Analysis of keyhole geometry in plasma arc welding

The key problem for numerical simulation of plasma arc welding （PAW） process is to develop a suitable and adaptive volumetric heat source mode which reflects the physical characteristics of keyhole PAW. To this end, the keyhole geometry under different PAW process conditions must be predicted. In this paper, a mathematical model for determining the keyhole shape is developed with considering the mass and momentum conservation of the in-keyhole plasma jet as well as the pressure equilibrium at the plasma jet/liquid metal boundary. A suitable heat source model related to the keyhole shape is applied to the calculation of PAW weld dimensions. The predicted results are in good agreement with the experimental ones.     

等离子弧焊接小孔形状和穿孔过程的数值分析

根据小孔壁面上的力学平衡条件,建立了穿孔等离子弧焊(PAW)的小孔模型.利用该模型,对6 mm厚不锈钢板PAW准稳态小孔的形成过程进行了数值计算,得到了不同工艺参数下准稳态小孔的形状和尺寸.根据达到准稳态时小孔壁面的受力状态,对PAW过程中小孔从盲孔到穿孔的转变机制进行了探讨,分析计算了小孔壁面上各区域的作用力大小.随...     

Measurement method of the arc welding current and voltage

Plasma arc welding can realize high-speed welding, deeper weld penetration and, furthermore, smaller thermal distortion. For these reasons, plasma arc welding is employed for keyhole welding. However, it has been pointed out that it is difficult to obtain the stability of the welding. In this study, we have developed a unified plasma arc welding model for analysing the welding mechanism and influence of the torch design and operation conditions of the arc on the welding process. In this paper, the keyhole welding of a thick aluminium plate employing the plasma arc was numerically analyzed for clarifying the mechanism determining the keyhole size which is important for improving the stability of the process. As a result, it was found that the keyhole size is determined mainly by a force balance between the surface tension of a weld pool and metal vapour pressure.     

不锈钢PA-GTA双面弧焊工艺特点分析

详细分析了不锈钢等离子弧(PA)-钨极氩弧(GTA)双面弧焊(DSAW)的工艺特点,该工艺可以增加熔深,减小焊后热变形,尤其适用于中厚板的焊接.当小孔效应建立后,PA-GTA双面弧焊过程中的电弧均得到了不同程度的压缩,两焊枪之间的电弧电压出现下降趋势,节省了能源.形成小孔后,电弧穿过工件从工件内部进行加热,提高了热效率.表面张力、电弧吹力和电磁搅拌力均有利于获得较大的熔深,浮力有利于增加焊缝中间部位的宽度.     

受控脉冲PAW过程小孔动态变化的数值模拟

受控脉冲穿孔等离子弧焊接(PAW)过程中,小孔形状随焊接电流动态变化,经历形成—长大—缩小—闭合的变化过程.本文在对受控脉冲PAW瞬态温度场进行数值模拟的基础上,通过分析焊接熔池表面的受力状态,建立了小孔形状的模型,考虑了盲孔(小孔深度小于工件厚度)和穿透小孔2类情况.对焊接熔池内三维小孔在一个脉冲周期内的变化过程进行了数值计算.进行了受控脉冲PAW工艺实验,验证了穿孔持续时间的数值分析结果.     

等离子弧焊中小孔检测的研究

在小孔等离子弧熔透焊接中，利用等离子云电压能够检测小孔的成形。本文首次应用等离子鞘层理论，指出尾焰电压和等离子云电压的本质特点，提出计算尾焰电压和等离子云电压公式。为用简单方法检测小孔成形奠定了基础。     

A computer-based control system for keyhole plasma arc welding

A new kind of control system for keyhole plasma arc welding （K-PAW） was developed based on the computer and the Graphics Language--LabVIEW. It can set and output the required current waveforms with desired decreasing slopes so that the corresponding ＂opening and closing＂ of keyhole can occur periodically. With this control strategy of welding current waveforms, the workpiece is fully penetrated while no burn-through Occurs. Keyhole plasma arc welding experiments were conducted to verify the stability and reliability of the developed system.     

等离子弧焊中电弧反翘现象的数值模拟

根据流体的质量、动量、能量守恒方程,建立了穿孔等离子弧焊接过程中的等离子电弧三维数学模型,用磁矢量法求解磁场问题.模型包括了一部分喷嘴和钨阴极,小孔也被包含进模型中.利用ANSYS有限元分析软件求解模型,得到等离子电弧的温度分布,以研究等离子弧焊中电弧反翘现象.结果表明,等离子电弧反翘随小孔尺寸的增大而减弱,电弧尾焰随小孔尺寸的增大而增强;而适当的增加焊接速度以使小孔轴线与电弧轴线之间形成一定的偏差是形成等离子电弧反翘现象的必要条件;焊接电流主要是通过改变小孔尺寸而对电弧反翘产生影响.     

Experimental determination of the weld penetration evolution in keyhole plasma arc welding

Keyhole plasma arc welding experiments are conducted to measure the weld geometry and penetration at different moments during the initial phase from igniting arc to quasi-steady state. Indirect information on keyhole formation and evolution in plasma arc welding can be extracted based on the weld macrophotograph at cross section. It has laid foundation to verify the mathematical models of keyhole plasma arc welding.     

Modeling the keyhole shape and dimension in plasma arc welding

It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in keyhole plasma arc welding is determined firstly, and then the dynamic force-balance condition on the interface between the plasma jet and the molten metal is dealt with in describing the keyhole formation inside the weld pool. The effects of welding current on the shape and size of keyhole are numerically analyzed. The sharp transformation from a partial keyhole to a full-penetration keyhole is quantitatively demonstrated.     

小孔等离子弧焊接中小孔状态的传感技术研究

小孔等离子弧焊接是一种高能量密度的高效焊接方法。小孔的稳定性是影响小孔型等离子弧焊接过程稳定性和接头质量的重要因素。在焊接过程中及时获取表征熔池小孔特征行为的信息．就成为等离子弧焊接研究的前沿课题。介绍了小孔等离子弧焊接中小孔状态的传感检测原理，指出利用声音信号、电弧孤光强度、尾焰电压、熔池图像信号、多传感信息融合和等离子云导电性都能在一定条件下实现小孔状态的检测．并分析了这些传感方法的特点。     

穿孔等离子弧焊的熔深检测

在小孔等离子弧焊接过程中,首次利用鞘层电压获知等离子云喷封角,从而获知熔深情况。从以往研究只停留在实时检测小孔是否穿透的状态信息,前进到通过等离子云喷射角来检测熔池熔深的状态。设计了无源探针检测等离子云装置,该装置简单、可靠,具有较好的工业应用前景。     

穿孔等离子弧焊接中等离子云的检测

应用天体物理等离子鞘层理论的知识,分析金属板测量尾馅时产生电压和探针测量等离子云时产生电压的原因。当把探针放置在等离子云中,由于等离子体的特殊性,将在探针上产生了负电位,与工件电位差就是鞘层电压,并给出鞘层电压的计算公式,通过分析发现,鞘层电压大小仅仅与检测处等离子体温度和成分有关。提出了一种用无电源探针检测等离子云的新方法,通过检测等离子云中探针上产生的鞘层电压是否为零来判断小孔是否形成。试验验证了鞘层理论在等离子弧焊接中应用的正确性,同时给出了探针放置的最佳位置。     

等离子弧焊小孔行为的反翘电压检测

在穿孔等离子弧焊接过程中,小孔稳定性对焊接过程的稳定和优质的焊缝成形是非常关键的。文中采用无源探针对由等离子弧梯度电压和等离子鞘层电压构成的等离子反翘(等离子云)电压进行检测。根据等离子鞘层理论,随等离子反翘长度和角度变化的反翘电压可以反映小孔的状态信息及其形成、坍塌过程。文中讨论了检测信号的特征,以及材料、探针位置、焊接电流,等离子气流等因素对检测信号的影响。试验证明,该方法可以有效的预测小孔信息和焊缝熔透情况。     

NTWV-based sensing keyhole dimension in plasma arc welding

During stable keyhole plasma arc welding, the pilot arc and the transferred arc exist at the meantime, and the arcs can be considered as a composition of two parts inside and outside the nozzle, respectively. Under the mechanical constriction and thermal contraction effects, the inside arc has certain arc length, electron density and arc profile etc. inducing constant tungsten-to-nozzle voltage. However, the arc outside the nozzle diverges at about 5 degrees and has certain characteristics similar to the free arcs. The nozzle-to-workpiece voltage （NTWV） depends mainly on the length of the arc, which gets bigger as increasing of the weld penetration and keyhole size. The NTWV sensor is developed for monitoring NTWV in real time. The welding experiments are designed to get different penetrations and keyhole sizes. It is found that as the weld penetration and the keyhole size increase, NTWV also increases linearly. The NTWV signals can be used as the feedback variable in automatic control of keyhole plasma arc welding.     

基于有限元模拟的穿孔等离子超声电弧焊谐振频率的确定

根据穿孔等离子弧焊特点,首先利用改进型三维锥体热源模型建立准稳态条件下的三维熔池模型;然后在频率15～100kHz的范围内,对低活化马氏体钢（CLAM钢）穿孔等离子超声电弧焊接熔池模态进行分析,计算得到共14阶模态,分布于6个主要频率附近;最后分析了其中五阶模态的响应情况．结果表明,随频率增加,熔池局部的振动变形越来越剧烈,整体差异性增大．利用该方法可实现超声电弧焊接谐振频率的确定,文中也为超声电弧焊工艺优化提供了一定的参考,可缩短超声电弧工艺设计时间,降低研发费用．     

Finite element analysis of keyhole plasma arc welding based on an adaptive heat source mode

An adaptive heat source mode is proposed to account for the keyhole effect and the characteristics of volumetric distribution along the direction of the workpiece thickness. Finite element analysis of the temperature field in keyhole plasma arc welding is conducted and the weld geometry is obtained. The predicted results are in agreement with the measured ones.     

VPPAW背面匙孔状态正面检测技术

变极性等离子弧焊接(variable polarity plasma arc welding, VPPAW)过程中匙孔状态,特别是背面匙孔状态是决定焊缝成形质量的核心要素. 在实际焊接过程中,背面放置传感器检测匙孔状态存在难度. 文中提出了一种基于匙孔前壁面反光的等离子弧焊接背面匙孔正面检测方法. 在合适的拍摄角度下,该方法可以同时获得正面匙孔图像和背面匙孔在前壁面的反光成像. 通过不同焊接电流下的工艺试验,建立了焊接质量与匙孔反光形态的联系. 随着焊接电流的增大,检测到的前壁面匙孔图像位置逐渐向上偏移. 焊接出现切割时,背面匙孔反光形态消失;干扰稳定焊接状态,背面匙孔反光形态同时发生改变. 匙孔稳定与否与焊接状态稳定直接关联. 背面匙孔在前壁面的反光成像状态受焊接状态和熔池状态影响. 为等离子焊接正面检测焊接质量提供了指导意义.