Abstract: Orbital drilling is an advanced and improved technique over conventional drilling in producing holes in composites. Single layer diamond tools of different geometries and grain sizes were experimentally investigated to explore their performances in orbital drilling of multidirectional carbon/epoxy laminates. The effects of diamond grain sizes, types of flutes and tool end geometries were evaluated in terms of drilling forces, temperatures, drilling-induced defects and surface integrity. It was found that drilling with high spindle rotational speed results in significantly reduced forces. Tools with smaller grain sizes improve hole surface roughness at the cost of increased drilling forces and temperatures. Provision of flutes on tools lowers the tendency of tool clogging. Ball end tools perform better than tools with flat end geometry and without flutes.
Abstract: With the development of the manufacturing industry, the required parts are gradually moving towards larger sizes, complex shapes, and high surface processing quality. Moreover, detecting the quality of parts during the processing is an essential step. In order to improve the accuracy, the speed and the automation of quality inspection, the 3D inspection based on model analysis has replaced the traditional manual inspection and the 2D inspection, and becomes an important means in the field of industrial inspection. The accuracy of point cloud registration, as a key part of 3D inspection, directly affects the accuracy of detection results. Therefore, the main research achievements of scholars at home and abroad in point cloud registration technology are summarized. Based on algorithm principles, the current registration methods are summarized into traditional registration methods, registration methods based on affine swarm intelligent optimization algorithms, and registration methods based on deep learning. The characteristics, the advantages and the disadvantages, the typical algorithms and their variants of each method are introduced in detail. The technical difficulties of point cloud registration are summarized and the future development trend is prospected.
In order to improve the forming accuracy of grinding wheel, the pressing method of the four-column press for grinding wheel was investigated, tested, carded and analyzed. It was found that the traditional press generally had the phenomena of three centers with different shafts, easy unbalance loading pressure and uneven guidance during pressing. Based on the principle of linear transmission of force, a new scheme of pressure-center pressing was proposed, and a new test press was made and subjected to pressing tests. The new press removes the four-column guiding function, improves the system rigidity, redefines the position of the pressure-center, and completely eliminates the interference of all additional moments. The results of the batch forming test of grinding wheel show that the thickness difference of grinding wheel blank is reduced by 10.3% to 16.5%. The pressure-center pressing method is obviously superior to the traditional press pressing method, and is suitable for the near-net-size forming of small size products.
Ultra-fine iron powder was prepared by water-gas atomization process. The physical properties and the micro morphologies of the ultra-fine iron powder, the reduced iron powder and the carbonyl iron powder were compared. The sintered blocks of three kinds of iron powders were prepared under a certain hot pressing process, and their fracture morphologies and mechanical properties were investigated. At the same time, the three kinds of iron powders were applied to the transition layer of laser welding saw blades under certain welding conditions to investigate their welding performances. The results show that the ultra-fine iron powder prepared by water-gas atomization process has fine particles, lower oxygen content, higher purity and sphericity, and better sintering activity. There are obvious dimple structures on the fracture surface of the sintered block, which has higher toughness and can achieve greater density, hardness and bending strength at lower sintering temperature. When the ultra-fine iron powder is applied to the transition layer of the laser welding saw blade, the welding strength of the saw blade is much higher than 600 MPa specified in the EU EN13236 standard. When the sintering pressure is 35 MPa, the sintering temperature is 810 ℃ and the holding time is 3 min, the cutter head is made, and then the saw blade is made with this cutter head. The maximum welding strength of the saw blade is 1 900 MPa.
Abstract: The micro-dynamic process of diamond tool micro-nanometric cutting single crystal nickel was studied by molecular dynamics software Lammps. The types of defects, the relationship between cutting force and damage, and the evolution of dislocation lines during micro-nanometric cutting of single crystal nickel under different cutting directions and depths were analyzed. The results show that the high pressure phase transition zone and amorphous zone are formed in the single crystal nickel workpiece due to the extrusion and shearing of the tool, and there are atomic clusters and dislocation slip in the subsurface layer. The cutting along the [100] crystal direction has the smallest cutting force and the minimum thickness of the dislocation damage layer is 2.15 nm. The cutting along the [111] crystal direction has the best surface layer quality, but the maximum thickness of the damage layer is 3.75 nm. In the cutting process, the total length of dislocation line presents an overall upward trend, and the atom region removed in [110] direction as well as the dislocation line length are the largest. The greater the cutting depth is, the more serious the dislocation slip and the amorphous in the crystal become.
To study the tool wear mechanism of turning SiCp/6005Al and the influence of tool wear on cutting force, cutting temperature and workpiece surface quality, cutting experiments at different speeds V and different feed speeds f were carried out. Then the tool wear morphology of each group of experimental tools after cutting was observed and the tool wear mechanism was explored by monitoring the dynamic cutting force and cutting temperature. Finally, the influence of worn tools on cutting force, cutting temperature and surface quality under different process parameters was studied. The results show that the increase of workpiece speed significantly increases the cutting temperature, but it has little effect on the cutting force. However, the increase of feed speed significantly increases the cutting force and the variation range of cutting temperature is small. The change of force load caused by changing feed speed is the main factor affecting the wear of rake face. The change of cutting temperature caused by changing the workpiece speed is the main factor affecting the flank wear. In addition, tool wear is the comprehensive result of abrasive wear and bonding wear. And it will have an adverse impact on cutting force, cutting temperature and machined surface.
Abstract: In view of the long process route of high-precision gear machining, a method of creep feed deep profile grinding of small-module gears was proposed. The experiments of creep feed deep profile grinding of small-module gears were carried out. The effects of different feed speeds on the grinding power, the workpiece grinding burn and the grinding wheel wear were analyzed. The wear process of grinding wheels was studied by replica method. The results show that the grinding power peak increases with the increase of feed speed. When the feed speed exceeds 150 mm/min, the grinding burns occur on the workpiece surface. Besides, the hardness of the grinding surface is significantly higher than that of the initial hardness, and the martensitic phase transformation occurs on the workpiece surface. As the depth from the grinding surface increases, the hardness values show a downward trend, and the depth of the hardness layer at the tooth bottom is smaller than that at the both sides of the tooth profile. The wear process of grinding wheels is divided into initial wear stage, stable wear stage and rapid wear stage. The material removal volume of stable wear stage is about 2 000 mm3. Excessive feed rate will cause severe wear of the grinding wheel.
Abstract: Aiming at the problem that precision and efficient end grinding is required for the two-phase 3D reconstruction of SiCp/Al grinding layer by layer, an analytical model of end grinding force of SiCp/Al is established based on the grinding force of SiCp/Al grinding with a single abrasive particle, considering the chip deformation force, friction force and the breaking force of SiC particles. The effects of cutting speed, workpiece feed speed and axial grinding depth on the surface roughness were studied by experiments. The machining technology of SiCp/Al metallographic surface rapid grinding was also discussed. The results show that the overall average error between the analytical model of end grinding force and the experimental normal grinding force Fn is 12.98%, and that the overall average error of tangential grinding force Ft is 3.49%. The surface roughness decreases with the increase of cutting speed and increases with the increase of feed speed and axial grinding depth. The grinding time for obtaining a good metallographic surface is 600 s after 6 grinding times with a grinding tool of 13.0 μm grain size. The rapid grinding of SiCp/Al metallographic surface can be realized.
Abstract: In order to improve the grinding quality and efficiency of 20CrMo steel camshaft, response surface method was used to conduct grinding tests. The influence of grinding process parameters on surface roughness was analyzed, and the corresponding regression model was established. Based on the shape characteristics of the workpiece, the instantaneous material removal rate calculation model of the weak part of the workpiece was established. The model of surface roughness and material removal rate was taken as the optimization objective. The second generation of non-dominated sorting genetic algorithm was used to optimize the combination of multi-objective process parameters and test verification was carried out. The results show that the optimal combination of process parameters, namely the linear speed of the grinding wheel 60 m/s, the workpiece speed 96 r/min and the grinding depth 30 μm, can effectively improve the grinding efficiency under the premise of ensuring that the surface roughness of the weak part meets the machining requirements.
Aiming at the problem of grinding burns on the third-generation single crystal superalloy DD9, a three-factor and five-level experiment is designed in this paper. From the perspectives of surface morphology, microhardness and microstructure, the effect of grinding process parameters on grinding burns are studied. The experimental results show that: when the workpiece feed speed is less than 250 mm/min, the grinding surface roughness Ra changes slightly around 0.8 μm, and the surface quality is good. When the feed speed is more than 250 mm/min and the grinding depth is more than 1.0 mm, the temperature in the grinding area rises sharply, the grinding lines are destroyed, grinding defects such as coating and pits appear, and the surface of the workpiece burns. The surface and surface of DD9 alloy are work hardened by slow feed grinding. The microhardness range is 400 to 600 HV, the depth of hardened layer is 50 to 110 μm, and the thickness range of plastic deformation layer is 1 to 10 μm. The recommended combination of DD9 grinding process parameters is: grinding wheel linear velocity vs=20 m/s, feed speed vw=250 mm/min, grinding depth ap=0.6 mm.
Abstract: To study the influence of grain arrangement on the surface profile of the workpiece, a mathematical model and its corresponding analytical algorithm of pyramidal abrasive belt grinding were established. The roughness value was simulated and predicted with Abaqus software. Grinding tests were carried out on the robot grinding system platform with pyramidal abrasive belt, and the surface profile were inspected and then compared with the simulation. The results show that the simulated roughness and the measured values have similar variation trend with good consistency, where the error is within 0.03 μm and the maximum error rate is 16.6%. The theoretical simulation and test results remain consistent, indicating that the model could be used to predict the surface roughness of workpiece ground with pyramidal abrasive belt.
In order to obtain the optimal process parameter combination of double-sided grinding Si3N4 cylindrical rollers, the orthogonal experiment method was used to explore the influences of the grinding disc speeds, the grinding pressures and the basic particle sizes of the abrasive particles on the surface quality and the removal efficiency of Si3N4 cylindrical rollers. The results of the surface roughness and the material removal efficiency of the specimen are taken as the basis for optimizing the grinding process parameters. The results show that the surface roughness of the specimen first decreases and then increases with the increase of the grinding disc pressure and the grinding speed. The basic particle sizes of the abrasive are positively correlated with the surface roughness of the specimen, while the grinding disc speed and the grinding pressure are positively correlated with the removal efficiency. The optimum combination of grinding parameters for Si3N4 cylindrical rollers is that the basic particle size of diamond abrasive is 2.6 μm, the grinding disc speed is 20 r/min and the grinding pressure is 0.15 MPa. Under the optimal parameters, the smooth and undamaged Si3N4 cylindrical rollers with surface roughness of 0.0486 μm and removal efficiency of 1.20 μm/min can be obtained.
Abstract: The hardness of hard-brittle materials is high, which results in the low lapping efficiency of traditional silicon carbide magnetic abrasive and short abrasive life. In view of this situation, a magnetic abrasive with diamond particle as lapping grit was developed. Using high purity iron powder as iron-based phase and diamond particle as abrasive, diamond magnetic abrasives were prepared by resin bonding method. K9 glass was chosen as the part being machined. The service life and processing efficiency of magnetic lapping K9 glass were compared between with diamond magnetic abrasives and with silicon carbide magnetic abrasives. The lifespan of diamond magnetic abrasive is 60.00 min, and the number of work-piece which can be machined is 4.6 pieces in the service life. The average surface roughness of K9 glass reaches 0.036 μm. However, the service life of the silicon carbide magnetic abrasive particles is only 40 min, and the average surface roughness of the K9 glass workpiece can only be processed to 0.222 μm. Besides, the number of workpieces that can be processed during the service life is 3.6 pieces. Diamond magnetic abrasives can effectively improve the service life, the processing capacity of magnetic abrasives, and the processing efficiency of magnetic grinding.
Abstract: In order to improve the processing quality, processing efficiency and reduce the cost wastage of the dome surface, the effect of each motion parameter on the uniformity of material removal from the optical dome surface during the polishing process was investigated. In this paper, the dispersion coefficient was used as the evaluation index, and the single abrasive particle motion trajectory model was established based on the relative motion and vector method. A triangular mesh was used to iteratively divide the surface of the orthorhombic icosahedron, and the number of trajectory points in each triangular mesh was counted to characterize the number of polishing times. It can be concluded that the speed ratio has a significant effect on the distribution of abrasive trajectories and material removal. With the same speed ratio, increasing the radius of the polishing head, the dispersion coefficient gradually decreases and the uniformity of dome surface material removal changes from poor to good. Increasing the pendulum speed, the length and density of the trajectory gradually decrease, the dispersion coefficient becomes larger, and the non-uniformity of the dome surface increases. The change in the initial phase of abrasive particles has essentially no effect on trajectory uniformity.
In order to improve the surface quality of germanium wafer, the material removal behavior of germanium wafer under the action of solid-liquid two-phase flow was studied by means of rotating magnetic field magnetic fluid grinding and numerical simulation. Firstly, the grinding principle of magnetic fluid was introduced. Secondly, a simulation model was established. Starting from the process parameters of magnetic fluid grinding and combined with finite element analysis, the surface mechanical properties are taken as the breakthrough point. The effects of processing parameters such as different excitation gaps, magnetic pole rotation speeds, and particle phase volume fractions on the surface quality of the germanium wafer were analyzed. The optimal processing parameters were determined. Finally, the magnetic fluid grinding test was carried out. The results show that when the excitation gap is 5 mm, the magnetic pole rotation speed is 1000 r/min, and the volume fraction of the particle phase is 25%. After grinding for 60 minutes, the surface quality of germanium wafer was improved effectively, and the surface roughness Ra decreased from 500 nm to 47 nm, which realized the removal of small plastic materials on the surface of germanium wafer.
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