Experimental Study on Metal Transfer and Welding Spatter Characteristics of Cellulose Electrode

Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decrease the welding efficiency. Many factors affect the welding spatter, and metal transfer behavior is one of the main factors. Many studies concerning the spatter mechanism in arc welding process were made; most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported. In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer. The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient, which is for quantitative evaluation of welding spatter, with the statistical analysis of the large droplet transfer mode. The results showed that short circuiting transfer, large droplet spray transfer, fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding. Weld spatter occurred mainly in the deflection of large droplet process, explosive transfer process and fine droplet spraying process. Different metal transfer modes lead to different spatter. The deflection of large droplet and explosive transfer are the main factors of the spatter formation. Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.

Wire and arc additive manufacturing of 4043 Al alloy using a cold metal transfer method

Cold metal transfer plus pulse(C+P)arc was applied in the additive manufacturing of 4043 Al alloy parts.Parameters in the manufacturing of the parts were investigated.The properties and microstructure of the parts were also characterized.Experimental results showed that welding at a speed of 8 mm/s and a wire feeding speed of 4.0 m/min was suitable to manufacture thin-walled parts,and the reciprocating scanning method could be adopted to manufacture thick-walled parts.The thin-walled parts of the C+P mode had fewer pores than those of the cold metal transfer(CMT)mode.The thin-and thick-walled parts of the C+P mode showed maximum tensile strengths of 172 and 178 MPa,respectively.Hardness decreased at the interface and in the coarse dendrite and increased in the refined grain area.

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.

Analysis of metal transfer during electron beam welding with filler wire

The metal transfer mode of electron beam welding （EBW） with filler wire was studied experimentally. The spatial position between the electron beam and the filler wire was defined. Basing on the charge coupled device （CCD） visual sensing system, the metal transfer mode of filler wire was investigated. The results showed that there were five transfer modes during EBW process due to different wire feed rates and spatial positions between beam and filler wire, such as short-circuiting mode, molten metal bridge mode, small droplet mode, big droplet mode and mixed mode. By comparing the weld appearance of different transfer modes, the molten metal bridge transfer was proved to be the best transfer mode.

Influence of longitudinal magnetic field on metal transfer in MIG arc welding

Metal transfer is an important phenomenon in metal inert gas （MIG） arc welding with longitudinal alternating magnetic field. It is of great significance to observe the metal transfer modes under different excitatory currents and frequencies. However, it is very difficult to view the metal transfer process directly during welding, due to the strong interference from the arc light. To obtain the relationship between the metal transfer modes and the different magnetic fields, a high-speed video camera was used to acquire the images of globules. Different metal transfer modes under the conditions of different magnetic fields and welding parameters were studied. The experiment shows clear images of droplet transfer as well as influence of longitudinal magnetic field on both metal transfer and globule shape.

EXPERIMENTAL STUDY ON METAL TRANSFER OF CELLULOSE ELECTRODE IN VERTICAL DOWN WELDING

A high-speed photographic method is mainly used to analyze metal transfer ofa cellulose covered electrode in the vertical down welding. The experimental results show that finedroplets spraying transfer and globular transfer are the dominant transfer characteristic. The largedroplet spatter, especially the upwards spatter, is a particular phenomenon. It is found that thecombination action of gas blow force, surface tension, gravitational force and electromagnetic forcelead to globular transfer. Gravitational force and electromagnetic force, which hasten big dropletspatter, should not be neglected.

Study on arc characteristics and behavior of metal transfer in pulse current flux-cored arc welding of mild steel

The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.

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.

Metal transfer characteristics of tandem narrow gap GMAW for flat welding position

A series of experiments of tandem narrow gap GMAW for flat welding position were carried out. The arc behavior and metal transfer process were observed by a high-speed photography system. The effects of the welding parameters on the metal transfer were investigated. The results show that the arc behavior and metal transfer process of tandem narrow gap GMA W are different from these of bead-on-plate tandem GMA W. The arc behavior and metal transfer process are influenced by the distance between the two wires, the peak voltage, the pulse frequency and the peak time. With the increase of the distance between the two wires, the metal transfer mode gradually transforms from one pulse-multi droplets into one pulse-one droplet, and the average welding current increases. With the increase of the peak voltage, pulse frequency or peak time, the metal transfer mode transforms from one pulse-one droplet into one pulse-multi droplets, and the arc tends to occur between the wire and the sidewall.

Research on arc characteristics and metal transfer modes of ultrasonic assisted GMAW process

Ultrasonic assisted GMAW （U-GMAW） method is a novel process, which combines the ultrasonic wave with gas metal arc welding to improve the process stability and weld quality. The U-GMAW system is developed and the ultrasonic wave is applied by means of acoustic radiation. The arc characteristics and metal transfer modes are studied in comparison with conventional GMAW process. The arc plasma is compressed and the arc length is shorter than that in conventional GMAW process after the ultrasonic is applied onto the arc. The parameter range of short-circuiting mode is extended and the range of unstable transfer is minimized. The changes in arc characteristics are responsible for changes in metal transfer modes.

ACQUIRING AND PATTERN RECOGNITION OF SPECTRUM INFORMATION OF WELDING METAL TRANSFER

In order to recognize various metal transfer modes, by the creation of apattern recognition system for metal transfer mode, five kinds of spectrum signal in gas metal arcwelding (MIG, MAG and CO_2) are collected and taken as training samples. These samples arepretreated by computer. Several key characteristic parameters of the spectrum signal are creativelyextracted, and a corresponding recognition function and a minimum-distance-classifier areconstructed. The results show that using this method, the pattern recognition of several kinds ofmetal transfer mode for the metal gas arc welding can be done successfully. It has good accuracy andrecognition precision, basis for controlling the metal gas arc welding metal transferautomatically, and relative important parameters in welding process, such as the frequency ofdroplet transfer and the approximate diameter of each droplet, can also be obtained.

Microstructure and mechanical properties of dissimilar joint between aluminum and aluminum-coated steel by cold metal transfer process

Two dissimilar materials, aluminum alloy and aluminum-coated steel, were joined by cold metal transfer process using AlSi5 filler wire. To this end, the steel was coated with Al-Si. The steel did not melt and aluminum was melt to form the joint during the process, it was actually cold metal transfer welding-brazing. The macrostructure, microstructure, alloy element distribution, and inter-metallic compounds were analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. It was found that the Al-Si coating dissolved into the weld metal. The pre-existing thin Fe-Al- Si ternary inter-metallic compounds in the interface between the Ak-Si coating layer and base metal steel also partially dissolved into the weld zone, tending to reduce the thickness of inter-metallic compounds. Approximate 3 μm thick undissolved intermetallic compound was found at the interface after welding which could guarantee sound bonding strength in dissimilar materials joining. The sample was fractured at the fusion zone near the aluminum side in the tensile test. The ultimate tensile strength was about 156 MPa, and the fracture mode is ductile failure in nature according to its morphology.

Bayesian decision-based pattern recognition on spectrum signal of metal transfer modes

A software system of pattern recognition on spectrum signal of metal transfer mode has been developed using Visual Basic under Windows environment. On the basis of the coincidence relation between the spectrum signal and metal transfer mode, according to the geometrical pattern feature of the spectrum signal, several key characteristic parameters are extracted. The correspondent recognition function and a minimum distance classifier have been constructed based on Bayesian decision theory. The results show that using this system, the metal transfer mode of MIG, MAG, CO2 welding can be recognized automatically which provides the basis for automatically controlling of the metal gas arc welding metal transfer.

Effect of laser power on metal transfer in laser-double arcs P-MAG hybrid welding with single power source

The effect of laser power on metal transfer is studied under conditions of alternating combustion of double arcs in order to develop the welding process of the laser-double arcs pulsed metal active gas （P-MAG） hybrid welding with single power. Different laser power corresponds to different interactive mechanisms of laser and arc and to different methods of metal transfer in the hybrid welding. When the laser power ascends from 500 W to 1 500 W, the methods of metal transfer change from the complex transfer of one droplet per pulse, one droplet two pulses and one droplet much more pulses during the mixture of globular and projected transfer of the lead wire, and from one droplet two pulses and one droplet three pulses during globular transfer of the follow wire to the methods of the metal transfer of both lead wire and follow wire are stable one droplet two pulses and one droplet three pulses when the metal transfer is mainly globular. The arc sharps and pressure of droplet are altered with the laser power changing. The compression of the arcs is strengthened by the laser and the offset of the center of droplet mass is much more obvious with the increasing of the laser power.

Study on Relationship Between Arc Behavior and Joint Forming in Cold Metal Transfer Welding Technology with Polarity⁃Exchanging

Cold metal transfer with polarity⁃exchanging is a new integrated welding technology based on MIG.Due to the alternation of the positive and negative polarities of the wire,favorable control upon the deposition rate and the welding shape coefficient was obtained in order to meet the desired joint design,and the related controlling principles and joint characteristics were reported.Droplet transfer physical behavior exhibited strong dependability on the studied welding parameters,such as welding voltage,welding current,wire feeding speed,and polarity⁃exchanging.This welding technology provides a new way for the welding of body⁃in⁃white(BIW)thin sheet with special demands.Moreover,the typical quality defects of MIG were greatly improved.Our study provides important technical information from the perspective of industrial application of MIG and sheds light on the higher application level of MIG in BIW welding.

Cold metal transfer(CMT) technology-An overview

Cold Metal Transfer technology has revolutionized the welding of dissimilar metals and thicker materials by producing improved weld bead aesthetics with controlled metal deposition and low heat-input. In this study, the process, weld combinations, laser-CMT hybrid welding and applications of CMT welding are critically reviewed. Microstructure and other weld characteristics have been discussed at length for various base metal combinations. Particularly, the welding of aluminium and steel with better results has been possible with CMT Welding. The results reviewed in this article indicate that the CMT-Laser hybrid welding is more preferable to Laser or Laser hybrid welding. CMT welding has found applications in automobile industries, defence sectors and power plants as a method of additive manufacturing.

Arc Characteristic and Metal Transfer of Pulse Current Horizontal Flux-Cored Arc Welding

In this work, we utilized high-speed video photography to investigate the arc characteristics, metal transfer behavior, and welding spatter of the pulse-current flux-cored arc welding (P-FCAW) process in the horizontal position. The results indicate the presence of a stable “flux pole” during both the pulse-on and pulse-off periods when the mean current ranged from 140 to 170 A. The existence of this “flux pole” was beneficial for droplet transfer in the “axial droplet transfer” mode. With respect to welding spatter, with an increase in the welding current, we observed three kinds of spatter—explosive spatter, rebounded droplet spatter, and scattering spatter. With an increase in the pulse current from 310.6 to 345.6 A, the deflection of the arc reduced from 30.4° to 16.6°, which positively influenced the arc rigidity, particularly in the horizontal position. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Fabrication of patterned transparent conductive glass via laser metal transfer for efficient electrical heating and antibacteria

Vapor deposition and three-dimensional(3D)printing technology are considered to be conventional methods to achieve patterned metal film preparation through the assistance of masks and high temperature.Therefore,there are still some challenges in fabricating metal films in template-free and normal temperature environment.In this work,we report a flexible and rapid laser metal transfer(LMT)technique for fabricating the various metal films(Cu,Ni,Sn,Al,Fe,and Ag)with different patterns without templates on arbitrary substrates(glass,polyimide(PI)films,and aluminum nitride(AlN)ceramic).Especially,the obtained transparent conductive glass displays high transmittance(more than 90%)and adjustable resistances(≈5Ω).According to the Joule effect,the interface resistance between Cu particles and copper oxide coating produces the high temperature approximately 280℃ at 2 V in a short time(≈60 s)and remains stable at 120℃ over 12 h.At last,the multifunctional glass with Cu patterns also shows excellent bactericidal activity(≈95%).This work demonstrates that laser metal transfer is an exceeding effective means of fabricating the micro/nano structures with potential applications in functional devices.

Temperature Drop of Molten Metals in Open Channels

The temperature drop of molten metal flowing in open channels is numerically determined. Rectangular, trapezoidal and triangular geometries are considered. The overall heat transfer coefficients for the bottom, side walls and free surface of the channel have been taken from the literature. For each geometry, the volumetric flow rate, mean residence time and temperature drop as a function of the channel inclination angle were determined. The rectangular and trapezoidal geometries present the smallest temperature drops, while the triangular geometry presents the greatest temperature drop. The factors that most affect this drop are the value of the free surface area of the channel, and the average residence time of the molten metal in the channel.

Simulation of Metal Transfer in GMAW Based on FLUENT

A new numerical approach is presented, which is used to simulate the dynamic process of metal transfer. The process of metal transfer in gas metal arc welding is simulated based on FLUENT. A two-dimensional axisymmetric numerical model is developed using volume of fluid method and the distributions of physical quantities including pressure, current density, electric potential in the droplet are investigated. For improving the veracity of the simulated results and decreasing the effect of the uncertain surface tension coefficient on the simulated results, the relationship between the welding current and surface tension coefficient is modified by analysis of regression. Meanwhile for testing the accuracy of simulated results, the welding experiments are performed and the high-speed photography system is used to record the real process of metal transfer. The results show that the simulated results are in reasonably good agreement with the experimental ones.