Table of Content

10 October 2020, Volume 31 Issue 19

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Nonlinear Synchronous Robust Control for 3-PPR Parallel Servo Platforms

WANG Xinyu；QIN Wei；SUN Xiaojun；HU Xiaoliang

2020, 31(19):  2269-2275.  DOI: 10.3969/j.issn.1004-132X.2020.19.001

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A 3-PPR parallel servo platform was driven by three servo motors to achieve precise adjustments of plane poses. Aiming at the problems that the trajectory accuracy decreased due to the non-coordination of each axis motions, based on the kinematics analysis and dynamics model of the platforms, a concept of virtual motor was introduced herein. The nonlinear synchronization errors of the platforms were defined, and a nonlinear synchronization robust controller was designed, which made tracking errors and synchronization errors of three axes converge gradually. Results of simulations and experiments show that the control strategy may improve the nonlinear synchronization performance of three axes, effectively improve the system synergy, and the position tracking errors of the platform are less than 0.1mm, which satisfies the requirements of 3-PPR parallel servo platforms in practical applications.

Study on Chip Shapes and Drilling Forces of Low Frequency Vibration Drilling of TC4 Titanium Alloy

ZHAO Ting;XIAO Jiming;FAN Simin;YANG Zhenchao;YANG Fujie

2020, 31(19):  2276-2282.  DOI: 10.3969/j.issn.1004-132X.2020.19.002

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In order to study the chip shapes and the influence law of drilling parameters and vibration parameters on drilling forces (thrust force and torque) during low frequency vibration drilling of TC4 titanium alloy. Based on a self-developed low-frequency vibrating tool holder, low-frequency vibration drilling tests of titanium alloy were carried out by single factor method and orthogonal test method respectively. Chip shapes and drilling forces under different drilling conditions were analyzed. Empirical formulas of thrust force and torque were established. The influence factors of drilling forces were analyzed by visual analyses and variance analyses. Results show that when TC4 titanium alloy is drilled in low frequency vibration, the ratio of amplitude and feed is close to the critical chip breaking value of 0.81, the chip breaking is reliable, and the chip discharging is smooth. The instantaneous drilling force of low frequency vibration presents regular sine wave, and the dynamic component of drilling force is much larger than the ordinary drilling. The thrust force and torque mean may be reduced by  10%~15% and 15%~20% respectively than that of the ordinary drilling. The feed rate has the most significant influences on the drilling forces, the amplitude takes second place, the drilling speed has the least influence. The established vibration drilling experience model error is kept within 10%, which may accurately predict the drilling forces within the selected parameters of the test systems.

Optimization Design of Wind Turbine Airfoils Based on Aerodynamic Performance and Stiffness Characteristics

WANG Quan;CHEN Xiaotian;HU Mengjie;ZENG Lilei

2020, 31(19):  2283-2289.  DOI: 10.3969/j.issn.1004-132X.2020.19.003

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Combining the airfoil functional integration theory and the mathematical model of the blade cross-section stiffness matrix, an integrated design method of aerodynamic performance and structural stiffness characteristics for the medium thickness airfoils was presented. It may make the aerodynamic performance and the blade cross-sectional stiffness characteristics both increase. The aerodynamic performance and structural characteristic  of WQ-B300 airfoils which were designed considering the change of blade cross-sectional ply parameters were compared and analyzed  with DU97-W-300 airfoils. Results show that compared with DU97-W-300 airfoils, the aerodynamic performance and blade cross-sectional stiffness performance of WQ-B300 airfoils improve largely. The flapwise stiffness and edgewise stiffness are increased by 6.2% and 8.4% respectively. This study verifies the feasibility of the novel design method, and provides a good design idea for wind turbine airfoils and blade structural properties with medium or large thickness.

A Dynamic Detection Method of Capillary Forces Based on Microscopic Vision

FAN Zenghua1；RONG Weibin2 ；LIU Zixiao1 ；TIAN Yebing1

2020, 31(19):  2290-2294，2303.  DOI: 10.3969/j.issn.1004-132X.2020.19.004

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For the requirements of real-time detection of capillary forces during the  micromanipulation processes, a dynamic detection method of capillary forces was proposed based on microscopic vision. The positioning of microsphere based on Hough transform and the operation tool tracking method by means of  the normalized sum-of-squared difference  correlation were employed to obtain the real-time location informations. Then, the liquid bridge region of interest  was determined. The contour of liquid bridge was extracted by  using the terminal identification method of liquid bridge based on Shi-Tomasi corner detection. And, the capillary forces were solved. An experimental setup of capillary force measurement was established based on microscopic vision. The detection processes and detection precision of visual inspection method were discussed. Experimental results indicate that the average detection errors of the dynamic liquid bridge are less than 1.65 μN under a plane-sphere configuration. Parameters including the contact angle and liquid bridge volume may be obtained in real time.

Thermal-fluid-solid Coupling Model and Performance Analysis of Single Metal Seals in Cone Bits

MA Yi1,2；NI Yang1；MENG Xiangkai1,2；PENG Xudong1, 2；JIANG Jinbo1,2

2020, 31(19):  2295-2303.  DOI: 10.3969/j.issn.1004-132X.2020.19.005

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The asperity contacts, thermal-mechanics deformations and viscosity-temperature characteristics of seal end faces were considered comprehensively, the interrelated systems of sealing rings and auxiliary seals, lubricant films and sealing mediums were constructed, a thermal-fluid-solid coupling mathematical model was established for single metal seals in cone bits. Furthermore, the influences of key parameters such as environmental pressures and bit speeds on the film thickness distribution, temperature rises and sealing performances of single metal seals were studied. The results show that the gaps of single metal seal end faces gradually evolve from convergent to divergent with the increasing of drilling depths and environmental pressures. The extreme points of film thicknesses and temperature rises migrate from outer diameter to inner diameter, and the critical turning point of environmental pressures is around p0=11 MPa. Under the high pressure conditions, the contact pressures on the inner diameter sides of seal end faces increase, which is not conducive to the formation of lubricating films. The leakage rates and frictional forces of the sealing systems increase with the increasing of bit speeds, while the drilling efficiency may be improved by increasing the bit speeds reasonably under low pressure conditions.

Vibration Reduction Optimization of Constrained Damping Variable Density  RAMP Interpolation Model Based on Global Sensitivity Criteria

YUAN Weidong1,2 ;MA Junsheng1,2 ;HE Honglin3;MIU Guofeng1,2;LANG Xudong1,2

2020, 31(19):  2304-2315.  DOI: 10.3969/j.issn.1004-132X.2020.19.006

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Aiming to solve the topology vibration reduction optimization problems of cylindrical shells with constrained damping, a topology vibration reduction model was built based on variable density RAMP interpolation model, with the minimum model loss factor as optimal objective, and MAC factor was introduced to evaluate the step states of the vibration pattern, so as to find the optimal solution of vibration reduction within the design domain of the iterative lightweight constraints. The interpolation model of the objective sensitivity was deduced, the global optimization algorithm was calculated, and the global sensitivity topological variable optimization criterion method of ∞-norm was established to avoid the partial objective sensitivity of non-convex optimization function participating in the local optimal solution and jump of optimization iteration. The topological optimization analysis for constrained damping structures in vibration control of shell components was carried out by programming. The results show that the global optimization algorithm has wide optimization domain, stable and short iteration processes, and it is easy to obtain effective damping effectiveness by laying some damping materials.

Study on Cutting Temperature Distribution of Coated Tools Based on Thermal Quadrupole Methods

GAO Jian;ZHAO Ziqiang;WANG Wenzhong

2020, 31(19):  2316-2321.  DOI: 10.3969/j.issn.1004-132X.2020.19.007

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In order to study the influences of coating on tool temperature distribution during cutting processes, a three-dimensional transient heat conduction analysis model of coated tools was established, the solving algorithm for three-dimensional temperature field of coated tools was developed based on thermal quadrupole methods and transient temperature distribution of  coated tools was obtained. The effects of coating thickness, thermal convection and thermal resistance at interface on the cutting temperature distribution of coated tools were studied, which provide theoretical bases for the determination of coating thickness, choice of cutting fluid and failure diagnosis of coated tools.

Multi-body Dynamics Analysis and Test Verification for Inertia Cone Crushers

CHENG Jiayuan;REN Tingzhi;ZHANG Zilong ;LIU Dawei ;JIN Xin

2020, 31(19):  2322-2331.  DOI: 10.3969/j.issn.1004-132X.2020.19.008

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Inertial cone crushers had the problems of large amplitude and high energy consumption, which restricted the further development in the industrial field. The multi-body dynamics solution may provide a theoretical calculation method for clarifying the relationship of the main dynamics parameters and the amplitude and energy consumption of the whole crushers. When absolute coordinate method was used for model, the constraints of pure rolling of moving cones were equivalent to holonomic and linear nonholonomic constraints.The differential-algebraic equations(DAEs) with first-order liner nonholonomic constraints were obtained. A LU state space method with variable step size was proposed based on implicit Runge-Kutta integration. To verify the validity of the model and numerical algorithm, under the stable conditions, the simulation results of dynamic response of each measuring point of fixed cone were compared and analyzed
 with the industrial field test results. Results show that driving speed, mass of fixed cone, damping coefficient and mass of moving cone have great influences on the amplitude, but the stiffness coefficient has little effects on the amplitude. Increase of the mass of fixed cone may effectively reduce the specific energy consumption, and increase of the damping coefficient in a certain range may increase the damping dissipation and the specific energy consumption.

Scattering Point Cloud Local Topography Frame Quantization and Feature Recognition Method

SUN Dianzhu1;SHEN Jianghua1;JIA Zongfu1;LI Yanrui2;LIN Wei1

2020, 31(19):  2332-2339.  DOI: 10.3969/j.issn.1004-132X.2020.19.009

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A method for identifying the features of point cloud was proposed based on local topography frame of the surfaces to solve the problems of noise points and feature omissions  in the recognition results of the existing methods. Based on the isolation effect of local central axis of the point cloud on sample points, the non-geodedic neighborhood points in Euclidean neighborhood of the sample points were eliminated, and the local sample model was optimized for the surface construction. The set of quasi-common normal section line point pairs in the local discrete samples was extracted to construct the local topography frame of scattering point cloud. Based on the differences of the included angles of the frame, the surface sample shape was quantitatively analyzed, and the feature areas such as smoothness, boundary, edge and sharp corner were distinguished, so as to realize the robust judgment of the attributes of the center sample point. Experimental results show that the method applies to point cloud with different sampling densities and may significantly reduce the scale of noise points in the point cloud feature identification results and feature omissions.

Root Cause Diagnosis of Head Narrowing in Hot Rolled Strip Based on Comparative Granger Causality

HE Fei1,2;DU Xuefei1,2;WANG Chaojun1,2

2020, 31(19):  2340-2346.  DOI: 10.3969/j.issn.1004-132X.2020.19.010

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A root cause diagnosis model of head narrowing in hot rolled strip was proposed based on the dissimilarity index and comparative Granger causality analysis. Firstly, kernel entropy component analysis (KECA) was used to extract the feature of the original data, and  the dissimilarity evaluation was realized based on the dimensionality reduction under the nonlinear relationship. Secondly, comparative Granger causality analysis model was established. Therefore, the allowable fluctuation range of each causal relationship was calculated by batch data under a large number of normal conditions, which was regarded as a criterion corresponding to judge whether the causal relationship was abnormal. The final root cause diagnosis of the abnormal was determined by the causal relationships. Finally, the diagnosis model of the head narrowing in hot rolling was established to verify the effectiveness of the method using real industrial data. Results show that the method has better performance, which may accurately detect abnormal batches, and locate root cause of abnormal batches.

Optimization of Support Structures Based on Numerical Simulation of SLM Temperature Field

HUANG Renkai;DAI Ning;CHENG Xiaosheng

2020, 31(19):  2346-2354.  DOI: 10.3969/j.issn.1004-132X.2020.19.011

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Support structures were required in SLM processes to support overhanging features in order to hold the work piece in the place and remove heat away from the processes. If heat accumulation in overhangs was too large, it would cause defects such as warpage, collapse, residual thermal stress，et al. Therefore, the influences of support structures on the temperature field of SLM were studied, and  support structures with good comprehensive heat conduction were designed. Firstly, a three-dimensional finite element model of SLM was established. Then, the influences of the traditional support structures on the temperature field were studied. Finally,  support structures were designed and optimized based on the numerical simulation results. It was verified by finite element analyses and manufacturing experiments. Results show that compared with the traditional support structures, the top sintering layers of the thin plates supported by the new support structures have the lowest average node temperature and small temperature difference, showing good comprehensive heat conduction, and the degree of warpages of the thin plates is significantly reduced.

Study on Process Optimization and Properties of PLA/HA Composites by SLS

LIN Kesheng;LIU Jie;ZHANG Yuanling;YAN Chunze

2020, 31(19):  2355-2362，2370.  DOI: 10.3969/j.issn.1004-132X.2020.19.012

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PLA(a biodegradable material) and HA(the main inorganic component) were used as research objects. In order to obtain the optimal parameters of SLS parts of composite materials, the SLS process of pure PLA was optimized firstly. It is found that the tensile strength of pure PLA prepared by SLS are over 23 MPa when the laser energy density range is as 0.040~0.075 J/mm2, and the highest strength is as 27.28 MPa. The PLA/HA composites with different HA contents were processed with laser energy density of 0.040 J/mm2, laser power of 12 W and scanning speed of 1 500 mm/s, to study the influences of HA contents on the microstructure and mechanics properties of PLA/HA composites. The experimental results show that the composite with 10% mass fraction HA has the best mechanics properties and micromorphology. The water contact angle tests also exhibit that the contact angles of the materials decrease from 69.52° to 57.96°, which indicate that the hydrophilicity of the materials is improved.

Study on Material Removal and Surface Quality in Titanium Alloy Grinding with Alumina Hollow-sphere Abrasive Belt

LUO Geshan;ZOU Lai;HUANG Yun;GONG Mingwang

2020, 31(19):  2363-2370.  DOI: 10.3969/j.issn.1004-132X.2020.19.013

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To solve the problems of shortlife of abrasive belt in aero-engine titanium alloy blade grinding, experimental research on abrasive belt grinding processes of titanium alloy samples was carried out on a new type of alumina hollow-sphere abrasive belt. The effects of processing parameters on the surface roughness and grinding ratio of titanium alloy sample processed by alumina hollow-sphere abrasive belt were analyzed through single-factor experiments, and the reasonable grinding parameter ranges of titanium alloy with hollow-sphere abrasive belt were determined. Then the influence degrees of grinding force, grinding speed, feed speedand grain size on surface roughness and grinding ratio were studied through orthogonal experiments to determine the optimal combination of processing parameters for titanium alloy grinding with hollow-sphere abrasive belt.

Effects of Seven-axle HPS Coupling Scheme on Vehicle Body Attitude

TIAN Wenpeng1;DOU Jianming2,3;XU Xinxin3

2020, 31(19):  2371-2378，2387.  DOI: 10.3969/j.issn.1004-132X.2020.19.014

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The HPS system of seven axle platform fire truck was divided into four parts by the center plane of rolling and pitching. After parallel connection of inner suspension cylinders for each part, the four coupling schemes were designed as follows:four part independent, contralateral rod cavity connection, contralateral cross connection and diagonal cross connection. The mathematical model and AMESim simulation model for each HPS were established. The dynamometer characteristics and stiffness characteristics of vertical, rolling, pitching and torsional were analyzed. The body vibration responses of vehicles with these four kinds of coupled HPS were studied under driving, braking and steering conditions on a multi-axle coupled road simulation test rig. The test results are almost the same with theoretical results. Comparison analyses show that the HPS coupling scheme has less effect on vehicle vertical vibration but greater effect on vehicle attitude stability. The scheme of contralateral cross connection is most suitable for seven axle high platform fire trucks with high centroid position and low rollover threshold.

Welding Process Optimization on Robot Welding of the Backward Centrifugal Fan Impeller

WANG Lin1;PAN Jun1;HE Qingchuan1;DING Wei2;GU Liwei2

2020, 31(19):  2379-2387.  DOI: 10.3969/j.issn.1004-132X.2020.19.015

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To ensure weld seam quality and minimize post-welding deformation on robot welding of the backward centrifugal fan impeller, a combined approach integrating TEP-FEM and ISM were applied for welding process optimization. Optimal welding parameters were obtained through a numerical simulation and experimental validation of molten weld pool at weld seam by utilizing TEP-FEM-based Visual-Environment software, in combination with double ellipsoidal heat source model. Given the known inherent strain of weld seams, the post-welding deformations of the backward centrifugal fan impellers were numerically predicted under different welding sequences and welding directions with Weld Planner software based on ISM, the optimal welding sequence and welding direction were located. Pilot production is conducted by utilizing the optimal welding processes on backward centrifugal fan impellers. The resultant post-welding deformations are consistent with the numerical simulations, which meets the quality requirements of the products.

Research on High-speed Milling Transition Criteria and Chip Edge Formation Mechanism of DD5 Ni-based Single Crystal Superalloys

LI Qiang;GUO Chenguang;ZHAO Lijuan;LENG Yuefeng;YUE Haitao

2020, 31(19):  2388-2393.  DOI: 10.3969/j.issn.1004-132X.2020.19.016

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In order to improve the difficult-to-machine property of DD5 Ni-based single crystal superalloys, a high-speed milling transition criteria and chip edge formation mechanism were proposed with the variable of cutting speed based on adiabatic shear theory and using the method of single factor experiments and FEM simulation. According to the measurement results of the chip sawtooth level and intervals, the chip free surface transforms from lamellar structure to serrated structure when cutting speed reaches 37.7 m/min, which shows the milling has entered into high-speed zone. The stress concentrated on the grooves intersected between the chip side and adiabatic shear band induces the longitudinal crack formation and expansion, which causes the transverse and longitudinal stress distribution variations. Then, the transverse cracks were generated. The longitudinal and transverse crack formation was the main reason of the chip edge generation. With the increasing of milling speed, the chip edge morphology transformed from flat and smooth trapezoid to narrow and defective triangle. Compared with the traditional machining, high-speed cutting is beneficial to the reduction of cutting force, chip edge height and intervals, and restrain the lateral crack expansion at the same time.