Subsurface Damage Depth Research Articles

Analysis of subsurface damage inhibition in magnetization-enhanced force-rheological polishing

Subsurface damage (SSD) during polishing silicon carbide (SiC) is an unavoidable problem in mould production. However, studies on the law of SSD generation in the magnetisation-enhanced force-rheological polishing process are limited. An SSD depth prediction model is established considering factors such as strain rate effect, elastic-plastic deformation, and dynamic changes in mechanical properties. A detection technology for the SSD depth of aspheric mould was proposed, and the influence mechanism of orthogonal tests on the SSD state of SiC mould was studied. The results show that the maximum deviation between the calculated and experimental results is less than 7%. The SSD depth dropped to the minimum threshold (< 0.5 µm) under a specific combination of parameters.

Research on CFRP cutting mechanism by the micro-textured tool using macroscopic and microscopic numerical simulations

Carbon fiber reinforced plastics (CFRP) composites are the most widespread advanced composite materials. Still, machining with traditional tools quickly generates defects such as high cutting forces and severe subsurface damage, while micro-textured tools can improve CFRP machining performance. Therefore, to reveal the cutting mechanism of CFRP processing by micro-textured tools and guide the tool design, macroscopic and microscopic orthogonal cutting models were established in this study, which compared and analyzed the material removal process and the indicated topography of unidirectional CFRP with different fiber orientations (0°, 45°, 90°, and 135°) by traditional tools and micro-textured tools, and the accuracy of the models was verified with experiments. Compared with traditional tools, micro-textured tools reduce cutting forces by minimizing the tool-chip contact length to reduce friction and converting the fiber failure form from crush failure to shear failure. Meanwhile, the texture on the rake face enables cutting burrs, effectively improving the surface quality of the workpiece and suppressing the depth of subsurface damage. In addition, the influence of different texture parameters on the machining quality of the workpiece was analyzed.

Atomistic study of nano-cutting bicrystal cubic silicon carbide

To solve problems of low machining efficiency and surface/subsurface damage of silicon carbide (SiC), mechanisms of material dislodging and subsurface destruction of bicrystal SiC under nano-cutting were studied by using three-dimensional molecular dynamics (MD) simulation method. Effects of grain boundary (GB) tilt angle and cutting speed on stress, hydrostatic pressure, cutting force, temperature, and subsurface damage depth were analyzed. Results show that GB slope angle has important influence on the spread of strain, hydrostatic stress, and temperature, especially on subsurface damage depth. Specifically, with the increase in GB slope angle, subsurface damage layer decreases, and machined surface morphology improves. The machinability of small GB angle is better than the large GB angle, and the model with grain boundary angle of 4.24° has the best machinability. It is also found that with the increase in cutting velocity, the temperature increases, whereas cutting force and friction coefficient are reduced, which indicates that the increase in cutting velocity can effectively improve surface machined morphology. The research results provide a theoretical reference for future experimental research.

Molecular dynamics simulation of laser assisted grinding of GaN crystals

Gallium nitride crystal is a typical difficult-to-machine material due to its distinct anisotropy, high brittleness, and high hardness. The molecular dynamics simulations of traditional grinding and laser assisted grinding of GaN single crystals with a single grit were performed, and the influences of the laser power density on grinding force, stress distribution, material damage mechanism, subsurface damage depth, and abrasive wear were systematically studied. The results demonstrated that dislocations, stacking faults, hexagonal-to-cubic phase transition, and amorphous transition were generated during both traditional grinding and laser assisted grinding processes. Compared with the traditional grinding, laser assisted grinding with an appropriate laser power density reduced the grinding force, stress distribution, phase transition percentage, dislocation loop length, subsurface damage depth, and wear damage of the abrasive. However, excessive laser power densities caused deeper subsurface damage depth and severer amorphous damage for the rake face of the abrasive particle, which seriously deteriorated the integrity of the ground surface and subsurface. The results not only enhance the understanding of material removal and damages under the coupling actions of the laser and abrasive machining, but also provide a theoretical basis for parameter optimization during the machining of GaN single crystals.

Finite element analysis and experimental study on the cutting mechanism of SiCp/Al composites by ultrasonic vibration-assisted cutting

SiCp/Al composites are considered difficult to machine due to the relatively high hardness of SiC particles. In this paper, ultrasonic vibration-assisted cutting (UVAC) technology is used to improve the machining of SiCp/Al composites. Firstly, cutting process of conventional cutting (CC) and UVAC of SiCp/Al composites are simulated by the finite element simulation method. Moreover, damage characteristics of SiC particles are explored when tool cutting path is located at different positions of SiC particles within the two machining methods. Machined surface/subsurface damage of workpiece is observed, and consistency with simulation results is verified. Then, combined with energy dispersive spectroscopy analysis technology, tool wear mechanism of UVAC and CC is explored, and wear characteristics of tool flank are analyzed. Moreover, chip formation features of UVAC and CC are also compared. Finally, relationship between the cutting force and surface roughness during CC and UVAC regarding different cutting process parameters is compared. According to obtained results, UVAC technology could reduce tool wear, improve machinability of SiCp/Al composites, and improve surface integrity of SiCp/Al composites, where cutting force is reduced by about 40%, surface roughness is reduced by 34%, and subsurface damage depth is reduced by 86%.

An investigation of monitoring the damage mechanism in ultra-precision grinding of monocrystalline silicon based on AE signals processing

Ultra-precision grinding has become one of the most important processes in the production of high-end optics made of hard and brittle materials. Due to the effects of ultra-precision grinding being the results of the joint action of many cutting edges, the monitoring and characterization of material damage mechanisms in ultra-precision grinding are full of challenges. Fortunately, the acoustic emission (AE) sensor has the excellent abilities of high signal-to-noise ratio, high sensitivity, and rapid response to transient events on an ultra-precision scale, which is eminently suitable for monitoring, characterizing, and optimizing the material damage mechanism in ultra-precision grinding. In this paper, the damage mechanisms of monocrystalline silicon in ultra-precision grinding were successfully monitored based on AE signals processing. Firstly, a novel AE signals processing method based on fuzzy C-means clustering and wavelet transform was proposed innovatively (FCWT). Secondly, the damage types in ultra-precision grinding were revealed and characterized using the evolution characteristics of the energy spectrum of AE signals. Then, the damage evaluations and critical characteristics of the material removal mechanism were thoroughly studied based on the characteristics of the time-frequency spectrum of AE signals. Ultimately, the subsurface damage depths in ultra-precision grinding of monocrystalline silicon were accurately predicted through the processed AE signals.

Research on mechanism of ultrasonic-assisted nano-cutting of sapphire based on molecular dynamics

Ultrasonic vibration grinding improves the surface quality and processing efficiency of sapphire machining compared with conventional grinding, but its nano-scale deformation mechanism is still unclear. In this study, the molecular dynamics method was used to simulate the ultrasonic vibration cutting of a single abrasive grain along the [010] direction on the sapphire (0001) surface to study the effects of different vibration directions, amplitudes and frequencies on the cutting force, stress, temperature, number of amorphous atoms, surface morphology and subsurface damage layer. The results show that the tangential and radial vibration cutting reduces the tangential force, normal force and total force compared with conventional cutting. At the same time, it is also found that different vibration directions have different effects on material removal efficiency and subsurface damage depth. In the material removal efficiency, the radial vibration cutting has the highest removal efficiency, and the tangential vibration cutting and conventional cutting have the same removal efficiency. In the subsurface damage depth, the subsurface damage depth in tangential vibration cutting is the smallest, the subsurface damage depth in conventional cutting is the second, and the subsurface damage depth in radial vibration cutting is the largest.

Image-processing-based model for the characterization of surface roughness and subsurface damage of silicon wafer in diamond wire sawing

The damages of silicon wafer in diamond wire sawing have a significant impact on its mechanics, economy, and use properties, which should be evaluated accurately and quickly. A theoretical model is developed to determine the surface roughness Rz (ten-point mean height) and subsurface damage (SSD) depth by the fracture width of silicon wafer. The model takes into account the scratch groove direction and material pile-up effect of silicon wafer. A digital image processing method is integrated into the model to extract the fracture parameters of silicon wafer. Many silicon wafers are processed under different slicing parameters, for which the fracture parameters and surface roughness Rz are measured by confocal microscopy, and the SSD depth is measured with the method of cross-section scanning microscopy. The scratch-induced material pile-up height is evaluated by nanoscratching. The calculated and measured fracture parameters, surface roughness Rz, and SSD depth are analyzed by contrast. The result shows that the model can accurately and quickly determine the surface roughness Rz and SSD depth with an average relative error of less than 12.0% in 20 s. The distribution characteristics of fractures, surface roughness, and SSD are analyzed. The result shows that more fractures have relatively smaller fracture width, depth, length, or related SSD depth. The image-processing-based model would be a reasonable approach for estimating the damages in silicon wafers during wire sawing.

Revealing nanoscale material deformation mechanism and surface/subsurface characteristics in vibration-assisted nano-grinding of single-crystal iron

Ultrasonic vibration-assisted grinding (UVAG) has attracted extensive attention as it can significantly improve the surface integrity of the machined workpiece. However, the atom-scale material deformation mechanism with the presence of ultrasonic vibration is still unclear, which hider the application of the UVAG to the ultra-precision machining process. To fill this gap, we present a molecular dynamics (MD) model for the vibration-assisted nano-grinding process (VANG) of single-crystal iron. The characteristics of the material deformation process induced by ultrasonic vibration are studied, including material accumulation, temperature, dislocation, subsurface damage (SSD), contact area, and grinding force. The results show that vibration changes the dislocation distribution in the plastic zone, forms the phenomena of expansion and contraction and causes the fluctuation of SSD depth. Due to the different distribution of stress and temperature during VANG, the details of plastic deformation, such as dislocation movement, dislocation nucleation and phase transformation, change with the varying vibration frequency. In addition, the reduction of the projected contact area is the main reason for the reduction of grinding force. However, dislocation pileup in the grinding zone and chips further increase the grinding hardness. This research could enrich the understanding of nano-scale deformation mechanisms in vibration-assisted processing of metallic materials.

Subsurface damage detection of optical elements by analyzing the photobleaching properties of quantum dots

Tagging the lapping and polishing slurries with quantum dots (QDs) is a promising method for detecting the distribution and depth of subsurface damage (SSD) in optical element at the same time. However, QDs are prone to photobleaching which affects the detection accuracy of SSD distribution and depth. The photobleaching properties of QDs with different structure and composition are different. This paper proposes a SSD detection method of optical element by analyzing the photobleaching properties of QDs. C QDs, CdSe QDs, CdSe/ZnS QDs, InP/ZnS QDs, and CuInS2/ZnS QDs were selected to tag SSD of optical element. A fluorescence detection system for SSD was developed to collect fluorescence images of QD-tagged optical elements under various excitation intensities, excitation time, and excitation numbers. The photobleaching properties of the QDs in SSD of optical elements were quantitatively analyzed by two parameters: (1) fluorescence conversion efficiency under various excitation intensities and (2) fluorescence stability index under various excitation time and excitation numbers. The distribution and depth of SSD were detected to comprehensively analyze the influence of the photobleaching properties of QDs on the SSD detection accuracy. The results show that the anti-photobleaching properties of C QDs, InP/ZnS QDs, CdSe/ZnS QDs, and CuInS2/ZnS QDs were strong, and they can detect SSD distribution and depth with high accuracy; while the anti-photobleaching property of CdSe QDs was poor, and they can detect SSD distribution and depth with low accuracy, making them unsuitable for tagging SSD. For CdSe/ZnS QDs, they can be used to detect SSD accurately only when the excitation intensity was higher than 33 mW. This paper lays a foundation for investigating the formation mechanism of SSD and detecting SSD non-destructively and accurately.

Theoretical model and digital extraction of subsurface damage in ground fused silica.

Based on the fracture mechanics and grinding kinematics, a theoretical model is developed to determine various subsurface damage (SSD) parameters and roughness Rz of the ground brittle material with consideration of the material removal mode and spring back. Based on the image processing, a digital method is proposed to extract various SSD parameters from the cross-section micrograph of the ground sample. To verify the model and method, many fused silica samples are ground under different processing parameters, and their SSD depth and roughness Rz are measured. The research results show the average SSD depth (SSDa) can be expressed as SSDa = χ1Rz4/3 + χ2Rz (χ1 and χ2 are coefficients). The SSDa is closer to half of the maximum SSD depth (SSDm) as the wheel speed decreases or the grinding depth, feed speed, or abrasive diameter increases. The SSD length or density basically increases linearly with the increase of the SSDm. The digital method is reliable with a largest relative error of 6.65% in SSD depth, extraction speed of about 1.63s per micrograph, and good robustness to the micrograph size and small-scale residue interference. The research will contribute to the evaluation of SSDs and the optimization of the grinding process of fused silica.

A study of surface integrity in carbon fiber-reinforced polymer composites cutting with the coupling effect of the multiple machining parameters

In the paper, a three-dimensional (3D) micromechanical numerical cutting model with three phases was developed to study the surface integrity in cutting of Carbon fiber-reinforced polymer (CFRP) composites. The surface roughness and the depth of subsurface damage were predicted by using the numerical model, which were used to characterize the surface integrity. The machined surface observations and surface roughness measurements of CFRP composites at different fiber orientations were also performed for model validation. It is indicated that the 3D micromechanical cutting model is capable of precisely predicting the surface integrity of CFRP composites. To investigate the complex coupling influences of multiple machining parameters on the surface integrity, the factor analysis of multiple machining parameters was performed, and then the effects of these machining parameters on the surface roughness and subsurface damage depth were obtained quantitatively. It was found that the coupling effect of fiber orientation and cutting speed are the most significant factors to affect the surface roughness with the contribution rate of 4.8%, and the interaction between fiber orientation and edge radius has the most important effect on the subsurface damage depth with the rate of 5%. The results also reveal that coupling effects of cutting speed and rake angle should be considered for improving the surface integrity of CFRP composites.

Experiment and theoretical prediction for subsurface microcracks and damage depth of multi-crystalline silicon wafer in diamond wire sawing

Diamond wire saw slicing is an important process of multi-crystalline silicon (mc-Si) solar cell substrate processing. In wire sawing of silicon crystal, the brittleness removal of materials will lead to subsurface microcrack damage, reduce the fracture strength, increase the breakage probability of the as-sawn wafer and affect the subsequent surface etching texture of wafer. In this paper, a mathematical model calculating subsurface damage depth (SSD) of mc-Si is established based on the analysis of subsurface crack system in diamond wire sawing process. The correctness and rationality of the model are verified by experiments. Then, the model is used to predict the variation trend of the microcracks number (CN) and subsurface damage depth under different process parameters and saw wire parameters. The results show that the SSD decreases and CN increases with the increase of wire speed and decrease of feed speed; With the increase of abrasive density on wire surface, the SSD decreases and CN increase. The change of abrasive average size has little effect on the SSD and CN; a smaller abrasive size range is beneficial to reduce the SSD and increase CN.

Sensitivity of polarized laser scattering detection to subsurface damage in ground silicon wafers

Silicon is the primary substrate material in the semiconductor industry. Since surface integrity of a silicon wafer is crucial to the performance of an IC chip made of the wafer, the subsurface damage (SSD) induced by machining to a silicon wafer has been intensively investigated. However, detecting SSD is a challenge due to a lack of an effective method. This study presents a novel method, the polarized laser scattering (PLS) method, for detecting SSD in ground silicon wafers. A PLS system is established to detect the grinding-induced SSD which is also evaluated by the destructive methods. The study shows that the PLS signal is sensitive to the SSD depth with a detection resolution of approximately 0.1 μm. In addition, the detectability of the PLS method is demonstrated and a relationship between the PLS signal and SSD depth is established to facilitate the practical applications of the PLS method.

Investigation on surface evolution and subsurface damage in abrasive lapping of hard and brittle materials using a novel fixed lapping tool

Novel fixed abrasive lapping (NFAL) is used in this study to quickly remove the surface damage layer and control the depth of subsurface damage (SSD), thus saving overall machining time and reducing the costs of large-aperture optical manufacturing. The influence of lapping parameters on the surface and subsurface state is studied through a series of experiments to better understand the material removal and damage mechanisms during NFAL. A surface evolution model for NFAL was established based on indentation fracture mechanics, mathematical statistics, abrasive wear theory and convolution iteration principle. Experimental results show that the model can predict the surface topography well. Further simulation experiments were also conducted to study the effects of the tool load and particle size on the microscopic removal characteristics of the NFAL process. The results show that NFAL can quickly produce submicron-level surface roughness and restrain SSD with the reasonable selection of lapping parameters.

Fundamental investigation of subsurface damage on the quality factor of hemispherical fused silica shell resonator

Hemispherical resonator gyroscope is an ultra-high precision and reliability solid-wave gyroscope. The quality factor (Q factor) is an important performance parameter of the resonator which is made of high purity fused silica. The subsurface damage (SSD) is generated due to brittle defects of fused silica during the grinding process. However, surface quality reduction caused by SSD significantly reduces the Q factor of the resonator. In this paper, the influence of SSD removal on the Q factor variation of the hemispherical fused silica resonator is investigated via the chemical etching method. The SSD depth of the hemispherical fused silica resonator fabricated by the precision grinding is measured. A device for Q factor measurement in high vacuum is built by employing the ring-down time method, which is composed of an impact exciter for excitation and a laser Doppler vibrometer for detection. The SSD is removed by chemical etching with several processing rounds. The Q factor and surface morphology of the resonator are evaluated after each round. The effect of residual subsurface damage depth on Q factor as etching processing is demonstrated. The experimental results indicated that the Q factor in the vacuum can be improved via chemical etching by 354% from the initial value of 1.84 × 105 into the final value of 8.36 × 105. The obtained results indicate that chemical etching can effectively remove the SSD on the subsurface of the fused silica resonator and significantly improve the Q factor.

Study on cutting force and induced thermal damage of carbon fiber reinforced polymer composites using microscopic simulation modeling

AbstractA three‐dimensional (3D) microscopic finite element (FE) cutting model was developed with the thermo‐mechanical coupling for carbon fiber reinforced polymer (CFRP) composites in this article. The model predictions of cutting force, machined surface, and cutting temperature at various fiber orientations were obtained and compared with the experimental data. It was shown that the 3D microscopic cutting model can predict the cutting force, cutting temperature, and subsurface damage precisely. The behavior of cutting force has presented an obviously cyclical variation characteristics at the fiber orientations of 0°, 45°, and 90°, and different chip morphologies were obtained correspondingly. The temperature fields of machined surface were studied at the four different fiber orientations, in which the maximum residual temperature on the machined surface occurs at 90°. The heat‐induced resin coating and resin ridges on the machined surface were obviously observed at the fiber orientations of 45° and 135°. The trend curve of cutting temperature is more similar with that of thrust force by comparing with cutting force, which meaning, unlike the isotropic metal materials, the thrust force has the direct effect on the heat generation. In addition, the comparison of depth of thermal and mechanical subsurface damage was also performed, it was showed that the depths of thermal subsurface damage are close to that of mechanical subsurface damage in the range of 0°–45°, and the thermal subsurface damage decrease while the mechanical subsurface damage increases with the increase of the fiber orientation range from 90° to 180°.

Optimization of the continuity of the aspherical production processes in asphericon s.r.o based on subsurface damage and microroughness analysis

In the paper is presented an analysis and optimization of the standardized sub-apertural grinding process used in the serial production in asphericon s.r.o. The monitored parameter was the depth of subsurface damage and surface microroughness. Tested were five grinding processes, which were automatically generated by the internal system, for five different diamond grit sizes (D151, D91, D64, D30, and D15). For evaluation of the depth of the defected layer was used modified wedge polishing method which is suitable for analysis of the rotationally symmetrical sub-apertural grinding processes [1]. For identifying the presence of the subsurface damage two methods were used. Defect detection using an optical microscope, as the broadly used and reliable method, and detection by standard ISO control to get the comparison with the method used in common serial production. The microroughness was measured using a white-light microscope concerning the used grinding tool and the amount of removed material. Within the experiment was found as the most effective two-step process uses D91 for rough grinding and D30 for fine grinding. D91 provides a very good removal characteristic with final subsurface damage of 44 µm which is possible to grind out using the D30 tool in two steps with final subsurface damage 22 µm in a total processing time of 137 minutes. This grinding process is timewise in best balance with 80 minutes long polishing process and therefore minimize the production cost. Result microroughness around 2 nm Sq in the fully polished zone is already limited by the polishing process. Using a finer grinding tool is not bringing improvement in the surface microroughness just shortening polishing time due to lower subsurface damage.

The influence of subsurface damage depth on fracture strength of ground silicon wafers

A grinding process is required to thin the back of the semiconductor chips to meet the requirements of chip thickness. Subsurface damage caused by the grinding can result in fracture strengths degradation, which has an impact on the safety and reliability of the chip. In this paper, the fracture strengths of silicon wafers ground using wheels with different grit size were obtained by the ball-on-ring method, and the Weibull distribution function was used to fit the fracture strengths. The subsurface damage depths at different radial positions of the ground silicon wafer were measured by cross-section polishing microscopy. Results showed that the fracture strengths decreased with the increase of subsurface damage depths, and the relationship between the fitted minimum strength and the maximum depth of subsurface damage was in good agreement with the prediction result of the classical fracture mechanics formula.

Prediction for subsurface damage depth of silicon wafers in workpiece rotational grinding

Prediction for subsurface damage depth of silicon wafers in workpiece rotational grinding