Papers by Author: Jian Zhong Zhou

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Authors: Yong Kang Zhang, Xu Dong Ren, Jian Zhong Zhou, Ai Xin Feng
Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Three different ablative, sacrificial coating were chosen to protect the 6061-T651 alloys from surface melting by laser pulse. This paper analyzes the effect of the paint and foil coatings on the shock wave propagation into the 6061-T651 alloys and the resulting change in mechanical properties. The depths of hardening by laser processing of 6061-T651 alloys up to 1 mm, and the surface hardness reach to 138HV. When the laser pulse energy density increase from 2.8 GW/cm2 to 3.6 GW/cm2, the surface hardness of the black paint, aluminum foil and silica acid black paint samples increase to 19, 27, 36 respectively.
Authors: Y.Y. Xu, Xu Dong Ren, Yong Kang Zhang, Jian Zhong Zhou, Xing Quan Zhang
Abstract: Laser shock processing is an important surface treatment that induces compressive residual stress to components, where the coating plays an important role. This paper deduce a general formula of the optimum thickness of coating according to the law of energy conservation and analysis the influence of coating on residual stress of the titanium alloy in laser shock processing. Titanium alloy with black paint, silica acid black paint and without coating were shocked by laser system respectively. It was found that coating could increase shock pressure amplitude and laser density absorption. Compressive residual stresses at the surface of the sample with the black paint and silica acid black paint are about -212.2MPa and -264.2MPa respectively, while the surface stress on the uncoated specimen is very high tensile stress. The bare surface due to melting and vaporization, leads to a very rough surface. The depth of induced compressive stress could reduce stress corrosion cracking in titanium alloy and improve fatigue lifetime.
Authors: W.S. Tan, Jian Zhong Zhou, J. Guo, Shu Huang, Cheng Dong Wang, B. Gao, J. Sheng
Abstract: . Progressive dies are widely used for the mass production of sheet metal components due to the high productivity, high precision and low cost, but the design of progressive die is a complex and highly specialized procedure. In this paper, a design method of progressive die based on component was presented. Based on the technology of component object module, a number of key techniques in the design of progressive die design were addressed, the knowledge-based design frame system was developed, and the assembling model under UG environment was established. Finally, a practical design process for progressive die of complex panel was demonstrated, and the 3D integrated mould was realized.
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.
Authors: Xia Ji, Jian Zhong Zhou, Hua Feng Guo, Da Peng Xu
Abstract: This paper presents an experimental investigation on the metal components fabricated by laser cladding. In the present study, two process of laser cladding were conducted, that is pre-placed powder cladding and coaxial powder-feed cladding. The effect of processing parameters was studied and optimum set of parameters for the superior surface quality was established by employing the orthogonal design. The fabricated components were subjected to metallographic examinations and micro-hardness measurement. Results indicated that the microstructure of coaxial cladding components was finer than pre-placed powder cladding components. The micro-hardness of the fabricated specimen along and vertical the scanning direction were measured using a HVS-1000 micro-hardness tester with a 200 g applied load. Analysis of the physical properties provided further evidence of differences in micro-hardness produced by different process conditions, and the average micro-hardness value of pre-placed power cladding layer was lower than the coaxial powder-feed cladding layer.
Authors: W. Zhu, Jian Zhong Zhou, M Wang, Shu Huang, Deng Hui Wei, Yu Jie Fan
Abstract: Micro-scale laser shock peening (μLSP) is a flexible and precise process that can potentially be applied to metallic structures in micro devices to improve strength and reliability performance. In order to understand the mechanism of μLSP process, a typical experiment was carried out for copper foils specimen with various process parameters. Surface morphology, deformation and hardness of the specimens were observed and characterized by 3D microscope system and situ nano-mechanical test system respectively. It was found that overlapping rate of laser spot has a little effect on microscopic deformation depth which increases slowly with the increasing of laser energy, and micro-hardness of the laser treated specimens was improved significantly.
Authors: Wen Sheng Tan, Jian Zhong Zhou, Shu Huang, Yu Jie Fan
Abstract: Considering the efficiency and microscale requirement of melting polymer in micro-injection process, we present an experimental analysis of the CO2 laser irradiating Polyamide 12 (PA12) based on the photo-thermal effect of laser-materials interaction. The orthogonal experiments of laser plasticizing were designed by Taguchi method of Minitab software, the influence of process parameters on PA12 plasticization was investigated, and the effect sequence rule of the experiment parameters to melting depth was analyzed. Accordingly,the optimal process parameters combination on PA12 plasticization were obtained,i.e. laser power 3 W, beam diameter 2 mm, scanning velocity 200 mm/min, scanning distance 0.5 mm and environment temperature 20°C.
Authors: Shu Huang, Jian Zhong Zhou, Su Qing Jiang, X.D. Yang, Cheng Dong Wang, Y.C. Dai
Abstract: Typical specimens of AZ31B Magnesium alloy were processed by single point and continuous laser shock peening (LSP). The selected laser energy was 25 J, spot diameter was 8 mm, peening spacing was 8 mm and peening times were 2. The obtained value of residual compressive stresses were -144.3 MPa and -230 MPa for single and continuous LSP respectively, and the magnitude of residual stress was in direct proportion to the depth of deformation in definite micro-deformation range. The average surface micro-hardness in the laser spot zone was 92.42 HV, which increased by 26% as compared to 73.2 HV of substrate, the depth of hardened layer was about 0.3 mm, and the maximum micro-hardness was about 109.86 HV beneath surface of 0.05~0.075 mm. Large amount of crystal chunks appeared at the crystal grain boundaries and inside the grains, and the average grain size decreased from the untreated 7 μm to the peened 4 μm. The results show that the nucleation of fatigue crack can be retarded and the mechanical properties of AZ31B magnesium alloy sheet can be improved greatly with LSP process.
Authors: Yi Bin Chen, Jian Zhong Zhou, Shu Huang, Yue Qing Sun
Abstract: Laser bending is a flexible forming process which forms sheet metal by means of stresses induced by external heat instead of external forces. In this paper, a three-dimensional coupled thermal-mechanical model for numerical simulation is established with finite element code ABAQUS. Some key problems about the simulation of laser bending are investigated in detail, and the reasonable solutions are presented. Taking AISI-1008 steel as an example, numerical simulations are carried out for the complex contour forming of sheet by using Sequentially Coupled Thermal-Stress Analysis technique. Then the corresponding experiments are performed to validate the simulation results. Good correlation between the numerical simulation and the experimental results was demonstrated.
Authors: Xu Dong Ren, Yong Kang Zhang, Jian Zhong Zhou, Yong Yu Gu, Y.Y. Xu, Xing Quan Zhang
Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser system to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Residual stress of Ti6Al4V alloy both before and after LSP with multishocks was analysised. The depth of compressive residual stress was found to have a dependence on the number of shocking layers and a slight dependence on the level of irradiance. Surface stress improvements of more than 50% increases are possible after laser shock processing with either large spot or small spot patterns. The large spot gave a surface stress of 432MPa and a depth of over 1mm. The low intensity small spot gave a surface stress of 285MPa with a depth comparable to the large spot. Laser shock processing induces a compressive residual stress field, which increases fatigue crack initiation life and reduces fatigue crack growth rate.
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