GMAW短路过渡动态模型的建立

从全系统的角度建立了短路过渡GMAW系统的动态模型.在研究了短路过渡GMAW过程各物理量相互关系的基础上,在一定的条件下,以焊接回路模型为主体,进行了短路过渡GMAW过程全系统的动态模型建立,其中的液桥形状动态模型则采用了能量最小原理.在建立的动态模型基础上进行了仿真计算和误差分析,并进一步与实际的焊接过程进行了比较.     

Effect of power source characteristic on CO2 short circuiting arc welding

Abstract

Some problems are reported concerning the observation of the weld pool and effects of the power source characteristic on arc stability in CO₂ short circuiting arc welding. First, the effect of a power source with a constant voltage characteristic on CO₂ short circuiting arc welding is investigated by analysing the behaviour of the voltage and the current. From the results of this analysis, the cause of spatter generation is identified. A new power source characteristic is then proposed to improve the stability and the self-regulation of the arc. By adjusting the power source characteristic, the metal transfer can be stabilised in the CO₂ short circuiting arc welding process, i.e. the present authors have developed a power source having a non-linear characteristic. Its performance is verified by carrying out experiments.     

GMAW短路过渡过程中瞬时短路现象的分析

对GMAW短路过渡过程中的瞬时短路现象进行了力学动态分析,建立了基于熔滴液体压力、电磁收缩力、表面张力的瞬时短路力动态平衡临界条件.通过微距高速摄影技术和图像处理技术,获得了熔滴半径的变化数据,并结合电信号分析.结果表明,计算所得数值所反映的短路进程状态和图像所示的完全吻合,认为瞬时短路力动态平衡临界条件真实有效.并进一步基于此临界条件分析了熔滴形态对瞬时短路的影响,认为熔滴和熔池接触瞬间的径向半径如果小于轴向半径,则接触处的径向表面张力所产生的压力大于零,瞬时短路开始且不可逆,即纺锤形熔滴易造成瞬时短路.最后对瞬时短路现象进行了分类和定量研究,并提出了瞬时短路现象的新的解释.     

New stability index for short circuit transfer mode in GMAW process using acoustic emission signals

Abstract

A new index for the analysis of stability of GMAW processes taking as a base the acoustic emission generated by the arc during the short circuit metal transfer is presented in the present work. The incidence of parameters of process is analysed in the indices of the acoustic emission signal, as well as its influence on the stability, evaluated through a new proposed index. The results obtained allowed having a relationship between acoustic signals and arc voltage signals, and demonstrated the validity of proposed index of acoustic emission for analysis of stability of GMAW process. The obtained results were then compared with other classic stability analysis methods based on statistical analysis of temporal signals of arc voltage. Finally a statistical analysis for the validation of the obtained experimental results was carried out. As a result of the investigation, the effectiveness of the method proposed as a new way for the analysis of stability is demonstrated. The research can contribute towards a new standard to evaluate the stability in welding processes.     

短路过渡GMAW系统中参数变化的预测分析

在建立了短路过渡GMAW系统动态模型的基础上，研究了与GMAW短路过渡过程有重要关系的动态参数，特别涉及到一些无法通过试验获取的参数的动态变化，并进一步讨论了有关参数间的内在联系。焊丝熔化速度与焊接电流变化规律一致，但在燃弧和短路的交替瞬间发生跳变；焊丝熔化速度直接影响到焊丝干伸长的变化和短路液桥高度的变化；短路期液桥的体积同时受到焊丝熔化和液桥金属向熔池过渡的影响。     

Research on short circuiting transfer mode of ultrasonic assisted GMAW method

Abstract

Ultrasonic assisted gas metal arc welding (U-GMAW) has been recently developed to improve the metal transfer characteristics. The ultrasonic wave is applied on the metal transfer process by means of an acoustic field. Welding electrical signal measurement and high speed camera are employed to study the differences of short circuiting metal transfer between conventional GMAW and U-GMAW. Compared with the conventional GMAW, the short circuit frequencies of U-GMAW are obviously increased under the same welding parameters. Moreover, the voltage range of the stable short circuiting transfer is enlarged, and the weld appearances become more uniform with the action of the ultrasonic wave. The high speed video images indicate that the U-GMAW arc is compressed and the electrical field intensity is increased. The decrease in the arc length is the main reason for the increase in the short circuit frequency.     

受控短路过渡CO2焊焊接电流波形参数优化

对于波控短路过渡CO₂焊,电弧峰值电流I_pa,电弧基值电流I_ba以及由峰值电流切换到基值电流所用的时间(拖尾时间t_w)等电流波形参数是可调的,它们对过渡稳定性和焊缝质量具有很大影响,利用正交试验,对不同送丝速度下电流波形参数进行了优化.结果表明,电弧峰值电流的影响最大.送丝速度为320 cm/min时,电流波形参数I_pa,I_ba和t_w无论如何调整,飞溅率均在2.5%以上,焊缝表面质量差;送丝速度为360~400 cm/min时,最优电流波形参数为:I_pa=440 A,I_ba=50 A,t_w=0.6 ms.而在400 cm/min的送丝速度下,在宽广的电流波形参数范围内(I_pa为440~480 A,I_ba为30~50A,t_w为0.6~0.8 ms)均可获得飞溅率极低、焊缝表面质量好的稳定焊接过程.     

熔化极气体保护焊熔滴过渡检测方法现状与展望

熔化极气体保护焊熔滴过渡检测具有重要的实际意义。本文回顾了近年来国内外这一领域的研究现状,阐述了每一种检测手段的原理、优点及局限性。最后,对现有的熔滴过渡检测方法作出了综合评价。     

环境压力对高压干法GMAW熔滴过渡影响分析

采用红外激光作为背光源,应用高速摄像系统对高压干法GMAW熔滴过渡进行了研究.通过0.4 MPa以内氩气环境的试验发现,环境压力超过临界压力后熔滴过渡形式会发生转变.随着环境压力的增加,在小电流情况下,过渡形式先由大滴过渡转变为短路过渡,进而转变为排斥过渡;在焊接电流较大情况下,熔滴依次呈现射流过渡、短路与射流混合过渡、排斥过渡.并从熔滴受力的角度分析了压力环境熔滴过渡形式转变机理.指出产生排斥过渡的原因是在环境压力的作用下电弧与弧根收缩,改变了熔滴的受力状态而产生的.     

Metal transfer characteristics of GMAW with strip electrode

Abstract

The metal transfer process of gas metal arc welding with strip electrode is observed by a high speed digital camera system. Because the rectangular strip electrode has a large width/thickness ratio, the pendant droplet is elliptical in shape, and multicurrent channels are generated. The Lorentz force induced between the multicurrent channels drives the droplet and welding arc to move along the strip electrode end, but the droplet always lags behind the welding arc. The movement results in uncertain droplet’s detaching location and transition trajectory. The projected transfer mode is promoted, and the streaming and rotating transfer modes are restrained. With the increase in welding power, the droplet motion is faster but more stable. The stability can be reflected from the fluctuation of the welding current and arc voltage waveforms.     

激光增强GMAW熔滴短路过渡行为分析

高能量密度的激光照射熔滴,使熔滴局部产生强烈蒸发,利用蒸发反力驱动熔滴受迫短路,促进熔滴脱离焊丝.以低碳钢为研究对象,搭建激光增强GMAW短路过渡焊接试验系统,对比研究了激光增强GMAW短路过渡焊接过程中激光入射位置、电弧高度对熔滴短路过渡行为的影响规律.结果表明,在焊接过程中施加一定功率的激光对熔滴短路过渡行为有明显的改善作用,可以通过激光改变熔滴的受力状态,控制过渡熔滴的尺寸,熔滴短路时间减小,燃弧时间增加,增加过渡频率,提高了焊接过程中的稳定性,激光增强后,焊缝表面成形均匀饱满,焊缝成形良好.     

脉冲GMAW熔滴过渡动态过程的解析模型

在脉冲GMAW过程中，电流的突然转变会引起熔滴在焊丝末端的明显振荡，合理的利用向下振荡的动量可控制熔滴过渡。该文基于熔滴受力分析，建立了脉冲GMAW熔滴过渡的解析模型，并对熔滴的振荡和脱离过程进行分析，定量计算焊接工艺参数对熔滴过渡过程动态行为的影响，可用于指导脉冲GMAW主动控制模式下一脉一滴过渡工艺参数的优化设计。     

局部干法环境下GMAW横向焊接熔滴过渡特性

提出了一种水下结构件局部干法横向焊接方法,该方法通过对排水罩结构进行设计,使高压气体在排水的同时在排水罩内部形成向上流动的风场,利用风场对熔池的吹袭作用来抑制熔池下淌. 采用高速摄像技术研究了在侧向风场作用下GMAW焊的熔滴过渡特性. 结果表明,在短路过渡状态下,由于受到侧向风场的影响,更容易发生B型短路过渡. 在滴状过渡时,由于熔滴体积较大,侧向风场的支托作用不明显,熔滴沿焊丝倾斜向下过渡到熔池中. 在射流过渡时,侧向风场对电弧的影响较小,使熔滴略微向上偏斜,有助于减小熔池下淌程度,获得较好的焊缝成形质量. 研究结果对于水下结构件横向焊接质量控制有一定的参考价值.     

基于脉冲激光的GMAW熔滴过渡解耦控制

实现电流解耦的熔滴过渡,在足够低的焊接电流下仍能获得稳定的细颗粒或射滴过渡,将从根本上提升熔化极气体保护焊（GMAW）过程的稳定性和焊接质量.为此,文中提出了一种采用激光脉冲照射熔滴,利用蒸发反冲力驱动熔滴过渡的新方法.首先试验观测了光致蒸发现象,初步分析了激光蒸发反冲力的特征.进而观测分析了小电流下脉冲激光控制熔滴过渡的效果.结果表明,采用激光脉冲照射能够实现熔滴过渡与焊接电流的完全解耦,熔滴过渡随激光脉冲表现为一脉一滴的形式,熔滴飞行轨迹沿激光入射方向有一定偏转,但对焊缝成形无不良影响.     

Arc light sensing of droplet transfer in pulsed GMAW process and its mechanism

ＡｒｃｌｉｇｈｔｓｅｎｓｉｎｇｏｆｄｒｏｐｌｅｔｔｒａｎｓｆｅｒｉｎｐｕｌｓｅｄＧＭＡＷｐｒｏｃｅｓｓａｎｄｉｔｓｍｅｃｈａｎｉｓｍＬＩＰｅｎｇｊｉｕａｎｄＷＡＮＧＱｉｌｏｎｇ（ＷｅｌｄｉｎｇＤｅｐａｒｔｍｅｎｔＨａｒｂｉｎＩｎｓｔｉｔｕｔｅｏｆＴｅ...     

Effects of electrical current on transport processes in resistance spot welding

Abstract

The effects of alternating current (ac) and direct current (dc) on cooling rate, solute distribution and nugget shape after solidification, which are responsible for microstructure of the fusion zone, during resistance spot welding, are realistically and extensively investigated. The computer program developed by Wang and Wei is used to predict transport variables in workpieces and electrodes during heating, melting, cooling and freezing periods. The model accounts for electromagnetic force, heat generations at the electrode/workpiece interface and faying surface between workpieces, and dynamic electrical resistance including bulk resistance and contact resistances at the faying surface and electrode/workpiece interfaces, which are functions of hardness, temperature, electrode force and surface condition. The computed results show that in contrast to dc, using ac readily produces the nugget in an ellipse shape. Deficit and excess of solute content occur in a thin layer around the boundary and interior of the nugget respectively.     

低频相位对双丝双脉冲GMAW熔滴过渡和焊缝成形的影响

为了提高双丝双脉冲熔化极气体保护焊(gas metal arc welding, GMAW)的焊缝成形质量,探究低频相位对熔滴过渡和焊缝成形的影响,在高频同步的前提下分别对低频同步和交替模式进行了试验.通过高速摄影拍摄了低频同步和交替模式的熔滴过渡过程,再结合焊接过程中电流变化,分析了熔滴过渡对熔池的影响机制.结果表明,交替模式可以减少熔滴的碰撞融合,进而减少大体积熔滴对熔池的冲击,减少了飞溅.交替模式比同步模式的焊缝平整性更好,余高方差更小,鱼鳞纹规则,焊缝成形美观.     

Random nature of droplet size and its origins in short circuit CO2 arc welding

Abstract

The nature of the droplet size variation and its effect on the process behaviour were investigated for short circuit CO₂ arc welding using a power supply with constant voltage output. To obtain the droplet images and record the welding current and voltage transient waveforms in phase, an integrated experimental system was established by combining a high speed charge coupled device camera based on laser shadowing and a related optical system with a dual channel analog/digital converter. The droplet size in short circuit transfer mode is defined as the maximum diameter of the molten droplet just before short circuiting. The experimental results reveal that the distribution of droplet size typically has a random nature with a range of between 1 and 2 times the electrode diameter. Excessively large or small droplet size is markedly unfavourable to the process stability. The droplet shape just before short circuiting and the short circuiting experience are also critical factors affecting the process behaviour. The main factors influencing the droplet size and shape are analysed in detail and approaches to control their evolution are then proposed.     

GMAW短路过渡液桥形状动态模型

GNAW(熔化极气体保护焊)短路过渡中的液桥形状变化受诸多因素影响,是一个复杂的动态变化过程.基于能量最小原理,在一定的假设条件下,建立了GMAW短路过渡液桥形状动态变化的模型;结合焊接回路的动态模型,对液桥形状动态变化进行了仿真计算;并在此基础上,进一步进行了模型的试验验证和模型的误差分析.结果表明,建立的GMAW短路过渡液桥形状模型所描述的液桥轮廓动态变化趋势与试验结果比较吻合,实际焊接过程中的液桥形状还受到磁偏吹、焊接运动过程、熔池作用、保护气体流动等的影响,这些影响是造成液桥形状模型误差的主要因素.     

Metal transfer characteristics of tandem narrow gap GMAW for flat welding position

A series of experiments of tandem narrow gap GMAW for flat welding position were carried out. The arc behavior and metal transfer process were observed by a high-speed photography system. The effects of the welding parameters on the metal transfer were investigated. The results show that the arc behavior and metal transfer process of tandem narrow gap GMAW are different from these of bead-on-plate tandem GMAW. The arc behavior and metal transfer process are influenced by the distance between the two wires, the peak voltage, the pulse frequency and the peak time. With the increase of the distance between the two wires, the metal transfer mode gradually transforms from one pulse-multi droplets into one pulse-one droplet, and the average welding current increases. With the increase of the peak voltage, pulse frequency or peak time, the metal transfer mode transforms from one pulse-one droplet into one pulse-multi droplets, and the arc tends to occur between the wire and the sidewall.