Showing papers on "Shielding gas published in 2020"

On the effect of shielding gas flow on porosity and melt pool geometry in laser powder bed fusion additive manufacturing

Abstract: Metal additive manufacturing is moving from rapid prototyping to on-demand manufacturing and even to serial production. Consistent part quality and development of a wider range of available materials are key for wider adoption. This requires control and optimization of various laser and scanning parameters. Therefore, process modeling has been extensively pursued to reduce experimental runs in the search for parameters that produce dense, high-quality parts for the given alloy. However, these optimal parameters remain machine-specific if conditions defined by the machine architecture are not considered. Previous studies have shown that shielding gas flow is one such parameter that affects porosity and mechanical properties of parts produced with laser powder bed fusion. However, a lack of consensus remains regarding which phenomena are responsible for the observed decrease in quality. In this study, the effect of shielding gas flow velocity on porosity and melt pool geometry in laser powder bed fusion additive manufacturing is studied. It is shown that decreasing the gas flow velocity leads to a drastic loss of penetration of single scan tracks, leading to increased lack-of-fusion porosity at the part level. This is attributed to the obstruction of the laser beam by the process-induced vapor plume emissions of the individual tracks being scanned. As the vapor plume, and how effectively it is removed by the shielding gas flow, have a significant effect on the melt pool geometry in laser powder bed fusion, models aiming at predicting the melt pool geometry and attempts to transfer process parameters from one machine to another should consider the effect of the shielding gas flow.

Comparative study on the microstructures and properties of wire+arc additively manufactured 5356 aluminium alloy with argon and nitrogen as the shielding gas

Abstract: This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection. However, the sample protected by N2 contained many flaky nitrides, whose presence improved the microhardness but reduced the ultimate tensile strength (UTS) and plasticity. The average UTS of the thin-wall sample protected by N2 in the horizontal direction was 82.5 % of the UTS of the samples shielded using Ar. However, the average elongation in the horizontal direction of the samples protected by N2 was 18.6 % of that of the samples shielded by Ar. The mechanical properties of the sample protected by argon were more excellent.

Hydrogen and molybdenum control on laves phase formation and tensile properties of inconel 718 GTA welds

Abstract: Gas Tungsten arc welding (GTAW) process was employed for welding of Inconel 718 with two different shielding gases, namely argon (Ar) and argon with a 5 vol% hydrogen mixture (ArH) and two fillers viz., ERNiCrMo-10 and ERNiCrMo-4. The effects of gas composition and filler wires on the laves phase formation were studied in detail. The results revealed that hydrogen addition through ArH shielding gas mixture resulted in better grain refinement in the welds than pure Ar. The hydrogen addition induced a steep thermal gradient in the weld, which lowered the segregation of elements like Niobium (Nb) and Molybdenum (Mo) at the interdendritic regions. The laves phase formation in Mo-rich filler addition welds was minimized due to restriction of Nb segregation by Mo at the interdendritic region. Tensile test results indicated that the strength and ductility of the joints of both autogenous and filler added welds of Ar were higher than the ArH shielded welds. In the case of filler added welds, higher Mo content filler exhibited better tensile properties in both shielding gas combinations due to solid solution strengthening of Mo. Nano-sized hydrogen assisted cracks observed in ArH autogenous welds caused a reduction of strength and ductility.

Arc deposition of wear resistant layer TiN on Ti6Al4V using simultaneous feeding of nitrogen and wire

Abstract: As an admirable surface improvement method, arc surface cladding has been widely used in various fields. The surface properties of titanium alloy were improved by gas tungsten arc cladding. In the process of arc claddings, a certain amount of nitrogen was added in the shielding gas to form the hard phase of TiN in the cladding layer. Titanium alloy surface was cladded with the same process parameters and different nitrogen flow rate. The effects of nitrogen flow rate on the microstructure and mechanical performance of the cladding layer were studied through an optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), Vickers hardness and friction wear testing machine. The results show that the increase of the nitrogen flow rate not only changes the shape of the arc but also forms a large number of TiN hard phases in the cladding layer. With the increase of the nitrogen flow rate, the number of TiN hard phases in the cladding layer increases gradually, which improves the mechanical property of the cladding layer. The Vickers hardness of the cladding layer is much larger than 600 HV and the friction coefficient is 0.419 when the nitrogen rate is 2 L/min.

Optimization of metal inert gas-welded aluminium 6061 pipe parameters using analysis of variance and grey relational analysis

Abstract: It is an underlying fact for the case of the joining process especially welding to have optimized parameters in order to achieve joints with outstanding mechanical characteristics. In the current work, aluminium 6061 pipes were welded using gas metal arc welding process with appropriate ER 4043 electrode and argon shielding gas. Optimum welding parameters (namely, current, voltage and travel speed) are investigated using analysis of variance ANOVA and grey relational analysis GRA statistical approaches. High tensile strength and low corrosion rate were set as required characteristics of quality welds. Since there are two responses and two objectives, multiple-criteria decision-making approach—GRA, and ANOVA are performed. Optimal parameters from these statistical approaches are converged to 110 A, 19 V and 3 cm/min, respectively. It is deduced from this study that the optimal parameters are convergent irrespective of the two used techniques for the investigated experimental data.

Controlling inclusion evolution behavior by adjusting flow rate of shielding gas during direct energy deposition of AISI 316 L

Abstract: To reveal the mechanism of oxidation and the effect of inclusion characteristics on the mechanical properties of additively-manufactured metal matrix, two groups of AISI 316 L stainless steel samples were fabricated under different flow rates of shielding gas (Ar) at two intensities of laser beam. As flow rates of shielding gas increased from 5 L/min to 25 L/min, the oxygen content in the melt pool decreased from 775 ppm to 375 ppm at low intensity of laser beam (73 W/m2), and from 677 ppm to 1470 ppm at high intensity of laser beam (725 W/m2). Variation in oxygen content affected melt pool shape, solidification texture, and the mechanical properties of the material. In each intensity of laser beam group, optimal flow rates of shielding gas condition for tensile property existed. As inclusion number density increased from 8866/mm2 to 45909/mm2, yield stress increased to 26 %. A rapid drop in ductility occurred at flow rate 5 L/min, because independently-nucleated spinel accelerated inclusion coalescence in the melt pool.

Discussion of the Effect of Shielding Gas and Conductivity of Vapor Core on Metal Transfer Phenomena in Gas Metal Arc Welding by Numerical Simulation

Abstract: Gas metal arc welding is indispensable in many fields of industry. In this process, various kinds of shielding gas are used, and they significantly affect the behaviors of the arc plasma and metal transfer. In this study, these behaviors with various kinds of shielding gas are numerically investigated. In addition, the influence of the electrical conductivity of the metal vapor is discussed. Simulation results show that with Ar gas, spray transfer occurs at an arc current of more than 240 A, and with CO2 gas, the transfer mode is globular, even at an arc current of 300 A. The calculation results show that the current path near the wire tip critically determines droplet behavior. With Ar gas, the current path is spread out, covering the molten wire, whereas with CO2 gas, the current path is concentrated at the bottom of the molten wire. Therefore, to achieve spray transfer, the current path needs to be spread at the wire tip; however, if the spreading is excessive, the transfer mode becomes streaming transfer. To investigate the influence of the metal vapor, a numerical experiment using pseudo metal vapor was carried out. Even with CO2 gas, the electrical conductivity of the metal vapor was low, and thus the current path was not concentrated at the bottom of the molten wire, allowing spray transfer. The numerical results show that metal transfer phenomena can be regulated by controlling the electrical conductivity of the metal vapor.

Effect of local gas flow in full penetration laser beam welding with high welding speeds

Abstract: Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.

Microstructural characterization and toughness evaluation of 10 wt% Ni steel weld metal gas tungsten arc and gas metal arc weld fusion zones

Abstract: A novel 10 wt% Ni steel weld metal under development for use in high strength/high toughness applications was used to fabricate gas tungsten arc (GTAW) and gas metal arc (GMAW) welds. Both welds exhibit excellent toughness at sub-ambient temperatures, yet the toughness of the GTAW is superior to the GMAW. Using scanning electron microscopy, three differences in microstructure were identified in the GMAW compared to the GTAW, all of which are known to be detrimental to toughness: (1) an overall coarser effective grain size of the martensitic microstructure, (2) a larger presence of a coarse martensite constituent, and (3) a higher number density of oxide inclusions. The difference in the effective grain size of the two welds is rationalized based on inherent differences in the welding processes that produces much larger weld beads and a finger penetration profile in the GMAW thereby limiting the amount of reheating each bead receives. The higher number density of oxide inclusions in the GMAW is from the use of a 98% Ar/2% O2 shielding gas, as compared to 100% Ar used in the GTAW. A GMAW produced using 100% Ar as the shielding gas demonstrated improvements in toughness because of smaller oxide inclusions, yet the toughness was not as high as the GTAW, demonstrating the complexity of the interactions of the three different toughness influences. These results are significant in that they allow modifications to be made to the alloy composition and/or welding process parameters based on a sound scientific basis.

Investigation of the effect of torch tilt and external magnetic field on arc during overlapping deposition of wire arc additive manufacturing

Abstract: The purpose of this paper is to find a theoretical reference to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition in wire arc additive manufacturing (WAAM) and ensure the effect of the gas shielding and stable heat and mass transfer in deposition process. The multiphysical numerical simulation and physical experiment are used for validation.,In this study, welding torch tilt deposition and external parallel magnetic field–assisted deposition are presented to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition, and a three-dimensional numerical model is developed to simulate the arc of torch tilt overlapping deposition and external parallel magnetic field–assisted overlapping deposition.,The comparison of simulated results indicate that the angle of welding torch tilt equal to 20° and the magnetic flux density of external transverse magnetic field equal to 0.001 Tesla are capable of balancing the electric arc and shielding gas effectively, respectively. The arc profiles captured by a high-speed camera match well with simulated results.,These studies of this paper can provide a theoretical basis and reference for the calibration and optimization of WAAM process parameters.

Material Flow Behavior on Weld Pool Surface in Plasma Arc Welding Process Considering Dominant Driving Forces

Abstract: In this study, the effect of oxygen in the shielding gas on the material flow behavior of the weld pool surface was discussed to clarify the dominant driving weld pool force in keyhole plasma arc welding (KPAW). To address this issue, the convection flow on the top surface of weld pool was observed using a high-speed video camera. The temperature distribution on the surface along keyhole wall was measured using the two-color pyrometry method to confirm the Marangoni force activity on the weld pool. The results show that the inclination angle of the keyhole wall (keyhole shape) increased especially near the top surface due to the decrease in the surface tension of weld pool through surface oxidation when a shielding gas of Ar + 0.5% O2 was used. Due to the change in the keyhole shape, the upward and backward shear force compositions created a large inclination angle at the top surface of the keyhole. From the temperature measurement results, the Marangoni force was found to alter the direction when 0.5% O2 was mixed with the shielding gas. The shear force was found to be the strongest force among the four driving forces. The buoyant force and Lorentz force were very weak. The Marangoni force was stronger than the Lorentz force but was weaker than shear force. The interaction of shear force and Marangoni force controlled the behavior and speed of material flow on the weld pool surface. A strong upward and backward flow was observed in the case of mixture shielding gas, whereas a weak upward flow was observed for pure Ar. The heat transportation due to the weld pool convection significantly changed when only a small amount of oxygen was admixed in the shielding gas. The results can be applied to control the penetration ratio in KPAW.

The Effect of Process Parameters on the Microstructure and Mechanical Properties of AW5083 Aluminum Laser Weld Joints

Abstract: In this article, the effect of process parameters on the microstructure and mechanical properties of AW5083 aluminum alloy weld joints welded by a disk laser were studied. Butt welds were produced using 5087 (AlMg4.5MnZr) filler wire, with a diameter of 1.2 mm, and were protected from the ambient atmosphere by a mixture of argon and 30 vol.% of helium (Aluline He30). The widest weld joint (4.69 mm) and the highest tensile strength (309 MPa) were observed when a 30 L/min shielding gas flow rate was used. Conversely, the narrowest weld joint (4.15 mm) and the lowest tensile strength (160 MPa) were found when no shielding gas was used. The lowest average microhardness (55.4 HV0.1) was recorded when a 30 L/min shielding gas flow rate was used. The highest average microhardness (63.9 HV0.1) was observed when no shielding gas was used. In addition to the intermetallic compounds, β-Al3Mg2 and γ-Al12Mg17, in the inter-dendritic areas of the fusion zone (FZ), Al49Mg32, which has an irregular shape, was recorded. The application of the filler wire, which contains zirconium, resulted in grain refinement in the fusion zone. The protected weld joint was characterized by a ductile fracture in the base material (BM). A brittle fracture of the unshielded weld joint was caused by the presence of Al2O3 particles. The research results show that we achieved the optimal welding parameters, because no cracks and pores were present in the shielded weld metal (WM).

Influence of the Inert Gas Flow on the Laser Powder Bed Fusion (LPBF) Process

Abstract: The inert gas flow is known to have a significant impact on the laser powder bed fusion (LPBF) process in terms of process stability and consistent process results across the whole build platform. Thus, the optimization of the inert gas flow leads to both direct and indirect improvements of the part quality as follows. If the gas flow can steadily and efficiently remove soot particles emerging from the melting process, scattering and attenuation of the laser beam or debris on the laser windows can be avoided, which would indirectly impair the quality of the built parts. Spatter particles should be removed as well because they can directly lead to bonding defects inside the produced parts. Therefore, the gas flow in a self-constructed LPBF machine has been optimized systematically based on computational fluid dynamics (CFD), particle tracking and experimental studies. Herein the effect of the process gas flow and gas type on spatter and soot particles is presented in detail. According to the simulation results, the soot removal is improved by a smaller shielding gas inlet height at the cost of a potential deterioration of the soot removal at extreme process parameters. The simulation results have been validated by measurements of the gas flow velocity and of the density of the built parts. The advantages and disadvantages of different process gas types are shown and recommendations for the gas flow design are derived.

An experimental investigation of the effectiveness of Ar-CO 2 shielding gas mixture for the wire arc additive process

Abstract: Wire arc additive manufacturing (AM) is the process by which a large, metallic structure is built layer-by-layer using a welding arc to melt a wire feedstock. A novel opportunity exists to alter the shielding gas composition to fabricate distinct geometrical features without altering the other AM parameters. In the following study, shielding gases with varied concentrations of Argon (Ar) and CO2 was used to deposit three distinct geometric shapes (walls, infill, and overhang) using a wire-based additive manufacturing system utilizing the gas metal arc welding (GMAW) surface tension transfer (STT) process. Computer-aided design (CAD) models were sliced with a custom-built slicer, and the sliced algorithm was converted into optimal robotic toolpaths. A custom virtual instrument (VI) was built in LabVIEW to compare the temperature profiles on the surface during each deposition process. After each deposition, the geometric features were scanned, and the surface waviness value was evaluated. Tensile and Charpy impact coupons were extracted from the wall geometries in the longitudinal and transverse directions and tested. The results indicated that a higher CO2 content produced higher melt pool temperatures to an extent, while lower contents of CO2 resulted in a dimensionally accurate geometry. The data also indicated that the 2%/98% CO2/Ar blend produced scatter in tensile strength and the analysis of variance (ANOVA) shows significant difference. However, the intermediate range of CO2 (5–10%) resulted in uniform tensile properties. Altogether, these results indicate that a 5%/95% CO2/Ar blend is the ideal shielding gas for lowering process temperatures and improving mechanical properties in wire arc additive manufacturing using the gas metal arc welding surface tension transfer process. Additionally, varying concentrations of Ar/CO2 can be used within the same part in order to modify the local properties or process parameters such as strength, toughness, temperature, or dimensional features. This may improve overall manufacturing quality without sacrificing specific properties.

Corrosion Resistance and Microstructure of Welded Duplex Stainless Steel Surface Layers on Gray Cast Iron

Abstract: The degradation of pump components by corrosion and complex, simultaneous damage mechanisms, e.g., erosion–corrosion and cavitation–corrosion leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, surface welding of duplex stainless steel on gray cast iron parts was performed using inert shielding gas metal arc surface welding (GMA-SW) and plasma transferred arc surface welding (PTA-SW). The thermal conductivity of the used shielding gas and the preheating temperature influenced the dilution of the surface layers, which had a major impact on the corrosion resistance and the microstructure. Lower cooling rates enhanced diffusion and lead to precipitation of carbides. High heat input and prolonged cooling times during surface welding resulted in high dilution and a carbide network. The corrosion resistance in artificial seawater of those surface layers was substantially reduced compared to surface layers with lower heat input and higher cooling rates. The corrosion of the surface layers in the potentiodynamic polarization test was driven by selective corrosion of the phase boundary between Cr–carbides and Cr–depleted austenite. Passive behavior was observed for surface layers with low dilution, which had homogeneous chromium distribution and no carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surface welding with duplex stainless steel. The corrosion resistance of the surface layers produced with PTA-SW with no preheating exceeded that of the surface layers produced with GMA-SW and came close to those of a commercially available duplex stainless steel used as reference material.

Heat input and shielding gas effects on the microstructure, mechanical properties and pitting corrosion of alternative low cost stainless steel grade 202

Abstract: The intention of this study was to create information for welders and engineers in regards to 202 (200-series) austenitic grade stainless steel as a low cost alternative for the replacement of 300-series stainless steel The content of this paper discusses the effects of different heat inputs and different nitrogen mixes in the argon shielding gas using the GTA welding process This paper discusses the effects to the microstructure, mechanical properties and corrosion resistance of the weld metals The results of this study indicate that reducing the heat input when welding caused the width of the face and root of the weld bead to be narrower The microstructure (delta ferrite, dendrite length and interdendrite spacing) tended to decrease and the hardness and ultimate tensile strength tended to rise In addition, the percentage of elongation decreased while the pitting corrosion resistance increased An increase of nitrogen in the argon shielding gas did not cause the width of the weld bead to change However, the volume of delta ferrite, dendrite length and inter-dendrite spacing reduced and the hardness and ultimate tensile strength increased The percentage of elongation was shown to decrease and the pitting corrosion resistance tended to increase The test results of this work focused on increasing productivity and reducing the cost of production from the use low nickel stainless steel in the fabrication industries of Southeast Asia

Optimization of TIG Welding Parameters for the 202 Stainless Steel Using NSGA-II

Abstract: Tungsten Inert Gas welding is a fusion welding process having very wide industrial applicability. In the present study, an attempt has been made to optimize the input process variables (electrode diameter, shielding gas, gas flow rate, welding current and groove angle) that affect the output responses i.e. hardness and tensile strength at weld centre of the weld metal SS202. Process variables play an important role for a good quality weld. Taguchi based design of experiments was used for experimental planning and the results were studied using analysis of variance. The results shows that for tensile strength of the welded specimens, welding current and electrode diameter are the two most significant factors with P-values of 0.002 and 0.030 for mean analysis, respectively leading to changes in tensile strength. Whereas higher tensile strength was observed when electrode diameter used was 1.5 mm, shielding gas used was helium, gas flow rate 15 L/min, welding current 240A and groove angle 60o was used. Welding current was found to be most significant factor with P-value 0.009 leading to change in hardness at weld region. The hardness at weld region tends to decrease significantly with the increase in welding current from 160-240A. The different shielding gases and groove angle does not show any significant affect on tensile strength and hardness at weld centre. These response variables were evaluated at 95% confidence interval and the confirmation test were performed on suggested optimal process variable. The obtained results were compared with estimated mean value, which were lying within ±5%.