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Zirconia ceramics have been extensively applied in dental restoration due to their superior properties and excellent functionalities. Green-compact sintering and mechanical processing have become critical operations to shape these denture materials to target dimensions and desired quality. Improper sintering regulations and cutting-induced damages are crucial issues when dealing with the manufacturing of ceramic dentures as they adversely affect the performance and acceptance of eventually-machined denture products. In this paper, a critical review has been conducted to offer a scientific understanding of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) processing, focusing on illustrating the characteristics and properties of the materials as well as the influence of the sintering process on the microstructure and machinability of the workpiece. Recent advances addressing the processing issues of zirconia ceramics for dental applications are carefully reviewed by critically analyzing the scientific findings reported in the open literature. The fundamental influences of the working conditions on the machining quality of ceramic materials are discussed. The features of emerging non-traditional machining technologies are compared and analyzed. Dentures manufacturers will benefit from this review article as they seek to achieve high-quality processing for zirconia ceramics. [ABSTRACT FROM AUTHOR]

Diamond wire saw cutting technology has been widely used in the slicing of sapphire crystal. The ultra-high hardness of sapphire makes the sawing characteristics of diamond saw wire constantly change. At present, there is a lack of in-depth understanding about the influence of sawing characteristics on the quality of sapphire as-sawn wafer, which leads to the unreasonable matching between the process parameters and the sawing characteristics of the saw wire, and reduces the as-sawn wafer quality and the saw wire life. In this paper, the slicing sapphire crystal experiment was carried out with constant process parameters and the variation of saw wire bow angle, nominal diameter and saw kerf loss, surface morphology and surface roughness of the as-sawn wafer during the whole life cycle of the saw wire from initial cutting to breakage was studied. The evolution mechanism of wear and sawing characteristics in the whole life cycle of saw wire was explored, and a reasonable processing scheme which can match the sawing characteristics was put forward. The research results show that in the whole life cycle of the saw wire, the abrasives emerge from the plating layer in turn, then the cutting edge are blunted, and finally the abrasives are greatly flattened and a small amount of falling off. Saw wire has experienced initial wear, stable wear and sever wear, and the proportion of three stages in the whole life cycle is about 0.3: 0.6: 0.1. Compared with the initial stage of wear and the late stage of rapid wear, the saw wire has higher sawing characteristics and better as-sawn wafer quality in the middle stable wear period. The sawing characteristics of new saw wire is relatively weak at the beginning of cutting, so the feed speed of workpiece should be increased gradually from low to high; When most of the abrasives finish sharpening edge, a relatively stable and high feed speed can be adopted; When the abrasives are obviously flattened or fall off, the feed speed should be decreased to accommodate the significantly reduced. cutting performance of diamond saw wire. [ABSTRACT FROM AUTHOR]

• A mathematical model of diamond wire sawing was established. • The numerical calculation of the sawn SSD in slicing silicon wafers was carried out. • The effect of process and saw wire parameters on critical speed ratio was analyzed. • The critical speed ratio was predicted when generating a crack-free wafer surface. At present, diamond wire sawing technology has been widely used in slicing photovoltaic polysilicon. Improving the surface quality of the slices to obtain a sawn surface without microcrack damage can greatly increase the fracture strength of polycsilicon wafers and reduce the cost of wet black silicon texturing, which is beneficial to improve the final photoelectric conversion efficiency of solar cells. In this paper, a mathematical model of diamond wire sawing was established based on the machining mechanism of brittle material removal and surface generation, and the numerical calculation of the sawing process was carried out. The validity of the model was verified by sawing experiments. The critical ratio of workpiece feed speed to saw wire movement speed was obtained when generating a crack-free slice surface under the combination of different process parameters and saw wire parameters. Based on the established theoretical model of sawing, the influence of saw wire movement speed, abrasives density and abrasives size on the critical speed ratio was analyzed, and the critical speed ratio (CSR) corresponding to the finer diameter wire and the higher wire speed which will be gradually applied in industry in the future was analyzed. The research results show that it is more conducive to obtaining a crack-free sawn surface by reducing the workpiece feed speed or increasing the saw wire movement speed, and the workpiece feed speed has a greater impact on the sawn surface quality. The CSR will slightly decrease within a small change range when increasing the saw wire movement speed. Increasing the density of abrasives on the saw wire surface within a certain range or decreasing the abrasives size is more inclined to obtain a crack-free sawn surface. The CSR will decrease slightly in a small range when decreasing the abrasives density or increasing the abrasives average size. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymers (CFRPs) have been extensively used in diverse industrial fields owing to their superior properties and excellent functions. Mechanical drilling has become a compulsory operation to shape these composites to target dimensions and desired quality for assembly purposes. Cutting-induced damages are critical issues when dealing with the manufacturing of CFRPs as they adversely affect the performance and acceptance of eventually-machined composite parts. In this paper, a critical review has been conducted to offer a comprehensive understanding of drilling-associated damages for CFRPs by focusing on illustrating the damage formation mechanisms, classification, evaluation, and suppression. Recent advances addressing the damage issues in drilling CFRPs are also carefully reviewed by critically analyzing the scientific findings reported in the open literature. The fundamental effects of the fiber layup, process parameters, tool geometries/materials, cutting environments and process strategies on the formation and progression of composite damage are discussed. The article also outlines potential solutions and strategies to suppress the formation of drilling-induced damages for CFRP composites. Both researchers and manufacturers will benefit from this review article as they seek to achieve damage-free drilling of CFRP composites. [ABSTRACT FROM AUTHOR]

At present, polycrystalline silicon photovoltaic cells play a dominant role in silicon-based solar cells because of its advantages such as relatively simple preparation process and relatively low cost. Slicing is the first mechanical processing procedure for battery cells, the quality of sawn surface affects the cost of subsequent processes such as texture making, also affects the breaking strength of battery cells and the photoelectric conversion efficiency and other performances. In this paper, polycrystalline silicon sawing experiments are carried out, and the effects of main process parameters, such as the workpiece feed speed, the wire moving speed, the ratio of the workpiece feed speed to the wire moving speed, and the sawn workpiece size, on the surface morphology and roughness R a of the photovoltaic polycrystalline silicon slice are analyzed. Orthogonal experimental method was used to analyze the primary and secondary order and positive and negative effects of various factors on surface morphology and surface roughness, the optimum process parameters were obtained, and the wear morphology and mechanism of wire were analyzed. The research results show that: within the range of process parameters studied in this paper, the surface morphology of polycrystalline silicon slices shows a comprehensive effect of material ductility and brittleness removal. Reducing the workpiece feed speed and size, increasing the wire moving speed will increase the proportion of the ductile smooth area on the slice surface and decrease the surface roughness R a value, the slice surface roughness R a value is basically unchanged when workpiece feed speed and wire speed change at the same time but the ratio of them remains constant. Compared with the wire moving speed and the workpiece size, the workpiece feed speed has the greatest influence on the surface morphology and roughness. Abrasive falling off and coating wear are the main wear forms of the wire. [ABSTRACT FROM AUTHOR]

Ultrasonic elliptical vibration cutting (UEVC) is a promising technique to realize the crack-free machining of ceramic materials. However, the underlying crack suppression mechanism and its impact on the ductile-brittle transition (DBT) behavior of ceramics still remain poorly understood. In the current work, the material removal characteristics of 3Y-TZP ceramics under UEVC, including the crack propagation process, stress distribution condition, and critical transition depth, were rigorously studied by using both the smoothed particle hydrodynamics (SPH) simulation and the experimental method. It was found that the material removal behavior and critical transition depth were highly related to the ultrasonic speed ratio (R s) that defines the ratio of the nominal cutting speed to the maximum ultrasonic velocity along the cutting direction. A critical (R s) value of 0.128 was determined by the analytical method, beyond which the crack suppression mechanism of UEVC is mainly due to the time-varying cutting speed and angle. When the R s is lower than the critical value, the reduction of the effective cutting thickness caused by the overlapping trajectory becomes a dominant factor in enlarging the ductile regime and in improving the machining quality of 3Y-TZP ceramics. [ABSTRACT FROM AUTHOR]

• A numerical model for analysis the fracture strength of silicon wafer is established. • The effects of process and wire parameters on wafer fracture strength are analyzed. • The relationship between the wafer fracture strength and the SSD is studied. The fracture strength of photovoltaic silicon wafers is affected by factors such as slicing process parameters and saw wire parameters. This paper numerically simulates the process of diamond wire sawing silicon crystals combined with the linear elastic fracture mechanics. A mathematical analysis model has been established to calculate the fracture strength of diamond wire cut silicon wafers in the light of the half-penny crack system. The effect of cutting conditions and saw wire conditions on wafers' fracture strength, and the relationship between wafers' fracture strength and subsurface micro-crack damage depth (SSD) were studied. The study results show that the numerical calculated values are equivalent to the experimental values of the reference, which proves the correctness of this model. It is found that the wire speed and the abrasive density are positively correlated with the wafers' fracture strength. The feed rate and the maximum size difference of the abrasives are inversely correlated with the wafers' fracture strength. When the ratio of wire speed to feed rate is constant, the wafers' fracture strength has no obvious change. And if the ratio becomes larger, the wafers' fracture strength will become larger. Besides, the wafers' fracture strength is not affected by the change in the abrasive size under the condition that the maximum size difference of abrasives remains unchanged and the wire inner diameter's change. The SSD is inversely correlated with the wafers' fracture strength. The study results of this paper can provide theoretical guidance for parameter optimization in the sawing process and reduction of wafer breakage probability. [ABSTRACT FROM AUTHOR]

Subsurface microcrack damage depth (SSD) in silicon wafer processed by diamond wire sawing has a great influence on the subsequent processing process and fracture strength of silicon wafer. Based on the indentation fracture mechanics, a new numerical model for predicting the SSD of silicon wafer on the basis of half-penny crack system is proposed in this paper. In this model, effect of the random distribution characteristics of size, position and tip half angle of abrasives and different material removal modes to the contour of workpiece cutting groove are all considered. Median cracks and radial cracks are regarded that propagating into one body, that is half-penny crack system. Validity of this model is verified by comparing with experimental results in the literature. From this model, the relationship between SSD and feed rate, wire speed, size of abrasives and density of abrasives on the surface of saw wire is analyzed, the critical speed ratio of feed rate to wire speed that can achieve pure ductile processing is discussed as well. The results show that using the maximum extended length of half-penny crack system as the SSD of silicon wafer is more reasonable than using the maximum extended length of median cracks as the SSD of silicon wafer. As wire speed increases, feed rate decreases, or density of abrasives on the surface of saw wire increases, the SSD will decrease. Keeping other parameters of saw wire unchanged, the size of abrasives has no significant effect on the change of SSD. Keeping the ratio of feed rate to wire speed unchanged, the SSD varies within a small range. When the speed ratio is in the range of 10.43–16, the slice surface tends to be formed by pure ductile removal of material. The results can be used to guide the optimization of diamond wire sawing process. [ABSTRACT FROM AUTHOR]