Table of Content

    25 March 2021, Volume 32 Issue 06
    Review on Management at Mechanical Design and Manufacturing Discipline of NSFC in 2020
    YE Xin, LI Hongwei, YANG Zhibo, LAI Yinan
    2021, 32(06):  631-637.  DOI: 10.3969/j.issn.1004-132X.2021.06.001
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    The applications, evaluations and funding of projects at mechanical design and manufacturing discipline (division Ⅱ of engineering science) of the NSFC in 2020, as well as the research progresses and achievements of the executing and finished projects were reviewed. Specific measures of Mechanical Design and Manufacturing Discipline were stated, such as controlling the COVID-19, performing the new age reform of scientific fund, launching academic exchange and cooperation, enhancing talent cultivation and academic team construction and so on. Finally, the strategic researches on the 14th five-year and medium and long-term development plan were briefly introduced.
    Kinematics of a Novel Three-translation and One-rotation(3T1R) Semi-symmetry Parallel Manipulator
    SUN Chiyu, SHEN Huiping, YUAN Juntang, YANG Tingli
    2021, 32(06):  638-647.  DOI: 10.3969/j.issn.1004-132X.2021.06.002
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    A novel 3T1R parallel manipulator 2RRPaR+2RSS synthesized was proposed based on the topological structure design theory and method of POC equation. The structural analysis was described, the DOF and the POC set of the mechanisms were calculated, and proving that the coupling degree is equal to 2. According to the structural characteristics of the mechanisms and the constraint conditions of the bar, the forward kinematics was established by two-dimensional search method, the inverse kinematics was derived, and the correctness of them was verified. Then, based on the inverse kinematics, the 3D model of the workspace of the mechanisms was calculated by MATLAB programming, and a group of section shapes of different sections in Z direction were obtained. Meanwhile, the rotation ability was analyzed at the section where Z=1000 mm. Finally, the singularities of the mechanisms were analyzed based on Jacobian matrix. The results show that when the main dimensional parameters are the same, the working performances of the proposed 2RRPaR+2RSS parallel manipulator are superior than that of H4 mechanism. Compared with H4 mechanism, the workspace and rotation capability of the proposed parallel manipulator are increased by 27.87% and 4.35% respectively.
    Modeling and Experimental Study on Cutting Forces of 2D Vibration Assisted Micro-milling
    SHANG Peng, HUANG Sishuo, LIU Xiaopeng, YANG Zhuang, LIU Teng, ZHANG Jianjun
    2021, 32(06):  648-657,665.  DOI: 10.3969/j.issn.1004-132X.2021.06.003
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    Based on the mechanics analysis method and the force model of oblique cutting element, considering the influences of tool run-out, size effect and cumulative effect on the instantaneous depth of cut in the actual cutting processes, combining the kinematics characteristics of 2D vibration assisted micro-milling, the instantaneous depth of cut model of 2D vibration assisted micro-milling was established according to the differences of cutting forces for shear areas and plough areas. In order to achieve the purpose of vibration assisted machining, based on the self-designed and optimized non resonant 2D compliant vibration stage, the corresponding 2D vibration assisted micro-milling tests of aluminum alloy Al6061 were carried out, the cutting force curves of Al6061 were simulated by MATLAB software, and the correctness of the established 2D vibration assisted micro-milling cutting force model was verified by comparative analysis. Finally, based on the established cutting force model, the influences of vibration amplitude and frequency on the milling forces were analyzed.
    Fatigue Crack Growth and Nondestructive Quantitative Characterization in Centrifugal Wheels
    WU Yinglong, XUAN Haijun, SHAN Xiaoming, FU Rulong
    2021, 32(06):  658-665.  DOI: 10.3969/j.issn.1004-132X.2021.06.004
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    In order to study the internal fatigue crack growth and the nondestructive quantitative characterization of the centrifugal wheels, the high-speed and low cycle rotating fatigue tests were carried out, and a variety of nondestructive quantitative characterization, fracture analysis and fatigue crack growth simulation were compared. The results show that after the fatigue cracks reach to the surfaces, the fatigue cracks are in the unstable growth stage. During 20 000~21 700 cycles, the simulation values of the interval fatigue crack growth rate are close to the non-destructive characterization values. During 21 700~21 789 cycles, the non-destructive characterization values of the interval fatigue crack growth rate are about 2.5 times larger than that of the simulation values. When the fatigue cracks propagate inside the centrifugal wheel and outside the inclusion areas, the fatigue cracks are in a stable growth stage. Total focusing method(TFM) ultrasonic testing and time of flight diffraction(TOFD) ultrasonic testing may identify the inclusion / fatigue crack internal growth of the centrifugal wheels. At 0 and 6000 cycles, the fatigue cracks are in the inclusion area, the nondestructive characterization values remain unchanged. After 9000 cycles, the TFM ultrasonic nondestructive characterization values of cracks height H and radial length LR increase significantly, the change is similar to the fracture values, but the increased amplitude is smaller.
    Numerical Simulation of Inlet Flow Characteristics of Mixed Flow Pumps during Start-up
    LI Wei, MA Lingling, SHI Weidong, JI Leilei, LI Enda
    2021, 32(06):  666-673,680.  DOI: 10.3969/j.issn.1004-132X.2021.06.005
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    Based on an established three-dimensional closed-loop model including impeller, guide vane, volute, valve, surge tank and pipeline,the numerical simulation for the start-up of mixed flow pumps was carried out. The generation reasons for form of reverse flow were analysed. 
    The disributions of the axial length, axial and circumferential velocities of reverse flow, the variations of reverse flow rates and reverse flow areas at different axial positions were studied. The results show that the numerical computation results are reliable according to the comparison between test and numerical results. The separation flow of suction surfaces and leakage flow of tip clearances are mainly as the reasons for reverse flows. The each reverse parameter increases first and then decreases with time, the axial velocities of main flow and reverse flow present symmetrical distribution in the early stage of the start-up. After 0.8 s, the axial velocities of the reverse flow appear asymmetric distribution. Additional, the farther away from the impeller inlet, the more obvious the asymmetric distribution is. The axial velocity distribution of the main flow presents different changing tendency at different sections. The circumferential velocity gradually presents asymmetric distribution and the velocity direction at the circular section of the inlet pipe gradually deviates from the tangential direction of the circumference. The tendency of reverse flow rate and area at each axial section are basically consistent, and each section gradually presents a maximum return area. 
    Research on Friction Energy Dissipation Mechanism of Rear-view Mirror Spherical Joints Based on Vibration Control
    SONG Haisheng, WANG Lei, TIAN Xuewu, CHEN Zhiyong
    2021, 32(06):  674-680. 
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    An energy dissipation model was established for rear-view mirror spherical joints based on micro-slip friction theory. The micro-slip contact between a rigid ground and an elastic beam was used to simulate the real situation of the joints. The pressure distribution was presented by exponential law and the energy dissipation equation led by micro-slip friction was used to calculate the curves describing the influences of the pressure and the slip areas on energy dissipation. Finally, the model was used to control the idle vibration of the rear-view mirror for a heavy truck, the tests and simulation calculations were done for trouble shooting, and the results show that the established model may describe the friction energy dissipation mechanism of rear-view mirror spherical joints accurately and may provide some references for the general applications of engineering.
    Optimization of Air-jet Structure for Automobile Wind Buffeting Noises
    GU Zhengqi, LIU Zhuangzhi, YANG Zhendong, ZHENG Ledian, YIN Shanbin
    2021, 32(06):  681-688,733.  DOI: 10.3969/j.issn.1004-132X.2021.06.007
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    The research of wind buffeting noise control was currently one of the research hotspots and focuses in the automotive fields. The effectivenesses of air jet method on wind buffeting noise suppression were studied by numerical simulation analysis. The LES was used, as well as a more accurate and effective sound quality evaluation parameters was introduced. The air-jet structures of the sunroof and the right rear window were optimized respectively, and the optimal structural parameters were obtained. The simulation results show that the air-jet structures have a significant effectiveness on the suppression of wind buffeting noises.
    Human-imitative Autonomous Driving Decision-making Algorithm Based on Switched Deep Neural Networks
    WANG Yulong, PEI Feng, LIU Wenru, YAN Chunxiang, ZHOU Weilin, LI Zhi
    2021, 32(06):  689-696.  DOI: 10.3969/j.issn.1004-132X.2021.06.008
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    Human-imitative autonomous driving based on deep neural networks provided a new idea for advanced autonomous driving under complex environments. However, it was difficult for upper driving instructions to enter the network due to the closeness of the network. Therefore, a switched deep neural network was designed, which consisted of convolutional neural network layers and long short-term memory network layers. A feature selection network layer was embedded in the two sub-networks, and then different feature branches were activated by different driving instructions to complete the corresponding driving tasks. Vehicle test results show that the switched deep neural network does not greatly increase the inference time and the different driving tasks will be accomplished according to the different driving instructions, such as the left-turn, right-turn, straight-go at the intersection and obstacle-bypass in the roads.
    Reverse Design and Kinematics Analysis of Reciprocating Linear Mechanisms  Based on Non-circular Differential Gear Trains
    WANG Feixue, LIU Ya, ZANG Xinliang
    2021, 32(06):  697-704.  DOI: 10.3969/j.issn.1004-132X.2021.06.009
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    In order to achieve the desired reciprocating motions concisely and effectively, a new mechanism was proposed by combining non-circular differential gear trains with a rack to realize reciprocating linear motions. It was simple in forms and reliable in operations, through the reasonable pitch curve design, the ideal output motion curves might be obtained. The kinematics analysis of the mechanisms was carried out, and the influences of the pitch curve on the motion characteristics were analyzed. Taking the execution parts following the law of the cosine acceleration and sine acceleration as an example, the non-circular gear pitch curves were obtained in reverse. The influence laws and design criteria of different factors on pitch curve, such as swing angle of output gear, the transmission ratio of the differential gear train and the order of pitch curve, were researched. Besides, the influence laws of the above two motion laws on the transmission ratio, the pitch curve and the characteristics of quick return were compared. The principle prototype of non-circular differential gear trains with rack transmission system was built, and the feasibility and correctness of the new transmission system was verified.
    Charging Path Planning Strategy of Electric Vehicles with Integrating Dynamic Energy Consumption and Network Information
    LIN Xinyou, ZHOU Binhao, XIA Yutian
    2021, 32(06):  705-713.  DOI: 10.3969/j.issn.1004-132X.2021.06.010
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    Aiming at the range anxiety problems of electric vehicles, taking the electric vehicles as the research objects, based on the “vehicle-road-network” intelligent system, the road topology model, impedance evaluation model and vehicle energy consumption model were established, the optimal driving time, optimal energy consumption and comprehensive optimization were as the objectives respectively, and the A* algorithm was used to plan the charging path of electric vehicles. Taking Fuzhou urban cycle as an example, the main driving cycle data was collected, the planned road sections were matched with the driving cycle data to predict the vehicle driving time and energy consumption, and the impedance cost of each objective was calculated by combining the waiting time for charging. The results show that the proposed charging path planning strategy may respectively plan the optimal charging path considering time, energy consumption and comprehensive optimization according to the needs of drivers.
    An Improved DE Algorithm for Solving Hybrid Flow-shop Scheduling Problems
    ZHANG Yuan, TAO Yifei, WANG Jiamian
    2021, 32(06):  714-720.  DOI: 10.3969/j.issn.1004-132X.2021.06.011
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    Aiming at solving the hybrid flow shop scheduling problems, the standard DE algorithm had the disadvantages of easily falling into local extremum. Therefore, an improved DE algorithm was proposed to solve the simulation optimization model based on the minimization of makespan. The proposed algorithm was combined with the reverse learning strategy to generate the initial population, the  adaptive difference factor was further introduced into DE, and the Metropolis criterion of simulated annealing algorithm was introduced in the individual selection mechanism, which effectively improved the global search ability of the algorithm. Finally, the simulation results of the proposed algorithm and the classical algorithms were compared based on different scale examples to verify the effectiveness and superiority of the proposed improved DE algorithm.
    Motion Detection for Soft Manipulators Based on Three-wire Structures
    LI Jingyi, YAO Ligang, DONG Hui
    2021, 32(06):  721-728.  DOI: 10.3969/j.issn.1004-132X.2021.06.012
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    For detecting the movement shape of pneumatic soft manipulators, a kinematic parameter detection device was designed with a measure structure of three wires based on wire-drawing encoders. According to piece-wise constant curvature method, the motion detection model was established for soft manipulator with pneumatic modularization. Based on flexible material characteristics of manipulators, the stiffness method was introduced to derive the map from actuation pressure to configuration shape and kinematic parameters precisely. A novel soft manipulator with pneumatic modularization was presented to verify the accuracy of modelling and the device. The presented manipulator was consisted of silicon backbone, motion chambers and connecting plates for modularizing assembly. The relative errors of motion detection model were obtained via derivation and simulation. Finally, the accuracy of modelling and the features of manipulator in actuation, configuration and movement were verified by tests. The results showed that compared with traditional visual tracking method, the designed device achieved the highly precise detection for movement shapes of soft manipulators.
    Design Method of Undermatching Butt Joints for ELC of Impact Resistance
    DONG Zhibo, LU Weize, XIANG Jingyu, FANG Hongyuan
    2021, 32(06):  729-733.  DOI: 10.3969/j.issn.1004-132X.2021.06.013
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    In order to solve the problems of insufficient impact load-carrying capacity of undermatching butt joints of A921 high-strength steel,based on the idea of ELC, the impact energy was taken as the parameter of the load-carrying capacity of impact load, and the relationship of ELC was established. Through Charpy impact tests of A921 steel specimen, it is found that there is a linear relationship between impact toughness and bending resistance, and the quantitative relationship between the impact toughness and component geometry size is obtained. The impact test results of Q345 steel specimen show that the relationship is still valid, which indicates that the relationship may be generalized to a certain extent. The impact toughness of two materials may be compared and the mechanics response of specimens with different sizes may be predicted by this relationship. Finally, the design scheme of ELC impact resistance was proposed: the optimal joint thickness was calculated to make the base metal and the welded joint fracture consume the same impact energy, then making the thickness as the design conditions of ELC joints under the impact loads, thus the design was carried out in combination with the geometric parameter optimization method of ELC joints.
    Milling Force Modeling of DD5 Ni-based Single Crystal Superalloy with Crystallographic Anisotropic Characteristics
    LI Qiang, GUO Chenguang, ZHAO Lijuan, LENG Yuefeng, YUE Haitao
    2021, 32(06):  734-740.  DOI: 10.3969/j.issn.1004-132X.2021.06.014
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    In order to research the milling force characteristics of DD5 Ni-based single crystal superalloy with crystallographic anisotropy, based on the molecular dynamics simulation, P-N force calculated expression, directional cutting method and slot milling experiments, and based on the preliminary exploration on single crystal alloy milling deformation mechanism, the milling forces along the feed direction of tools were qualitatively modeled, the slot bottom surface quality milled along the different crystal directions on the (001) crystal plane were evaluated. The research results show that the single crystal material removal is depended on the stacking fault structure destruction and chip atoms climb along the slip system, and the milling starts to enter into the stable processes when the bulk stacking fault structures are destoried. Based on the slip system and effective resolved shear stress theories, it is found that the milling force are fluctuated between the range of 18~27 N, the milling force, surface roughness, the adjacent tool feed track spacing and micro peak-valley height difference increase from the crystal direction [110] to [470], [100] and [740], [010]. Therefore, during the milling processes of DD5 Ni-based single crystal superalloy, the milling along the [110] crystal direction may show the best performance.
    New Variable Stiffness Vibration Isolation Method for Vehicle Power Packs
    LIU Yong, ZHOU Yifan, XU Kaitong, JIANG Wei
    2021, 32(06):  741-747,755.  DOI: 10.3969/j.issn.1004-132X.2021.06.015
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    The conventional vibration isolation system of vehicle power packs might not guarantee both of the low-frequency vibration isolation performance and high load-bearing stability. New methods and new technologies were urgently demanded to achieve the unity of them. The influences of the stiffness in different regions on the isolation performance and stability were analyzed, and a novel isolation configuration was proposed, which consisted of preloaded constant spring with variable spring in parallel. Design method of the proposed variable vibration isolators was illustrated, where the stiffnesses and preloads of constant spring were determined based on vibration isolation ratio and payload, and parameters of variable spring were optimized based on stability requirements. The new vibration isolator has high payload capacity and wide frequency domain of vibration isolation, and particularly, the isolation performance in low-frequency working domain is significantly improved. Experimental results on a new special vehicle by adopting the proposed vibration isolation system show that, besides guarantee of sufficient stability, the vibration isolation ratio is increased from 30.3% to 83.5% under rated working conditions.
    Effects of Preheating and Heat Preservation on Microstructure and Properties of Fully Automatic External Welding Seams of X80 Steel Pipes in Severe Cold Environment
    WANG Honghui, DONG Shulei, QIAN Jiankang, TANG Kegang, WANG Zhihang, QIN Xikun, LEI Zhenglong
    2021, 32(06):  748-755.  DOI: 10.3969/j.issn.1004-132X.2021.06.016
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    X80 pipeline steel arc welded was studied with different preheating and heat preservation measures in -30 ℃ severe cold environment. The microstructure characteristics of each region of the joints were observed under different welding conditions. The mechanics properties of the joints were characterized by hardness tests, tensile tests and low temperature impact tests. The results show that the welding seams of X80 steel welded are mainly columnar crystal in severe cold environment, and the filling areas are mainly composed of acicular ferrite, proeutectoid ferrite and a small amount of Widmanstatten structure. With the increasing of preheating and holding temperature, the size and quantity of Widmanstatten structure decrease. The maximum and minimum values of joint hardness appear in the coarse-grained areas and the incomplete recrystallization areas respectively. With the increasing of preheating and holding temperature, the overall hardness of the joints decreases, the low-temperature impact toughness of the weld areas increases, and the tensile strength increases first and then decreases. Preheating and heat preservation are effective measures to obtain joints with good comprehensive performance in severe cold environment. The joint performance is the best when preheating and holding temperature is as 100 ℃.