金刚石与磨料磨具工程

, Available online , doi: 10.13394/j.cnki.jgszz.2022.0052

Abstract(69)

Abstract:
This experiment introduces a method of removing cobalt using a sulfuric acid-hydrogen peroxide mixed solution. It was observed by SEM that a large depth of corrosion pits appeared on the surface of polycrystalline diamond after cobalt removal at room temperature for 48h , and the cobalt phase was basically removed. The depth of surface cobalt removal was 164 μm and 172 μm, Through EDS, it can be determined that the residual cobalt content in the de cobalt layer is 0.93%, while the residual cobalt content in the non de cobalt layer is 7.64%. The results show that 87.83% of cobalt is dissolved by the mixed solution of sulfuric acid and hydrogen peroxide in the experiment. After the sample is cobalt removed, the hardness test is performed on it. Compared with before cobalt removal, the hardness changes little. The edge point hardness is the highest at 89.7 GPa, the center point hardness is the lowest at 81.26 GPa, and the average hardness is 86.25 GPa. The residual stress of the polycrystalline diamond sample was measured, and it was 483.91 MPa before cobalt removal and 330.35 MPa after cobalt removal, a decrease of 31.73%, indicating that cobalt removal can effectively reduce the internal residual thermal stress of PCD.

Effect of B₂O₃on the structure and properties of SiO₂-B₂O₃-Al₂O₃-Na₂O system ceramic bond

, Available online , doi: 10.13394/j.cnki.jgszz.2022.0041

Abstract(67)

Abstract:
The effective reduction of sintering temperature and thermal expansion coefficient of ceramic bond used for superhard abrasives is one of the research hotspots in this field. In this paper, SiO₂-B₂O₃-Al₂O₃-Na₂O glass samples and ceramic bond series samples with different B₂O₃ contents were prepared, using electronic multi-function experimental machine, scanning electron microscope, microhardness tester, plane flow method, thermal expansion coefficient tester and other instruments. The density and microhardness of different glass samples, the bending strength and micromorphology and thermal expansion coefficient of the bond samples were measured respectively. The structure and composition of the ceramic bond were analyzed by X-ray diffrotometry and Fourier transform infrared spectroscopy (FTIR). The results show that the introduction of B₂O₃ into the ceramic binder can effectively reduce the sintering temperature, improve the thermal stability, adjust the thermal expansion coefficient and other functions, among which, the highest bending strength of the ceramic binder spline with 15mol% B₂O₃ is 78.11MPa, the density and hardness of glass are the highest, 2.45g/cm³ and 856MPa, respectively. In addition, the thermal expansion coefficient of the ceramic bond with 7mol% B₂O₃ is the best match for diamond. X-ray diffractometer results show that the ceramic binder has a typical glass phase structure, which will play a good coating bonding effect on the abrasive. The influence of B₂O₃ on the structure and properties of ceramic bond in borosilicate glass system was discussed.

Experimental study on Optimization of PDC cutting tool for conglomerate layer

, Available online , doi: 10.13394/j.cnki.jgszz.2022.0072

Abstract(51)

Abstract:
For the conglomerate layer, the tooth shape optimization and preliminary tooth layout design of PDC bit are carried out. The single tooth rock breaking experiment of ordinary plane tooth, conical tooth and axe tooth is carried out in the conglomerate rock sample, and then the optimized axe tooth is simulated and analyzed to optimize the optimal tooth surface angle of axe tooth, and then the cutting simulation is carried out with ordinary plane tooth to verify the experimental results. The results show that the axe tooth has the highest cutting efficiency and the most stable stress in the conglomerate layer; The drilling effect of 140 ° axe tooth in conglomerate is better; The cutting efficiency is the highest when 140 ° axe teeth are matched with 30 ° caster angle.

Experimental study on precision polishing of resin-rich layer on CFRP surface

, Available online , doi: 10.13394/j.cnki.jgszz.2022.0044

Abstract(52)

Abstract:
Aiming at the high-quality processing requirements of the resin-rich layer reflecting surface of the new generation antenna, the resin-rich layer polishing process experiment was carried out to study the effects of polishing time, abrasive particle size, abrasive particle concentration, loading pressure and polishing speed on the surface roughness of the resin-rich layer. The results show that: under the current experimental conditions, the surface roughness first decreases, then tends to be stable with the increase of polishing time, increases with the increase of the abrasive particle size, first decreases and then increases with the increase of the abrasive particle concentration, increases with the increase of the loading pressure, and decreases first with the increase of the polishing speed, increased later. On this basis, an optimized process parameter combination is formed to obtain a high-quality resin-rich polished surface with a surface roughness of S_a 4.73 nm.

Effect of pad and slurry on fixed abrasive polishing of gallium oxide crystal

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0043

Abstract(66)

Abstract:
Gallium oxide crystal is the most representative fourth generation semiconductor material with the advantages of high band gap, high voltage resistance and short absorption cutoff edge, and has broad application prospects. Gallium oxide crystal is prone to micro-cracks, scratches and other surface defects in the polishing process, which is difficult to achieve high-quality surface processing and cannot meet the requirements of the corresponding devices. Moreover, the existing polishing process of gallium oxide crystal is complex and inefficient. Fixed abrasive polishing technology has the advantages of controllable abrasive distribution and depth of cut, and high utilization rate of abrasive grain. Fixed abrasive polishing was used, and the effect of pad and slurry on material removal rate and surface quality were explored in fixed abrasive polishing of gallium oxide crystal. The results show that when the hardness of the polishing pad is moderate II, the abrasive concentration is 100%, and the slurry additive is oxalic acid, material removal rate is 68 nm/min, and the surface roughness Sa value is 3.17 nm in fixed abrasive polishing gallium oxide crystal. Fixed abrasive polishing technology can achieve efficient and high-quality polishing of gallium oxide crystal

Experimental study on sawing force in axial feed grinding of cemented carbide with diamond grinding wheel

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0040

Abstract(69)

Abstract:
In this paper, the axial feed grinding experiment of cemented carbide is carried out with diamond grinding wheel. The transformation models of horizontal grinding force and tangential force, vertical grinding force and normal force are established; The variation of grinding force under different process parameters was measured; The effects of process parameters on normal force, tangential force and axial force are analyzed; The empirical formula of grinding force is established. The results show that in the process of axial feed grinding, the maximum grinding force is the normal force, and the axial force is slightly less than the tangential force. The influence of grinding wheel linear speed on grinding force in three directions is roughly the same. The influence of grinding depth on grinding force in three directions is obviously different. The effect of feed rate on grinding force is not significant.

Development of CAM system for automatic compound dressing of superabrasive grinding wheels

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0061

Abstract(35)

Abstract:
In the field of superabrasive wheel dressing, multi-process composite dressing has obvious advantages, but there is no research related to the automation system of grinding wheel composite dressing. In order to make the integration of multiple processes in the composite dressing method more systematic and improve the dressing efficiency of shaped grinding wheels, this paper develops a CAM system by self-developed laser-mechanical composite dressing equipment, which can, according to different grinding wheel section shapes, automatically plan the dressing trajectory under multiple processes and dressing strategies, calculate the dressing toolpath with planar three-axis linkage, automatically generate the machining code, and at the same time design a visualisation interface to simulate the machining process. The results of dressing experiments on 150# diamond bronze bonded grinding wheels show that the system can generate machining programs for laser roughing, semi-finishing and mechanical finishing without collision and overcutting of the machine tool, and significantly improve the programming efficiency of the compound dressing method. And the dressing wheel profile error is within 9.1 µm and circular runout error is 6.1 µm.

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0001

Abstract(71)

Abstract:
The new high temperature γ-TiAl alloy has low density and high specific strength, and has broad application prospects in the field of engine blades. In order to study the influence mechanism of machining process parameters (cutting speed and depths of cut) on the surface quality and subsurface damage of nano-cutting single crystal γ-TiAl alloy, molecular dynamics(MD) was used as the basic theory. Using a non-rigid diamond tool, a three-dimensional nano-cutting model was established, and the influence of different cutting speeds and depths of cut on the surface and subsurface structure were analyzed in detail by studying chip volume, surface roughness, workpiece hydrostatic pressure distribution, dislocation density, dislocation evolution, and phase transitions atomic number. The results showed that with the increase of cutting speed, the chip volume increases, the surface roughness first decreases and then increases but there is a critical value, the complexity of dislocations and the density of dislocations decrease, and the degree of plastic deformation increases; however, with the increase of cutting depth, the surface roughness, the density of dislocations and the degree of plastic deformation increase significantly, and it was found that the dislocations were mainly distributed in front of and below the tool during cutting process, and there were V-shaped dislocations and Stair rod dislocations in the direction of 45^o in front of the tool, as well as dislocations reacting with each other, and stable defects such as vacancies and atomic clusters remained after the cutting process.

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0051

Abstract(59)

Abstract:
To solve the problems of low efficiency and poor uniformity in polishing blisk, a rotary-assisted horizontal vibration mass finishing process was adopted. Based on the discrete element method (DEM), the behavior of particles in the process was simulated to study the characteristics of the particle behavior on the blisk, and the variation law and the distribution of the particle acting force. The results show that the particles have different movement feature in the flow passage area and the non-work-piece area, and the particles on both sides, where there is no workpiece, can only act on the two sides of the blisk. During the rotating process of the blisk, the blade would experience some sudden forces when entering or exiting the particle flow field. The force on blade surface increases at first and then decreases along the rotating direction. Moreover, changing the rotating direction affects the fluctuation range of the forces acting on the back surface and the basin surface of blade. The effect of particle on the blade surface is obviously different, whose RSD value is between 0.3 and 0.6, and the strong force of the back surface of blade mainly appears in the areas of inlet and tip while at the basin surface of blade is generally focused in the areas of exhaust and tip.

Study on the Mechanism and Process Magnetorheological Variable Gap Dynamic Pressure Planarization Finishing

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0004

Abstract(101)

Abstract:
In order to improve the polishing efficiency of magnetorheological polishing and realize the high-efficiency, high-quality and ultra smooth planarization of photoelectric wafer, a magnetorheological variable gap dynamic pressure planarization method is proposed. In this paper, the changes of material removal rate and surface roughness of sapphire wafer surface polishing with processing time under different variable gap conditions are studied, and the dynamic pressure flattening mechanism of magnetorheological variable gap is deeply analyzed. The results show that the dynamic change of polishing pressure and the extrusion strengthening effect of MR fluid can be produced by applying axial low-frequency extrusion vibration to MR polishing fluid, and the polishing efficiency and polishing effect can be significantly improved. After 120 min of magnetorheological variable gap dynamic pressure flattening, the surface roughness of sapphire wafer decreased from Ra 7 nm to Ra 0.306 nm, and the material removal rate was 5.519 nm / min. Compared with constant gap magnetorheological polishing, the surface roughness decreased by 49% and the material removal rate increased by 55.1%; By changing the moving speed of variable clearance, the flow field characteristics can be controlled. Choosing the appropriate workpiece pressing speed and workpiece lifting speed is conducive to improve the polishing efficiency and surface quality.

Effect of Fe₃O₄ Characteristics on Properties of Solid-phase Fenton Reaction Lapping Pellets for Single-Crystal SiC

, Available online , doi: 10.13394/j.cnki.jgszz.2022-0008

Abstract(52)

Abstract:
To improve the lapping quality and processing efficiency of single-crystal SiC, solid-state Fenton reaction lapping pellets were prepared. Effects of particle size and concentration of Fe₃O₄solid-phase catalyst on the physical properties (hardness, flexural strength, porosity), catalytic performance, and lapping performance of single-crystal SiC were studied. The results showed that with the increase of Fe₃O₄ particle size, the hardness, flexural strength, porosity, and catalytic performance of the lapping pellets all decreased, the material removal rate (MRR) decreased from 43.12 nm/min to 36.82 nm/min, and the surface roughness (Ra) increased from 1.06 nm to 3.72 nm. As the Fe₃O₄ concentration increased, the hardness and flexural strength of the lapping pellets decreased, and the porosity and catalytic performance increased. Although the material removal rate decreased, the surface roughness (Ra) decreased firstly and then increased. The MRR decreased from 40.14 nm/min to 33.51 nm/min, the surface roughness (Ra) was 3.25 nm, 1.75 nm and 1.88 nm. In this experiment, when the Fe₃O₄ particle size and the concentration was 0.5 µm and 29 wt.%, the processing effect was the best, the MRR and the surface roughness (Ra) was 43.13 nm/min and 1.06 nm.

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