To obtain the high consistency passivation of cutting edge of the cemented carbide insert with complex shape and improve the tool performance and life, the flexible fiber assisted stress rheological polishing method, which utilizes the rheological properties of non-Newtonian fluid under shear stress and the flow control effect of flexible fibers, was proposed to polish the complex shape edge of cemented carbide insert. The deviation value K of the passivation radius of the cutting edge was used as the evaluation index, and Taguchi method was employed to analyze the effects of the polishing speed, the fiber density and the fiber-insert contact length on the edge passivation radius and its consistency. The weight of each factor was evaluated by variance analysis method, and the optimal process parameters were obtained by combining the influence of the polishing parameters on the cutting edge at different positions. The optimal combination of process parameters is that the fiber density is 200 to 250 fibers/cm2, the contact length is 4 mm and the polishing speed is 55 r/min. Under the optimal combination of process parameters, the passivation radius of seven cutting edges can reach (50.0 ± 5.0) μm after polishing for 10 min, the surface roughness Ra of the cutting edges are reduced from (118.00 ± 10.00) nm to (9.35 ± 0.75) nm and the cutting edge is complete and free of defects.
Abstract: As the core device of the hemispherical resonator gyroscope (HRG), the processing accuracy and the surface quality of hemispherical resonator directly affect the working accuracy and the service life of HRG. To solve the problem of hemispherical resonator processing and improve the performance of HRG, the interference in the processing of hemispherical resonator is analyzed theoretically according to the structural characteristics of the hemispherical resonator. Then, the grinding trajectory is planned by using the characteristics of the grinding area distribution of the ball-end grinding wheel, and the optimal turning angle of the ball-end grinding wheel during different grinding processing sections of the hemispherical resonator is determined. Finally, grinding experiments of hemispherical resonator are conducted on the developed hemispherical resonator ultra-precision grinding machine tool. The surface roughness (Ra value) of hemispherical resonator is improved from 0.615 8 μm to 0.040 2 μm after ultra-precision grinding processing, while the profile accuracy (PV value) is improved from 4.590 4 μm to 0.339 0 μm. The surface roughness Ra of the hemispherical resonator is further improved to 0.003 2 μm after magnetorheological polishing. The research shows that the grinding process after trajectory planning can avoid the interference between the grinding wheel rod and the workpiece. High-quality hemispherical resonator component is produced by using the above grinding process.
Abstract: An in-situ measurement device combining contact probe and capacitive displacement sensor is developed. An aspherical measurement and compensation machining software is also developed. The single point diamond ultra precision cutting experiments for C3604 brass spherical and aspherical surface are carried out. The in-situ measurement and compensation machining experiments are also carried out. After compensation machining, the spherical surface form accuracy PV reaches 231.4 nm, and the aspheric surface form accuracy PV reaches 206.3 nm. Compared with the off-line measurement results, the difference between the results is 3.0 nm, 7.0 nm respectively, the measuring accuracy of the in-situ measurement system and the validity of compensation machining are verified.
Abstract: The blisk has the characteristics of complex structure and difficult material processing. Its machining accuracy and surface quality have a crucial impact on the overall performance of the aero-engine. At present, the robotic belt grinding has been applied to grinding the complex surface of the blisk. However, since the target points are usually distributed evenly in the grinding trajectory plan, it requires a large amount of points, which leads to low processing efficiency. In this paper, the trajectory is optimized based on the improved equal chord height error method, and relevant simulation and experimental verification are carried out. The results show that the improved equal chord height error method can optimize the grinding trajectory according to the curvature change, reduce the number of target machining points and improve the machining efficiency. Experiments indicate that the machining efficiency of the blisk, compared with that before trajectory optimization, is increased by 42.9%. The surface roughness Ra after optimization can reach 0.26 μm, and the blade consistency is good, especially in the positions where the curvature changes greatly.
Abstract: High entropy oxide ceramics are stable solid solutions with single-phase structure, which are synthesized from five or more oxides with equal molar ratio and have excellent thermal, magnetic, electrical and corrosion resistance properties. At present, the researches mainly focus on the in-depth exploration and expansion of the existing properties of high entropy oxide ceramics, as well as their applications based on its excellent properties in lithium ion battery electrode materials, dielectric materials, magnetic materials and catalytic materials, etc. In this paper, the classification, the preparation methods and the properties of high entropy oxide ceramics are reviewed, and the development direction of high entropy oxide ceramics is analyzed and prospected.
Abstract: A plasma torch with split anode and rotating arc was developed. The diamond was coated on the inner wall of large diameter annular workpiece by the torch. The umbrella-like arc formed by the movable anode makes the axial working gas blow vertically to the inner wall of the annular workpiece. The parameters of arc under different anode diameters were tested, and the arc shap was taken by camera. High quality diamond coatings were successfully deposited on the inner surface of cemented carbide drawing die with inner diameter of 180 mm and graphite with inner diameter of 100 mm. The composition and surface morphologies of the coating were analyzed by Raman spectroscopy and scanning electron microscopy. The diamond coating cemented carbide die has been successfully applied in the drawing equipment of aluminum sheath of extra-high voltage cable.
Abstract: Using M(Mn or Cr)/Al/B/diamond powders as raw materials, the multicomponent composite coatings were formed on the surface of diamond by thermal explosion reaction technology. The effects of two raw material systems and different Al contents on the phase compositions and the microstructures of ceramic matrix and coatings were studied by X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer. The results show that under the protection and detonation of N2, the thermal explosion reaction of Cr/Al/B/diamond powder forms CrB-AlN based multicomponent composite coating and by-products such as Cr5Al8 and Cr2AlB2 on the surface of diamond. Under the protection of Ar gas, Mn2AlB2 based composite coating is formed on the surface of diamond by thermal explosion reaction of Mn/Al/B/diamond powder. The two coatings wrap diamond well. Due to the small heat release of the two thermal explosion reactions, the reaction products are difficult to sinter into blocks. The prepared loose porous blocks are easy to crush and separate.Therefore, the ceramic matrix can be separated from diamond particles.
Abstract: Cr-coated diamonds with different coating weight gains were prepared by one pot reaction in a vacuum reactor, and the crystal phases and the thickness of the coatings were identified and analyzed. The results showed that the coating thickness varied with the temperatures and the holding time during coating. The crystal phases of the coating were related to the coating weight gains, which means that there appeared only Cr3C2 with 10% coating weight gain but Cr7C3 with 20% coating weight gain. It is also found that from the diamond surface to the Cr coating, the crystal phases are gradually transited from Cr3C2 to Cr7C3. For diamond with a certain particle size, there was a certain correspondence between the coating thickness and the coating weight gains. For example, when the coating thickness of the Cr-coated diamonds with 10% weight gains was 0.77 μm and that of diamonds with 65% coating was 4.76 μm, which was consistent with the SEM results.
Abstract: The orthogonal experiment of laser planarization of CVD polycrystalline diamond film was carried out, and the morphology was analyzed by using scanning electron microscope (SEM). The surface roughness Ra, the surface roughness Sa and the taper of kerf were measured by confocal laser scanning microscope. The influence of laser parameters on cutting quality was analyzed. The results show that the factors affecting kerf taper are pulse width, pulse frequency, feed speed and laser current in turn, and the factors affecting line roughness are feed speed, laser current, pulse frequency and pulse width in turn. After optimization by orthogonal test, the best groove surface morphology can be obtained with laser current of 64 A, pulse width of 400 μs, pulse frequency of 275 Hz and feed speed of 100 mm/min. Using the optimized parameters, the surface roughness Sa was measured to be 11.7 μm. When the incident angle increased to 75°, the surface roughness Sa decreased to 1.9 μm, and the actual removal efficiency reached 1.1 mm3/min.
Abstract: To improve the grinding efficiency and service life of rail grinding wheels, a surface porous CBN/Cu-Sn-Zn compact abrasive is prepared. This work discussed the performance of Cu-Sn metal bond used for preparing agglomerated abrasives, the influence of pore structure on CBN agglomerated abrasive and the effect of agglomerated abrasive on the structural strength of grinding wheel. The grinding effect of grinding wheel before and after compound abrasive addition was evaluated by rail grinding experiment. The results show that the best porous CBN agglomerated abrasive sample has a flexural strength of 78.5 MPa, an impact strength of 5.5 kJ/m2, and a surface porosity of 30%～40%. The combined use of abrasive can effectively combine the high hardness of CBN with the good impact toughness of zirconium corundum. The grinding efficiency and grinding quality of rail grinding wheels with 20% volume concentration accumulated abrasives are further improved.
Abstract: The cemented carbide matrix and the preferred main crystal of 25 μm diamond particles as raw materials, the polycrystalline diamond composites (PDC) was prepared by domestic hinge-type cubic-anvil press at high temperature and high pressure (HPHT) under two processes. Effect of microstructure at PDC interface on its properties was studied. The results show that there is a dendrite-like growth metal pool at the interface of PDC prepared by process 1, which is formed by the migration of metal elements in cemented carbide to polycrystalline diamond layer, and the main elements are C, W and Co. This phenomenon does not exist in the interface of PDC prepared by process 2. The heat resistance temperature is 870 ℃, the impact resistance grade is 32 and the grinding area is 5.860 mm2 of PDC prepared by process 1. The heat resistance temperature is 920 ℃, the impact resistance grade is 45, and the grinding area is 5.166 mm2 of PDC prepared by process 2. Compared with the PDC prepared by process 1, the heat resistance, the impact resistance and the wear resistance of the PDC prepared by process 2 are increased by 50 ℃, 40.6% and 11.8%, respectively.
Abstract: SiC fiber reinforced SiC ceramic matrix composites (SiCf/SiC) have problems such as poor machining quality and difficult material removal. To study these problems, SiCf/SiC composites were processed by ultrasonic-assisted helical grinding. The exit quality of hole, hole wall morphology and three-dimensional surface roughness of hole wall were explored. The results show that compared with traditional hole making, the material at the exit of the hole made by ultrasonic-assisted helical grinding has no large area chipping. The periodic change of the angle θ between the direction of the cutting speed of the grinding wheel and the fiber direction leads to regular changes in the surface morphology of the hole wall. When θ is 0°/180°, the fiber and the matrix are debonded. When θ is 45°, the fiber is sheared and fractured. When θ is 90°, the fiber is crushed and fractured. When θ is 135°, the fiber has both shear fracture and extrusion fracture. The hole wall surface roughness Sa is the lowest value when θ is 90°, and Sa is the highest value when θ is 135°. Within a certain range, the surface roughness value Sa decreases with the increase of the ultrasonic amplitude, with a maximum decrease of 38.7%, and increases with the increase of the feed rate, with a maximum increase of 39.3%.
Abstract: To accurately describe the undeformed chip thickness characteristics in ultrasonic vibration assisted grinding, the grain space and grain protrusion height of a metal bond multi-layer diamond wheel were measured. According to the particle trajectory equation of ultrasonic vibration assisted grinding and the trajectory interference theory of two nearby grains, the undeformed chip thickness in a complete grain-workpiece contact zone was solved by using the bisector method and MATLAB software. Then the influence of the main parameters on the undeformed chip thickness characteristics was analyzed. The results show that the undeformed chip thickness varies linearly against the distance between adjacent grains and the height difference of adjacent grains, increases linearly with the increase of ultrasonic amplitude and changes periodically with the increase of ultrasonic vibration frequency. In ultrasonic vibration assisted grinding, the undeformed chip thickness characteristics are greatly affected by the grinding wheel speed and grinding depth, and relatively less affected by the workpiece feed speed.
Abstract: To solve the problems of poor surface quality and unevenness during the processing of TiBw mesh reinforced titanium matrix composites, the normal grinding forces of rotary ultrasonic grinding were studied. The motion law of abrasive particles in rotary ultrasonic grinding was analyzed, the normal grinding force model of rotary ultrasonic grinding TiBw mesh reinforced titanium matrix composites was established, and the model was verified by single factor grinding experiment. The results show that under certain spindle speed, feed speed, grinding depth, fixed grinding width, ultrasonic amplitude and ultrasonic vibration frequency, the normal grinding forces decrease with the increase of spindle speeds and increase with the increase of feed speeds and grinding depths, and the absolute values of relative error between the grinding experimental values and the model calculated values are within 6%. The model well predicts the normal grinding force during grinding of TiBw mesh reinforced titanium matrix composites, which verifies the effectiveness of the prediction model.
Abstract: To improve the ability of the machine tool to identify chatter during the grinding process, a chatter recognition method is proposed based on the BP (back propagation) neural network model. By extracting the relevant feature values of the high-frequency acoustic emission signals and vibration signals in the processing process, multi-feature signal samples library about flutter are obtained. The multi-feature signal sample library is used to learn and train the BP neural network to establish recognition model. The model realizes on-line monitoring and accurate identification of whether chattering occurring during machine tool processing. The experimental results show that the flutter recognition based on the BP neural network model verifies that the measured test results are consistent with the actual flutter and network recognition results. Therefore, this method can effectively identify the flutter phenomenon in the processing process and play the role of online intelligent monitoring.
Abstract: The wear condition of diamond tools determines its service life. The 6061-T6 magnesium-aluminum alloy workpiece was cutted with diamond PCD tool. Through the changes of cutting forces and cutting temperatures at different cutting speeds, cutting depths, vibration frequencies and tool back angles, the workpiece surface roughnesses and tool wear areas at different tool back and forth angles, feed values and speeds of revolution were studied. The results show that the cutting forces and the cutting temperatures increase with the increase of cutting speeds and cutting depths, and decrease with the increase of vibration frequencies. With the increase of the tool back angles, the cutting forces of diamond tool decrease first and then increase slowly, but it has little effect on the cutting temperatures. When the rake angle of the tool is 10°, the back angle of the tool is 8°, the cutting speed is 0.46 m/s, the cutting depth is 28 μm, the feed value is 0.10 mm/r, the speed of revolution is 4 100 r/min, the vibration frequency is 22 kHz and the cutting amplitude is 9 μm, the diamond tool has the smallest wear area, the lowest degree of wear and the longest service life, but the surface roughness of the workpiece is slightly higher.
Abstract: The ultra-thin dicing blades are prone to radial machining deformation during work. The research status of machining deformation of ultra-thin dicing blades is summarized from theoretical analysis of stress and deformation, finite element simulation analysis and experimental research. In addition, the existing problems are analyzed, and the related research results of grinding wheels and circular saw blades with similar structures are introduced. The results show that: the research on the influence of the cutting blade rotation speed on the deformation of the ultra-thin dicing blade is relatively systematic, but there is still a certain gap in the related researches on the influences of the grinding depth and the feed speed. Meanwhile, the lack of measurement methods when cutting into the workpiece also limits the further research. Therefore, the theoretical formula still needs to be constantly improved, and the finite element simulation should be fully applied, so as to optimize and compensate the deformation of ultra-thin dicing blades and improve the machining accuracy of workpieces.
Abstract: Based on the magnetorheological chemical composite polishing principle of Fenton reaction, the magnetorheological chemical composite polishing experiment was carried out on single crystal SiC substrate, and the influence of process parameters on the polishing effect was studied. The results show that with the increase of diamond particle size, material removal increases first and then decreases, while surface roughness decreases first and then increases. With the increase of abrasive mass fraction, material removal rate increases, and surface roughness decreases first and then increases. When the mass fraction of carbonyl iron powder increases, material removal rate increases, while surface roughness decreases first and then increases. With the increase of oxidant mass fraction, material removal increases first and then decreases, while the surface roughness decreases first and then increases. The influence of machining gap on material removal rate varies greatly. When machining gap is 1.0 mm, machined surface quality is better. With the increase of workpiece speed and polishing disc speed, the material removal rate first increases and then decreases, and the surface roughness first decreases and then increases. The optimized process parameters are as follows: the abrasive particle size is 1.0 μm, the mass fraction is 5%, the mass fraction of carbonyl iron powder is 25%, the mass fraction of hydrogen peroxide is 5%, the machining gap is 1.0 mm, the workpiece speed is 500 r/min, and the polishing disc speed is 20 r/min. The single crystal SiC with surface roughness of about 40.00 nm was processed with optimized process parameters to obtain a smooth surface with surface roughness of less than 0.10 nm.
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