AC TIG Welding Research Articles

Influence of AC frequency, current and stand-off distance on bead profile in AC TIG welding of aluminium

Influence of AC frequency, current and stand-off distance on bead profile in AC TIG welding of aluminium

Experimental investigation of dominant factors for droplet ejection from electrode during AC TIG welding

Experimental investigation of dominant factors for droplet ejection from electrode during AC TIG welding

High-frequency pulse-modulated square wave AC TIG welding of AA6061-T6 aluminum alloy

Bead-on-plate welding of 6-mm thick AA6061-T6 aluminum alloy is used to characterize the high-frequency (HF) pulse-modulated square wave AC TIG (HFPM AC TIG) welding. The modulation HF pulse reduces the reignition voltage of negative half-wave arc. However, its effectiveness on increasing weld penetration is not evident until the penetration rate (penetration-to-workpiece thickness ratio) exceeds 45%. Above this value, the weld penetration increases significantly with increasing peak current of the HF pulse, and first increased and then decreased with increasing pulse frequency from 10 to 40 kHz. Maximum penetration achieved at optimal welding condition increases by 120% compared with that of conventional AC TIG welding. The grain size and width of partially melted zone are visibly reduced. The average equiaxed grain size, pore number density, and average pore size in HFPM AC TIG weld metal decrease with increasing pulse frequency.

Development of New AC TIG Welding Power Source and its Improvement of Productivity

Development of New AC TIG Welding Power Source and its Improvement of Productivity

Influence of shielding gas on cathode spot behaviours in alternating current tungsten inert gas welding of aluminium

ABSTRACTThe influence of shielding gas (argon, helium) on the cathode spot (CS) behaviours in aluminium AC TIG welding was investigated by the high-speed (500,000 fps) observation. Moreover, the temperature of the weld pool surface was measured by the two-wavelength pyrometer method to discuss its relationship with the CS. Consequently, the average current per CS in the helium case was 16.7 A, higher than 7.6 A in the argon case. The larger current per spot is considered to cause the higher velocity of the CS on liquid surface in the helium case (168 ± 41 m s−1) than that in the argon case. The average number of the CS was almost zero within around a radius of 2.0 mm in helium, which had the temperature above 1300 K.

Arc Controllers for TIG Welding Applications:A Review

An arc welding joint could utilize the features of discretely different arc welding methods to obtain the desired joint characteristics. The continuous improvement in arc welding controllers has helped redefine the need of proper parametric control of the process. For efficiency and productivity improvement, modern arc controllers come handy to re-define various aspects of the process (e.g. metal transfer, arc stiffness, etc.). One fascinating outcome is the virtual convergence of complete multi-functional arc welding process to GMAW. Still, there are applications where SMAW and TIG welding processes are regularly being used. Like other welding methods, TIG welding, as well, consists of several derivative approaches. For example, for creating joints of reactive metals (aluminum or magnesium), the AC-TIG welding is commonly employed. Here, the role of arc controller is to generate consistent pattern of desirable rectangular shape AC current waveform through the arc gap. It could cause severe stress (during polarity transition) in all secondary side components of the controller. This review, using indigenously designed peripheral interface controller (PIC) based arc welding inverter, explains the role of arc controllers to handle issues of majority of TIG welding applications.

Arc Controllers for TIG Welding Applications:A Review

An arc welding joint could utilize the features of discretely different arc welding methods to obtain the desired joint characteristics. The continuous improvement in arc welding controllers has helped redefine the need of proper parametric control of the process. For efficiency and productivity improvement, modern arc controllers come handy to re-define various aspects of the process (e.g. metal transfer, arc stiffness, etc.). One fascinating outcome is the virtual convergence of complete multi-functional arc welding process to GMAW. Still, there are applications where SMAW and TIG welding processes are regularly being used. Like other welding methods, TIG welding, as well, consists of several derivative approaches. For example, for creating joints of reactive metals (aluminum or magnesium), the AC-TIG welding is commonly employed. Here, the role of arc controller is to generate consistent pattern of desirable rectangular shape AC current waveform through the arc gap. It could cause severe stress (during polarity transition) in all secondary side components of the controller. This review, using indigenously designed peripheral interface controller (PIC) based arc welding inverter, explains the role of arc controllers to handle issues of majority of TIG welding applications.

Influence of the magnesium content on cathode spot behavior in AC TIG welding of aluminum alloy

Influence of the magnesium content on cathode spot behavior in AC TIG welding of aluminum alloy

Influence of welding current on the mechanical property of 3 mm thick commercial 1050 aluminium butt joint weld by AC-TIG welding method

This paper describes an experimental approach to study the effect of welding current on butt joint of 3 mm thick commercial 1050 aluminium plate. Bead geometry, microstructure and tensile strength of the weld joint is analysed to evaluate the mechanical properties of weld joint. Analysis of bead geometry shows increment in depth of penetration and width of melt zone with increasing welding current. Microstructural analysis of the weld joint reveals columnar dendritic structure in fusion zone while mixed columnar and equiaxed dendritic structures in HAZ. Tensile testresults confirm the improvement of mechanical strength with increase in welding current. However, porosity and incomplete joint penetration adversely affects the mechanical strength of weld joint

Study of 2219 aluminum alloy using direct current A-TIG welding

Direct current A-TIG (DCEN A-TIG) welding using special active agent had eliminated the pores and the oxidation of 2219 high-strength aluminum alloy in welding. Addition of AlF3–25% LiF active agent to DCEN A-TIG welding and arc morphology showed a trailing phenomenon. However, the change in arc morphology was not remarkable when AlF3–75% LiF active agent was added. Addition of AlF3–75% LiF active agent can refine the grain size of DCEN A-TIG joint. The mechanical properties of the weld were optimal at 10% AlF3–75% LiF active agent. Compared with AC TIG and AC A-TIG welding, DCEN A-TIG welding yielded better results for 2219 Al alloy.

Observation of the Behavior of Cathode Spots in AC Tungsten Inert Gas Welding on Aluminum Plate

The cleaning action in AC TIG welding is attributed to the oxide film removal process caused by cathode spots. Clarifying the behavior mechanism of these cathode spots will enable the control of the cleaning action. However, the behavior mechanism of cathode spots has not yet been experimentally clarified. This study reports that observations by high-speed video camera revealed the absence of cathode spots at the center of the molten pool, when shot in the vicinity of a molten pool after AC TIG welding using helium as shield gas on aluminum plates.

Investigation of Hot Cracking Behavior in Transverse Mechanically Arc Oscillated Autogenous AA2014 T6 TIG Welds

Hot cracking studies on autogenous AA2014 T6 TIG welds were carried out. Significant cracking was observed during linear and circular welding test (CWT) on 4-mm-thick plates. Weld metal grain structure and amount of liquid distribution during the terminal stages of solidification were the key cause for hot cracking in aluminum welds. Square-wave AC TIG welding with transverse mechanical arc oscillation (TMAO) was employed to study the cracking behavior during linear and CWT. TMAO welds with amplitude = 0.9 mm and frequency = 0.5 Hz showed significant reduction in cracking tendency. The increase in cracking resistance in the arc-oscillated weld was attributed to grain refinement and improved weld bead morphology, which improved the weld metal ductility and uniformity, respectively, of residual tensile stresses that developed during welding. The obtained results were comparable to those of reported favorable results of electromagnetic arc oscillation.

Numerical analysis of AC tungsten inert gas welding of aluminum plate in consideration of oxide layer cleaning

A unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.

Experimental Observation of Cleaning Action of Cathode Spots in AC TIG Welding of Aluminum Plates

Since it is indispensable to remove oxide layer on aluminum for realizing high quality weld joint in arc welding of aluminum plates, AC TIG welding is generally employed. In periods of EP (Electrode Positive) of AC TIG welding, the oxide layer is removed by cleaning action of cathode spots. In this paper, results on experimental observations of the cleaning action of the oxide layer by cathode spots in AC TIG welding of the aluminum plate with a high speed video camera will be reported. As a result, it was found that cathode spots moved slowly on the oxide layer and their averaged velocity was 26.1m/s. On the other hand, cathode spots near the center of the weld pool, where the oxide layer had been mostly removed, moved at high speed and their averaged velocity reached 121.9 m/s. Furthermore, the velocity greatly changed depending on the position of the cathode spot and exceeded 1 km/s at the maximum.

Grain Refinement in Ferritic Stainless Steel Welds: The Journey so Far

The ferritic stainless steel is a low cost alternative to the most often adopted austenitic stainless steel due to its higher strength, better ductility and superior corrosion resistance in caustic and chloride environments. However, the application of ferritic steel is limited because of poor ductility and notch impact toughness of its weld section with differential grain structures. Several techniques have been explored to control the grain features of the weld to minimize these problems. In the present effort, a review of these options in relation to the degree of grain refinement in ferritic stainless steel weld is conducted in order to have a better understanding about the grain refining phenomenon in the weld microstructure. So far, the most effective technique is found to be the pulse AC TIG welding which can produce weld with mechanical properties equivalent to 65% to those of the base metal. The refinement in this process occurred through dendrite fragmentation and grain detachment in the weld pool producing small-grained microstructures with a large fraction of equiaxed grains. However, in friction welding process where heat input and heat transfer are effectively controlled, the strength can be as high as 95% of the parent metal. This suggests that the total energy input for welding and heat transfer phenomenon mainly control the development of microstructural feature in the weld pool and hence the strength.

Effect of Cadmium Chloride Flux in Active Flux TIG Welding of Magnesium Alloys

The Cadmium Chloride flux increases the weld penetration evidently in the Alternating Current Tungsten inert gas (AC TIG) welding of magnesium alloy. In the present study, in order to investigate the effect of the CdCl 2 active flux on the weld shape and arc voltage, bead-on-plate specimens are made on AZ31B magnesium alloy pre-placed with CdCl 2 active flux by the AC TIG process. Weld pool cross-sections and the arc voltage are analyzed under different welding parameters, welding speed, weld current and arc length. The results showed that compared to the conventional AC-TIG, welding penetration and the weld depth/width with CdCl 2 flux are both two times greater than that of without flux under optimal parameters. The voltage decreases with decreasing of travel speeds and arc length decreasing. Besides, the phenomenon of arc trailing in the EN period and arc contraction in the EP period were observed in AC TIG welding of magnesium alloy with CdCl 2 flux. It found that the arc voltage increases with the increases of welding current, more energies are supplied for welding, resulting in the increases of arc voltage and weld penetration.

Effect of current wave-form on AC TIG welding of aluminium alloys

Because of their superior properties (low specific gravity, corrosion resistance, recyclability etc.), aluminium alloys are currently employed in various sectors and their applications are still expanding. It is well-known that it is necessary to eliminate the oxide film formed on the aluminium alloy surface prior to welding, this characterises the welding of aluminium alloys.

アルミニウム合金の交流ＴＩＧ溶接に対する電流波形の影響

Aluminum alloy has been used in various industrial sectors because of such a desirable mechanical or metallurgical property as low density, high tolerance to corrosion and high recycling efficiency. On the welding of aluminum alloys, it is required to remove the oxide layer from the surface which prevents from making a proper weld joint. AC method is used in the TIG arc welding of aluminum alloys where the cathode spot breaks down the oxide layer covering the material surface during the period of the electrode positive (EP). The object of this study is to make clear the influence of AC current waveform on AC TIG welding of aluminum alloys. Especially, the influence of frequency and EP time ratio on the bead profile and cleaning width has been discussed in the present paper. As a result, it is made clear that the power consumption in arc space is an important factor governing the bead size, and the power consumption in EP alternation is strongly related to the cleaning action.

ＡＺ３１マグネシウム合金ＴＩＧ溶接継手の諸性質

AZ31 magnesium alloy plates 4mm in thickness were welded without addition of filler wire using a pulsed AC TIG welding machine. Microstructural observations have been carried out together with the mechanical tests on the welded joints, with the special reference to the effects of pulse frequency on the optimum welding conditions. In case of the pulse frequency of 20Hz, the crystal grains of the fusion zone are most fine. The hardness of the fusion zone of welded joints are nearly equal to that of the base metal. The welded joints without pulse have the same tensile strength and elongation as those of the base metal. The highest tensile strength and elongation of pulsed welded joints can be obtained with the pulse frequency of 20Hz, but they are inferior to those of the base metal. All the welded joints are fractured at the center of the fusion zone regardless of the pulse frequency. The bending angle of welded joints is smaller than that of the base metal. Fatigue limit of the welded joints with the pulse frequency of 20Hz is 92% of the base metal. And the fatigue limit of the pulse welded joints depends on the grain size of the fusion zone.

矩形波交流アーク溶接に関する研究 Ｉ アルミニウム合金の矩形波交流ＴＩＧ溶接

Rectangular wave AC TIG arc welding phenomena were investigated with respect to the welding current waveform, using an experimental AC power source of the transistor controlled inverter type, which was designed and set up. Current level and duration of each polarity in a cycle were separately varied from 0 to 300 amp. in the frequency range up to 500 Hz. It is shown that the current level and the duration of EN polarity in a cycle are dominant parameters in the current waveform for the arc pressure and the bead formation, but those of EP polarity are responsible for the cleaning action in AC TIG welding of Al alloy.