双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

Approximate entropy a new statistic to quantify arc and welding process stability in short-circuiting gas metal arc welding

Based on the phase state reconstruction of welding current in short-circuiting gas metal arc welding using carbon dioxide as shielding gas, the approximate entropy of welding current as well as its standard deviation has been calculated and analysed to investigate their relation with the stability of electric arc and welding process. The extensive experimental and calculated results show that the approximate entropy of welding current is significantly and positively correlated with arc and welding process stability, whereas its standard deviation is correlated with them negatively. A larger approximate entropy and a smaller standard deviation imply a more stable arc and welding process, and vice versa. As a result, the approximate entropy of welding current promises well in assessing and quantifying the stability of electric arc and welding process in short-circuiting gas metal arc welding.     

基于DSP的氩弧焊焊池实时监控图像分析技术

针对氩弧焊的特性，利用机器视觉技术实现了一种对氩弧焊熔池宽度进行测量的实时视频测量分析系统。在焊池宽度测量中采用了基于DSP的图像分析技术，不仅保证了测量精度，而且提高了系统的实时性。实验表明：该系统对氩弧焊焊池宽度测量精度高（10μm），响应时间快（50ms）。这种在线式氩弧焊监控系统相对于离线式氩弧焊产品来说，在加工产品的质量控制效果以及成本上都有更大的优势，非常适合流水线上不间断的高质量焊接加工，具有良好的应用前景。     

Structure and optical properties of tungsten oxide nanomaterials prepared by a modified plasma arc gas condensation technique

With the use of a modified plasma arc gas condensation technique and control of the processing parameters, namely, plasma current and chamber pressure, we synthesized tungsten oxide nanomaterials with aspect ratios ranging from 1.1 (for equiaxed particles with the length and width of 48 nm and 44 nm, respectively) to 12.7 (for rods with the length and width of 266 nm and 21 nm, respectively). The plasma current and chamber pressure, respectively, ranged from 70 to 90 A and from 200 to 600 Torr. We then characterized the tungsten oxide nanomaterials by means of X-ray diffraction, high-resolution transmission electron microscope, UV–visible spectroscope, and photoluminescence (PL) spectroscope. Experimental results show that equiaxed tungsten oxide nanoparticles were produced at a relatively low plasma current of 70 A, whereas nanorods were produced when plasma currents or chamber pressures were increased. All of the as-prepared tungsten oxide nanomaterials exhibited a WO_2.8 phase. Compared to the nanoparticles, the nanorods exhibited unique properties, such as a redshift in the UV–visible spectrum, a blue emission in PL spectrum, and a good performance in field emission. With respect to the field emission, the turn-on voltage for WO_2.8 nanorods was found to be as low as 1.7 V/μm.     

考虑金属蒸汽的钨极惰性气体保护焊电弧与熔池交互作用三维数值分析

基于局域热平衡状态假设并考虑金属蒸汽的作用, 建立了钨极惰性气体保护焊电弧与熔池交互作用的三维数学模型. 电弧等离子体的热力学参数和输运系数由温度和金属蒸汽浓度共同决定, 并使用第二黏度近似简化处理金属蒸汽在氩等离子中的输运过程. 在考虑熔池流动时, 主要考虑了浮力、电磁力、表面张力和等离子流拉力的作用. 通过对麦克斯韦方程组、连续性方程、动量守恒方程、能量守恒方程和组分输运方程的耦合求解, 得到了金属蒸汽在电弧中的空间分布、电弧和熔池的温度场、速度场和电流密度分布等重要结果. 通过与未考虑金属蒸汽的结果对比, 研究了熔池上表面产生的金属蒸汽对电弧等离子体行为的影响, 以及电弧等离子对熔池行为的影响. 结果表明, 金属蒸汽主要富集在熔池上表面附近; 金属蒸汽对电弧等离子体有明显的收缩作用, 而对等离子速度和电势影响较小; 金属蒸汽的出现对熔池上表面速度分布和剪切力分布以及熔池形貌并无明显影响. 求解结果与已有的实验结果和计算结果符合良好.     

微束等离子体弧焊电弧物理特性多场耦合分析

根据磁流体动力学方程组,建立了微束等离子电弧模型,使用有限元分析软件COMSOL进行模拟计算。结果表明,电弧中心温度分布从钨针至焊件整体呈"毛笔"状,其中,喷嘴下方电弧形态呈"钟罩"形,在焊件上温度分布符合高斯分布特征;电弧等离子体在喷嘴内部速度较大,离开喷嘴后,其方向由喷嘴内的竖直向下逐渐变为到达工件时的向四周扩散;电流由焊件表面流出,经过弧柱区域流入钨针下端面,在钨针下端面附近取得最大值;电弧磁通密度分布呈"肺叶"状。最后进行了相应的熔焊试验,试验过程中拍摄的电弧轮廓与仿真电弧形态基本一致。     

Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires

In the present study, different amounts of graphene nanosheets (GNSs) were added to the 4043 aluminum alloy powders by using the mechanical alloying method to produce the composite filler wires. With each of the produced composite filler wires, one all-weld metal coupon was welded using the gas tungsten arc (GTA) welding process. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. As the amount of GNSs in the composition of filler wire is increased, the microstructure of weld metal was changed from the dendritic structure to fine equiaxed grains. Furthermore, the tensile strength and microhardness of weld metal was improved, and is attributed to the augmented nucleation and retarded growth. From the results, it was seen that the GNSs/Al composite filler wire can be used to improve the microstructure and mechanical properties of GTA weld metals of aluminum and its alloys.     

Numerical analysis of hybrid plasma generated by Nd:YAG laser and gas tungsten arc

When the output from a high power Nd:YAG laser irradiates a metallic surface, metal vapor is generated and changes into the plasma state, which is called a laser-induced plasma plume. If the high power laser is combined with an arc plasma, they mutually attract and influence each other. In this study, several analytic steps are introduced to analyze the laser-arc hybrid welding plasma. A conduction equation is first solved to obtain the temperature distribution on the metallic surface. Next, an analysis of the metal vapor is conducted to investigate the Ar–Fe mixture using a numerical method. As a result of the analysis, it is revealed that the plasma is concentrated in the vicinity of the laser-irradiation position and that the local temperature of the plasma is increased. Plasma flow and current density profiles are also affected by the laser irradiation.     

脉冲电流作用下TIG电弧的数值分析

建立了脉冲电流下自由燃烧的TIG电弧的二维轴对称数学模型,利用FLUENT软件,通过选择合适的边界条件和强烈耦合控制方程组对脉冲TIG电弧进行了数值模拟,得到了在焊接电流周期性变化下电弧形态、电弧温度场、电弧轴线方向上的温度和速度及焊接工件表面电弧压力的变化情况;针对电弧压力,得到了不同峰值电流、占空比、脉冲频率作用下的分布情况,并分析了它们在脉冲电流作用下的周期性变化规律.分析结果表明:当脉冲电流发生突变时,它们的变化滞后于脉冲电流的变化,且从基值电流向峰值电流变化时的响应速度更快,并最终达到一个相对稳 关键词： 脉冲TIG焊 电弧 数值模拟 FLUENT     

Thermal and electrical properties of heavy current arc column in SF6 gas

Numerical computations of the electrical properties and temperature profiles of wall-stabilized arcs in sulphur hexafluoride, SF₆, at 1 ata are presented. The voltage gradient vs. arc current characteristic curve has a minimum point at which the axial temperature is the same inherent value of the gas independent of the arc radius. Also, the radial temperature distributions up to several hundreds of amperes corresponding to the axial temperature of some 20000 °K have been computed.     

Energy law preserving continuous finite element schemes for a gas metal arc welding system

In this paper a modifed continuous energy law was explored to investigate transport behavior in a gas metal arc welding(GMAW)system.The energy law equality at a discrete level for the GMAW system was derived by using the finite element scheme.The mass conservation and current density continuous equation with the penalty scheme was applied 10 improve the stability.According to the phase-field model coupled with the energy law preserving method,the GMAW model was discretized and a metal transfer process with a pulse current was simulated.It was found that the numerical solution agrees well with the data of the metal transfer process obtained by high-speed photography.Compared with the numerical solution of the volume of fuid model,which was widely studied in the GMAW system based on the finite element method Euler scheme,the energy law preserving method can provide better accuracy in predicting the shape evolution of the droplet and with a greater computing efficiency.     

Effect of CO2 shielding gas on metal droplet formationin arc welding

We have developed a unified arc electrode model that enables us to make predictions of the time development of molten drops from the welding wire in gas metal arc welding. The wire is taken as the positive electrode, and the effects of surface tension, magnetic pinch forces, and convection within the drop are taken into account to predict drop detachment for any given arc current. For pure argon, we have previously predicted the sharp transition that is observed experimentally at about 300 A between globular transfer at low current, when drop diameters are larger than the wire diameter, and spray transfer, for currents above 300 A, when drop diameters are smaller than the wire diameter. In this paper, we predict that addition of 25% of CO₂ to the argon leads to an increase in the transition current to more than 325 A, also in agreement with published experimental results. For pure CO₂, we find a significantly different drop behavior due to the more constricted arc. Both small and large drops are produced, with many very small drops being produced successively between each large drop     

A comparison in a back-bead prediction of gas metal arc welding using multiple regression analysis and artificial neural network

This research was done on the basis of prediction that there is a relationship between welding parameters and geometry of the back-bead in arc welding which is a gap. Multiple regression analysis and artificial neural network were used as methods for predicting the geometry of the back-bead. The multiple regression analysis and the artificial neural network were formed, and the analysis data or verification data which were used in the formation process of the multiple regression, and the training data or test data which were used in the formation process of the artificial neural network, were used to perform the prediction of the back-bead. Through this research, it was found that the error rate predicted by the artificial neural network was smaller than that predicted by the multiple regression analysis, in terms of the width and depth of the back-bead. It was also found that between the two predictions, the prediction of the width of the back-bead was superior to the prediction of the depth in both methods.     

双面电弧焊接的传热模型

将等离子焊接(PAW)电弧和钨极氩弧焊(TIG)电弧串接,相对作用于工件的正反面形成双面电弧焊接(DSAW)系统,可以引导焊接电流沿工件厚度方向流过小孔,补偿等离子电弧穿透工件时消耗的能量,以有效地提高等离子弧的穿透能力.综合考虑影响双面电弧焊接正反面熔池几何形状的力学因素,建立了熔池表面变形的控制方程,以此为基础并采用帖体曲线坐标系建立了DSAW焊接传热的数学模型,分析了DSAW,PAW焊接传热的差异,从传热的角度解释了DSAW焊接熔深增加的原因.焊接工艺实验表明,计算结果与实测结果吻合良好. 关键词： 双面电弧焊接(DSAW) 传热模型 熔池表面变形模型     

Vibration states of hydrogen on tungsten

The vibrational excitation of hydrogen adsorbed on the low-index faces of tungsten have been investigated using electron energy-loss spectroscopy. The results indicate the same vibrational force constant in “on-top” sites independent of substrate-atom geometrical environment.     

Interference of coherently scattered signals in the laser SRS-CARS monitoring of hydrogen concentration in gas mixtures

The possibility of measuring the hydrogen impurity concentration in dense gas mixtures by coherent anti-Stokes Raman scattering (CARS) is studied. In this technique, biharmonic laser pumping based on stimulated Raman scattering (SRS) in compressed hydrogen is used. Because of the interference between the coherent scattering components from buffer gas molecules and molecules of the impurity to be detected, the signal recorded may depend on the hydrogen concentration by a parabolic law, which has a minimum and makes the results uncertain. It is shown that this uncertainty can be removed if the frequency of the biharmonic laser pump, which is produced by the SRS oscillator, somewhat differs from the frequency of molecular oscillations of hydrogen in the test mixture. A sensitivity of 5 ppm is obtained as applied to the hydrogen-air mixture under normal pressure. The coefficients of the nonresonance cubic hyperpolarizability of molecules and atoms are measured relative to nitrogen in a number of gas media.     

Morphology and electronic properties of carbon nanotubes synthesized by arc discharge in CF4gas

The morphology of carbon nanotubes synthesized by arc discharge in a CF₄gas atmosphere was investigated by scanning electron microscopy and transmission electron microscopy. The electronic properties of these nanotubes were investigated by electron spin resonance. The synthesis conditions in CF₄gas were then compared with those in CH₄, H₂and He based on these results. Furthermore, the mechanism of tube growth in CF₄gas was discussed briefly.     

短路过渡电弧焊电流信号的近似熵分析

依据近似熵的理论和算法，从非线性角度对纯CO₂保护气体条件下短路过渡电弧焊的电流信号进行了近似熵分析.通过对不同的送丝速度、给定电压及气体流量下电流信号的近似熵计算和比较，表明近似熵可以作为短路过渡稳定性的评判标准.近似熵越大，波动越小，焊接过程就越稳定. 关键词： 非线性 近似熵 短路过渡 稳定性     

Interaction of hydrogen with indiumvacancy clusters in tungsten

Hydrogen trapping at specific¹¹¹In-vacancy complexes in tungsten was studied by means of perturbed angular correlations. The hydrogen was either implanted into the sample or diffused from the gas. We observed desorption of the trapped hydrogen in the temperature range 450–550 K.