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.

Numerical simulation of deep cryogenic treatment electrode tip temperature for spot welding aluminum alloy

Deep cryogenic treatment technology of electrodes is put forward to improve electrode life of resistance spot welding of aluminum alloy LF2. Deep cryogenic treatment makes electrode life for spot welding aluminum alloy improve. The specific resistivity of the deep cryogenic treatment electrodes is tested and experimental results show that specific resistivity is decreased sharply. The temperature field and the influence of deep cryogenic treatment on the electrode tip temperature during spot welding aluminium alloy is studied by numerical simulation method with the software ANSYS. The axisymmetric finite element model of mechanical, thermal and electrical coupled analysis of spot welding process is developed. The numerical simulation results show that the influence of deep cryogenic treatment on electrode tip temperature is very large.

Effect of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding

The effects of deep cryogenic treatment on mechanical behavior of a Cu-Cr-Zr alloy for electrodes of spot welding were investigated employing Brinell-hardness testing unit, abrasion examination machine, electronic almighty testing machine and X-ray stress analyzer. Tensile fracture surfaces of the alloy were characterized by scanning electronic microscope （SEM） with energy dispersive X-ray spectroscopy （EDS）. The results showed that, after deep cryogenic treatment, σb and σ0.2 increased 23 MPa and 21 MPa respectively, the wear rate of the alloy exhibited the trend of decrease with the decreasing temperature and increasing time of deep cryogenic treatment, and the surface residual stress of the alloy was partially eliminated by deep cryogenic treatment.

New Developed Welding Electrode for Improving the Fatigue Strength of Welded Joints

A new welding electrode, low transformation temperature electrode (LTTE), was introduced in this paper. It was described in design principle, mechanics, chemical compositions of their deposited metal and manufacturing methods. It was proved that the best transformation starting temperature from austenite to martensite of the deposited metal of LTTE was at about 191℃ and it was obtained by adding alloying elements such as Cr, Ni, Mn and Mo. The microstructure of the weld metal of the LTTE was low carbon martensite and residual austenite. The compressive residual stress was induced around the weld of the LTTE and the -145 MPa in compression could be obtained in middle of weld metal. The fatigue tests showed that the fatigue strength of the longitudinal welded joints welded with the LTTE at 2×106 cycles was improved by 59% compared with that of the same type of welded joints welded with conventional E5015 and the fatigue life was increased by 47 times at 162 MPa. It is a very valuable method to improve the fatigue performance of welded joints.

MATHEMATICAL SIMULATION OF HEAT AND MASS TRANSFER IN PULSED ARC WELDING BY MELTING ELECTRODE

In this paper the processes of melting and transfer of an electrode metal to the molten pool, hydrody- namics of molten pool in controlled pulsed arc welding in carbon dioxide have been investigated.The process of pulsed arc welding with systematic short - circuits of the arc gap is realized by adaptive algo- rithms of pulsed control over main energetic parameters of welding - arc current and voltage,arc heated efficiency,peak,short - circuiting current, which provide the dosage of energy for energy for melting and transfer of every for of an electrode metal, the control over fluidity of the weld pool. Physica and mathematical models describing such processes in CO2, origind software hare been developed.The re- sults of physical simulation and mathemaical modelling permit to determine the influence of energetic parameters of the process on the condition of the 'power source-electrode-arc-molten pool' electrodynamic system at each moment of time.

Gas Pool Coupled Activating TIG Welding Method with Coupling Arc Electrode

Gas pool coupled activating TIG(GPCA?TIG) welding put forward in?house can dramatically enhance weld penetration of TIG welding through introducing active element oxygen to reverse the Marangoni convection flow in the molten pool. In order to further improve the welding productivity, the normal solid tungsten electrode is replaced by a kind of coupling arc electrode. The changes of arc pressure distribution along anode surface and the weld appearance were evaluated. On this basis, the dependences of weld shape characterized with weld depth, width and undercut on the main welding parameters were discussed. The results indicate, the substitution of coupling arc electrode can lead to an obvious decrease of arc pressure. Compared to hollow tungsten electrode and twin tungsten electrodes, the coupling arc electrode is much easier to manufacture and has more compacter structure. Combined with the symmetric distribution of arc pressure in di erent directions, this electrode has extensive adaptability. In the GPCA?TIG welding with coupling arc electrode, both the substitution of coupling arc electrode and the introduction of outer active gas oxygen can reduce the possibilities of producing humping bead and undercut. Their joint action makes this welding method have the capability of realizing high travel speed and deep penetration welding.

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.

Metal vapor behavior in double electrodes TIG welding

In present paper, the metal vapour behavior in double electrodes TIG welding was investigated by a numerical model, including the arc plasma and weld pool. The thermodynamic parameters and transport coefficients of the arc plasma were dependent on both the local temperature and the mass ratio of the metal vapour. A second viscosity approximation was used to formulate the diffusion coefficient of the metal vapour in the arc plasma. The temperature and flow fields together with the metal vapour concentration were simulated, and the influences of metal vapour on the arc plasma and the weld pool were analyzed. It was found that the metal vapour transport in the arc plasma was significantly influenced by the flow of the arc plasma, and the distribution of the metal vapour was more extended in the direction perpendicular to the line through the double electrodes tips. Both the arc plasma and the heat flux at the weld pool were constricted by the presence of the metal vapour, while the metal vapour had a minor effect on the total heat input to the work piece and the weld pool profile as a whole.

Electrode degradation mechanism during resistance spot welding of zinc coated steel using Cu-TiB_2 electrodes

The TiB2 dispersion-reinforced copper-matrix composite used as electrode material in resistance spot welding of zinc coated steels was studied. The service life of the composite electrode reaches （7700） welds, which is 4 times that of the conventional Cu-Cr-Zr electrode. Little gross deformation is observed on the composite （electrodes） because of the higher thermal strength; therefore, it is believed that wear is the only mechanism for the composite （electrode） deterioration. However, both wear and plastic deformation are responsible for the large increase in the tip diameter of the Cu-Cr-Zr electrodes. Moreover, the large deformation of the Cu-Cr-Zr electrodes may contribute to the increased wear rate of the tips.

Polarities effect on arc interference in triple-electrode CO2 fillet welding

The occurrence of arc interference between the adjacent arcs becomes an important problem in triple-electrode high speed CO2 fillet welding. To clarify this problem, polarities effects on arc interference were investigated. The experimental results and theoretical analysis showed that the reverse magnetic field generated by the middle wire （ DCEN or DCEP ） decreased the arc deflection due to arc interference. The average arc voltage fluctuations induced by DCEP/DECN/DCEP and DCEN/DCEP/DCEN were smaller than those induced by the other polarities.

Evaluation model for arc fluctuations of triple-electrode high speed fillet welding

To improve the welding efficiency of conventional arc welding, triple-electrode fillet welding was proposed and developed. Stability of triple-electrode fillet welding process is the assurance for ideal joint. The evaluation model for arc fluctuations of triple-electrode fillet welding was established based on the characteristic parameters and their variation coefficients. This model indicated that variation coefficients could reflect arc voltage flnctuations of welding process, and its analysis result was consistent with the actual welding process.

Analysis on the stability of the single weld pool formed during the triple-electrode high speed CO2 welding

The pinch instability theory with free surface and wave superposition principle was applied to understanding the critical disturbance wavelength and the theoretical bead width for the single weld pool formed during the triple-electrode high speed CO2 welding. In addition, the reason for higher stability in the single weld pool was analyzed. Then single-, twin-, and triple-electrode overlaying experiments were conducted. It was found that triple-electrode CO2 welding can improve welding efficiency greatly without reducing the weld quality. The results indicated that the oscillation frequcncy of the weld pool increased, oscillation wavelength decreased, and bead width increased with the increase of welding electrodes under the same disturbance circumstances.

THE DEVELOPMENT OF COLD WELDING SURFACING ELECTRODE FOR BLAST FURNACE VALVE

The Authors of this Article have done research on the cracking resistance of cold welding surfacing electrodes for blast furnace valves by adjusting the basicity of slag component, decreasing the hydrogen content and improving microstructure. The DF 2 Cold Welding Surfacing Electrodes prove to possess the following characters: 1) Excellent cracking resistance for surfacing alloys at normal temperature. 2) Excellent cracking resistance for repair welding and rewelding. 3) Excellent machinability for surfacing alloying.

MICROSTRUCTURE AND PROPERTIES OF DEEP CROGENIC TREATMENT ELECTRODES FOR SPOT WELDING HOT DIP GALVANIZED STEEL

The microstructure and elements distribution of the deep cryogenic treatmentelectrodes and non-cryogenic treatment electrodes for spot welding hot dip galvanized steel areobserved by a scanning electrical microscope. The grain sizes, the resistivity and the hardness ofthe electrodes before and after deep cryogenic treatment are measured by X-ray diffraction, the DCdouble arms bridge and the Brinell hardness testing unit respectively. The spot welding processperformance of hot dip galvanized steel plate is tested and the relationship between microstructureand physical properties of deep cryogenic treatment electrodes is analyzed. The experimental resultsshow that deep cryogenic treatment makes Cr, Zr in deep cryogenic treatment electrodes emanatedispersedly and makes the grain of deep cryogenic treatment electrodes smaller than non-cryogenictreatment ones so that the electrical conductivity and the thermal conductivity of deep cryogenictreatment electrodes are improved very much, which make spot welding process performance of the hotdip galvanized steel be improved.

Effect of electrode wear on weld nugget formation in resistance spot welding of magnesium alloy

The effect of electrode wear on the formation and growth of weld nugget in resistance spot welding of AZ31B Mg alloy was studied by an axisymmetric finite element model, employing a contact resistance model based on the micro-contact theory. The results show that electrode wear causes the growth of electrode tip diameter, which leads to the current density and temperature at the sheet/sheet interface reduced and diameter of nugget decreased, has been shown to be dominant in determining the deterioration in weld quality. Alloying and pitting at electrode surface decrease the electric conduction of electrode, resulting in non-uniform distribution of temperature and current density and contribution to the further damage, at the same time initiate expulsion and electrode sticking during welding process and worse the quality of weld.

Microstructure of deep cryogenic treatment electrode for resistance spot welding of aluminium alloy

Cr-Zr-Cu alloy electrodes for resistance spot welding of aluminium alloy are treated by deep cryogenic treatment processes. The Cr-Zr-Cu alloy electrodes are analyzed by transmission electron microscope（ TEM ） , and results show that the common dislocation in Cr-Zr-Cu alloy electrodes is changed into the dislocation loop, and twin crystal is found after deep cryogenic treatment. The parallel twin crystal band is observed by selected electron diffraction（SED） and the twin crystal plane is marked as （ 111 ）. The Cr-Zr-Cu alloy electrode is studied by X-ray diffraction（ XRD ） and results show that the intensity of diffraction peak is obviously changed after deep cryogenic treatment, and the grain rotates to preferred orientation. The Cr-Zr- Cu alloy electrode is studied by positron annihilation technique （PAT） and results indicate that the amount of vacancy defects is less than that of Cr-Zr-Cu alloy before deep cryogenic treatment. The main elements in Cr-Zr-Cu alloy are studied with X- ray photoelctron spectroscopy（ XPS ） and the intensity of spectrum peak is increased after deep cryogenic treatment.

Study on parameters optimization in resistance spot welding of stainless steel with rectangular electrodes

By means of the quadratic regression orthogonat combination design, a mathematical model of the relationship between the quality of spot welds and the welding parameters, including welding current, welding time and electrode force, is established. The influences of welding parameters on long-axis dimension of the nugget and shearing resistance of spot welds are studied and the welding parameters are optimized. The results show that the regression equation obtained can realize the accurate prediction of long-axis dimension of the nugget and shearing resistance of spot welds.

Current Density-Sensitive Welding of a Semiconductor Nanowire to a Metal Electrode

In situ welding of a single ZnSe nanowire(NW)to an Au electrode has been successfully achieved by means of current-induced Joule heating.The parameter governing the welding of semiconductor NW to the metal electrode is highly dominated by the current density at the Au-ZnSe NW(M-S)contact because current density at the M-S contact can change the temperature profile along the NW.The self-heating behaviors of the Au-ZnSe NW-Au(M-S-M)nanostructure can be changed from the electrical failure of the ZnSe NW to the melting of the Au electrode localized at the M-S contact when the current density at the M-S junction was adjusted to be larger than in the NW.Consequently,the self-welding is the current density-sensitive and controllable since the current density at the M-S contact can be controlled by adjusting the contact area between the NW and metal electrode.This controlled self-welding may have potential applications in the construction of a complex nanostructure and improvement of the thermal stability of the M-S contact as well as the enhanced performance of the nanodevices based on the M-S-M nanostructure.

Self-Adaptive Control System for Additive Manufacturing Using Double Electrode Micro Plasma Arc Welding

Wire arc additive manufacturing(WAAM)has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost.However,in the process of automatically manufacturing the high-quality metal parts by WAAM,several problems about the heat build-up,the deposit-path optimization,and the stability of the process parameters need to be well addressed.To overcome these issues,a new WAAM method based on the double electrode micro plasma arc welding(DE-MPAW)was designed.The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically.The effects between the parameters,wire feed rate and torch stand-off distance,in the process of WAAM were investigated experimentally.In addition,a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance.Finally,a series of tests were performed to evaluate the control system’s performance.The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system.Further,the deposition paths about the metal part’s layer heights in WAAM are simplified.Finally,the appearance of the WAAM-deposited metal layers is also improved with the use of the control system.

A twin-electrode alternating current to direct current synergetic pulsed arc welding control method

A novel synergetic arc control method was used to control twin-electrode alternating current （ AC） to direct current （DC） pulsed arc welding and the mechanism of poor sidewall fusion in narrow gap welding was investigated. The synergetic arc control method easured that the arc voltage of DC welding source could switch in phase with the AC welding source. To test the reliability and operability of this method, a twin-electrode AC to DC pulsed arc welding system was set up and data was acquired through high-speed photography and electrical signal measurement system. The results show that the interactions between the two arcs can be controlled effectively and the control method is a sensitive and efficient control method.