Table of Content

25 December 2020, Volume 31 Issue 24

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Applications and Research Status of Compliant Transmission Mechanisms in Fast-steering Mirrors

FAN Dapeng;TAN Ruoyu

2020, 31(24):  2899-2909.  DOI: 10.3969/j.issn.1004-132X.2020.24.001

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Based on the movement characteristics of the compliant transmission mechanisms, the typical flexible supporting transmission structures applied in fast-steering mirrors were introduced, several foreign early characteristic fast-steering mirrors and advanced fast-steering mirrors at the present stage were introduced and analyzed from the aspects of drive modes, structural layouts, supporting transmissions and working principles. In view of the current research situations of the compliant transmission mechanisms, the design methods, spatial mechanism configurations, stiffness analysis and overall dynamics analysis of the compliant transmission units applied in the fast-steering mirrors were concluded. Finally, the research and development directions of the compliant transmission mechanisms using in fast-steering mirrors were summarized.

Effects of Bubble Collapse of Near-ball Wall Jet Flows on Crushing Effectiveness of Fine Particles

SUN Yi;ZHU Lihao;MAO Yalang;LU Peiqi;HUANG Shaowei

2020, 31(24):  2910-2917，2923.  DOI: 10.3969/j.issn.1004-132X.2020.24.002

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In order to effectively solve the problems of fine particles agglomeration and grinding limit in mechanical large-scale powder preparation, the fine particles preparation method was adopted by cavitating jet impacts combined with grinding. The effective impact of the near-ball wall cavitating jet on particle crushing was studied. Based on the theoretical analysis of the impact characteristics of near-ball wall bubble collapse on fine particles, the effective dimensionless distance and the maximum radius of the critical bubble were obtained. Numerical simulation of the impact of cavitating jets on the spherical wall was performed, and the influences of the nozzle inlet pressures and the target distances on the distribution of near-ball wall cavities were analyzed. In order to verify the theoretical and numerical analysis results, a series of quartz sand crushing comparison experiments were carried out based on multiple factors such as target distance, rotation rate, particle mass fraction, and number of nozzles. The experimental results are in good agreement with the theoretical and numerical analysis ones, which proves the effectiveness of this method. The results show that crushing rate of fine particles in cavitation impact combined with grinding is higher than that of single grinding. Under the cavitation jet inlet pressure of 5 MPa, target distance and rotation rate are the main factors affecting the crushing effectiveness of quartz sand fine particles, followed by number of nozzles.

Surface Formation Mechanism and Surface Roughness Theoretical Model of Fluorophlogopite

CHEN Jingqiang1;MA Lianjie1,2;MENG Bo1;ZHOU Yunguang2

2020, 31(24):  2918-2923.  DOI: 10.3969/j.issn.1004-132X.2020.24.003

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According to the turning dynamics theory, the contact stress of the rack face and flank surface were calculated, then the stress intensity factor of the crack tips was determined. The crack growth angle of the tip was determined based on the fracture mechanics theory. The microscopic mechanism of surface formation was analyzed, and the theoretical model of surface roughness was established according to the interference relationship between cutting tool and workpiece in turning. The accuracy of the model was verified by a single factor turning experiment of fluorophlogopite. The results show that with the increase of cutting speed, feed and cutting depth, the plastic-brittle transition occurs. The surface roughness decreases firstly and then increases with the increase of cutting speed and feed, and increases with the increase of cutting depth. Under the conditions of plasticity removal, the predicted values are opposite to the experimental ones, and under the condition of brittleness removal, the predicted values are the same as the experimental ones. The accuracy of the roughness model is improved obviously. It is proved that the modified model is reliable.

Study on Modeling and Simulation of Surface Topography of Spherical Milling with Ball-end Milling Cutters

FAN Simin;XIAO Jiming;DONG Yongheng;HONG Xiantao;ZHAO Ting

2020, 31(24):  2924-2930，2936.  DOI: 10.3969/j.issn.1004-132X.2020.24.004

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Based on the principles of homogeneous coordinate matrix transformation and the vector algorithm, a mathematical model of the swept surfaces for the ball-end milling cutters was established under the workpiece coordinate system. Based on Z-MAP method, a spherical surface topography generation algorithm was designed. This algorithm was used for machining the convex spheres with the ball-end milling cutters by two typical moving paths of 3D surrounding method and radiation processing method respectively, and the machined surface morphologies were simulated. Through the analysis and comparison of the simulation results, it is found that the 3D surrounding method is more conducive to reduce the surface roughnesses. At the same time, the simulation results and the test results have a high degree of agreement, which indicates that the simulation method is reliable and may be used to predict the spherical milling surface topography with ball-end milling cutters in actual productions.

Non-Masing Characteristic Analysis and Fatigue Life Prediction for 316L Stainless Steels

2020, 31(24):  2931-2936.  DOI: 10.3969/j.issn.1004-132X.2020.24.005

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The low cycle fatigue tests for 316L stainless steels were conducted at test temperatures of 293 K and 873 K respectively under different strain ranges. The amplitude correlation and temperature correlation of material cyclic properties were discussed. Non-Masing characteristics were compared under different conditions and the low cycle fatigue life was predicted by using energy method. The testing results show that at the initial of the cycle under various conditions, different degrees of cyclic hardening phenomena may occur, and then cyclic softening and saturation may occur until the materials fail. Compared with the testing condition of 873 K, the non-Masing characteristics of the material at 293 K is more significant. The non-Masing characteristics at two temperatures are more obvious under large strain range. When using the energy method to predict fatigue life, the predicted results are all located in the twofold scatter band, and the results considering non-Masing characteristics are more accurate than those of considering Masing characteristics. Under the temperature of 873 K and large strain range, the significant dynamic strain aging effect leads to subtle difference between the predicted results considering the non-Masing and Masing characteristics.

A Clearance Arrangement Method for Screw Rotors of Twin-screw Compressors Based on Discrete Pixel Method

CHEN Guanfeng1;CHEN Songping1;CAI Sijie2

2020, 31(24):  2937-2942，3023.  DOI: 10.3969/j.issn.1004-132X.2020.24.006

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To ensure the stability of the twin-screw compressor rotors, a meshing clearance arrangement method was proposed based on the discrete pixel method. According to the principles of the pixel selection and clearance determination, combined with the principles of gear engagement and wear, the inter-lobe clearance arrangement method of the male and female rotors for twin-screw compressors was studied based on the characteristics of the tooth profiles of the twin-screw compressor rotors and the thermal expansion simulation results of the rotors under the processing conditions. The proposed method was used to arrange the inter-lobe clearances on the end face profiles of a pair of male and female rotors without meshing clearances reasonably, adjust the rotor meshing positions, reduce the vibrations and wear during the operations of the twin-screw compressors, and reduce the operation power consumptions.

Parameter Solution of Instantaneous Milling Force Model of Variable Cross-section Scroll Plates Based on Improved PSO Algorithm

LIU Tao;ZHANG Lifang

2020, 31(24):  2943-2949.  DOI: 10.3969/j.issn.1004-132X.2020.24.007

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In order to solve the multivariate nonlinear problems in the prediction of instantaneous milling forces in variable cross-section scroll plate machining processes, a mathematical model for instantaneous milling force considering the tool runout was established based on the actual milling processes, and an improved PSO algorithm was proposed to solve the mathematical model to improve the accuracy of the instantaneous milling force prediction model. The method was verified by the instantaneous milling force experiment results under four groups of milling parameters. The results show that the instantaneous milling force curves obtained by the proposed method have a high degree of agreement with the experimentally measured ones in terms of the shape and peak value, and the peak errors of the four groups of tests is within 15%. The proposed PSO algorithm could effectively improve the convergence rate of instantaneous milling force identification of variable cross-section scroll plate machining. The model parameters can be identified with higher precision and fewer trials, which reduces the test costs compared with the average milling force solving method.

Study on Relationship between Fatigue Life of Steering Knuckles and Shock Absorber Damping

DONG Guojiang;YAN Feng;HAN Jie;ZHOU Teng

2020, 31(24):  2950-2958.  DOI: 10.3969/j.issn.1004-132X.2020.24.008

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In order to study the influences of shock absorber damping coefficients on fatigue life of steering knuckles, taking a compact SUV(sport utility vehicle) as the research object, through modal analysis and testing of steering knuckles, the flexible body models and the fatigue simulation analysis models of steering knuckle were established. The rigid-flexible coupling multi-body dynamics models of the whole vehicle were established based on the parameters of the real vehicles, and based on the six-component forces of the wheel center and the strain signals of the steering knuckle monitoring points collected by the real vehicles in the testing proving ground, using virtual iteration method simulation the load time history(modal displacement) of steering knuckles was obtained. The fatigue life of steering knuckles in different shock absorber damping coefficients was analyzed by using modal stress recovery method, and the relationship between both of them was discussed. The results show that the fatigue life of steering knuckles increases first and then decreases with the increase of damping coefficients in the range considering both of comfort and safety of the whole vehicle, that is, the damage areas of the main area affecting the fatigue life of steering knuckles decreases first and then increases. The damage areas of the secondary area which affects the fatigue life of steering knuckles always increases with the increase of damping coefficients.

A Method for Extruding Grinding Dressing Super-abrasive Grinding Wheels Using Free Grains under Constraint of Diamond Abrasive Surface

CUI Zhongming;WANG Xing;HE Qingshan;ZHOU Baocang

2020, 31(24):  2959-2965.  DOI: 10.3969/j.issn.1004-132X.2020.24.009

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In view of the difficulty of dressing super-abrasive grinding wheels, a dressing method was proposed, which was a combination of the grain extrusion and grinding under the constraints of diamond profiles. This method was based on the characteristics of the great differences in strength between diamond and ordinary materials and the principles were as follows. Diamond tools with precision shapes on the surfaces produced high-strength surfaces with constraints through high-speed rotation. Free grains under the constraints of diamond constraint profiles had a squeeze-scratching effect on the grinding wheels and destroyed the adhesive of the grinding wheels to complete the dressing of grinding wheels in high efficiency. Meanwhile, the shape of the grinding wheels was further refined by the micro-grinding effect of the high-strength diamond abrasives of the dressing tools. Herein, the formation of the constraint profiles and the mechanism of extrusion and cutting of the free grinding grains under the diamond constraint profile were analyzed. The composition and characteristics of the extruded dressing systems were introduced. The influence laws of parameters such as dressing force, grinding speed and free grinding grain were explored experimentally. The results show that precision dressing of ultra-hard abrasive grinding wheels in high efficiency may be achieved by extrusion of free grains under the constraints of diamond profiles.

Sensitivity of Structural Parameters of Ventilated Brake Disc to Brake Jitters

LONG Jiangqi1;LIN Jian1;CHEN Xianbing2;WANG Zining2

2020, 31(24):  2966-2971.  DOI: 10.3969/j.issn.1004-132X.2020.24.010

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For the brake jitters of a ventilated brake disc, the orthogonal experimental design method was used to obtain the optimal horizontal combination of the structural parameters of the ventilated brake disc. The finite element method was used to simulate 15 cycles of braking. By analyzing the differences of thermal deformations between the front and rear brake discs before and after optimization, the sensitivity of each structural parameter to the thermal deformations of the brake disc was obtained. Then bench-test was carried out to verify the results of simulation. The results show that the sensitivity of the structural parameters of the ventilated brake disc to the brake jitters from high to low are as follows: thickness, cap height, angle of the neck, outer diameter of brake disc, inner diameter of brake disc, radius of the neck.The increasing of thickness cap height and angle of the neck induces the increasing of brake jitters, while the outer diameter of brake disc and inner diameter of brake disc increase, the brake jitter decreases.

Research on Cutting Layer Geometry of Positive Eccentricity Orthogonal Turn-milling in Finish Machining

SUN Tao1;QIN Lufang1;HOU Junming2;FU Yucan3

2020, 31(24):  2972-2978.  DOI: 10.3969/j.issn.1004-132X.2020.24.011

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For orthogonal turn-milling, as the cutting layer geometry of positive eccentricity was not considered, the overall change rules of cutting layer geometry were difficult to describe. To solve the above problems, formation processes of cutting layers were analyzed statically without consideration of kinetic influences based on motion law of orthogonal turn-milling. The mathematic models of cutting layer geometry of orthogonal turn-milling with positive eccentricity were set up and some mathematical expressions were gained such as entrance and exit angle, cutting thickness and cutting depth of side and bottom cutting edges. The above mathematic models were verified by experiments. Finally, some influences of cutting parameters on cutting layers of tool were researched. The above studies provide quantitative analyses for changes of cutting layer geometry on positive eccentricity orthogonal turn-milling and detailed theoretical guidelines for cutting forces and chatters.

Multi-objective Job Shop Scheduling Based on Hybrid Evolutionary Algorithm and Knowledge

QIU Yongtao1;JI Weixi1,2;ZHANG Chaoyang1,2

2020, 31(24):  2979-2987.  DOI: 10.3969/j.issn.1004-132X.2020.24.012

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A new multi-objective job shop scheduling method was proposed based on hybrid evolutionary algorithm and knowledge, the better non-dominant Pareto solutions might be obtained for production scheduling with limited time or iterations. The knowledge mining attributes were determined by the optimized objects and attribute-oriented induction and deduction method. Then, the rule-based initial population was acquired by the priority weight. The proposed addition-deletion sorting method overcame the problems of insufficient or oversaturated operations by re-assigning the positions in the initial population locally. Finally, a benchmark and non-dominated sorted genetic algorithm-Ⅱ (NSGA-Ⅱ) hybrid simulated annealing algorithm were used to verify the proposed scheduling method. The results obtained are superior to the traditional stochastic evolutionary method in terms of the optimized function values or the distribution of solution set under different iterations and initial population sizes.

Fault Feature Extraction Method for Gears Based on ISSD and SVD

TANG Guiji;LI Nannan;WANG Xiaolong

2020, 31(24):  2988-2996.  DOI: 10.3969/j.issn.1004-132X.2020.24.013

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Aiming at the problems that the gear fault features were weak and difficult to extract effectively under strong background noises, a fault feature extraction method for gears was proposed based on ISSD and SVD.  Considering the defects that the modal parameters needed to be selected by experience in the SSD algorithm, the SSD algorithm was improved based on dispersion entropy optimization algorithm. On the basis of getting a set of singular spectrum component(SSC), the optimal SSC was selected according to the kurtosis maximum criterion and the SVD processing was carried out. The singular value energy standard spectrum was used to adaptively determine the signal reconstruction order to restore the signals and improve the noise reduction effectiveness. Finally, the gear fault features were extracted by using envelope demodulation. The proposed method was applied in simulated signals and gear measured signals, and compared with the traditional envelope spectrum, SSD envelope spectrum and empirical mode decomposition combined with SVD(EMD-SVD) methods. The results show that the proposed method has better effectiveness of noise reduction and feature extraction, and may realize the identification of gear faults more effectively.

Design and Optimization of Soft Start for Hydrostatic Drive Systems of Passenger Devices

MAO Haozhen1;HU Junke1;YE Mengqi1;XIAO Gongping2

2020, 31(24):  2997-3005.  DOI: 10.3969/j.issn.1004-132X.2020.24.014

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In the coal mine environments, it was required that the mechanical equipment should have dustproof, explosion-proof and high reliability performance. A soft start method for the driving systems of the passenger devices was proposed by adjusting the pilot-oil circuit of the variable pumps in the hydrostatic drive systems. The speed of the motor and the pilot-oil pressure could increase steadily by changing the parameters of the accumulators and the damping holes. The results show that the pilot-oil circuit with a single damping hole reduces the boost rate significantly in the late stages, and the drive-motor may not reach the expected speed within the rated time. In the later stages of boosting, increasing the charging flow of accumulator by parallel flow or switching oil circuit may shorten the boosting time significantly. Selecting the accumulator volume as 0.4 L, when the oil is switched from the oil path where the 1.1 mm damping orifice locates to the oil path where the 1.4 mm damping orifice locates in the 9th second of the boosting processes, the system may have the optimal boosting curve of pilot-oil pressure from 4×105 Pa to 16×105 Pa within 15 seconds. In the meantime，the system may get the optimal soft start performance.

Experimental Study of Bionic Wear Resistance Optimization for Middle Plates in Scraper Conveyors

ZHAO Baolin1,2;LI Bo1,2;XIA Rui1,2;WANG Xuewen1,2;WANG Yun3

2020, 31(24):  3006-3015.  DOI: 10.3969/j.issn.1004-132X.2020.24.015

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The wear failures of the middle plates in the scraper conveyors became one of the main reasons for the malfunctions of the conveyors. In order to improve the wear resistance of the middle plates,the design of bionic middle plates was carried out based on the non-smooth units of dung beetles. The single factor and response surface method optimization tests were carried out with the amount of wear as the response value. According to the testing results of response surface method, the order of significant influence factors(from high to low) is radial distance, depth-diameter ratio, diameter, pitch angle. And the regression prediction model of wear amount and factors was established based on the testing results. By comparison of the tests, it is found that the relative errors between the prediction model and the real test are as 3.2%. Under the specific working conditions (particle size of coal powder is as 6~8 mm, load is as 20 N, scraper chain speed is as 0.65 m/s and testing time is as 6 600 s), when the depth-diameter ratio is as 1.41, the diameter is as 0.69 mm, the pitch angle is as 6.55° and the radial distance is as 4.66 mm, the wear amount is the least, the wear resistance of bionic middle plate is improved by 12.6%. By analyzing the mechanism of wear resistance, it is found that compared with the smooth plates, the bionic plate has less abrasive wear and adhesive wear. The pit distribution may destroy the coal particle movement on the surfaces of the continuous cutting middle plates. The bionic optimization of the middle plates may provide some references for the design of scraper conveyors in the future.

Computational Model and Experimental Study for Bone Tissue Grinding Forces

ZOU Lei;WEN Donghui;ZHANG Lihui;CHEN Zhenzhen;XIAO Yuting;LIANG Jun

2020, 31(24):  3016-3023.  DOI: 10.3969/j.issn.1004-132X.2020.24.016

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The tactile interaction system was an important part of the neurosurgical simulator. The key of this system was to establish a realistic force feedback model for the bone grinding processes. A three-dimensional grinding force computational model was established for bone grinding processes of the medical spherical grinding tools, which calculated the grinding force distributions on the surfaces of grinding tools based on grinding specific energy Ues  and material removal rate. Bone grinding experiments were carried out by using the cortical portion of bovine femur bones, and the influences of spindle inclination angle and feed direction on the grinding forces were investigated. The results show that the calculation results of the model are in good agreement with the experimental ones in the terms of magnitudes and variation trends of grinding forces. The average relative errors of the calculated values of the grinding force with variable Ues is less than 23%. The spindle inclination angle and feed direction have greater influence on the grinding forces, the spindle inclination angle may change the average linear velocity of the abrasive particles in the grinding arc zones, and the changes of the grinding force have a certain relationship with the average linear velocity of the abrasive particles.