Table of Content

25 August 2022, Volume 33 Issue 16

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Establishment and Research of Prediction Model of Discharge Gap Voltages in Discharge Arc Milling

ZHANG Jin, HAN Fuzhu,

2022, 33(16):  1891-1896.  DOI: 10.3969/j.issn.1004-132X.2022.16.001

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It was difficult to directly measure the discharge gaps during arc milling. The changes of the discharge gaps were judged by the changes of the discharge gap voltages. The system identification theory was used to determine the structure and model parameters of the discharge gap voltage prediction model. The method for establishing the prediction model was elaborated, and the degree of fit of the prediction model was verified by experiments. The experimental results show that the fit accuracy of the prediction model decreases with the increase of the fitting time. Therefore, the recursive least squares method was used to perform the online discharge gap voltage measurements. It is predicted that the average error of online prediction is as 6.82%. The results show that the discharge gap voltage prediction model may predict the discharge gap voltage stably and effectively one step ahead, with fewer model identification parameters and high prediction accuracy.

Influences of Crack Faults on TVMS of Gear Teeth

MENG Zong, LI Jiasong, PAN Zuozhou, PANG Xiushen, CUI Lingli, FAN Fengjie

2022, 33(16):  1897-1905，1911.  DOI: 10.3969/j.issn.1004-132X.2022.16.002

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 Aiming at the decreases of TVMS caused by cracks, the influence laws of crack faults on TVMS were studied. Firstly, the complete tooth profile curve was constructed. The influences of the coupling effects of adjacent teeth on TVMS were analyzed. The calculation formula of TVMS was modified based on the traditional potential energy method. Secondly, the location of crack initiation points was determined by FEM. A crack curve extending along the depth was proposed. The effects of crack depth on TVMS and load sharing ratio were analyzed. A model of mid-early fault cracks with both of length and depth was studied. Finally, the models of different fault gear pairs were constructed. FEM was used to verify the results of cracks along the depth. The results show that the potential energy method is consistent with the FEM.

Research on Wheel Grinding Trajectory Algorithm of Straight Blade Flank Faces of Drill Tips

WANG Chengbing, XIONG Jianjun, JIANG Lei, MA Shuwen

2022, 33(16):  1906-1911.  DOI: 10.3969/j.issn.1004-132X.2022.16.003

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In order to improve the machining accuracy of the flank faces of drill tips and ensure the flexibility of the grinding position and attitude of the wheels, a method of solving the grinding wheel trajectory of the straight blade flank faces in the CNC grinding processes was proposed. The structural parameters of straight blade flank faces of drill tips were defined, and the mathematical model was established. The coordinate of the straight blade flank faces of drill tips and the datum grinding attitude of the wheels were defined. Then, the coordinate transformation matrix was used to describe the motion mode of the wheels, and the method of the grinding positions and attitudes of wheels was deduced based on the workpiece coordinate system by means of the kinematics principle. With the proposed method, the precision of straight blade flank faces of drill tips may be ensured. Meanwhile, the grinding positions and attitudes of the wheels may be flexibly adjusted. The computational program was developed based on VC++, and the effectiveness of the algorithm was verified with machining simulations.

Wettability of High-performance Aluminum Alloy Surfaces Machined Longitudinal-torsion Ultrasonic-assisted Milling

ZHAO Chongyang, LU Junyu, WANG Xiaobo, ZHAO Bo

2022, 33(16):  1912-1918，1927.  DOI: 10.3969/j.issn.1004-132X.2022.16.004

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To address the phenomenon that ultrasonic-assisted machining might improve the microstructural properties of high-strength aluminum alloy surfaces by forming micro-scoring surfaces on the workpiece surfaces, an experimental study on the microstructure of surfaces milled by single-excitation rotary ultrasonic longitudinal torsion composite milling was conducted: the effects of machining parameters on the water contact angle were analyzed based on the water contact angle theory and the kinematic theory of longitudinal torsion milling; secondly, a single-excitation ultrasonic longitudinal torsion milling test platform was built, and the orthogonal method was used to study the effects of different machining parameters on the surface roughness, milling forces and surface wetting performances. The results show that the surface quality is best when the ultrasonic amplitude is as 4 μm, and the cutting speed and feed are positively correlated with the surface roughness and water contact angle; the surface water contact angle under ultrasonic machining mode is larger than that of the normal mode, and the surface water contact angle machined by low amplitude is larger than that of high amplitude during ultrasonic machining. And the differences between the surface water contact angle machined by high amplitude and low amplitude are not significant when the speed reaches a certain amount. Suitable machining parameters under the ultrasonic longitudinal twist processing method may reduce the roughness of the machined surfaces and change the wettability of the surfaces.

Configuration Synthesis of Working Mechanisms of Face-shovel Hydraulic Excavators by Adding Ⅱ-class Basic Bar Group

LIU Wenlan, YU Haixia, QU Huaiyu, MA Pengfei, GAO Xiaojun, WANG Jiansen

2022, 33(16):  1919-1927.  DOI: 10.3969/j.issn.1004-132X.2022.16.005

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A method of configuration synthesis for the working mechanisms of face-shovel hydraulic excavators was proposed， that was the superposition method based on Ⅱ-class basic bar group. Considering the number and property of degree of freedom（DOF）and driving elements of the working mechanisms of a face-shovel hydraulic excavator， the structure was divided into basic structure and auxiliary links. Eight constraints for configuration synthesis were given. Then， according to the number of joints on the auxiliary links， Ⅱ-class basic bar group RRR was added in five cases to carry out configuration synthesis of the working mechanisms of face-shovel hydraulic excavators， and a series of configurations with 12 links were obtained. Three configurations were selected from them， and in view of the multi-loop coupling structural characteristics of those three configurations， their DOFs were analyzed by using the link-demolishing and equivalent method. Further， the simulation models of three working mechanisms were established， and the motion simulation was carried out， which verified the feasibility of the proposed method. 

A Real-time Control Method for Optimal Overall Performances of Planar Redundant Robots

RONG Yu, DOU Tianci, ZHANG Xingchao, ZHANG LeiZ, HAO Jingyu

2022, 33(16):  1928-1939.  DOI: 10.3969/j.issn.1004-132X.2022.16.006

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The concept of redundant robot structure design with centralized driving layout was proposed. In the inverse kinematics of robot, a prespecified space dimensionality reduction method was proposed based on weighted M-P pseudo-inverse, and the weighted matrix was analyzed numerically. The swing amplitudes of each joint angles were changed by changing the values of the elements on the diagonal of the weighted matrix and then changing the instantaneous velocity. The dynamics analysis of a planar 4R redundant robot was carried out, and the total energy, total torque and total time were taken as the optimization objectives. The particle swarm optimization method was used to optimize the three objectives simultaneously, and the motion end time was optimally obtained when the total performances of the redundant robot were reached. The experimental results show that the proposed method is feasible.

Tool Wear Detection Based on Improved CNN-BiLSTM Model

LIU Huiyong, ZHANG Song, LI Jianfeng, LUAN Xiaona,

2022, 33(16):  1940-1947，1956.  DOI: 10.3969/j.issn.1004-132X.2022.16.007

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In the automatic cutting processes， accurate and reliable detecting of tool wear states was the key to ensure the processing quality and efficiency. Aiming at the problems of tedious feature extraction with low accuracy and traditional deep learning network could not extract the hidden information of data comprehensively， an improved model was proposed based on integration of CNN and BiLSTM by adding batch standardization layer to CNN and using two BiLSTM layers. The model could automatically extract the spatial and temporal features of cutting forces， vibration and sound signals after wavelet threshold denoising and down sampling to realize tool wear detection. Compared with CNN-BiLSTM model and traditional deep learning model， the accuracy and stability of the improved model are greatly improved. The proposed method provides technical support for accurately detecting the tool wear states in the automatic machining processes and improves the production efficiency and machining quality. 

Research on Open Control Systems and Tangent Tracking of Friction Stir Welding Machines

LIU Liye, CHEN Yongliang, TANG Weili, WEI Yunpeng, SUO Shucan

2022, 33(16):  1948-1956.  DOI: 10.3969/j.issn.1004-132X.2022.16.008

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 Most of the existing friction stir welding equipment lacked effective monitoring of processing variables. The establishment of an open control system was an effective means to solve this problem. However， there were two major differences between the friction stir welding processes and the traditional metal cutting processes， namely the welding inclination and arc tangent tracking functions. Existing equipment integrated the arc tangent tracking function into the control system， which led users to special design for this function if they studied open controllable systems， which in turn led to longer equipment development cycles and to increase costs. An open control system was built based on Ether CAT， and then a gantry type friction stir welding machine (tool) was taken as an example， the D-H method was used to derive the machine (tool) full-parameter forward and reverse kinematics mathematical model， and a simple plane the two-dimensional arc tangent tracking method was proposed， which might complete friction stir welding without studying the three-axis interpolation algorithm on the basis of the existing two-axis arc interpolation. Finally， a typical welding seam trajectory was selected for motion simulations and welding tests， which verified the correctness of the parameterized kinematics model of the machine (tool) and the feasibility of the arc tangent tracking method. 

Posture Optimization Based on Stiffness Orientation Method for Industrial Robotic Milling

YANG Jing, ZHANG Xiaojian, WU YiYE Songtao, YAN Sijie, LU Jialin

2022, 33(16):  1957-1964.  DOI: 10.3969/j.issn.1004-132X.2022.16.009

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In order to solve the problems of the difficulty of determining the principal stiffness directions of industrial robots due to asymmetric structures and mode coupling chatters occurred in robotic milling processes caused by poor rigidity, a stiffness orientation method was proposed.Moreover, the stability of milling processes was improved by controlling the robot functional redundancy and optimizing the posture. Firstly, the stiffness ellipsoid in Cartesian coordinate system at the end of industrial robots was calculated to determine robotic principal stiffness directions in the cutting planes. Then, the stability criterion of mode coupling chatters was obtained by establishing the dynamics model of the machining system. Further, based on the stiffness orientation method, a posture optimization algorithm was proposed for robotic milling. Cutting experiments confirm that stability in robotic milling along the given trajectory may be guaranteed through the optimization of industrial robot configurations without changing other parameters.

Research on Thermal Characteristics of Motorized Spindles Based on Digital Twin

XU Rongfei, FAN Kaiguo

2022, 33(16):  1965-1971.  DOI: 10.3969/j.issn.1004-132X.2022.16.010

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 In order to improve the simulation accuracy of thermal characteristics， adigital twin-based simulation method for thermal characteristics was proposed. The physical space of digital twin for thermal characteristics of a motorized spindle was built based on the IoT data acquisition system. A digital twin system for thermal characteristics was developed based on Java， ANSYS and MATLAB. Correction models of thermal boundary conditions were proposed based on the temperatures of thermal key points. Data mapping between physical space and virtual space and digital twin for thermal characteristics of motorized spindles were realized using the proposed method. Experimental results show that the simulation accuracies of temperature field and thermal deformation are as 98% and 95% respectuely using the proposed digital twin-based simulation method for thermal characteristics， which effectively improves the accuracy of finite element analysis of thermal characteristics. 

Analyses of Limit Reduction and Processing Parameters in Soft Reduction Processes of Continuous Casting

QIN Qin, WANG Wenzhi, ZHANG Sheng, ZANG Yong

2022, 33(16):  1972-1982.  DOI: 10.3969/j.issn.1004-132X.2022.16.011

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In view of the characteristics of drastic changes in shell thickness and temperature field of continuous casting billets in each sector, the variation law of limit reduction of billets in different reduction intervals was studied systematically. Taking A36 steel continuous casting billets as the research object, a three-dimensional thermodynamic coupling model including billet, casting roller and the multi-body contact between them was established. Under the premise of ensuring the processing quality, the limit reduction, reduction zones and reduction distributions of the casting billets were studied systematically. The results show that the limit reduction of A36 steel billets from the first section of bending section to the tenth section of horizontal section is as 3.87~6.96 mm. The suitable reduction sections at the end of solidification are the 8th～10th sections, and it is suitable to distribute the reduction evenly in these reduction sections.

Effects of Frequency Features Generated in Machined Surface on Subsurface Temperature Field of KH2PO4 Crystals

SHU Zihao, PANG Qilong, KUANG Liangjie

2022, 33(16):  1983-1991.  DOI: 10.3969/j.issn.1004-132X.2022.16.012

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To analyze the influences of surfaces topography on the laser damage and performance of KH2PO4（KDP） crystal, the frequency features of machined surface KDP crystal surfaces were extracted and reconstructed by power spectral density and continuous wavelet transform. Wave optics theory was used to analyze the influences of frequency features on the subsurface light temperature fields of KDP crystals irradiated by 1.064 μm laser wavelength with the power of 20 MW/μm2 for 1ns. The results show that temperature of KDP crystals becomes larger with wavelength of surface frequencies closer to incident laser wavelength(1.064 μm). If the wavelength is over 20 μm, temperature of KDP crystals is unchanged with the changing of frequency features. The obvious wavelengths on the machined surface of KDP crystals obtained by cutting experiments are as 14 μm, 50 μm and 140 μm respeclively, and the subsurface temperature of KDP crystals affected by these frequency features rises are as 56 K, 22 K and 12 K. Maximum temperature of KDP crystals increases with the increasing of amplitude under the same wavelength. With the increasing of surface frequency wavelength, the position of the maximum temperature extends to the interior of the KDP crystals.

Prediction of Five-point Bending Springback of Ti-6Al-4V Plates Based on Variable Elastic Modulus

QU Cong, MENG Zhijuan, ZHAO Liang, CHEN Yao, MA Lidong

2022, 33(16):  1991-1999.  DOI: 10.3969/j.issn.1004-132X.2022.16.013

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Larger springback might be produced in the bending processes of the Ti-6Al-4V titanium alloys, and the elastic modulus has a greater impact on the springback, but previous studies did not considered the changes of elastic modulus during the plastic strain changes of the materials. The uniaxial tensile tests and cyclic loading-unloading tests of Ti-6Al-4V titanium alloys were carried out to determine the anisotropy parameters and the change rule of elastic modulus with plastic strains herein. Then, a mathematical model of variable elastic modulus of Ti-6Al-4V titanium alloys was established. Based on two different constitutive models of YLD2000-2D yield criterion with variable elastic modulus and Mises isotropy, the five-point bending processes of Ti-6Al-4V titanium alloy sheets were numerically simulated at room temperature. In order to verify the results of the numerical simulation,the five-point bending experiments of the Ti-6Al-4V sheets were carried out at room temperature. The results show that the former significantly improves the springback prediction accuracy of Ti-6Al-4V titanium alloys, which is an increase of 31.18% compared with the latter.

Research on Multi-objective Optimization of Vehicle Compatibility of Automobile Exhaust Thermoelectric Generator Systems

QUAN Rui , LI Tao , YUE Yousheng , CHANG Yufang , TAN Baohua

2022, 33(16):  2000-2007，2015.  DOI: 10.3969/j.issn.1004-132X.2022.16.014

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When the automobile exhaust thermoelectric generator system was connected to the exhaust pipe of the engine, the airflow would be changed. In order to minimize the impacts on the original performance of the engines and improve the electrical power generation performance of the automobile exhaust thermoelectric generator systems, a hexagonal heat exchanger used for an automobile exhaust thermoelectric generator system was optimized for the on-board compatibility with the goal of the highest average surface temperature and the smallest pressure loss. A finite element simulation model of the heat exchanger was built based on CFD software to study the influences of the inlet gas speed of the heat exchanger on the surface temperature and pressure loss, as well as the influences of the inlet gas temperature on the surface temperature. The fins length, fins angle, fins width and fins spacing were taken as the design variables. The Gaussian process regression proxy model was established based on the test data, and the grey wolf algorithm was used to obtain the optimal solution in the multi-objective optimization function space. The results show that compared with the classical NSGA-Ⅱ algorithm, the Pareto solution set obtained by multi-objective grey wolf algorithm is more concentrated and the evaluation index is higher. The optimized heat exchanger with multi-objective grey wolf algorithm has a lower surface average temperature than that of several structures before optimization, but the pressure loss is significantly reduced. Compared with the cavity structure heat exchanger, the surface average temperature and pressure loss of optimized heat exchanger increase, and the pressure loss increasing amplitudes are within the acceptable ranges. The optimized heat exchanger may effectively take into account the power generation of the automobile exhaust thermoelectric generator systems and the on-board compatibility.

A Double-layer Energy Management Strategy for HEVs under Urban Traffics

TANG Xiangjiao, GAO Zucheng, ZENG Lingquan, ZHAO Yifan

2022, 33(16):  2008-2015.  DOI: 10.3969/j.issn.1004-132X.2022.16.015

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The optimal speed planning for connected HEVs under urban traffics with multiple intersections was investigated. The feasibility of using the double-layer pseudo-spectral method to optimize the energy management strategy of HEVs was discussed. Firstly, based on signal phases and timing, the optimal speed was obtained via pseudo-spectral method to ensure that the vehicle might pass through the intersections without stopping. Then, based on the planned speed, the power distribution between engine and battery was arranged with the goal of minimizing vehicle energy consumption. Simulation results show that the proposed method may reduce fuel consumption by 6.9% compared with manual driving, and the effectiveness of the proposed strategy is further verified by real vehicle tests.