Abstract: There is a large demand for aluminum alloy assembly hole machining in aerospace manufacturing industry. The assembly hole is mainly realized by drilling, and there is a problem that the aluminum alloy exit burr is too large in the processing. The exit burr directly affects the accuracy, fatigue strength and assembly performance of the workpiece. The deburring process will greatly increase the man hour and cost. Therefore, it is necessary to study the exit burr of aluminum alloy assembly hole drilling to realize the control of exit burr. This paper systematically discusses the types, measurement methods, formation mechanism, height prediction and gross control methods of exit burr in aluminum alloy drilling, in order to provide help for the research of exit burr in aluminum alloy drilling.
Abstract: Using sol-gel technology and hydrolysis condensation reaction of tetraethyl orthosilicate (TEOS), a nano silica amorphous gel film with a thickness of 2～10 nm and rich in active oxygen groups is coated on the surface of diamond powder. When the gel film is heated to a certain temperature, the silicon dioxide in it can change from amorphous phase to crystalline phase. The initial oxidation temperature of diamond powder in air increases from 500 ℃ of raw diamond to 550 ℃ after TEOS coating modification. After adding nano silicon powder to TEOS coating, the initial oxidation temperature of diamond powder sample in air can be further increased to 610 ℃. After 800 ℃ heat treatment, the residual amount of the sample is significantly higher than that of the raw diamond, which indicates that the high temperature oxidation resistance of diamond powder can be further improved by adding nano silicon powder to TEOS coating. The rich reactive oxygen groups in TEOS coating can produce chemical reaction with resin/ceramic bond, which is conducive to improving the holding force of bond on diamond, and can provide good functional modified raw materials for preparing high-performance resin/ceramic bond diamond tools.
Abstract: In view of the problem that B element is easy to cause more hard and brittle phases in brazed diamond joints, a new type of Ni–Cr–Si–Cu–Sn boron free active solder was prepared, and the effects of Cr element on the microstructure of solder and the properties of brazed diamond were analyzed. The results show that Cr element can refine the solder grain and regulate the distribution of elements in the solder, which can improve the microhardness of the solder alloy. Excessive Cr addition will cause the melting point of the solder to increase and the wettability of the solder to decrease. In general, the boron free solder containing 15% Cr has the best performance, the grinding performance of brazed diamond is better, and Cr7C3 phases of various shapes appear at the joint, realizing the high-strength connection of the solder to the diamond.
Abstract: To obtain homogeneous submicron cerium dioxide (CeO2) polishing powder, CeO2 was synthesized by solvothermal reaction using cerium nitrate (Ce(NO3)3·6H2O) as cerium resource and alcohol-water mixed solution as solvent. The phase composition and morphology of CeO2 were characterized by X-ray diffraction (XRD), laser particle size analyzer and scanning electron microscope (SEM). The formation process of CeO2 particles was analyzed by changing the concentration of Ce3+ and alcohol-water ratio. The synthesized CeO2 was used for chemical mechanical polishing (CMP) Si-face of 6H-SiC. The polishing characteristics were tracked by atomic force microscopy (AFM) and electronic balance. The results indicates that when the Ce3+ concentration is 0.10 mol/L and alcohol/water volume ratio is 3∶1, the as-prepared particles have regular morphology, moderate particle size and uniform particle size distribution. After polished by using the as-prepared CeO2, the Ra of wafer surface reached 0.243 nm and the dMRR 287 nm/h. The as-prepared CeO2 can be used for chemical mechanical polishing.
Abstract: The aim of present work was to investigate the tribological behavior of CVD nano-crystalline diamond (NCD) films with laser-induced periodic surface structures (LIPSS). The LIPSS textures were fabricated in ambient air using a Yb-doped photonic crystal fiber amplifier femtosecond (fs) laser with pulse duration of 200 fs and central wavelength of 1040 nm. Two types of LIPSS texture, namely continuously distributed LIPSS (CDL) texture and a complex texture formed of evenly spaced LIPSS stripes (ESLS), were obtained with the above processing conditions. The tribological behavior of as-fabricated LIPSS textures was evaluated via ball-on-disc tests in dry reciprocating sliding motion, and ZrO2 ceramic balls were used as counterparts. In addition, there were two types of reciprocating direction involved in the frictional tests, namely the direction parallel/vertical to the orientation of LIPSS ripples. The results indicate that as the LIPSS can work as reservoir for wear debris and reduce the contact area during the friction process, the LIPSS textured NCD surface showed obviously reduced friction coefficient in comparison with the conventional NCD surface, which was reduced from 0.42 to 0.09. Besides, for the CDL surface, the friction coefficient as the LIPSS ripples vertical to the reciprocating direction was higher than that as the LIPSS ripples parallel to the reciprocating direction. In the case of ESLS surface, however, the direction of the LIPSS ripples had little influence on the friction coefficient.
Abstract: The effect of the content and the size (0.2, 0.4, 0.6 mm) of the hollow corundum microspheres on the total porosity, the flexural strength, the hardness and the microstructure of vitrified bond was investigated. The ceramic bonded diamond grinding wheel with hollow alumina microspheres as pore forming agent was prepared, and the grinding performance of the grinding wheel on quartz glass was studied. The results show that with the increase of the content of hollow corundum microspheres, the porosity increases, and the flexural strength and the hardness decreases at the same time. With the same content of hollow corundum microspheres, addition the smaller size of microspheres could lead to the increase of the porosity and the decrease of flexural and hardness. The vitrified bond diamond wheel contained with hollow corundum microspheres can used to grind quartz glass, and the surface roughness can be reduced from 0.5113 μm to 0.0206 μm. Diamond wheel contained with hollow corundum microspheres can used to grind quartz glass, and the surface roughness can be reduced from 0.5113 μm to 0.0206 μm.
Abstract: In order to further improve the self sharpening performance, the chip removal and the chip holding capacity of the ultra-thin resin cutting grinding wheel, the water-soluble pore-forming agent NaCl was added into the cutting grinding wheel, and the effects of its content on the micro morphology, the mechanical property and the cutting property of the ultra-thin resin cutting grinding wheel were studied. The results show that when the volume fraction of pore-forming agent is 10%, the pores in the grinding wheel are uniform and moderate, the cutting efficiency is the highest and the maximum feed speed can reach 20 mm/s. However, the addition of pore-forming agent will have a certain impact on the flexural performance and the cutting life of the grinding wheel. The higher the content of pore-forming agent, the lower the flexural performance and the shorter the cutting life.
Abstract: To study the influence mechanism of machining process parameters on 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 machining efficiency improves and there is a critical value of the cutting speed of 100 m/s, the surface roughness first decreases and then increases and there is also a critical value of the cutting speed of 100 m/s, the complexity of dislocations reduces, the density of dislocations decreases, and the degree of plastic deformation increases. However, with the increase of cutting depth, the chip volume increases, the machining efficiency improves, 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 45o 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.
Abstract: Aiming at grinding quality of polycrystalline diamond (PCD) tools, the grinding experiment was carried out to optimize the process parameters with cutting edge radius, cutting edge defect and flank roughness as the indexes. The grinding removal mechanism of PCD was also studied. The results show that the worktable setting pressure has the most significant effect on cutting edge radius. The diamond grinding wheel has the most significant effect on cutting edge defect. The grinding wheel speed has the most significant effect on flank roughness. PCD tools with high grinding quality can be obtained by using 4/5 ceramic-based diamond grinding wheel, 1 000 r/min grinding wheel speed and 170 N worktable setting pressure. Under the experimental conditions, the main removal methods of PCD are sliding effect and micro cracking. Smaller cutting edge radius, cutting edge defect and smoother surface of PCD can be obtained by micro cracking under the 1 000 r/min grinding wheel speed and the 170 N worktable setting pressure.
Abstract: The nano-diamond film coated tool was prepared by hot wire CVD method. The surface morphology of the film was characterized by field emission scanning electron microscopy. The prepared CVD diamond coated tool was used to mill 7075 aluminum alloy workpiece at high speed under the condition of dry cutting without lubrication. The single factor and the orthogonal experiments were carried out on the finish milling process parameters to explore the variation law of the surface roughness of the workpiece after finish milling and optimize the process parameters. The results show that with the increase of spindle speed n from 5 000 r/min to 8 000 r/min, the average surface roughness of the workpiece decreases gradually. When the feed rate vf is in the range of 1 000～7 000 mm/min, the average surface roughness of the workpiece increases rapidly with the increase of vf, and when vf is 7 000 mm/min, its value reaches 1.790 μm. When the axial cutting depth ap is in the range of 0.1～0.4 mm, the average surface roughness of the workpiece increases gradually with the increase of ap, but the increasing trend slows down after ap is 0.2 mm. The Vf has the greatest influence on the finish milling surface roughness of 7075 aluminum alloy workpiece, followed by n and ap. The optimal parameter combination of finish milling 7075 is ap = 0.2 mm, vf = 1 000 mm/min, n = 8 000 r/min, and the average surface roughness after finish milling is 0.516 μm. When using nano-diamond film coated tools to finish milling 7075 aluminum alloy, the high spindle speed, the low feed rate and the appropriate axial cutting depth should be selected to obtain low surface roughness.
Abstract: According to the characteristics of elbow erosion damage position, a new differential processing technology was proposed. Using the flexibility of the manipulator, the machining gap between the inner and the outer side of the elbow was changed in the process of elbow machining, so as to realize the differential grinding of the inner wall of the elbow and improve its surface quality. The results show that when the machining time is 75 min and the machining gap between the inner and the outer side of the elbow is 2.0 mm, the inner surface roughness of the outer arc of the elbow is reduced from 0.70 μm to 0.34 μm, and the inner surface roughness of the inner arc of the elbow is reduced from 0.82 μm to 0.32 μm. During differential grinding, the outer machining gap of the elbow is 1.5 mm, the inner machining gap remains unchanged at 2.0 mm, the inner surface roughness of the outer arc of the elbow is reduced from 0.70 μm to 0.26 μm, and the inner surface roughness of the inner arc of the elbow is reduced from 0.82 μm to 0.29 μm. Differential grinding can effectively improve the inner surface quality of the elbow.
Abstract: In order to improve the magnetorheological polishing efficiency of photoelectric wafer and realize its ultra smooth planarization, the magnetorheological variable gap dynamic pressure planarization method is proposed. The changes of material removal rate and surface roughness of sapphire wafer with processing time under different variable gap conditions are studied, and the magnetorheological variable gap dynamic pressure planarization finishing mechanism is analyzed. The results show that the axial low-frequency extrusion vibration is applied to the magnetorheological polishing fluid through the sapphire wafer, the polishing pressure changes dynamically, and the magnetorheological fluid produces extrusion strengthening effect, which significantly improves the polishing efficiency and polishing effect. Under the conditions of workpiece pressing speed of 1.0 mm/s, lifting speed of 3.5 mm/s and extrusion vibration amplitude of 1 mm, the surface roughness Ra of sapphire wafer decreased from 6.22 nm to 0.31 nm and the material removal rate was 5.52 nm/min. Compared with constant gap magnetorheological polishing, the surface roughness decreased by 66% and the material removal rate increased by 55%. Changing the moving speed of variable gap can regulate the flow field characteristics of magnetorheological fluid, and the appropriate workpiece pressing speed and workpiece lifting speed are conducive to improve the polishing efficiency and surface quality of workpiece.
Abstract: According to the structural characteristics and the surface quality requirements of aspheric optical elements, a hemispherical head polishing head with radial magnetized permanent magnet as rotating magnetic field source is designed and manufactured on the basis of magnetic compound fluid (MCF) polishing. Firstly, through Ansoft Maxwell magnetic field simulation, the distributions of magnetic field around each magnet with different shapes, sizes and eccentricities are analyzed and compared, and the cylindrical magnet with diameter of 10.0 mm, height of 5.0 mm, eccentricity of 2.5 mm and radial magnetization is selected. Secondly, by observing and comparing the behaviors of MCF with different compositions, formula and supplies on the polishing head, the compositions of MCF polishing slurry is determined. Finally, the aspheric PMMA workpiece is polished with the prepared MCF polishing slurry and the self-made polishing head. After polishing for 15 min, the surface quality of the PMMA workpiece is significantly improved, its surface accuracy Rq is decreased from 0.703 μm to 2.433 nm, and the surface roughness Ra is reduced from 0.545 μm to 1.786 nm, indicating that the developed polishing head can realize the nano-polishing of aspheric workpiece.
Abstract: To solve the problem of low polishing efficiency of silicon carbide crystal, electrochemical mechanical polishing (ECMP) of silicon carbide was carried out to study the effect of NaOH, NaNO3 and H3PO4 electrolytes on electrochemical oxidation of silicon carbide. NaNO3 of 0.6 mol/L was selected as the electrolyte in the ECMP process and so were the diamond-alumina mixed abrasive particles. The influence of load, rotational speed, voltage and particle size on the surface quality and material removal rate of ECMP silicon carbide was studied by using orthogonal experiment. With the optimized processing parameters, the combined polishing experiment can achieve a high-efficiency material removal rate of 20.259 μm/h in the rough polishing stage, and finally obtain the surface roughness of Sa 0.408 nm through precision polishing.