金刚石与磨料磨具工程

Molecular dynamics simulation of cutting graphene with diamond probe

YUAN Zewei, HAN Hui, TANG Meiling, ZHOU Xinbo

2019, 39(3): 1-6. doi: 10.13394/j.cnki.jgszz.2019.3.0001

Abstract(395)

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Abstract:
Graphene is considered to be the most promising two-dimensional nanomaterial with excellent physical chemical characteristics and wide application. However, the zero bonding gap limits the application in electronic fields. The precision cutting can open a proper bonding gap for graphene. The research presents a molecular dynamics simulation of cutting graphene. The micro-morphology of graphene by diamond probe cutting in different directions was analyzed. The effects of substrate or not and different cutting directions on edge energy and cutting force of graphene were studied. The simulation results show that there is anisotropy in the scratch edge of graphene. The cutting edge is rough without the features of armchair and zigzag.

Effect of titanate nanowires on properties of vitrified bonds

JIA Kunlun, LIU Shikai, WANG Shaochuan, CHEN Shuanghui, DONG Hang, WANG Shijie, YIN Yihang, SUN Yaguang, LI Zhengxin

2019, 39(3): 7-12. doi: 10.13394/j.cnki.jgszz.2019.3.0002

Abstract(302)

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Abstract:
A certain amount of titanate nanowires prepared at hydrothermal temperature 150 ℃ and held for 24 hours were added into CaO-Na₂O-B₂O₃-Al₂O₃-SiO₂ system to prepare nano-ceramic binder.The flexural strength, hardness and fluidity of nano-ceramic binder were tested by electronic multi-functional testing machine and Rockwell hardness tester.The results show that when the mass fraction of titanate nanowires in nano-ceramic binder is 1.0% and the sintering temperature of nano-ceramic binder is 610 ℃, the flexural strength and hardness of nano-ceramic binder are 92.54 MPa and 86 HRB, respectively, which are 51.5% and 62.3% higher than 61.09 MPa and 53 HRB of basic ceramic binder. The fluidity of nano-ceramic binder is improved remarkably and the material distribution is more uniform with less pores. Therefore, the comprehensive performance is improved.

Contrast and power monitoring of wheel wears in roller grinding processes

WANG Chunfeng, LI Yuanyuan, CHEN Mingying, SANG Zhenyuan

2019, 39(3): 13-16. doi: 10.13394/j.cnki.jgszz.2019.3.0003

Abstract(384)

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Abstract:
To solve the problems of uneven cutting and low efficiency when machining large components, roller grinding is taken as an example to compare and study the spindle powers and wheel performances of CBN or Al₂O₃ grinding wheels. Results show that the efficiency and accuracy of roller grinding are low due to wheel wear. It is also found that at the same condition, the efficiency of CBN wheel is 150% higher than that of Al₂O₃ wheel, and that the wear of CBN wheel is one ninth of that of the other wheel when removing the same amount of material. In conclusion, CBN grinding wheel could improve the cutting uniformity and efficiency when machining large components due to its high grain hardness and strong bond.

Measurement of grinding wheel surface morphology based on two-dimensional displacement sensor

ZHANG Xia, CAI Shunyan, LI Hongmei, LIN Mei

2019, 39(3): 17-22. doi: 10.13394/j.cnki.jgszz.2019.3.0004

Abstract(355)

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Abstract:
The three-dimensional surface morphology of grinding wheel is very important to ensure its grinding quality. A high precision two-dimensional displacement sensor is used to measure the surface topography of grinding wheel on-line, and then the evaluation parameters of the three-dimensional surface topography of grinding wheel are calculated by establishing the reference plane of the three-dimensional topography of grinding wheel and digital filtering method.The results show that the evaluation parameters are basically the same as those measured by Zeta automatic three-dimensional measurement system, which verifies the validity and practicability of the evaluation method, and can provide indexes for grinding wheel dressing and grinding.

Process exploration of lapping TC4 Ti alloy with spherical fixed abrasive head

WANG Jianjie, LI Jun, HUANG Junyang, MING Shun, ZHU Yongwei, ZUO Dunwen

2019, 39(3): 23-28. doi: 10.13394/j.cnki.jgszz.2019.3.0005

Abstract(440)

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Abstract:
TC4 titanium alloy is a typical difficult-to-process material, which has problems such as difficult cutting and easy surface burn. The lapping experiments of TC4 Ti alloy were carried out using self-designed spherical fixed abrasive head as the lapping tool. In order to optimize the lapping process, the effect of different abrasives and lapping processes on material removal rate and surface quality of TC4 titanium alloy were investigated, and the mechanism of material removal was analyzed. The abrasive of 20 to 30 μm SiC is found to has the best lapping effect, and the optimal processes are lapping speed 2 000 r/min, lapping angle 30°, lapping time 10 s. Under the conditions, the material removal rate is 22.2 mg/min and surface roughness R_a is 0.7 μm. The requirements on both material removal efficiency and surface quality are satisified.

Effects of lights modes and abrasives on UV-photocatalysis assisted polishing of 6H-SiC single crystal

LU Jiabin, XIONG Qiang, YAN Qiusheng, WANG Xin, BIN Shuiming

2019, 39(3): 29-37. doi: 10.13394/j.cnki.jgszz.2019.3.0006

Abstract(421)

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Abstract:
UV-photocatalysis assisted polishing of 6H-SiC single crystal was studied. The color change of methyl orange and the concentration of hydroxyl radical (·OH) under different photocatalytic reaction time were qualitatively detected by spectrophotometry. The effects of three kinds of illumination methods, namely no light, light polishing plate and light polishing liquid, and five kinds of abrasives namely diamond, silicon carbide, silicon dioxide, titanium dioxide and colloidal silica on the polishing of 6H-SiC single crystal were studied. The results show that the concentration of ·OH increases with the increase of illumination time. Under all three illumination modes, the material removal rate (MRR) of different abrasives showed the same pattern, which is light polishing liquid>light polishing disk>no light, and the MRR of at light polishing liquid is 18% to 58% higher than that at no light. Meanwhile, the enhancement of MRR by UV-photocatalysis is greater with the decrease of abrasive hardness, which means that UV-photocatalysis shows greater auxiliary effects. The surface roughness of wafers polished with diamond, silicon carbide, silicon dioxide and colloidal silica decreases with the increase of MRR, while that of wafers polished with the titanium dioxide shows the opposite rule. The reason is that titanium dioxide acts as photocatalyst at the same time, which enhances the chemical reaction, resulting in the chemical reaction rate of SiC surface is greater than the mechanical removal rate.

Material removal mode of lapping Si₃N₄balls

ZHANG Ke, WANG Dingwen, LI Songhua, SUN Jian, WU Yuhou

2019, 39(3): 38-44. doi: 10.13394/j.cnki.jgszz.2019.3.0007

Abstract(370)

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Abstract:
To explore the effect of grinding parameters on surface quality and the mechanism of material removal mode in lapping process, lapping experiment on Si₃N₄ bearing balls was carried out by vertical grinder. And the lapping process was designed according to different speeds of lapping panel and lapping pressure. The surface morphology was examined using SEM and 3D optical microscopy and the FEM simulation was combined to analyze the material removal mode and the surface quality in the grinding process. The results indicate that the speed of lapping panel and the lapping pressure have great influence on the removal mode, surface defect and surface quality of ceramic balls during lapping. With the decrease of speed of lapping panel and pressure, the surface defects such as scratches, pits and snowflakes are obviously reduced, and the surface quality is improved accordingly. The material removal mode is mainly 2-body abrasion when the lapping load and speed are high, and 3-body abrasion at low lapping load and speed. Compared with two-body abrasion, the subsurface cracks by three-body abrasion are deeper.

Development of automatic double-spindle precise dicing saw

YIN Shaohui, LIAO Qisheng, HU Tian, GONG Sheng, CHEN Fengjun

2019, 39(3): 45-50. doi: 10.13394/j.cnki.jgszz.2019.3.0008

Abstract(369)

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Abstract:
In order to improve dicing quality and efficiency, a double-spindle precision dicing saw is developed. It adopts a gantry structure with parallel axes Y1 & Y2 and closed-loop control. The rotary table is driven directly by DD motor. Loading and unloading system of the saw can realize multi-plate automatic feeding. Test results show that the positioning accuracy of axes Y1 & Y2 is up to 1.5 μm, that the repeatability accuracy of axes Z1 & Z2 is up to 1.0 μm, and that the table flatness is up to 4.3 μm. After dicing test, it is found that the maximum error between actual depth and designed depth of groove is 5.2 μm, and that the maximum error between actual position and designed position of dicing trace is 4.8 μm, the trace surface of which is smooth with small chipping but no burrs. Compared with traditional single-spindle dicing saw in China, the developed one has 80% higher dicing efficiency obviously improved dicing quality.

Performance of tool with hard coating when cutting compacted cast iron under different spray filed

LIN Haisheng, WANG Chengyong, LUO Jie, LAI Zhiwei, YANG Jianzhang, ZHENG Lijuan

2019, 39(3): 51-57. doi: 10.13394/j.cnki.jgszz.2019.3.0009

Abstract(328)

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The spraying field and cutting performance of oils on water (OoW) in the machining of compacted graphite iron (CGI) using cutting tools with hard coatings has been investigated in this paper. Three types of spray nozzles with different structures were used to explore their spray filed, as well as their chip flow during the machining of CGI. Cutting force by using specified spray nozzle and different coated tools were further analyzed under different spray locations. The results showed that, compared to the ordinary cylindrical- and flat-typed spray nozzles, the sharp mouth-typed one had concentrated jet flow, stable and continuous spray low, and no droplets of large size, hence better atomization effect. The ordinary cylindrical- and sharp mouth-typed spray nozzles had the ability to break chips when the spray position of only spraying to the rake face was applied during the machining of CGI. When spraying to the rake and flank faces simultaneous, the chip flow can obtain good flowing orientation, only with the sharp mouth- and flat-typed spray nozzles. Using the sharp mouth-typed spray nozzles, the cutting forces of OoW were 30 to 60 N lower than the cryogenic air cooling and dry cutting. The OoW with only spraying to the rake face has the lowest cutting force. Moreover, the cutting tools with hard coatings should be matched with the spray position of OoW in order to obtain the lowest cutting force.

Research progress of PCBN superhard cutting tools

LI Yanguo, CHENG Zhaonan, ZOU Qin, WANG Mingzhi, YIN Yuhang

2019, 39(3): 58-68. doi: 10.13394/j.cnki.jgszz.2019.3.0010

Abstract(665)

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Abstract:
The continuous improvement of cutting speed of modern tools and the development of advanced integrated manufacturing system put forward higher requirements for the performance of modern tools. The quality, performance and reliability of cutting tool materials directly affect the production efficiency and processing quality, as well as the level of production technology and economic benefits of the whole manufacturing industry. Therefore, the development of superhard cutting tools with high stability and good wear resistance is a trend. This paper introduces the development and application of superhard material PCBN tool at home and abroad, the preparation method of PCBN tool material and the manufacturing process of PCBN tool, the chip breaking groove, polishing edge structures and new PCBN tool, the related research of turning simulation, and the prospect of PCBN tool and the whole tool industry.

Numerical analysis and experiment of PDC tool′s temperature during high-frequency induction brazing

ZHU Yuanqi, DONG Hai, XU Peng, LI Qinan

2019, 39(3): 69-74. doi: 10.13394/j.cnki.jgszz.2019.3.0011

Abstract(348)

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Abstract:
Based on the theory of magnetic-thermal bidirectional coupling, the 3D nonlinear high-frequency induction brazing temperature field model of the polycrystalline diamond compact (PDC) tool is established with COMSOL Multi-physics software. The PDC temperature field of high-frequency induction brazing is calculated and then verified by experiment designed in accordance with the model to analyze the law of temperature change at brazing position. The results show that the variation of PDC brazing temperature is approximately linear before it reaches 700 ℃. The effective temperature of the brazing can be reached when the PDC is heated for about 12 s. Within the effective temperature range of brazing, the error between the actual temperature value of brazing position measured in the experiment and the caculated is less than 5%. The brazing parameters can be determined on the basis of this model.

Advances in constitutive model of metal cutting process

LV Minghang, LI Anhai, LV Haojian, GE Dejun

2019, 39(3): 75-80. doi: 10.13394/j.cnki.jgszz.2019.3.0012

Abstract(451)

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Abstract:
As the basis of metal forming theory, material constitutive model plays an important role in machining simulation. In this paper, the research status of constitutive relation in metal cutting is reviewed. It mainly introduces the advantages and disadvantages of several typical constitutive models, their applications in the actual machining process and their correction, also the acquisition and correction methods of original parameters of the constitutive model. Finally, some deficiencies in the constitutive model of metal cutting and the future research direction are analyzed.

Abrasive machining simulation technology for hard-brittle materials

LI Long, GE Peiqi, WANG Peizhi, LI Zongqiang

2019, 39(3): 81-87. doi: 10.13394/j.cnki.jgszz.2019.3.0013

Abstract(376)

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Abstract:
Hard-brittle materials such as monocrystalline silicon have high hardness, low fracture toughness and other characteristics, which belong to difficult-to-machine materials. Their machined surfaces are prone to produce micro-cracks, sub-surface damage layers and other defects . The factors affecting abrasive processing of hard-brittle materials are complex. Generally, simulation technology is used to study the removal mechanism of hard-brittle materials in abrasive processing.This paper summarizes the mesh methods, meshfree methods and the combination of mesh and meshfree methods widely used in the research of abrasive machining of hard-brittle materials. The characteristics and limitations of each simulation method are compared and analyzed, and the future research directions are put forward.

Measuring volume density of working layer of ceramic superhard abrasive tools

XING Bo, LI Bingwen, CHEN Xuewei, ZHANG Linzhou, CHEN Xuebin, ZHAO Yanjun, YAN Ning

2019, 39(3): 88-92. doi: 10.13394/j.cnki.jgszz.2019.3.0014

Abstract(326)

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Abstract:
According to JB/T 7999—2013 “Bonded abrasive products—Testing methods for the volume density, general porosity and water absorption”, the volume density of working layer of ceramic superhard abrasive tools was measured, and the influencing factors were analyzed.The results show that when measuring, the sampling quantity should be more than 0.50 g, the sample quantity decreases, the testing results show a downward trend.When the volume density of the sample exceeds 2.85 g/cm³, the vacuum treatment procedure can be omitted. When the volume density ranges from 2.50 to 2.85 g/cm³, the vacuum treatment operation can be changed to soak in deionized water for 1 hour.When the volume density is less than 2.50 g/cm³, it needs to be vacuum treated.

Preparation and wear properties of brazed diamond wear-resistant coatings

CAO Zhongxi, ZHOU Yumei, ZHANG Fenglin, ZHANG Guixia, LUO Shaoming

2019, 39(3): 93-101. doi: 10.13394/j.cnki.jgszz.2019.3.0015

Abstract(410)

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Abstract:
In order to improve the abrasive wear resistance of tool parts for agricultural machines, a preparation method of diamond wear-resistant coating based on brazing was proposed. The coatings were prepared on Q235 steel substrate with different particle sizes and plating states of diamond grits, the friction and anti-abrasive wear properties of brazed diamond coatings were studied comparing to 65Mn steel. Scanning electron microscopy (SEM) was used to characterize the microstructure of coating surface before and after wear test, and the interface between coatings and steel substrate. The wear law and mechanism of the coatings were also analyzed. The results showed that the brazed diamond coatings were bonded well with the steel matrix, and that the diamond grits were evenly distributed in the coatings with a thickness of about 370 μm. The wear resistance of brazed diamond coatings was better than that of 65Mn steel, and with the decrease of particle size of diamond grits, the friction coefficient decreased and the wear resistance increased. The friction and anti-abrasive wear resistance of brazed tungsten-plated diamond coatings were higher than those of brazed uncoated diamond coatings.

2019 Vol. 39, No. 3

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