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.-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.


Wan J.,Tsinghua University | Wan 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.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture | Year: 2016

The edge chipping of holes, which is induced by mechanical machining, restricts the applications of brittle materials. Rotary ultrasonic machining is considered a suitable approach to machine holes in brittle materials with a smaller edgechipping size. However, obvious edge chipping at the hole exit in rotary ultrasonic machining remains observable. In this study, conical diamond core drills with various characteristic angles (u) were designed to further reduce the edgechipping size for rotary ultrasonic machining. Machining tests on quartz glass were conducted to evaluate the effectiveness of this new type of drill. Experimental results show that the conical drill can obviously reduce the edge-chipping size only when certain conditions are satisfied. The mechanism of edge-chipping reduction using a conical drill was revealed by the theoretical analysis and detailed observation of the thrust force and obtained cylinder. To guarantee the feasibility of the conical drill, its characteristic angle should exceed a critical value at a certain feed rate. A higher feed rate requires a higher critical characteristic angle. The other advantage of the conical drill is its ability to suppress the bad effects of increasing the feed rate on the stability of ultrasonic vibration. © IMechE 2015.


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.


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

Drilling induced tearing defects at the hole exit restrict the reliability of C/SiC production. In this study, the drilling induced tearing defects in rotary ultrasonic machining of C/SiC composites were investigated quantitatively. The mechanism of tearing defect formation was studied through the detailed observation of thrust force. Experimental results indicate a positive dependence of tearing defect on the thrust force. A larger thrust force corresponds to a larger drill displacement during the formation process of tearing defect, resulting in larger tearing defect. RUM can averagely reduce the tearing defect at the hole exit more than 60%. Tearing defects can be further reduced by increasing the spindle speed and the ultrasonic amplitude, or decreasing the feed rate. © 2016 Elsevier Ltd and Techna Group S.r.l.


Wang J.,Tsinghua University | Wang J.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | Zha H.,Tsinghua University | Zha H.,Beijing Key Laboratory of Precision Ultra precision Manufacturing Equipments and Control | And 3 more authors.
Precision Engineering | Year: 2016

Edge chipping induced by the mechanical machining of holes in brittle materials restricts the applications of the brittle materials. Rotary ultrasonic drilling is a suitable approach for the machining of holes in brittle materials with a smaller size of edge chipping. A good understanding of the mechanism of edge chipping reduction when employing rotary ultrasonic drilling is helpful to the application and optimization of the drilling technique. In this study, a novel edge chipping mechanism for the machining of holes considering machining-induced cracks was proposed and verified by experiments on quartz glass. The size of the machining-induced crack was evaluated experimentally. Experimental results indicate that the initiation of edge chipping is determined by both the magnitude of the driving force and the size of the machining-induced crack. However, the size of edge chipping strongly depends on the undrilled thickness following a directly proportional relation. Moreover, the geometric similarity of edge chipping is evidence for the consistency of the crack propagation direction when edge chipping begins. Finally, experiments conducted under various machining conditions demonstrate that the reduction of the size of machining-induced cracks in rotary ultrasonic drilling is another important factor contributing to the reduction of the size of edge chipping in rotary ultrasonic drilling, comparing with conventional diamond drilling. © 2016 Elsevier Inc. All rights reserved.


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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