Removal Mode Research Articles

Material removal and surface generation mechanisms in diamond wire sawing of silicon crystal

Silicon crystal is usually first cut into wafers in the applications of electronic devices and photovoltaic solar cells. At present, fixed abrasive wire sawing technology has been widely used in slicing. The mechanism of material removal and surface generation during wire sawing is the key basic problem to study the surface quality of sliced wafers, which is important to realize high-precision slicing. This paper presents theoretical analysis on the relationship between the average cutting depth of abrasives distributing in different positions along the wire circumferential surface and the process parameters. The wire sawing experiments of single crystal silicon were carried out, then the morphologies of sawn surface and swarf were observed, the surface roughness was measured and analyzed, the material removal and surface generation mechanism of single crystal silicon cut by electroplated diamond sawing wire were addressed. Research results show that there is an approximate non-linear increasing relationship between the average cutting depth of the abrasives and the ratio of the workpiece feed speed to the wire speed, and the abrasives cutting depth and surface roughness of sliced wafers increases with the increasing of ratio value. It is difficult to obtain the sliced surface in a fully ductile mode of material removal in the actual wire sawing process because there are always a small amount of abrasives with high protrusion on the wire surface whose cutting depths are greater than the critical ductile regime cutting depth, but adopting a low ratio can make the generation of the sliced wafer surface in near-ductile or local-ductile material removal mode which can produce high quality wafer surface. This research is expected to be useful in optimizing the combination of process parameters in fixed abrasive diamond wire saw precision slicing of silicon wafers.

Flexible Bronchoscopic Removal of Foreign Bodies from Airway of Children: Single Center Experience Over 12 Years

To report our experience of tracheobronchial foreign body removal in children using flexible bronchoscopy as the primary mode. Hospital records of tracheobronchial foreign body extractions between January, 2006 and January, 2018 were reviewed. Clinical presentations, radiological findings, location and types of tracheobronchial foreign bodies, types of bronchoscopes, complications and outcome of the procedures were analyzed. 283 extractions in children with median (range) age of 18 (5-168) months were reviewed. Extraction by flexible bronchoscope, using wire baskets or grasping forceps, was successful in 260 cases. No major complications were encountered. Mean (SD) time for the procedure was 31 (6.3) minutes. Airway foreign bodies can safely be removed by flexible bronchoscopy with minimal complications. This procedure can be considered the primary mode for removal of airway foreign bodies by a trained and experienced person.

Specific cutting energy index (SCEI)-based process signature for high-performance milling of hardened steel

The specific cutting energy can characterize the machinability of the cutter for a material, and its change is a reflection of the size effect in the metal cutting process. It is critical to study the cutting process using an energy-based processing signature method with the purpose of improving the machining performance. In this paper, a specific cutting energy calculation method is presented based on a mechanistic model, and an exponential function is used to describe the trend in the specific cutting energy with the average undeformed chip thickness. A dimensionless index with value of greater than 1, referred to as the Specific Cutting Energy Index (SCEI), is proposed to address the energy efficiency of the milling process and reflect the machining performance for different machining parameters. Machining experiments with 300 M steel are conducted to validate the effectiveness of the proposed model. Analyses are performed to determine the relationships between SCEI and the material removal mode, chip morphology, tool wear rate, and surface roughness. Based on these results, a feed rate scheduling method is proposed to obtain optimal machining strategies using SCEI, which is an effective way to achieve high-performance machining.

Micro-ultrasonic drilling of monocrystalline silicon: An experimental investigation on machined surface topography and optimization using User's preference rating based TOPSIS

In the current scenario, silicon is extensively used as raw material in microelectromechanical systems and microelectronic devices. But, it has low fracture toughness that renders it difficult to process by conventional machining techniques. Thus, to overcome the barriers of conventional machining, rotary tool micro-ultrasonic drilling (RT-MUSD) process has been attempted for machining of silicon in this research endeavour. Taguchi's L9 orthogonal array was adopted as experimental design. The influence of variable parameters viz. rotation speed, power rating and abrasive size were analysed on performance characteristics (i.e. hole overcut (HOC), taper angle (TA) and material removal rate (MRR)) of RT-MUSD process. Analysis of variance (ANOVA) was applied to determine the significant parameters affecting the RT-MUSD process. Subsequently, optimal parametric setting for minimum HOC and TA and maximum MRR was obtained through user's preference rating based technique for order preference by similarity to ideal solution method. The ANOVA results showed that rotation speed was the most influencing parameter affecting the HOC, TA and MRR. The optimal parametric combination resulted in an average improvement of 26% in the performance of RT-MUSD process. The machined surface topography revealed that two types of material removal mode (i.e. pure brittle fracture and ductile + brittle fracture) occurred during RT-MUSD of silicon.

Modes of occurrence and removal of toxic elements from high‐uranium coals of Rongyang Mine by stepped release flotation

AbstractThe Rongyang coals from Guizhou, southwestern China, are significantly enriched with uranium (U) and other toxic elements, such as vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co), copper (Cu), and selenium (Se). Therefore, it is necessary to remove these toxic elements from high‐U coals before combustion. Previous studies have shown that U cannot be effectively removed by flotation and gravity separation. In this study, the stepped release flotation and acid leaching tests were conducted for coals of the Longtan Formation from the Rongyang Mine. The results from these analyses are as follows: (a) Stepped release analyses revealed that a multistage cleaning process can help to separate toxic elements from cleaned coals; (b) The removal of toxic elements by stepped release and acid leaching is closely related to their mode of occurrence. Vanadium, Cr, Mo, and U were difficult to be removed by stepped release flotation, which due to a significant proportion of them occur in organic matter and fine‐grained minerals; (c) Compared to flotation, most elements were better to be removed by stepped release flotation. In comparison with gravity separation, U had a higher removability by stepped release flotation, while the removal effect of thiophilic element by gravity separation was greater than by flotation; (d) After stepped release flotation, toxic elements Sc, V, Cu, Se, Mo, Hg, and U are still enriched in cleaned coals, suggesting that these elements cannot be fully removed through stepped release flotation.

Development of boronic acid-functionalized mesoporous silica-coated core/shell magnetic microspheres with large pores for endotoxin removal

Endotoxins are found almost everywhere and possess high toxicity in vivo and in vitro. Here we design a novel boronate affinity material, called boronic acid-functionalized mesoporous silica-coated core/shell magnetic microspheres (Fe3O4@nSiO2@mSiO2-BA) with large pores (pore size > 20 nm) based on the chemical structure and physical properties of endotoxins, for facile and highly efficient removal of endotoxins. Dual modes for endotoxin removal were proposed and confirmed in this work: the endotoxin aggregates with size < 20 nm were bound with boronic acid ligands chemically modified on the inner and outer surface of the large pores of Fe3O4@nSiO2@mSiO2-BA microspheres; while the larger endotoxin micelles (size >20 nm) were absorbed on the outer surface of the prepared material based on boronate affinity. Transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms and Fourier transform infrared (FT-IR) spectroscopy confirm that Fe3O4@nSiO2@mSiO2-BA microspheres possess core/shell structure, uniform diameter (520 nm), high surface area (205.57 m2/g), large mesopores (21.8 nm) and boronic acid ligands. The purification procedures of Fe3O4@nSiO2@mSiO2-BA microspheres for endotoxin were optimized, and 50 mM NH4HCO3 (pH 8.0) and 0.05 M fructose were selected as loading/washing, elution buffers, respectively. The binding capacity of Fe3O4@nSiO2@mSiO2-BA microspheres for endotoxin was calculated to be 60.84 EU/g under the optimized conditions. Finally, the established analytical method was applied to remove endotoxins from plasmid DNA. After endotoxin removal, the endotoxin content in plasmid DNA was reduced from 0.0026 to 0.0006 EU/mL for two-fold concentration, and from 0.0088 to 0.0022 EU/mL for five-fold concentration after binding, respectively. Additional advantages of the prepared boronate affinity material include excellent stability, reusability/repeatability, and low cost. Boronate affinity materials with large pores could thus prove to be powerful adsorbents for endotoxin removal and the potential applications in the aspects of biological research, pharmaceutical industry, and life health.

Studies on the grinding force, size effect, surface texture, and mechanism of material removal in the grinding of AA6061-TiB2/ZrB2 in situ composite

Machining and conversion of aluminum matrix composites into a desired shape with accuracy has been a challenge for many years. Grinding is a process aimed at achieving better-quality surface finish along with reasonable rate of material removal. The present article describes the influence of operating parameters on the tangential grinding force, size effect, and surface integrity in the grinding of in situ aluminum matrix composites using various grinding wheels. The material removal mechanism of the in situ composite under different grinding conditions is established. Experimental results show that the grinding operating parameters have significant influence on the tangential grinding force, size effect, surface integrity, and material removal. Scanning electron and atomic force microscopy findings indicate presence of numerous surface defects on the grounded surface under all grinding conditions. Diamond grinding wheel outperformed the CBN and Al2O3 wheels by requiring lower grinding force and specific grinding energy and generating lower surface defects. Surface defects, including grinding striation, delamination, and ridge formation are unavoidable under all machining conditions. However, the aforementioned surface defects indicate the ductile mode of material removal at all experimental conditions. Undeformed chip thickness under various grinding conditions plays a significant role in material removal and surface generation. These findings help to understand the mechanism of material removal in machining of in situ composites under various grinding conditions, which helps in attaining the economic production rate without compromising the surface integrity.

Study of the influence of tool rake angle in ductile machining of optical quartz glass

The SPH simulation model of optical quartz glass was established to study the ductile machining process with different tool rake angles. The material removal mode, stress distribution, cutting force, and subsurface damage during machining were analyzed. The critical cutting depths of brittle-ductile transition under different tool rake angles were obtained. The simulation results show that the tool negative rake angle is better than the positive rake angle in promoting the ductile machining of optical quartz glass. When the tool rake angle is negative, significant compressive stress which suppresses the crack generation by reducing the stress intensity factor KI is generated in the chip forming area, thus realizing the ductile machining of optical quartz glass. The greater the tool negative rake angle is, the more stable the cutting force and the greater the critical cutting depths of brittle-ductile transition are. When the tool negative rake angle is greater than − 35°, the subsurface damage of the optical quartz glass is aggravated, and the subsurface residual stress is complicated. When the tool negative rake angle ranges from − 15° to − 35°, the optical quartz glass is not only machined in a stable ductile region but also has less subsurface damage. Finally, nano-scratch experiments were carried out, and the critical depths of the brittle-ductile transition obtained by the experiments are basically consistent with the simulation results, which verify the correctness of the simulation results. The research results in this paper could provide a theoretical basis for the optimal selection of tool rake angle in the ductile machining of optical quartz glass.

Renal Effects of Intensive Volume Removal in Heart Failure Patients With Preexisting Worsening Renal Function.

Background The relationship between intensive volume removal in acute decompensated heart failure patients with preexisting worsening renal function (WRF) and renal tubular injury, postdischarge renal function, and clinical outcomes is unknown. Methods and Results We used data from the multicenter CARRESS-HF trial (Cardiorenal Rescue Study in Acute Decompensated Heart Failure) that randomized patients with acute decompensated heart failure and preexisting WRF to intensive volume removal with stepped pharmacological therapy or fixed rate ultrafiltration. Patients in the urinary renal tubular injury biomarker substudy (NAG [N-acetyl-b-D-glucosaminidase], KIM-1 [kidney injury molecule-1], and NGAL [neutrophil gelatinase-associated lipocalin]) were evaluated (N=105). The severity of prerandomization WRF was unrelated to baseline renal tubular injury biomarkers ( r=0.14; P=0.17). During randomized intensive volume removal, creatinine further worsened in 53% of patients. Despite a small to moderate magnitude increase in creatinine in most of these patients, postrandomization WRF was strongly associated with worsening in renal tubular injury biomarkers (odds ratio, 12.6; P=0.004). This observation did not differ by mode of volume removal (stepped pharmacological therapy versus ultrafiltration, Pinteraction=0.46). Increase in renal tubular injury biomarkers was associated with a higher incidence of hemoconcentration (odds ratio, 3.1; P=0.015), and paradoxically, better recovery of creatinine at 60 days ( P=0.01). Conclusions In acute decompensated heart failure patients with preexisting WRF, intensive volume removal resulted in a further worsening of creatinine approximately half of the time, a finding associated with a rise in tubular injury biomarkers. However, decongestion and renal function recovery at 60 days were superior in patients with increased tubular injury markers. These data suggest that the benefits of decongestion may outweigh any modest or transient increases in serum creatinine or tubular injury markers that occur during intensive volume removal. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT00608491.

A Nanomechanical Analysis of Deformation Characteristics of 6H-SiC Using an Indenter and Abrasives in Different Fixed Methods.

The super-precise theory for machining single crystal SiC substrates with abrasives needs to be improved for its chemical stability, extremely hard and brittle. A Berkovich indenter was used to carry out a systematic static stiffness indentation experiments on single crystal 6H-SiC substrates, and then these substrates were machined by utilizing fixed, free, and semi-fixed abrasives, and the nanomechanical characteristics and material removal mechanisms using abrasives in different fixed methods were analyzed theoretically. The results indicated that the hardness of C faces and Si faces of single crystal 6H-SiC under 500 mN load were 38.596 Gpa and 36.246 Gpa respectively, and their elastic moduli were 563.019 Gpa and 524.839 Gpa, respectively. Moreover, the theoretical critical loads for the plastic transition and brittle fracture of C face of single crystal 6H-SiC were 1.941 mN and 366.8 mN, while those of Si face were 1.77 mN and 488.67 mN, respectively. The 6H-SiC materials were removed by pure brittle rolling under three-body friction with free abrasives, and the process parameters determined the material removal modes of 6H-SiC substrates by grinding with fixed abrasives, nevertheless, the materials were removed under full elastic-plastic deformation in cluster magnetorheological finishing with semi-fixed abrasives.

Mathematical model for cutting force in ultrasonic-assisted milling of soda-lime glass

Ultrasonic-assisted milling (UAM) has an outstanding performance in machining hard and brittle materials, such as glass. The cutting force which has been investigated both experimentally and theoretically is the key factor that affects the machined surface quality. This paper presents a mechanistic mathematical model for the axial cutting force in UAM of soda-lime glass. This model is based on the process mechanism of material removal and can be used to predict the cutting force without the need of performing actual experiments. The mathematical model is proposed taking into consideration two different material removal mechanisms, that directly affect the final material removed volume for the brittle material. The first model is the ductile model which is described by the ductile mechanism where the material is removed by the plastic flow, while the other is the brittle model described by the brittle mechanism where the material is removed due to the crack formation that cause material fracture. In the present models, the effects of both the rotation and ultrasonic vibration motion of the cutting tool were taken into consideration through their effects on the indentation volume, by each diamond grain, into the workpiece. The development of the model started by the analysis of the behaviour of a single diamond grain and obtaining the cutting force for an individual diamond grain first. The total cutting force then was derived by summing up the forces caused by all diamond grains taking part in the cutting process. From the developed models results, the trends of the predicted results from the ductile model agree well with the results determined experimentally at low feed rates and low depths of cut. However, the predicted results from the brittle model agree well with the results determined experimentally at high feed rates and high depths of cut. These results explain that the ductile mode of the material removal is occurring at low feed rates and low depths of cut. Then it changes to the brittle mode of material removal by further increasing of the feed rate and depth of cut.

Material removal mode and friction behaviour of RB-SiC ceramics during scratching at elevated temperatures

Thermal assistance is considered a potentially effective approach to improve the machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by deliberately introduced heat is crucial to obtain a high-quality machined surface. This paper aims to reveal the material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. The material-removal mode, scratching hardness, critical depth of the ductile–brittle transition, scratching force, and friction are discussed under different penetration depths. The size effect of scratching hardness is used to assess the plastic deformation at elevated temperatures. A modified model is established to predict the critical depth at elevated temperatures by considering the changes in mechanical properties. The results reveal that the material deformation and adhesive behaviour enhanced the ductile-regime material removal and the coefficient of friction at elevated temperatures.

Optimizing selectivity of anion hydrophobic multimodal chromatography for purification of a single-chain variable fragment.

Single-chain variable fragments (scFv) are widely used in several fields. However, they can be challenging to purify unless using expensive Protein L-based affinity adsorbents or affinity tags. In this work, a purification process for a scFv using mixed-mode (MM) chromatography was developed by design of experiments (DoE) and proteomics for host cell protein (HCP) quantification. Capture of scFv from human embryonic kidney 293 (HEK293) cell feedstocks was performed by hydrophobic charge induction chromatography (MEP HyperCel™), whereafter polishing was performed by anion hydrophobic MM chromatography (Capto Adhere™). The DoE designs of the polishing step included both binding and flow-through modes, the latter being the standard mode for HCP removal. Chromatography with Capto Adhere™ in binding-mode with elution by linear salt gradient at pH 7.5 resulted in optimal yield, purity and HCP reduction factor of 98.9>98.5%, and 14, respectively. Totally, 258 different HCPs were removed, corresponding to 84% of identified HCPs. The optimized conditions enabled binding of the scFv to Capto Adhere™ below its theoretical pI, while the majority of HCPs were in the flow-through. Surface property maps indicated the presence of hydrophobic patches in close proximity to negatively charged patches that could potentially play a role in this unique selectivity.

Simultaneous photodegradation and removal of organic-inorganic pollutants over zeolite prepared from Saudi Arabia kaolin

In this paper , TiO2 impurities exists in kaolin were investigated for the first time as an active centers for photo degradation of M.B ( Methylene Blue) dye. The study extends to examine the same impurities after its transformation into NaP zeolite. Simultaneous removal of heavy metals (Pb2+, Cu2+, Ni2+, Co2+) in presence of organic dye over metakaolinite phase and NaP zeolite was performed in presence and absence of UV irradiation. The samples were characterized using XRD, SEM , EDX, Diffuse UV-Vis spectrophotometer and finally drawing the kinetic curves of removal of heavy metal ions and M.B dye. The results showed that the TiO2 impurities in metakaolinite exists in anatase form and maintain its existence in the transformed Na-P zeolite with the same phase. Both NaP and metakaolinite showed photo catalytic activity towards degradation of M.B dye. However, the NaP zeolite showed superior behavior for simultaneous removal of both pollutants with UV Irradiation. Investigation and mode of removal of both samples were investigated.

Ultra-precision grinding of AlON ceramics: Surface finish and mechanisms

Aluminum oxynitride (AlON) can be effectively finished by ultra-precision grinding. In this work, the ultra-precision grinding experiment was conducted on AlON to investigate surface characteristics and material removal mechanism. The ground surface has an unusual non-uniform morphology resulted from the different material removal modes. Grazing incidence X-ray diffraction (GIXRD), nanoindentation and Electron Back-Scattered Diffraction (EBSD) were carried out to study the micro-properties of AlON. The results revealed that the micro mechanical properties vary with the grain orientation on the surface. The morphologies of ground surface are consistent in the twinned grains and change with the grain orientation. By comparing the relationship of machining size and grain size, the material removal modes of individual grains should be taken into consideration during ultra-precision grinding. Based on this, a simple theoretical model was proposed to explain the material removal mechanism of AlON under ultra-precision grinding.

Removal Mechanism of Ship Materials by Micro Ultrasonic Machining

Miao, X.; Wang, W., and Geng, Q., 2018. Removal mechanism of ship materials by micro ultrasonic machining. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 68–73. Coconut Creek (Florida), ISSN 0749-0208.Based on indentation fracture mechanics and force analysis of abrasive grains on the bottom of the workpiece micro ultrasonic machining hole, the mathematical model of ship material removal mode is established, and the roughness value is utilized as the removal standard for the brittle plastic of ship materials. The experiments is designed based on the theoretical model. The results show that the abrasive grain size has the biggest impact on the removal rate of ship materials. In different material removal modes, when the roughness value is >480 nm, the ship material is removed in the brittle mode. When the roughness value is <400nm, the material is removed in the plastic mode. The applicability of the model is proved by comparing the actual machining results and the expected machining results.

Scratching-induced surface characteristics and material removal mechanisms in rotary ultrasonic surface machining of CFRP

Rotary ultrasonic machining has been successfully explored in surface machining of carbon fiber reinforced plastic (CFRP) composites. It has been proven to be an effective and efficient CFRP machining method. Both theoretical and experimental investigations have been conducted with the assumption that the CFRP is removed by brittle fracture removal mode. However, in brittle material machining, ductile flow phenomenon still exists. Ductile scratching marks are also observed on the machined CFRP surfaces. It is still unknown that what actual material removal modes are under different machining variables. To investigate the material removal mechanisms in rotary ultrasonic surface machining (RUSM) of CFRP, single abrasive scratching tests were conducted. The scratching induced characteristics and scratching forces were analyzed. Both the ductile removal mode and the brittle fracture removal mode were observed and identified in both carbon fiber layers and epoxy resin layers on the machined marks by using scanning electron microscopy (SEM) imaging. With the increase of scratching depth, the material removal mode of CFRP was changed from the ductile removal mode to the brittle fracture mode. From the analysis of kinematic trajectory of diamond grain, the scratching cutting forces were decreased in the tests with the assistance of ultrasonic vibration under the same machining variables. The generation mechanisms of the delamination were analyzed and discussed.

Research on Abnormal Identification Technology of Circuit Breaker extinction based on wavelet analysis

Circuit breaker is the actuator of power network fault removal and operation mode conversion. If the circuit breaker itself cannot complete the breaking operation, it may cause the accident impact range to expand, or even cause more serious chain failure. The fault phase current is decomposed based on wavelet analysis and Fourier transform, and the unstructured recorded wave data is converted into structured fault characteristic quantity to realize the analysis of current mutation characteristics. The high frequency characteristic singular value at the occurrence of arc is obtained by wavelet transform, which provides the key characteristic quantity for the identification of abnormal arc extinguishing performance of circuit breaker and realizes the identification of abnormal arc extinguishing state of circuit breaker. Issue an alarm before abnormal expansion of circuit breaker or adverse impact, remind relevant personnel to timely check and deal with defects, reduce the occurrence of abnormal tripping circuit breaker phenomenon.

Rotary ultrasonic machining of carbon fiber reinforced plastic composites: a study on fiber material removal mechanism through single-grain scratching

Rotary ultrasonic machining (RUM) has become an effective process for both hole making and surface grinding of carbon fiber reinforced plastic (CFRP) composites. Unlike other brittle materials such as ceramic, glass, silicon, etc., CFRP composites exhibit inhomogeneous and anisotropic properties, thereby resulting in different material removal mechanisms. However, the material removal mechanism in RUM of CFRP is still not clearly recognized in the literature. The lack of such knowledge would significantly limit the optimization and practical applications of RUM technique. In this work, single-grain diamond scratching tests without and with ultrasonic vibration are conducted to study the material removal mechanism in RUM of CFRP. Morphology of scratched groove, cross-sectional profiles, and scratching forces are analyzed. The results indicate that CFRP workpiece is extensively removed by the brittle removal mode, causing matrix damage, severe fiber pull-out, and macro-cracks in the conventional scratching test. Whereas, ultrasonic vibration-assisted scratching of CFRP leads to a larger ductile removal region before the successive brittle fractures and cracks. The fiber-matrix debonding and pullout phenomena are also remarkably reduced with only matrix buckling and fiber breakage occurring within the groove. The obtained results will enrich the understanding of the material removal mechanism in RUM of CFRP and contribute to the improvements of part quality during RUM of CFRP.

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.