Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control

Beijing, China

Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control

Beijing, China
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Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Feng P.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Feng P.,Tsinghua University | Zha T.,China Academy of Engineering Physics
Journal of Mechanical Science and Technology | Year: 2017

The precision cylindrical traverse grinding process of slender bar is very complex for the strongly time dependent properties of the wheel. Therefore, it is very difficult for operators to properly judge the grinding state using naked eyes and ears. This calls for automatic monitoring technology that can monitor the process in precision cylindrical traverse grinding to guarantee machining quality and productivity as well as reduction in cost. This study developed an automatic monitoring system for precision cylindrical traverse grinding of slender bar using Acoustic emission (AE) technology. Grinding tests on molybdenum were conducted under traverse conditions in a conventional cylindrical grinder. It was found that larger radial material removal depth results in larger root mean square value of Acoustic emission signals (AERMS). Based on this, the AERMS was analyzed and used to determine the finishing of spark-out process and the pre-processing of tool alignment. The variation tendency of AERMS in one spark-out process was applied to determine when a wheel wears out and has to be dressed. The experimental results showed that the AE system was effective to monitor the pre-processing of tool alignment, spark-out and wheel wear in precision cylindrical traverse grinding of slender bar. © 2017, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Wang J.,Tsinghua University | Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Zhang J.,Tsinghua University | Zhang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Feng P.,Tsinghua University
Composites Part B: Engineering | Year: 2017

The carbon fibers fracture mechanism depending on fiber orientation significantly affects the machined surface quality of C/SiC composites. The rotary ultrasonic machining (RUM) has been proved to be a beneficial method for C/SiC composites drilling with minor tearing defects at the hole exits. In contrast, the effects of tool vibration on surface topography in RUM of C/SiC composites considering fiber orientation have not been reported. In order for a unique evaluation of surface generating mechanism in RUM of C/SiC composites, several RUM experiments were conducted on 2D-C/SiC composites. The micro structural characteristics of the hole surfaces under various fiber directions, ultrasonic amplitudes and spindle speeds were analyzed. The fiber fracture mechanism in RUM of C/SiC was discovered through theoretical analysis. The results displayed that both fiber cutting direction and cutting speeds significantly affect the surface topography in RUM and CG of C/SiC composites. The tool ultrasonic vibration could contribute to the hole surface quality improvement in RUM of C/SiC composites by the fiber fracture mechanism alteration. With the ultrasonic vibration contribution, the fiber cutting direction tended towards 90° and the cutting speeds were increased. In contrast, due to the non-monotonic effect of the cutting speed on the surface roughness, only when the spindle speeds were relatively low, the higher ultrasonic amplitude apparently contributed to the hole surface quality further improvement. © 2017


Wang J.,Tsinghua University | Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Feng P.,Tsinghua University | Zhang J.,Tsinghua University | And 3 more authors.
Machining Science and Technology | Year: 2017

Ultrasonic vibration is assumed to be stable or unchangeable during the process of rotary ultrasonic machining (RUM) on brittle materials, neglecting the effects of different processing parameters. However, no experimental evidence has been reported to validate this assumption. In this study, the effect of thermomechanical load on the stability of ultrasonic amplitude during RUM was investigated by theoretical analysis and experimental procedures on quartz glass and sapphire. It was shown that the instability of ultrasonic amplitude during the machining process is mainly attributed to variation of resonant frequency under the implementation of thermomechanical load. The thermal effects of ultrasonic vibration decrease the resonant frequency of the ultrasonic machine, while mechanical loading during the machining process increases the resonant frequency. Furthermore, a higher feed rate or a harder material leads to a higher resonant frequency change. The variation of ultrasonic power can be used to review the validity of difference-neglected assumption when different values of processing variables, materials, or even machine tools are used during modeling. The results of this study should be well considered for future references when designing an ultrasonic machine. © 2017 Taylor & Francis Group, LLC.


Wang J.-H.,Kunming University of Science and Technology | Wang J.-H.,Tsinghua University | Wang J.-H.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Du M.-H.,Kunming University of Science and Technology | And 3 more authors.
Applied Surface Science | Year: 2014

The micro-arc oxidation (MAO) has increasingly gained attention as a novel and unique technique for depositing thick, dense, and ultra-hard ceramic coatings on aluminum and its alloys substrates. For the MAO technology, discharge parameter, especially the cathodic current, has an important effect on the characteristics of ceramic coatings. But the effects of the ratio of anodic and cathodic currents on properties of the ceramic coatings on Al alloys are rarely studied. This work investigates the effects of the ratio of anodic and cathodic currents under the constant current density on morphology, phase composition, microstructure, and properties of ceramic coatings on 6061 Al alloys. It is found that the ceramic coatings surface roughness Ra is decreasing, and the hardness of ceramic coatings is increasing with the decrease of the ratio. The ceramic coatings are mainly composed of a large amount of α-Al2O3 and γ-Al2O3. The content of α-Al2O3 in the ceramic coatings increases with the decrease of the ratio. © 2013 Elsevier B.V.


Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Li T.,Tsinghua University | Li T.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 2 more authors.
Journal of Mechanical Science and Technology | Year: 2013

This paper deals with the counterweight optimization of an asymmetrical hybrid machine tool based on dynamic isotropy. The dynamic model is derived and the dynamic manipulability ellipsoid is studied. Based on dynamic manipulability ellipsoid, the dynamic isotropy is defined. Counterweight block and fluid counterweight are presented to balance the weight of moving parts. The mass of the counterweight block is optimized to obtain the maximum dynamic isotropy in the workspace. The dynamic isotropy of the machine tool after counterweight optimization is compared with that before counterweight optimization. Furthermore, the dynamic isotropy of the machine tool with fluid counterweight is investigated and compared with that of the machine tool with counterweight block. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Chen X.,Tsinghua University | Chen X.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 4 more authors.
Nonlinear Dynamics | Year: 2014

Conveyors are important equipment in the painting shop. Conveyors with cantilever beams have low load-carrying capacity and can carry small cars. To solve this problem, this paper presents a novel conveyor that uses redundantly actuated parallel manipulators. A method is proposed to obtain the maximum dynamic load-carrying capacity of the conveyor by optimizing the internal forces of the redundantly actuated parallel manipulators. To improve the dynamic load-carrying capacity, approaches using counterweights are utilized and compared. Furthermore, the maximum dynamic load-carrying capacity of the redundant parallel manipulator is compared with that of its nonredundant counterpart. © 2014, Springer Science+Business Media Dordrecht.


Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Wang L.,Tsinghua University | Wang L.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 2 more authors.
Nonlinear Dynamics | Year: 2013

This paper studies the effect of structure parameters on the dynamic characteristics of a planar PRRRP parallel manipulator. The stiffness model is derived by considering the effect of joint. Based on the stiffness matrix, the vibration equation of this parallel manipulator is investigated to study the dynamic characteristics. The natural frequency is computed, and the effect of Y and Z coordinate on the natural frequency is discussed. Moreover, the sensitivity model of the dynamic characteristic to critical structure parameters is proposed. The thickness of column and leg, the radial stiffness of bearing, and the lumped mass on the end-effector are determined based on the natural frequency and sensitivity index. The results are useful to the structure design of parallel manipulators. © 2013 Springer Science+Business Media Dordrecht.


Wang J.,Tsinghua University | Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Feng P.,Tsinghua University | Feng P.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 2 more authors.
International Journal of Advanced Manufacturing Technology | Year: 2016

The mechanical machining induced edge chipping at hole exit restricts the applications of brittle materials. Rotary ultrasonic machining (RUM) is regarded as a suitable approach for the holes-manufacturing of brittle materials with reduced edge chipping, comparing with conventional grinding. However, obvious edge chipping can still be observed in RUM. In this research, a novel step diamond core drill for RUM was designed to further reduce the edge-chipping size. RUM tests on both quartz glass and sapphire were conducted to evaluate the effectiveness of this new type drill. Experimental results show that the step drill can reduce the edge-chipping size by approximately 60 % without bringing obvious bad influences on the tool life. The mechanism of edge-chipping reduction was revealed by the detailed observation of thrust force and theoretical analysis. In order to guarantee the effectiveness of step drill, the step thickness should be smaller than the thickness of drill end face and the step height should exceed a critical value. © 2016 Springer-Verlag London


Wu J.,Tsinghua University | Li T.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Wang L.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control
Robotics and Autonomous Systems | Year: 2013

This paper investigates the stiffness and natural frequency of a 3-DOF parallel manipulator with consideration of additional leg candidates. The stiffness model and natural frequency are derived, and then the stiffness and natural frequency of the manipulators are compared. The simulations show that the stiffness and natural frequency of the parallel manipulator with one or two additional legs are higher than those of the manipulator without additional leg. The stiffness performance and natural frequency of the manipulator with one additional leg can only be improved little by adding the second additional leg. It is better to develop this parallel manipulator by adding only one additional leg to construct a symmetrical architecture. © 2013 Elsevier B.V. All rights reserved.


Wu J.,Tsinghua University | Wu J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Li T.,Tsinghua University | Li T.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 4 more authors.
Journal of Intelligent and Robotic Systems: Theory and Applications | Year: 2013

This paper constructs a symmetrical 3-DOF parallel manipulator with one and two additional branches, respectively. The conditioning, stiffness, velocity and payload indices are developed to compare the performance of the two parallel manipulators, one with one additional branch, and the other with two additional branches. The optimum performance region with desirable performance is investigated. The simulations show that the redundant manipulator with one additional branch has a larger optimum performance region with the given conditioning, velocity, payload and stiffness performance. The results are not only important for designers to design the 3-DOF parallel manipulator, but also helpful for researchers to determine how many additional branches are added to develop a redundant parallel manipulator. © 2013 Springer Science+Business Media Dordrecht.

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