Numerical simulation of argon twin torch plasma arc for high heating efficiency

Plasma arc heating technology has been applied for volume reduction through melting of bottom and fly ash, and for producing slag. Recently, a twin torch plasma arc, which has two torches at the cathode and anode, has been anticipated for application to disposal of medical waste because it can treat a wide area and can treat non-conductive materials. For this study, a numerical simulation model of a twin torch plasma arc at opposite electrodes was developed to elucidate high-efficiency heating using a twin torch plasma arc. It is defined as Local Thermal Equilibrium (LTE) and calculated in Magneto-Hydro-Dynamic (MHD) equations. Furthermore, the temperature distribution and conditions of high heating efficiency with the radiation loss were addressed and compared to those of a single torch. The heating efficiency decreases with increasing radiation efficiency because of the temperature increment caused by the current and input power. The radiation efficiency of a twin torch is about 5% higher than that of single torch.     

Mechanism of Metal Transfer in DE-GMAW

Modification of conventional gas metal arc welding (GMAW) process is of great potential to achieve high productivity with low cost and strong usability.Double-Electrode GMAW (DE-GMAW) is such a modified arc welding process which is formed by adding a bypass torch (gas tungsten arc welding torch) to a conventional GMAW system.The mechanism of metal transfer in DE-GMAW was proposed and verified in this paper.Experiments show that the critical current is decreased so that spray transfer can be obtained at a lower current level in DE-GMAW.Analysis of this significant change in metal transfer phenomena is conducted, and explanation is given out.It is found that the bypass arc in DE-GMAW lifts the anode point on the droplets such that the electromagnetic force becomes larger and squeezes the droplets so that spray transfer can take place under welding current lower than that in conventional GMAW.     

磁控电弧离子镀阴极斑点特性的高速摄影研究

利用高速摄影技术，对磁控电弧离子镀中阴极斑点大小、寿命及运动轨迹进行了观测，获得了阴极斑点电流密度、运动速度随磁场、电弧电流及背景气体压力改变而变化的关系曲线。     

Tri-Arc与Tandem双丝电弧焊的工作原理对比分析

目的 介绍一种称为Tri-Arc的新型双丝电弧焊接方法。方法 将Tri-Arc双丝电弧焊与应用较广的Tandem双丝电弧焊的系统构成和焊接电流波形进行对比分析。结果 Tri-Arc和Tandem两种双丝电弧焊接方法所使用的双丝焊枪相近,双电源相位同步控制和U/I脉冲控制方式类似。Tri-Arc和Tandem两种双丝电弧焊接方法的差异在于:Tandem双丝电弧焊的2个电弧是相对独立的,而Tri-Arc双丝电弧焊的2个电弧是相互耦合的,因此Tri-Arc双丝电弧焊又具有旁路耦合电弧的某些特点。结论 这种新型的Tri-Arc双丝电弧焊不仅具有与Tandem双丝电弧焊一样的高焊丝熔敷率,而且具有比Tandem双丝电弧焊更低的焊接热输入。     

Investigating effects of resistance wire heating on AISI 1023 weldment characteristics during ASAW

In this article, effects of advanced submerged arc welding process parameters on weld bead geometry have been investigated. A novel water-cooled torch has been developed which allow a use of higher preheat current values for a continuous advanced submerged arc welding (ASAW) operation. Weld beads have been deposited on AISI 1023 steel plates by varying open circuit voltage, wire feed rate, welding speed, nozzle to plate distance, and preheat current as per central composite design. The relationships between welding parameters and weldment characteristics namely bead width, penetration, reinforcement, and dilution have been developed using multiple linear regression. The effects of individual process parameters and their interactions on response parameters were examined. Finally, single and multiobjective optimization of process parameters were performed using desirability approach and Jaya algorithm. The results reveal that a smaller bead width and lower dilution can be achieved with the developed torch by allowing the use of higher preheat current values.     

Anodic current density of an electric arc with carbon electrodes

We present the results obtained in measuring the current density of anode spots in a carbon arc in air and we show its relationship to the magnitude of the arc current, analogous to the cathode spot.     

真空阴极弧离子镀阴极斑点的移动研究

建立了真空阴极弧离子镀圆形平面靶侧面引弧时 ,阴极斑点的受力模型 ,分析了影响电弧运动的因素 ,改进了圆形平面靶侧面形状 ,大大提高了石墨靶阴极斑点从侧面到靶平面的过渡速度     

Optimization of Plasma Arc Welding Parameters by Using the Taguchi Method with the Grey Relational Analysis

The optimal parameters process of plasma arc welding (PAW) by the Taguchi method with Grey relational analysis is studied. The Grey relational grade is used to find optimal PAW parameters with multiple response performance characteristics. The welding parameters (welding current, welding speed, plasma gas flow rate, and torch stand-off) are optimized with consideration of the multiple response performance characteristics (the penetration of root, the weld groove width, and the weld pool undercut). As a result, the improvement percentage of the Grey relational grade with the multiple performance characteristics is 31.8%. It is shown that the multiple response performance characteristics are greatly improved through this study.     

Retrograde motion of cathode spots of the first type in a tangential magnetic field

We consider the dynamics of dense plasma of an explosive-electron-emission center—a cell of cathode spot of a vacuum arc in an applied magnetic field. It is established that the explosive expansion of plasma in a transverse magnetic field induces an electric field and an associated current. It is shown that this current initiates the cells of cathode spots of the first type in the direction opposite to the Ampere force action. In this case, the ignition time of a new spot does not exceed a few nanoseconds at a magnetic field of a few kilogauss.     

基于回归方法和神经网络的电弧增材制造单道成形形貌预测

目的 针对电弧增材制造技术实际应用中工艺参数选取困难和成形结果难预测的问题,确定高效、准确的电弧增材制造单道成形形貌预测的数学方法,以快速、方便地选取丝材电弧增材制造工艺参数并指导成形质量控制。方法 在单道单层丝材电弧增材制造实验的基础上,采用多种回归方法和神经网络方法分别建立焊接电流、电压和焊枪移动速度等多个工艺参数与增材层宽度、增材层高度及熔池深度等成形形貌参数之间的数学关系模型。结果 电弧增材制造单道成形形貌与焊接电流、电压和焊枪移动速度显著相关,且各参数间存在非线性交互作用;采用多元线性回归法可较准确地预测单道增材层宽度,但对于增材层高度和熔深的预测效果较差;神经网络可良好地处理各工艺参数间复杂的非线性关系,其对增材层宽度、增材层高度和熔深的预测平均误差率分别为4.17%、6.60%和7.01%,显著优于多元线性回归法。结论 采用神经网络法可以准确预测电弧增材制造单道成形的形貌参数,进而指导增材制造工艺参数的选取和成形质量的控制。     

The effect of axisymmetric two-dimensional magnetic field on the configuration of vacuum-arc plasma

An experimental investigation is made of the effect of axisymmetric two-dimensional magnetic field on the forming of plasma and on the configuration of cathode spots in a vacuum-arc discharge. It is demonstrated that a magnetic field with a transverse (relative to the discharge axis) component has a significant effect on the shape of plasma column and on the rate of expansion of the cathode spot region. In a magnetic field, arc plasma has the form of truncated cone expanding toward the anode. The cathode spots take up a part of the cathode area which decreases with increasing magnetic field. Arguments are given in support of the assumption that the arrangement of cathode spots and the form of arc plasma are defined by the minimum principle similar to the Steinbeck principle. In so doing, the displacement of spots is caused by their emergence in a new region corresponding to a lower arc voltage. Also discussed is the mechanism associated with retrograde motion of cathode spot in view of the effect of azimuthal magnetic field on the axial component of current and of the effect of axial magnetic field on the azimuthal component of current.     

Magnetic‐Field Effect on Heat Transfer within a Cathode Arc Spot

The authors present results of an experimental study of the heat flux within the arc spot of the copper cathode of an electric‐arc heater with magnetic‐field‐induced displacement of the arc in an air medium — one of the most important parameters determining the erosion and service life of such a cathode. The investigations were carried out at a current strength of 110–?450 A, a magnetic induction of 0.009–0.38 T, and atmospheric pressure.     

An investigation of weld fracture surfaces and mechanical properties of two gamma titanium aluminide alloys

Two gamma titanium aluminide sheet materials were investigated to characterize the fusion zone cracking and mechanical properties that occur for specimens subjected to gas tungsten arc welding (GTAW). The materials used in this study consisted of essentially the same composition; however, one was received in the primary annealed (PA) condition and the other in the designed fully lamellar (DFL) condition. For both materials, all of the specimens welded with a stationary torch (spot welds) cracked catastrophically immediately after welding. The PA specimens exhibited a different mechanism of fracture in the fusion zone compared with the DFL specimens. The fractures that occurred in the PA specimens followed an interdendritic path through regions that did not completely solidify prior to the occurrence of cracking, whereas for the DFL specimens the primary mechanism of fracture was cleavage. For the butt welded specimens, no cracking occurred. For both materials, specimens welded parallel to the rolling direction exhibited more distinct preferred growth of columnar grains than those welded perpendicular to the rolling direction. The weld structure/property relationship is also discussed.     

Metal transfer modes of twin-wire indirect arc welding

Metal transfer modes of twin-wire indirect arc welding are studied and the effects of welding parameters on transfer modes are investigated in this paper. The progress of transition is captured by a high speed camera system with a xenon lamp as light source in order to remove the intense arc light. An oscilloscope is used to record the values of the parameters. Results show that anode and cathode have different transfer modes under certain conditions because of different melting rates. All the transfer modes are classified as short-circuiting transfer and free-flight transfer. The latter could be subdivided into globular transfer, projected transfer, streaming transfer, etc. The metal transfer modes of TWIAW are influenced by the welding current, arc voltage and shielding gas. With an increase in welding current and arc voltage, the transition frequency increases and droplets become smaller. Images indicate that the metal transfer modes influence arc shape periodically because of the detaching force and retainable force changing periodically.     

Metal transfer modes of twin-wire indirect arc welding

Metal transfer modes of twin-wire indirect arc welding are studied and the effects of welding parameters on transfer modes are investigated in this paper. The progress of transition is captured by a high speed camera system with a xenon lamp as light source in order to remove the intense arc light. An oscilloscope is used to record the values of the parameters. Results show that anode and cathode have different transfer modes under certain conditions because of different melting rates. All the transfer modes are classified as short-circuiting transfer and free-flight transfer. The latter could be subdivided into globular transfer, projected transfer, streaming transfer, etc. The metal transfer modes of TWIAWare influenced by the welding current, arc voltage and shielding gas. With an increase in welding current and arc voltage, the transition frequency increases and droplets become smaller. Images indicate that the metal transfer modes influence arc shape periodically because of the detaching force and retainable force changing periodically.     

真空电弧沉积多元膜复合靶成分离析效应的研究

用Ti/Mo ,Ti/W和Ti/Me(Me为Fe Cr Al合金 )复合靶采用真空电弧技术沉积了多元膜 ,并对成分离析效应及组织和性能进行了研究。结果表明 ,工作弧电流和阴极镶嵌体的弧斑平均电流对成分离析效应影响程度较大 ,Ti/Me复合靶存在一个无成分离析效应的平衡点。多元膜结构主要为组元原子固溶于Ti2 N中的结构形式 ,并具有较高的显微硬度     

锁孔TIG焊接技术的研究进展

锁孔TIG焊接技术具有不开坡口、单面焊双面成形的特点,尤其适用于中厚板焊接。首先介绍了锁孔TIG焊的基本原理,然后分析了目前锁孔TIG焊接波形控制技术的研究现状,主要包括恒流锁孔TIG焊、单脉冲锁孔TIG焊和高低频双脉冲锁孔TIG焊。针对现有锁孔TIG焊接技术存在热输入量过大、接头组织晶粒粗大等缺点,重点介绍了一种新型的快频脉冲TIG焊接技术,它通过快频脉冲电流产生的电磁场对电弧进行压缩,控制焊接过程的热输入量,达到提高焊接质量的目的。与传统脉冲电弧相比,快频脉冲电弧的收缩效果更为明显,可细化焊接接头组织,将快频脉冲焊接技术应用于锁孔TIG焊是今后研究的热点和主要发展方向。     

核用小直径传热管自动化衬管焊接系统的研制

目的 针对核用小直径传热管长期服役于高温高压环境时易产生表面腐蚀缺陷等问题,研制一套自动化衬管焊接系统,以高效修复腐蚀传热管,并验证该焊接系统的可行性。方法 采用以STM32F405RGT6微处理器为控制核心、植入FreeRTOS实时操作系统的方式设计了一款焊接控制系统;以微型TIG焊枪为执行机构、数字化焊接电源为功率输出设备,研制了一套自动化衬管焊接系统;最后以304不锈钢管为试样进行了衬管脉冲焊接试验。结果 焊接试验过程稳定,无断弧现象,得到的焊缝衬管完全焊透,基管适度熔透,焊缝成形良好。可通过调整基值电流、峰值电流、脉冲频率和占空比等参数调控焊接热输入,获得优质的焊缝。结论 研制的微型焊枪可适应传热管内部的狭小焊接工况;焊接电源能够满足焊接过程中的能量需求,提高了焊接过程的动态响应能力;焊接控制系统在硬件和软件层面上实现了焊枪和焊接电源的宏观调度,能够对焊接波形进行精细化调控。所研制的衬管焊接系统各项性能优秀,满足压水堆核用蒸汽发生器水箱内不锈钢传热管内衬管焊接高质量修复的需求。     

Charge distribution of ions in low-current vacuum-arc plasma

The charge distribution of vacuum-arc ions has been investigated for the arc between copper electrodes at currents varied from 8 to 60 A (with the arc voltage increased from 21 to 24 V). Plasma contains copper ions with charge states from +1 to +4. The mean ion charge state increases from 2.15 to 2.24 (i.e., by only 4%) due to a small increase in the fractions of multiply charged ions (Cu²⁺ and Cu³⁺) in the total ion flux. This conclusion does not contradict that of the ecton model of vacuum-arc cathode spot, according to which the number of cells in the spot that are due to microexplosions on the cathode increases proportionally to the arc current.     

空心阴极穿透电弧焊接工艺探索研究

详细介绍了空心阴极穿透电弧焊接工艺方法。真空穿透型电弧焊接工艺与熔透型电弧焊接工艺的不同在于其具有成形更好、更窄的焊缝和较大的焊接工艺裕度 .对钛合金焊缝成形控制作了初步的分析 ,并对焊接工艺裕度作了计算和比较 .