Showing papers on "Shielding gas published in 2008"
15 Nov 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of the concentration of O-2 and CO2 in the shielding gas on the weld shape was studied for the bead-on-plate TIG welding of SUS304 stainless under He-O2 and He-CO2 mixed shielding gases.
Abstract: A new type of tungsten inert gas (TIG) welding has been developed, in which an ultra-deep penetration is obtained. In order to control the Marangoni convection induced by the surface tension gradient on the molten pool, He gas containing a small amount of oxidizing gas was used. The effect of the concentration Of O-2 and CO2 in the shielding gas on the weld shape was studied for the bead-on-plate TIG welding of SUS304 stainless under He-O-2 and He-CO2 mixed shielding gases. Because oxygen is a surface active element for stainless steel, the addition of oxygen to the molten pool can control the Marangoni convection from the outward to inward direction on the liquid pool surface. When the oxygen content in the liquid pool is over a critical value, around 70ppm, the weld shape suddenly changes from a wide shallow shape to a deep narrow shape due to the change in the direction of the Marangoni convection. Also, for He-based shielding gas, a high welding current will strengthen both the inward Marangoni convection on the pool surface and the inward electromagnetic convection in the liquid pool. Accordingly, at a welding speed of 0.75 mm/s, the welding current of 160 A and the electrode gap of I mm under the He-0.4%O-2 shielding, the depth/width ratio reaches 1.8, which is much larger for Ar-O-2 shielding gas (0.7). The effects of the welding parameters, such as welding speed and welding current were also systematically investigated. In addition. a double shielding gas method has been developed to prevent any consumption of the tungsten electrode. (c) 2008 Elsevier B.V. All rights reserved.
123 citations
TL;DR: In this paper, the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5mm thick austenitic stainless steel plates.
Abstract: The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al2O3, Cr2O3, TiO2, SiO2 and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The experimental results indicated that the increase in the penetration is significant with the use of Cr2O3, TiO2, and SiO2. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment. It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration.
109 citations
TL;DR: In this article, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique, which leads to relatively finer and more equi-axed grain structure in GTA and GMA welds.
Abstract: High strength aluminum alloys (Al-Zn-Mg-Cu alloys) have gathered wide acceptance in the fabrication of lightweight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminum alloy are frequently the gas tungsten arc welding (GTAW) process and the gas metal arc welding (GMAW) process due to their comparatively easy applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results in inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique. Rolled plates of 6 mm thickness were used as the base material for preparing single pass welded joints. A single ‘V’ butt joint configuration was prepared for joining the plates. The filler metal used for joining the plates was AA 5356 (Al-5Mg (wt%)) grade aluminum alloy. Four different welding techniques were used to fabricate the joints: (1) continuous current GTAW (CCGTAW), (2) pulsed current GTAW (PCGTAW), (3) continuous current GMAW (CCGMAW) and (4) pulsed current GMAW (PCGMAW). Argon (99.99% pure) was used as the shielding gas. Tensile properties of the welded joints were evaluated by conducting tensile tests using a 100 kN electro-mechanical controlled universal testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in tensile strength and tensile ductility.
93 citations
TL;DR: In this article, the influence of shielding gas composition on arc properties including temperature, voltage, heat flux and shear stress at the anode and also the weld depth as indicated by the maximum temperature of a water cooled anode is investigated.
Abstract: The influence of shielding gas composition on arc properties including temperature, voltage, heat flux and shear stress at the anode and also the weld depth as indicated by the maximum temperature of a water cooled anode is investigated. It is found that the additions of helium, hydrogen and nitrogen to argon all increase the arc and anode temperature. For helium, this is due to the lower electrical conductivity; in the other cases, it is due to the higher specific heat.
78 citations
TL;DR: In this paper, an experimental and modeling investigation of gas tungsten arc butt welding of stainless steel plates containing different sulfur concentrations was performed, and the results showed significant shift of the fusion zone toward the low sulfur steel.
70 citations
TL;DR: In this paper, the effects of various gas metal arc welding (GMAW) and universal GMAW process parameters on dilution in single layer stainless steel cladding of low carbon structural steel plates were analyzed.
67 citations
TL;DR: In this article, the influence of pulsed current welding and post weld aging treatment on fatigue crack growth behavior of AA7075 aluminium alloy (Al-Zn-Mg-Cu alloy) was reported.
64 citations
TL;DR: In the case of gas tungsten arc (GTA) welding, the pulsed current has been found to be beneficial primarily due to its advantages over the conventional continuous current process as mentioned in this paper.
60 citations
TL;DR: In this paper, a 200-A high-tolerance plasma arc cutting (HTPAC) system is used to cut plates from 15mm thick mild steel sheets metals, and the analysis indicates that cutting speed and arc voltage affect the kerf formation mechanism and their interaction is also important in defining the inclination of the cut.
58 citations
TL;DR: In this article, an attempt has been made to study the effect of pulsed current Gas Tungsten Arc (GTA) welding parameters on corrosion behavior of Ti-6Al-4V titanium alloy.
48 citations
TL;DR: In this paper, the authors used response surface methodology to predict and optimize the percentage of the dilution of a cobalt-based hard-faced surface produced by the PTA process.
Abstract: Control of dilution is important in hardfacing, where low dilution is typically desirable. At present, most fabrication industries use shielded metal are welding, gas metal arc welding, gas tungsten arc welding and submerged are welding processes for hardfacing purposes. In these processes, the percentage of the dilution level is higher, ranging between 10% and 30%. In Plasma Transferred Arc (PTA) hardfacing, a solidified metallurgical bond between the deposit and the substrate is obtained with minimum dilution (less than 10%). This paper highlights the application of response surface methodology to predict and optimize the percentage of the dilution of a cobalt-based hardfaced surface produced by the PTA process. Experiments were conducted based on a fully replicable five-factor, five-level central composite rotatable design and a mathematical model was developed using response surface methodology. Furthermore, the response surface methodology was used to optimize the process parameters that yield the lowest percentage of dilution.
TL;DR: In this paper, the process of heat tint formation is discussed in terms of transport phenomena to explain the effect of atmosphere, temperature and composition of weld oxides formed were found to be enriched in manganese and corrosion testing shows that nitrogen has a strong influence on the weld oxide.
TL;DR: In this paper, a gas tungsten arc in helium and argon was modelled taking into account the contamination of the plasma by metal vapour from the weld pool, and the transient distribution of the temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the weld penetration as a function of time for a 150 A arc current at the atmospheric pressure.
Abstract: A gas tungsten arc in helium and argon was modelled taking into account the contamination of the plasma by metal vapour from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapour. The transient two-dimensional distributions of the temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the weld penetration as a function of time for a 150 A arc current at the atmospheric pressure, both for helium and argon welding gases.It was shown that the thermal plasma in gas tungsten arcs is influenced by iron vapour from the weld pool surface and that the concentration of iron vapour in plasma is dependent on the temperature of the weld pool.
TL;DR: In this paper, a keyhole gas tungsten arc welding (K-GTAW) was used to join commercially pure zirconium and the mechanical properties and the microstructure of the resulting joints were characterised.
Abstract: Keyhole gas tungsten arc welding (K-GTAW), a novel variant of GTAW, has been used to join commercially pure zirconium. The process enables single pass welding of 6˙35 mm thick zirconium using conventional GTAW equipment and a high current torch, without expensive filler metal addition or joint preparation. The mechanical properties and the microstructure of the resulting joints were characterised. It is concluded that the K-GTAW process, with its high productivity combined with low capital investment requirements, can be successfully used for welding relatively heavy section zirconium.
TL;DR: In this paper, an attempt has been made to study the effect of pulsed current gas tungsten arc welding parameters on Ti-6Al-4V titanium alloy, which is one of the best engineering metals for industrial applications.
TL;DR: In this article, a gas tungsten arc in helium is modeled taking into account the contamination of the plasma by the metal vapor from the weld pool surface, and a viscosity approximation is used to express the diffusion coefficient in terms of the viscosities of the helium gas and the iron vapor.
Abstract: A gas tungsten arc in helium is modeled taking into account the contamination of the plasma by the metal vapor from the weld pool surface. The whole region of gas tungsten arc welding, namely the tungsten cathode, arc plasma and weld pool, is treated using a unified numerical model. A viscosity approximation is used to express the diffusion coefficient in terms of the viscosities of the helium gas and the iron vapor. The time-dependent two-dimensional distributions of temperature, velocity and iron vapor concentration are predicted, together with the weld penetration as function of time for a 150 A arc current at atmospheric pressure. It is shown that the thermal plasma in gas tungsten arcs is markedly influenced by iron vapor from the weld pool surface and that the concentration of the iron vapor in the plasma is dependent on temperature of the weld pool surface.
TL;DR: In this article, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique, which leads to relatively finer and more equi-axed grain structure in gas tungsten arc (GTA) and gas metal arc welding (GMA) welds.
TL;DR: In this article, the optical interaction between a fiber laser beam and a weakly ionised plasma was investigated in stainless steel welding with a 10 kW laser beam at the ultra high power density of ∼1 MW mm-2 in Ar shielding gas.
Abstract: A weakly ionised plasma can be generated in stainless steel welding with a 10 kW fibre laser beam at the ultra high power density of ∼1 MW mm–2 in Ar shielding gas. The objectives of this study are to obtain a fundamental knowledge of optical interaction between a fibre laser beam and the weakly ionised plasma, and to evaluate effects of the plasma on weld penetration. The optical interaction was investigated by the high speed video observation or the power meter measurement of another probe fibre laser beam, which passed horizontally through the weakly ionised plasma induced during bead on plate welding of a 20 mm thick type 304 plate with a 10 kW fibre laser beam of 0˙9 MW mm–2 in power density. The probe laser observed was refracted at 0˙6 mrad angle in average, which was much lower than the 90 mrad divergence of the focused fibre laser beam. The attenuation of the probe laser was measured to be ∼4%, which was not mainly caused by Inverse Bremsstrahlung but by Rayleigh scattering. Moreover, a s...
TL;DR: In this article, a series of CO2 laser-metal inert gas arc hybrid welding experiments was carried out to investigate the effects of laser/arc energy ratio and groove parameters on the shape and microstructure of hybrid weld.
Abstract: A series of CO2 laser–metal inert gas arc hybrid welding experiment was carried out to investigate the effects of laser/arc energy ratio and groove parameters on the shape and microstructure of hybrid weld The results showed that increasing arc current and groove cross-section area can reduce dimension difference of laser zone and arc zone by enhancing the uniform of energy distribution in molten pool The arc current can speed the melted metal flow to the pool root and drive more heat to the pool below by the arc pressure, and groove area can reduce the resistance of melted metal flowing to the pool root The microstructure of hybrid weld is simultaneously determined by the total line energy of hybrid welding and energy ratio of laser/arc (ER LA), and only under the proper or relatively smaller total line energy ER LA has obvious effects on microstructure Increasing the ER LA can increase the tendency of hybrid weld to obtain structure with higher hardness Furthermore, the mechanical performan
TL;DR: In this paper, the relationship between weldability and the process parameters of the laser beam-arc distance, welding current and welding speed were investigated using a full factorial experimental design, and the weld quality was evaluated using the weight of the spatter, as porosity formation is a major weld defect in the lap welding of zinc-coated steel sheets.
Abstract: In the lap welding of zinc-coated steel, porosity formation is one of most significant weld defects. It is caused by zinc vapor generated between the steel sheets. Various solutions have been proposed in the past but development of more effective method remains a valuable subject to be investigated. In this study, laser-TIG hybrid welding was applied to the lap welding of zinc-coated steel without a gap. The weld defects could be eliminated by laser-TIG hybrid welding, as the leading TIG arc partially melted the upper sheet, and the coated zinc on the lapped surfaces were vaporized or oxidized before the trailing laser irradiated on the specimen. Optimization of the process parameters for laser-arc hybrid welding process is intrinsically sophisticated because the process has three types of parameters-arc, laser and hybrid welding parameters. In this paper, the relationship between weldability and the process parameters of the laser beam-arc distance, welding current and welding speed were investigated using a full factorial experimental design. Weld quality was evaluated using the weight of the spatter, as porosity formation is a major weld defect in the lap welding of zinc-coated steel sheets. It was found that the weld quality was increased as the laser beam-arc distance and welding current increased, and that this decreased as welding speed increased.
Patent•
23 Jul 2008
TL;DR: In this paper, the second peak period (Tp1) and current (Ip2) are determined so that an arc anode point (3a) is formed at the top of the droplet (1b) even if the shield gas mixing ratio deviates from a standard value.
Abstract: In pulse arc welding, a welding wire (1) is fed at a rate corresponding to a current average set value (Iar). An arc (3) is struck by passing a peak current (Ip) for a peak period (Tp) and a base current (Ib) for a base period (Tb), where the peak and base periods (Tp,Tb) make one pulse period (Tf). The arc (3) transfers a droplet (1b) from the wire (1). The peak period (Tp) includes a first peak period (Tp1) for a first peak current (Ip1) and a second peak period (Tp2) for a smaller second peak current (Ip2). The first peak period (Tp1) and current (Ip1) are determined so that an arc anode point (3a) is formed at the top of the droplet (1b) even if the shield gas mixing ratio deviates from a standard value. The second peak period (Tp2) and current (Ip2) are determined so that one droplet (1b) is transferred during every pulse period (Tf), and beads are formed with no undercuts.
TL;DR: In this paper, the welding temperature field of AZ31B magnesium alloy plate in Gas Tungsten Arc Welding (GTAW) is measured by IR, the isothermal map of magnesium Alloy plate is measured using IR device, and cooling curves are measured by thermocouple.
TL;DR: In this paper, the effect of postweld aging treatment on fatigue behavior of pulsed current welded AA 7075 aluminum alloy joints was investigated and four different welding techniques were used to fabricate the joints.
Abstract: This article reports the effect of postweld aging treatment on fatigue behavior of pulsed current welded AA 7075 aluminum alloy joints. AA7075 aluminum alloy (Al-Zn-Mg-Cu alloy) has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers, and railway transport systems. The preferred welding processes of AA7075 aluminum alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Rolled plates of 10 mm thickness have been used as the base material for preparing multipass welded joints. Single V butt joint configuration has been prepared for joining the plates. The filler metal used for joining the plates is AA 5356 (Al-5Mg (wt.%)) grade aluminum alloy. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW), and (iv) pulsed current GMAW (PCGMAW) processes. Argon (99.99% pure) has been used as the shielding gas. Rotary bending fatigue testing machine has been used to evaluate fatigue behavior of the welded joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. Grain refinement is accompanied by an increase in fatigue life and endurance limit. Simple postweld aging treatment applied to the joints is found to be beneficial to enhance the fatigue performance of the welded joints.
TL;DR: In this article, the effect of carbon dioxide gas in the helium base shielding on the oxygen content in the weld pool and the weld shape variations was investigated in bead-on-plate GTA welding.
Abstract: Bead-on-plate GTA welding (gas tungsten arc welding) on a SUS304 substrate is carried out to investigate the effect of carbon dioxide gas in the helium base shielding on the oxygen content in the weld pool and the weld shape variations. Experimental results show that small addition of carbon dioxide to the shielding gas can precisely adjust the weld metal oxygen content and change the weld shape from wide shallow type to narrow deep one when the weld pool oxygen content is over the critical value, which is from 68 to 82 ppm, due to the Marangoni convection reversal from the outward to inward mode on the pool surface. The weld depth/width ratio increases two times suddenly when the carbon dioxide content in the torch gas is over 0.4 or 0.2% for 1 mm or 3 mm arc length, respectively. The GTA weld shape depends to a large extent on the pattern and magnitude of the Marangoni convection on the pool surface, which is influenced by the active element oxygen content in the SUS304 pool, temperature coefficient of the surface tension (dσ/dT), and the temperature gradient on the pool surface (dT/dr, r is the radius of the weld pool surface). Changing the welding parameters will alter the temperature distribution and gradient on the pool surface, and thus, affect the magnitude of the Marangoni convection and the final weld shape.
01 Nov 2008
TL;DR: In this paper, a shielding gas consisting of helium, argon, and CO2 was used, and its effects on the composition of the welding phenomena, such as behaviours of laser-induced plasma generation, molten pool flow, and droplet transfer in gas metal arc welding, were investigated.
Abstract: In carbon dioxide (CO2) laser—gas metal arc hybrid welding, a shielding gas is supplied to isolate the molten metal from the ambient air, suppress the laser-induced plasma, remove the plume out of the keyhole, and stabilize the metal transfer. In this study, a shielding gas consisting of helium, argon, and CO2 was used, and its effects on the composition of the welding phenomena, such as behaviours of laser-induced plasma generation, molten pool flow, and droplet transfer in gas metal arc welding, were investigated. High-speed video observation was used to investigate the welding phenomena inside the arc regime. Consequently, helium was found to have a dominant role in suppressing laser-induced plasma; minimum helium content at a laser power of 8 kW was suggested for laser autogenous and hybrid welding. Argon and CO2 govern the droplet transfer and arc stability. A 12 per cent addition of CO2 stabilizes the metal transfer and eliminates undercut caused by insufficient wetting of molten metal.
Patent•
01 Sep 2008
TL;DR: In this article, a shielding gas (SG) flow controller for an arc welder includes SG input/output with a controllable valve there between, and having a control input, and a controller having a first input receiving a welding signal representing arc current and a gas flow setting controller generating a flow setting output based on the welding signal, representing a desired SG flow.
Abstract: A shielding gas (SG) flow controller for an arc welder includes SG input/output with a controllable valve therebetween, and having a control input, and a controller having a first input receiving a welding signal representing arc current and a gas flow setting controller generating a flow setting output based on the welding signal, representing a desired SG flow. Input and output pressure sensors provide SG input and out pressure to second and third controller inputs, respectively. A flow setting output modifier modifies the flow setting output of the gas flow setting controller based on the SG input/output pressure, the welding signal, and a characteristic of the controllable valve into a control signal input to the control input of the controllable gas valve to maintain a substantially constant SG flow corresponding to the flow setting output substantially independent of actual SG input/output pressures.
TL;DR: In this paper, the authors used response surface methodology (RSM) to predict and optimize the percentage of dilution of nickel based hard-faced surface produced by the plasma transferred arc (PTA) process.
Abstract: Control of dilution is important in hardfacing, where typically low dilution is desirable. At present, majority of the fabrication industries use shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and submerged arc welding (SAW) processes for hardfacing purposes. In these processes, the percentage of dilution level is higher, ranging between 10–30%. In plasma transferred arc (PTA) hardfacing, a solidified metallurgical bond between deposit and substrate is obtained with minimum dilution (less than 10%). This article highlights the application of response surface methodology (RSM) to predict and optimize the percentage of dilution of nickel based hardfaced surface produced by PTA process. The experiments were conducted based on five-factor, five levels central composite rotatable design with full replications technique and mathematical model was developed using RSM. Further, the RSM is used to optimize the process parameters that yield the lowest percentage of...
TL;DR: In this article, the effects of welding speed, weld current and electrode gap on the weld shape and the weld arc voltage in AC TIG welding with oxide fluxes were investigated on an AZ31B magnesium alloy substrate.
Abstract: Magnesium-based alloys are finding extensive applications foreground in aerospace and automotive applications. Weldability of magnesium alloys has recently been investigated with a variety of processes. In this article, the activating flux TIG (ATIG) welding of magnesium alloys with three single-component fluxes (TiO2, Cr2O3 and SiO2) under alternating current (AC) mode was studied. The effects of welding speed, weld current and electrode gap on the weld shape and the weld arc voltage in AC TIG welding with oxide fluxes were investigated on an AZ31B magnesium alloy substrate. The mechanisms of oxide fluxes on the arc shape and the arc voltage on the weld shape are discussed. The result showed that the TiO2 and Cr2O3 increase the weld penetration of AC TIG welding of magnesium with good bead cosmetics. The SiO2 increased the weld penetration with very poor formation of the weld surface. However, the arc voltage decreased with the used of TiO2 flux, and increased with the used of Cr2O3 flux. The mechanism of TiO2 and Cr2O3 fluxes increasing penetration should not accord with the “arc constriction”. It would comply with some potential effects of the flux interacting with the liquid metal of fusion zone.
TL;DR: In this article, the use of the stochastic search process based on genetic algorithms (GA) in estimating the strength value of the welded parts was described, and non-linear estimation models were developed using GA.
TL;DR: In this article, the MIG/MAG welding arc plasma was investigated for different mixtures of argon and carbon dioxide in the shielding gas, and it was shown that there is a limit in the relative concentration CO 2 /Ar beyond which the arc shape is significantly modified.
Abstract: Composition of the applied shielding gas has a strong influence on physical properties of the plasma and parameters of the welding process. In particular, increase of the percentage of carbon dioxide in argon results in an increase of the transition current value while changing from the globular to spray mode of metal transfer during the welding process. In order to explain this phenomenon, the MIG/MAG welding arc plasma was investigated for different mixtures of argon and carbon dioxide in the shielding gas. Applying a fast camera, recording distribution of spectral lines of the plasma components, we noticed some phenomena not described yet in the literature. Especially, there is a limit in the percentage of relative concentration CO 2 /Ar beyond which the arc shape is significantly modified.