), for use in evaluating the quantity of particle emissions relative to the quantity of chips produced during a machining operation. In this study, a model for predicting the particle emission (dust unit) during orthogonal turning is proposed. This model, which is based on the energy approach combined with the microfriction and the plastic deformation of the material, takes into account the tool geometry, the properties of the worked material, the cutting conditions, and the chip segmentation. The model is validated using experimental results obtained during the orthogonal turning of 6061-T6 aluminum alloy, AISI 1018, AISI 4140 steels, and grey cast iron. A good agreement was found with experimental results. This model can help in designing strategies for reducing particle emission during machining processes, at the source.     

Modeling of eutectic macrosegregation in centrifugal casting of thin walled ZA8 zinc alloy

The maximum segregation zone and microstructure formation during the solidification of thin walled ZA8 zinc–aluminum alloy produced by centrifugal casting are investigated. From the results obtained, it is seen that the maximum segregation zone of the eutectic through the part section corresponds to the zone of final solidification point. The concentration of eutectic through the section changes depending on the initial mold temperature, pouring temperature, and cooling rate. A high cooling rate reduces the rate of change in eutectic concentration across the section. The distance separating the maximum segregation zone from the inner and outer faces of the casting can be controlled by controlling the ratio between the speeds of the solidification fronts advancing from opposite sides. The microstructure obtained becomes finer as the cooling rate increases. The structure of eutectic changes according to the cooling rate, and may be granular or lamellar.     

Neuro-fuzzy predictive model for surface roughness and cutting force of machined Al–20 Mg2Si–2Cu metal matrix composite using additives

Neural Computing and Applications - Today’s metal matrix composites are widely used due to their excellent properties, which are useful for high-performance applications in the automotive and...     

Understanding and Characterizing the Drilling of Recycled Plastics

Recycled plastics are increasingly being used to manufacture planks used in large-volume applications, including decks, garden, and cloakroom chairs. These products, although manufactured near-to-net shape, often require drilling for assembly purposes. There are very limited data on the machining of plastic material. Manufacturers often rely on data and models established for metals. The machining of plastics, although limited to assembly purposes, or to the removal of excess materials, requires an understanding of the behavior of these materials during the machining in order to obtain better quality parts. It is even more important for recycled plastics, which are inhomogeneous, contain pores, and most often, are made with more than one type of product. This work analyzes the machining of recycled plastics in order to establish and compare their machining models with those traditionally used for metals, and to better understand the behavior of the plastics during machining. The workpiece is drilled at different process conditions and at different temperatures. The process performance indicators such as cutting forces, chip formation, and chip form are analyzed. The originality of this work resides in its study of chip formation and the effects of the preset workpiece temperature on the drilling mechanisms. It is found that there is a range of critical temperatures of transition for plastics similar to the Charpy impact ductile-brittle temperature separating the domain of low cutting force and long and spiral chip from that of high cutting force corresponding to the accordion-type of chip. A parameter describing this phenomenon is defined. It is also found that for low- to moderate-speed operations, the cutting speed has very little effect on the cutting forces, which depend mainly on the feed rate and the workpiece temperature. The relationship between the drilling forces and the feed rate established for metals remain valid, but the exponent of the feed rate for the thrust force is lower. The thrust force and the tangential force are proportional to the feed rate exponent 0.4 compared to 0.8 for metals when drilling workpiece at room temperature or below.     

A simple analytical model for burr type prediction in drilling of ductile materials

This paper proposes a new analytical model to predict the type of burr at drilling exit. The model is based on the theory of slip-planes and is specially developed to predict burr type formation in drilling of ductile materials. First the analytical model is set up, based on mechanical and geometrical considerations. Then it has been validated through experimental drilling tests on aeronautical aluminum by predicting burr type and thickness. The experimental results show that the model is suitable in the drilling of ductile materials and its validity domain has been established.     

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.     

Analytical modelling of slot milling exit burr size

A computational model was recently proposed by authors to approximate the tangential cutting force and consequently predict the thickness of the exit up milling side burr. To calculate the cutting force, the specific cutting force coefficient with respect to material properties was used. The model was sensitive to material yield strength and few cutting and tool geometrical parameters. However, the effects of cutting speed, tool coating, and tool rake angle on burr size were neglected. Other phenomena that could affect the burr size such as friction and abrasion were not taken into account either. Therefore, in the current work, a mechanistic force model is incorporated to propose a burr size prediction algorithm. The tangential and radial forces are calculated based on using specific cutting force coefficients in each direction. Furthermore, using the new approach, the burr size is predicated and the effects of a broad range of cutting parameters on burr size and friction angle are evaluated. Experimental values of burr size correlated well with prediction. It was found that the cutting speed has negligible effects on force and burr size. Lower friction angle was recorded when using larger feed per tooth. Consequently, thinner exit up milling side burr was obtained under high friction angle.     

Modeling of burr thickness in milling of ductile materials

Accuracy and surface finish play an important role in modern industry. The presence of undesired projections of materials, known as burrs, negatively affect the part quality and assembly process. To remove burrs, a secondary operation known as deburring is required for the post-processing and edge finishing of machined parts. The thickness of the burr is of interest as it describes the time and method necessary for deburring of the machined part. Burr thickness (B _t) measurements are costly and non-value-added operations that in most cases require the use of a scanning electron microscope for accurate burr characterization. Therefore, to avoid such expenses, the implementation of alternative methods for predicting the burr thickness is strongly recommended. In this research work, an analytical model for predicting the burr thickness in end milling of ductile materials is presented. The model is built on the geometry of burr formation and the principle of continuity of work at the transition from chip formation to burr formation that also takes into account the cutting force influence on burr formation. A very good correlation was found between the modeled and experimental B _t values. The model has shown a great sensitivity to material properties such as yield strength and specific cutting force coefficient (K _c). In addition, the sensitivity of the proposed model to the feed per tooth (f _t) and depth of cut (a _p) was considerably high. The proposed model allows the prediction of the thickness of the exit up milling side burr, without the need for experimental measurement and/or approximation of shear angle (Φ), friction angle (λ), and the tool chip contact length (L), unlike existing analytical burr size prediction models. Besides analytical modeling, statistical analysis is performed on experimental results in order to distinguish dominant process parameters on B _t. It is observed that the depth of cut and feed per tooth are the main parameters which significantly affect the B _t, while the speed has only a negligible effect on it.