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Relationship between dynamic characteristics of air film of aerostatic spindle and mid-frequency of surface topography

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Advances in Manufacturing 2022年第3期10卷 428-442页

作者： Dong-Ju Chen Shu-Pei Li Xuan Zhang Jin-Wei Fan Mechanical Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124People's Republic of China

The dynamic characteristics of the gas film of an aerostatic spindle primary affect workpiece waviness in ultra-precision *** improve the machining accuracy of the machine tool and provide a firm theoretical basis for the design of an aerostatic spindle,a simulation model combining transient computational fluid dynamics(CFD)analysis and transient dynamic analysis is established in this study to investigate the dynamic characteristics of the spindle under unstable operating *** on a large eddy simulation,a three-dimensional flow model of an air film in an aerostatic spindle is *** simulation results show that the gas flow in the throttle chamber is turbulent,and that complex vortices are *** dynamic grid modeling technology,a CFD numerical model for the unsteady calculation of the spindle is established,and the dynamic characteristics of the gas film are obtained.A transient dynamic simulation model of an aerostatic spindle is established,and the effect of the nonlinear dynamic characteristics of the gas film on the spindle displacement response is ***,a surface morphology prediction model is *** show that film fluctuation significantly affects the dynamic characteristics of the spindle and subsequently affects the generation of surface ripples on the workpiece.

关键词： Dynamic characteristics Aerostatic spindle Surface formation Ultra-precision flying cutting

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Study on the microcosmic superlubricity mechanism of PVPA affected by metal cations

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Friction 2023年第7期11卷 1150-1164页

作者： Hongyun CAI Caixia ZHANG Fuping LI Mengmeng LIU Tao ZHANG Hongyan CHU Zhifeng LIU Institute of Advanced Manufacturing and Intelligent Technology Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China Key Laboratory of CNC Equipment Reliability Ministry of EducationSchool of Mechanical and Aerospace EngineeringJilin UniversityChangchun 130025China

Hydrophilic polymer coatings on artificial implants generate excellent tribological *** friction properties of polymer coatings are affected by salt ion ***,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt *** results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA *** electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the *** analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be *** study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.

关键词： atomic force microscopy(AFM) superlubricity poly(vinylphosphonic acid)(PVPA) cation adhesion molecular dynamics(MD)simulation

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Reliability prediction model of bolted connection based on uncertainty 10

Reliability prediction model of bolted connection based on u...

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2024 10th International Conference on Applied Materials and Manufacturing technology, ICAMMT 2024

作者： Niu, Nana Zhao, Yongsheng Zhang, Caixia Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Beijing University of Technology Beijing100124 China Institute of Advanced Manufacturing and Intelligent Technology Beijing University of Technology Beijing100124 China

During the service of bolts, their preload exhibits a random decreasing trend due to external loads, affecting contact stiffness and connection reliability. System uncertainties can also lead to preload variations within the same group of bolts. In this paper, we use the Wiener process to model this preload decrease, incorporating drift and wave coefficients to capture temporal variability and system uncertainty. This approach accounts for monotonic preload reduction and random fluctuations, enabling accurate calculations. By integrating the time-varying preload uncertainty into the bolted structure's contact stiffness model, we establish a limit state function for structural failure and assess the reliability of the bolted connection over time. © Published under licence by IOP Publishing Ltd.

关键词： Bolted joints

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Study on chip shape and cutting force model of milling process in any direction of space 66

Study on chip shape and cutting force model of milling proce...

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66th International Conference on Vibroengineering

作者： Wu, Shuiyuan Chen, Dongju Jiang, Zhiwen Mechanical Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Faculty of Materials and Manufacturing Beijing University of Technology Beijing China Beijing Key Laboratory of Advanced Manufacturing Technology Faculty of Materials and Manufacturing Beijing University of Technology Beijing China

This paper considers the calculation process for chip shape and cutting force of milling process in any direction of space. In the milling process with the existence of lead and tilt angle, the edges and boundary curves go through the process of one intersection, two intersections, tangency and non intersection in a milling cycle, thus the chip thickness needs to be calculated in various regions. The milling force is calculated by using the differential method. Then by comparing the milling forces when the lead angle is 5° and the tilt angle is 10° with when there is no inclination angle, the influence of inclination angle on machining process is studied. Meanwhile, by comparing the milling forces calculated by geometric analysis method with those calculated by classical Altintas model, the validity of the proposed method is verified. In addition, by comparing the milling forces obtained using the classical Altintas model with those obtained in published literature, the rationality of the method is further demonstrated. Copyright © 2023 Shuiyuan Wu, et al.

关键词： Milling (machining)

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Exact Inverse Solution for a 7R Manipulator Based on a Novel Screw-Based Sub-problem 23rd

Exact Inverse Solution for a 7R Manipulator Based on a Novel...

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23rd IFToMM China International Conference on Mechanism and machine Science and Engineering, IFToMM CCMMS 2022

作者： Liu, Tiantian Liu, Zhifeng Gan, Tianyue Xu, Jingjing Institute of Advanted Manufacturing and Intelligent Technology Beijing University of Technology Beijing100124 China Key Laborary of CNC Equipment Reliability Ministry of Education School of Mechanical and Aerospace Engineering Jilin China Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Beijing100124 China

ISBN: (纸本)9789811993978

Inverse kinematics (IK) is a significant theoretical foundation for the real application of redundant manipulators. In existing methods, the Denavit-Hartenberg (DH) conversion and screw-based IK sub-problems have been utilized to calculate the inverse solution, but would be limited by some special manipulators’ configurations or cannot obtain exact solutions. In this paper, an exact inverse solution for a 7R manipulator is modeled based on screw theory. In the modeling, firstly assuming that the first joint is known, the total motion of all joints are divided into three steps of operational motions: Rotation about the second, third and fourth joints;Rotation about the five and six joints;And rotation about the last joint. Problems for the first two rotations can be both modeled based on a novel screw-based sub-problem. Finally, the angular displacements of six joints are formulated explicitly in terms of the redundant joint angle. Using the proposed method, all exact solutions can be obtained by traversing values of the redundant angle. The effectiveness and efficiency of the proposed technique is validated using a simulation in MATLAB. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Inverse kinematics

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Research on contact mechanics of a 3D self-affine surface topography using mesh regeneration technology 2

Research on contact mechanics of a 3D self-affine surface to...

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2nd International Conference on Algorithms, High Performance Computing and Artificial Intelligence, AHPCAI 2022

作者： Jiang, Kai Liu, Zhifeng Zhang, Tao Beijing University of Technology Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Beijing100124 China Ministry of Education Key Laboratory of CNC Equipment Reliability School of Mechanical and Aerospace Engineering Jilin University Changchun Jilin130012 China

ISBN: (纸本)9798350334784

Micro-topography directly affects the contact characteristics of rough surfaces. The GW model and MB model have well explained it, which has been recognized by many scholars. To truly explore contact mechanical characteristic of rough surfaces, this paper reconstructs the real surface topography using the mesh regeneration technology, and analyses the contact process of rough surfaces in the elastic and elastic-plastic state. Firstly, based on the real machined surface topography, the fractal parameters are estimated by the FPENN method. Then, the discrete digital WM surface is reconstructed, and the finite element model is generated based on the mesh regeneration method to study different surface contact characteristics considering the interaction of the asperity-substrate. Finally, the ball-surface contact is verified by the UMT-5, compared with the finite element results. The results show that the displacement deformation curve and stiffness curve are closer to the experiment when considering the elastic-plastic interaction. More importantly, plastic deformation of the asperity is inevitable. © 2022 IEEE.

关键词： Finite element method

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Development of Intelligent Post-processing Algorithm for Three Degrees of Rotation Freedom CNC machine tools

Development of Intelligent Post-processing Algorithm for Thr...

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International Conference on mechanical design, ICMD 2021

作者： Zhao, Pengrui Liu, Zhifeng Li, Zhixiong Cao, Zirui Su, Lihang Institute of Advanced Manufacturing and Intelligent Technology Beijing University of Technology Beijing100124 China Beijing Key Laboratory of Advanced Manufacturing Technology Beijing University of Technology Beijing100124 China Mechanical Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Beijing University of Technology Beijing100124 China

ISBN: (纸本)9789811673801

In this paper, the postprocessing algorithm of multi-axis CNC machine tool with three rotating degrees of freedom is studied and simulated. Firstly, the coordinate system and motion characteristics of multi-axis NC machine tool with three rotating degrees of freedom are analyzed, and the calculation method and formula of coordinate transformation of machine tool are presented. Secondly, by using MATLAB software, a universal postprocessor for NC program of three degrees of freedom machine tool is developed. Finally, the complex propeller as the processing object was used to verify the correctness of the post-processing algorithm through the VERICUT CNC machining simulation system. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： machine tools

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Experimental Study on Influence Factors of Clamping Force Attenuation of Threaded Fastener

Experimental Study on Influence Factors of Clamping Force At...

引用

International Conference on mechanical design, ICMD 2021

作者： Zheng, Mingpo Liu, Zhifeng Li, Ying Zhang, Tao Xu, Jingjing Cheng, Yanhong Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Beijing University of Technology Beijing100124 China Key Laboratory of CNC Equipment Reliability Ministry of Education School of Mechanical and Aerospace Engineering Jilin University Changchun130012 China Beijing Key Laboratory of Advanced Manufacturing Technology Beijing University of Technology Beijing100124 China

ISBN: (纸本)9789811673801

The clamping force attenuation of the fasteners at the long-term service used in steam-tight joints may lead to fasteners loosening, joint separation, leakage, or fatigue failure, and even cause a serious accident. The clamping force of threaded fasteners is an intuitive parameter to characterize the service state of the fasteners, but due to the complex service environment, the acquisition of clamping force is difficult. In this paper, a single bolt joint was used to study the influence of the amplitude and frequency of the external cyclic load as well as the tightening torque on the clamping force loosening. The orthogonal experiment was designed to reveal the characters of various factors on the clamping force attenuation of the threaded fasteners. The data is fitted by the double exponential equation to characterize the attenuation of clamping force. The range of clamping force attenuation by various factors was quantitatively analyzed for further prediction and control. According to the percentage of the clamping force attenuation, it can be divided into two stages: the rapidly decline stage and the gradually decrease stage. The experimental observations could be used to provide a reference for the assessment of service status. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Cyclic loads

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Methodology for optimization of preload in a bolted-flange connection based on Markov theory 9

Methodology for optimization of preload in a bolted-flange c...

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9th International Conference on Advanced Manufacturing technology and Materials Science, AMTMS 2021

作者： Wang, Yuezhen Liu, Zhifeng Li, Ying Yang, Congbin Institute of Advanced Manufacturing and Intelligent Technology Beijing University of Technology Beijing Beijing100124 China Key Laboratory of CNC Equipment Reliability Ministry of Education Jilin University Jilin Changchun130012 China Mechanical Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Beijing University of Technology Beijing Beijing100124 China

The bolted-flange connection is one of the most popular detachable mechanical joints in mechanical flange connection. It is well known that bolted-flange joints need to be tightened to meet the assembly performance in practical engineering applications. However, the dispersion of the pre-tightening force caused by the elastic interaction between the bolts has a serious impact on the sealing and safety of the product, and therefore the optimization of bolt preload has always been a hot spot in the assembly research field. Combining mathematical theory and experimental data, this paper proposes an optimization model for uniformly distributed preload based on the Markov theory. The torque method was utilized to fasten the bolt-flange joint. The bolt pre-tightening force in the final state was collected and used as sample data. A state transition model was constructed to determine the state transition matrix. Ultimately, an iterative model of the preload was deduced, and the rationality of the model was verified through experimentation. The proposed optimization method of bolt preload can be applied to determine the initial preload of each bolt. This method improves the assembly efficiency and accuracy, which provides a theoretical approach to effectively guide the tightening work of bolted-flange connections. © 2022 Institute of Physics Publishing. All rights reserved.

关键词： Bolts

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A Closure Contact Model of Self-Affine Rough Surfaces Considering Small-Meso-Large Scale Stage Without Adhesive

SSRN

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SSRN 2024年

作者： Jiang, Kai Liu, Zhifeng Zhang, Tao Wang, Yida College of Mechanical Engineering Chongqing University of Technology Chongqing400054 China Key Laboratory of CNC Equipment Reliability Ministry of Education School of Mechanical and Aerospace Engineering Jilin University Changchun Jilin130012 China Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Beijing University of Technology Beijing100124 China Shandong Institute of Space Electronic Technology Shandong Yantai264000 China

Contact interfaces is essential for the dynamic response of the bolted structures. To accurately predict the dynamic characteristics of bolted joint structures, a fractal extension of the segmented scale model, i.e., the JK model, is proposed in this paper to comprehensively analyze the dynamic contact performance of engineering surfaces and revisit the multi-scale model based on the concept of asperities. The influence of asperity geometry, dimensionless material properties, and elastic, elastoplastic, and full plastic mechanical models of a single asperity is established considering the asperity-substrate interaction. Then, a segmented scale contact model of rough surfaces is proposed based on the island distribution function in a strict sense. The mechanical contact process of determining rough surfaces is divided into small-scale, medium-scale, and large-scale stages. Moreover, cross-scale boundary conditions, i.e., al1', al2', and al3', are provided through strict mathematical deduction. Finally, the reliability of the proposed model is verified by setting up three groups of modal vibration experiments. © 2024, The Authors. All rights reserved.

关键词： Distribution functions

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