等离子云信号检测与影响因素分析

在等离子弧焊接中采用无电源探针法可以检测等离子云，判断焊接小孔是否形成。根据等离子体鞘层理论，伸入等离子云中的探针表面将产生一负电位，称其为鞘层电压。采用探针检测等离子弧焊接中的等离子云，其检测信号与鞘层电压密切相关。由于鞘层电压大小与探针检测处等离子体温度和成分有关，因此，在检测过程中，探针位置、焊接速度和焊接电流等影响等离子云温度的因素是影响检测电压大小的主要原因。试验证明，同样的焊接条件，探针位置不同，检测信号差别很大，甚至可能检测不到等离子云的信号。不同的焊接工艺参数，对应有不同的最佳探针位置，在最佳探针检测位置可以获得最大的检测电压值。     

穿孔等离子弧焊接热场和流场的数值模拟

考虑熔池和小孔的耦合作用,建立了穿孔等离子弧焊接热过程的三维瞬态模型.采用焓孔隙度法处理了凝固熔化过程中相变潜热以及动量损耗问题.基于流体体积函数法（VOF）对小孔界面实施追踪.对等离子弧焊从小孔形成到穿孔的瞬态演变行为、熔池流场的动态变化过程进行了数值模拟.开展了穿孔等离子弧焊接试验,对数值模拟结果进行了试验验证.结...     

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...     

三维静态锥体热源穿孔等离子弧焊接熔池的数值模拟

采用三维静态锥体热源对穿孔等离子弧焊接过程进行数值模拟.研究了三维锥体热源作用下焊接熔池流体流场、熔池内金属的流动方式以及熔池流体运动速度的变化.并与高斯热源条件下的模拟结果做比较.最后进行PAW焊接工艺试验,通过测量尾焰信号及焊缝尺寸等判断焊接熔池特征,将理论计算结果与试验测量值进行比较.     

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。     

激光等离子云穿孔检测技术的开发与应用

随着激光加工技术的快速发展及日益普及,生产加工效率成为行业关注重点。激光等离子云穿孔检测技术旨在最大程度减少加工过程中穿孔阶段设定的多余时间,实现穿孔转切割动作的无缝衔接,最大程度提高生产效率,提高产品的市场占有率。     

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。     

不锈钢制压力容器的等离子弧焊接

介绍了不锈钢制压力容器的等离子弧焊接，制定了合理的焊接工艺，并成功用于产品的焊接，为今后同类产品提供了参考和借鉴。     

脉冲等离子弧焊穿孔熔池的等离子云传感

在探针法检测等离子云理论基础上,研制了实用化的多探针等离子云传感器,并利用尾焰传感器对比检验了所设计传感器的可靠性和检测精度.将等离子云传感器应用于脉冲等离子弧焊穿孔熔池小孔状态检测,并对检测信号的波形特征做了深入研究.分析表明,等离子云检测信号中负脉冲信号可以作为脉冲等离子弧焊穿孔熔池的状态变化的特征判据,负脉冲信号的频率则可以作为脉冲焊接是否保持"一脉一孔"焊接的特征判据.等离子云电压信号可以很好的反映穿孔熔池的状态.     

微束等离子弧焊接焊缝熔宽的实时检测控制系统

采用微束等离子弧焊的方法直接制造金属零件是一种新型的快速成形制造工艺。控制累加层之间的累积精度，对控制成形零件的表面精度十分重要，用CCD对焊缝熔宽实行实时监控，考虑到弧光的干扰，对等离子弧光的光谱特性进行分析，采用窄带滤波方法，并对熔池图像进行处理，采用模糊控制实现对焊缝熔宽的实时监测，改善了成形零件的表面质量。     

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.     

Sensing controlled pulse key-holing condition in plasma arc welding

According to the strategy of controlled pulse key-holing, a new sensing and control system was developed for monitoring and controlling the keyhole condition during plasma arc welding (PAW). Through sensing and processing the efflux plasma voltage signals, the quantitative relationship among the welding current, efflux plasma voltage and backside weld width of the weld was established. PAW experiments show that the efflux plasma voltage can reflect the state of keyhole and backside weld width accurately. The closed-loop control tests validate the stability and reliability of the developed keyhole PAW 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.     

基于反翘电压的脉冲穿孔等离子弧焊熔透控制系统

采用无源探针检测系统从脉冲穿孔等离子弧焊的反翘电压信号中实时、准确、便捷地提取了熔池熔透信息.并以此作为反馈信号,以每个脉冲周期小孔存在时间作为被控制量,脉冲峰值电流作为控制量,采用MATLAB模糊逻辑工具箱进行熔透控制器的设计与仿真,以查表法完成了模糊控制系统的开发.结果表明,该系统可以在脉冲穿孔等离子弧焊接中实现"一脉一孔"过程,不仅保证了连续、稳定、可靠的穿孔焊接过程,而且可以得到良好的焊缝成形.     

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.     

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.     

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.