金刚石与磨料磨具工程

Review of research on arterial vascular calcified plaque grinding

ZHAI Shaobo, LIU Yao, SHEN Bin, LI Jiahao, GUO Zhanling

2024, 44(4): 415-427. doi: 10.13394/j.cnki.jgszz.2023.0162

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Significance Plaques are clogging deposits formed by the accumulation of fat and calcium on the inner walls of arteries. Their formation can lead to narrowing the inner diameter of the blood vessel and hardening the blood vessel wall, thereby limiting blood flow and inducing various cardiovascular diseases such as coronary heart disease and peripheral arterial disease. Numerous factors, such as lifestyle changes and population aging, have lead to an increase in the number of patients with cardiovascular disease in China in recent years. The annual growth rate of vascular interventional therapy has remained at around 17% for a decade due to the continuous development of interventional medical means. China's large population of vascular disease and the special situation of calcified plaque lesions have created a huge demand for rotational interventional therapy. By analyzing the current research on rotary grinding, this paper summarizes the existing deficiencies and suggests a follow-up research direction to accelerate the exploration of rotary grinding's mechanism and master the core technology theory. Progress: Firstly, the research on rotary grinding instruments is summed up in three parts: (1) The rotary grinding therapeutic apparatus mentioned here contains a description of its basic features, including the RA from Boston Science and the OA from CSI. The differences between the two were compared in terms of technical indications, clinical indications, mechanism of action, and product upgrades. (2) The preparation method for the grinding wheel and the differential cutting of the grinding wheel are presented in summary. Currently, grinding wheels are mostly created by electroplating, and some experts have suggested using the "engraving" technique. Differential grinding wheel cutting involves two primary principles. Boston Science proposed differential cutting that utilizes the theory of workpiece deformation during the cutting process of flexible materials. The second mechanism is based upon the theory of the dynamic pressure film in water. (3) A summary was provided regarding the structure and techniques of two different types of special rotary grinding guide wires, as well as the potential negative consequences during operation. Secondly, the differences between treatments are compared, such as rotational atherectomy, conventional balloon stenting, rotational resection, ELCA and shock wave balloon. The advantages of plaque rotary grinding are explained in detail. The likelihood of occurrence, explanations, methods of treatment, and other research on complications following rotational grinding are evaluated and summarized. Slow/non-reflow, vascular dissection, vascular perforation, grinding head incarceration, guide wire bias, etc., are all included. Engineering proposes controlling grinding parameters and improving the performance of related equipment to reduce the probability of complications. Finally, the research related to the mechanism of rotary grinding is examined. The main factors are rotary grinding force, rotary grinding heat, and rotary grinding debris. The grinding force is analyzed in a specific way by the current research, which focuses on the impact of grinding wheel speed and quality, blood vessel diameter, fluid dynamic pressure, and other factors on the grinding force. Research on rotary grinding heat focuses on reducing temperature through liquid scrubbing, but there is limited attention paid to thermal damage from an engineering perspective. The analysis of the wear debris mostly discusses the relationship between the size and the speed of the grinding wheel. Conclusions and Prospects (1) At present, the rotary grinding device and related consumables are all imported from the United States. In the future, Chinese substitution will be an important development direction. The development of Chinese rotary grinding products is under process now. (2) The study of the differential cutting mechanism and the design of the surface characteristics of the rotary grinding head to achieve non-invasive vascular tissue removal and efficient plaque tissue removal plays an important role in reducing other injuries caused by surgery. (3) The safety of the grinding process could be improved by optimizing the grinding parameters. There are few discussions on whether other factors in the grinding process will affect parameters such as grinding force, grinding debris and grinding heat. This is the direction of continuous research. (4) There are few theoretical studies on the grinding guide wire, and the performance of the guide wire is the main factor in determining whether it is biased or broken during the operation. Explore the possibility of processing different materials into high-performance grinding guide wires and new processing methods. On the premise of ensuring product performance, minimizing device costs and surgical costs is also a key research direction in the future. (5) According to the characteristics of plaque removal, the development of new products with better performance, such as laser plaque ablation products, shock wave balloons, etc., is also very marketable.

Report on operation of Chinese superhard industry in 2023

SUN Zhaoda, ZHANG Beibei, LI Lijuan, MA Ning, LI Zhihong

2024, 44(4): 428-432. doi: 10.13394/j.cnki.jgszz.2024.1004

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Objectives: It is important to analyze the status of each industry, which provides not only a direct vision but also a vital reference to all. Methods: The operation of China's superhard industry in 2023 was analyzed based on an in-depth investigation, as well as the national macroeconomic statistical data and the import and export data collected by customs in China, the United States, the European Union, and Japan. The overall development of the industry was explored and then compared with internationally advanced products. Results: Firstly, there are increases in sales volume of superhard material, but a general decrease in that of superhard products except diamond wire saws. This is mainly due to the great consumption of wire saws on diamond particles. The price are going down, especially those of gem-grade diamonds and wire saws, but not for cBN, saw blades, ceramic grinding wheels and resin grinding wheels. Secondly, China has provided the majority of superhard commodities to the world, with the average price going down for 9.8% compared with that in 2022. China also has bought about 5155 tons, or 393 million USDs, of superhard commodities from other regions at a steady price. In the superhard industry, China offers the world with stable supplies and acts as a big consumer to other economics. Conclusions: Despite that China’s manufacturing industry has shown significant robustness and is increasing steadily, the superhard industry endured a tough 2023, with its main indicators falling short of expectations and relatively slow development. However, there were positive factors in the downstream market, the increase in photometric battery productivity for example, and negative factors, especially a sluggish lab-grown diamond market. Despite the gem-grade single crystal diamond and the wire saw, other representative products saw their unit prices increase, generally by 10% to 20%. There was a sharp unit price ratio between some imported products and their exported counterparts, showing great potential in high-end applications.

Pressure-transmitting properties of pyrophyllites from different localities

LIU Li, SHAO Fangyuan, LUO Yucai, WU Qiang, YU Jiantao, YU Jinping, WANG Haikuo, HOU Zhiqiang, WANG Chao, YANG Yikan

2024, 44(4): 433-439. doi: 10.13394/j.cnki.jgszz.2023.0152

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Objectives Pyrophyllite, as a sealed pressure medium, has been widely used in high-pressure research for laboratories and industrial synthesis. A highly efficient pressure transfer medium can generate higher cell pressure at the same loading force. The use of a highly efficient pressure transfer medium reduces the risk of anvil rupture and production costs. Therefore, it is important to develop a suitable and efficient pressure-transmitting pyrophyllite. Methods The pressure calibration of four pyrophyllites from different localities at room temperature was conducted in a 6 × 8 MN multi-anvil large-volume press. The relationship between loading force and cell pressure at room temperature was established. The influence of mineral composition changes in pyrophyllite on pressure-transmitting efficiency was studied using X-ray diffraction. Results By investigating the influence of mineral composition changes in pyrophyllite on pressure-transmitting efficiency, the results are as follows: (1) When achieving the same cell pressure, the required loading force for Pyrophyllite 4 is 10% lower than those for the other three pyrophyllites, indicating that Pyrophyllite 4 has the best pressure-transmitting efficiency. (2) As cell pressure increases, the relationship between cell pressure and loading force begins to deviate from linearity, and the pressure-transmitting efficiency of pyrophyllite gradually decreases. When the cell pressure exceeds 5.00 GPa, applying higher loading force does not significantly increase the cell pressure. (3) Higher hardness minerals (such as Diaspore, Boehmite) in pyrophyllite can effectively improve pressure-transmitting efficiency in the low-pressure stage (cell pressure 2.55-3.68 GPa). When the minerals in pyrophyllite undergo phase transformation to form new minerals with higher hardness (such as Muscovite and Kaolinite) in the high-pressure stage (cell pressure of 5.50 GPa), pressure-transmitting efficiency can be effectively improved. Conclusions Pyrophyllite 4 has better pressure-transmitting efficiency than Pyrophyllite 2 does in the high-pressure stage, but it is prone to failure in sealing due to the changes in mineral composition. However, Pyrophyllite 2 shows good elastic recovery effect and sealing performance and can stably complete compression and decompression work. Considering both pressure-transmitting efficiency and sealing effect, Pyrophyllite 2 has better application value and economic benefits.

Preparation and properties of Mo₂C-TiN_0.3 composite materials at high temperature and high pressure

ZOU Qin, WANG Kuan, LI Yanguo, DAI Weiji, LUO Yongan

2024, 44(4): 440-448. doi: 10.13394/j.cnki.jgszz.2023.0157

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Objectives: This study aims to prepare sintered bodies of Mo₂C and TiN_0.3 and explore their phase compositions, microstructures, and mechanical properties. Using a combined approach of mechanical alloying and high-temperature high-pressure sintering, the research investigates the stratified sintering process of Mo₂C and TiN_0.3 powders, analyzes the influence of different sintering temperatures on the sintered body performances, and aims to optimize the preparation process to enhance the comprehensive properties of the sintered bodies. Methods: This experiment employed a combination of mechanical alloying and high-temperature high-pressure sintering to prepare the sintered bodies. Initially, Mo₂C and TiN_0.3 powders were mechanically alloyed in a 7:3 volume ratio. The powders were thoroughly mixed using a high-energy ball mill to ensure uniform mixing. Subsequently, the mixed powders were subjected to high-temperature and high-pressure sintering using a six-sided top press under various temperature conditions to obtain sintered bodies with different sintering parameters. During the sintering process, the temperature and pressure were strictly controlled to study their effects on the microstructure and mechanical properties of the sintered bodies. The phase composition of the sintered bodies was analyzed using X-ray diffraction (XRD) to identify the presence and changes of various phases. The microstructure of the sintered bodies was observed using a scanning electron microscope (SEM) to analyze the grain size and morphology. To evaluate the mechanical properties of the sintered bodies, Vickers hardness tests and fracture toughness tests were conducted. These test methods were used to comprehensively analyze the overall performance of Mo₂C and TiN_0.3 sintered bodies under different sintering conditions. Results: The experimental results indicate significant mutual diffusion between Mo₂C and TiN_0.3 during the sintering process, forming two distinct diffusion layers. The formation of these diffusion layers markedly affects the phase composition and microstructure of the sintered body. As the sintering temperature increases, the grain size of the Mo₂C-TiN_0.3 sintered body gradually enlarges, leading to a deterioration in mechanical properties. Specifically, at lower sintering temperatures, the sintered body exhibits higher hardness, but as the temperature rises, the grain size increases, resulting in decreased hardness. Additionally, the formation of a highly hard and brittle MoC phase was detected during high-temperature sintering. In addition, MoC phase formation with high hardness and brittleness was detected during high temperature sintering. The presence of the MoC phase helps maintain the hardness of the sintered body within the range of 19.0 to 20.0 GPa, but also leads to a reduction in fracture toughness. The microstructure of the sintered body varies significantly with different sintering temperatures. Under low-temperature sintering conditions, the grains of the sintered body are small and evenly distributed, and the phase composition is relatively stable. However, with the increase of sintering temperature, the grains gradually grow, and the phase distribution becomes uneven, which leads to a decline in the mechanical properties of the sintered body. Furthermore, SEM analysis reveals the presence of numerous pores and cracks on the surface of the high-temperature sintered body, which are crucial factors affecting its mechanical performance. Conclusions: Through the study of 30% Mo₂C-TiN_0.3 sintered bodies, it is found that: (1) The mutual diffusion between Mo₂C and TiN_0.3 plays a crucial role in the formation of the sintered body, directly impacting its phase composition and microstructure. (2) As the sintering temperature increases, the grain size of the sintered body enlarges, leading to a decline in its mechanical properties, particularly in its hardness and fracture toughness. (3) The MoC phase generated in the sintering process helps to maintain the high hardness of the sintered body, but also reduces fracture toughness. Therefore, in practical applications, it is necessary to find a balance between hardness and toughness to optimize the overall performance of the sintered body. (4) Different sintering temperatures significantly affect the microstructure of the sintered body, highlighting the importance of optimizing sintering process parameters to enhance the performance of the sintered body. Others: The mechanical alloying and high-temperature and high-pressure sintering methods used in this study demonstrate the potential for producing high-performance Mo₂C and TiN_0.3 sintered bodies. By optimizing sintering process parameters, the performance of the sintered bodies can be further enhanced. Furthermore, future research could explore the effects of other additives on the performance of Mo₂C-TiN_0.3 sintered bodies to obtain higher performance hard and brittle materials.

Effect of sintering process on properties of CuSnZn alloy powder

CAO Xinmin, BAO Li, LI Zhen, CHENG Chuanwei, CHEN Peng, PAN Jianjun, YU Qi, YU Xinquan

2024, 44(4): 449-455. doi: 10.13394/j.cnki.jgszz.2023.0173

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Objectives: Diamond tools are crucial in stone processing, and their performance is directly related to processing quality and cost. With the rise of stone and labor costs, the performance requirements on diamond tools are also increasing, including sharpness, self sharpening, tool life, and cutting efficiency. To improve efficiency and reduce costs, users often increase the cutting machine power and speed, which further requires diamond tools to have higher sharpness and strength at the risk of breakage. A practical method method is to increase the content of tin (Sn) in the segment to enhance its brittleness without changing the diamond concentration and particle size. However, an increase in Sn content will reduce the strength of the segment and may lead to a decrease in the holding force between CuSn alloy and diamond. For example, the commonly used CuSn10 and CuSn15 pre alloy powders in industry have low strength and weak holding force on diamond. Therefore, it is necessary to improve the powder properties and processing technology. Methods: Adding Zn element to CuSn10 alloy powder can improve powder strength and holding force. CuSnZn-x alloy powder (mass fraction of Zn, x=10.00%, 15.00%, 20.00%, 25.00%, 30.00%) was prepared by atomization process. The hot pressing sintering temperatures were 610 ℃, 615 ℃, 630 ℃, 645 ℃, 655 ℃, and the sintering pressure was 21 MPa. The melting temperature of CuSnZn alloy powder was tested using a differential thermal analyzer. The density of the sintered segment was tested using Archimedes drainage method. The bending strength of the sintered segment was tested using mechanical performance testing equipment. The Rockwell hardness of the sintered segment was measured using a Rockwell hardness tester. The microstructure morphology of the sintered segment and its fracture were analyzed using scanning electron microscopy. Other performances of samples with different Zn contents were analyzed and compared as well, namely theoretical density, Rockwell hardness, and flexural strength, to study the influence of Zn content on sample microstructure. Results: With the increase of Zn content, the rate of decrease in melting temperature of CuSnZn alloy powder first increases and then decreases. When the Zn mass fraction is 30%, the melting temperature decreases to 848 ℃, which is 164 ℃ lower than that of CuSn10. As the Zn content increases, the brass in the sintered segment gradually transforms from the α phase to the α+β phase and then the α+β+β´ phase, resulting in a significant increase in the Rockwell hardness of the segment. The bending strength of the sintered segment first increases and then decreases, reaching a maximum value of 542 MPa when the Zn mass fraction is 20.00%. When the mass fraction of Zn is 10.00% and 15.00%, obvious toughness dimples are observed on the fracture surface of the sintered segment, and particle peeling is observed on the fracture surface. The peeling surface is smooth and flat, indicating grain boundary peeling fracture of the phase structure. When the mass fraction of Zn is 20.00% and 25.00%, a large number of cleavage fracture surfaces are observed on the fracture surface of the sintered segment, and a small amount of smooth concave transgranular fracture is observed, which is partially intergranular fracture and partially transgranular fracture. When the mass fraction of Zn is 30.00%, the fracture surface of the sintered segment is flat and smooth, and the crack passes through the phase interface and grain along the hard and brittle structure, which is transgranular fracture. Conclusions: Adding Zn element can effectively reduce the melting point of alloy powder, and with the increase of Zn content, the hardness of sintered samples increases while the toughness decreases. When the Zn content is 30.00%, the melting temperature of CuSnZn alloy powder reaches its minimum value. When the Zn content exceeds 25.00%, the strength of the sintered samples will gradually decrease. Therefore, in actual production, the appropriate amount of Zn addition and sintering process should be selected based on comprehensive consideration of demand.

Preparation of diamond coated floating core head and its application in copper pipe production

CUI Yuming, WANG Yong, LI Guohua, JIANG Long, DONG Wang

2024, 44(4): 456-462. doi: 10.13394/j.cnki.jgszz.2023.0138

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Objectives: In the refrigeration industry, thin-walled copper tubes are crucial heat exchange devices, and during their drawing production process, the floating core head plays a significant role in the quality of the copper tubes. With the rapid development of chemical vapor deposition(CVD) diamond coating technology and its wide application in the field of molds, the DC arc plasma injection method is used to produce diamond-coated floating core heads to improve the quality of copper tube drawing and extend the service life of floating core heads. Methods: Using a deposition method and a rotating device design, the diamond coating was uniformly deposited on the surface of cemented carbide floating core heads by the DC arc plasma injection method. The surface roughness, morphology, mass uniformity, and film-base adhesion of the coating were tested and analyzed using a white light interferometer, scanning electron microscope, Raman spectrometer, and indentation method. The prepared diamond-coated floating core head was applied to a high-precision copper pipe production line, and the application effect was compared with that of a traditional cemented carbide floating core head. Results: SEM and Raman spectrum analysis showed that the diamond coating quality at each position of the floating core head was superior. The average thickness of the diamond in the cylindrical section of the floating core head was 13.3 μm, and in the fixed diameter section, it was 13.7 μm. At a room temperature of 20 ℃ and a relative humidity of 40%, with a filtering cutoff wavelength of 250 μm and a scanning area of 100 μm × 100 μm, the average surface roughness (R_a) of the polished diamond coating was 76.4 nm. Under the indentation test condition of loading to 1 000 N and holding constant force for 3 seconds at a fixed loading rate of 20.0 N/s, the average distance from the diamond coating shedding position to the indentation center was 287.9 μm. The prepared diamond-coated floating core head was then applied to the high-precision copper pipe production line. Compared with the cemented carbide floating core head, the following findings were observed: (1) Due to the excellent finish and self-lubrication characteristics of the diamond coating, the maintenance frequency of the floating core head decreased from once per frame to once every 20 frames, reducing labor intensity significantly. (2) Due to the excellent wear resistance of the diamond coating, the size of the fixed diameter section of the core head remained constant, ensuring that the wall thickness of the copper tube did not vary, therefore improving product consistency. (3) The service life of the diamond-coated floating core head was about 15 times that of the cemented carbide core head. Conclusions: The DC arc plasma injection method can uniformly deposit high quality diamond coating on the surface of cemented carbide floating core heads, reducing labor intensity effectively, ensuring consistency in copper tube production, and extending the service life of the core head in practical applications. Others: With the continuous progress of DC arc plasma jet deposition diamond coating technology, the quality of diamond-coated floating core heads will further improve. Diamond coatings can gradually be applied to various internal molds, such as fixed core heads and threaded cores. When used with diamond coated outer molds, these internal molds can replace traditional cemented carbide molds, reducing mold costs and labor costs, and improving the drawing quality of pipes significantly. This approach will help achieve the goal of reducing costs and increasing the efficiency in the copper, aluminum, stainless steel and other related industries.

Rapid formation of TiC coating on diamond surface through thermal explosion reaction

SHI Dongli, MA Yao, LI Tao

2024, 44(4): 463-469. doi: 10.13394/j.cnki.jgszz.2023.0170

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Objectives: Coating treatment on the surface of diamond particles is an important technique to effectively overcome the problem of difficult bonding between diamond and substrate, and the thermal explosion reaction is a common surface coating technique for diamond particles. However, this technology has disadvantages such as difficulty in separating diamonds from the product and a low proportion of diamonds, which increases its complexity and production costs, greatly limiting the promotion and application of this technology. This article aims to introduce polytetrafluoroethylene (PTFE) into thermal explosion reaction technology to form a coating mainly composed of TiC on the surface of diamond particles. It is expected to optimize the coating preparation process and promote the popularization and application of thermal explosion reaction technology in the field of diamond plating, so as to improve the wear resistance and service life of the diamond tools. Methods: Using two raw material systems, Ti/carbon black/diamond and Ti/carbon black/PTFE/diamond powders, the thermal explosion reaction of Ti/carbon black/diamond is induced by the chemical furnace method, and the intense chemical reaction between PTFE and titanium at low temperature ensures that the Ti/carbon black/PTFE/diamond system directly undergoes a thermal explosion reaction. At the same time, the TiC coating can be generated on the surface of diamond particles by adjusting the ratio of raw materials and triggering the thermal explosion reaction under high temperature conditions. The macroscopic morphology of diamond particles before and after coating is observed and compared by optical microscope to roughly infer the plating condition, and the phase compositions of the coating were analyzed by X-ray diffraction. Then the scanning electron microscope and the energy dispersive spectroscopy are used to observe the surface morphology of diamond particles, determine the elemental compositions, and infer the surface reaction state. Results: The thermal explosion reaction of both raw material systems can form a TiC coating on the surface of diamond. The main phase of the binder reaction product is TiC, and the main phases of the coating on the surface of diamond particles are TiC and Ti. But for the Ti/carbon black/diamond system, the chemical furnace method is needed to induce a thermal explosion reaction. When the diamond mass fraction in the raw material is 30% or lower, the TiC coating on the surface of the diamond particles is good. When a small amount of PTFE is introduced into the Ti/carbon black/diamond system, the reaction between Ti and PTFE releases a large amount of heat, which induces the thermal explosion reaction between Ti and carbon black and synthesizes TiC, and finally forms a TiC coating on the surface of diamond particles. In addition, the system does not need the chemical furnace method to detonate. When the diamond mass fraction in the raw material is less than or equal to 60%, the diamond particle surface coated with TiC coating is good. At the same time, appropriately reducing the content of carbon black in the raw materials can enable diamond to obtain a good TiC coating on its surface even when the mass fraction of diamond is 90% or higher. Conclusions: TiC coatings are prepared on the surface of diamond particles using thermal explosion reaction technology, and the important effects of raw material compositions and PTFE additives on the formation of diamond particles' surface coating are revealed. Adding an appropriate amount of PTFE can directly induce the thermal explosion reaction, which greatly promotes the increase of the proportion of diamond in the raw material, and effectively improves the formation quality of the coating. This can greatly save binder powder, thereby reducing production costs, while obtaining loose powder products that are easy to separate from diamonds. In addition, drawing on the work of this study, other carbide materials (such as SiC) can be analogously extended for coating on the surface of diamond particles, thereby promoting the promotion and the application of thermal explosion reactions in diamond coating.

Influence of diamond layer chamfer parameters on performance of PDC cutters

ZHANG Suhui, WANG Chuanliu, LI Geng

2024, 44(4): 470-475. doi: 10.13394/j.cnki.jgszz.2023.0209

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Objectives: The precise control of diamond layer chamfer parameters has a complex influence on the comprehensive performance of PDC cutters. This control not only helps to expand ideas in PDC cutter design but also improves the overall efficiency of drilling tools. To fully analyze the effect of diamond layer chamfer parameters on the performance of PDC cutters, this study examined the correlation between the chamfer size and chamfer angle of the diamond layer and the performance of PDC cutters, namely wear resistance, impact toughness, drilling efficiency, and damage forms. It provided a scientific basis for optimizing the structure of PDC cutters to enhance the operational efficiency and reliability of PDC bits under complex geological conditions. Methods: The study combined experimental research and theoretical analysis. Two types of PDC cutters, planar type and micro-arc type, which are widely used in the market at present, were selected as experimental objects. Samples with different chamfer sizes (0.2, 0.3, 0.4, 0.5 mm) and chamfer angles (15°, 30°, 45°) were prepared using precision machining techniques. The samples were systematically heat-treated to simulate the actual welding process before testing, and the performance of the PDC cutters was evaluated by analyzing wear resistance, impact toughness, and drilling efficiency. Additionally, the interaction between the PDC cutter and rock was simulated by turning experiments, and the wear area and the damage forms were observed, measured, and analyzed using a microscope. Results: The experimental results revealed the influence of diamond chamfer parameters on the performance of PDC cutters. On the one hand, the chamfer size had a critical value of about 0.3 mm. When the chamfer size was less than or equal to this critical value, the wear ratio of PDC cutters was high, the grinding time was short, the energy level of breakage was low, impact toughness was low, and the primary form of damage was broken edges, which adversely affected the service life and drilling efficiency of the cutter. When the chamfer size exceeded the critical value, the PDC cutter wear ratio decreased, the grinding time increased, the damage energy level was high, impact toughness nearly doubled, the accumulated absorbed energy reached more than 1 000 J, and the predominant damage form was delamination, effectively extending the service life of the cutter. On the other hand, the influence of chamfer angle on the wear resistance and impact toughness of PDC cutters exhibited a linear relationship. As the chamfer angle increased, the wear ratio of PDC cutters gradually decreased, the wear area increased, indicating a decrease in wear resistance, and impact toughness increased correspondingly. In addition, the influence of the PDC cutter's shape on wear resistance and impact toughness was similar to that of the chamfer angle, namely, planar cutters had a high wear ratio and short grinding time, while micro-arc cutters had a reduced wear ratio but improved impact toughness. This provided an important basis for optimizing the chamfer angle and designing the shape structure of PDC cutters. By moderately increasing the chamfer angle or adopting a camber design, the comprehensive performance of the cutter could be improved to a certain extent. Conclusions: Through systematic experiments and analysis, the effect of diamond chamfer parameters on the comprehensive performance of PDC cutters is revealed. Especially, the discovery of the critical value of chamfer size provides guidance for the optimal design of PDC cutters. The fine regulation of diamond layer chamfer parameters presents a new approach to improving the performance of PDC cutters. In the development and production of PDC bits, the influence of these parameters should be fully considered. The performance of PDC cutters can be optimized by accurately regulating the chamfer size, chamfer angle, and shape structure, thereby further enhancing the drilling efficiency and service life of PDC bits.

Numerical simulation of bottomhole flow field of PDC bit in horizontal well

LI Sai, WANG Hongbo, CHENG Shuting, CAI Maosheng, ZHANG Chunjiang

2024, 44(4): 476-484. doi: 10.13394/j.cnki.jgszz.2023.0129

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Objectives: Horizontal wells can effectively improve the economic benefits of shale oil and gas development. However, as the horizontal section extends, the rock debris transport efficiency of the PDC drill bit gradually decreases, which can lead to bit balling in severe cases. Consequently, it is costly to directly improve the hydraulic structure of PDC bits. This paper uses a multi-physics field coupling numerical simulation method to analyze the influence of the coupling of different drilling process parameters and drill bit structure parameters on the bottom hole flow field and improves the drill bit hydraulic structure to enhance the rock debris transport efficiency of the PDC drill bit. Methods: Using COMSOL multi-physics field coupling simulation software, a geometric model of the bottom hole flow field of the horizontal well was established. The low Reynolds number k-ԑ model was employed to simulate the coupling of fluid flow and particle motion in the fluid, and iterative calculations were performed. The low Reynolds number k-ԑ model could adapt to different Reynolds number regions, especially the influence of molecular viscosity in the viscous bottom layer in the low Reynolds number region on the mixed phase flow. Parameters close to the actual drilling conditions were used to set the boundary conditions of the coupling model, and the grid independence of the coupling model was verified to reduce simulation error. Changes in the bottom hole flow field and the movement of rock debris by the PDC bit in a horizontal well under different drilling fluid displacement, PDC bit rotation speeds, and rock debris particle sizes were analyzed. Results: In the numerical simulation results of the coupling model, the following findings were observed: (1) From the flow velocity distribution diagram on the bottom hole wall, it was observed that the hydraulic energy distribution on the bottom hole wall became more uniform with an increase in displacement. When the displacement is 35 L/s, the flow velocity distribution effect on the bottom hole wall is optimal. However, the low-speed flow area of drilling fluid at the bottom hole cannot be completely eliminated by increasing displacement. In the comparative analysis of the retention of bottom hole rock debris at different displacements, an increase in displacement can reduce the impact of gravity on the cleaning of bottom hole rock debris. However, once the displacement reaches a certain level, the degree of cleaning of bottom hole rock debris changes relatively little. (2) In the lateral drilling fluid flow line at different rotation speeds, the flow rate gradually increases with an increase in rotation speed, causing a significant deviation in the flow state of the drilling fluid. When comparing and analyzing the accumulation of rock debris particles and the average velocity of rock debris particles, it was found that as the drill bit rotation speed increases, the fluctuation of the average velocity of rock debris particles also gradually increases. Although increasing drill rotation speed raises the average velocity of rock debris particles, it does not improve the migration efficiency of rock debris beyond a certain rotation speed. When the rotation speed is 240 r/min, the rock debris migration efficiency is the lowest. (3) In the comparative analysis of the average speeds of different rock debris particles, the farther they are from the bottom of the well, the faster the speed of large-size rock debris decays due to gravity. The speed change of small-size particles is relatively stable, but the average speed of rock debris particles with mixed particle sizes falls in the middle. (4) With roughly the same displacement area, increasing the number of drill bit nozzles from six to eight significantly reduces the amount of rock debris retention. (5) Compared with the equal diameter nozzle combination, the combination of a large inside and small outside nozzle reduces the transport efficiency of large particle rock debris due to the weakening of the drilling fluid flow rate. However, the flow rate in the central area of the combination of a small inside and large outside nozzle is reduced, which fails to form a strong pressure difference, resulting in an overall reduction in rock debris migration efficiency. Conclusions: Increasing the drilling fluid displacement improves the hydraulic energy and the rock debris transport efficiency at the bottom hole wall, but after the displacement increases to a certain level, it has little effect on the change in the degree of rock debris cleanliness at the bottom of the well. The mismatch between the high speed of the drill bit and displacement increases the average speed of the rock debris, but does not improve rock debris transport efficiency. Within a certain range of rock debris particle sizes, gravity has a relatively small impact on larger-size rock debris due to the influence of rotational force and turbulent kinetic energy. The transport efficiency of larger-size rock debris is higher than that of smaller-size rock debris. However, the farther away from the bottom of the well, the greater the impact of gravity on larger-size rock debris, resulting in greater velocity attenuation than that of smaller-size rock debris. According to the bottom hole flow field state under different drilling process parameters, the number of drill bit nozzles increase from six to eight under roughly the same nozzle displacement area, the hydraulic energy distribution is more uniform and the transport efficiency of rock debris improves. Meanwhile, compared to non-equal diameter nozzle combinations, equal diameter nozzle combinations perform more balancedly.

Analysis and optimization of traveling wave vibration of large diamond thin-wall drill bits

LIU Xingdong, ZHANG Dechen, WANG Yubo, GAO Xianyi, MA Guoqing

2024, 44(4): 485-494. doi: 10.13394/j.cnki.jgszz.2023.0137

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Objectives: To reduce the vibration and noise generated by thin-walled drill bits during the drilling and cutting process, various designs of thin-walled drill bits were studied, including conventional thin-walled drill bits, open-hole thin-walled drill bits, open-hole and interlayer thin-walled drill bits, and thin-walled drill bits with positioning wheel. The reasons for vibration and noise reduction of thin-walled drill bits in different schemes were analyzed at a theoretical level. A new scheme for thin-walled drill bits was proposed, which exhibited good vibration reduction effects, protected the hearing of thin-walled drill bit operators, and complied with China's environmental indicators for workers. Methods: Modal analysis and traveling wave vibration analysis of thin-walled drill bits were performed using Workbench software to study the effects of different thin-walled drill bit designs on traveling wave vibration. First, a solid work model of the thin-walled drill bit was imported into Workbench software and meshed. The inner hole of the thin-walled drill bit was constrained (cantilever type), and the first 30-order modes of the thin-walled drill bit were calculated under standard earth gravity. Using traveling wave vibration theory, the δ value of the resonance margin of the thin-walled drill bit in different schemes was calculated to determine the effectiveness of avoiding traveling wave resonance. Results: At a drilling speed of 187.32 r/min, the conventional thin-walled drill bit had a δ value of 0, leading to rear traveling wave resonance. The opening of 8 groups of round holes and 8 S-hole thin-walled drill bits had a δ value of 5.18%, which was the best opening design scheme. Further interlayering the thin-walled drill bit resulted in a δ value of 6.11%, showing the best effect in avoiding traveling wave resonance. In the δ where 2 to 12 positioning wheels thin-walled drill bits were installed, the δ of 2, 3 and 11 positioning wheels thin-walled drill bits was less than 1.00%, effectively avoiding traveling wave resonance. Conclusions: Thin-walled drill bits with traveling wave resonance will produce strong vibration and noise. Reducing the deformation of the thin-walled drill bit increases the δ value, leading to better vibration and noise reduction. To ensure the precision of the drilled hole, the positioning theory was applied to the thin-walled drill bit. When comparing δ values for drill bits with 2 to 12 positioning wheels, the designs with 6 and 12 positioning wheels had larger δ values and better vibration damping effects. Considering installation convenience, 6 positioning wheels were determined to be the optimal number, providing a theoretical basis for reasonable determination of the number of positioning wheels.

Simulation and experimental study on micro-cutting silicon carbide crystal with single grain diamond

YANG Yufei, LI Xiang, HE Yan, LIU Ming, XU Zicheng, GAO Xingjun

2024, 44(4): 495-507. doi: 10.13394/j.cnki.jgszz.2023.0158

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Objectives The hardness of silicon carbide is second only to those of diamond, cubic boron nitride, and boron carbide, making its processing very difficult. Compared with plastic metal materials, the brittle and hard nature of silicon carbide makes it prone to brittle fracture and edge fragmentation during processing, greatly affecting its superior performance. Therefore, it is crucial to carefully select appropriate cutting methods and establish reasonable cutting process conditions. Methods The finite element software Abaqus was used to establish a model of micro-cutting silicon carbide crystal with a diamond conical grain, and the selection range of micro-cutting depth and speed was determined by the pre-simulation model. Then, the main and secondary factors affecting the cutting force were analyzed, and the influence of a single cutting parameter on the cutting effect was studied. In addition, with the help of Hertzian contact stress, the influence of the loading force on the friction force, the morphology of the cutting edge, and the cutting depth was verified by the tip scratching experiment. Results (1) The cutting depth is a crucial factor that greatly impacts the quality of the cutting process. When the cutting depth is less than 1.50 μm, the removal of silicon carbide material primarily occurs through plastic removal. However, when the cutting depth exceeds 1.50 μm, cracks of varying lengths and pits of different sizes gradually form at the cutting edge of the workpiece. As the cutting depth increases, the length of cracks and the number of pits also increase. This type of removal is known as brittle removal. To ensure the integrity of the cutting edge and minimize damage to the silicon carbide workpiece, it is essential to control the cutting depth of the abrasive particles during stages I and III, keeping it below 1.50 μm. (2) Through variance and range analysis of the main cutting force, the relationship between the three factors and the magnitude of the main cutting force is V > W > U, meaning that cutting depth is the most important factor affecting cutting force. The optimal solution V₁W₁U₂ and cutting parameters have been determined, namely a diamond abrasive cutting depth of 0.50 μm, a diamond abrasive cutting edge angle of 60°, and a cutting speed of 76 m/s. Cutting depth is the main factor affecting the magnitude of cutting force, while cutting speed and cutting edge angle are secondary factors. (3) As the cutting depth increases, the affected area surrounding the cut also expands, causing an increase in equivalent stress even in areas where the abrasive particles do not come into contact with the workpiece. This phenomenon is responsible for the development of cutting edge cracks and pits. Additionally, as the cutting depth increases, the main cutting force experiences greater fluctuations. To maintain cutting stability, it is important to control the cutting depth. In the high-speed cutting range of 60-106 m/s, the impact of cutting speed on cutting force is minimal. Therefore, increasing the cutting speed can be an effective method for improving cutting efficiency and ensuring high-quality cuts. For optimal results, a cutting depth of 0.50 μm and a cutting speed of 76 m/s are recommended. (4) The coefficient of friction is not only affected by the properties of the two materials in contact, but also by the depth of the diamond probe pressing into the workpiece. The greater the depth of pressing, the higher the coefficient of friction and the greater the frictional force. The surface of the microgrooves is clear and tidy, with relatively smooth edges. Under the same Hertz contact stress, the simulated depth values and experimental depth values show a consistent trend with the change in loading force. Conclusions Finite element simulation has become a valuable tool for studying the interaction and removal of materials in the precision machining of crystal materials. The purpose of this article is to investigate the removal characteristics of silicon carbide and determine the optimal range of cutting parameters. The study analyzes cutting force, stress distribution, and removal mechanisms, and proposes effective methods for enhancing cutting efficiency. The findings of this research can contribute to improving the smoothness of the cutting edge and reducing subsurface damage to the workpiece. Furthermore, this research has significant implications for understanding the impact of process parameters on cutting accuracy and the removal mechanism of hard and brittle materials during cutting.

Physical and chemical characterization of the surface and removal process of silicon carbide ceramics by femtosecond laser processing

XU Dongqu, WANG Chengyong, DU Cezhi, DING Feng, HU Xiaoyue

2024, 44(4): 508-517. doi: 10.13394/j.cnki.jgszz.2023.0088

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Objectives : Silicon carbide ceramics, as a typical hard and brittle material, are difficult to process, with challenges such as low efficiency, significant tool wear, and poor surface quality during processing. Ultrafast laser processing can effectively inhibit the processing damage, which is an important method for the precision processing of silicon carbide ceramics. However, existing research on femtosecond laser processing of silicon carbide primarily focuses on the laser ablation characteristics of the material. The specific removal process of the material, in relation to the composition distribution and laser ablation mechanism, is still lacking in the relevant research. This paper analyzes the microstructure of the surface of silicon carbide ceramics processed by femtosecond laser pulses and its evolution law. It reveals the material removal process by examining the changes in chemical components in the ablation area, further improving the femtosecond laser processing mechanism of silicon carbide ceramics from the perspective of changes in material's physicochemical properties. Methods : Under the premise of a fixed laser repetition frequency, the silicon carbide ceramics were processed by varying the laser energy density and the number of pulses. The changes in the physical and chemical properties of silicon carbide were observed and analyzed. A field emission scanning electron microscope was used to observe the microscopic morphology of the processed surface, while a matching energy spectrum analyzer was used to analyze the composition of the processed area. Additionally, X-ray photoelectron spectroscopy was employed to detect the chemical components of the surface before and after processing. A field emission transmission electron microscope was used to detect the cross-sectional morphology of the microstructure. An OLS4100 confocal laser microscope was used to scan the three-dimensional morphology of the micropores formed by the pulsed processing, measuring the diameter and depth of the micropores. The diameter and depth of the micropores were measured. Results : It was found that when femtosecond laser processing silicon carbide ceramics with a single pulse at low energy density, the surface of the processed ceramic was slightly ablated, forming a melting characteristic zone. At high energy density, localized high temperatures were generated in the central processed area, reaching the boiling point of the material, leading to the boiling of the material and the formation of a boiling characteristic zone. Simultaneously, due to the relatively lower energy in the edge area, the material melted, forming a melting characteristic zone. The surface morphology of the boiling region mainly consisted of gasification pits and micro-projectile structures formed by gasification, while the morphology of the melting region was not obvious, with the local appearance of unclear contours of a periodic stripe structure. Using the radius of the feature area and the Gaussian laser intensity function, the evaporation and melting thresholds for the formation of the boiling and melting zones were calculated to be 3.779 J/cm² and 0.860 J/cm², respectively. Under the influence of multi-pulse laser processing, the morphology of the processed area was primarily striped when the laser energy was between the melting and evaporation thresholds, with coarse stripe structures in the central area and fine stripe structures in the edge area. The center region produced coarse streaks, and fine streaks were produced in the edge region. When the laser energy exceeded the evaporation threshold, the central region's structural appeared as a hole structure formed by vaporization, followed by the formation of concentric coarse and fine stripe structures extending to the edge region. As the laser energy density and the number of pulses increased, the micropore diameter and ablation depth exhibited an increasing trend, with the micropore diameter leveling off after an energy density of 9.46 J/cm² and 50 pulses. Phase explosion performed a shielding effect on oxygen and material oxidation reactions; due to the decreasing distribution of laser energy and temperature from the center to the edge of the laser beam, the extent of the phase explosion decreased. In the central region, oxygen in the air did not center the material, while in the middle to the edge regions, exposure to oxygen increased, resulting in an increasing trend in oxygen content from the center to the edge. Meanwhile, through transmission and compositional analysis, it was found that the material subjected to laser action produced a metamorphic layer in the depth direction, showing a distribution pattern of an oxide layer-C-rich layer-silicon carbide matrix. Conclusions : This article investigates the ablation mechanism of silicon carbide ceramics processed by femtosecond laser. In terms of the removal process, laser removal of silicon carbide ceramics is a process in which photothermal and photochemical effects act sequentially. The laser beam irradiates the surface of the material, and the absorbed energy causes an internal temperature rise, accelerating atomic movement. As the energy continues to increase, it leads to a plasma phase explosion of the material, which jets outward, allowing oxygen from the air to react chemically within the material, completing the removal process. In terms of pulse processing, two characteristic regions, boiling and melting, are formed in the ablation region under the action of a Gaussian beam when processing with a single pulse. The evaporation threshold and the melting threshold of the characteristic region are 3.779 J /cm² and 0.860 J/cm², respectively. During multi-pulse processing, when the laser energy is between the melting and the boiling thresholds, the generation of structural defects in the hole structure can be avoided. The temperature of the ablation region decreases from the center of the laser beam to the edge region. In the high-temperature area, the material removal mechanism is primarily direct evaporation of the matrix, while in the low-temperature region, it is the thermal decomposition of the material and the oxidation reaction. This results in the formation of microstructures in the ablation region that are consistent from the center to the edge during multi-pulse processing.

Online recognition of contour error of diamond roller

ZHAO Huadong, HE Honghui, ZHU Zhenwei, ZHOU Shuaikang, LIU Chang

2024, 44(4): 518-527. doi: 10.13394/j.cnki.jgszz.2023.0148

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Objectives: With the development of the manufacturing industry, precision grinding has become an indispensable part of the high-end manufacturing field. As a key tool for precision grinding, the surface reshaping technology of diamond rollers is one of the critical technologies for making diamond rollers. Currently, the diamond grinding wheel grinding method is commonly used for diamond roller precision reshaping. In the process of precision reshaping, the surface profile of the diamond roller is an important indicator for assessing its reshaping quality. However, in the current reshaping detection, the workers often stop the machine to remove the rollers and place them on the profiler, which greatly increases the time and the cost of roller reshaping. Therefore, to improve the efficiency of diamond roller reshaping, a method based on sensors to monitor the state of contour reshaping during the process of diamond roller reshaping is explored. Methods: To realize online monitoring and discrimination of the diamond roller contour reshaping state, the diamond roller grinding monitoring platform was first built according to the structure of the GC-X3 machine tool, and LabVIEW was used to read and save the signals collected by the acquisition card. Secondly, the diamond rollers with different contour reshaping states were processed by the GC-X3 machine tool, and the signals with different reshaping states collected by the computer were analyzed in time and frequency domains. The wavelet packet decomposition method was used to decompose the signals according to the characteristics of time and frequency domains, and the signals of different nodes obtained after decomposition were calculated and compared to identify and determine the characteristic values of the signals. Finally, the machine learning method was used to establish the recognition model of the diamond roller contour reshaping state. The model is based on the mapping relationship between the characteristic values of the vibration signals and the contour reshaping state to realize the intelligent recognition of the contour reshaping state of the diamond roller. Results: After preprocessing the signal, it can be observed through the time and the frequency domains that the maximum amplitudes of the X and Y axis vibration signals decrease with the improvement of the roller profile accuracy. The amplitudes of the X and Y axis vibration signals during rough trimming are 1.00 and 0.50 V, respectively. The amplitudes of the X and Y axis vibration signals during fine trimming are 0.50 and 0.40 V, respectively. The amplitudes of X and Y axis vibration signals at the completion of trimming are 0.29 and 0.27 V respectively, and the main frequencies of signals at the completion of rough, fine, and finishing are all distributed within 1 000 Hz. The root mean square and the variance of wavelet packet coefficients mainly occur at nodes (3,0) to (3,3), and as the grinding accuracy increases, the root mean square and the variance of wavelet packet coefficients decrease gradually. When rough trimming diamond rollers with diamond grinding wheels, the roundness error value of the roller profile is larger than that after fine trimming and the completion of trimming, resulting in a larger local grinding allowance. A large number of abrasive particles from the diamond grinding wheel come into contact with the roller, which increases the material removal amount of the diamond roller, the grinding force also increases, and the resulting vibration also increases accordingly. During the fine trimming process, the roundness error of the roller contour is reduced, so that the diamond wheel cutting the diamond roller allowance is reduced, the removal amount is also reduced, the grinding force is reduced, and the vibration generated is also reduced. At the same time, the root mean square and the variance of the wavelet packet coefficients in the completion of trimming decrease correspondingly as the roundness error value of the roller profile decreases. As the trend and fluctuation of the root mean square and the variance of the wavelet packet coefficients in the X and Y axes are generally consistent, the root mean square and the variance of the wavelet packet coefficients in the direction of the X-axis are selected as the feature vectors for the classification of experimental data. The wavelet packet is used to decompose the X-axis signal, and the variance and the root mean square of each node are calculated to obtain 16 characteristic values of the vibration signal. There is a mapping relationship between these characteristic values and the reshaping state of the roller, and the random forest algorithm is used to classify the vibration signals based on these 16 characteristic values, and the recognition accuracy reaches 93.3%. Conclusions: The contour reshaping of the diamond roller is the key to the production of diamond rollers. In the process of roller machining, the method combining sensor monitoring and machine learning models is used to judge the reshaping state of the diamond roller. The method can be used to identify the modified state of the diamond roller profile, reduce the number of roller disassemblies and roller profile detections, and improve the processing efficiency.

Effect of lapping pressure on surface quality of polycrystalline diamond

SUN Guodong, LI Weicui, HU Jinzhao, LI Shuqiang, HUANG Shutao

2024, 44(4): 528-533. doi: 10.13394/j.cnki.jgszz.2023.0036

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Objectives Polycrystalline diamond (PCD), as a superhard material with high hardness, high wear resistance, and good impact toughness, has a wide range of applications in fields such as cutting tools for superhard materials. However, due to its high hardness, the precision surface processing of PCD has always been a technical challenge. This paper aims to study the influence of lapping pressure on the surface quality of PCD, particularly focusing on the material removal rate, surface roughness, and changes in surface morphology under high-speed grinding conditions. Methods The experiment adopts a single-factor test method, keeping the abrasive particle size W5 of the diamond flat grinding disc and the lapping speed of 43.3 m/s constant, while varying the lapping pressure (from 0.10 MPa to 0.18 MPa) to study its impact on the material removal rate, the surface roughness, and the surface morphology of polycrystalline diamond material. The experimental material is a ϕ13 mm × 2 mm polycrystalline diamond composite sheet with a diamond layer thickness of approximately 1 mm. The experimental apparatus is a high-speed grinding testing machine, which uses an electric spindle to drive the diamond flat grinding disc, with a lapping time of 20 minutes. The lapping process is conducted without the use of coolant to avoid its influence on the experimental results. Results The experimental results indicate that the lapping pressure has a significant impact on the material removal rate of PCD. As the lapping pressure increases from 0.10 MPa to 0.18 MPa, the lapping removal rate increases from 0.005 mg/min to 0.030 mg/min, indicating that an increase in lapping pressure significantly improves material removal efficiency. The influence of lapping pressure on the surface roughness of PCD is also significant. With an increase in lapping pressure, the surface roughness gradually decreases, reducing from a higher value at 0.10 MPa to a lower value at 0.18 MPa, with a roughness R_a reduction of approximately 0.020 μm. The impact of lapping pressure on the surface morphology of PCD is manifested by a reduction in surface defects and an expansion of smooth areas. At lower lapping pressures, the surface exhibits numerous pits, interstitial cracks, and mechanical scratches. As the lapping pressure increases, the number of these defects gradually decrease, and smooth areas gradually expand. Scanning electron microscope observations reveal that an increase in grinding pressure helps reduce defects such as intergranular fractures, minute pits, and mechanical scratches, resulting in a smoother surface. Conclusions This paper experimentally studies the influence of lapping pressure on the material removal rate, surface roughness, and surface morphology of PCD, and draws the following conclusions. The lapping removal rate of PCD material significantly increases with an increase in lapping pressure, primarily attributed to the high-frequency collisions and frictional heat between diamond abrasive particles and PCD during the lapping process. An increase in lapping pressure significantly reduces the surface roughness of PCD, primarily benefiting from the decreased cutting depth of abrasive particles and increased actual contact area caused by the increased lapping pressure, and the promotion of surface thermochemical reactions and mechanical thermal removal effects by frictional heat. An increase in lapping pressure leads to a reduction in surface defects, an expansion of smooth areas, smaller mechanical scratches, and a significant improvement in the surface quality of PCD.

CFD simulation and experiments of abrasive water jet polishing for micropores

CUI Zihan, HAN Bing, WU Pengcheng, LI Qing, MA Xiaogang, DING Yunlong

2024, 44(4): 534-543. doi: 10.13394/j.cnki.jgszz.2023.0120

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Objectives: Femtosecond laser technology has become the primary method for micropore processing due to its high precision and low energy consumption. However, during the process, it is easy to cause microcracks and burrs in the micropores. Additionally, due to the small size, low structural stability and weak wear resistance of the micropores, conventional methods are ineffective in polishing them. To address the challenge of polishing femtosecond laser-processed micropores, the abrasive water jet polishing method is employed. This method leverages the stable removal function and strong adaptability of the abrasive water jet to improve the quality of femtosecond laser-processed micropores. Methods: Computational fluid dynamics (CFD) simulations of the abrasive water jet micropore polishing process under different process parameters were carried out by using Fluent software. A finite element model of abrasive water jet polishing for femtosecond laser-processed micropores was established under various working conditions. The flow field distribution, the erosion rate and the wall shear force under different parameters were analyzed. Corresponding experiments were conducted for each variable discussed in the Fluent simulation, and the variation patterns of micropore inner wall roughness were summarized. Subsequently, optimization experiments were conducted on the three factors, namely jet target distance, jet pressure and abrasive particle size, using the response surface method. The mean square error of shear force on the inner wall of the hole was taken as the response value Y, and the response surface equation was established. The optimal polishing parameter combination was obtained through the response surface equation and experimentally verified. Results: A jet impact angle of 90° is suitable for polishing the inner wall of the micropore, as wall erosion is uniform and the shear force distribution is concentrated at this angle. At a target distance of 4.2 to 6.0 mm, the jet on the end face enters the deceleration stage, and the jet velocity decreases as the target distance increases. The shear force increases with increasing jet pressure. When the jet pressure is 0.80 MPa, the shear force is the smallest, concentrated in the range of 1 500 to 3 500 Pa. At a jet pressure of 1.50 MPa, the shear force is the largest, concentrated in the range of 3 500 to 5 500 Pa. When jet pressure increases from 0.80 to 1.50 MPa, the shear force on the inner wall of the hole increases more than twice. The effects of abrasive particle size and jet pressure on wall shear force are similar. When the abrasive particle size is 1.0 μm, the shear force is the smallest, concentrated in the range of 1 000 to 2 500 Pa. At an abrasive particle size of 30.0 μm, the shear force reaches its maximum, concentrated between 3 000 and 5 500 Pa. Corresponding tests are carried out for each variable discussed in the simulation, and the minimum roughness R_a of the inner wall of the micropore was 0.386 μm. The optimal process parameter combination obtained through response surface analysis is as follows: jet impact angle of 90°, jet target distance of 3.5 mm, jet pressure of 1.10 MPa, and abrasive particle size of 15.0 μm. Under the optimal parameter combination, with an abrasive mass fraction of 5% and a polishing time of 5.0 minutes, the surface roughness R_a of the polished micropore inner wall surface was reduced to 0.354 µm, which is better than the minimum roughness of 0.386 µm observed in the simulation. Polishing efficiency is improved by about 3%, and the quality of the micropore inner wall surface is further enhanced. Conclusions: When the impact angle is constant, the shear force on the inner wall of the hole increases with increasing jet pressure and abrasive particle size. It increases first and then decreases with the increase in jet target distance, with jet pressure having the greatest influence on the wall shear force. Different structural segments of the jet can be applied to different working conditions due to different properties. Additionally, the simulation and experimental results are in good agreement, and the improvement in roughness is significant. This indicates that abrasive water jet polishing significantly enhances the quality of micropore walls, and the data model for response surface prediction has high accuracy.

Experimental study on tangential vibration assisted abrasive flow finishing of circular tubes

WANG Shuo, DONG Zhiguo, ZHENG Zhixin, WEN Yongji, CHEN Pan

2024, 44(4): 544-552. doi: 10.13394/j.cnki.jgszz.2023.0189

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Objectives: When the traditional abrasive flow machining (AFM) technology is used to process workpieces with complex shapes and inner walls of the tunnels, the machining quality of the workpiece surface tends to be uneven in each directions. To address this, the vibration assistance is added to traditional abrasive flow machining, forming a wavy machining track on the workpiece surface. This technique generates interwoven scratch textures, reduces the roughness value of the workpiece surface in all directions, and improves the surface quality and material removal efficiency converging the surface roughness. Methods: By rotating a cam to drive a connecting rod, vibration is induced in a round tube, altering the flow field distribution characteristics of the fluid abrasive and the mode of abrasive phase movement. This enables a new relative movement between the fluid abrasive and the workpiece surface. The principle of vibration-assisted machining and the scratching effect of abrasive particles on the workpiece surface were analyzed. At the same time, different frequencies and amplitudes were achieved by varying the motor speed and adjusting the long and short half-axes of the elliptical cam. A test platform for vibration-assisted abrasive flow machining was built to study the effects of abrasive flow rate, amplitude, and frequency on workpiece surface roughness and topography. Results: (1) After 2, 4, and 6 processing cycles without vibration, the surface roughness of the Cu-1 workpiece was reduced to 0.187, 0.123, and 0.112 μm, respectively. After 2, 4 and 6 processing cycles with vibration, the surface roughness of the Cu-4 workpiece decreased from an initial 0.230 μm to 0.139, 0.114, and 0.106 μm, respectively. The surface roughness of the workpiece polished with vibration was lower than that without vibration. At the same time, under non-vibration conditions, the transverse fringes of the original surface of Cu-1 after machining remained visible, although its surface roughness were significantly reduced. When Cu-4 was processed for 6 times under vibration condition, the transverse stripes on the original Cu-4 surface were almost completely removed, and some fine circular scratches appeared, resulting in a relatively ideal machining surface. (2) The cam speed directly corresponded to vibration frequency, higher cam speeds resulted in higher frequencies. When the Cu-2 workpiece was machined at a cam speed of 150 r/min, its surface roughness decreased slowly and steadily. At the cam speed of 225 r/min, the Cu-3 workpiece was experienced a longer micro-cutting length between abrasive particles and the workpiece, resulting in lower surface roughness compared to those of Cu-2. When Cu-4, polished at a higher cam speed, these appeared a significant reduction in surface roughness, decreasing to 0.166, 0.130. and 0.106 μm in the order of Cu-2 > Cu-3 > Cu-4. Higher cam speeds produced more scratches on the workpiece surface under the same flow rate, leading to longer arc scratches and smaller curvature radii. (3) When Cu-3, Cu-7 and Cu-8 workpieces were processed for the same times with three different cam sizes, the surface roughness of Cu-3 slowly reduced to 0.130 μm with L76 cam. The Cu-7 was machined with L47 cam at lower amplitude and relatively stable vibration, had lower surface roughness of 0.111 μm, which was lower than that of Cu-3. The Cu-8 was machined with L102 cam, the connecting rod swings greatly, the vibration was extremely unstable, and the surface roughness of the workpiece changed little. The L76 cam had the larger and more intense amplitude on Cu-3, and the curvature radius of the scratch formed by the machining was larger, and the direction angle of the scratches formed by the abrasive particles on the Cu-3 surface was closer to the original direction angle of scratches of the workpiece. The vibration amplitude of the L47 cam was small, and the scratch amplitude on the Cu-7 workpiece was smaller, and the cutting condition was more stable and the surface roughness was lower. However, the machining of Cu-8 by L102 cam destroyed the surface morphology of the workpiece. (4) The abrasive flow rates for the Cu-3, Cu-6 and Cu-5 workpieces were 38, 28, and 19 mm/s, respectively. After processing, the surface roughness were 0.130, 0.156, and 0.178μm, respectively. Under the same vibration machining conditions, the higher the abrasive flow rate, the lower the workpiece surface roughness, and the relationship between the surface roughness of each workpiece after machining was Cu-5 > Cu-6 >Cu-3. Moreover, there were scratches on the workpiece surface with a certain angle from the original scratches, and the relationship between the curvature radius of the scratch on the surface of the workpiece was Cu-3 > Cu-6 > Cu-5. Conclusions: Compared with traditional abrasive flow machining, vibration-assisted abrasive flow machining extends the cutting path of abrasive particles on the workpiece surface, forming cross scratches and reducing the surface roughness of the workpiece. The higher the vibration frequency, the longer the micro-cutting length between abrasive particles and the workpiece surface, the lower the surface roughness of the workpiece. With the increase of abrasive flow rate, the cutting effect of the abrasive particles on the workpiece surface is enhanced, leading to greater reductions in surface roughness.

2024 Vol. 44, No. 4

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