Showing papers on "Shielding gas published in 2014"
TL;DR: In this article, a simple modeling approach combined with absorption spectroscopy of long living species generated by a cold atmospheric plasma jet yields insight into relevant gas phase chemistry, where reactive species output of the plasma jet is controlled using a shielding gas device.
Abstract: In this work, a simple modelling approach combined with absorption spectroscopy of long living species generated by a cold atmospheric plasma jet yields insight into relevant gas phase chemistry. The reactive species output of the plasma jet is controlled using a shielding gas device. The shielding gas is varied using mixtures of oxygen and nitrogen at various humidity levels. Through the combination of Fourier transform infrared (FTIR) spectroscopy, computational fluid dynamics (CFD) simulations and zero dimensional kinetic modelling of the gas phase chemistry, insight into the underlying reaction mechanisms is gained. While the FTIR measurements yield absolute densities of ozone and nitrogen dioxide in the far field of the jet, the kinetic simulations give additional information on reaction pathways. The simulation is fitted to the experimentally obtained data, using the CFD simulations of the experimental setup to estimate the correct evaluation time for the kinetic simulation. It is shown that the ozone production of the plasma jet continuously rises with the oxygen content in the shielding gas, while it significantly drops as humidity is increased. The production of nitrogen dioxide reaches its maximum at about 30% oxygen content in the shielding gas. The underlying mechanisms are discussed based on the simulation results.
122 citations
TL;DR: Inconel 718 (2mm thick) was welded using argon and helium gas shielded tungsten arc welding process with a filler metal and the cooling rates calculated as mentioned in this paper.
121 citations
TL;DR: In this paper, the effect of the processing parameters on the weld bead geometry was examined, and the microstructure and mechanical properties of the optimal joint were investigated, showing that the focal position is a key parameter in high power fiber laser welding of thick plates.
116 citations
TL;DR: In this paper, the microstructural properties, tensile properties and low-cycle fatigue properties of a dual-phase steel (DP780) were investigated following its joining by three methods: laser welding, tungsten inert gas (TIG) welding, and metal active gas (MAG) welding.
95 citations
TL;DR: In this article, the fatigue characteristics of a tensile shear specimen during spot welding was investigated with the welding parameters that occur in the surface crack of welds on Zn-coated steel.
Abstract: The development of the automotive industry is now focused not only on improving basic vehicle performance but also on reducing weight and enhancing safety and durability. Various automotive high-strength steels are being developed, and Zn-coated steels are being manufactured to prevent corrosion of the external white vehicle body. The most commonly used welding method in the car body assembly process is resistance spot welding (RSW), which has been extensively studied worldwide. In this process, the work piece is basically heated according to the contact resistivity of the interfacial between the electrode and the material as well as the bulk resistivity of the material itself. At this point, if the meta li s Zn, which has a lower melting point than the Fe base metal on the surface, it is mainly melted in the temperature range of 400900°C. It becomes easy to penetrate the grain boundary of the HAZ during welding. Also, the tensile stress in such a state decreases the ductility of the grain boundary and causes liquid metal embrittlement (LME). Cu5Zn8, an intermetallic compound, can be formed from the reaction of the alloy with the Cu material electrode in the expulsion current range at a high temperature. Its formation is likely to be facilitated by LME or a surface crack. In this study, the fatigue characteristics of a tensile shear specimen during spot welding was investigated with the welding parameters that occur in the surface crack of welds on Zn-coated steel. Finally, a controlled spot welding condition was suggested to prevent surface cracks. [doi:10.2320/matertrans.M2013244]
72 citations
TL;DR: In this paper, the influence of the balance of current between the TIG and MIG arcs was investigated, which is most important in determining arc stability and arc penetration, and it was shown that the welding time can be reduced to 17 ~ 44 % of the time required using a conventional TIG process.
Abstract: Tungsten inert gas (TIG) and metal inert gas (MIG) welding are the most popular gas-shielded arc-welding processes used in many industrial fields. MIG welding is a high-efficiency process compared to TIG welding. However, improvements are needed to reduce spatter and improve weld metal toughness. Although pure argon shielding gas is desirable for weld metal toughness, MIG arcs are unstable in pure Ar to the extent that executing welding is difficult. We have found that MIG arcs become stable even using pure argon by simply using a hybrid TIG and MIG system. This process has the possibility of becoming a new welding process giving high quality and efficiency. In this study, we investigate the influence of the balance of current between the TIG and MIG arcs, which is most important in determining arc stability and arc penetration. We have confirmed the suitable range of conditions both experimentally and through numerical simulation and have applied this process for butt and fillet joints. We show that the welding time can be reduced to 17 ~ 44 % of the time required using a conventional TIG process.
71 citations
TL;DR: In this article, a quantitative model of porosity defects induced by keyhole instability in partial penetration CO2 laser welding of a titanium alloy is proposed, and the results are compared to prior experimental results.
Abstract: Quantitative prediction of the porosity defects in deep penetration laser welding has generally been considered as a very challenging task. In this study, a quantitative model of porosity defects induced by keyhole instability in partial penetration CO2 laser welding of a titanium alloy is proposed. The three-dimensional keyhole instability, weld pool dynamics, and pore formation are determined by direct numerical simulation, and the results are compared to prior experimental results. It is shown that the simulated keyhole depth fluctuations could represent the variation trends in the number and average size of pores for the studied process conditions. Moreover, it is found that it is possible to use the predicted keyhole depth fluctuations as a quantitative measure of the average size of porosity. The results also suggest that due to the shadowing effect of keyhole wall humps, the rapid cooling of the surface of the keyhole tip before keyhole collapse could lead to a substantial decrease in vapor pressure inside the keyhole tip, which is suggested to be the mechanism by which shielding gas enters into the porosity.
69 citations
TL;DR: Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, nonconsumable or consumable, is added to bypass part of the wire current.
69 citations
TL;DR: In this article, cold metal transfer (CMT) spot plug joining of 1mm thick Al AA6061-T6 to 1.5mm thick galvanized steel (i.e., Q235) was studied.
66 citations
TL;DR: In this article, a hybrid fiber laser-MIG welding was applied to join 5mm thick AA6005-T5 alloy used in the carbody of high speed railway vehicles.
61 citations
TL;DR: In this article, the effect of current, welding speed, joint gap and electrode diameter on weld bead dimensions on 6-mm-thick dissimilar weld between carbon steel to stainless steel, was studied under Activated Flux-Tungsten Inert Gas Welding process.
TL;DR: In this paper, the simultaneous effects of welding parameters on tensile strength and hardness were obtained through two separate equations, and the optimized values of welding process parameters to achieve desired mechanical properties were evaluated.
TL;DR: In this article, the influence of the type of filler material on the emission of toxic substances, and the potential hazards of the filler material were investigated in microalloyed steel and self-shielded wire.
Abstract: Welding is the principal industrial process used for joining metals, but at the same time, it’s the significant source of toxic fumes and gases emission. With the advent of new types of welding procedures and consumables, the number of welders exposed to welding fumes is growing constantly in spite of the mechanisation and automation of the process. Having in mind that, in some cases, toxic fumes and gases can be over the respective limits for toxic substances, one of the most important requirements for chosen welding procedure is its harmlessness to the environment. The health aspects associated with welding are complex and the industry is continuing its research to evaluate the effects of the welder’s exposure to typical constituents of welding fumes and gases, as well as its impact on what concerns climatic changes. The aim of this paper is to estimate the influence of the type of filler material on the emission of toxic substances, and to show the potential hazards. In order to determine that effect, microalloyed steel has been welded using two different filler materials (metal cored wire and self-shielded wire). The concentrations of emitted total dust, CO 2 , CO, SO, Mn, Ni, Al, Cr, Cr(VI), Ca and P were measured. By comparing results for both filler materials, it was established that the special attention must be paid to the high concentration of manganese and CO in metal cored wire, as well as high concentrations of phosphorus and aluminum in self-shielded wire. Also, conducted experimental measurements of emission of certain elements did not show higher toxicity of self-shielded wire compare to metal cored wire, what is in the contrast with previous studies.
TL;DR: In this paper, the resistance to localised corrosion of AISI 2205 duplex stainless steel plates joined by Gas Metal Arc Welding (GMAW) under the effect of electromagnetic interaction of low intensity (EMILI) was evaluated with sensitive electrochemical methods.
TL;DR: In this article, an additive layer manufacturing (ALM) process based on gas tungsten arc welding (GTAW) was used to produce simple 3-dimensional titanium aluminide components, which were successfully in situ alloyed by separately delivering elemental Al and Ti wires to the weld pool.
Abstract: An additive layer manufacturing (ALM) process based on gas tungsten arc welding (GTAW) was used to produce simple 3-dimensional titanium aluminide components, which were successfully in situ alloyed by separately delivering elemental Al and Ti wires to the weld pool. The difference in microstructure, chemical composition, and microhardness of four wall components built with four different wire-feeding conditions has been evaluated. There was no significant change in the microstructure of the four walls. The composition and microhardness values were comparatively homogeneous throughout each wall except the near-substrate zone. However, with increasing the ratio of Al to Ti wire feed rates from 0.80 to 1.30, an increase of Al concentration and γ phases were observed. The situation was reversed for the effect of the Al:Ti ratio on microhardness. Additionally, an unexpected increase in the α2 phase was produced when the ratio was increased to 1.30.
TL;DR: Cap active flux tungsten inert gas (CA-TIG) welding using atmospheric oxygen was proposed to increase the penetration depth of a weld by using a simple nozzle cap with an air inlet as mentioned in this paper.
TL;DR: In this paper, the effect of current mode on size, distribution and volume fraction of pores generated in Fe-Al dissimilar materials lap joint was quantitatively studied, and the results showed that the difference of arc stirring force and linear heat input in these three processes caused by different current modes.
TL;DR: In this article, the authors investigated the joining mechanism of TiAl3 precipitations in the weld metal owing to metallurgical reactions of Al with dissolved Ti. Formations of precipitation and Ti/Al interface were discussed in detail.
Abstract: Butt joining of titanium alloy Ti–2Al–Mn to aluminum 1060 using AlSi5 filler wire was conducted using pulsed gas metal arc welding. Joining mechanism of Ti–2Al–Mn/Al 1060 dissimilar joint with different welding heat input was investigated. Formations of precipitation and Ti/Al interface were discussed in detail. Fusion zone near aluminum is composed of α-Al dendrites and Al–Si hypoeutectic structures. A few TiAl3 precipitations appear in the weld metal owing to metallurgical reactions of Al with dissolved Ti. When the welding heat input was in the range of 1.87–2.10 kJ/cm, titanium alloy Ti–2Al–Mn and Al 1060 were joined together by the formation of a complex Ti/Al interface. With a low welding heat input, a serrate TiAl3 interfacial reaction layer was formed near Ti/Al interface. With the increasing of the welding heat input, α-Ti, Ti7Al5Si12, and TiAl3 layers were formed orderly from Ti–2Al–Mn to weld metal.
TL;DR: In this paper, the double-shielded advanced A-TIG welding method was adopted in this study for the welding of the SUS329J4L duplex stainless steel with the shielding gases of different oxygen content levels.
TL;DR: In this article, the authors present the results of the effect of parameters of underwater local dry chamber welding on the properties of padding welds and the functions for estimating the maximum hardness of the heat affected zone have been also elaborated.
Abstract: The article presents the results of the effect of parameters of underwater local dry chamber welding on the properties of padding welds. The effect of heat input and the type of shielding gas on the structure and hardness of welds was established. the functions for estimating the maximum hardness of the heat affected zone have been also elaborated.
TL;DR: In this article, the authors evaluate the hypothesis that the greater transfer stability leads also to less volume of fumes, using an Ar + 25% CO2 blend as shielding gas and maintaining constant the average current, wire feed speed and welding speed, bead-on-plate welds were carried out with plain carbon steel solid wire.
TL;DR: In this article, the element distribution in S32101 welds performed autogenously bead-on-plate with and without nitrogen additions to the shielding gas has been quantified and illustrated with electron probe microanalysis mapping.
Abstract: Segregation of alloying elements and nitrogen loss may have a negative effect on the corrosion resistance of autogenously welded duplex stainless steel. The lean duplex LDX 2101® (EN 1.4162, UNS S32101) has less metal element segregation and improved austenite formation compared to other duplex grades and addition of filler metal is not always necessary to achieve good corrosion properties. In gas tungsten arc welding, nitrogen additions to the shielding gas can counteract nitrogen loss and thereby contribute to achievement of the required phase balance. The element distribution in S32101 welds performed autogenously bead-on-plate with and without nitrogen additions to the shielding gas has been quantified and illustrated with electron probe microanalysis mapping. Local segregation and depletion along the fusion line have been elucidated and explained in terms of epitaxial growth and dendritic solidification behavior. The resulting variations in the corrosion resistance are demonstrated by the pitting resistance equivalent distribution and compared to previously known corrosion data.
TL;DR: In this article, the microstructure and mechanical properties of the GTA and PCGTA welded dissimilar combinations of Inconel 625 superalloy and AISI 304 austenitic stainless steel were characterized by the combined techniques of optical microscopy and SEM/EDAX analysis.
Abstract: This investigation has been performed to characterize the microstructure and mechanical properties of the GTA and PCGTA welded dissimilar combinations of Inconel 625 superalloy and AISI 304 austenitic stainless steel. These welds were obtained by employing ERNiCrMo-3 filler metal. The weldments were characterized by the combined techniques of optical microscopy and SEM/EDAX analysis. Hardness and tensile studies were conducted to assess the mechanical properties of the weldments. Tensile studies showed that the fracture had occurred at the parent metal of AISI 304 side in both the cases.
TL;DR: In this paper, the interdendritic Laves phase and the microsegregation have been investigated in Alloy 718 fusion zone cooled with liquid nitrogen during welding, and the weld cooling rate was enhanced using liquid nitrogen cooling during Gas Tungsten Arc welding process.
TL;DR: In this article, the authors have shown that as almost all the evaporated atoms return back to the cathode, the net erosion rate is much lower than the evaporation rate.
Abstract: Thermionic arc cathodes are the cathodes where thermionic emission is the main electron emission mechanism. They are used in welding (Tungsten pure or doped with rare earth oxides) and plasma arc cutting (Tungsten for cutting with inert gas or Hafnium for cutting with Oxygen plasma). There are two different sources of erosion: constant current (CC) erosion and erosion during arc initiation and termination (cycling erosion). Available experimental data for both types of cathode and both types of erosion (CC and cycling) are presented and discussed. For quite some time, it has been clear that CC erosion is due to cathode evaporation. It has been shown that as almost all the evaporated atoms return back to the cathode, the net erosion rate is much lower than the evaporation rate. The existing model allows one to calculate the ratio of these two (escape factor). It is in the range 10-2-10-3. The important role of cathode geometry and plasma flow pattern in the cathode proximity is discussed. The nature of cathode erosion during arc start and arc termination is much less understood in spite the fact that the corresponding erosion could be very important and even dominate for multiple cycles. Different processes that lead to this type of erosion are considered.
TL;DR: In this article, the metal transfer in CO 2 Laser+GMAW-P hybrid welding by using argon-helium mixtures was investigated and the effect of the laser on the mental transfer was discussed.
Abstract: The metal transfer in CO 2 Laser+GMAW-P hybrid welding by using argon–helium mixtures was investigated and the effect of the laser on the mental transfer is discussed. A 650 nm laser, in conjunction with the shadow graph technique, is used to observe the metal transfer process. In order to analyze the heat input to the droplet and the droplet internal current line distribution. An optical emission spectroscopy system was employed to estimate default parameter and optimized plasma temperature, electron number densities distribution. The results indicate that the CO 2 plasma plume have a significant impact to the electrode melting, droplet formation, detachment, impingement onto the workpiece and weld morphology. Since the current distribution direction flow changes to the keyhole, to obtain a metal transfer mode of one droplet per pulse, the welding parameters should be adjusted to a higher pulse time ( TP ) and a lower voltage.
TL;DR: In this article, it was shown that the force of a shielding gas jet impact on a drop of an electrode metal in double-jet gas shielding is twelvefold as in one-jet one; it is directed along the electrode to a workpiece and stimulates stability of the electrode metal drops transfer into a weld pool.
Abstract: The processes taking place in a drop of a molten electrode metal and in a metal of a weld pool play the dominant role in formation of joint welds properties. In consumable electrode welding with jet gas shielding under certain conditions a drop of an electrode metal is influenced by the main forces as well as by the force of a shielding gas jet impact which depends upon the method and composition of a gas shielding in a welding area. The results of research have stated that the force of a shielding gas jet impact on a drop of an electrode metal in double-jet gas shielding is twelvefold as in one-jet one; it is directed along the electrode to a workpiece and stimulates stability of the electrode metal drops transfer into a weld pool.
TL;DR: In this paper, the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels were investigated using an in-house simulation code.
Abstract: In gas metal arc welding, gases of different compositions are used to produce an arc plasma, which heats and melts the workpiece. They also protect the workpiece from the influence of the air during the welding process. This paper models gas metal arc welding (GMAW) processes using an in-house simulation code. It investigates the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels. Pure argon, pure CO2 and different mixtures of argon and CO2 are considered in the study. The model is validated by comparing the calculated weld profiles with physical weld measurements. The numerical calculations reveal that gas composition greatly affects the arc temperature profile, heat transfer to the workpiece, and consequently the weld dimension. As the CO2 content in the shielding gas increases, a more constricted arc plasma with higher energy density is generated as a result of the increased current density in the arc centre and increased Lorentz force. The calculation also shows that the heat transferred from the arc to the workpiece increases with increasing CO2 content, resulting in a wider and deeper weld pool and decreased reinforcement height.
TL;DR: In this paper, experimental investigations are presented to identify arising process limits during laser welding of pure copper materials with multi-mode fiber lasers at near infrared wavelength depending on the applied laser power and welding velocity.
TL;DR: In this article, a TIG melted surface of a microalloy steel substrate, with or without incorporating pre-placed SiC particles, in either argon or argon-helium environments, was shown to reach a maximum temperature of 375°C in the second third of the track.
Abstract: The use of a tungsten inert gas (TIG) welding torch has resulted in the development of an economical route for surface engineering of alloys, giving similar results to the more expensive high power laser. Owing to the preheating generated by both techniques, the extent of the temperature rise is sufficient to produce significant changes to the melt dimensions, microstructure and properties between the first and last tracks melted during the coating of a complete surface. The present study examines if similar changes can occur between the start and finish locations of a single track of 50 mm length. The results show that for a TIG melted surface of a microalloy steel substrate, with or without incorporating preplaced SiC particles, in either argon or argon–helium environments, a maximum temperature of 375°C developed in the second third of the track. Even over this short distance, a hardness decrease of >300 HV was recorded in the resolidified SiC coated substrate melt zone, microstructure of a cas...