Closed-loop control of weld penetration in keyhole plasma arc welding

To improve the penetrating ability and the welding quality of keyhole plasma arc welding, a novel penetration closed-loop control system was established. In the system, welding current and plasma gas flow rate were selected as adjusting variables. The wavelet method was used to detect penetration status from welding arc voltage in real-time. The control strategy of one-keyhole-per-pulse was adapted to fulfill stable and high quality welding process. Experimental results show that the developed system can apparently increase the penetrating force of plasma arc and keyhole plasma arc welding is realized successfully in stainless steel with 10 mm in thickness. Moreover,the disturbances of gradual change and break change from 3mm to 6mm in thickness are come over due to the good response property of the developed system.     

一种新型等离子小孔焊接熔透闭环控制系统

建立了以电流和等离子体气流为控制变量的等子体小孔焊接熔透闭环控制系统，采用小波方法从焊接电弧电压信号中实时、准确地提取熔池穿孔信息，通过对2个参量的协调控制，成功地实现了“一脉一孔”的焊接工艺。实验表明，该系统不仅显著地提高了电弧穿透力，．能够有效地对10mm厚不锈钢进行小孔型焊接，而且具有良好的快速响应性能，成功克服了3－6mm厚度渐变及附跃变化带来的扰动，实现连续、稳定、可靠的较厚板穿孔焊接。     

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.     

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。     

焊枪行走角变化对等离子弧穿孔立焊焊缝成形的影响规律

以5 mm厚的5A06铝镁合金板材为主要研究对象,焊缝的正面熔宽和背面熔宽为成形特征参数,通过正交试验确定焊枪行走角变化对焊缝成形影响的显著性,从能量传递的角度研究了焊枪行走角的变化对等离子弧穿孔立焊焊缝成形产生影响的机理.结果表明,焊枪行走角对焊缝成形的影响在焊接电流和离子气体流量之间;焊枪与试板垂直时正面熔宽最大,而随着行走角的减小,焊缝背面熔宽逐渐增大.焊枪行走角的改变使熔池正面的能量密度以及背面最高温度截面和最大熔宽截面的相对位置发生变化,对焊缝背面熔宽的影响可归结于厚度方向不同截面热源位置的偏离与工件厚度导致的传热滞后之间相互作用的结果.     

铝合金变极性等离子弧穿孔横焊焊缝成形规律分析

以穿孔等离子弧焊接过程中形成的穿孔熔池为研究对象,根据熔池热源形态的特点,采用数值模拟与试验相结合的手段研究横焊位置下的铝合金变极性等离子弧焊缝成形.由于焊接速度波动和工件厚度的影响,体热源作用下的穿孔熔池背面存在最高温度点和最大熔宽截面相背离的现象;因此通过对穿孔熔池背面进行分区和定义,提出温宽偏离度概念,即熔池背面最高温度点和最大熔宽截面的偏离程度,用以描述穿孔熔池状态及焊缝成形;通过调节焊枪角度来改变焊接过程中的温宽偏离度,在其它参数不变的情况下减轻重力在焊接过程中对焊缝成形的影响,实现变极性等离子弧穿孔焊接在横焊位置上的良好成形.     

Simultaneous observation of keyhole and weld pool in plasma arc welding with a single cost-effective sensor

The dynamic behaviors of the keyhole and weld pool are coupled together in plasma arc welding, and the geometric variations of both the keyhole and the weld pool determine the weld quality. It is of great significance to simultaneously sense and monitor the keyhole and the weld pool behaviors by using a single low-cost vision sensor in plasma arc welding process. In this study, the keyhole and weld pool were observed and measured under different levels of welding current by using the near infrared sensing technology and the charge coupled device （CCD） sensing system. The shapes and relative position of weld pool and keyhole under different conditions were compared and analyzed. The observation results lay solid foundation for controlling weld quality and understanding the underlying process mechanisms.     

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。     

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。     

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。     

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.     

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.     

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.     

Numerical analysis of transient keyhole shape in pulsed current plasma arc welding

Based on the characteristics of ＂one keyhole in a pulse＂ in pulsed current plasma arc welding （PAW） , the transient variation process of weld pool in a pulse cycle is simulated through the establishment of corresponding heat source model. And considering the effects of gravitational force, plasma arc pressure and surface tension on the weld pool surface, the dynamic change features of the keyhole shape in a pulse cycle are calculated by using surface deformation equation. Experiments are conducted and validate that the calctdated weld fusion line is in good agreement with the experimental results.     

Numerical analysis of keyhole establishment time in keyhole plasma arc welding

Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional transient model is developed to analyze the evolutions of keyhole shape and keyhole establishment time in continuous current plasma arc welding process. Firstly, a combined volumetric heat source model is used to simulate the transient variation of temperature field. And then the surfaced formation equation is adopted to calculate dynamic features of the keyhole shape and keyhole establishment time inside weld pool, in which the force action on weld pool surface is considered. Experiment is conducted to validate the numerical simulation results. The predicted keyhole size and keyhole establishment time are in agreement with the experimental measurement. And the calculated fusion zone geometry is consistent with the measured one.     

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.     

等离子弧焊接小孔行为检测方法概述

阐述了小孔型等离子弧焊接的工艺特点,解释了检测小孔行为的原因;详细介绍了目前小孔型等离子弧焊接过程中检测小孔行为的主要方法,并分析了各种方法的利弊;最后对这种先进的材料加工技术作出了展望。     

铝合金等离子弧立焊穿孔熔池的计算机模拟

根据流体力学理论和传热学机理，建立了运动等离子弧作用下立焊穿孔焊接熔池流场和温度场的三维瞬态数值分析模型，并采用有限元法对模型进行离散化处理。模型中，考虑了熔池内部液态金属的对流传热和熔池外部的固体导热、材料热物理性能参数随温度的变化、焊件表面通过对流和辐射向周围环境的散热以及熔化／凝固相变潜热对熔池流场与温度场的影响，焊接热源采用高斯分布函数，计算中对边界条件进行了处理，根据穿孔熔池温度场与流场模型的特点，采用非均匀网格对单元进行划分，并采用分区异步长算法确定时间步长，利用ANSYS(一种有限元计算软件)有限元软件对所建立的模型进行了求解。通过试验测量焊缝几何尺寸与计算结果相比较，验证了本模型的计算结果和实际相差不大，是基本正确和可靠的。     

小孔等离子弧焊接能量分配及损失分析

通过公式计算对小孔等离子弧焊的等离子孤功率损失进行分析.等离子弧在焊接过程中的功率损失包括等离子弧通过喷嘴的功率损失、喷嘴出口到小孔的等离子弧功率损失、等离子弧穿过小孔的功率损失等.通过定量计算,研究了等离子弧在焊接过程中的功率损失以及在穿孔焊接过程中形成小孔所需要的等离子孤功率大小等问题.     

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.