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Characteristic of energy input for laser forming sheet metal

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Chinese Optics Letters 2003年第10期1卷 606-608页

作者：李俐群陈彦宾封小松 state key lab.ratory of Advanced welding production and technology Harbin Institute of Technology Harbin 150001

Laser forming is a process in which laser-induced thermal deformation is used to form sheet metal without a hard forming tool or external forces. The energy input of laser beam is the key factor for the temperature and stress distribution of sheet metal. The purpose of this work is to investigate the influence of energy input condition on heat input and deformation angle for two-dimension laser forming. Variations in heat input resulting from material deformation was calculated and discussed in this paper at first. Furthermore, in laser forming under the condition of constant laser energy input, the effects of energy input mode on deformation angle and temperature field were investigated.

关键词： Laser beams Metal forming Sheet metal

Three dimensional numerical simulation of welding temperature fields in stainless steel

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China welding 2004年第1期13卷 11-15页

作者：董志波魏艳红刘仁培董祖珏 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology Harbin welding Institute

Three kinds of mathematical models representing welding heat sources are presented. Among them, Gaussian model and double ellipsoidal model are used to analyze the thermal distributions with finite element method. At the same time, this paper analyzed the influences of the heat source models, the latent heat and the welding parameters on the temperature distributions. The comparisons between the simulated results and the experiments show double ellipsoidal model is good for three-dimensional numerical simulations. Furthermore, the adaptive mesh technique is applied in the three-dimensional model which greatly reduces the number of nodes and elements in the simulation.

关键词： double ellipsoidal model adaptive mesh technique welding temperature field stainless steel

Influence of shielding gas pressure on welding characteristics in CO2 laser-MIG hybrid welding process

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Chinese Optics Letters 2006年第1期4卷 33-35页

作者：陈彦宾雷正龙李俐群吴林 state key lab.ratory of Advanced welding production technology Harbin Institute of TechnologyHarbin 150001

The droplet transfer behavior and weld characteristics have been investigated under different pressures of shielding gas in CO2 laser and metal inert/active gas （laser-MIG） hybrid welding process. The experimental results indicate that the inherent droplet transfer frequency and stable welding range of conventional MIG arc are changed due to the interaction between CO2） laser beam and MIG arc in laser-MIG hybrid welding process, and the shielding gas pressure has a crucial effect on welding characteristics. When the pressure of shielding gas is low in comparison with MIG welding, the frequency of droplet transfer decreases, and the droplet transfer becomes unstable in laser-MIG hybrid welding. So the penetration depth decreases, which shows the characteristic of unstable hybrid welding. However, when the pressure of shielding gas increases to a critical value, the hybrid welding characteristic is changed from unstable hybrid welding to stable hybrid welding, and the frequency of droplet transfer and the penetration depth increase significantly.

关键词： Laser beam welding Pressure Welds

Investigations of microstructures and properties in electron beam welded joints of TiAl to TC4

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China welding 2007年第3期16卷 10-13页

作者：陈国庆何景山张秉刚冯吉才 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology

The normally centered electron beam and non-centered electron beam welding of TiAl to TC4 was investigated in order to analyze the electron beam weldability between TiAl/TC4 dissimilar materials. Macroscopic cold crack easily occurred near TiAl substrate in the joints. The optimal tensile strength was related to the welding heat input. The weld structures were composed of bulky columnar grains and equiaxed grains. The isolated phases consisted of large quantities of α2 -Ti3Al phase, small quantity of B2 phase, γ-TiAl phase and YAl2 phase. Insufficient melting of the base metal occurred in the weld when the beam position leaned to the TC4 side. The tensile strength could be improved when the deflection was limited in the optimum range. Otherwise, non-fusion zone was easily generated in the weld, which led to the low tensile strength.

关键词： TiAl intermetallie compound TC4 alloy electron beam welding non-centered welding

Effect of cooling rate on the microstructure of electron beam welded joints of two-phase TiAl-based alloy

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China welding 2007年第2期16卷 11-15页

作者：陈国庆张秉刚何景山冯吉才 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology

The analysis of the microstructural characterization and phase composition of electron beam welded joint zones of Ti- 43Al-9V-O. 3Y alloy has been done in this study. The welded seam is mainly composed of B2 phase, the partial γ ＋ α2 twophase lamellar structure and granular γm phase. And the lanthanon Y existed as YAl2 phase and served as grain refined. The impact of different cooling rates on joint microstructure, fracture characteristic and tensile strength were investigated. The high cooling rate restrained the structural transformation and resulted in the ordering structure. The fracture of the joint was brittle cleavage fracture because the ordering structure went against restraining the crack propagation. With the decrease of cooling rate, the transformation amounts of lamellar structure increased, and the fracture presented the layered and crosslayered characteristic.

关键词： TiAl-based alloy electron beam welding cooling rate structure

Advances in selective conversion of carbohydrates into 5-hydroxymethylfurfural

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Green Energy & Environment 2024年第9期9卷 1384-1406页

作者： Jie Liang Jianchun Jiang Tingting Cai Chao Liu Jun Ye Xianhai Zeng Kui Wang Institute of Chemical Industry of Forest Products Chinese Academy of Forestry National Engineering Lab.for Biomass Chemical Utilization Co-Innovation Center of Efficient Processing and Utilization of Forest Resources Nanjing Forestry University College of Energy State Key Laboratory of Physical Chemistry of Solid Surfaces Xiamen University

Converting carbohydrates into 5-hydroxymethylfurfural(5-HMF) is an attractive and promising route for value-added utilization of agricultural and forestry biomass resource. As an important platform compound, 5-HMF possesses high active furan structure with hydroxymethyl and aldehyde group for production of various bio-chemicals and materials, meanwhile, which suffer from low stability and poor yield during the industrial biorefinery process. Hence, selective production of 5-HMF with high-yield and low-cost has attracted extensive attention from scientific and industrial researchers. This review sorted and described the latest advanced research on solvent and catalyst system, as well as energy field effect for production of 5-HMF with different feedstock in detail, emphatically discussing the solvent effect and its synergistic effect with other aspects. Besides, the future prospects and challenges for production of 5-HMF from carbohydrates were also presented, which provide a profound insight into industrial 5-HMF process with economic and environmental feature.

关键词： 5-Hydroxymethylfurfural Biorefinery Solvent Selectivity Carbohydrate

Weld pool boundary and weld bead shape reconstruction based on passive vision in P-GMAW

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China welding 2006年第2期15卷 20-24页

作者：闫志鸿张广军高洪明吴林 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology

A passive visual sensing system is established in this research, and clear weld pool images in pulsed gas metal arc welding （ P-GMA W） can be captured with this system. The three-dimensional weld pool geometry, especially the weld height, is not only a crucial factor in determining workpiece mechanical properties, but also an important parameter for reflecting the penetration. A new three-dimensional （3D） model is established to describe the weld pool geometry in P-GMAW. Then, a series of algorithms are developed to extract the model geometrical parameters from the weld pool images. Furthermore, the method to reconstruct the 3 D shape of weld pool boundary and weld bead from the two-dimensional images is investigated.

关键词： weld pool visual sensing geometrical model image processing 3D reconstruction

Simulation and experiments of ultrasonic propagation in nickel-based alloy weldments

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China welding 2008年第4期17卷 17-21页

作者：赵新玉刚铁赵雪梅 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology

In order to obtain good understanding of complicated beam propagation behaviors in nickel-based alloy weldments , ray tracing simulation is established to predict the ultrasonic beam path in a special welded structure of dissimilar steels. Also experimental examinations are carried out to measure the ultrasonic beam paths in the weldment. Then comparisons of the modeling predictions with experimental results are presented to reveal the complicated beam propagation behaviors.

关键词： ray tracing nickel-based alloy weldments ultrasonic nondestructive testing

Numerical simulation about the effect of fixture on the welding stress and distortion of thin aluminum plate joints

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China welding 2008年第4期17卷 39-42页

作者：杨建国李军刘雪松方洪渊 state key lab.ratory of Advanced welding production technology Harbin Institute of Technology

The effect of welding jig on the welding stress and buckling distortion of thin aluminum plate joints was simulated by finite element method （FEM）. The results show that the restraint distance and the heat conduction ability of the fixture do have essential effects on the residual stress and distortion. The residual compressive stress and distortion will be increasing with the increase of the restraint distance, while the residual compressive stress and distortion will be decreasing with the increase of the heat conduction ability of the fixture.

关键词： fixture thin plate stress distortion numerical simulation