Showing papers on "Shielding gas published in 2016"
TL;DR: In this article, a theoretical approach for the formation of these process deviations and arising material defects is presented, and the impact of these deviations on building surface and part quality is investigated by 3D confocal microscopy, microsections and ultrasonic testing.
Abstract: Selective laser melting is a promising additive manufacturing technology for the production of complex metal components. The technique uses metallic powder as a starting material and a laser for melting and building-up parts layer by layer. One crucial factor influencing the process stability and therefore the part quality is the shielding gas flow. In addition to the shielding properties of the inert atmosphere the gas flow is responsible for the removal of process by-products like spatter and welding fumes originating from the process zone. Insufficient removal or inhomogeneous gas flow distribution may lead to increased interaction between laser and process by-products. Consequences are attenuation of the laser spot as well as redeposition of this by-products on surfaces which are exposed to the laser afterwards. Firstly, a conclusion on all known process by-products is drawn. Secondly, based on these considerations the uniformity of the gas flow is investigated by the width of single welds. Furthermore process deviations are provoked by unfavorable gas flow conditions. Thirdly, the impact of this deviations on building surface and part quality is investigated by 3D confocal microscopy, microsections and ultrasonic testing. Finally, theoretical approach for the formation of these process deviations and arising material defects is presented.
201 citations
TL;DR: Different forms of laser beam welding including single beam laser welding, dual-beam laser welding and laser arc hybrid fusion-brazing welding are reviewed in this paper, where the main problems are how to control the thickness of the intermetallic compound layer and reduce or avoid the generation of pores, cracks, and thermal stresses which severely limit the mechanical properties of welded joints.
Abstract: Joining aluminum to steel can lighten the weight of components in the automobile and other industries, which can reduce fuel consumption and harmful gas emissions to protect the environment. However, the differences of thermal, physical, and chemical properties between aluminum and steel bring a series of problems in laser welding. The main problems are how to control the thickness of the intermetallic compound layer and reduce or avoid the generation of pores, cracks, and thermal stresses which severely limit the mechanical properties of welded joints. Laser fusion-brazing technology utilizes the precise control of heat input with or without filler to partially melt the low melting temperature aluminum base material and promote wetting on the high melting temperature steel base material in order to achieve sound metallurgical by combining the advantages of fusion welding and brazing. Different forms of laser beam welding including single beam laser welding, dual-beam laser welding, and laser arc hybrid fusion-brazing welding are reviewed.
114 citations
TL;DR: In this article, the authors investigated the effect of welding parameters such as torch arrangement, distance between heat sources and shielding gas composition on the quality of laser-arc hybrid welds.
94 citations
TL;DR: In this paper, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas.
93 citations
TL;DR: In this paper, the microstructure, impact toughness, and pitting corrosion resistance of duplex stainless steel (DSS) welding joints fabricated by using gas tungsten arc welding (GTAW) and flux-cored arc welding with different shielding gas compositions were investigated.
89 citations
TL;DR: In this article, a 3D coupled Cellular Automaton (CA) and finite element (FE) model is presented that predicts the grain structure formation during multiple passes Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc welding (GMAW).
87 citations
TL;DR: In this paper, the influence of the shielding gas on the metal transfer was investigated and a unified model was developed for the gas metal arc welding (GMAW) process with argon shielding gas.
Abstract: The gas metal arc welding (GMAW) process involves arc plasma, metal transfer, and weld pool phenomena. In addition, metal vapor is formed by evaporation from the high-temperature metal and mixes with the arc plasma. These phenomena interact with each other and are very complicated. A numerical approach that includes their interaction is therefore important for clarifying the GMAW phenomena. We have developed a unified model and used the model to investigate the influence of the shielding gas on the metal transfer. When argon shielding gas was used, for an arc current of less than 230 A, globular transfer occurred. For higher currents, spray transfer occurred. On the other hand, when Ar + 18 %CO2 gas was used, the transition from globular to spray transfer occurred at around 280 A. This difference was caused by changes in the driving force exerted on the molten metal by the arc plasma. The arc pressure that lifts up the molten metal and interferes with its detachment from the wire tip becomes stronger when the gas mixture is used.
67 citations
TL;DR: In this article, the overlapping welding in a keyhole mode with a magnetic field perpendicular to the welding direction was carried out between stainless steel 301 and aluminum alloy 5754 in this study, which indicated that the application of the magnetic field can modify the weld bead appearance and microstructure of the weld by the Lorenz force and thermoelectric magnetic force induced in the molten pool.
66 citations
TL;DR: In this article, the influence of welding parameters on phase balance, microstructural changes and the protective properties of passive oxide films formed at the open circuit potential or during the anodic polarisation were studied.
52 citations
TL;DR: In this paper, the porosity formation in cold metal transfer (CMT) gas metal arc welding (GMAW) of zinc coated steel is studied over a wide range of the heat inputs, which shows low porosity in weld bead ( 350 J mm−
Abstract: The porosity formation in cold metal transfer (CMT) gas metal arc welding (GMAW) of zinc coated steel is studied over a wide range of the heat inputs (160–250 J mm− 1), which shows low porosity in weld bead ( 350 J mm− 1) heat inputs and maximum at medium (250–350 J mm− 1) heat inputs. The high speed imaging of weld pool shows that the highest frequency of zinc vapour escapes at high heat inputs compared to other conditions. Numerous experiments show that size and location of pores along with escaping of zinc vapour are the results of competition of viscosity of weld pool against buoyancy and vapour pressure within the time required to reach solidification temperature. Based on this concept, mechanisms involved in porosity formation, growth and escape phenomena are disclosed, which can help select the optimised welding conditions to obtain porosity free welds in CMT-GMAW of zinc coated steels.
50 citations
TL;DR: In this article, the effects of various welding conditions, such as laser power, root gap, and welding speed on the penetration, geometry, and defects of weld beads, were investigated and the results showed that the process window of welding conditions for the production of good welded joints was narrow.
Abstract: In this study, welding with hybrid heat sources combined with a high power disk laser and a metal active gas (MAG) arc was carried out on 780 MPa high strength steel plates of 12 mm in thickness. The effects of respective welding conditions, such as laser power, root gap and welding speed on the penetration, geometry, and defects of weld beads, were investigated. The results showed that the process window of welding conditions for the production of good welded joints was narrow. Also, the laser keyhole behavior, the molten pool geometry, and the melt flows inside the molten pool were observed by the high-speed x-ray transmission real-time imaging system. It was confirmed that the melt flows inside the molten pool during hybrid welding were different between humping and good weld beads. The melt flowed from the bottom tip of a keyhole to the humping portion and did not flow forward to the keyhole bottom tip, resulting in the formation of the humping defect. On the other hand, in the case of good weld beads, the tungsten particle flowed to the back part of the molten pool but then flowed to the forward keyhole. It was clarified that a good weld bead without humping nor underfilling could be produced due to the forward melt flow.
TL;DR: In this article, influence of 14 different oxide-, chloride-, and fluoride-based fluxes were evaluated on DOP and width-to-penetration ratio during flux-activated TIG (ATIG) welding of low alloy steel (AISI 4340), austenitic, AISI 304, and AisI 316) and duplex (Duplex 2205) stainless steels.
Abstract: In tungsten inert gas (TIG) welding, a low depth of penetration (DOP) is achieved during single pass. To achieve the required DOP, the speed of welding should be reduced; thus productivity reduces significantly. In this work, influence of 14 different oxide-, chloride-, and fluoride-based fluxes are evaluated on DOP and width-to-penetration ratio during flux-activated TIG (ATIG) welding of low alloy steel (AISI 4340), austenitic (AISI 304 and AISI 316) and duplex (Duplex 2205) stainless steels. The effect of welding current and three different shielding gas compositions is also studied during ATIG for these workpieces. Arc and weld metal pool behaviors are captured in order to study the physical behavior of the process. Results revealed that oxide-based fluxes like SiO2, MoO3, MoS2, CrO3, and TiO2 increases DOP significantly and in many cases through penetration (penetration reaches beyond plate thickness) is achieved. There is a noteworthy enhancement in penetration because of the addition of H2 in shiel...
TL;DR: In this article, the results of a research project which targets the qualification of laser beam welding under vacuum for the welding of heavy-walled steel structures made of unalloyed steel or duplex stainless steel are presented.
Abstract: Currently, three welding processes are used in the manufacturing of large scale work pieces with high weld seam depths. The gas metal arc welding and the submerged arc welding processes are characterized by a comparatively low penetration depth and welding speed, the use of welding consumables and a high energy input per length. Electron beam welding is suitable for single pass welding of high wall thicknesses, but a fine vacuum is needed, x-ray radiation is generated, the process is prone to magnetic fields, and the technology has to face a low market penetration. Laser beam welding under vacuum (“LaVa”) is on its way to become a new and superb option for these welding tasks. The paper at hand presents the latest results of a research project which targets the qualification of LaVa for the welding of heavy-walled steel structures made of unalloyed steel or duplex stainless steel. The achieved results demonstrate that, in comparison to laser beam welding at atmospheric pressure, an increase of the penetration depth and a high process stability can be achieved, whereby economic advantages and a high weld seam quality are realized. On the other hand, the latest results of the application of LaVa for the welding of nickel-base alloys, copper, and titanium are presented. It is shown that LaVa is suitable for the welding of these materials. A high process stability is achieved; spattering is minimized; and high penetration depths are achieved.
TL;DR: In this article, N 2 was added into shielding gas, which increased the nitrogen content at upper section and central section of laser weld metal and promoted the formation of allotriomorphic and penniform austenite.
TL;DR: In this paper, the authors used optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements.
Abstract: In this study, dissimilar 316L austenitic stainless steel/2205 duplex stainless steel (DSS) joints were fabricated by constant and pulsed current gas tungsten arc welding process using ER2209 DSS as a filler metal. Microstructures and joint properties were characterized using optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements. Microstructural observations confirmed the presence of chromium nitride and delta ferrite in the heat-affected zone of DSS and 316L, respectively. In addition, there was some deviation in the austenite/ferrite ratio of the surface welding pass in comparison to the root welding pass. Besides having lower pitting potential, welded joints produced by constant current gas tungsten arc welding process, consisted of some brittle sigma phase precipitates, which resulted in some impact energy reduction. The tensile tests showed high tensile strength for the weld joints in which all the specimens were broken in 316L base metal.
TL;DR: In this article, an optimization method by taking the integrity of the weld bead and weld area into consideration is proposed for FLW of dissimilar materials, the low carbon steel and stainless steel.
TL;DR: In this article, the effect of shielding gas on the penetration, defects, and mechanical properties of the hybrid weld beads was investigated using either 80%Ar-20% CO2 or 100%CO2 shielding gas.
Abstract: In this study, high-power disk laser–metal active gas arc hybrid welding was performed on thick plates of high-tensile-strength steel, HT780. The effect of shielding gas on the penetration, defects, and mechanical properties of the hybrid weld beads was investigated using either 80 %Ar–20 %CO2 or 100 %CO2 shielding gas. The results showed that the process window of laser powers for the production of sound welds was wider in 100 %CO2 gas, although more spatters occurred. Besides, the optimization of the arc parameters could reduce spattering significantly by controlling the globular transfer mode to form a buried arc. The Vickers hardness test was performed to identify the levels of hardening and softening in the bead and HAZ, respectively. The tensile test results showed that the tensile strengths of the joints hybrid-welded in either 80 %Ar–20 %CO2 or 100 %CO2 gas were much higher than those of the HT780 base material. The Charpy V-notch test results revealed that the values of the hybrid-welded joints in 80 %Ar–20 %CO2 gas were higher than those in 100 %CO2 gas. The reduction in toughness was attributed to the increase in the oxygen content and the consequent formation of a higher number of oxides in a weld bead made in 100 %CO2 gas.
TL;DR: In this article, a numerical model was used to investigate the arc properties and the metal transfer for a pulsed GMAW process of mild steel in argon shielding gas, and the results illustrate the high influence of the changing vaporization rate on the arc attachment at the wire electrode in the high current phase.
Abstract: The process capability of gas metal arc welding (GMAW) processes is mainly determined by the arc properties and the material transfer. In recent years, numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer in gas metal arc welding. In this paper, we summarize a procedure to describe the interaction between an arc and a melting and vaporizing electrode. Thereafter, the presented numerical model is used to investigate the arc properties and the metal transfer for a pulsed GMAW process of mild steel in argon. The results of the numerical simulation are compared with OES measurements as well as high-speed images at different times in the pulse cycle and show excellent agreement. The results illustrate the high influence of the changing vaporization rate on the arc attachment at the wire electrode in the high current phase. It could be shown that a substantial part of the current does not participate in the constriction of the wire electrode via the resulting lorentz force which explains the nearly spatter-free droplet detachment in pulsed GMAW processes of mild steel in argon shielding gas.
TL;DR: In this article, an artificial neural network (ANN) was implemented to investigate the main effects of process parameters on the laser welding process quality, and the statistical estimation revealed the relationship of the process parameters with the weld geometry, which provided a deeper understanding of the welding process.
TL;DR: In this paper, the effect of the commonly used thermal frequency on welding process suitability, weld profile, weld macrostructure, and weld hardness on AA6061 double pulsed gas metal arc welding was investigated.
Abstract: The present investigation aims to contrast the effect of the commonly used thermal frequency on welding process suitability, weld profile, weld macrostructure, and weld hardness on AA6061 aluminum alloy double pulsed gas metal arc welding. Material manufacturing processes and welding parameters with thermal frequencies of 2, 3, and 4 Hz are described in detail. Three defect-free welds were successfully formed at these thermal frequencies. The results indicate the following: (1) thermal frequency has no effect on welding process suitability when the welding parameters are self-matching; and (2) at increased thermal frequency, weld ripple distance reduces, maximum penetration depth decreases, grain size of the fusion zone decreases, and fusion zone hardness increases.
TL;DR: In this paper, AISI 316 types of austenitic stainless steels were welded by FCAW (flux-cored arc welding) using E316LT1-1/4 flux cored wire under various shielding gas mixtures containing CO2 at different ratios.
Abstract: In this study, AISI 316 types of austenitic stainless steels were welded by FCAW (flux-cored arc welding) using E316LT1-1/4 flux-cored wire under various shielding gas mixtures containing CO2 at different ratios. Effects of mixed ratio of Ar and CO2 in the in the shielding gas on the microstructure, impact toughness, and microhardness of welded materials were studied. Stereo optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and TEM/mapping analysis techniques were used for microstructural characterizations. The impact toughness values of the weldments were decreased as a result of the formation and growth of inclusions in the microstructure due to the increases amount of CO2 in the shielding gas. The hardness values and δ-ferrite amount in the weld metal were affected by depending on of the shielding gas mixtures.
TL;DR: In this paper, a non-consumable tool for joining abutting plates of magnesium alloy AZ91 having 6mm thickness was used for joining the plates with advantages such as low distortion, no shielding gas required, and fine recrystallized microstructure.
TL;DR: In this article, the effects of mixtures with different composition have been considered for the arc welding of austenitic steels, and the welded sections have been undergone to visual and optical microscopy observations, microhardness, indentations and tensile tests.
Abstract: During fusion welding the molten metal is shielded from contact with the atmospheric gas by means of a gaseous flux. The shielding gas prevents weld embrittlement, affects welding quality, because of its influence on filler metal transfer, and has a direct impact on welding costs as well. Argon is the most common shielding gas, often used with some adds of other gases that can be inert, as helium, or active, as CO 2 , O 2 or H 2 . In this work the effects of mixtures with different composition have been considered for the arc welding of austenitic steels. Metallographic samples of welded sections have been undergone to visual and optical microscopy observations, microhardness, indentations and tensile tests.
TL;DR: In this article, the effect of hot wire gas tungsten arc welding (HW-GTAW) parameters such as welding current, hot wire current and the wire feed rate during welding of super ASS 304H stainless steel tubes were evaluated in terms of heat input, voltage-current (V-I) characteristics and weld bead characteristics such as bead weight and geometry.
Abstract: Hot wire gas tungsten arc welding (HW-GTAW) process is the one where the filler wire is pre-heated close to its melting point before it is fed in to the arc. The effect of HW-GTAW parameters such as welding current, hot wire current and the wire feed rate during welding of super ASS 304H stainless steel tubes were evaluated in terms of heat input, voltage-current (V-I) characteristics and weld bead characteristics such as bead weight and geometry. The results obtained indicate that for a constant welding current, increasing the hot wire current and wire feed rate provides a stable V-I characteristics and higher bead weight. Further, increasing the hot wire current and wire feed rate also provides better or desired weld pool and hence the bead geometry was described in terms of width, penetration depth, area of fusion and toe angle. By utilising the above knowledge, the tube to tube butt welding of SS 304H material was carried out. It was observed that, the weld joint is qualified as per the quality requirement of ASME: Sec IX standard.
TL;DR: An alternative to the conventional weld penetration sensing methods in pulsed gas tungsten arc welding is proposed for implementation at manufacturing sites in this paper, where the fluctuation amplitude of arc voltage in the peak duration (ΔUk) reflects the weld penetration status in a single-weld spot; a fully penetrated weld spot is obtained in the step-by-step welding process when the abrupt change of ΔUk (denoted as ΔU’k) is above the threshold (1.50
TL;DR: In this paper, the effect of laser cleaning on surface preparation for tungsten inert gas (TIG) welding of commercial aluminum alloy was investigated and the feasibility of using laser cleaning method to minimize the oxides layer of Al alloy for TIG welding was demonstrated.
Abstract: Surface preparation is known to have critical effect on welding quality of engineering materials, for instance, oxidation layer may reduce the weld performance significantly due to porosity issue. Laser cleaning is considered as a promising technique to do surface preparation for welding process. This paper presents the effect of laser cleaning on surface preparation for tungsten inert gas (TIG) welding of commercial aluminum alloy. We demonstrated the feasibility of using laser cleaning method to minimize the oxides layer of Al alloy for TIG welding. This one-step process without use of chemicals or any other additives is environmentally friendly. Comparison of the performance between conversional cleaning method and laser cleaning method was examined carefully to identify the changes in microstructure and chemical analysis of Al alloy welds after TIG welding processing. Special attention was paid to porosity distribution in the fusion zone after laser cleaning. In addition, some thermal melting was found to occur and refined microstructure took place between the fusion zone and the substrate after rapid solidification. It is further proposed that laser cleaning can refine microstructure of the interface between filter wire and the substrate during TIG welding, which may play a significant role in affecting the weld quality.
TL;DR: In this paper, the effect of plasmatorch arc current and amount of propane-butane in the plasma flow on the structure and properties of coatings was analyzed, and the results of tribological testing of the coatings under the conditions of sliding friction with a lubricant by the discplane scheme were presented.
Abstract: The structure and tribological properties of coatings made of PN85YU15 powder were studied. The coatings were deposited on the mild steel blanks by the technology of air-plasma spraying using a unit of annular input and gas-dynamic powder focusing. Efficiency of heating and acceleration of powder particles was studied preliminarily. Measurement results on temperature and velocity distributions of particles at a certain spraying distance by the method of spectral pyrometry and time-of-flight method are presented. The effect of plasmatorch arc current and amount of propane-butane in the plasma flow on the structure and properties of coatings is analyzed in this paper. It is determined that the phase composition of coatings and initial powder is the same: the main phase is Ni3Al compound; moreover, the structure contains Ni5Al3 phase. It is shown that an increase in the amount of propane-butane increases coatings porosity. The densest coatings (5.77%) were obtained at the plasmatorch arc current of 200 A with the reduced amount of propane-butane. The coatings obtained at the minimal arc current of 100 A with an increased amount of propane-butane are characterized by maximal porosity (20.38%). The results of tribological testing of the coatings under the conditions of sliding friction with a lubricant by the disc-plane scheme are presented. From the standpoint of obtaining the densest coatings with high performance, the optimal regimes of plasma spraying of PN85YU15 powder are the current from 140 A to 200 and using the air and propane-butane mixture only as the shielding gas (anode curtain).
TL;DR: In this paper, the effect of double-layer shielding and five other process parameters, namely welding voltage, current, primary shielding gas type, its flow rate, and filler material, was studied during dissimilar gas metal arc welding (GMAW) between austenitic and duplex stainless steels (SSs).
Abstract: In the present work, the effect of double-layer shielding and five other process parameters, namely welding voltage, current, primary shielding gas type, its flow rate, and filler material, is studied during dissimilar gas metal arc welding (GMAW) between austenitic and duplex stainless steels (SSs). A simple modification over the GMAW setup is made for additional supply of secondary shielding gas at different flow rates. Two different sets of welding are performed between austenitic and duplex SSs, i.e., AISI 304 with Duplex 2205 and AISI 316 with Duplex 2205, and the contributions of process parameters, their interactions on joint distortion, tensile strength, toughness, and fusion zone microhardness are evaluated. Improvements in joint quality due to the double-shielding environment are also highlighted. Double-layer shielding with secondary shielding by CO2 supply significantly improves tensile strength and toughness and reduces distortion. Fusion and interface zone microstructures are observed by sca...
01 Dec 2016
TL;DR: In this paper, a comparison of the weld geometry, distortion, microstructure and mechanical properties of thin SS 304'L sheets (0.8'mm thickness) welded using micro-plasma arc welding is presented.
Abstract: This research work focuses on comparison of the weld geometry, distortion, microstructure and mechanical properties of thin SS 304 L sheets (0.8 mm thickness) welded using micro-plasma arc welding ...