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.     

Determining the critical transition current for metal transfer in gas metal arc welding (GMAW)

It is of great significance to determine the critical transition current from globular transfer to spray transfer in gas metal arc welding (GMAW) because metal transfer modes affect the weld quality and welding productivity. In this study, a simple model is developed to calculate the critical transition current based on the analysis of various forces exerted on a pendent droplet at the electrode tip. It is found that the force exerted by the incoming molten metal from the wire on the drop, i.e., the term 相似文献   

Determining the critical transition current for metal transfer in gas metal arc welding (GMAW)

It is of great significance to determine the critical transition current from globular transfer to spray transfer in gas metal arc welding (GMAW) because metal transfer modes affect the weld quality and welding productivity. In this study, a simple model is developed to calculate the critical transition current based on the analysis of various forces exerted on a pendent droplet at the electrode tip. It is found that the force exerted by the incoming molten metal from the wire on the drop, i.e., the term ṁ _c v _c, plays an important role in determining the critical transition current. For mild steel wires and argon shielding gas, the critical transition current is predicted with different levels of wire diameter and extensions. The calculated results match the experimental ones.     

CMT能量输入特点与熔滴过渡行为

为分析CMT焊接方法的工艺特点,采用高速CCD摄像机建立了电弧形态和熔滴过渡视觉传感系统并且通过电流、电压传感器建立了波形采集系统,以此分析其能量输入特点和熔滴过渡行为.结果显示,CMT焊接波形控制呈现典型的直流脉冲特征,焊接时热输入较低;在CMT短路过渡过程中,熔滴尺寸随焊接电流的增加幅度不大,将熔滴尺寸控制在一定范围内可实现稳定的短路过渡.CMT短路过渡通过焊丝回抽,避免了大的电磁力,有效地消除了飞溅.当电流增大到一定值时,其过渡形式将转变为射滴过渡和短路过渡的混合过渡.     

Effects of process parameters on arc shape and penetration in twin-wire indirect arc welding

In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera, and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welding arc, which would increase the depth of penetration as the incensement of the arc force. Several principal parameters including the distance of twin wires intersecting point to base metal, the included angle, and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased, the arc turned brighter while unobvious change of penetration occurred as the arc voltage increased, and the deepest penetration was obtained when the welding speed was 10.5 mm/s.     

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.     

Acquisition and pattern recognition of spectrum information of welding metal transfer

With the creation of a pattern recognition system for metal transfer mode, this article has collected five kinds of spectrum signals in gas metal arc welding (MIG, MAG and CO₂) and take them as training samples. These samples have been pretreated by computer, several key characteristic parameters of the spectrum signal have been creatively extracted, and a corresponding recognition function and a minimum-distance-classifier have been constructed. The results show that the pattern recognition of several kinds of metal transfer modes for the metal gas arc welding can be done successfully, and relative important parameters in welding process, such as the frequency of droplet transfer and the approximate diameter of each droplet, can also be obtained.     

Numerical investigation of droplet impact on the welding pool in gas metal arc welding

A transient three‐dimensional model that describes physical phenomena inside a welding pool during gas–metal arc welding process is presented. The model considers such phenomena as heat‐mass transfer, electromagnetics, hydrodynamic processes and deformation of the weld pool free surface. The fluid flow in the weld pool is induced due to the presence of the mechanical impact of the droplets, thermo‐capillary surface tension, thermal buoyancy and electromagnetic forces. The weld pool surface deformation is calculated by considering arc pressure and droplet impact force. A comparative analysis of the impact of the electric current of the welding arc and different force factors causing the motion of liquid metal in the weld pool on the shape of the welded seam was carried out and discussed.     

粗丝CO_2气体保护焊熔滴过渡与潜弧机理的研究

本文详细分析了粗丝CO_2气体保护潜弧焊熔滴过渡的特点和潜弧机理。潜弧状态可以分为三种类型:半潜弧(熔滴主要以较大的颗粒形式过渡)、临界潜弧(熔滴主要以较小颗粒的射滴形式过渡)和深潜弧(熔滴以细小射滴与射流混和形式过渡)。大电流、低电压、粗焊丝、反极性和氧化性气氛是形成潜弧过程的必要条件,其中电流是最重要的条件。潜弧后弧柱气氛改变,焊丝端部的弧根由集中形态扩展为覆盖整个端部形态,使得熔滴尺寸变得细小,熔滴过渡形式发生变化。采用临界潜弧区域的焊接规范参数施焊,飞溅小,工艺过程稳定,焊缝成形优良。     

Robust sensing of arc length

During arc welding, the arc heats and melts the workpiece as heat flux. When the welding current is given, the distribution and the intensity of the heat flux are determined by the length of the are. The measurement and control of the are length are fundamental in robotic and automated welding operations. Length of welding arc determines the distribution of the arc energy and thus the heat input and width of the weld. This work aims at improving the measurement accuracy of arc length using the spectrum of are light at a particular wavelength during gas tungsten arc welding (GTAW) with argon shield. To this end, effects of welding parameters on spectral distributions were studied. To verify the effects of base metal and arc length, the arc column was also sampled horizontally as Layers for spectral analysis. Results show that spectral lines of argon atoms are determined by are length, independent of welding parameters other than the current. Based on these findings, a compact arc light sensor has been designed to measure the arc length with adequate accuracy. A closed-loop arc length control system has been developed with the proposed sensor     

Virtual welding equipment for simulation of GMAW processes with integration of power source regulation

A two dimensional transient numerical analysis and computational module for simulation of electrical and thermal characteristics during electrode melting and metal transfer involved in Gas-Metal-Arc-Welding (GMAW) processes is presented. Solution of non-linear transient heat transfer equation is carried out using a control volume finite difference technique. The computational module also includes controlling and regulation algorithms of industrial welding power sources. The simulation results are the current and voltage waveforms, mean voltage drops at different parts of circuit, total electric power, cathode, anode and arc powers and arc length. We describe application of the model for normal process (constant voltage) and for pulsed processes with U/I and I/I-modulation modes. The comparisons with experimental waveforms of current and voltage show that the model predicts current, voltage and electric power with a high accuracy. The model is used in simulation package SimWeld for calculation of heat flux into the work-piece and the weld seam formation. From the calculated heat flux and weld pool sizes, an equivalent volumetric heat source according to Goldak model, can be generated. The method was implemented and investigated with the simulation software SimWeld developed by the ISF at RWTH Aachen University.     

Investigation on various welding consumables on properties of carbon steel material in gas metal arc welding under constant voltage mode

In this present work, the influence of different consumables on weld properties of carbon steel plate was studied by automatic gas metal arc welding under constant voltage mode. For all experiments, the process parameters such as welding current of 200 A, voltage of 28 V and welding speed of 200 mm/min were kept constant. The results indicate that the angular distortion remained higher for solid wire, whereas it was minimum for flux-cored wire and the lowest in metal-cored wire. Mechanical properties such as yield strength, tensile strength, elongation and joint efficiency remained high for solid wire relative to cored wire. Excellent impact toughness of the weld metal and heat-affected zone was reported for the flux-cored welds compared with solid wire and metal-cored welds.     

Welding current influences on Inconel 625/X65 cladding interface

The pulsed gas tungsten arc welding with hot wire was used to clad Inconel 625 on the surface of X65 steel. The influences of welding current in horizontal welding position on the dilution, in further the composition, microstructure, and property of the Inconel 625/X65 cladding interface were investigated. Experimental results show that with the increase in welding current, namely, in heat input and arc force, dilution rate increased; the composition transition region in the cladding layer close to the fusion line, controlled by the cladding temperature, would be widen; in further, the microstructure would be different due to the heat transfer and composition change; the precipitates were niobium-rich MC carbide with a low welding current, but tended to be the intermetallic compounds, Laves phase, with a high welding current; the highest and lowest hardness values appeared on the heat-affected zone and cladding layer next to the bonding interface, respectively.     

Residual stresses due to gas arc welding of aluminum alloy joints by numerical simulations

This study deals with the numerical simulation of the gas arc welding process of Aluminum tee joints using finite element analysis and evaluation of the effect of welding parameters on residual stress build up. The 3D simulations are performed using ABAQUS code for thermo-mechanical analyses with moving heat source, material deposition, solid-liquid phase transition, temperature dependent material properties, metal elasticity and plasticity, and transient heat transfer. Quasi Newton method is used for the analysis routine and thermo-mechanical coupling is assumed; i.e. the thermal analysis is completed before performing a separate mechanical analysis based on the thermal history. The residual stress build up and temperature history state in a three-dimensional analysis of the tee joint is then compared to experimental results. Hole drilling method is used for measuring the residual stress, while temperature history is measured by thermocouples. After carrying out numerical simulations, the effects of voltage/current, welding speed, material thickness and size of electrode on residual stress build-up and resulting distortions are evaluated.     

高铝粉煤灰活性剂影响TIG电弧行为研究

为了研究高铝粉煤灰作为活性剂对钨极氩弧焊电弧特性的影响规律,继而明确复合成分活性剂调控焊接电弧增加焊缝熔深的机制。基于自行开发的数据采集平台,进行了实时焊接电流、电压、焊接热循环的数据采集;基于霍尔传感器测量了电弧电流密度及其作用半径;用自制的电弧力测量装置,研究了工件表面涂覆活性剂对电弧综合作用力的影响。实验结果说明,涂覆在工件表面的活性剂在高能的等离子弧的作用下将形成复杂气氛,复杂的气氛导致焊接过程中的电弧动态特性及其电弧力产生改变,继而影响焊缝的形貌。     

A Novel Method of Triple-Wire Gas Indirect Arc Welding

This paper proposes a novel triple-wire gas indirect arc welding process. The welding system consists of two power sources and three wires. The effects of the power source mode and the wire configuration on arc stability and behavior are studied. The metal transfer is analyzed and bead-on-plate welding is employed. Results show that two direct current power sources cannot produce a stable process, but the combination of a direct current with a pulsed direct current can produce a stable process. The reason is that the pulsed direct current can boost and stabilize the metal transfer. For the wire configuration, a smaller contact angle between the main wire and the side wire is more desirable. Compared with the traditional gas metal arc welding, this novel process has the advantages of high wire melting rate, low penetration depth, and low dilution rate. Compared with twin-wire gas indirect arc welding, it provides a broader range of applicable currents with sufficient heat input.     

Real-time monitoring of abnormal conditions based on Fuzzy Kohonen clustering network in gas metal arc welding

A real-time monitoring system based on through-the-arc sensing is developed for detecting abnormal conditions in gas metal arc welding. The transient signals of welding voltage and current during the welding process are sampled and processed by statistical analysis methods. It is found that three statistical parameters (the standard deviation, variance, and kurtosis of welding current) show obvious variations during the step disturbance, which is intentionally introduced into the T-joint test pieces by cutting a gap in the vertical plane. A Fuzzy Kohonen clustering network (FKCN) is put forward to monitor the abnormal conditions in real-time. Ten robotic welding experiments are conducted to verify the real-time monitoring system. It is found that the correct identification rate is above 90%.     

Measurement and calculation of plasma drag force in arc welding based on high-speed photography technology and particle dynamics

To investigate the plasma drag force acting on the droplet in gas metal arc welding (GMAW), we used a high-speed photography system to image the metal transfer process, and proposed a method employing particle dynamics to measure the plasma drag force. Experimental results of the droplet diameter, mass, acceleration, plasma drag force and gravity acting on the droplet are presented. The results indicate that, with the increase of welding current, the droplet diameter, mass and gravity decrease, the droplet acceleration and plasma pressure increase, while the plasma drag force and the gravity acting on the droplet decrease. Moreover, we find that the plasma drag force is 10 and near 100 times the gravity acting on the droplet. The experimental values of plasma drag force and plasma pressure show good agreement with the theoretical value by fluid theory; their order of magnitudes are 10^− 4 N and 10³ Pa, respectively, which demonstrates that it is an effective method to analyze the plasma drag force of welding arc.     

Experimental Investigation of Wire Arrangements for Narrow-Gap Triple-Wire Gas Indirect Arc Welding

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root.     

新型微束等离子弧焊接电源的研制

鉴于高频电弧具有较强的自收缩作用及较好的电弧稳定性的特点 ,研制了调制型脉冲微束等离子弧电源 .本电源可通过对高频电流的低频脉冲调制调节电弧对焊缝的热输入 ,同时具有电弧能量密度大、主弧空载电压低及起始电流递增和熄弧电流递减等功能 ,适用于铜、钛、不锈钢等金属薄件、微细件的焊接 .