Critical Undeformed Chip Thickness Research Articles

Ductile–brittle transition and ductile-regime removal mechanisms in micro- and nanoscale machining of ZnS crystals

The ductile–brittle transition and ductile-regime removal mechanisms of ZnS crystal, a typical soft-brittle infrared optical material, have remained unclear at the micro- and nanoscale. In this context, this study modeled the energies consumed in two machining modes, namely ductile deformation and brittle fracture, during the ultraprecision cutting of ZnS crystal. Subsequently, based on the transition point of the energy mode, the critical undeformed chip thickness (CUCT) for the ductile–brittle transition of the material was determined. Additionally, the effect of tool parameters on CUCT was quantitatively analyzed, and the correctness of the model was verified by scratch experiments. Moreover, the cutting parameters that affect the maximum undeformed chip thickness (MUCT) were analyzed. By comparing the MUCT and CUCT, the cutting conditions to realize ductile-regime machining were predicted. The correctness of the ductile-regime machining conditions was also verified through surface quality characterization after face-cutting experiments. The MUCT can be controlled to be less than the CUCT by using a cutting tool with a sufficiently large tool rake angle, a nose radius and a reduced feed rate, thus realizing the ductile-regime removal of the material. The surface morphology, chip morphology, and surface roughness of machined ZnS crystal confirmed the validity of the model. Using a diamond cutting tool with a large cutting edge angle (–25°) and nose radius (1.2 mm) as well as a low feed rate (0.5 μm/rev) and depth of cut (3 μm), the generation of cracks and pits was effectively inhibited, resulting in a smooth surface with a surface roughness of 1.60 nm. Overall, the findings of this study provide important insights into the superfinishing of soft–brittle materials such as ZnS crystal.

Modeling and investigation of minimum chip thickness for silicon carbide during quasi-intermittent vibration–assisted swing cutting

In micromachining, the quasi-intermittent vibration—assisted swing cutting technology alleviates the residual height problem of elliptical vibration–assisted cutting (EVC) and inherits its intermittent machining characteristics. The minimum chip thickness has a significant impact on cutting forces, tool wear, and process stability when working with difficult-to-machine materials. This study thoroughly examines the impact of cutting parameters and tool parameters on the quality of the workpiece during machining in order to better understand the time-varying characteristics of the quasi-intermittent vibration–assisted swing cutting (QVASC) machining process and the size effect on micro-cutting of silicon carbide crystal. This paper created the minimum chip thickness prediction model suited to QVASC machining process. The effects of variables such as cutting velocity and tool inclination on the minimum chip thickness were discussed as well as the scribing tests that were conducted on such challenging materials as silicon carbide. The research findings shown that during the machining process, the critical undeformed chip thickness of silicon carbide decreased continuously as the cutting velocity sequentially increased (1.51 mm/min, 1.88 mm/min, 2.26 mm/min); under the down inclination angle (0–10°), the critical undeformed chip thickness also continuously decreased. These results confirm that cutting too fast reduces the instantaneous undeformed chip thickness, which is not conducive to ductile removal.

Shoulder Damage Model and Its Application for Single Point Diamond Machining of ZnSe Crystal.

The damaging of ZnSe crystal has a significant impact on its service performance and life. Based on the specific cutting energies for brittle and ductile mode machining, a model is proposed to evaluate the damage depth in the shoulder region of ZnSe crystal during single point diamond machining. The model considers the brittle-ductile transition and spring back of ZnSe crystal. To verify the model, the elastic modulus, hardness, spring back, and friction coefficient of ZnSe crystal are measured by nanoindentation and nanoscratch tests, and its critical undeformed chip thickness is obtained by spiral scratching. Meanwhile, orthogonal cutting experiments are conducted to obtain the different shoulder regions and cutting surfaces. The shoulder damage depth is analyzed, indicating that the effect of the feed on the damage depth at a high cutting depth is stronger than that at a low one. The model is verified to be effective with an average relative error of less than 7%. Then, the model is used to calculate the critical processing parameters and achieve a smooth ZnSe surface with a roughness Sa = 1.0 nm. The model is also extended to efficiently predict the bound of the subsurface damage depth of a cutting surface. The research would be useful for the evaluation of surface and subsurface damages during the ultra-precision machining of ZnSe crystal.

Feasibility study of single-crystal silicon ductile-regime turning via fast tool servo

Due to the material properties of single-crystal silicon, it is difficult to achieve high-efficiency processing in conventional turning. Fast tool servo (FTS) turning has emerged as a favorable technology for processing brittle materials. This paper investigates the tool radius, feed speed, and cutting depth effects on the maximum undeformed chip thickness (MUCT). A high-frequency low-coupling FTS system is designed for processing experiments. Effects of the tool rake angle, tool radius, cutting speed, and vibration frequency on the critical undeformed chip thickness (CUCT) are explored in this paper. Experimental results indicate FTS technology can increase the CUCT from 80 nm to 580 nm. Surface and subsurface morphology tests of conventional and FTS single-crystal silicon cutting verify that FTS technology can obtain an optical surface roughness of 5 nm and lower subsurface damage. Moreover, FTS turning can reduce tool wear. Lastly, through Raman spectroscopy analysis, the amorphous phase remaining on the machined surface is lower when FTS turning is employed.

Damage formation mechanisms of sintered silicon carbide during single-diamond grinding

In this research, a single-diamond grinding test was performed on sintered silicon carbide (SSiC) to explore the damage formation mechanism. A scanning electron microscope and a transmission electron microscope (TEM) were used to examine the surface and subsurface morphologies of the grinding groove, respectively. The characteristics of the ground surface morphologies reveal that the single-diamond grinding process of SSiC can be classified into purely ductile, primarily ductile, primarily brittle, and purely brittle stages. Based on the high-resolution TEM (HRTEM) images and the corresponding Fast Fourier transform images of the near-surface region, results reveal that the high density of dislocations and amorphization of SiC grains are responsible for the plastic deformation of SSiC. Most of the cracks congregate on the top grains of the ground surface due to the distinct obstruction of the grain boundary on the cracks propagation, and the cracks generated at the grain boundaries emit into the top grain interiors and go up toward the exposed surface for the distortedly deformed region with higher strain energy; Furthermore, stress concentration caused by the dislocation pileups at grain boundaries represents the crack initiation mechanisms for SSiC. Finally, based on the dislocations pile-up theory, a critical undeformed chip thickness model for boundary crack system nucleation is established, which considers the cutting-edge radius, grinding wheel speed, material properties, and grain size of ceramics.

Grinding characteristics of CVD diamond grits in single grit grinding of SiC ceramics

Single crystalline diamond (SCD) grits are usually made by a high-pressure and high-temperature (HPHT) method and exhibit cuboctahedral shapes and smooth surfaces. In this paper, we synthesized new kinds of SCD grits and nanocrystalline diamond (NCD) grits by a chemical vapor deposition (CVD) method and explored their grinding performance by single grit grinding of SiC ceramics. Grinding by HPHT grits was also conducted for comparison. The CVD-SCD grits exhibit cuboctahedral shapes, but surfaces are covered by protruded twin crystals of several microns, while the NCD grits are spherical agglomerations of nano-grains. We demonstrated that these morphological features have profound influences on material removal behavior. Results show that the wear of NCD grits is dominated by wear flat and intergranular cracks. The worn NCD grits can exert intense rubbing and ploughing effects on the workpiece. In contrast, the wear of CVD-SCD grits is dominated by fracture of the protruded twin crystals. It is proved that the twins on the grit surface are effective cutting edges to remove the material in a micro scale and thus lead to the formation of fine grinding striations and smaller cracking pits, but this process has little influence on specific grinding energy. Besides, grits with rough twins, especially on the flank face, tend to exhibit lower grinding force ratios and thus better sharpness. Moreover, for grits with smooth rake faces, there exists an explicit critical undeformed chip thickness value around 0.4–0.6 μm, above which the material removal mechanism changes from ductile to brittle rapidly. However, for grits with rough twins on rake faces, this transition process becomes vague.

Prediction of critical undeformed chip thickness for ductile mode to brittle transition in the cutting of single-crystal silicon

In order to achieve the ductile mode cutting of silicon and avoid the generation of subsurface crack damage, the undeformed chip thickness in the diamond cutting process must be controlled below the critical value. Therefore, the critical undeformed chip thickness (CUCT) for the ductile mode cutting of silicon is studied in this paper for guiding the selection of cutting parameters in the diamond cutting of silicon. Considering the anisotropy of single-crystal silicon, the prediction method of the CUCT in the ductile cutting of silicon is proposed on the basis of calculating the anisotropic fracture strength of silicon and subsurface stress distribution induced by the cutting force. Moreover, the influence of the anisotropy of single-crystal silicon, cutting tool parameters and friction coefficient in the cutting process on the CUCT are discussed, respectively. The results show that the anisotropic CUCT depends on the cutting surfaces and cutting directions. In addition, the diamond cutting tool with a negative rake angle of −40° is generally suitable for ductile cutting on the silicon (001), (110) and (111) surface when the friction coefficient in the cutting process is in the range of 0.05–0.30. Under this cutting condition, the minimum CUCT on the silicon (001), (110) and (111) surface is in the range of 150 ∼ 250 nm, 160 ∼ 290 nm and 150 ∼ 250 nm, respectively. The lower limit of the minimum CUCT on the three surfaces corresponds to the friction coefficient of 0.30 in the cutting process, and the upper limit corresponds to the friction coefficient of 0.05. Furthermore, a sharp-nosed cutting tool is also beneficial to improve the CUCT in the cutting process.

MICROMECANIZADO DE UN MATERIAL BIOCOMPATIBLE PARA LA PRODUCCIÓN DE PRÓTESIS: TÁNTALO DE 99.9 % DE PUREZA

During the last decades, micromilling has been widely researched for a wide variety of materials. However, the behavior of many materials has not yet been studied in the micro-machined area. Among these materials we can highlight those that have wide applications in industries such as aerospace, nuclear and biomedical. Within these last ones those biocompatible materials are the focus of this work. Thanks to its high melting point and its high resistance to corrosion, tantalum can have diverse applications in the above mentioned areas. In this paper we present the study of the cutting forces, mainly in the feed direction, and the acoustic emission in the micro-milling of 99.9 % purity tantalum with cemented carbide tools without coating and with two different coatings, (Ti,Al)N and DLC. The diameter of the tools was 500 µm, the cutting speed and the cutting depth of the test were kept constant with values of 63 m/min and 40 µm respectively, while 6 feed rates were in order to observe the influence of the critical undeformed chip thickness in the micro-milling operation. The recorded emission acoustic results allowed to identify the value of minimum chip thickness for each tool, while the power spectrum density results allowed to identify dominant frequencies of machining for different feeds per tooth. Regarding the feed force, it was possible to identify a minimum value for each tool as function of feed rate and the specific cutting force values showed the typical nonlinear behavior of the size effect. Keywords: micro-milling, tantalum, acoustic emission, cutting forces, specific cutting force.

Key machining characteristics in ultrasonic vibration cutting of single crystal silicon for micro grooves

Structured complex silicon components have been widely used in solar cells, biomedical engineering and other industrial applications. As silicon is a typical brittle material, ultrasonic vibration cutting (UVC) is a promising method to achieve better cutting performance than conventional techniques. High-frequency 1D UVC possesses higher nominal cutting speed and material removal rate than many 2D/3D UVC systems, and thus, it has great development potential in industrial applications of structured silicon components. However, few researchers have applied 1D UVC to the cutting of structured silicon surfaces, since its main drawback is tool marks imprinted by the vibration on machined surface. In this study, to uncover the key machining characteristics under the condition of 1D UVC, a series of tests involving diamond cutting grooves were first performed on the silicon surface. The machined surface and chips were subsequently measured and analyzed to evaluate the critical undeformed chip thickness, surface characteristics, and chip formation. Regarding the main drawback of 1D UVC, a novel theoretical model was developed for predicting the length of tool marks and evaluating the impact of tool marks on the surface finish. The results demonstrated that the critical undeformed chip thickness of silicon reached 1 030 nm under a certain vibration amplitude and that an array of micro grooves was generated at the plastic region with a surface roughness (Ra) as low as 1.11 nm. Moreover, the micro topography of the continuous chips exhibited discontinuous clusters of lines with diameters of dozens of nanometers, only composed of polysilicon. The novel theoretical model was able to predict the length of tool marks with low error. Thus, the impact of tool marks on the surface finish can be reduced and even eliminated with help of the model.

Influence of buried modified layer on crack propagation and diamond turning of silicon

Ductile-regime machining of brittle materials is a critical issue for ultra-precision manufacturing, because the machined surface is prone to be damaged by brittle fracture. Previous studies have showed that surface modification by ion implantation can be used to reduce the brittleness and improve the machinability. However, most researches focus on the formation of a continuous modified layer extending from surface to a specific depth. Although this configuration could provide a remarkable modification, it always requires a large ion dose and is time consuming. For this reason, a buried modified layer model is proposed in this paper. Firstly, the effect of the modified layer on crack propagation is studied by molecular dynamics simulation, which indicates an increase in fracture resistance of the buried modified layer model. Then, ion implantations are conducted on the (100) surface of silicon, and modification on the lattice structure is evaluated by Raman spectrum and transmission electron microscopy. Finally, diamond turning test is conducted and the critical undeformed chip thickness is measured. The results show that the buried modified layer is a potential configuration for improving the diamond turning process on brittle material.

Experimental study on “ductile-brittle” transition in micro-grinding of single crystal sapphire

Micro grinding is catching an increasing concern in manufacturing industries from scholars all over the world. The researches on “Ductile-brittle” transition in micro-grinding of brittle materials are important to the machining results, and this transition process could be affected by various factors, such as micro grit-material interaction, grinding force, material crystal structure, and so on. In this study, a series of scratching tests are carried out by two different apex angle indenters to analyze the effect caused by grain shape or indenter shape, corresponding machined surfaces, and scratching forces are observed and measured. It is found that scratched surface of obtuse indenter is almost intact and there are smooth fish bone shape apophyses on it; scratched surface of acute indenter is severely cracked. In respect of scratching force, force generated by obtuse indenter is much lower and much more stable than acute indenter. Based on the above differences, a new grinding force model considering grain shape effect in micro-grinding is built; micro grinding experiments conducted by different grain sizes micro grinding tools were designed and carried out to verify the proposed grinding force model. Three machining modes during the grinding experiment are defined; grinding force and quality of the machined surface are observed and compared. Rough critical undeformed chip thickness for different machining modes are given, when grain size of grinding tool is 800 #, hm ≤ 0.265 nm or 500 # hm ≤ 0.8 nm, it is ductile mode; tool 800 #, 0.265 nm < hm ≤ 1.35 nm or 500 # 1 nm ≤ hm ≤ 4 nm, it is ductile-brittle mode; tool 800 #, hm ≥ 2 nm or 500 # hm ≥ 5 nm, it is brittle mode. According to the experimental results, it is found that small grain size grinding tool is easier to generate a worse surface quality and a big crack size. Crack size is rising with the increasing of feeding velocity, and is decreasing with the rising of rotation speed. The conclusions made in this study provide a theoretical reference and experimental basis for ductile zone micro-grinding of hard and brittle materials.

Effect of cutting edge radius on micro end milling: force analysis, surface roughness, and chip formation

Producing miniaturized components from a wide variety of engineering materials is one of the most important fields of interest in manufacturing industry. Micro end milling is considered to be one of the efficient methods to produce complex 3D micro components. In micro machining, undeformed chip thickness is comparable to the tool edge radius, which introduces a critical undeformed chip thickness. Below the regime of critical undeformed chip thickness material is not removed but plowed. Ti-6Al-4V is one of the most popular titanium alloy because of its superior properties such as resistance to heavy loads, corrosion resistance, lightness, and bio-compatibility. This paper investigates micro end milling characteristics of the Ti-6Al-4V titanium alloy through a series of cutting experiments. Here the size effect in micro end milling was observed by studying the effect of the cutting edge radius on process performance. In order to understand the effect of the cutting edge radius on machining performance, range of feed per tooth was selected in such a way that it includes both within and outside the size effect region. This paper explores how cutting edge radius affects the cutting force, coefficient of friction, surface roughness, and chip formation during the micro end milling process. A size effect region was obtained from the variation of cutting force with feed per tooth. It was found that feed per tooth in the vicinity of 1-μm range is critical feed per tooth value, which is approximately one third of the cutting edge radius. Below this value, the cutting edge radius effect is predominant which would result in more ploughing mechanism. This was evident from the deviation of cutting force from the linear trend, increase in coefficient of friction, and surface roughness value at lower feed per tooth. In addition, a cutting force model was proposed considering the cutting edge radius effect and has been validated with experimental results.

Study on machinability of silicon irradiated by swift ions

Diamond cutting of hard and brittle materials is difficult owing to poor surface quality and severe tool wear. It has been clear that ion implantation can be used to improve the machinability. In previous studies, surface modification is realized by the nuclear collision cascade that induces phase transition during the implantation. Except for the nuclear collision process, electronic interaction between the incident particles and the target material, such as ionization, also occurs particularly during a high-energy ion implantation. However, the influence of ionization on the machinability has not been studied. In this paper, modification on the nanocutting of silicon by MeV oxygen ions is studied. Molecular dynamics simulation is conducted to reveal the nanocutting process on silicon with irradiation damages. Experiments show an enhancement in the critical undeformed chip thickness that is crucial in machining of brittle materials.

Determination of the critical undeformed chip thickness in micromilling by means of the acoustic emission signal

In the last decades, micromachining has gained increased relevance as an alternative method to produce miniaturized parts for a wide range of products. Nevertheless, micromachining differs considerably from conventional machining in many aspects. This work is concerned with the investigation of size effect when micromilling three distinct materials (pure nickel, electrolytic copper and AA 6262-T6 aluminium alloy). The friction coefficient between each work material and (Ti,Al)N coated tungsten carbide (cutting tool material) was determined and employed to calculate the critical chip thickness. Micromilling tests were performed and additionally to the specific cutting force, the critical chip thickness was identified using the acoustic emission signal. The findings indicate the suitability of the model based on the friction coefficient and cutting edge radius to determine the critical undeformed chip thickness. For each work material, it was found that feed rate values below the critical undeformed chip thickness led to ploughing (higher acoustic emission signal), whereas feed rate values above the critical undeformed chip thickness cause chip formation. Furthermore, the reduction in the shear plane area resulted in higher specific cutting force.

Theoretical study on brittle–ductile transition behavior in elliptical ultrasonic assisted grinding of hard brittle materials

The elliptical ultrasonic assisted vibration can lead to a higher comprehensive performance with better machined quality and lower grinding force during brittle materials machining. The undeformed chip thickness in grinding can be defined as the distance between two consecutive grinding surfaces formed by the adjacent abrasive grain trajectories. The ductile–brittle transition point of chip formation in brittle materials machining is believed to be represented by the threshold value of undeformed chip thickness (critical undeformed chip thickness). In this paper, an energy based method is proposed to predict the critical undeformed chip thickness in elliptical ultrasonic assisted grinding (EUAG). The effects of vibration parameters on grinding force and specific grinding energy are analyzed in detail. Results show that the axial vibration amplitude leads to a slight reduction in grinding force, whereas the vertical vibration amplitude results in a significant reduction of grinding force. The increase of wheel speed and ultrasonic vibration frequency can reduce the grinding force as well. Nevertheless, the grinding force ratio remains relatively steady fluctuating from 1.37 to 1.56. Additionally, the critical undeformed chip thickness increases with the increasing grinding speed, axial vibration amplitude and ultrasonic vibration frequency, while firstly increases and then decreases with the increasing vertical vibration amplitude. Especially, a ductile-mode grinding in micron-level can be achieved when the axial vibration amplitude is above 3μm and a totally brittle fracture occurs when the axial vibration does not exist. Thus, a reasonable selection of vibration parameters in EUAG process is required. The above theoretical evaluations coincide well with the variable experimental results.

Effects of non-amorphizing hydrogen ion implantation on anisotropy in micro cutting of silicon

Modification of semiconductors by ion implantation is a promising technology for improving their machinability. As well as ion implantation that induce amorphization, non-amorphizing ion implantation is also reported to improve the machinability of silicon. However, the anisotropy in micro cutting of crystalline silicon modified by non-amorphizing ion implantation is not clear. In this study, hydrogen is implanted in (001) silicon wafer with implantation energies and doses up to 175KeV and 3×1016cm−2, respectively. Transmission electron microscopy, numerical simulations and X-ray diffraction are carried out to confirm that point defects and strain are introduced by the implantation, and that crystalline damage is below the amorphization level. Plunge cutting experiments in two crystal directions are performed to study the effects of limited crystal damage induced by ion implantation on the anisotropy in micro cutting of silicon. The plunge cutting experiments show that the anisotropic behaviour is significantly changed. The critical undeformed chip thickness (CUCT) in the direction with lower CUCT before implantation exceeds that in the other direction after implantation. The ductile-regime cutting force is significantly reduced in one direction, while nearly un-affected in the other direction. The results are discussed from the perspective of the effects of ion implantation on the interaction between restricted slip systems. In addition, it is found that the scenarios of brittle-ductile cutting mode transition are significantly different in the <110> and <100> directions for both implanted and bare silicon, and the mechanisms are discussed from the perspective of the anisotropic cleavage systems.

Critical undeformed chip thickness of brittle materials in single point diamond turning

In this work, the ultimate compression force that enables the plastic removal of brittle materials in diamond turning is initially modeled according to the theory of rigid-plastic mechanics. And subsequently, an independent oscillator model is reconstructed to calculate the microfriction force that appears at contact interface. As expected, a predictive model considering the ultimate compression force and microfriction force is finally established to calculate the critical undeformed chip thickness of brittle materials in diamond turning, in which a crack-free surface of brittle materials can be achieved as quickly as possible in a brittle-ductile coupled cutting mode. Based on the theoretical predictions and experimental observations, the “size effect” of the critical undeformed chip thickness is discovered, i.e., that the ratio of the critical undeformed chip thickness to tool cutting edge radius increases with the decrement of tool cutting edge radius. Such interesting variation law is attributed to the strengthening of the effect of the microfriction and concentration of the compressive stress under a small enough cutting edge radius, which produces more favorable conditions for the brittle-ductile coupled removal of brittle materials.

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses.

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.

Molecular dynamics modelling of brittle–ductile cutting mode transition: Case study on silicon carbide

The mechanism of brittle–ductile cutting mode transition has received much attention over the past two decades. Due to the difficulties in directly observing the cutting zone during the brittle–ductile cutting mode transition by experimental techniques, many molecular dynamics (MD) studies have been conducted to investigate the atomicscale details of the phenomena, e.g. phase transformation, stress distribution and crack initiation, mostly under nanoscale undeformed chip thicknesses. A research gap is that direct MD modelling of the transition under practical undeformed chip thicknesses was not achieved in previous studies, due to the limitations in both computation capability and interaction potential. Important details of the transition under practical undeformed chip thicknesses thereby remain unclear, e.g. the location of crack formation and the stress distribution. In this study, parallel MD codes based on graphics processing units (GPU) are developed to enable large-scale MD simulations with multi-million atoms. In addition, an advanced interaction potential which reproduces brittle fracture much more accurately is adopted. As a result, the direct MD simulation of brittle–ductile cutting mode transition is realised for the first time under practical undeformed chip thicknesses. The MD-modelled critical undeformed chip thickness is verified by a plunge cutting experiment. The MD modelling shows that tensile stress exists around the cutting zone and increases with undeformed chip thickness, which finally induces brittle fractures. The location of crack formation and direction of propagation varies with undeformed chip thickness in the MD simulations, which agrees with the surface morphologies of the taper groove produced by the plunge cutting experiment. This study contributes significantly to the understanding of the details involved in the brittle–ductile cutting mode transition.

Simulation of Chip Formation Behavior during Single Diamond Grains Grinding by CEL Method

The grain orientation plays a great important role during single grain grinding. Single grain grinding simulation could offer an insight into the material removal behavior. However, grinding simulation with FE methods has problems arising from large deformations at the chip root and negative rake angles of the grain. In this work, a coupled Eulerian-Lagrangian method (CEL) is used to model the grinding behavior of single diamond grain in different orientations. The influence of the grain orientations on the grinding forces, grinding process (sliding, ploughing and cutting) and critical undeformed chip thickness are analyzed. The force ratio shows great accordance with the analytical calculation data. The simulation results show that the chip generates quickly and the special grinding force is relatively small when the diamond particle is in octahedral orientation (111)-(100). The workpiece material flows to the side and front owing to the pressing of cutting crystal face. The swelling of the material is generated beside the abrasive grain. The range and height of swelling are increased gradually and kept invariant after chip formation. The deformation of workpiece material contacting with grain edge is very severe. Therefore the biggest residual stress appears at the grain edge of the groove.