Table of Content

10 March 2020, Volume 31 Issue 05

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Nonlinear Stiffness Characteristic Analysis of Cylindrical Roller Bearings Considering Variation of Roller Positions

LIU Guanghui1;HONG Jun1;SUN Yanhui1;WU Wenwu2

2020, 31(05):  505-512. 

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Taking the cylindrical roller bearings as the research object, considering the periodic variation of the roller positions in the circumferential direction during bearing rotating, the classical theory of the load distribution for the cylindrical roller bearings was modified.The time-varying characteristics of bearing stiffness as well as the nonlinear variations of average bearing stiffness and average contacted roller numbers with radial forces were analyzed.In order to verify the accuracy of the modified theoretical method, a finite element/contact mechanics method was utilized to analyze the cylindrical roller bearing stiffnesses and roller contact conditions.The results show that both of the modified theoretical method and the finite element/contact mechanics method may accurately predict the time-varying characteristics of the instantaneous bearing stiffness and the nonlinear features of the mean bearing stiffness.The results also verify that the changes of average contacted roller numbers are the primary factor of bearing stiffness variations.Based on the modified theoretical method, the influences of bearing initial radial clearances, radial forces and the number of designed bearing rollers on bearing characteristics are further conducted quantificationally.

Design and Grinding Wheel Dressing of Vertical Super-hard Grinding Wheel Arc Dressers

LI Songhua1,2;HAN Tao1;WANG Weidong1;SUN Jian1;HAN Guangtian1

2020, 31(05):  513-518,526. 

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Aiming at the problems that the arc-shaped super-hard grinding wheel dressing was difficult and had low precision,a resin-bonded arc-shaped diamond grinding wheel was precisely dressed.A vertical super-hard grinding wheel arc dresser was designed and manufactured to study the changes of surface roughness, arc accuracy, roundness and surface topographies of arc-shaped grinding wheels with different grain sizes before and after dressing.The channels of the silicon nitride ceramic bearing rings were ground before/after the dressing of the grinding wheel, and the groove-shaped accuracy of the bearing rings after grinding was measured.The results show that compared to before dressing, the average value of surface roughness of the grinding wheel is decreased from 1.731 8 μm to 0.772 4 μm, which is reduced by 55.4%.The average arc error is decreased from 33.604 7 μm to 8.527 6 μm, which is reduced by 74.6%.Besides, the arc accuracy of four grinding wheels was more stable after the dressing, and the arc accuracy decreases slightly with the decreasing of the grinding wheel grain sizes.The average value of grinding wheel roundness is decreased from 43.721 μm to 18.002 μm, which is reduced by 58.8%, and a large number of new abrasive grains were exposed after dressing.The vertical super-hard grinding wheel arc dresser may precisely dress the arc-shaped grinding wheel, and greatly improve the arc accuracy and roundness of the arc-shaped grinding wheel by dressing.The groove-shaped accuracy of bearing rings is greatly improved after dressing.

Robot Polishing Technology of Spherical Grinding Head with Revolution and Rotation Motion Based on Constant Pressure Control

HUANG Zhi1;WU Xiang1,2;LIU Haitao2;WAN Yongjian2;ZHENG Xiao2;CHEN Xiang1

2020, 31(05):  519-526. 

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Aiming at the problems that the fluctuation of polishing pressures was caused by positioning errors of industrial robot and thus the stability of removal function was affected during the polishing processes of largeaperture optical elements, a kind of robot polishing method of spherical grinding head with revolution and rotation motion based on constant pressure control was proposed.The structure, working principle, positioning characteristics of the robot and output characteristics of polishing pressure were studied.Firstly, the material removal model was constructed based on Preston theory, the shapes of the removal function were analyzed, and the mechanics mechanism and working principle of the designed polishing grinding head were introduced.Then, the positioning errors of the robot as well as the response and stability of the output forces of the grinding head were measured, which proved that the proposed method might adapt to the pressure fluctuation of robot polishing and make the corresponding force response control.Finally, the fixed point polishing and rough and precision polishing experiments were carried out.The experimental results show that the removal function is stable by using the proposed method.After 10 cycles of rough and precision polishing, the convergence rates of the surface are as 90.95% and 72.61% respectively, and may obtain high machining precision and quality.

Calculation Method of Response Time of Semitrailer Relay Emergency Valves

HE Ren;XU Chang

2020, 31(05):  527-534,542. 

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In order to determine the quantitative relationship between the control pressure and response time of the semitrailer relay emergency valves and investigate the influences of the structure parameters on the response time, the AMESim simulation model of the relay emergency valves in different braking stages was established and the influences of parameter changes on response time were analyzed.According to the theoretical deduction, a calculation method of the response time of a semitrailer relay emergency valve was proposed.A semitrailer pneumatic braking tester was built in combination with the data acquisition system based on LabVIEW for verifying the AMESim model and calculation method.The results show the AMESim model may predict the pressure changes of braking processes well.The relative errors between the calculated values and the experimental ones are less than 6.4%, which proves the feasibility of the calculation method and the calculation method may be used to study the influences of the internal structure parameters of the relay emergency valves on response time as well as the further optimization of the response time on the semitrailer brake systems.

Research on Design Methods for Vehicle ISRA Mounting System

LIU Xiaoang1,2,3;JIAO Xianghe2,3;WU Yimin1,2,3

2020, 31(05):  535-542. 

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Based on a six degrees of freedom model of a vehicle ISRA mounting system, the design requirements of natural frequencies and energy distributions of the model, zero-roll condition, static roll condition and dynamic roll condition were presented, respectively.The optimization and design methods for the ISRA mounting system were proposed.Under the torque excitation around torque axis, the designed static stiffness of each mount were optimized.Natural frequencies and energy distributions of the ISRA mounting system were calculated.Under zero-roll conditions, the displacements of centriod of the rear axle, one point on the Ya-axis of the centroid coordinate system, the vertical displacements and vertical dynamic reaction forces of each mount were also calculated, respectively.Under static roll conditions, the displacement of centriod of the rear axle, one point on the torque axis were calculated, respectively.The results show that the ISRA mounting system designed by the proposed method may satisfy the design requirements, which may provide references for the design of rear axle mounting system.

Research on Load Spectrum Accelerated Editing Method for Fatigue Test of Vehicle Parts

DONG Guojiang1;HAN Jie1;YAN Feng1;LANG Yuling2

2020, 31(05):  543-552. 

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Taking the wheel center six-component force signals and key point monitoring signals collected in a test field as the basic data, the pseudo-damage retention method, damage retention method and peak-valley extraction method were used to accelerate the editing of the measured signals respectively.The accelerated spectrums were discussed and analyzed from five aspects: time compression ratio, power spectral density, statistical parameters, level crossing counting and rain flow counting statistics.The accuracies from different accelerated editing methods in solving fatigue issue were further discussed by fatigue simulation, and the efficiency of accelerated spectrums was evaluated.The results show that the relative error gaps of the steering knuckle fatigue life analyzed by three accelerated editing methods are relative small, all within 3.72%, but the efficiency of fatigue simulation is much higher than original load spectrum.Taking comprehensive consideration of various aspects of analysis, the damage retention method may accurately delete the non-damaged segments in the original signals, the shortest time acceleration spectrum with the best coincidence of power spectral density will be obtained.This method has the highest efficiency in analyzing component fatigue problems and the accuracy of analysis results.The damage retention method has more advantages than the pseudo damage retention method and the peak-valley extraction method.

Research on Controllable Parameter Modeling Technology of Functional Microstructures

LEI Pengfu;DAI Ning;WANG Zhipeng;CHEN Wei;HUANG Renkai

2020, 31(05):  553-560. 

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Aiming at the problems of difficulty in porous structural-functional integration material design, a large-scale microstructure automatic modeling technology driven by composite functions was proposed.Three groups of microstructure basic units parallel to the three-axis directions were generated by function-driven, which were combined by intersection and union operations defined by set theory.By performing affine and bending operator operations on the generated regular microstructures, a certain conformal effect iveness of complex surfaces might be obtained.The natural fillet transition formed at cell nodes was analyzed, compared with the two node processing methods of direct transition and sphere transition, the mechanics properties of the cells by natural fillet transition are increased by 43.6% and 27.9%, respectively.The circular cross-section microstructures of three different orders were filled into the rotor section model, and the node stiffness curves of the model were obtained by calculating the stiffness values of the three variable-order rotor models at the specified ten sampling points.The results show that the stiffness distribution of the model may be changed by adjusting the distribution orders of the microstructures.

Experimental Study on Vibration Characteristics of ZNR2.4 Roots Type Superchargers

LIU Hougen;FAN Caiming

2020, 31(05):  561-566. 

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In order to study the vibration characteristics of the ZNR2.4 Roots type supercharger, the prototype was subjected to vibration tests.The LMS test equipment was used to collect the vibration signals of the ZNR2.4 Roots type supercharger under different pressure ratios and different speeds.The spectrum analysis was performed on the signals with the largest mean square value under each parameter.The characteristic frequencies of airflow pulsation, reflow equalization vibration and bearings, gears, etc.were calculated.The modal analyses of the rotor were carried out.The results show that airflow pulsation and recirculation equalization vibration are as the main vibration source.When the speed is as 2 800 r/min, the meshing frequency of the gear resonates with the 38 times frequency of the shaft fundamental frequency.Finally, the method of noise reduction and vibration reduction was proposed for each vibration source, which provided reference for designing and using Roots type superchargers.

Technology System of Individualized Redesign for In-service Machine Tools Based on Monitoring and Diagnosis

DU Yanbin1;CAO Huajun2

2020, 31(05):  567-575. 

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In-service machine tool remanufacturing had typical individualized characteristics.Based on the analyses of the individualized requirements of in-service machine tool remanufacturing, the concept of individualized redesign for in-service machine tools was proposed and the connotation of multiple individualization was analyzed.In addition, the technology system of individualized redesign for in-service machine tools was established based on monitoring and diagnosis.The theoretical basis included product life cycle theory of machine tools, performance evolution and damage theory of machine tools and components.The supporting technologies included data acquisition and monitoring during operations, data storage and processing, operation state diagnosis and decision making as well as support tools for individualized redesign.The key technologies included individualization matching, remanufacturability evaluation, quality improvement redesign, intelligent upgrading redesign and green improvement redesign.Finally, case study was carried out in conjunction with a redesign process of an in-service heavy duty horizontal lathe.

Green Scheduling of Flexible Job Shops Based on NSGA-Ⅱ under TOU Power Price

LIU Caijie;XU Zhitao;ZHANG Qin;ZHANG Libo;YAO Kun

2020, 31(05):  576-585. 

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The coordinated optimization of time, economic and energy consumption was realized by planning the green production scheduling.Considering the TOU price policy of the electricity, the energy cost models under different production conditions were established based on the flexible job shop.Incorporating the green production shops management requirements, such as carbon emissions and order delivery, a green scheduling multi-objective optimization model was formulated to minimize carbon emissions, energy costs and makespan.In order to avoid the premature convergence of algorithm and maintain the diversity of population, the non-dominated sorting genetic algorithm-Ⅱ(NSGA-Ⅱ) with dynamic control parameter and improved elite retention strategy was proposed to solve this problem.Finally, the feasibility of the model and the superiority of the improved algorithm were verified by a real-world case.

On-line Monitoring Method and System for Energy Efficiency of Die Casting Cells

YAN Jiahao;CAO Huajun;CHEN Erheng;SONG Dandan;ZHU Linquan

2020, 31(05):  586-594. 

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Due to the problems that the energy efficiency of die casting cells was complex and changeable, which was difficult to be effectively monitored in real time, an on-line monitoring index system was established by analyzing the composition of energy consumption of die casting cells, and the on-line monitoring method for data analysis was proposed based on power information.In this method, the real-time measured power information of die-casting cells was analyzed by wavelet transform, and the operation states and the number of processing pieces of the equipment were identified online by using the extremum search method, so as to obtain the energy efficiency information of die casting cells.The on-line monitoring system for energy efficiency of die casting cells was developed based on C#.The effectiveness and practicability of the proposed method and monitoring system were verified through experiments.

Experimental Research on Laser Engineered Net Shaping of Thin-walled Structures with Large Inclination Angles

YU Chao1;MIAO Qiuyu1;SHI Longfei1;MA Guangyi1;WU Dongjiang1;DENG Dewei2

2020, 31(05):  595-602. 

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Aiming at the problems of rapid forming and repairing complex equipment parts, a method of setting preset angles between laser beam and vertical direction was proposed, and the forming experiments of the unsupported inclined thin-wall structures were carried out under different preset angles.The large-angle forming mechanism of the inclined thin-walled structure was studied, and the selected basis of the preset angle ranges was given to generate the unsupported large-angled thin-wall structures.The results show that the collapse of the unsupported molten powder during the forming processes is the main reason for the low shape accuracy and the angular forming accuracy of the final formed structure.When the preset angles between the laser beam and the inclined thin-walled structure are less than 30°, the shapes of unsupported inclined thin-wall structures are good, and the actual tilt angles are consistent with the design angles.Under the given processing conditions, the inclined thin-wall structure with inclined angle of nearly 60° is finally formed by adopting the preset angle, which breaks the tilt limit of the unsupported inclined thin-walled structure formed by the laser engineered net shaping method, and the three-dimensional blade sample is successfully prepared.

Experimental Study on 3D Printing Silicone Soft Materials for Soft Robots

CHEN Youxu1,2;WANG Deshan1;ZHANG Wei1,2;JIN Guoqing1,2

2020, 31(05):  603-609,629. 

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Based on the independently built direct ink writing（DIW）platform, DC 737 silicone was used as printing materials and the mechanics model of the extrusion system was analyzed to determine the type of processing parameters.Single-factor tests were used to determine the parameter ranges of layer thickness, printing speed and driving pressure which were suitable for printing.Orthogonal experiments were used to study the influences of each process parameter on printing time and dimensional errors, which was successfully applied to the body printing of soft robots.The results show that the printing speed has the most significant effect on the printing time within a certain range, and the driving pressure has the greatest effect on the dimensional errors.The optimal processing parameters are layer thickness of 0.4 mm, printing speed of 15 mm/s, and driving pressure of 124 110 Pa(18 psi).Soft caterpillars robots were printed by using the optimal parameter combination, and dynamic performance experiments were performed to verify the feasibility of high efficient and high-precision in 3D printing soft robots.

Analyses of Combination Process on Microsturctures and Properties of Friction Stir Welded Joints for 2198-T3S Aluminum-Lithium Alloy

HE Diqiu1,2;WANG Dongyao2;HU Lei2;WANG Haijun2

2020, 31(05):  610-615. 

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In order to explore the optimum parameters of FSW for Al-Li alloy sheets, the combination processes were carried out in the welding processes.A cylindrical threaded tool was used during welding processes, the back of the sheets was slotted before welding and the experiments of 2198-T3S Al-Li alloy sheets were carried out at different rotational speeds under the conditions of maintaining the unchanged welding speed.The microstructures and mechanics properties of the joints were analyzed after welding.The results show that there is no weak connection defects at the root of the welds.With the increasing of rotational speeds, the defects inside the welds disappear, the grains in the nugget zones become coarser and the second phase particles dissolve, which lead to the trends of “first rising and then falling” in the mechanics properties of the welds.Under the optimum combination parameters, the tensile strength and yield strength of the joints are as 359 MPa (81.5% of base material) and 248 MPa (77.5% of base material) respectively.Meanwhile, with the increasing of rotational speeds, the fracture mode of welds is changed from brittle-ductile mixed fracture to ductile fracture.

New Technology and Experimental Study on Fatigue Fracture Separation of Seamless Steel Tubes

ZHAO Renfeng1;ZHENG Jianming1;GUO Lei1;WANG Zhanjun1;LIU Yanwei1;ZHAO Shengdun2

2020, 31(05):  616-622. 

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The traditional separation processes of metal tubes had some disadvantages，such as low productive efficiency, high energy-consumption and waste of raw materials.A new method for separating tubes was adopted.The eccentric loading technology and stress concentration effect were used to promote the rapid initiation of fatigue cracks at the bottom tip of V-shaped groove and control the steady propagation of fatigue cracks.The working principles of fatigue fracture separation device under eccentric cyclic loadings were described.The judgment formula of crack initiation at the root of V-shaped groove of tubes under fatigue loadings was deduced.The four experimental control curves including linear decrement control curve, multi-step decrement control curve, 1/4 convex arc decrement and 1/4 concave arc decrement control curve were designed.The 304 stainless steel tubes were studied by experiments under the control curves, finally the tube precision separation was achieved.The experimental results show that using the stress concentration effect of V-shaped groove and the continuous action of eccentric loading forces, the loading frequencies are gradually reduced from high to low by using multi-step decrement control curve, then the rapid initiation and stable propagation of cracks at the root of V-shaped groove of tubes may be ensured.Finally, tube fast fracture is realized and good cross-section quality is obtained.

Effects of Surface Morphologies on Injection Bonding Properties of Aluminum Alloy Surfaces

XU Zhenyu1,2;XU Donghou1;MAO Jian1;GONG Ningning1;LI Xiping1

2020, 31(05):  623-629. 

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By treating the aluminum alloy surface with anodizing and coupling agent, a method for directly forming an Al-polyamide(PA) composite part by injection technology was proposed.The structures and compositions of treated aluminum alloy surfaces were analyzed by laser confocal scanning microscopy and Fourier transform infrared(FTIR) spectrometer, the results show that the aluminum alloy surface roughness and the chemical bonds of Si—O—Al and C—N formed during the coupling agent curing process have important influences on the interface bonding forces.The effects of anodizing process parameters and coupling agent curing conditions on the morphologies and compositions of aluminum alloy surfaces and mechanics properties of the injected composite parts were discussed.The tensile shear failure mechanism of the composite parts was analyzed by scanning electron microscopy (SEM).