Analysis of arc voltage,current, and light signals in pulsed gas metal arc welding of aluminium

Abstract

The use of readily acquired weld arc data such as voltage, current, or light emissions to identify droplet transfer events or transfer mode, or for quality purposes such as seam tracking is of interest for thin section applications in arc welding of aluminium. In the present study, voltage, current, and light emission signals are acquired at high rates, and synchronised with high speed shadowgraphing. The usefulness of the various signals for identifying droplet detachment events and transfer modes during pulsed gas metal arc welding of aluminium is compared. It is found that individual droplet detachments are consistently identifiable during globular, spray, and streaming transfer, and during peak and background current detachment, using the voltage signal. Although the arc light signal also contains droplet detachment data, it is difficult to identify droplet detachments occurring during the background phase at low background current levels. Preliminary measurements show that these signals can also be used for seam location in thin section lap fillet welding.     

基于独立元分析的GMAW缺陷在线监测

采用独立元分析(ICA),用于气体保护焊过程在线监测.通过对过程的电参数进行独立元分析,去除焊接电流和电弧电压之间的相关性并提取出独立元.通过试验验证ICA对GMAW过程在线监测的可行性,发现当焊接过程有突变性干扰时,独立元(IC)能够对干扰做出反应.结果表明,IC可以作为表征过程是否异常的一个状态变量,通过对IC进行统计过程控制,能够分离出焊穿缺陷.并将ICA与主元分析(PCA)的结果进行了比较.     

Characterization of GMAW arc instability phenomena related to low oxidation potential shielding gases

Characterizing instability phenomena in arc welding may be a complex task, since they depend on a number of interrelated factors. Such phenomena may manifest themselves in various ways, acting on the characteristics of the arc, the metal transfer, the amount of splatter and fumes formed, the arc format, the geometry of the bead and other aspects of welding. The literature on the subject reports diverse forms of instability associated with arc welding with solid wire and gas shielding (GMAW). This work aimed to define the instability phenomena associated with the GMAW process in welding with gases with a low oxidation potential. To do so, the welding current and voltages were monitored and metal transfer was filmed at high speed. The welding tests were carried out on plates of common carbon steel with a source operating at a constant current and an electrode with positive polarity. By synchronizing the filming with the welding current and voltage signals, the results showed that, during the periods of highest voltage, the transfer tended to be globular repulsive, as opposed to spray transfer during the lowest voltage periods. The synchronization of the electrical signals with the optical sensor indicates that, during periods of unstable operation, the arc is more luminous. It also showed that more fumes were generated during these periods.     

Wire melting phenomena in gas metal arc welding

Abstract

The wire melting rate in gas metal arc welding using constant voltage power supplies is well described by a parabolic model that considers the effects of electrical resistance and arc heating. However, tests performed with constant current power supplies indicate that the melting rate can deviate from this model when welding current is close to the globular–spray transition value. Although the causes of this anomaly have not yet been well established, most authors consider them to be related to variations in liquid metal temperature close to the metal transfer mode transition current. The present work evaluates the effect of welding parameters on the wire melting rate when a constant current power supply is used. A numerical model that considers the contribution of both Joule and arc heating was developed to calculate the temperature distribution in the wire and its melting rate. The model was used to assess the changes in either arc heating or metal vaporisation that might explain the melting irregularities. High speed cinematography was used to analyse metal transfer in the current range associated with the melting irregularities.     

Measurement and theoretical investigation of arc sensor sensitivity in dynamic state during gas metal arc welding

Abstract

This paper shows the experimental and the theoretically predicted results of the sensitivity characteristics of the arc sensor in a dynamic state during gas metal arc welding. First, a mathematical model of the sensor for theoretical prediction was introduced, and then the rationality of the model was confirmed by a series of corresponding experiments. Finally, simulation analyses were made in order to clarify how the welding system and welding conditions affect the sensitivity characteristics of the arc sensor. It is shown that the frequency of torch height variation (the sensor's input) significantly affects the sensitivities of the welding current and the welding voltage (the sensor's outputs). The current sensitivity is highest when the frequency of torch height variation is ～5 Hz, but the voltage sensitivity simply increases with the increase of torch height variation frequency. It is also clarified that a decrease in the welding loop's inductance and/or the equivalent output resistance of the welding power source improves the sensor's current sensitivity but decreases voltage sensitivity. Decreasing the electrical resistance, but with an increase in electric field intensity of the arc column, or using a shorter setting electrode extension are useful ways of increasing the current and voltage sensitivities of the sensor.     

Measurement and calculation of arc power and heat transfer efficiency in pulsed gas metal arc welding

Abstract

This study investigates the heat transfer efficiency of the pulsed gas metal arc welding (GMAW-P) process. The arc power and heat input were calculated from arc current and voltage measurements and the heat input was also measured with a liquid nitrogen calorimeter. The measured heat transfer efficiency for GMAW-P varied slightly over a wide range of pulse parameters, with an average value of 70%, a maximum of 72% and a minimum of 68%. Welding heat transfer efficiency based on arc power calculated as the product of average current and voltage was too high (averaging 82%), while that calculated using the product of the root mean square (RMS) of the average current and voltage was too low (averaging 61%). Both also varied significantly with pulsing parameters. Mathematical analysis shows that average instantaneous power values must be used when current and voltage vary significantly with time. The experimental differences between the average instantaneous power and the other calculated values are explained by the relative phases of the pulsed current, voltage and arc resistance waveforms.     

Computer-based sensing and visualizing of metal transfer mode in gas metal arc welding

Using Xenon lamp lights to overcome the strong interference from the welding arc, a computer-based system is developed to sense and visualize the metal transfer in GMAW. This system combines through-the-arc sensing of the welding current and arc voltage with high speed imaging of the metal transfer. It can simultaneously display the metal transfer processes and waveforms of electrical welding parameters in real-time The metal transfer videos and waveforms of electrical welding parameters can be recorded. Metal transfers under various welding conditions have been investigated with the system developed.     

交流脉冲MIG弧焊电源及弧长控制

AC PMIG的控制模式是一周一脉一滴，脉冲电流设计在电弧EP极性时间里，其余时间均为基值电流。弧焊电源一次逆变控制电流快速动态过程，二次逆变控制电弧极性。控制系统采用双闭环结构，内环模拟控制电弧电流，外环80C196KC单片机控制电弧电压及电弧极性。根据电弧电压偏差信号及电弧状态，设计了四个控制规则及其控制参数的计算方法。正常焊接状态时变频控制交流脉冲频率。采用这种控制方案，获得了稳定性高、熔滴过渡均匀的焊接过程。     

压力对水下焊条局部干法焊接电弧稳定性的影响

在压力舱中进行不同压力下的水下焊条局部干法焊接试验,采用统计分析和快速傅立叶变换研究了压力对水下电弧稳定性的影响.结果表明,铁粉低氢钾型焊条焊接主要进行粗熔滴短路过渡,随着压力的增加,短路时间由常压焊接的5~7 ms增加到8~10 ms,表明熔滴的平均尺寸增大.压力环境下,焊条熔化速度增大,弧压反馈调节系统的工作点上移,电弧电压增大.傅里叶变换结果表明,常压电弧电压信号的主要特征频率低于10 Hz,压力下电压信号的频谱图中出现大量高于10 Hz的谱线,说明信号突变性更强,电弧稳定性降低.     

CO2气体保护焊的新型全数字化波形控制技术

对于逆变弧焊电源,采用基于 DSP 的全数字控制策略.针对短路过渡 CO2 气体保护焊特点,提出了准恒压全数字化新型波形控制策略,不再根据输出电压区分短路和燃弧过程,使得短路和燃弧过程过渡自然,适应于所有的焊接工艺,提高了系统的适应性.同时在短路初期采用瞬态电流抑制技术减少了飞溅,建立了包含实时燃弧能量补充机制的全数字化电压电流瞬时反馈的全数字三闭环控制模型.结果表明,所提出的全数字化软开关控制策略灵活、可靠;所采用的数字波形控制技术适应性好、灵活、焊接过程稳定、焊缝成形优良.

Abstract：

According to the characteristics of short circuit transfer of CO2 gas metal arc welding, a novel full digital waveform control scheme called quasi-constant voltage control is presented for inverter type arc welding power based on DSP. Short circuit and arc ignition process are not judged according to the output voltage and transfer process between them is smooth. The strategy is also applied to all welding conditions. Initial current at the instant of short-circuit is suppressed to reduce spatter generation. A triple closed loop control model including real time energy compensation for the arc state based on instantaneous voltage and current feedback control is estabhshed. Flexibility and reliability of the proposed fully digitalized softswitching control strategy is validated by experimental results of 400 A welding machine. The experimental results show that proposed digital waveform control scheme is applicable for different wire feeding speed conditions, and the welding process is stable and the welding bead appearance is good.     

熔化极气体保护焊的直接自适应控制

焊接电流和电弧长度是熔化极气体保护焊(GMAW)焊接过程的主要状态变量,决定了熔滴的过渡过程、热量输入和焊缝成形.文中在分析GAMW焊接工艺过程的基础上,建立了焊接电流和电弧长度的数学模型,采用基于二次型性能指标的直接自适应控制算法,通过调节焊接电源输出电压和送丝速度的大小,使焊接电流和电弧长度能跟踪参考模型的输出.同时,针对实际应用中难以检测的电弧长度,建立了电弧长度估计模型,实现了对电弧长度的软测量.结果表明,该算法可以实现弧长和电流的精确控制.     

双丝旁路耦合电弧高效熔化极气体保护焊“弧长-电流”双路闭环控制

针对新型双丝旁路耦合电弧高效熔化极气体保护焊过程极不稳定、焊缝成形差的问题,模拟分析了焊接参数之间的影响规律,提出了通过旁路送丝速度控制旁路弧长、通过旁路电流控制母材电流的"弧长-电流"双路闭环控制方案并进行了控制模拟分析与预测.在此基础上,采用快速原型试验系统,利用Matlab/Simulink,进行了"弧长-电流"双路闭环控制焊接试验并与模拟结果进行了对比、验证与分析.结果表明,采用"弧长-电流"双路闭环控制方案,可以在有效地解决焊接过程稳定性问题的同时保证流经母材电流的稳定,并得到了成形良好的焊缝.     

激光功率对激光-双丝脉冲MIG复合焊接电弧形态及熔滴过渡的影响

通过搭建激光-双丝脉冲MIG复合焊接系统,利用高速摄像与电信号采集系统对激光-双丝脉冲MIG复合焊接在不同激光功率下的电压电流信号及高速摄像信号进行同步采集,研究激光功率对焊接过程的电弧形态、熔滴过渡过程的影响.结果发现,由于激光等离子体与电弧等离子体的相互作用,电弧形态和熔滴受力状态发生改变.随着激光功率的增大,激光对电弧的吸引能力增强,促进熔滴过渡的等离子流力竖直向下的分力减小,熔滴过渡频率降低.     

Gas metal arc weldability of 1.5 GPa grade martensitic steels

The gas metal arc weldability of 1.5 GPa grade martensitic (MART) steel was evaluated using both inverter direct current (DC) and DC pulse power type welders, under conditions of different welding currents, welding speeds, and shielding gasses. By investigating the bead appearance, tensile strength, and arc stability, it was determined that DC pulse power is better than inverter DC power for arc welding of 1.3 mm thick 1.5 GPa grade MART steel. Further, from the results of the weldability for various shielding gases, it was determined that mixed shielding gas is more effective for welding 1.5 GPa grade MART steel than is pure inert gas (Ar) or active (CO₂) gas. In the case of pure shielding gas, no sound bead was formed under any conditions. However, when the mixed shielding gas was used, sound and fine beads were obtained.     

Determining the boundaries of globular-to-spray transfer in robotic GMAW

Robotic gas metal arc welding （GMAW） experiments were conducted using an ERTOS-1 electrode with Ar ＋ 10% CO2 shielding gas, and the welding current and arc voltage signals were collected by a data acquisition system. The boundaries between globular transfer and spray transfer in terms of the welding current and arc voltage were determined according to the waveform of electric signals and the Fourier transform results of arc voltage. The optimum welding parameters for the two transfer modes were obtained, which laid a foundation for the numerical simulation and control of GMAW process.     

金属粉末再压缩等离子弧焊接工艺

提高电弧穿透能力是等离子弧焊接领域的重要课题.自主设计并搭建了金属粉末再压缩等离子弧焊接新工艺试验平台,采集焊接过程电信号、视觉信号、弧光光谱信号等,并从焊缝成形、电弧电压、熔融金属过渡、弧光光谱等方面对金属粉末再压缩等离子弧焊接过程进行了初步的研究.在相同焊接电流195 A条件下,与常规等离子弧焊接工艺相比,金属粉末再压缩等离子弧焊接焊缝熔深增加1.29 mm、熔宽减少1.65 mm、电弧电压升高0.63 V.在波长为230 ~ 270 nm范围内,与常规等离子弧焊接相比,金属粉末再压缩等离子弧焊接中Fe和Cr元素的特征谱线明显增多. 结果表明,在相同电流条件下,与常规等离子弧焊接相比,金属粉末再压缩等离子弧焊接电弧穿透能力增强.     

TIG焊电弧辅助MIG焊引弧过程分析与机理探讨

在TIG-MIG复合焊中,先引燃的TIG焊电弧能够辅助MIG焊实现非接触引弧,且在整个非接触引弧过程中不产生焊接飞溅. 利用电信号与高速摄像同步采集系统获取MIG焊引弧过程的电弧电压、焊接电流和电弧图像,研究了先引燃的TIG焊电弧及其参数变化对MIG焊引弧过程及引弧方式的影响. 结果表明,细长放电通道形成于MIG焊丝末端与TIG焊电弧之间是TIG焊电弧辅助MIG焊实现非接触引弧的关键;TIG焊电弧辅助MIG焊实现非接触引弧对TIG焊接参数的变化具有良好的适应性. 此外,基于气体间隙击穿的流注理论,探讨了细长放电通道的形成过程,揭示了TIG焊电弧辅助MIG焊实现非接触引弧的机理.     

基于自相关分析的电弧焊熔滴过渡过程稳定性的定量评价

文中提出了基于自相关分析的定量评价方法,从电弧焊的电压电流信号中提取自相关函数峰值间距变异系数,作为电弧焊熔滴过渡过程稳定性评价的量值.结果表明,该方法所得的结果与人工分析判定的结果一致,切实可行.此外,该方法所提取的量值与其它量值联合使用,还较好地实现了CO2弧焊电源动特性的自动化评定.其准确率达97.4359%,已接近实际应用的要求.     

Parametric approach to positional fault detection in short arc welding

Abstract

This work investigates a parametric technique for short arc welding fault detection. The independent component analysis algorithm is applied to split welding voltage and current signals into arcing and short circuiting regions. A series of parameters including means, medians and normalised inner products are calculated by processing the different sections of welding electrical data. Out of position welds in overlap joints are studied with investigation of the connection between parameters and short arc welding features. The effect of changing shielding gas is also illustrated. Figures of merit to quantify the change in various parameters between faulty and good welds are compared and discussed. It is shown that the data separation into two regions with independent component analysis is useful in providing various parameters that can assist in short arc welding fault detection under different conditions.