Papers by Author: Jian Jun Du

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Authors: Chao Jun Yang, Yong Kang Zhang, Jian Zhong Zhou, Ming Yong Ni, Jian Jun Du, Xing Quan Zhang, Jun Zhou, Xiang Guang Cao
Abstract: Laser shot peen-forming of sheet metal(or LasershotSM Peening) is a new plastic forming technique for metallic materials, which uses high-power pulsed laser replacing the tiny balls to peen the surface of sheet metal. When the pressure of shock waves induced by laser impresses an inhomogeneous residual stresses distribution in a given depth on the surface of sheet, it responds to the stress by elongating at the peened surface and effectively bending the sheet. In order to investigate the mechanism of laser shot peen-forming, the narrow strip peen-forming experimental of aluminum alloy 6061-T6 was carried out by using a pulsed Nd:glass laser with 0.5Hz repetition-rate. Here, under some given laser energy, laser pulse width, laser beam diameter and pulse repetition frequency and so on, the influence of shot strip interval and shot times on surface residual stresses and the deformation of the sheet is analyzed. The results show that the bending forming of the sheet metal can be found, and the peened surface of sheet metal becomes convex. That the bending increases with shot strip interval increase is not obvious, but it increases with the shot times increase in a proper range of shot times. Besides, because laser shot peen-forming generates compressive residual stresses on the surface, it offers many desirable characteristics in shaped metals and is a valuable technique for producing components for a range of industries.
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Authors: Jian Zhong Zhou, Hui Xia Liu, Chao Jun Yang, Xiang Guang Cao, Jian Jun Du, M.X. Ni
Abstract: Traditional forming process of sheet metal is realized with Die and Mould, this technique lacks flexibility and used in the Volume production. The forming process of sheet metal based on laser shock waves is a novel and developing technique. Laser shock forming (LSF) and Laser peen forming (LPF) are two different forming process of sheet metal, both of them are based on a mechanical effect of shock waves induced by laser. In this paper, after introducing the mechanism of laser shock wave generating, these two forming process and technique feature are analyzed and compared, some research progresses are presented. It is indicated that forming technique based on laser shock waves are of high-flexible and great potential application in the fields of plastic forming of sheet metal.
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Authors: Su Qing Jiang, Jian Zhong Zhou, Shu Huang, Jian Jun Du, Yue Qing Sun, Ji Chang Yang
Abstract: The principle of laser peen forming (LPF) is introduced, the loading model of laser shock wave is established. This paper focuses on applying finite element analyses, instead of a complicated experimental procedure, to predict the development, magnitude and distribution of residual stresses induced by laser impacts on a metal plate, and dynamic process of laser continuous peen forming is realized with the FEM code ABAQUS. Based on the numerical analysis, the laser processing parameters can be optimized and the deformation contour of metal plate can be analyzed. The results calculated by the finite element method are correlated well with the available experimental results. The simulated results also reveal that adjusting the laser energy appropriately can result in an anticipated shape of plate in LPF process.
603
Authors: Jian Zhong Zhou, Yu Jie Fan, Shu Huang, Su Qing Jiang, Jian Jun Du
Abstract: In order to understand and control the process of laser peen forming (LPF) of sheet metal, a developed FEM model was established and the process of LPF was simulated by FEM code ABAQUS. Special emphasis was posed on the part of the model devoted to the analysis of 3D residual stress distribution under laser shock wave loading. With the aid of simulation method, the influence of laser parameters, number of shots, peening tracks and the characteristics of sheet bending were investigated. The results indicate that the bending deformation of metal sheet is relative to laser peening numbers, peening coverage and the plate’s thickness, both upper and back layers of the deformed sheet exists residual compressive stresses.
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Authors: Shu Huang, Jian Zhong Zhou, Yi Bin Chen, Yue Qing Sun, Jian Jun Du
Abstract: An emerging process named laser compound forming of plate was presented by analyzing the advantages of laser thermal-stress forming (LTF) and laser peen forming (LPF) respectively. This technique combined the heat effect of continuous laser and mechanical effect of pulsed laser. Based on introducing the process of laser pre-stressed compound peen forming, the mechanism of plastic deformation and residual stress were analyzed. In order to apply pre-stressed load, a CO2 laser was used to scan SUS304 stainless plate according to the designed tracks firstly, the basic shape were formed and the contours of plate’s surface were measured by the optical scan measuring system, reverse engineering software Imageware was used to establish the virtual models of plate. Then the virtual models were inverted into finite element models by FEM code ABAQUS. The optimum distribution of residual stress field was obtained by adjusting laser parameters and controlling tracks of LPF. Finally, the optimized laser parameters and processing condition were used for LPF experiment. The results indicated that the anticipated shape could be obtained, and both side of the plate hold residual compressive stress after laser compound forming.
343
Authors: Jian Zhong Zhou, Shu Huang, Xia Ji, Jian Jun Du, Chao Jun Yang, Yong Kang Zhang
Abstract: The laser peen forming (LPF) uses high-power pulsed laser beam replacing the tiny medium balls to peen the surface of plate and generate compressive stress near the surface, the metals respond to this residual stresses by elongating at the peened surface and effectively bend the overall shape. In this paper, the deforming process of metal plate induced by repetitive pulsed laser was discussed from theory firstly, and the bending mechanism of LPF was investigated. Then a mathematical model of bending curvature concerning the depth of residual stress was presented, the influence of residual stresses on the deformation of plate was analyzed. Lastly, the line-track-peening experiment for SUS 304 plate was carried out to evaluate the reasonability of the theoretical analysis model.
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Authors: Shu Huang, Jian Zhong Zhou, Jian Jun Du, Yue Qing Sun, M.X. Ni
Abstract: In order to control surface microscopic quality of sheet metal after laser peen forming (LPF), visual numerical analyses for SUS304 plate was employed. Based on the FEM code ABAQUS/CAE, a conversion model of laser shock wave loading was established. The tracks controlling technology of LPF was solved by functional element programs. The micro-plastic flow process of surface material was analyzed, and the change of residual stress distribution as well as micro-topography in real time can be shown with the movement of pulsed laser beam. On the basis of FEM simulation, LPF experiments were carried out. The micro-topography and section analysis were analyzed by AFM, surface residual stress was measured by X-ray diffraction method. It was found that after LPF, the surface irregularity was less than 0.15μm, the variation of average surface roughness was slight, both sides of deformed sheet existed useful residual compressive stress, and the maximum stress was -616.1MPa, meanwhile average surface micro-hardness in the peened zone was higher than the base’s surface. Simulative results show a good agreement with experimental results.
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