Chip Formation Process Research Articles

Finite Element Modelling and Experimental Validation of the Graphite Cutting Process

Graphite is extensively used in the engineering field due to its unique properties, and the study of its cutting mechanism has become particularly important. However, the brittle fracture mechanism of graphite makes it rather easy for cracks with a unique pattern of initiation and growth to develop when processing. Herein, the ABAQUS was selected to establish a finite element model (FEM) of the graphite cutting process. The internal crystal structure of graphite was modelled by a Voronoi structure, and a cohesion unit was globally embedded into the solid unit to simulate crack initiation and growth. In addition, the complete process of chip formation and removal was demonstrated. The analysis of the simulation results showed that the graphite material underwent three periodic cycles of material removal during the cutting process, i.e., large, tiny, and small removal stages. Meanwhile, the simulation results indicated that when ac was large enough, the crack gradually grew inside the graphite and then turned to the upper surface of the graphite. However, when ac was tiny enough, the cracks hardly expanded towards the inside of the graphite but grew upwards for a short period. Then, orthogonal cutting experiments of graphite were conducted, and the FEM was verified based on the experimental chip morphology, machined surface morphology, and current geometric model of the graphite cutting process. The simulation and experimental results were consistent. The hereby-presented FEM was a complement to simulations of the processing of brittle materials.

Investigation of the Cutting Fluid Incidence Angle Direction in Turning Grade 5 ELI Titanium Alloy under High-Pressure Cooling Conditions.

The use of high-pressure cooling (HPC) in machining can increase the efficiency and improve process stability through more effective breaking and chip evacuation. Turning tests of the Grade 5 ELI titanium alloy were carried out using cemented carbide tools and taking into account the direction of feeding of the cutting liquid. Measurements of the components of the total cutting force were carried out for feeds in the range f = <0.08; 0.13> mm/rev and two angular settings (i.e., angle α = <30°; 90°> and β = <0°; 60°>) of the nozzle. The chip breakage coefficient was determined. It was shown that the cutting force values depended on the feed value, and the angle of feeding of the cutting fluid did not significantly affect the values of the cutting forces. Despite the different forms of chips obtained, the applied method of searching for the best conditions was unsuccessful and no significant effect on the values of the chip breaking coefficient Cch was observed. To determine the best nozzle setting, it is useful to determine the working area of the chip breaker. Due to the shape of the chip, the optimal angular setting for the nozzle that supplied the cutting fluid was α = 60° and β = 30°. In addition, it was observed that the angle of incidence of the cutting fluid jet could affect the chip formation process and support the chip cracking process.

Analytical prediction of chip flow direction in cylindrical turning considering rounded edge effect

The flow direction of a no-free chip has a vital influence on chip control and the machined surface's integrity. In order to establish an accurate prediction model of chip flow direction, a new analytical model considering the effect of workpiece materials and tool nose radius on chip flow direction is proposed for cylindrical turning. The rounded edge engaged in cutting is segmented into many oblique cutting units to consider the effect of the nose radius on the chip flow, whose thermomechanical process of chip formation is characterized by the unequal division shear zone method. The mutual action forces of each discrete chip are calculated to determine the resultant chip flow direction, and the interaction between the constrained chip units is comprehensively considered as non-free chip flow. Simultaneously, the influences of material constitutive and cutting parameters on the flow direction of discrete chip and resultant chip are analyzed by thermomechanical coupling method. The conducted mechanism of the nose radius and the main cutting edge angle on unconstrained and constrained chips is studied. The predicted results of chip flow direction were validated with experimental values and Colewell's model, and the FE simulation was also used to compare with the proposed model, interesting agreement was found.

Силовой анализ процесса резания единичным зерном сферокорунда при шлифовании древесины

The productivity of the wood grinding process can be increased by using abrasive wheels with spherical corundum grains. They also expand the area of application of rigid abrasive instruments by reducing soiling and eliminating burns on the treated surface. The studies revealed several advantages of the abrasive wheels over sanding paper: very precise processing, achievement of the desired grade of the treated surface, high durability of the instrument, and low cost. A force analysis of a grinding surface with micro-cuttings made of spherical corundum grains was performed depending on the degree of its wear. The results revealed that chip removal by the spherical corundum grains was possible only under certain conditions when the cutting edges of the grains were exposed. Besides, the theoretical dependencies of forces in micro-cutting were obtained from every principal condition for the process of grinding wood and wooden materials: properties of the spheres, treatment modes, and material-related factors. The special properties were analyzed by the chip formation process and self-sharpening conditions of the spherical corundum wheels. The grain size had the greatest influence on the thickness of chips which were cut by one grain. The grain content and bonding, like other properties of the internal volumetric structure, had a less substantial impact. The abrasive tool characteristics must complement the processed material, such as grain size, hardness, and structure. On the other hand, spherical corundum has optimal physical and mechanical properties for grinding, particularly the thickness of the grain’s edges, which primarily determine the material’s tensile strength. The grinding depth and feed rate mostly define the parameters of the grinding performance of wood and wood-based materials. An increase in those leads to a rise in cutting forces, roughness of the ground surface, a reduction in the grinding length over the period of the wheel’s durability, and the grinding coefficient. If the grinding depth and feed rate are constant, the performance can be improved by increasing the cutting rate. For citation: Sergeevichev A.V., Sokolova V.A., Mikhailova A.E., Ovcharova E.O., Voinash S.A. Force Analysis of a Single Grain Cutting Process in Wood Grinding Using Spherical Corundum. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 3, pp. 140–154. (In Russ.). https://doi.org/10.37482/0536-1036-2023-3-140-154

Modeling energy consumption inside cutting deformation zone to predict the stress distributions, temperature and microstructure by micro irreversible entropic thermodynamics

It is important to analyze the process of chip formation by means of the energy consumption during metal cutting, which is related to the cutting power (or cutting force), the cutting temperature and the machined surface integrity. In this study, the consumed energy field inside the cutting deformation zone is established by considering four micro irreversible processes including the dislocation generation, annihilation, movement, and continuous dynamic recrystallization. A new shear-angle solution is proposed on the basis of the steady conditions of irreversible processes (i.e., the entropy production rate reaches the minimum), whose adequacy is verified by the experimental results of the shear angle and friction coefficient along the tool-chip interface. Based on the predicted consumed energy field inside the cutting deformation zone, the deformation mechanism, microstructure, stress and temperature are predicted and analyzed. The results show that three stages including the loading stage, unloading stage and steady stage are divided during chip formation according to the consumed energy field. The consumed energy and statistically stored dislocation density are both of gradient distribution in the primary shear zone, and continuous dynamic recrystallization is the main mechanism of grain refinement during chip formation, which is dominated in the secondary deformation zone. The stress and temperature inside the cutting deformation zone as well as the hardness of the machined surface are predicted according to the energy balance relationship and consumed energy field, indicating the feasibility of using energy consumption to comprehensively describe the internal changes of workpiece material inside the cutting deformation zone.

Numerical and experimental investigations on the laser assisted machining of the TC6 titanium alloy

In order to improve the machinability of difficult-to-machine materials in aviation, laser-assisted cutting technology has received extensive attention. This method of machining allows the workpiece to obtain a localized high temperature prior to cutting in order to benefit from thermal softening. A 3D transient laser heating model was developed for the finite element method to predict the preheating temperature of the cutting layer. The effect of cutting parameters (cutting speed, feed rates, depth of cut) on the magnitude, frequency and amplitude of the cyclic cutting forces was investigated both in conventional machining and in laser assisted machining. It is founded that the laser assistance decreases the flow stress of the material, magnitude of cutting forces and the amplitude of cutting forces. But the frequency of circulating cutting forces increase comparing with the CM (conventional machining). In addition, this paper considers the effect of the LAM (laser-assisted machining) technique on reducing the magnitude of cutting force fluctuations, which results in a flatter machined surface profile and reduces the number of surface defects. A chip morphology different from that of CM is created due to the influence of the cutting force by the temperature field in LAM. Furthermore, a “transitional chip” is discovered, which is a transition from a continuous chip to a segmented chip. The completely thermal-mechanical coupled orthogonal cutting model was established to reveal the evolution mechanism of shear band formation with laser assistance. The results show that shear bands can be formed faster and with less stress in LAM compared to CM. The model can effectively predict the shear angle and keep the prediction error within 10 %. The shear band formation processes in both machining methods were uncovered according to the models. The developed model is very useful for understanding the chip formation process and the cutting force variation in laser assisted machining.

Study on the cutting force responses in machining multiscale carbon nanotube/carbon fiber reinforced polymer composites

Orthogonal cutting experiments were performed on the multiscale carbon nanotube/carbon fiber (CNT/CF) reinforced polymer composites with various wt. fractions of multiwalled CNTs (MWCNTs) filled in the epoxy to investigate the machinability of the material. In particular, the characteristics of the cutting force were studied as a response to the CNT content, the fiber orientation and the depth of cut. Results show that the effect of the CNT content on the principle cutting force in 135° orientation shows a different pattern than that in the other orientations. The mechanism was studied with an analytical mode proposed for the chip formation process. The depth of cut has a more significant effect on the principle cutting force for the tested condition, with the effect further enhanced by the inclusion of CNTs. Furthermore, with increasing CNT content or depth of cut, the resultant cutting force tends to shift along the cutting direction with a decreased coefficient of friction along the tool/chip interface.

Study on nanometer cutting mechanism of single crystal silicon at different temperatures

Thermal-assisted single point diamond turning technology is currently one of the most important methods for realizing nano-scale machining. However, the nano-chip formation mechanism as the core of the nano-cutting mechanism is still unclear, which limits the development of this advanced technology. In this study, based on the molecular dynamics simulations, the nano cutting behaviour of single crystal silicon at different temperatures were studied. The cutting force, crystal structure, particle motion characteristics, stress-strain distribution and temperature distribution during chip formation process were systematically analyzed. The underlying mechanism of nano-chip formation in single crystal silicon was summarized. The results showed that the chip formation mechanism can be divided into two types: crack and shear. At low temperatures, chips are formed by crack propagation. The concentrated distribution of high stress triaxiality and local high temperatures at the crack tip are the main causes of crack propagation. With an increase in temperature, the chip formation mode gradually changed from crack to shear. The highly resolved shear stress distributed along the slip plane is the main reason for the expansion of the amorphous bands. In addition, it's found that higher quality machined surfaces can be obtained through chip formation process by shear than by crack.

The Chip Formation Process When Cutting High-Speed Steels and Ti3SiC2 Ceramics

The paper presents the microstructural characterization of the chip roots in high-speed steels and ceramic Ti3SiC2. The process of chip formation and the obtaining of adequate samples were carried out using the quick-stop method. The tests were carried out during the milling process; the “quick stop” method was carried out in order to obtain samples of the chip roots. This method was developed in-house by the authors. The chip roots were microscopically studied by means of a light microscope (LM) and a scanning electron microscope (SEM). Before the actual analysis, preparation was performed based on the standard metallographic technique. The analysis of the high-speed steels samples showed that, for the used cutting conditions, a discontinuous chip with a built-up edge (BUE) was formed. During the processing of the Ti3SiC2 ceramic, a significant difference was manifested in the chip formation process and a powder-like chip was produced. After utilizing a careful cutting process, a chip pattern was observed, from which it is evident that chip breakage during ceramic processing occurs without prior plastic deformation. In addition, the cutting force Fc was also measured during the milling process of the high-speed steels and the ceramic, and it was correlated with the cutting speed, feed per tooth and depth of cut.

Cutting tool wear minimization in drilling operations of titanium alloy Ti-6Al-4V

Cutting tool wear during drilling operations can cause damage to cutting tools, machine tools, and workpieces which should be analyzed and minimized. Cutting tool wear impacts not just tool life but also the quality of the final product in terms of dimensional accuracy and surface integrity. High mechanical and thermal loads are generated during drilling operations of difficult-to-cut materials such as Ti-6Al-4V alloy which can reduce the life of cutting tool during chip formation process. Thus, to increase the accuracy of drilled parts from titanium alloy Ti6-Al-4V, the cutting tool wear during drilling operations should be accurately predicted in order to be minimized. Application of virtual machining systems is developed in the study in order to predict and minimize the cutting tool wear during drilling operations of titanium alloy Ti-6Al-4V. To predict the tool wear during drilling operations, cutting forces and temperature are calculated. Then, the finite element method (FEM) is utilized to predict the tool wear using the analytical model of Takeyama–Murata and updating the cutting tool geometry during chip formation process. To minimize the cutting tool wear during drilling operations, the optimum drilling parameters of feed rate and spindle speed are obtained using the Taguchi method-based response surface analysis algorithm. As a result, optimized drilling parameters are used in order to minimize the cutting tool wear during drilling operations. To validate the study, the experimental works are implemented to the sample workpiece from titanium alloy Ti6-Al4-V and the values of tool wear are then measured. To present the effectiveness of the proposed virtual machining system in minimization of cutting tool wear, the obtained results with and without optimized machining parameters are evaluated and compared. So, precision and productivity in drilling operations of titanium alloy Ti6-Al4-V can be enhanced using the developed virtual machining system in the study.

Cutting Parameter Optimization based on Online Temperature Measurements

The deformation of metallic materials during the machining operation requires a significant amount of energy. During the chip formation process and due to the plastic deformation of the metal and the friction along the tool-part interface, the thermal loads generated are strongly impacted by the cutting factors. Thus, the choice of optimized cutting conditions is essential to control the quality of the work required. The aim of the present experimental study is to optimize the cutting parameters using temperature measurements. The average temperature of the cutting tool is studied using a FLIR A325sc type infrared camera. Optimal cutting parameters for each performance metric were obtained using the Taguchi techniques.

Combined analysis of acoustic emission and vibration signals in monitoring tool wear, surface quality and chip formation when turning SCM440 steel using MQL

With modern production, Minimum Quantity Lubricant (MQL) technology has emerged as an alternative to conventional liquid cooling. The MQLs is an environmentally friendly lubricant method with low cost while meeting the requirements of machining conditions. In this study, the experimental and analytical results show that the obtained acoustic emission (AE) and vibration signal components can effectively monitor various circumstances in the SCM440 steel turning process with MQL, such as surface quality and chip formation as cutting tool conditions. The AE signals showed a significant response to the tool wear processes. In contrast, the vibration signal showed an excellent ability to reflect the surface roughness during turning with MQL. The chip formation process through the cutting mode parameters (cutting speed, feed and depth of cut) was detected through analysis amplitude of the vibration components Ax, Ay and Az and the AE signal. Finally, Gaussian process regression and adaptive neuro-fuzzy inference systems (GPR-ANFIS) algorithms were combined to predict the surface quality and tool wear parameters of the MQL turning process. Tool condition monitoring devices assist the operator in monitoring tool wear and surface quality limits, stopping the machine in case of imminent tool breakage or lower surface quality. With the unique combination of AE and vibration analysis model and the training and testing samples established by the experimental data, the corresponding average prediction accuracy is 97.57 %. The highest prediction error is not more than 3.8 %, with a confidence percentage of 98 %. The proposed model can be used in industry to predict surface roughness and wear of the tools directly during turning

Effects of tool angles and uncut chip thickness on consumption of plastic deformation energy during machining process

Research on the underlying mechanism that controls the chip deformation and energy consumption is a basis to instruct the cutting process planning and improve the machining efficiency. The metal cutting process can be treated as purposeful separation of workpiece material, and the stress state located at the tool tip has great effect on the fracture of material being removed. Through studying the relationship between the stress triaxiality and chip formation process, this paper aims to reveal the effects of tool rake angle, inclination angle and uncut chip thickness on chip deformation behavior and associated energy consumption during machining of 1045 steel based on finite element method (FEM). A two-dimensional FEM model for orthogonal cutting is developed to study the effect of tool rake angle and uncut chip thickness on chip deformation, while a three-dimensional FEM model for oblique cutting is developed to investigate the effect of tool inclination angle. The parameter of chip compression ratio (CCR) is adopted to assess the chip plastic deformation and energy consumption under varied machining conditions. The cutting force component calculated based on CCR is compared with the total cutting force to demonstrate the dominant role of chip plastic deformation in cutting energy consumption. The results indicate that larger rake angle and smaller inclination angle of cutting tools as well as larger uncut chip thickness lead to increase of stress triaxiality near the tool tip, which can reduce the material fracture strain and be beneficial for the separation of material being removed from the bulk workpiece. This paper will be attractive from both practical and fundamental perspectives devoted to instructing the optimization of cutting parameters to improve the processing efficiency and reduce the energy consumption.

Surface integrity in 3D ultrasonic vibration-assisted turning driven by two actuators

The surface integrity of machined parts is critical to their in-service function, longevity and overall performance. The integrity of the surface is dominantly affected by the chip formation process that can be significantly altered and controlled, among other methods, by ultrasonic vibration assistance. This work will explore the integrity of surfaces generated in three-dimensional ultrasonic vibration-assisted turning (3D-UVAT). The integrity of the obtained workpiece surfaces will be systematically explored in terms of surface roughness, the microstructure of the surface obtained by heat-assisted turning, surface hardness and wettability. A comparative assessment with other surface generation methods, i.e., common turning (CT), one-dimensional (UVAT) and two-dimensional elliptical ultrasonic vibration-assisted turning (EUAT) is also given. The results show that 3D-UVAT can reduce the depth of surface damage and enhance the hydrophobicity of the surface while reducing surface roughness.

Simulation and analytical studies of chip formation processes in the cutting zone of titanium alloys

The low machinability of titanium alloys is determined by the physical, mechanical, and chemical properties of these materials and their mechanical characteristics. It is also evident in the hardened state of the material being processed during cutting, as well as in the initial state. This phenomenon is caused by thermodynamic parameters that determine the properties of titanium material at elevated temperatures. The peculiarities of the cutting and chip formation processes during titanium alloy machining are presented in this article. The peculiarity of the described approach is the analysis of the results of simulation modeling of cutting in Deform 2D software. It is proved that the frictional factor in the formation of the thermal characteristics of the cutting process, which arises as a result of the chip sliding along the tool, dominates the load factor (caused by force and deformation processes in the chip root). It has been established that the length of contact between the chips and the tool’s rake face has a certain tendency to change: the contact length first increases and then decreases with increasing cutting speed. An analysis of the dependence of the chip compression ratio on changes in cutting speed has shown that with an increase in cutting speed, the average value of the compression ratio practically does not change, but the amplitude of its oscillation increases significantly, which is equivalent to a change in the shear angle. This parameter changes dynamically due to the adiabatic nature of chip formation

Control of roughness of surface during processing of workpieces made of hard-to-process and hardened materials

The paper presents the results of an experimental study of the roughness of the treated surface using various methods of data analysis, such as the analysis of Fourier spectra. Also in the work, the process of mechanical processing is considered from the standpoint of mesomechanics, which makes it possible to re-evaluate the process of chip formation. The paper says that the roughness of the treated surface, as an output parameter of the cutting process, has a special effect not only on the quality of the surface layer, but also on the performance characteristics of machine parts operating in extreme conditions. Also, the paper considers the nature of the formation of micro-roughness on the surface of parts after machining, and lists the factors that affect the roughness parameters. Conclusions are drawn about what determines the different frequencies of micro-roughness of the treated surface.

Chip profile studies on SiC reinforced mono and SiC and graphite reinforced hybrid ZA43 MMCs

ABSTRACT This paper depicts an experimental model for investigating the mechanism and nature of chip formation during the machining of Zinc-Aluminium alloy-based SiC reinforced mono and SIC and graphite reinforced hybrid metal matrix composites. The stir casting process is followed for the fabrication of both categories of composites. The morphology of the fabricated specimen tells the uniform distribution of reinforcing particles. Machining trials are done on mono and hybrid composites using coated carbide tool. The chips produced during the machining process are carefully collected and examined for their nature and shape. It is concluded that mono composite materials show lengthier chips than hybrid composite materials. The machining parameters and material composition influence the chip formation process. Due to retained ductility in the mono composites, lengthier chips are produced and hybrid composite being more brittle than mono composite material produces short segmental chips.

Regime features of austempered ductile iron cutting

Machining regimes and sub-regimes of dry straight finish-turningof structural austempered ductile iron (ADI) with low cBN-content PcBN-based cutting inserts were examined. The global and local characteristics of TC contact and chip formation processes tied to this turning, as estimated by Katuku [Journal of Manufacturing Processes 78, 2022, 288–307], were used in this attempt. The significance of each prominent feature of these regimes was discussed from multiple perspectives. Across primary deformation zones (PDZs) and secondary deformations zones (SDZs), drag-controlled (or shock-induced) and defect-controlled plasticity regimes are, in turn, dominant and secondary. Coupled shear localisations in PDZs and SDZs occur via strain softening for cutting speeds beyond ~175 m min−1. BUE softening turns active at ~650 °C (~125 m min−1). Two bordering machining regimes emerged in close link with this cut-off temperature alongside a ⁓16 % cut-off SDZPDZ softening-degree, to name a few. Higher SDZPDZ softening-degree and moderately low mean contact stresses (high TC contact-length factor), TC contact temperature and sliding-friction coefficient, prevailing for Machining-regime-I (50–150 m min−1), hint at lower-pace wear regimes. The opposite conditions, standing for Machining-regime II (200–800 m min−1), suggest temperature-affected and stress-backed higher-pace wear regimes. Mean total energy levels (3476–7122 and 4364–4596 MPa) imply residual stresses built-up and microstructure damage below the machined surface. Machining sub-regimes are linked to solid-state phase transformations in PDZs/SDZs. Shear energy stored in PDZs/SDZs (166–291/1.5–43 MPa and 159–134/33–72 MPa) matches these transformations. Machining sub-regimes are sensitive to shallow variations in TC settings past ~175 m min−1. Powder lubrication by smeared-out graphite nodules is worthless in Machining-regime II. Cutting speeds of 150–400 m min−1 (TC contact temperature of ~685–930 °C and chip compression ratio of 3.4–2.32), sampled at the confluence of Machining-regimes I and II, are recommended for dry straight finish-turning structural ADI with low cBN-content PcBN-based cutting inserts.

Study on Chip Formation Mechanism of Single Crystal Copper Using Molecular Dynamics Simulations

Nano-cutting is an important development direction of the modern manufacturing technology. However, the research on the mechanism underlying nano-cutting lags far behind the practical application, which restricts the development of this advanced manufacturing technology. The chip formation process is the basic process of nano-cutting, and it is of key importance for the mechanism research of nano-cutting. In this paper, the nano-tensile behavior of single crystal copper was studied based on the molecular dynamics simulations. The toughness and brittleness characteristics of the copper at different temperatures were analyzed. Then, the molecular dynamics simulations of nano-cutting for single crystal copper with different toughness and brittleness were studied. The crystal structure, cutting force, stress–strain distribution and atomic motion characteristics were systematically investigated. The nano-chip formation mechanism of single crystal copper was revealed. The results show that the chip is formed through two ways, namely the shear and extrusion. The material near the free surface of the workpiece undergoes continuous shear slip and periodic long-distance slippage along the primary shear direction, forming the block chip in which the FCC and HCP structures are orderly distributed. The material near the tool-chip interface is extruded by the tool, block chip and stagnation zone to form the flowing chip with amorphous structure. As the temperature increases, the occurrence frequency of long-distance slippage in the block chip increases, while the slippage degree decreases. Besides, with the increase in temperature, the thickness of block chip formed by shear slip decreases, while the thickness of flowing chip formed by extrusion increases.

Influence of Machining Parameters on Cutting and Chip-Formation Process during Cortical Bone Orthogonal Machining.

Cortical bone machining is commonly used in craniofacial surgery. The shaping of bone surfaces requires a precise determination of the process’s complexity due to the cutting tool’s defined or undefined geometry. Therefore, research was carried out to assess the impact of the rake angle (γ), clearance angle and depth of cut (d) on the cortical bone machining process. Analysis was carried out based on the orthogonal cutting in three directions. The cutting tool shape was simplified, and the cutting forces and the chip-formation process were monitored. The highest values of the resultant cutting force and shear force were recorded for γ < 0. The specific cutting force decreases with the increase of d. Cutting in the transverse direction is characterized by the highest values of resultant cutting force and shear force. The coefficient of friction depends primarily on the d and takes a constant value or increases with the increase of γ. The tests showed that the chips are formed in the entire range of d ≥ 0.5 µm and create regular shapes for d ≥ 10 µm. The research novelty confirms that even negative cutting angles guarantee controlled cutting and can find wider application in surgical procedures.