Plasma arc brazing in sheet metal construction

Abstract

Because of the high heat input required, conventional welding methods may not always be ideal for mild and high strength steel sheets. A possible alternative in some applications is plasma brazing, which can also serve as a supplement to other joining techniques. A characteristic feature of the process is the separation between the energy input and filler material. Compared with high heat processes, plasma brazing causes considerably less distortion of joints or panels. Almost no spatter results from the process. The brazed seams exhibit sound mechanical properties as well as good appearance. However, there are difficulties associated with brazing some high strength steels using the filler wires commercially available at present.     

Pseudorandom noise injection as diagnostic tool for gas metal arc welding systems

Abstract

The present work reports results obtained by applying pseudorandom noise injection to the gas metal arc welding process to determine the impulse response of the system (the response to a short pulse of energy). The phenomena having the longest time constants are investigated and it is found that there is a damped oscillation associated with delayed heating of the anode wire stickout. Properties of the oscillation are measured and found to agree with previous research. It is demonstrated that the pseudorandom noise injection technique has advantages in investigating welding processes in which it is desired to determine operating characteristics without significantly perturbing welding.     

Investigation on arc sound and metal transfer modes for on-line monitoring in pulsed gas metal arc welding

The arc sound was found to be strongly related to both process parameters and weld quality, like voltage and current signals, in gas metal arc welding. In this investigation, the acquired welding arc sound signal along with current and voltage signals were analyzed in time domain as well as frequency domain to correlate them with the various process parameters and metal transfer modes. The arc sound of continuous as well as pulsed gas metal arc welding at various process parameters was also compared. A major variation of auxiliary arc sound frequency peaks was observed due to change of pulse shape as evidenced by frequency domain analysis. The arc sound was also used to detect welding defects.     

Plasma channel formation for triggering arc welding

Abstract

A method of starting arc welding using a plasma channel formed between electrodes in a tungsten inert gas arc welding system was demonstrated. The plasma channel was generated by gas breakdown in the laser beam path. In a previous study by the present authors, the arc welding could be started using a laser produced plume. Results in the present study indicated that the laser energy required to start the process using the plasma channel was lower than that using the plume.     

发动机排气门等离子熔覆再制造

介绍了粉末等离子熔覆再制造系统.选择ST6合金粉末为熔覆材料,对失效发动机排气门进行再制造等离子熔覆试验,并通过OM和EDS对熔覆组织的显微形貌进行观察与分析.结果表明,熔覆层组织由Co中固溶Ni、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,熔覆层平均硬度达552.8 HV0.1,性能检测表明采用粉末等离子熔覆技术熔覆ST6合金粉末完全能够达到排气门再制造的要求.     

熔化极气体保护焊电流与电压调节

在应用熔化极气体保护焊的基础上,分析焊接电流和电弧电压对焊缝成形的影响,探究焊接电流与电弧电压匹配对焊接电弧特性的影响规律,总结正确调节焊接电流与电弧电压的基本方法和操作技能,正确调节焊接电流与电弧电压是熔化极气体保护焊技术推广与应用的关键因素。     

旁路耦合电弧高效焊接工艺的数字化与智能化

旁路耦合电弧GMAW在实现提高焊丝熔敷率的同时减少了母材热输入,大幅降低电弧压力和熔滴射滴过渡的临界电流,实现高速焊接与异种金属间的焊接.近年来,兰州理工大学针对该方法展开了一系列研究,利用数字化模拟技术,采用多场全耦合方法,模拟了双旁路耦合电弧形态及热场、流场、电磁场的分布;模拟分析旁路耦合电弧脉冲GMAW在铝-钢异种金属焊接过程中,工件温度场的变化与接头界面上的原子扩散行为;建立了双丝旁路耦合电弧GMAW的数字化自动控制平台,并采用模糊控制算法实现了单闭环智能控制与双闭环解耦的智能控制.     

推动电子废弃物处理产业与再生金属产业联动发展迫在眉睫

<正>以稀贵金属、有色金属作为主要目标产品和收益点的电子废弃物处理产业,已成为我国再生有色金属产业的重要组成部分,其环境效益和经济效益明显。自《废弃电器电子产品回收处理管理条例》(以下简称《条例》)、《废弃电器电子产品处理基金征收使用管理办法》等法规政策实施以来,废弃电器电子产品拆解处     

双丝间接电弧氩气保护焊的熔滴过渡与电弧形态

用高速摄像系统及示波器对双丝间接电弧氩弧焊的熔滴过渡及电弧形态和电弧电压之间的关系进行了深入分析.结果表明,熔滴过渡和电弧电压、电弧形态的规律性变化存在密切的对应关系.熔滴形成、长大、脱离焊丝端部的规律性变化使极性斑点间距及弧柱电阻发生变化导致了电弧电压的波动,从而使电弧形态发生由暗到明、由小到大的规律性变化.随着焊接电流的增大熔滴的过渡形式发生变化,熔滴尺寸减小.不同的熔滴过渡形式其电弧电压的波动也有所不同,射流过渡电压波动较小,而短路过渡电弧电压的波动最大.     

焊接电弧的等离子流力

以试验为基础，分析了直流ＴＩＧ电弧阳极热斑表面等离子流力的径向分布，数学表达式，电弧长度及电流的影响，阐述了该力在整个电弧机械作用力中的地位。     

Plasma transferred arc deposition of beryllium

The exceptional properties of beryllium (Be), including low density and high elastic modulus, make it the material of choice in many defense and aerospace applications. However, health hazards associated with Be material handling limit the applications that are suited for its use. Innovative solutions that enable continued use of Be in critical applications while addressing worker health concerns are highly desirable. Plasma transferred arc solid free-form fabrication is being evaluated as a Be fabrication technique for civilian and military space-based components. Initial experiments producing Be deposits are reported here. Deposit shape, microstructure, and mechanical properties are reported. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Plasma arc cutting torch tracking control

Abstract

The present paper is concerned with a tracking system for cutting torch height in the plasma arc process. The computer based control system consists of the sensing and detection unit, controller, and servo actuator. The use of arc and laser sensors to detect the torch height is presented, and their applied characteristics are investigated in detail. A feedforward compensation of workpiece position is introduced to improve tracking properties. Moreover, to address the non-linear characteristics of the arc sensor, deviation classification and adaptive control approaches are also proposed. Tracking experimental results show acceptable tracking precision and strong noise restraining capability for the system. These demonstrate the effectiveness of the sensing and detection, and the proposed control algorithms. It is also shown that the arc sensing approach is more attractive, owing to its merits of synchronous sensing, high reliability, and low cost.     

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.     

焊条电弧焊电弧物理及化学冶金若干问题

通过焊条熔化和熔滴过渡的基础研究,分析了不锈钢焊条发红开裂的问题,把一个焊条工艺问题转化为电弧物理的研究问题予以解决,说明焊条研制中基础研究的重要性,同样也阐述了碱性焊条飞溅的问题要由其化学冶金的基础研究来解决,文中也示出了电弧物理及化学冶金研究的方法和装置以及研究得到的主要结果.     

Through arc sensing in gas metal arc welding with signature images

Abstract

This work presents a new method for through the arc estimation of welding parameters in gas metal arc welding based on signature images. The method is generally applicable and makes use of a novel data fitting procedure. The work covers unassisted through the arc estimation, without auxiliary techniques such as welding head oscillation. The technique is demonstrated for both pulse and short circuiting welding, with estimation of position relative to an overlap joint and a narrow gap weld, and estimation of the width of a 'V' groove. The accuracy of the technique is affected by how closely the welding signatures match the fitting data and the signature image quality match provides a valuable check which shows when through the arc estimates cannot be relied on. Overall, the results demonstrate that through the arc measurements can have application in specialised situations, although accuracy is ultimately limited by phenomena that affect the arc and are not correlated with the measurement.     

Mapping transfer modes for stainless steel gas metal arc welding

Abstract

A methodology for the construction of transfer mode maps for stainless steel gas metal arc welding, with argon and argon–oxygen shielding gases, is presented. A back lighting laser and high speed video camera were used for visualisation and measurement of droplets and electrode extension. The reasons for the use of a groove, instead of the traditional bead on plate method, and of same volume beads are discussed and the results assessed. Unlike in other mapping procedures, mapping was conducted as a function of welding current and arc length. In addition, transfer rate v. welding current or wire feedrate curves were plotted. The results show the importance of the use of both maps and curves for identification and quantification of the shielding gas effects on the transfer mode. The results also suggest that an increase in oxygen content in the shielding gas reduces the values of transition current and transition wire feedrate (as expected), but also that it reduces the transfer rate and droplet size at the globular–spray transition.     

Alternating current-gas metal arc welding for application to thin sheets

The metal transfer in alternating current-gas metal arc welding (AC-GMAW) was analyzed in order to predict the drop size. The effects of complex waveforms of the process, involving both the electrode positive (EP) and the electrode negative (EN) pulse regions, were investigated analytically. The force-displacement model was modified to predict the drop size in AC-GMAW. Experiments were conducted using different types of wires for validating the predicted results. The effect of EN pulse parameters on the drop size was modeled, eliminating the need for experimental trial and error. The drop size information can be used to predict the range of the joint gap that can be bridged effectively. The proposed technique was found to be equally applicable to both direct current-gas metal arc welding and P-GMAW.     

铜钢异种材料等离子弧焊接头性能

采用LHM-200等离子弧焊机对1 mm紫铜与低碳钢异种材料进行了熔透型等离子弧焊试验,得到了内部无缺陷、外观成形良好的接头.观察了接头的显微组织,并分析了工艺参数对接头力学性能的影响.结果表明,焊缝区中心显微组织呈细胞群状,界面两侧的组织特征呈现显著的不同,焊缝与铜侧界面没有明显的熔合线,局部呈漩涡状,钢侧与焊缝连接处出现了明显的分界线;最佳工艺为焊接电流为65 A,焊接速度为0.4 cm/s,离子气流量为0.7 L/min,此时接头抗拉强度可达176 MPa,试样断裂于铜母材热影响区.     

Plasma transferred arc welding—modeling and experimental optimization

Plasma transferred arc (PTA) welded coatings are used to improve surface properties of mechanical parts. Advantages are the high reliability of the process and the low dilution of substrate and coating material. Processing of surfaces by PTA welding is restricted at the time to flat horizontal position. Furthermore, industry is interested in the development of strategies for coating with PTA in constraint position as complex three-dimensional (3D) parts could be then easily processed as well. Under commercial aspects, the process design can be optimized to increase process efficiency and to reduce heat input during the welding process. Process optimization involves the determination of guidelines for PTA welding in constraint positions as well. Modeling the process gives an alternative to reduce the experimental effort to optimize the welding process. Results of simulation studies of the PTA welding process are given in the present work. It will be shown that coating conditions can be optimized by varying plasma gas flow, heat input and heat flow, process speed, or powder injection with regard to welding in constraint positions. The defined controlling of the PTA welding allows modification of process management with less experimental effort and to develop coating strategies for processing in different positions. In experimental investigations, the developed coating strategies are confirmed by producing PTA coatings in constraint position as well as complex 3D parts. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.