Effects of friction conditions on the formation of dead metal zone in orthogonal cutting – a finite element study

A numerical study of the effects of friction conditions on the formation of dead metal zone (DMZ) is presented. The friction conditions are classified as three different cases in the form of coefficient: (1) constant coefficient of friction, (2) “smooth” and “sharp” change of the friction coefficient and (3) time-dependent friction coefficient. These friction cases are numerically investigated using the finite element (FE) code ABAQUS/Explicit. A FE model based on the arbitrary-Lagrangian–Eulerian approach is developed to simulate the cutting process and investigate the influences of the friction conditions. The simulated results, for a wide range of friction conditions, are obtained, analyzed and compared with previously published experimental/numerical data. It has been found that the friction coefficient has a direct effect on the amount and shape of DMZ, the sharp change of coefficient has a larger effect on the DMZ formation than the smooth one and the formation of DMZ is more determined by the value of the friction coefficient than its duration

Microstructural and Mechanical Characterizations of Natural Long Alfa Fibers Obtained with Different Extractions Processes

This study investigates the morphological changes and tensile properties of Alfa fibers extracted mechanically after two treatments namely water retting and alkali treatment. The Scanning Electron Microscopy technique is used in this experimental work. The main observation reveals the decrease of noncellulosic component in the fibers which is inversely proportional to the concentration of sodium hydroxide solution in the case of the alkali treatment. Tensile tests were carried out using tensile machine for determining the tensile properties mainly the tensile strength and the elastic modulus. The tensile strength and young’s modulus of retted fibers are assumed constant. The results relative to the alkalized fibers show an improvement of tensile strength and young’s modulus and are proportional to the sodium hydroxide concentration up to 14%

Interaction between the local tribological conditions at the tool–chip interface and the thermomechanical process in the primary shear zone when dry machining the aluminum alloy AA2024–T351

International audienceIn this work, a predictive machining theory, based on a finite element model, were applied to dry orthogonal cutting of aluminum alloy AA2024–T351. In order to analyze the effects of chip formation process and local friction coefficient on the thermomechanical load along the tool rake face and the round cutting edge, an Arbitrary Lagrangian Eulerian (ALE) model was developed. To validate the present model, the FE results have been compared to the experimental data for a wide range of cutting speed. This shows a good agreement in both trends and values for cutting forces and tool–chip contact length. The ALE approach appears as an appropriate formulation to reproduce: (i) the tribological conditions corresponding to large values of friction coefficient such as in dry machining of aluminum alloys, and (ii) the material flow process around the round cutting edge. It was observed that a transition from a sliding contact to a sticking–sliding contact occurs when the local friction coefficient and the thermal softening are large enough. Predicted results show also that the decrease of the cutting forces as the cutting speed increases is mainly due to the variation of the tool–chip contact length in terms of cutting velocity. The effect of material flow around the round cutting edge on the distributions of frictional stress and pressure has also been analyzed

Characterization and Modelling of the Rough Turning Process of Large-scale Parts: Tribological Behaviour and Tool Wear Analyses

AbstractMachining large-scale parts in several industries (nuclear, naval, energy…) is a challenge for machine tools operators. Various problems are encountered, like respecting specified dimensions, deformation of the workpiece during machining, limit of the cutting speed, excessive tool wear, etc. All these difficulties are related to the large size of the machined part, which may have several meters and weigh several hundred kilograms. This study focuses on analysis of the rough turning process of a shell component, having few meters, as a part of steam generators of nuclear power plants. During the rough turning step, a high material removal rate (moderate cutting speed, but high depth-of-cut and feed rate) is necessary to achieve the workpiece in reasonable time. Experimental and theoretical analyses are conducted to highlight the intense thermomechanical loading at the tool–workmaterial interface. Revealed physical phenomena at the tool rake face, like adhesion and abrasive wear types, using various characterization techniques, are reproduced by a numerical model developed to simulate the cutting process. As an interest result, contact discontinuities at the tool–chip interface as well as where the wear is highly localized are well predicted as observed on scanning electron microscope. These contact discontinuities are attributed to the grooved rake face of the insert, designed with a chip breaker to reduce the tool–chip contact area and to promote the chip fragmentation. This study can be helpful for the design of rough turning inserts, by analysing the effectiveness of the rake face geometry (contact area, chip breaker…)

Experimental and analytical analyses of the cutting process in the deep hole drilling with BTA (Boring Trepanning Association) system

This paper deals with analysis of the cutting process, on a macro and micro scale, in the deep hole drilling with BTA system. An experimental procedure is developed to highlight the impact of cutting speed and feed rate on the cutting process when machining the 18MND5 steel. Parameters based on dimensional characteristics of chips are introduced to quantify the morphology of chips generated by central, intermediate and external inserts of the complex BTA drilling tool. From observation of the chips morphology (flat, curved and spiral) and the measurement of the chips width, the provenance of each chip with respect to cutting inserts is identified. Then, the Chip Compression Ratio is evaluated for each cutting condition, indicating the amount of plastic strain in chips. Thanks to the introduction of a new parameter, denoted as Chip Fragmentation Ratio, it is found that the cutting speed has a little influence, compared to the feed rate, on the chips size. Based on this quantitative analysis, the optimal range of cutting conditions for the BTA deep hole drilling is discussed. It is mentioned that although increasing the feed rate promotes the chips fragmentation and increases the material removal rate (increasing productivity), an upper limit is to determine to prevent excessive flank wear. Also, the cutting speed should be limited to avoid excessive crater wear

Identification des propriétés effectives d’élasticité d’un polymère obtenu par fabrication additive SLS à partir d’une modélisation du volume élémentaire représentatif

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