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.

Closed-loop control system design and experimental study for controlled pulse keyhole plasma arc welding

The controlled pulse waveform is newly applied in keyhole plasma arc welding process. Two additional descending slopes can guarantee stable and smooth transition of keyhole closing and opening periodically. To develop a closed-loop control system for this special welding process, the key point is the determination of system input and output variables. The averaged efflux plasma voltage during a pulse cycle is defined as the characteristic variable reflecting the real keyhole dimension. Research and experiments are conducted to explore the relationship between the characteristic variable and weld pe^Cormance. Results show that alternated peak current can significantly change the keyhole dimension and the penetration. It is proposed that the keyhole average dimension is taken as the controlled variable, and the peak pulse current value and slopes are taken as control variables.

System Identification of Controlled Pulse Keyhole Plasma Arc Welding Process

The development of closed-loop control systems is one of the most effective ways to improve the stability of the keyhole status during keyhole plasma arc welding （K-PAW）. Due to the disadvantages of the ＂one-pulse-one-keyhole＂ technology based on the conventional square current waveform, the controlled pulse welding current waveform is newly applied to control the keyhole open and close periodically. In order to realize the real-time control on the keyhole behavior with this advanced current waveform, welding experiments and system identification are conducted based on the classical control theory. One complete welding cycle can be divided into 3 periods. The keyhole establishing time is the most important time variable, which determines the keyhole behavior and welding process stability. At the same time, the averaged effiux plasma arc voltage during one pulse cycle can reflect the real keyhole dimension and status in a real-time manner. Therefore, two single-input-single-output （SISO） systems are proposed, in which keyhole establishing time and keyhole average dimension are taken as the system controlled variables respectively. Welding experiments are designed with the peak current varying randomly. Experiments show that the keyhole establishing time changes in an opposite direction to the varied peak current, and the averaged efflux plasma arc voltage varies with the same trend as the peak current. Based on the least squares technique and F test of classical system identification, second order difference equation for keyhole establishing time/peak current system and first order difference equation for keyhole average dimension/peak current system are obtained. It is proved that the calculated data by the two mathematical expressions are well matched with the measured data. The proposed research provides mathematical expressions and theoretical analysis to develop closed-loop systems for the controlled pulse K-PAW.

Welding of Ti-6Al-4V alloy using dynamically controlled plasma arc welding process

A novel dynamically controlled plasma arc welding process was introduced,which is able tominimize heat input into the workpiece materials while maintaining desired full penetration,and it was used to weld Ti-6Al-4V alloy sheets.The microstructures,facture surfaces and microhardness of the welded joints were characterized by using optical microscope,scanning electron microscope （SEM） and Vickers microhardness tester.Comparing with welds such as gas tungsten arc and conventional plasma arc processes,the experimental results revealed the improvements when using the present process including：1） reducing prior-beta （β） grain size and prohibiting formation of hard martensite phases in the fusion zone due to the decreased heat input;and 2） better toughness and higher hardness.

Effects of controlled pulse current waveform on key-holing condition in plasma arc welding

To overcome the shortcomings of conventional plasma arc welding （ PAW）, the ＇ controlled pulse key-holing＇ strategy is proposed and the keyhole PAW experiment system is developed. ＇The efflux plasma voltage signal is detected in realtime to characterize the keyhole size and dimension. The welding current waveform for controlled pulse key-holing strategy is implemented, and two slow-decreasing slopes are added at the dropping point from peak current to base current to further reduce both heat input and arc force so that the controllability of keyhole dynamics is improved. Two kinds of PAW tests are conducted, anti the different parameters of the controlled pulse current and the relevant efflux plasma voltage are measured in real-time to investigate ihe effects of welding current waveform parameters on the key-holing condition.

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.

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 3 mm to 6 mm in thickness are come over due to the good response property of the developed system.

BASIC THEORY AND APPLICATIONS OF WELDING ARC SPECTRAL INFORMATION

Welding arc spectral information is a rising welding information source. In some occasion, it can reflect many physical phenomena of welding process and solve many problems that cannot be done with arc electric information, acoustic information and other arc information. It is of important significance in developing automatic control technique of welding process and other similar process. Many years study work on welding arc spectral information of the anthor are discussed from three aspects of theory, method and application. Basic theory, view and testing methods of welding arc spectral information has been put forward. In application aspects, many applied examples, for example, monitoring of harmful gases in arc （such as hydrogen and nitrogen） with the method of welding arc spectral information; welding arc spectral imaging of the welding pool which is used in automatic seam tracking; controlling of welding droplet transfer with welding arc spectral information and so on, are introduced. Especially, the successful application in real time controlling of welding droplet transfer in pulsed GMAW is introduced too. These application examples show that the welding arc spectral information has great applied significance and development potentialities. These .content will play an important role in applying and spreading welding arc spectral informarion technology.

BASIC THEORY AND METHOD OF WELDING ARC SPECTRAL INFORMATION

Arc spectral information is a rising information source which can solve manyproblems that can not be done with arc electric information and other arc information. It is ofimportant significance to develop automatic control technique of welding process. The basic theoryand methods on it play an important role in expounding and applying arc spectral information. Usingconcerned equation in plasma physics and spectrum theory, a system of equations including 12equations which serve as basic theory of arc spectral information is set up. Through analyzing ofthe 12 equations, a basic view that arc spectral information is the reflection of arc state andstate variation, and is the most abundant information resource reflecting welding arc process isdrawn. Furthermore, based on the basic theory, the basic methods of test and control of arc spectralinformation and points out some applications of it are discussesed.

变极性等离子弧焊技术发展及其在航天制造领域应用现状

变极性等离子弧(VariablePolarityPlasmaArc,VPPA)焊是一种高效的铝合金和镁合金焊接方法,其主要优势在于等离子电弧具有高能量密度,可以在焊接时穿透熔池形成小孔,大幅度降低焊接变形和残余应力,提高焊接质量。了解熔池小孔行为、电弧物理特性和控制方法对于优化和提高焊接过程的稳定性至关重要。本文综述了VPPA焊接技术发展的最新情况,对VPPA焊接过程信息的检测研究为深刻认识焊接稳定性机理提供了有力保障,尤其是利用X射线成像系统观测熔融金属流动的研究,对提升VPPA穿孔熔池物理本质的认识做出了重要贡献。此外,针对不同位置VPPA焊接的研究增加了这一焊接工艺的灵活性,由VPPA焊接衍生的多种拓展工艺拓宽了该焊接方法的适用范围。VPPA穿孔焊接技术以其焊接变形小、焊后无缺陷、单面焊接双面一次成形等优势,成为航空航天领域铝合金中厚板材焊接制造的优选工艺。

增量型PID恒流恒压控制的Plasma-MIG复合电弧焊接

Plasma-MIG复合电弧焊接对电源的外特性输出及焊接过程控制有着很高的要求,以VC++软件开发工具为平台,推导了适合于Plasma-MIG复合电弧焊接的增量型PID控制算法,实现了对复合电弧焊接过程控制及电源外特性的要求.结果表明,增量型PID恒流恒压控制能够满足Plasma-MIG对电源外特性的输出要求.Plasma电弧和MIG电弧并不是相互独立的,两者以共享的电磁空间、导电气氛和焊丝为媒介建立起耦合关系.Plasma-MIG复合电弧焊接过程中,增量型PID控制下的Plasma电弧能够自发的调节自身电参数,来稳定电弧空间的电流密度,使得焊接过程中无飞溅.采用控制后,Plasma-MIG复合电弧焊焊接过程焊缝铺展好,焊接过程稳定,焊缝成形好.

厚板铝合金变极性等离子弧焊电弧物理特性

为克服厚板铝合金穿孔焊接熔池极易失稳的难题,该研究从厚板焊接时电弧温度场出发,旨在探究厚板穿孔焊接熔池稳定性的机理。通过建立三维数值模型,研究了焊接母材厚度分别为5 mm和16 mm下变极性等离子电弧的温度场、流场和电流密度分布。结果表明,随着板厚的增加,变极性等离子电弧温度场分布发生改变,5 mm板厚电弧温度的衰减情况为线性,而16 mm厚板焊接的电弧温度衰减情况为二次型,使得温度变化更加复杂。变极性等离子弧焊接5 mm厚度铝合金时,整个小孔熔池的电流密度呈1.0×10^(6) A/m^(2)以上,但是在焊接16 mm厚板铝合金时,相同电流密度仅达到小孔深度的12 mm处。该研究有望对实现大厚度铝合金稳定焊接,拓宽变极性等离子弧焊接应用范围提供理论指导。

TA2中厚板低功率激光诱导双电弧高效焊接及机理

采用低功率脉冲激光诱导双TIG复合焊接热源(LITTW)实现了6 mm厚TA2纯钛中厚板的高效焊接,基于Ti粒子的动力学行为,研究了激光脉冲对电弧等离子体的影响.结果表明,LITTW比激光诱导单TIG焊接(LISTW)的电弧能量更加集中,焊接能耗仅为LISTW的50.9%,速度却达到LISTW的2.3倍.激光脉冲作用后,电弧等离子体由能量集中状态恢复到原始电弧形态存在一个恢复时间,在本试验条件下,LITTW的恢复时间为6.5 ms,比LISTW延长了3 ms.LITTW中稳定的匙孔形态为Ti粒子持续向电弧等离子体转移提供了条件,延长了电弧等离子体的恢复时间。

基于机器学习的薄板等离子弧搭接焊的熔深预测

在等离子弧搭接焊中,搭接焊接头的焊缝熔深是评价焊接质量的关键指标之一,而焊接过程中的热输入信息和熔池图像信息都与焊缝熔深有密切关系。本文通过建立304L不锈钢薄板等离子弧搭接焊数据采集系统,利用LabVIEW实时检测电信息,采用视觉传感技术实时获取薄板等离子弧搭接焊过程中的熔池图像,并通过图像处理方法获得熔池的几何参数信息,结合焊接工艺参数,选择峰值电流、峰值电压、焊接速度、离子气流量、保护气流量、熔池宽度和熔池后端长度作为输入量,焊缝熔深作为输出量,建立了基于支持向量机回归和BP神经网络的熔深预测模型。实验验证表明,采用径向基函数的支持向量机回归模型可以有效地对焊缝熔深进行预测,并具有很好的泛化能力,可为进一步实现在线优化焊接工艺参数提供依据。

基于遗传算法的超薄板焊接接头检测识别

超薄板在切割过程中会产生毛刺和剪切不齐的现象,大大增加了焊接过程中出现烧穿、焊接变形等焊接缺陷的几率。因此,本文计划使用图像检测平台,通过检测识别实时调节焊接过程中的热量输入,以降低超薄板焊接缺陷出现的几率。优化后的算法可迅速、精细地检测和识别超薄板的剪切不齐和毛刺,将此检测平台应用于智能化焊接设备,可实时检测、识别与调节焊接参数,抑制超薄板焊接缺陷的产生,形成完整的超薄板缺陷抑制系统。

超薄板脉冲微束等离子弧焊熔池振荡特征

由于熔池的振荡行为,熔池轮廓的动态变化具有一定的波动性.基于视觉传感检测方法,研究0.1 mm厚超薄板不锈钢脉冲微束等离子弧焊接的熔池振荡行为,讨论焊接电流的不同脉冲参数对熔池振荡频率和振幅的影响.结果表明,在基值电流和峰值电流作用期间,熔池的大小是小幅度波动的,这是由熔池振荡引起的;熔池的振荡频率在一定范围内随着脉冲电流的频率增加而增加,而熔池振荡幅度随脉冲电流频率的加大而减小.熔池的振荡频率可以反映焊缝成形质量的好坏.

基于机器学习和Modbus的超薄板微束等离子弧焊控制系统设计

微束等离子弧焊接超薄板在工业中应用广泛,但焊接难度大、焊缝对中和焊接热输入要求高。焊接过程需要进行参数的超精细调节以获得良好的焊接质量。针对这一问题,提出了超薄板微束等离子弧焊控制系统。系统基于机器学习和Modbus通讯协议对下位机进行指令输出。利用VisualStudio 2015开发环境,设计了图像预处理模块、视觉测量模块、电流输出模块和通讯模块,实现了焊缝对中和焊接热输入的精确实时调整,改善了焊缝成型,提升了焊接质量。

焊接电弧光谱信息的基本理论和基本方法

电弧光谱信息是继电弧电信息后的一种新兴的信息源 ,对发展焊接过程自动控制技术有重要意义。有关它的基本理论和基本的测控方法对阐明和应用电弧光谱信息技术有重要作用。利用等离子体物理学和光谱学的现有理论 ,组织起包括 12个物理方程的方程组 ,作为电弧光谱信息的基本理论。对基本理论的 12个方程进行分析 ,得出了电弧光谱信息是电弧状态和状态变化的反映 ,它是反映电弧过程的最丰富的信息源的基本观点。从已建立的基本理论还可以得出电弧光谱信息测控的基本原理和基本方法 。

自动化等离子堆焊技术在发动机缸体再制造中的应用

在构建自动化粉末等离子堆焊再制造系统的基础上,选择Ni15合金粉末为堆焊材料,通过发动机缸体止推面再制造堆焊试验对再制造系统进行了验证,并对堆焊组织进行了金相及能谱分析,表明堆焊层组织没有任何气孔、裂纹等冶金缺陷。底部能谱分析表明,底部组织由Ni、Fe中固溶Cr形成的奥氏体基体和基体上弥散分布的碳化物硬质相及其共晶组织组成,平面晶区域有明显的溶碳现象。硬度测试表明,堆焊层除熔合区因溶碳硬度较高,达200HV,其余区域硬度值与基体相当,达130HV。每再制造一个发动机缸体止推面,约消耗合金粉末40g,材料成本不到20元,具有显著的节材及经济效益。

受控脉冲穿孔等离子弧焊接控制系统

穿孔等离子弧焊接过程中存在的一些问题制约了该工艺在现代工业中的推广和应用,如焊接工艺合理参数区间窄,可调裕度小,导致焊接过程中小孔的稳定性较差等。熔池的小孔行为是直接影响焊接过程稳定性和接头质量的关键因素,为拓展合理工艺参数范围,提高焊接过程稳定性和焊缝质量,研制出受控脉冲穿孔等离子弧焊接控制系统。基于简易测试装置,实时采集焊接过程中的尾焰电压信号,可靠描述焊缝熔池穿孔与否以及小孔尺寸;采用受控脉冲穿孔的控制策略,适时调整峰值电流和基值电流的作用时间,使得小孔一直处于'准稳态'。实现'一脉一孔',但脉冲时间和基值电流并不固定,取决于每个脉冲过程小孔的建立时间和存在时间;保证穿孔,使小孔尺寸在预定值附近波动,并防止烧穿的发生;大幅拓展穿孔等离子弧焊接合理工艺参数区间。工艺试验结果表明,当工件散热条件和厚度发生变化时,控制系统能够迅速做出调节,运行稳定可靠,控制效果显著。