Gas Pool Coupled Activating TIG Welding Method with Coupling Arc Electrode

Gas pool coupled activating TIG(GPCA?TIG) welding put forward in?house can dramatically enhance weld penetration of TIG welding through introducing active element oxygen to reverse the Marangoni convection flow in the molten pool. In order to further improve the welding productivity, the normal solid tungsten electrode is replaced by a kind of coupling arc electrode. The changes of arc pressure distribution along anode surface and the weld appearance were evaluated. On this basis, the dependences of weld shape characterized with weld depth, width and undercut on the main welding parameters were discussed. The results indicate, the substitution of coupling arc electrode can lead to an obvious decrease of arc pressure. Compared to hollow tungsten electrode and twin tungsten electrodes, the coupling arc electrode is much easier to manufacture and has more compacter structure. Combined with the symmetric distribution of arc pressure in di erent directions, this electrode has extensive adaptability. In the GPCA?TIG welding with coupling arc electrode, both the substitution of coupling arc electrode and the introduction of outer active gas oxygen can reduce the possibilities of producing humping bead and undercut. Their joint action makes this welding method have the capability of realizing high travel speed and deep penetration welding.

Reconstruction of Emission Coefficients for a Non-axisymmetric Coupling Arc Based on MALDONADO's Method

The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to study non-axisymmetric arc plasmas.In order to reveal temperatures of a non-axisymmetric coupling arc,the distribution of emission coefficients must be reconstructed in advance.In this paper,the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter.The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO＇s method.A displaced Gaussian model is used for evaluating the validity of the converted programme.Then,the emission coefficients of a free burning arc are reconstructed by MALDONADO＇s method and an Abel inversion,respectively,and good agreement is obtained.Finally,the emission coefficient profiles of the coupling arc are achieved.The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric.The emission coefficient profile is similar to an ellipse,and the short axis of the ellipse is in the direction that the two electrodes are arranged along.The peak temperature of the coupling arc is in the middle of both electrodes.There is a strong interaction between both arcs within the coupling arc.The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.

Physics characteristic of coupling arc of twin-tungsten TIG welding

Twin-tungsten TIG welding was developed, in which two electrodes were placed in a single welding torch. In order to master this process, the arc physics characteristic was studied. The twin-tungsten coupling arc shape was observed by using CCD camera, and the arc pressure was measured. The results show that the coupling arc includes two arcs that pull each other according to Lorentz force and one big coupling arc is formed; the coupling arc pressure is much lower than that of conventional TIG arc. In the end, a simple welding experiment was carried out. This proves that stable welding process can be achieved by twin-tungsten TIG at higher current than that of conventional TIG because of its low arc pressure and the high efficiency welding is realized.

Tri-Arc双丝焊“Γ”形电弧及其促进方法

Tri-Arc双丝三电弧焊通过中间第3弧的M弧重新分配焊接热输入,实现高熔覆率低热输入焊接.M弧与主电弧耦合,在整个动态周期表现为“Γ”形和“μ”形及其镜像形态.该文研究“Γ”形电弧的形成机理和热输入调控机制,结果表明,“Γ”形态由“μ”形态转变而来,熔滴振荡引起焊丝末端间距的变化,从而促进耦合电弧“Γ”形态的形成,此时M弧不作用于母材,比“μ”形电弧焊接热输入更低.为提高Tri-Arc双丝焊接低热输入效果,在维持导电嘴末端到工件距离不变的前提下,提高焊枪枪体抬升距离从而改变焊丝末端间距.当导电嘴长度由30 mm增加至35 mm时,随着焊枪抬升,“Γ”形电弧作用时间逐渐增加,能更好地促进电弧热分配,降低Tri-Arc双丝焊接热输入,从而降低熔池最高温度,获得更小宽高比和更小熔深的焊缝.

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission.Pantograph-catenary arc vertical drift is more severe than the case under normal pressure,as it is easy to develop the rigid busbar,which may lead to the flashover occurring around the support insulators.We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment.Meanwhile,the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed.Moreover,arc drift characteristics and influencing factors are explored.The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized.In order to further explore the mechanism of the above physical process,a multi-field stress coupling model is built,as the multi-stress variation law of arc is quantitatively evaluated.The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored,as the physical mechanism of arc drifting under low pressure is theoretically explained.The research results provide theoretical support for arc suppression in high-altitude areas.

用MSC.MARC实现大转矩三段弧鼓形齿联轴器应力分析研究

应用有限单元法及MSC.MARC有限元分析程序,对我公司设计生产的新型三段弧鼓形联轴器进行了分析研究,从应力分布及接触状态等方面探讨了这种新型联轴器的结构力学特性,得出了这种新型联轴器既保持了一般鼓形联轴器的挠性特点,又可增大外齿轴套与内齿圈齿间接触面积,有效减小其接触应力峰值的结论,为进一步推广应用这种新型联轴器提供了理论依据。

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics （MHD） model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.

Numerical Simulation for Arc Windshields of Aircrafts Subjected to Bird Impact

A finite element model including full-scale circular arc windshield glass and the relative parts of the military plane is established in this paper. The model is analyzed by using an explicit element code LS-DYNA3D for analyzing the nonlinear dynamic response of structures. The data in aspects of displacement, strain, stress and contact force in the process of deformation are obtained. The deformation and failure mechanism of circular arc windshield glass are discussed. The possible location at which failure may take place is given. The valuable data are provided for designing,researching and producing new windshields with high crashworthiness.

Numerical simulation of influence of nozzle structure on arc characteristics of GPCA-TIG welding

This work mainly articulated the effects of nozzle structure on arc characteristics in gas pool coupled activating TIG （GPCA-TIG） welding process by using Fluent Software. Different models were set up to adapt the different torch structure during computer progress. The specific configuration of the welding torch made the gas flow in outer gas passage constrained. The nozzle structure has great influence on outer gas distribution because of the changing of coupling region between the outer active gas and molten pool surface. When the coupling degree is reduced or the outer gas passage become smaller, the oxygen in outer gas penetrates into the arc plasma and spreads to the arc region more easily. Owing to its cooling effects, the morphology of arc is contracted, and the arc temperature is increased. When the inner wall and the outer wall of outer gas passage are not parallel, the wide top and narrow bottom nozzle shape can bring more oxygen into the arc plasma, the arc is contracted and the peak temperature of arc rises a little more comparing to the narrow top and wide bottom one.

Influence of laser on arcs in alternate arcing during laser-twin-arc hybrid welding process

In this study, multi-information including spectrum, high-speed photograph and electrical signal was adopted to explore the coupling mechanism of alternate burning in laser-twin-arc welding process. Laser provides a conductive, stable plasma channel for arcs. Plasma radiation strengthened especially in the center of the arc after hybrid. High temperature plasma erupting from keyhole provides an upward reacting force which can prevent droplet from transfer. The charged particles consisted in high temperature plasma reduce the voltage that maintains arc ignition or burning. The results show that laser can influence the arc shape, prevent droplet transfer, reduce resistivity and stabilize arcs.

Conversion of coalbed methane surrogate into hydrogen and graphene sheets using rotating gliding arc plasma

The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surrogate.Based on a previous investigation of discharge properties,product distribution and energy efficiency,the operating parameters such as CH4 concentration,applied voltage and gas flow rate can effectively affect the CH4 conversion rate,the selectivity of H2 and the properties of solid generated carbon.Nevertheless,the basic properties of RGA plasma and its role in CH4 conversion are scarcely mentioned.In the present work,a 3D RGA model,with a detailed nonequilibrium CH4/Ar plasma chemistry,is developed to validate the previous experiments on CBM conversion,aiming in particular at the distribution of H2 and other gas products.Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection,electron migration and electron diffusion,and is prominently determined by the variation of the gas flow rate and applied voltage.Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction,taking into consideration the formation and loss pathways of crucial targeted substances(such as CH4,C2H2,H2 and H radicals)and corresponding contribution rates.Additionally,the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM)and Raman spectroscopy.The results show that increasing the applied voltage and decreasing CH4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets,while the size of the graphene sheets is slightly affected by the change in gas flow rate.

STUDY ON MECHANISM OF ARC-EXCITED ULTRASONIC

A mechanism of excited arc to be an controlled “ultrasonic emission source” is described. An developed electrical source with an certain frequency bandwidth for the purpose of the arc excited is connected with an conventional welding power supply through coupling the cables for the experiment. Some resonant frequency bands for the arc excited ultrasonic are discovered in the welding process, and its frequency, amplitude and phase'shift are recorded. This principle demonstrates that arc can be used not only for a thermal source, but also for an ultrasonic emission source, which may be extent to the industrial application in some new ways, such as for automatic welding process control and quality inspection.

Measurement of cathode surface temperature using the method of CCD imaging in arc discharge

A two-wavelength pyrometry device using ordinary array CCD (charge coupled device) to collect the ra- diation data in the horizontal and vertical directions has been developed for measuring the cathode surface temperature during the arc discharge. Analyses of experimental results show that the device can make the measurement of the cathode surface temperature feasible. The cathode surface temperatures measured are lower than the melting point of tungsten (3653 K), and the arc current, cathode diameter, and the cathode length are the main influencing factors of the cathode surface temperature.

基于高频变极性电流源的交叉耦合电弧焊摆动行为抑制

交叉耦合电弧焊工艺理论上可以实现焊接过程中传热、传质解耦和独立控制,具有很大的发展潜力,然而,传统的交叉耦合电弧工艺中旁路电弧电流一般由低频交流焊接热源提供,工作过程中会出现主电弧随着旁路电弧的极性改变而发生电弧摆动现象,使各个电弧之间的热力分配不平衡,传热、传质解耦不彻底.在增材制造应用中,会面临熔滴落点位置不可控、成型精度低等问题,为了解决主电弧的摆动问题,设计开发了旁路电弧为高频变极性电弧的交叉耦合电弧焊接热源.试验结果表明,这种焊接热源可以通过提高旁路电弧的变极性频率,有效地抑制主电弧的摆动行为,进一步实现交叉电弧中填充焊丝熔化速率与工件热输入之间的传热解耦,同时,抑制主电弧摆动后的现象表现为主电弧高频小幅度振动,理论上可以实现对熔池的搅拌作用,利于枝晶破碎、促进焊缝晶粒细化.

电弧超声耦合波形对铝合金MIG焊缝成形、组织及性能的影响

通过超声频脉冲电信号与直流MIG焊接电信号耦合,可将超声引入焊接过程。通过改变耦合电容参数获得三种不同的耦合波形,采用超景深三维数码显微镜、扫描电镜及全自动硬度计等分析测试手段,研究了电弧超声耦合波形对铝合金焊缝成形、组织及力学性能的影响。结果表明:采用电容为0.033μF所获得的耦合波形进行焊接时,焊缝成形最佳,焊缝气孔率最低,接头各区域硬度高于利用另外两种波形焊接得到的接头硬度。分析认为,焊接质量改善的根本原因在于电容为0.033μF所对应耦合波形的附加热输入最小。合理的耦合波形可以明显抑制焊缝区与熔合区中第二相的析出,但电弧超声反而会促进热影响区内第二相的析出,导致热影响区的第二相面积占比增大。

冷凝型矿热炉三维热力耦合过程数值模拟

为解决冷凝型矿热炉熔炼过程中应力集中和热变形过大的问题,建立了一个三维冷凝型矿热炉电磁-热-应力多物理场耦合模型,预测了冷凝型矿热炉中电流密度的分布,并研究了冷却水温度对冷凝型矿热炉应力、应变以及热变形的影响.利用弹塑性力学理论研究了应力、应变和热变形与温度间的作用机制.结果表明:电弧区电流密度分布满足邻近效应和趋肤效应;当冷却水温度由288 K升至313 K时,炉壳在喷淋区的温度随之升高了23 K,炉壳最大应力由193 MPa减小至175 MPa,最大变形量由7.09 mm增至7.45 mm;炉壳最大应力、应变和变形量均位于z=3.2 m处;炉壳上的轴向应力和环向应力受高温电弧影响呈现周期性变化,且环向应力总是大于轴向应力.

小电流真空电弧多物理场仿真耦合机理研究

真空开关开断过程中产生的真空电弧涉及电、磁、热等多物理场耦合及多物性参数变化,研究其特性对于改进真空开关至关重要。为此,建立小电流真空电弧多物理场耦合模型,利用COMSOL Multiphysics对燃烧过程中的温度、压力、速度、电流密度、磁场强度等关键参量进行仿真,并分析多物理场间耦合机理。结果表明:等离子体温度、压力、电流密度最大值均在阴极表面中心处,磁场最大处靠近阴极侧,速度最大处靠近阳极侧;温度场、电流密度场、磁场随时间变化波动趋势基本一致,速度场波动滞后于压力场。

弧触头烧蚀程度对灭弧室内短路开断过程多物理场的影响

为研究SF 6断路器开断过程中弧触头烧蚀程度对灭弧室内多物理场变化的影响,建立了弧触头接触行程分别减小0、5 mm、10 mm和15 mm下灭弧室内开断过程的多物理场耦合仿真模型,获得了短路电流开断过程中灭弧室内温度、气流和电场分布特性。计算结果表明:开断过程中,弧道最高温度出现在弧根处,其值随弧触头烧蚀程度变化不大;随着弧触头烧蚀程度的加剧,SF 6气体最高速度不断减小,吹弧效果减弱;最大场强集中在静弧触头端部或动弧触头弧角处,且随弧触头烧蚀程度加剧而畸变更严重。基于此,根据流注理论的气体击穿判据计算了不同弧触头烧蚀程度下SF 6介质恢复特性,发现当弧触头接触行程减小15 mm时,临界击穿电压低于瞬态恢复电压,触头间隙可能再次击穿造成电弧重燃。研究结果可为SF 6断路器电寿命退化机理提供理论支撑。

00Cr13Ni5Mo不锈钢四钨极耦合电弧双丝增材制造工艺

为解决现有基于GTA热源增材制造工艺存在的熔覆效率较低、焊接效率较低的突出问题,该文提出一种四钨极耦合电弧双丝增材制造工艺,并通过控制变量的试验方法研究熔覆电流、行走速度与送丝速度对单层单道沉积层成形质量的影响。结果表明,熔池面积的波动与电弧压力是四钨极热源单道沉积层出现单道沉积层不连续、咬边等缺陷的主要原因,在保证成形质量的前提下,四钨极热源最大行走速度为400 mm/min、最大送丝速度为12 m/min、熔覆效率为6.24 kg/h,沉积件微观组织由回火索氏体、逆变奥氏体及碳化物组成,沉积件冲击吸收能量达到208 J,为MAG热源的2.5倍。综上所述,四钨极耦合电弧双丝增材制造工艺可以在保证优良冲击性能的前提下显著解决GTA热源增材制造工艺存在的熔覆效率较低、焊接效率较低的问题。

C_(4)F_(7)N二元混合气体电弧温度特性研究

为实现“2030年碳达峰,2060年碳中和”的减排目标,推进电力行业绿色发展,开发环保型绝缘气体以减少SF_(6)使用已成为研究热点。环保型绝缘气体C_(4)F_(7)N凭借优良的绝缘和环保性能被广泛关注。文中基于磁流体力学方程搭建二维轴对称喷口电弧模型,通过数值计算对比研究C_(4)F_(7)N/CO_(2)与C_(4)F_(7)N/N_(2)二元混合气体、SF_(6)、CO_(2)4种气体介质电流过零前后电弧温度特性,分析4种介质灭弧性能差异原因。研究表明,与CO_(2)气体相比,C_(4)F_(7)N二元混合气体电弧径向温度分布及弧芯温度冷却速度更接近SF_(6)气体,灭弧性能介于SF_(6)与CO_(2)之间;电弧辐射吸收区的能量堆积造成C_(4)F_(7)N二元混合气体与SF_(6)气体之间灭弧性能差异。综合考虑气体传热能力与电弧散热速度,C_(4)F_(7)N二元混合气体具有较高替代潜力。