Material Removal Behavior Research Articles

Insight into crack propagation induced by fiber orientations during single grain scratching of SiCf/SiC composites using FEM

Due to the multiphase structure and anisotropy of ceramic matrix composites (CMCs), crack propagation is extremely complex during grinding. However, there is no full comprehension of the crack propagation law of CMCs in varying fiber directions, which limits high-quality CMCs machining. Based on experimental and numerical results, the effect of fiber directions on crack propagation of SiCf/SiC composites was analyzed. Results demonstrate that the change in crack propagation path is the primary reason why the removal behavior of CMCs is different from traditional ceramics. For CMCs, the interface is the priority path of crack propagation no matter along any fiber direction. Besides, the fiber orientation determines the propagation paths of radial and subsurface cracks, which affects material removal behavior. Comparing the scratched groove, the groove edge damage is the most severe when scratching along the fiber transverse direction, whereas the scratched groove surface quality is best in the perpendicular direction.

EFFECT OF CRYSTALLOGRAPHIC ORIENTATION ON MATERIAL REMOVAL BEHAVIOR DURING HIGH SPEED SCRATCHING OF MONOCRYSTALLINE SILICON

Monocrystalline silicon has anisotropic attributes due to asymmetric and non-uniform interatomic lattice structures, which affects its deformation and fracture properties. This paper aims to investigate the effect of crystallographic orientation on the material deformation and removal behavior during high speed scratching of monocrystalline silicon. A high-speed scratching setup is developed which can achieve the highest scratching speed of 40 m/s. Inclined scratching experiments are conducted on (001), (110) and (111) crystallographic planes over the speed range of 1 m/s to 30 m/s. As the scratching depth increases, the ductile-to-brittle transition of silicon at different crystallographic orientations are analyzed. The experimental results suggest that scratching in the direction of "[" ¯("1" ) "10]" on (111) plane presents the largest critical residual depth of ductile-to-brittle transition. Phase transformation from Si-I to the phases of Si-IV and a-Si dominates ductile deformation of silicon during scratching process, while scratching tests in "[" ¯("1" ) "10]" direction on (111) plane demonstrates the largest degree of material amorphization. This study can provide guidance for optimizing processing parameters of monocrystalline silicon components with different crystallographic orientations.

Research on Multiscale Modeling and Experiment of CFRP Milling.

High-quality milling of carbon fiber reinforced polymer (CFRP) composites is of great importance for the high-performance manufacturing of structures made of this hard-to-machine material. In this paper, a multiscale finite element (FE) model, considering the thermal-mechanical coupling effect, was developed to simulate the milling process and reveal its material removal mechanism. The corresponding milling experiments were conducted to validate the simulated cutting forces and temperature, which were in good agreement with the experiment results. In the macroscale model, the Hashin failure criteria were used to estimate the failure of the composites. In the microscale model, the fibers, matrix, and the fiber-matrix interface were modeled separately, to investigate the mechanisms of material removal behavior during milling, among fiber breakage, matrix cracking, and fiber-matrix debonding. Based on the macroscale numerical and experimental results, the higher cutting speed was demonstrated to improve the surface quality of CFRP milling. According to the results from the microscale model, the material removal mechanism varies depending on the orientation of the fibers and can be divided into four stages. The outcome of this work provides guidelines to further investigate optimal manufacturing parameters for the milling of CFRP composites and their cutting mechanisms.

Ductile deformation and subsurface damage evolution mechanism of silicon wafer induced by ultra-precision grinding process

In the field of advanced packaging, large-size silicon wafers are usually thinned by ultra-precision grinding technology relying on the process of workpiece self-rotation. However, the damage caused by mechanical material removal deteriorates the wafer surface flatness and die strength, while its atomic-scale formation principle has yet to be revealed. This work explores the ductile deformation and subsurface damage evolution mechanism of silicon wafer during the ultra-precision grinding process. Some grinding tests are first conducted using different diamond wheels. The surface topography and energy dispersive spectroscopy (EDS) mapping of ground wafers are measured by scanning electron microscope (SEM). The phase transition properties of the ground silicon wafer are confirmed via Raman spectrum. Next, the specimen of groove cross-section is fabricated and its morphology is examined via transmission electron microscopy (TEM) to analyze the subsurface damage characteristics. The subsurface defects at the atomic scale, involving amorphous layer, dislocations, stacking faults and lattice distortions, are observed. Due to its controllable load and similarity of the cutting motion, nanoscratch is utilized for investigating the influence of abrasive interactions on subsurface deformation during the grinding process. Thus, a series of multiple nanoscratch tests are performed in both varied and constant force modes. The material removal behaviors under different scratching conditions are illustrated. This work provides a fundamental understanding of developing a high-efficiency and low-damage thinning method for 12-inch silicon wafers.

Effects of feed direction on material removal behavior in belt grinding of titanium alloys

For abrasive belt grinding, although machine processing selection has been well studied to achieve good machinability, there is still a lack of understanding regarding the influence of feed direction and its mechanism, even though it is a common matter. This paper investigates the differences between up- and down-grinding in belt grinding of TC4, where the grinding forces, material removal performance, surface quality, and chip morphology are captured for the grinding process evaluation and mechanistic analysis In up grinding, it was observed that approximately 21.1 % more material removal can be achieved due to the larger penetration depth of scratching grains when maintaining a constant normal grinding force. Furthermore, the higher tangential grinding force resulting from increased cutting behavior and an additional sliding phase leads to more severe abrasive belt wear, as evidenced by a 22.7 % higher grinding ratio. Comparatively, down grinding mode generates a machined surface with lower roughness in the transverse and longitudinal direction, which can be explained by the minimum chip thickness effect and undeformed chip thickness model. The microscopic characteristics of chips and ground surface provide more evidence on the different chip formation mechanisms between two grinding modes.

Investigation of CFRP damages induced by the interface high temperature and mixed tool wear mechanism in drilling of thin-walled CFRP /Ti stacks

Due to the poor thermal conductivity and machinability of CFRP and Ti6Al4V, significant heat accumulation at the interface and rapid tool wear are considered the main factors restricting the hole quality. This study conducted a thin-walled CFRP/Ti stack drilling experiment to investigate the evolution of the thrust force, temperature and tool wear versus different drilled hole numbers and spindle speeds, affected by which the novel material removal behavior was revealed. Results showed that the thrust force and interface temperature increased with the hole number and spindle speed, causing a significant increase in the cutting edge rounding and flank face wear dominated by the many fiber bundles and metal debris. In turn, the various tool wear led radial interface temperature to alternately transfer between Φ = 45° and 135°. Under the cyclic thermo-mechanical function, the fibers underwent significant bending deformation as they lost the support of the degenerated matrix resin, forming severe subsurface damage when the interface temperature exceeded the matrix glass transition temperature (Tg = 110 °C). Combined with the comprehensive evaluation of exit damages, a relatively higher spindle speed was preferred for selecting the initial drilling of thin-walled CFRP/Ti stack and gradually reducing the spindle speed with increasing tool wear extent.

Simulation of machining behaviour of two-phase brittle materials during grinding by modelling single-grain scratching using a combination of FE and SPH methods

Two-phase, brittle-hard materials are widely used not only in the tool industry but also increasingly in the aerospace industry. Due to the two-phase nature, the materials have unique material properties adapted to the respective application. But the material properties also lead to challenging machinability. Therefore, two-phase, brittle-hard materials are mostly ground. The analogy process of single-grain scratching is used to analyse the material removal behaviour and design the grinding process. Since single-grain scratching is time-consuming and costly, it is desirable to substitute the analogy process with numerical simulation. This paper discusses the suitability of the Smooth Particle Hydrodynamic (SPH) simulation method in combination with the Finite Element Method (FEM) for single-grain scratching of two-phase, brittle-hard materials. The approach is validated using the examples of tungsten carbide-cobalt (WC-Co) cemented carbides and Silicon carbide fibre-reinforced silicon carbide (SiC/SiC) ceramics. For both applications, the material removal behaviour was optically analysed and in good agreement with the experimental results and theoretical assumptions. For SiC/SiC ceramics, several surface phenomena could be identified in the simulation as well as in the experimental results. The scratching forces were compared qualitatively and were in good agreement with the experimental results for both applications.

Strain rate effect on material deformation and removal behavior during high speed scratching of 4H‐SiC

The effects of strain rate on material deformation and tribology behavior of 4H‐SiC are studied with high speed scratching tests, which represent typical processing modes of SiC wafers such as abrasive grinding/polishing. The results show that higher scratching speeds tend to induce more surface defects at the same scratching depth, which leads to the occurrence of ductile-to-brittle transition at smaller scratching depths. The relationship between the strain rate and scratching stress is analyzed, based on which a novel material model of 4H‐SiC is proposed considering the strain rate effect. The research reflects a close correlation between scratching speed-dependent stain rate and material deformation behavior of 4H‐SiC, and it can provide guidance for process optimization during manufacturing of 4H‐SiC components.

Analytical modeling of subsurface damage and material removal energy in elliptical vibration cutting of micro-structures on brittle materials

Elliptical vibration cutting (EVC) is a promising technique for the fabrication of micro-structures on brittle materials. In this work, the surface quality and material removal energy in ultra-precision machining of micro-structures on brittle materials by EVC were investigated. Theoretical models were first established for predicting subsurface damage and specific cutting energy (SCE) based on the intermittent material removal characteristics of EVC. The models correlated cutting parameters with the tool vibration trajectory parameters, target surface geometry parameters, and material removal modes. Furthermore, the material removal behaviors in the nominal cutting direction and the feeding direction were comprehensively considered. To verify the model, the experiments of EVC and ordinary cutting (OC) were performed on single crystal silicon, and the surface morphology and cutting force were characterized. The results indicated that, compared with OC, the maximum subsurface damage depth is reduced by 61.82% and the SCE stability value is reduced to 45.87% by applying EVC to fabricate micro-structures. EVC could significantly improve the machining quality and reduce energy consumption. In addition, increasing the vibration amplitude in the depth of cut direction could further save energy, but a larger amplitude would increase subsurface damage. This work not only promotes the recognition of the material removal mechanism of EVC, but also presents effective guidance for achieving high-quality and sustainable machining of micro-structured surfaces.

Influence of anisotropy on material removal and deformation mechanism based on nanoscratch tests of monocrystal silicon

With its merits of excellent electrical properties and chemical durability, monocrystal silicon has been widely used as the substrate material in photovoltaic and integrated circuit fields. However, surface and subsurface damages caused by the machining process significantly reduce the chip life and the impacts of anisotropy remain poorly understood. Herein, this study employs nanoscratch tests to explore the anisotropy dependence on material removal and deformation mechanism for monocrystal silicon. Nanoscratch tests, under varied and constant load modes, are first carried out on a silicon surface along different crystal orientations. The surface morphologies of generated groove are observed to identify the surface crack system and depict the material removal behaviors. Then, a transmission electron microscope is applied to analyze the subsurface damage characteristics of deformation regions along different scratch directions. The results present the lattice defects close to the atomic scale, such as amorphous layer, stacking faults and phase transformation, and reveal the damage evolution mechanism considering material anisotropy. In addition, a molecular dynamics simulation model of monocrystalline silicon scratch is developed to expose the diversity of dislocation and stress distribution along different crystal orientations. This work provides a theoretical basis for realizing efficient and precise machining of anisotropic hard-brittle materials.

Mechanochemical removal of lithium aluminosilicate glass-ceramics

In this study, the material removal behaviors of diamond and SiO2 tips on lithium aluminosilicate (LAS) glass-ceramics surface were investigated in vacuum and deionized water using atomic force microscope. Two types of mechanochemical removal, stress corrosion and tribochemical removal were identified depending on counter-surface chemical activity. Their mechanisms were revealed using Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. In addition, combined with Raman spectra detection and thermal annealing experiments of removal areas, it was confirmed that compared with stress corrosion removal which reduced the removal energy threshold, tribochemcial removal was dominated by mechanochemical interaction without structural damage. The findings enrich the mechanochemical removal theory and furnish theoretical guidance for nano-precision machining of LAS glass-ceramic surface.

Surface quality and burr characterization during drilling CFRP/Al stacks with acoustic emission monitoring

Riveting and screwing are generally used as an important joining technique of composite/metallic stacks, which require one shot drilling of hybrid stacks to improve productivity and geometrical accuracy. However, due to the different optimal machining parameters between CFRP composites and Al alloys, surface damage is prone to occur during drilling process, which significantly affects the fatigue life of components. In this work, acoustic emission (AE) technology was firstly employed to investigate the characteristics of AE signal corresponding with material removal behavior and machining defect during drilling CFRP/Al stacks. Fast Fourier transform and short-time Fourier transform were used in processing AE signals. Results showed that time-frequency diagram and root mean square (RMS) curve of AE signals could be used to distinguish different stages of drilling process with sufficient accuracy. The specific frequency range of damage pattern when drilling CFRP composite was determined by analyzing the frequency domain characteristics of AE signals. In addition, AE signals had significant correlation with machined surface quality. Amplitude and fluctuation of AE signal generally increased with the increase of hole surface roughness. Moreover, by extracting the amplitude characteristics of AE signal in time domain, the initial fracture and formation mechanism of burrs at hole exit could be further understand.

Experimental research on material removal in robot abrasive belt grinding

ABSTRACT In order to reveal the material removal behavior of robot abrasive belt grinding (RABG) of nickel-based superalloy, the experimental research method of single grit grinding is proposed. In the research, ceramic alumina grits are used to scratch superalloy K438 based on the experimental setup of RABG. Four material removal parameters, namely real cutting depth, number of cutting edges involved in grinding, effective cutting area of cutting edges and pile-up ratio, are used to quantitatively describe the material removal behavior. The experimental results show that the grits have good cutting performance. And the cutting edges involved in grinding change dynamically, which has a significant influence on material removal. In addition, this paper analyzes the differences between RABG and wheel grinding (WG), studies the effect of cutting depth on material removal, and determines the factors that affect the material removal ability by evaluating the material removal ability of different grits.

Material removal behaviors of FCC metals in nanoscale and microscale scratching: Theoretical model and experiments

Material removal behaviors of FCC metals in nanoscale and microscale scratching: Theoretical model and experiments

Evaluation of grinding characteristics for sapphire ultra-precision grinding using small grit sizes wheels based on AE signals

This paper focused on the grinding characteristics for sapphire ultra-precision grinding with small grit size grinding wheels and acoustic emission signal monitoring of material removal mechanism under the action of multiple abrasive grain. The results show that the use of small grit size grinding wheels allowed for effective removal of sapphire and they facilitated the production of ductile surfaces at the correct parameters. The grinding depth was the most significant effect on the grinding characteristics, the grinding force and subsurface damage scale increased with the grinding depth, and the grinding surface morphology developed from ductile surface to low damage ductile surface and brittle fracture surface. The material removal behavior can be monitored with acoustic emission signals, the original signal, frequency domain and wavelet decomposition features were distinct attributed to the different material removal modes. Besides, low-scale subsurface damage also occurred at the parameters of small size grits and minimal grinding depth.

Highly dispersed Gd-CeO2 nanocrystals supported on mesoporous silica composite particles towards photochemical (photo-assisted chemical) mechanical polishing

Nanoparticles (NPs) are widely used in polishing slurries for ensuring desired material removal and global planarization. Herein, novel multicomponent core–shell abrasive systems have been fabricated via an efficient chemical approach towards photochemical (photo-assisted chemical) mechanical polishing (PCMP) processes. The developed composite particles involved low-modulus mesoporous silica (mSiO2) cores and high-activity Gd-doped ceria (CeO2) shells. Compared to commercial CeO2 NPs, the mSiO2@CeGdO2 abrasives enabled superior fused silica surface quality in both CMP and PCMP tests. Furthermore, the as-proposed composites allowed an evident removal efficiency enhancement in the presence of ultraviolet light radiation. The improved polishing performance can be attributed to (i) the optimization of interfacial contact state and material removal behavior, (ii) the increasements of trivalent cerium and oxygen vacancy, and (iii) the enhancement of photochemical and tribochemical activities of the mSiO2@CeGdO2 heterostructured abrasive systems. The purpose of this work is to provide some contributions to the rational design and fabrication of functional abrasive systems for high-performance PCMP and other field-assisted finishing practices through abrasive structure regulation, surface chemistry, and defect engineering.

Monitoring of ductile–brittle transition mechanisms in sapphire ultra-precision grinding used small grit size grinding wheel through force and acoustic emission signals

Progressive ultra-precision grinding experiments used small grit size grinding wheels were performed to investigate the ductile–brittle transition process of sapphire, force and AE signals were employed to monitor the material removal behavior. Precision dressing and measurement of circular arc grinding wheels were performed to meet the minimum grinding depth for ultra-precision grinding. A grinding force model was proposed to interpret the grinding forces in different materials removal modes. A continuous complete ductile–brittle transition process was observed and monitored, the progressive grinding was divided into three stages: ductile dominant, ductile–brittle transition and brittle eruption. The grinding force, surface profile, micro morphology and brittle fracture percentage were discussed. Brittle fracture will not entirely occur, but rather brittle fracture and ductile grooves were coexisted on the surface in the brittle eruption stage, which was attributed to the grinding characteristics of small grit wheels. In addition, raw AE signals and multiple transformation forms were utilized to monitor the material removal behavior and their respective roles were analyzed. The Fourier transform, discrete wavelet, continuous wavelet and wavelet coefficients in different stages can all establish a mapping relationship with material removal modes.

Material Removal Behavior of Ultrasonic Vibration Helical Grinding of SiCf/SiC Composites

Abstract To reveal the material removal mechanism of silicon carbide fiber reinforced silicon carbide ceramic matrix (SiCf/SiC) composites during the ultrasonic vibration helical grinding (UVHG) of hole-making process, a hole-making experiment of UVHG was conducted, and the contact behavior between a grain and different components in the SiCf/SiC was analyzed. The evaluation index of the hole wall quality Cw which comprehensively considers the overall level and local defects of surface quality was proposed, while the evaluation index of the hole exit quality Ce which comprehensively considers the area and depth of edge chipping was proposed too. The results show that the periodic changes of the fiber cutting angle θ will lead to different fracture mechanisms of the fibers and the interfaces, so the surface topography will change regularly. The brittle fracture of the matrixes under different process parameters is different, so the surface topography is different. The quality evaluation indexes Cw and Ce are highly reliable. Within the experimental parameters, selecting a smaller pitch, a smaller helical feed rate, and an appropriate ultrasonic amplitude can obtain better hole-making quality.

Effect of a water film on the material removal behavior of Invar during chemical mechanical polishing

Understanding polishing mechanisms in water-lubricated environments has an important guiding value for surface engineering of precision devices. This work reveals the chemical mechanical polishing (CMP) mechanism of the Invar alloy under water lubrication by use of molecular dynamics simulation. The results show that the appropriate thickness of the water film and polishing speed can significantly reduce the surface roughness of the work piece and eliminate subsurface defects. With the increasing rolling speed, the variation of the surface roughness and subsurface damage thickness exhibits a trend of slowly decreasing and then reaching stability. In addition, with an increase in water film thickness, more defects were formed in the subsurface region due to greater surface stresses, although the roughness could be reduced due to an increase of passivated atoms on the work piece surface. These results would be helpful for understanding the CMP mechanism under water-lubricated conditions and for promoting the development of surface engineering for micro/nano components.

Classification of different post-hyperdoping treatments for enhanced crystallinity of IR-sensitive femtosecond-laser processed silicon

Crystalline silicon becomes photosensitive and absorbing in the sub-bandgap spectral region if hyperdoped, i.e. supersaturated to a level above the solubility limit in thermal equilibrium, by deep impurities, such as sulfur. Here we apply femtosecond laserpulses to crystalline silicon in a SF6 atmosphere as hyperdoping method. The ultrashort laser pulses cause crystal damage and amorphous phases that would decrease quantum efficiency in a potential optoelectronic device application. We investigate five different post-hyperdoping methods: three etching techniques (ion beam etching IBE, reactive ion etching RIE, and wet-chemical etching HNA) as well as ns-annealing and minute-long thermal annealing and study their impact on crystallinity by Raman spectroscopy and absorptance in the visible and near infrared wavelength regime. We use femtosecond laser hyperdoped silicon (fs-hSi) with two different levels of surface roughness to study a potential dependence on the impact of post-treatments. In our investigation, ns-annealing leads to the best results, characterized by a high Raman crystallinity and a high remaining absorptance in the sub-bandgap spectral region of silicon. Within the used etching methods IBE outperforms the other etching methods above a certain level of fs-hSi surface roughness. We relate this to the specific anisotropic material removal behavior of the IBE technique and back this up with simulations of the effect of the various etching processes.