Abstract: Objectives The single-layer brazed diamond core drill generally exhibits poor protrusion height uniformity of grains, making it difficult to control the hole diameter and the accuracy when machining SiCf/SiC composites. Pulsed laser is used to dress the core drill to improve grain height uniformity, thereby enhancing hole accuracy on SiCf/SiC composite.Methods Firstly, a pulsed laser dressing platform for the single-layer brazed diamond core drill is developed, and the influence of laser dressing parameters on grain height uniformity and morphology is revealed. Then, the aperture accuracy of the core drill before and after dressing is compared and analyzed to verify the benefits of laser dressing in improving hole accuracy. Finally, high-quality processing of SiCf/SiC composite holes is achieved using the dressed drill. During the process, the total cutting depth of the pulsed laser is determined by dressing a standard rod to the target aperture size and then replacing it with the core drill for further dressing. The relative distance between the abrasive grains and the laser beam is adjusted, and the laser beam focus is aligned with the cutting point. The laser beam is reciprocally scanned along the tool axis to remove the protruding diamond grains and improve core drill height uniformity.Results The experiments show that pulsed laser dressing can effectively enhance the height uniformity of the side grains on the single-layer brazed diamond core drill. The discrete coefficient of grain height after dressing is reduced by 64%, from 0.11 to 0.04. Following pulsed laser dressing, the contour lines of side grains on the core drill become smoother, indicating improved height uniformity. The surface of diamond grains after pulsed laser ablation appears black due to a graphitization reaction, forming a thin black metamorphic layer that does not affect diamond grain performance. The laser-dressed single-layer brazed diamond core drill exhibits improved hole-making performance with a smaller variation range in hole diameter (4.00 - 4.02 mm) and higher hole-making accuracy. In contrast, the untrimmed core drill shows a larger variation range in hole diameter (4.06 - 3.98 mm) during the hole-making process. Furthermore, pulsed laser dressing has no negative impact on the grinding ability of the core drill. The average drilling force is 13.72 N before dressing and 12.43 N after dressing, with a difference of 1.29 N consistent with the change trend of the drilling force during the entry stage. The laser-dressed core drill maintains aperture accuracy better throughout its lifespan, with aperture deviation being only 0.02 mm, meeting the requirements on hole accuracy and showing a 75% reduction compared to the undressed condition.Conclusions The study applies pulsed laser dressing to enhance the protrusion height uniformity of grains on single-layer brazed diamond core drills. A laser dressing device is constructed, and a method is proposed. Using a graphite rod as the standard rod for determining the laser dressing depth reduces the diameter deviation. Pulsed laser dressing effectively improves grain height uniformity, with the discrete coefficient reduced by 64%. The dressed core drill demonstrates smaller aperture deviation (0.02 mm), meeting accuracy requirements without adversely affecting grinding ability or service life. This verifies the advantage of laser-dressed core drills in improving hole-making accuracy.
Abstract: Objectives To improve the grinding quality and efficiency, reveal the material removal mechanism of SiCf/SiC composites, and determine the coupling effect among abrasives during grinding.Methods Firstly, uniaxial tensile, shearing, and bending experiments of SiC fiber bundles are conducted to observe damage modes. Secondly, double-abrasive scratching experiments are carried out on the woven surface (WS) and stacking surface (SS) of 2D SiCf/SiC composites along the 0°, 45°, and 90° fiber directions, respectively. The scratch surface topographies are observed and the scratch force is measured to reveal the material removal mechanism and abrasive coupling effect.Results The tensile-fractured SiC fiber shows a 45° bevel fracture surface at the tip. The shear-fractured SiC fiber tip surface is perpendicular to the axis of the SiC fiber. The bending-fractured SiC fiber shows a hybrid of bevel and perpendicular surfaces, indicating both tensile and shear fracture characteristics. In the longitudinal fiber cut-in direction on WS0, the matrix shows a large area of ductile removal scratching. The fiber shows tensile fracture, and the broken fiber is peeled off from the matrix, with some fiber tips showing tensile fractures. Bending fracture also occurs in the cutting direction of WS0 longitudinal fibers, and a large number of fiber peel-off marks are observed on the surface. At the same time, ductile removal marks of the matrix and some large-sized fibers appears on the surface. The transverse fibers on WS0 show the characteristics of tensile fracture, bending fracture, and shear fracture simultaneously. There are tensile fractures, bending fractures, and shear fractures on the surface of WS45 fiber. The ductile removal and fiber peeling also appear on the fiber. A shear fracture occurs on the SS0 fiber and bending fracture occurs at the boundary of the woven structure. The removal modes of SS0 longitudinal fibers are mainly tensile and shear fractures, accompanied by secondary scratches formed by fiber exposure. SS90 fibers show shear and bending fractures at the boundary. The transverse fibers show tensile, shear, and bending fractures while the matrix shows strong brittle removal. The scratching force varies significantly with fiber orientations. The order of scratching force is FSS0 > FWS45 > FSS90 > FWS0. Under the same scratching depth, the normal scratching force of the double abrasives is much smaller than that of a single abrasive.Conclusions (1) In scratching of 2D SiCf/SiC, the transverse fibers undergo shear, tensile, and bending fractures. The fiber is removed by shearing, with a small amount of bending removal occuring at the woven boundary. The longitudinal fibers mainly exhibit tensile (cut-in) and bending (cut-out) fractures, accompanied by a large number of fiber peeling. The removal forms of the matrix include crack propagation, ductile scratching, powder removal, and brittle peeling. (2) 2D SiCf/SiC shows strong anisotropy. The order of scratching force obtained under different surfaces and scratching directions is FSS0 > FWS45 > FSS90 > FWS0. The material removal energy consumed in the WS0 direction is the lowest while SS0 consumes the most. At this time, a large number of matrices are powdery. The normal scratching force of the double abrasives is much smaller than that of the single abrasive. For the same volume of material removed, the first abrasive causes more surface damage after scratching, reducing the scratching force of the second abrasive. This indicates a strong coupling relationship between the abrasives, which can effectively reduce the normal scratching force when processing 2D SiCf/SiC composites.
Abstract: Objectives SiCf/SiC fiber-reinforced ceramic matrix composites have been widely used in aerospace, nuclear energy, and high temperature structural parts due to their excellent high-temperature resistance, high specific strength, and oxidation resistance. However, due to the high hardness and brittleness of the material, its machinability is poor, and the traditional machining methods tend to cause serious tool wear, workpiece surface damage, and processing defects. Therefore, optimizing the grinding process to improve processing quality and efficiency has become one of the key issues in current research. Orthogonal grinding experiments of SiCf/SiC composites were carried out using electroplated diamond grinding wheels and sintered diamond grinding wheels, with or without coolant. Grinding force, surface roughness, and wear degree of grinding wheel were used as evaluation indexes to explore the effects of different grinding wheel types and cooling methods on the grinding quality of the material.Methods An orthogonal experimental design was used to systematically analyze the effects of different grinding wheel types (electroplated diamond grinding wheel, sintered diamond grinding wheel) and cooling methods (dry grinding, water cooling) on the grinding performance of SiCf/SiC composites. The experiment was conducted on a VMC850B CNC machine using a diamond grinding wheel with a diameter of 20 mm. Test parameters such as cutting speed, feed rate, and grinding depth were kept consistent to ensure comparability of results and scientific rigor of the experiment. During grinding, a KISTLER 9257B three-component dynamometer was used to measure tangential and radial grinding forces in real time to quantify the mechanical response under different grinding conditions. To evaluate the surface quality of the processed material, a ZYGO9000 white light interferometer was used to measure the surface roughness Sa of the workpiece. Three different regions of each sample were selected for measurement, and average values were taken to reduce the measurement error. Additionally, to analyze the wear mechanism of the grinding wheels, the wear morphology of the grinding wheel surface after grinding was observed using a VHX2000c ultra-depth-of-field three-dimensional microscope, and the failure modes of different grinding wheels under different grinding conditions were compared and analyzed.Results Grinding wheel type and cooling method have a significant effect on the grinding performance of SiCf/SiC composites. The grinding force of the sintered diamond grinding wheel is lower than that of the electroplated diamond grinding wheel, which is attributed to the higher abrasive retention and wear resistance of the sintered diamond grinding wheel. Compared with dry grinding, the grinding force is reduced under water-cooled conditions, indicating that the coolant can alleviate friction and heat accumulation during grinding to a certain extent, thereby reducing grinding force. At the same time, the sintered diamond grinding wheel can obtain lower surface roughness of the workpiece, the surface of the workpiece after processing is smoother, and the micro-defects such as cracks and tears are also significantly reduced. Furthermore, water-cooled assisted grinding can effectively reduce the surface roughness of workpiece and further improve the surface quality of workpiece, indicating that coolant positively influences surface integrity. The main wear form of the sintered diamond grinding wheel is the normal wear of abrasive particles, shweing strong abrasive retention and overall durability. In contrast, the electroplated diamond grinding wheel tends to flake off under the action of large grinding force, leading to rapid abrasive failure. Additionally, the electroplated diamond grinding wheel also has abrasive burn and falling off phenomenon, further reducing its service life. Therefore, from the perspective of processing performance and durability, the sintered diamond grinding wheel in grinding SiCf/SiC composite materials shows better comprehensive performance, especially under water-cooled conditions, where processing quality and stability are more advantageous.Discussion and optimization suggestions Based on experimental data analysis, to optimize the grinding process of SiCf/SiC composites, the grinding wheel type and cooling method should be reasonably selected according to different processing stages. In the rough machining stage, the electroplated diamond grinding wheel is prone to abrasive detachment under the action of higher grinding force, so it is suitable for dry grinding condition to reduce coolant impact on abrasive particles. At the same time, it is recommended to use high speed, low feed speed and shallow grinding depth to reduce wheel wear and improve processing efficiency. In contrast, during the precision machining stage, to achieve better surface quality, it is recommended to use a sintered diamond grinding wheel combined with water-cooled grinding method to reduce the surface roughness of the workpiece, minimize micro-defects, and thus improve the surface smoothness and machining stability of the workpiece.Conclusions The sintered diamond grinding wheel exhibits lower grinding force and better surface quality during grinding, especially under water-cooled conditions, where its advantages are more obvious. The electroplated diamond grinding wheel is suitable for rough machining, but there is a risk of abrasive peeling and burning, which affects its service life. Therefore, in practical applications, the grinding wheels and cooling methods should be reasonably selected based on different processing requirements to improve the processing quality and the efficiency of SiCf/SiC composites. Future research can further optimize the grinding parameters and explore the effects of different grinding environments (such as micro-lubrication) on machining performance to further enhance the controllability and applicability of grinding processes.
Abstract: Objectives To explore the grinding damage mechanism and surface/subsurface damage distribution law of silicon carbide ceramics. Methods Combined with single-particle scratching experiments, grinding experiments, and finite element simulation analyses, the critical stress value of the plastic-brittle transition of the material, as well as the trend of the influence of the grinding parameters on the damage distribution, are clarified. Results The ultimate fracture strength of the silicon carbide ceramics used in this experiment is about 344 MPa, and the grain boundary fracture strength is about 25.9 MPa. Both the experimental and simulation results show that the microstructure of the material plays different roles under different loads. When the contact stress is less than the critical fracture strength of the grain boundaries, the grain boundary structure plays a viscous role, consuming stresses to inhibit the expansion of cracks. With a further increase in load, although not reaching the critical stress value of the grain boundaries, the cracks are still generated but not as severe. Further increase in load, although the material fracture limit is not reached, the material surface will still exhibit cracks and pits due to microstructural damage caused by grain boundaries, graphite, and pores. When the contact stress exceeds the critical strength of the material and the grain boundaries, the microstructure promotes the growth of cracks, further expanding the damage area of the SiC ceramics. In the paper, through the optimization of the grinding process parameters, the best parameters for achieving the minimum grit undeformed chip thickness and grinding force are determined, thus minimizing the percentage of material surface damage and the depth of subsurface damage, which are 0.396% and 4.768 μm, respectively. Compared with the worst parameters, the damage values are only 16.01% and 13.22% of their respective counterparts. Conclusions The process of material grinding damage is similar to that of single grit scratch damage, which progresses three stages: plastic removal, plastic-brittle removal, and brittle removal. The grinding force, the change in maximum grit thickness without deformation, and the extent of material damage all tend to increase with the increase of feed rate and grinding depth, and decrease with the increase of grinding wheel speed. The microstructure of ceramic materials is an important reason for their machining susceptibility to machining damage. In order to achieve low-defect processing of silicon carbide ceramics, it is not only necessary to optimize the grinding process parameters but also to consider the role of the microstructure. The experimental results provide theoretical guidance for achieving low-damage and high-quality processing.
Abstract: Objectives CFRP circular cell honeycomb consists of thin-walled circular cells and are applied in the aerospace. It is difficult to machine the CFRP honeycomb due to its characteristics of thin walls, weak rigidity and non-continuous periodicity. During grinding, there are sharp noises and intense fluctuations of grinding force, reflecting the instability of the process. Considering the structural characteristics of thin-walled CFRP circular cells, this paper conducts end-face grinding experiments and explores the influence of the exit angle, grinding speed, feed rate, and grinding depth on grinding stability. Methods The machining of CFRP honeycomb is a repetition of machining thin-walled CFRP circular cells. Taking a single cell as the research object, the end-face grinding experiment is carried out by defining the exit angle and the interaction angle of grinding based on its structural characteristics. The influence of the exit angle on grinding stability is analyzed using the time-domain and frequency-domain characteristics of the axial force. The standard deviation of the resultant force in the horizontal plane is used to quantitatively describe the grinding stability of the thin-walled CFRP circular cell. Moreover, the influence of the exit angle on the interaction angle of grinding is analyzed based on the magnitudes of the tangential and the radial forces. The relationship between the interaction angle of grinding and the grinding stability is established to analyze the influence of grinding speed, feed rate and grinding depth on the interaction angle of grinding and the grinding stability. Furthermore, the influence of processing parameters on the radial, the tangential and the resultant forces in the horizontal plane is studied. Results It is found that the exit angle is the main factor affecting the grinding stability. Compared with other exit angles, when the exit angle is 60° − 90°, the fluctuation range of the axial force in the time domain increases dramatically and a significant peak appears in the frequency domain. The standard deviation of the resultant force in the horizontal plane increases sharply. The interaction angle of grinding is small, and the direction of the resultant grinding force is close to the tangential direction of the thin-walled CFRP circular cell, resulting in poor grinding stability. The interaction angle of grinding increases linearly with the increase of the exit angle, which strengthens the grinding stability. With the increase of grinding speed, the interaction angle of grinding increases gradually, and grinding stability improves. With the increase of feed rate, the interaction angle of grinding shows no obvious change, and the grinding stability remains nearly unchanged after an initial decrease. With increasing grinding depth, the interaction angle of grinding decreases gradually, and the grinding stability declines. In terms of grinding force, with increasing exit angle, the radial force and the resultant force in the horizontal plane first decrease and then increase, while the tangential force decreases. With increasing grinding speed, the tangential force and resultant force in the horizontal plane gradually decrease, though the overall change range is small, and the radial force shows no obvious change. With increased feed rate and grinding depth, the radial force, tangential force, and resultant force in the horizontal plane increase approximately linearly. Conclusions For thin-walled and weakly rigid CFRP circular cell honeycomb, grinding stability is significantly affected by machining parameters. This paper investigates the influence of machining parameters on grinding stability through end-face grinding experiments of CFRP circular cells and reveals the relationship between the interaction angle of grinding and grinding stability. To enhance grinding stability of the CFRP circular cell honeycomb, the exit angle should avoid the range of 60° − 90°, and a larger grinding speed should be used with a smaller feed rate and grinding depth.
Abstract: Objectives To improve the quality of chemical plating on diamond micropowders, an experimental analysis was conducted on the influence of key process parameters on the plating quality during the chemical plating process. The experimental results were then predicted using artificial neural networks.Methods Nickel plating experiments were carried out on the surfaces of M1/2, M6/12, and M20/30 micron diamond powders using the electroless plating method. The effects of electroless plating process parameters—such as diamond particle size, concentration of sodium hypophosphite, plating solution temperature, and plating solution pH—on the coating properties were investigated. The performance of the coatings were evaluated as follows: (1) The deposition rate of the coating was expressed as the difference in the quality of diamond powder before and after electroless plating per unit time. (2) The coating density was expressed as the mass of the coating per unit volume. (3) Each group of coated diamond powders was immersed in hydrochloric acid solution with a mass fraction of 10% for 24 hours, and the corrosion weight loss of diamond powder was used to indicate the coating's corrosion resistance of the coating—where higher corrosion weight loss indicates poorer corrosion resistance. Data on the influences of process parameters, such as diamond particle size, sodium hypophosphite concentration, plating solution temperature, and plating solution pH on coating performance were used as the training set. Both BP and GRNN artificial neural networks were applied to predict the deposition rate, coating density, and corrosion resistance under four different conditions. The accuracy of the models was evaluated by comparing experimental data with predicted values. Results The BP neural network model and the GRNN model can be used to predict the coating performance of micron diamond powders after training on sample data. The absolute relative error between the predicted coating performance values of the BP neural network model and the experimental values was less than 15.00%, with an average absolute relative error of 9.14%. The absolute relative error between the predicted coating performance values and experimental values of the GRNN model was less than 10.00%, with an average absolute relative error of 5.07%. In predicting the performance of electroless nickel plating on diamond micro powders, the predictive performance of GRNN is superior to that of BP neural network.Conclusions The prediction error values of BP neural network and GRNN for the chemical plating performance of diamond micropowder are both less than 10.00%, which proves that they can be used to predict the relevant results and reduce the number of experiments to obtain optimal process parameters. And the prediction error of GRNN is smaller than that of BP neural network, which proves that the performance of GRNN in prediction experiments is better than that of BP neural network.
Abstract: Objectives Chemical vapor deposition (CVD) diamond has excellent material properties and a wide range of application prospects, but due to its high hardness, brittleness and chemical inertness, microstructure processing on the surface and inside is extremely difficult. Based on the advantages of high precision, high efficiency and easy automation of laser processing, this paper adopts the ultraviolet nanosecond laser for CVD single diamond etching, and combines the laser line etching energy model with the basic research on the law of laser processing and etching principle.Methods A UV nanosecond laser is used to carry out basic research on the laws of laser processing and etching principle through the ablation threshold test, laser energy modeling and line etching test, scanning electron microscope observation and energy spectrum analysis test. The purpose of the ablation threshold test is to obtain a suitable range of processing parameters, set the laser scanning speed of 1 mm/s, the number of scans for 1 time, the laser repetition frequency range from 20 to 50 kHz with 10 kHz increment, and the laser power range from 1.2 to 12.0 W with 1.2 W increment, and observe the erosion situation by engraved lines. After obtaining a suitable range of processing parameters, a laser energy density model is established in which the main variables are laser power and scanning speed. Changes in the model are observed by varying different combinations of parameters, and the processing law is predicted and verified by combining with the actual line etching test. The test situation is mainly through the scanning electron microscope observation and record test data, one of the line etching groove of the internal and peripheral energy spectrum analysis, through the comparison of elemental changes and combined with the literature on the principle of ablation to carry out certain analysis. Results From the results of the ablation threshold test, when the laser repetition frequency is 20 kHz, the etching traces can be produced in the range of power 1.2-12.0 W, when the repetition frequency is 30 kHz, the etching traces start to be produced when the power is increased to 7.2 W, and when the repetition frequency is 40 and 50 kHz, the etching traces are not produced in the range of power 1.2-12.0 W, therefore, in order to obtain stable etching results, fixed the laser repetition frequency of 20 kHz in the subsequent line etching test. Therefore, in order to obtain stable etching results, the laser repetition frequency is fixed at 20 kHz in the subsequent line etching test, and the results of the line etching test can be seen from the side of the CVD diamond, the groove basically appears as a “V” shape, and in combination with the line etching model of the laser, the energy density of the laser shows a high distribution in the middle and low distribution around the edges, i.e., the center of the spot is high and the edges are low. Furthermore, the energy at the center of the spot is high, and the energy at the edge is low. In the one-factor test of power, when the power is 1.2, 3.0, 5.4, 10.8 W, the width of the line etching groove is 39.8, 39.8, 41.0, 38.8 μm, and the depth is 35.7, 41.1, 42.1, 57.2 μm, respectively, and the width and depth of the diamond line etching groove increase with the increase of the laser power. In the one-factor test of scanning speed, when the scanning speed is 3, 13, 21 and 29 mm/s, the widths of the wire-etched grooves are 39.5, 39.9, 35.6 and 26.3 μm, and the depths are 77.6, 37.9, 22.3 and 18.0 μm, and the widths as well as the depths of the grooves gradually decrease with the scanning speed increasing.The results of EDS analysis show that, compared with the unfinished area, the proportions of C elements in the grooves' interior, sidewalls and peripheral areas show a decrease in the proportion of C elements and an increase in the proportion of N and O elements compared to the unprocessed area, and they are nearly the same. Conclusions (1) Combined with the line etching energy model, the increase in power leads to an increase in the energy density of the laser, and at the same time, the peak energy increases, increasing the degree of ablation of the material, resulting in deepening the depth of the groove, in addition, when increasing the laser power, the height of the model increases more than the increase in the magnitude of the edges, and therefore it can be observed that the width and depth of the diamond line etching groove increases with the increase in laser power, but the impact on the depth is greater than the impact on the width phenomenon. Scanning speed increase leads to increase the spacing between individual laser pulses, the amount of superposition between the pulses and the superposition area decreases, making the energy at the superposition decreases, which leads to a reduction in the peak value of the energy at the superposition, in addition, the scanning speed increase also leads to the reduction of the number of laser pulses irradiated in the unit area, which, under the combined effect, reduces the depth of the wire etching groove. (2) EDS analysis shows that, compared with the unprocessed area, the C element content in the processed area is reduced, and the N and O element content is increased, so it can be initially judged that the mechanism of nanosecond laser processing of single-crystal diamond is the phase transformation of diamond at high temperatures, graphite oxidation, and sputtering of graphite and heterogeneous compounds.
Abstract: Objectives With the rapid development of diamond tool quality and varieties, the requirements for diamond tool properties are increasingly rigorous, and the uniformity of diamond distribution in diamond tools is an important index affecting its performance. The imperfect granulation process of mixed powder containing diamond is one of the reasons for the uneven distribution of diamond in diamond tools. By studying the secondary particle morphology obtained by different granulation processes and the influence of mixed powder with different particle sizes on the uniform distribution of diamond, the distribution uniformity of diamond in the mixed powder is improved, so as to improve the performance of diamond tools.Methods Using the same premixed powder as raw material, three different granulation processes—disk granulation, cold press crushing granulation, and diffusion crushing granulation—were used to carry out experiments. The powders of the three granulation processes were sieved using stainless steel standard sieves, and the particle size samples of 180 to 380 μm, 120 to 180 μm, and 75 to 120 μm were obtained under the same process. The effects of different granulation processes and different powder particle sizes on the distribution of 250 to 380 μm diamond in the same mixed powder were studied. At the same time, the nine-point sampling method was used to sample. The actual numbers of diamond particles in each sample were counted manually, the actual numbers of particles were compared with the calculated theoretical numbers of diamond particles and the deviation values were obtained. The averages and the ranges of the deviation values were used to determine the uniformity of diamond distribution in the mixed powder containing diamond.Results (1) From the morphology of the powder particles, it can be seen that the circular granulation produces spherical-shaped powder, the cold press crushing granulation produces irregularly shaped powder with distinguishable original particle morphology on its surface, and the diffusion crushing granulation produces irregularly complex shaped powder. (2) The loose packing ratio of powder produced by cold press crushing granulation is the highest, while the loose packing ratio of powder produced by disk granulation and diffusion crushing granulation is not significantly different. Under the same granulation process, the loose packing ratio of large particles is smaller, but as the particle size decreases, the influence of particle size becomes smaller. The flow rate of disk granulation is the highest and decreases with the decrease of particle size, but the flow rate of cold press crushing granulation is the lowest and the change is not significant, while the flow rate of diffusion crushing granulation is in the middle. (3) Under the same granulation process conditions, the distribution uniformity of diamond in mixed powder samples of 180 to 380 μm with three different granulation processes is the best. Under the same particle size range conditions, the distribution uniformity of diamond is the best in the mixed powder samples which are all diffusion crushing granulation. Compared with the diamond distribution in the different particle size mixed powder of the three methods of granulation process, the distribution of diamond controlled in the particle size interval of 180 to 380 μm by diffusion granulation process is the best.Conclusions The influences of the same kind of premixed powder on the distribution of diamond in the mixed powders under different granulation process conditions and different particle sizes is studied, and the following conclusions are drawn: (1) The particle morphology of different granulation processes is different. The powder particle morphology of disk granulation is a pseudo-spherical shape like "potato", the powder particle morphology of cold press crushing granulation is irregular shape and the surface can distinguish the original particle morphology, and the powder particle morphology of diffusion crushing granulation is complex irregular shape. (2) Under the same granulation process conditions, the distribution uniformity of diamond in the mixed powder with particle size of 180 to 380 μm (original particle size of 250 to 380 μm) is obviously better than that of the mixed powders with particle size of 120 to 180 μm and 75 to 120 μm. (3) Under the condition of the same particle size range, the distribution uniformity of diamond in the mixed powder under the diffusion crushing granulation is obviously better than that under the disk granulation process and the cold press crushing granulation process.
Abstract: Objectives In response to the defects of diamond abrasive particle aggregation and large density fluctuations on the surface of traditional electroplated diamond wire saws, an innovative design of a combination device of spiral bath flow and rotating magnetic field is proposed to break through the technical bottlenecks of existing electroplating processes in terms of coating uniformity, orderly arrangement of diamonds and tool life. The research focuses on solving three core problems: (1) the structural design of the spiral bath flow electroplating device and the optimization of flow rate and spiral speed of the spiral bath flow; (2) the structural design of the rotating magnetic field device and the optimization of rotation speed and magnetic field strength; (3) the optimal process parameters for electroplating diamond wire saws in the new composite field electroplating device, and the production of wire saws for silicon wafer cutting experiments.Methods The electroplating mixture spirals in the same direction around the baseline, which can improve the consistency of diamond particle concentration around the baseline circumference and enhance the uniformity of the mixed solution stirring. Based on this, the spiral bath flow electroplating device is designed. Then the rotating magnetic field device is designed by experiment, and a suitable alternating magnetic field is applied to the plating solution, which is beneficial to improve the deposition rate and the consolidation strength of the diamond particles with the baseline. The spiral bath flow electroplating device and the rotating magnetic field device together form the electroplating combination device. Through the data accumulation of continuous experiments and production practice, the basic parameters such as permanent magnet material, magnet size, inner wall size of the glass tube, baseline travel speed, and bottom diameter of the spiral blade in the combined device are determined. The optimal technological parameters of the electroplated diamond wire saw for the combined device are obtained by the single-factor experiment method, and the wire saw is made. The surface morphologies of electroplated diamond wire saws prepared under different processes are observed by scanning electron microscope, and the monocrystalline silicon is sliced by an ultra-high speed multi-wire cutting machine. The surface roughness of the silicon wafer in the feed direction is measured by a surface roughness tester.Results The mixed liquid of the spiral bath flow electroplating device enters the glass tube from the spiral blades of the spiral guide inner core, rotates spirally upward around the baseline in the glass tube under the action of the spiral blades, and flows out from the outlet of the mixed solution in the glass tube. Four symmetrical grooves are set on the inner wall of the glass tube for placing nickel anodes to avoid hindering the flow of the spiral liquid. The baseline enters from the hollow center of the spiral guide core and passes upward through the electroplating device, and the baseline is not in direct contact with the spiral guide inner core. According to the inner diameter value of the glass tube d = 56 mm, the minimum flow rate of the mixed liquid calculated is Q = 4.43 L/min. The inner core material of the spiral guide is TA2 titanium alloy, the bottom diameter of the spiral blade is 12 mm, the helix angle is 60°, the thickness is 2 mm, and the outer diameter and the height are consistent with d. The rotating magnetic field device is composed of NdFeB alloy cylinders and a fixed holder, etc., which rotates precisely around the center line of the spiral bath flow electroplating device at the appropriate rotation speed. The basic parameters of the combined device are: the magnet size is φ20 mm × 30 mm, the inner wall diameter × length of the glass tube is φ56 mm × 850 mm, the baseline travel speed is less than or equal to 20 m/min, the bottom diameter of the spiral blade is 5 mm, the blade thickness is 2 mm, and the concentration of diamond abrasive is 1.55 g/L. The optimal process parameters for electroplating diamond wire saws in the combination device, determined by single-factor experiment are: the spiral blade number is 5, the spiral angle is 60°, the mixed liquid flow rate is 4.80 L/min, the fixed holder number is 12, the staggered arrangement angle of the permanent magnets is 60°, the magnetic field rotation speed is 60 r/min, and the magnetic field strength of the N38M permanent magnet is 0.549 T. The electroplating line produced under the optimal process parameters shows that the diamond particles are evenly distributed on the baseline surface without any stacking or agglomeration phenomenon, and the particle distribution density is basically uniform. The number of diamond particles is 15 to 25 particles/mm, and the fluctuation range of diamond particle numbers is controlled within 11 particles/mm. Using this wire saw to slice a single crystal silicon rod with φ50.6 mm, the surface roughness Ra value of the silicon wafer in the feed direction is 0.583 μm, which is 35.9% and 28.2% lower than the literature values, respectively.Conclusions The combined device of spiral bath flow and rotating magnetic field is designed to make the diamond abrasive particles in the mixed liquid evenly distributed in the bath flow mode, and orderly arranged according to the magnetic field line and rotated around the baseline. This can basically eliminate the diamond agglomeration defect on the surface of the wire saw and improve the uniformity of the distribution density of diamond particles. The average surface roughness of the silicon wafer in the feed direction is lower, so the workload of the subsequent grinding process can be reduced.
Abstract: Objectives CVT technology has the advantages of a simple and compact structure, low cost, and convenient operation. It is the most ideal automobile transmission. The processing of its core component—the pulley block—is a difficult point in CVT manufacturing, especially the processing of the ball track on the pulley and pulley shaft. Electroplated cBN grinding wheels have the advantages of a high grinding ratio, low grinding force, less heat, environmental friendliness and good consistency in machining accuracy. They are ideal grinding tools for raceway machining. However, due to the high geometric accuracy required for the raceway—especially the allowable tolerance of the contact angle and its narrowness—it brings great difficulties to the precision dressing quality of the grinding wheel. Therefore, the precision forming and truing technology of cBN grinding wheels for CVT pulley raceway forming grinding is one of the key technologies that restrict the progress of CVT gearbox manufacturing technology in China. Methods Based on the technical problems existing in the current optical guided dressing method in engineering, this paper analyzes the principle of raceway forming grinding and the geometric feature structure of the raceway, and combs through the geometric accuracy control principle of the cBN grinding wheel in raceway grinding. The proportional dressing method is proposed and adopted. The feasibility of the method is verified by a dressing experiment. It is verified that the contact angle error of the raceway grinding wheel can be stably controlled within ± 1°, and the contact angle deviation of the left and right arcs is less than 1°.Results (1) The dresser "cross + ceramic grinding wheel up and down reciprocating" tool grinding wheel dressing method, can ensure that each point on the arc of the ceramic grinding wheel contacts the highest point on the cylindrical surface of the grinding wheel being dressed. This method is beneficial for ensuring the sharp angle dressing accuracy of the ceramic grinding wheel. The R value accuracy of arc dressing of the ceramic grinding wheel can reach 0.9980 and 1.0020 mm, and the arc profile accuracy can reach 0.002 and 0.003 mm. (2) Within the tolerance range, the change of contact angle α with Xi and Rg is approximately linear, and the smaller the tolerance range, the better the straightness. (3) During the dressing process of the electroplated cBN grinding wheel in CVT raceway grinding, as the dressing process continues, the arc loss at the tip of the ceramic grinding wheel increases, and the arc values on both sides of the cBN grinding wheel gradually increase, resulting in a smaller contact angles on both sides. In the actual machining process, the dressing results can be detected in time, and the contact angle dressing accuracy can be controlled by adjusting the compensation value of the controller. The arc wear of the ceramic grinding wheel tip has little effect on the center distance of the double arcs on both sides of the tooth profile of the cBN grinding wheel. (4) When the ceramic diamond grinding wheel is used to dress the cBN grinding wheel, arc wear of at the ceramic grinding wheel tip is inevitable. In fact, a binder with better wear resistance can be selected, or the diameter of the grinding wheel can be increased to reduce the influence of ceramic grinding wheel wear on dressing quality. When adjusting the program, the contact angle is adjusted to a negative difference, and the allowable wear amount of the tool grinding wheel is increased to prolong the service time of the tool grinding wheel. Conclusions Due to factors such as drawing accuracy, minimum feed, and operation experience, the optical guidance method has problems such as poor trimming accuracy, time-consuming and laborious programming correction. At the same time, this method results in a low degree of smoothness in the grinding wheel contour, and sharp points often appear on the surface.This can easily cause quality problems such as scratches on the pulley ball track or unstable quality when the cBN grinding wheel grinds the ball track. Based on the optical-guided dressing method, this paper proposes a proportional dressing method. The dressing process of the grinding wheel is adjusted by the proportional adjustment principle, which can effectively control the dressing results. The dressing method of the tool grinding wheel using the dresser "cross + ceramic grinding wheel up and down" ensures that all points on the arc of the ceramic grinding wheel are in contact with the highest point on the outer cylindrical surface of the dressing grinding wheel being dressed. This method is conducive to ensuring the sharp angle dressing accuracy of the ceramic grinding wheel.
Abstract: Objectives Precision micro through-hole parts are widely used. However, due to the limitations of manufacturing technology, precision parts with complex shapes, such as cross micro-holes, may have defects such as burrs, scratches, and nodules during the manufacturing process. In view of the problems of conventional finishing processing of cross deep micro-holes being limited by size, uneven processing, and poor quality, and combined with the characteristics of a stable removal function and strong adaptability of the abrasive jet, the magnetic micro-abrasive jet technology finishing processing method is proposed to improve the quality of the inner wall of cross deep micro-holes.Methods An independent magnetic abrasive jet device was used to carry out finishing tests on the cross deep micro-holes, and an electromagnetic device was used to generate a focusing magnetic force near the nozzle outlet. The magnetic abrasive was concentrated towards the center during the internal movement of the nozzle, alleviating the problem of rapid divergence of the magnetic abrasives with the jet after spraying and further improving the efficiency of finishing processing. A simulation mathematical model was established to explore the influence of different process parameters on the finishing effect. The finite element method and the discrete element method were coupled to simulate the polishing process of the inner wall of deep micro-holes by the magnetic micro-abrasive jet under different process parameters. The flow field distribution, the erosion rate, and the action law of wall shear force under different parameters were analyzed, and the key factors were identified. Finally, the response surface method was used to optimize the three factors of jet target distance, jet pressure, and nozzle diameter. The response surface equation was established and solved by taking the comprehensive influences of wall shear force and erosion rate on the orifice, the inner wall of the hole, and the cross part of the hole as the response value, and the optimal combination of process parameters was obtained and verified by the test.Results Adding a focusing magnetic field near the nozzle can effectively reduce the divergence of the abrasive after jet ejection, and further improve the efficiency and quality of magnetic abrasive ejection polishing of cross deep micro-holes. The simulation results show that the main parameters affecting micro-hole finishing are jet target distance, jet pressure, and nozzle diameter. By using the response surface method combined with experiments for parameter optimization, the optimal process parameter combination for magnetic micro-abrasive jet finishing of cross deep micro-hole inner walls is obtained, which includes a jet target distance of 7 mm, a jet pressure of 1.0 MPa, and a nozzle diameter of 1.4 mm. Under the optimal combination of process parameters, the inner wall quality of the cross deep micro-holes is significantly improved, the burrs at the cross-holes are completely removed, the wall roughness Ra is reduced from 0.49 μm to 0.13 μm, and the orifice has a good rounding effect.Conclusions By combining magnetic fields and abrasive jets, the magnetic micro-abrasive jet technology provides a new method for the finishing of cross deep micro-holes. Due to the ability of the magnetic abrasive micro-jet to achieve focused fixed-point machining, it has significant processing advantages in cross deep micro-hole finishing and deburring. By constructing a physical model of the machining process and using the simulation form of coupling the finite element method and the discrete element method, it is possible to more clearly simulate the motion of the abrasive and flow field in the abrasive water jet during the machining process, as well as the force situation of the workpiece being machined. In the finishing process of cross-hole parts, the nozzle diameter, pressure, and target distance have a direct impact on the finishing effect. However, parameter adjustment is required for finishing workpieces of different sizes and shapes. Finding suitable processing parameters will further improve the quality and efficiency of workpiece processing.
Abstract: Objectives With the rapid development of industrial automation and intelligent manufacturing, the application of industrial robots in the stone processing industry has garnered increasing attention. However, compared to other advanced manufacturing sectors, the mechanization, automation and intelligence of the stone processing industry remain relatively underdeveloped. This study aims to explore the optimal processing methods for stone industrial robots' grinding operations using BP neural networks and genetic algorithms, taking the processing of sandstone as an example.Methods Taking the KUKA KR60L30HA industrial robot equipped with a brazed flat grinding head as the representative, the effects of different grinding process parameters on grinding force signals were systematically analyzed by the orthogonal test method. Firstly, the grinding force signal data were collected using different grinding test settings. Subsequently, a three-layer grinding force prediction model based on a BP neural network was established, and linear regression analysis was conducted using the orthogonal experimental data as samples to compare the predicted values with the experimental values. Finally, the genetic algorithm was applied to optimize grinding process parameters with material removal rates as the indicator.Results The grinding process parameters have significant effects on grinding forces, but the order of major and secondary effects of different parameters varies with grinding force components. The order of influence on tangential grinding force is the axial cutting depth ap, followed by radial cutting depth ae, the feed rate vw and the spindle speed n, while the order of influence on normal grinding force is ap, vw, ae and n. In contrast, the order of influence of axial grinding force is n, ae, vw and ap, while the total grinding force is most affected by vw, in the order of vw, ae, n and ap. Additionally, all components of grinding force generally increase with the rise of ae, ap and vw, and decrease with the increase of spindle speed n. As the radial cutting depth ae increases, the ratio of normal to tangential grinding force shows a continuous downward trend. As the axial cutting depth ap increases, the grinding force ratio fluctuates within a certain range. As the spindle speed n increases, the grinding force ratio first increases, then decreases, and then slightly increases. When the feed rate vw increases, the grinding force ratio shows an initial decrease followed by an increasing trend. After training and predicting using the BP neural network model, the predicted values of tangential, normal and axial grinding forces are compared with the experimental data. The maximum absolute relative error of the axial grinding force is 7.84%, and the correlation coefficient of the model is as high as 0.998 09, indicating significant prediction accuracy of the mpdel. The optimal process parameter combination determined through genetic algorithm optimization is a radial cutting depth of 2.28 mm, an axial cutting depth of 2.98 mm, a spindle speed of 9 586.65 r/min and a feed rate of 2 207.67 mm/min. Under the optimal process parameter combination, the predicted material removal rate of the workpiece is 14 999.79 mm3/min, with a relative error of −5.37% compared to the actual experimental value of 14 194.44 mm3/min. This further demonstrates the effectiveness of the proposed optimization strategy.Conclusions The constructed grinding force prediction and process parameter optimization model has achieved systematic analysis and optimization of grinding force in robot sandstone processing. This model can clearly reveal the role of various grinding process parameters in machining and reflect their importance in improving machining efficiency and material removal rate. The changing trend of grinding force varies with different processing conditions, and there are significant differences in the influences of different parameter combinations on grinding forces, especially the influences of axial cutting depth and the feed rate, which are particularly significant. The optimal process parameter combination for material removal rate in stone processing is determined through BP neural network and genetic algorithm, and the relative error between the predicted value and the experimental value is relatively small.
Abstract: Objectives The EA4T axle is a critical load-bearing component of electric multiple unit (EMU) train bodies, directly influencing operational safety and reliability. As a high-end product with stringent technical requirements and complex manufacturing processes, the shoulder position of the EA4T axle is stressed repeatedly and there is stress concentration during service. Consequently, in the process of axle production, it is necessary to grind the axle shoulder to control its surface roughness and material removal depth. Current manual grinding methods for EA4T axle shoulder suffer from high labor intensity, inconsistent surface quality, and low efficiency. In order to effectively break through the current manual grinding dilemma of the EMU EA4T axle, the implementation of flexible grinding using an industrial robotic intelligent grinding system equipped with a constant-force control device presents a feasible solution to replace manual operations and achieve automated processing. Therefore, it is essential to carry out research on the grinding process of EA4T steel components, and explore the grinding process methods that meet the surface quality requirements of EA4T axle machining. Combined with the off-line programming method for EA4T axle robot grinding trajectory, the axis shoulder grinding trajectory is planned and the robot machining program is generated to realize high-quality and efficient automatic grinding of the EA4T axle by robot.Methods Firstly, an independently developed robotic intelligent constant-force grinding system serves as the experimental platform. EA4T steel specimens with dimensions of 150 mm × 63 mm × 9 mm are prepared as test pieces. Based on the quality control requirement that the surface roughness of the EA4T axle after grinding must not exceed 0.4 μm, and considering the actual situation of manual grinding process parameters, a Taguchi method-based orthogonal experiment with four factors and four levels is designed and implemented. In the experiment, a hand-held surface roughness measuring instrument is used to measure the surface roughness after grinding, and a precision analytical balance is used to measure the weight of the specimen before and after grinding to calculate the material removal depth. Thus, the surface roughness and the material removal depth of the specimen under different process parameters are obtained. Secondly, analysis of variance and significance testing are conducted to determine the significance level of the influence of each process parameter on the experimental results. The influence of the grit size of grinding tools, grinding force, feed speed, and spindle speed on the surface roughness and material removal depth is analyzed. Then, by calculating the entropy of each index to determine the weight coefficient, the surface roughness and material removal depth in the experimental results of each group are converted into comprehensive score values for evaluation. The optimal grinding process parameter combination with minimum surface roughness and material removal depth is obtained through comprehensive score range analysis. Finally, the off-line programming method is employed to establish a virtual model of the robotic intelligent grinding system within the robot off-line programming software. The 3D model of the EA4T axle is imported into the virtual environment. Based on the flexible grinding module at the end-effector, parameters including grinding head dimensions, end-effector tools, and trajectory configurations are defined. The robot machining system program SRC file is generated and subsequently transferred to the robot teach pendant. The grinding force, feed rate and spindle speed corresponding to the optimal grinding process parameters are entered into the control system. Physical grinding experiments are conducted on EA4T axle prototypes to validate the feasibility of the proposed grinding methodology.Results Through the grinding orthogonal experiments and physical verification experiments, the following results are obtained. (1) The order of influence of grinding process parameters on the surface roughness of EA4T steel is: abrasive grit size > spindle speed > feed rate > grinding force, with abrasive grit size exhibiting the most significant impact on surface roughness. The order of influence of process parameters on material removal depth is spindle speed > abrasive grit size > feed rate > grinding force, with spindle speed being the most influential. (2) With the goal of minimizing the comprehensive score of surface roughness and material removal depth, the optimized grinding parameter combination is selected by choosing the levels with the lowest mean values across all parameter groups. The selected parameters are brasive grit size 400#, grinding force 15 N, feed rate 50 mm/s, and spindle speed 750 r/min. Using this parameter combination, the post-grinding surface roughness reaches 0.338 μm, and the material removal depth is 1.67 μm, effectively improving surface quality while meeting specification requirements. (3) The off-line programming method is used to plan the grinding trajectory. The simulation and experiment trajectories of EA4T robot grinding completely coincide, realizing automatic grinding robot of the EA4T axle shoulder position without interference, singularities and with full reachability.Conclusions The paper conducts experimental research on process optimization and trajectory planning for robotic intelligent grinding of the EA4T axle. Through orthogonal experiments combined with the entropy weight method, the influence patterns of grinding processes on quality are revealed. The optimal process parameter combination for minimizing surface roughness and material removal depth is determined. The off-line programming method enables quick and accurate planning of a robot grinding trajectory that is non-interfering, non-singular and fully reachable. The proposed method improves grinding efficiency and surface quality, meets the requirements of grinding efficiency and surface quality of EA4T axle, and can be applied in actual production and processing, effectively breaking through the predicament of low efficiency and poor consistency of EA4T axle.
Abstract: To promote the international cutting-edge technical exchange in the field of abrasives, the Group G (abrasive processing) papers in the 2024 CIRP Annals – Manufacturing Technology journal have been specially selected for introduction. A total of 9 papers on this topic have been published, numbered G1 to G9 in the order of submission. The research topics of these papers include grinding models (G1/G2), grinding machinability (G3/G4), polishing tools (G5), inner surface polishing (G6), chemical mechanical polishing (G7), polishing edge effects (G8), and electrochemical mechanical polishing (G9). This paper summarizes and introduces the main innovations and conclusions of each study to facilitate learning and communication among scholars in related fields.
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