Shielding Gas Composition Research Articles

On the plasma chemistry of a cold atmospheric argon plasma jet with shielding gas device

A novel approach combining experimental and numerical methods for the study of reaction mechanisms in a cold atmospheric plasma jet is introduced. The jet is operated with a shielding gas device that produces a gas curtain of defined composition around the plasma plume. The shielding gas composition is varied from pure to pure .The density of metastable argon in the plasma plume was quantified using laser atom absorption spectroscopy. The density of long-living reactive oxygen and nitrogen species (RONS), namely , , , , and , was quantified in the downstream region of the jet in a multipass cell using Fourier-transform infrared spectroscopy (FTIR).The jet produces a turbulent flow field and features guided streamers propagating at several that follow the chaotic argon flow pattern, yielding a plasma plume with steep spatial gradients and a time dependence on the scale while the downstream chemistry unfolds within several seconds. The fast and highly localized electron impact reactions in the guided streamer head and the slower gas phase reactions of neutrals occurring in the plasma plume and experimental apparatus are therefore represented in two separate kinetic models. The first electron impact reaction kinetics model is correlated to the LAAS measurements and shows that in the guided streamer head primary reactive oxygen and nitrogen species are dominantly generated from . The second neutral species plug-flow model hence uses an source term as sole energy input and yields good agreement with the RONS measured by FTIR spectroscopy.

보호가스 종류에 따른 고출력 레이저 용접특성

Laser-gas metal arc hybrid welding has been considered as an alternative process of gas metal arc welding for offshore pipe laying. Fiber delivered high power lasers which enable deep penetration welding were recently developed but high power welding characteristics were not fully understood yet. In this study, the influence of shielding gas composition on welding phenomena in high power laser welding was investigated. Bead shapes, melt ejection and dropping were observed after autogenous laser welding with 100% Ar, Ar-20% CO2, Ar-50% CO2, and 100% CO2 shielding gas. Process parameter window was widest with Ar-50% CO2 shielding gas and the penetration was deepest with 100% CO2 shielding gas. The melt dropping was not observed when Ar-50% CO2 or 100% CO2 shielding gas was supplied.

Effect of Shield Gas Composition on Cold Cracking Susceptibility of YS 600 MPa Flux Cored Arc Weld Metal

Effect of Shield Gas Composition on Cold Cracking Susceptibility of YS 600 MPa Flux Cored Arc Weld Metal

Activated-TIG Welding of Different Steels: Influence of Various Flux and Shielding Gas

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 shielding gas. Addition of helium also helps to increase DOP. Arc behavior reveals the constriction of arc column during activated TIG welding, and positive surface tension-induced flow in centripetal (inward) direction is observed.

The spatio-temporal distribution of He (23S1) metastable atoms in a MHz-driven helium plasma jet is influenced by the oxygen/nitrogen ratio of the surrounding atmosphere

The density of helium He (23S1) metastable atoms is measured in a 1.6 mm diameter MHz-driven atmospheric pressure helium plasma jet by laser absorption spectroscopy with spatial and temporal resolution. The surrounding atmosphere of the jet is varied from pure oxygen to pure nitrogen with a gas shielding device. The highest metastable density of 1.3 × 1013 cm−3 is obtained in the center of the jet close to the nozzle exit at normal atmospheric air conditions. Within 0.3 mm in the radial direction and 2 mm in the axial direction, the He metastable density drops below the detection limit. The obtained He metastable lifetime is almost independent of the shielding gas composition. By analyzing the diffusion of shielding gas species into the effluent it is concluded that their density is too low to explain the observed He metastable lifetime. Instead, impurities from the feed gas, especially water molecules, are more likely to be responsible. However, a drastic change in metastable He density is observed when decreasing the amount of oxygen in the shielding gas. The lower the oxygen amount, the lower the metastable He density. For pure nitrogen, no He metastables are detected at all. By exchanging nitrogen with argon, a similar behavior is observed. Thus, it is concluded that it is the absence of ambient oxygen rather than the elevated presence of nitrogen, which is responsible for the observed decrease in the He (23S1) density.

Avaliação do Uso de Curto-Circuito Controlado em Soldagens de Passes de Enchimento por MIG/MAG Duplo Arame

Neste trabalho foi realizada uma avaliação técnico-econômica do processo de soldagem MIG/MAG Duplo Arame para soldagens de passes de enchimento na posição plana, empregando o modo operacional Curto-Circuito Controlado (CCC) no arame-seguidor, como forma de melhorar o controle da poça de fusão e reduzir respingos. A avaliação foi feita através de um estudo comparativo entre a técnica MIG/MAG Duplo Arame convencional (com uso da corrente pulsada em ambos os arames) e uma combinação de Pulsado no arame-líder e CCC no arame-seguidor. Foram mantidos constantes os valores das correntes médias para cada arame, o volume de material depositado por unidade de comprimento de solda, o tipo e dimensão do chanfro e o arame, a composição do gás de proteção e a DBCP. Avaliou-se o acabamento superficial e a geometria dos cordões de soldas, a taxa e a eficiência de deposição e as velocidades limites de soldagem resultantes do uso de cada técnica. Os resultados mostram que o uso do modo CCC no arco seguidor aumenta levemente a capacidade de produção do processo, faz gerar menos respingos, melhora o acabamento do cordão, produz ZF e ZAC menores e ainda mantem similar envelope operacional (quanto à faixa de velocidades de soldagens úteis), o que são fatores positivos. Por outro lado, como desvantagem, o uso de CCC levou a cordões mais convexos e com uma penetração menor.

Assessment of the Use of Negative Polarity in Double-Wire MIG/MAG-Welding Filling Passes

The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wire MIG/MAG-welding filling passes. A comparative study of the conventional technique (two wires working with pulsed DCEP) and the proposed combinations of pulsed DCEP in the lead wire with pulsed DCEN in the trail wire and pulsed DCEP in the lead wire with controlled short-circuit CSC(-) in the trail wire was carried out. The mean current in each wire and the ratio of travel speed to wire feed rate (for the same bead volume per unit weld length), as well as wire type and size, shielding gas composition and joint type (a butt joint in a flat position), were kept constant. Bead surface finish and geometry, deposition efficiency and maximum travel speed for each combination were evaluated. In conclusion, the use of negative polarity in the trail wire increased the deposition rate (higher travel speeds for the same bead) compared with the use of pulsed DCEP in both wires but at the cost of reduced operational robustness, as the conventional technique allowed a sound bead to be produced over a wider range of travel speeds. In addition, beads welded using negative polarity had smaller fusion zones and narrower heat-affected zones but higher convexities.

Influence of the shielding gas composition on the passive film and erosion corrosion of tube-to-tube sheet welds of hyper duplex stainless steel

Resistance to erosion corrosion was determined by degree of repair of passive film under flowing conditions combined corrosive solution. To examine effects of nitrogen addition to argon shielding gas on erosion corrosion of hyper duplex stainless steel welds, stability of oxide film passivity of hyper duplex stainless steel welds was measured through electrochemical tests and X-ray photoelectron spectroscopy analyses. The results indicated the resistance to erosion corrosion was improved due to the increase of austenite phase and the stability of the passive film resulting in change of chemical species as supplemented with the nitrogen gas in the argon shielding gas.

Effects of shielding gas composition on arc profile and molten pool dynamics in gas metal arc welding of steels

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.

Influence of the CO2 content on operational performance of short-circuit GMAW

CO2 blended with Ar is the most common shielding gas used for short-circuit gas metal arc welding (GMAW). There has been some technical knowledge devised from the process application over the years (personal opinion and results from practice) on the selection of the gas blend composition. However, there is still a lack of more scientific data to explain the performance of the mixtures. This paper presents a systematic study of the influence that CO2 content in mixture with Argon has on the operational performance of the short-circuit GMAW. The objectives of this study were to describe, to quantify and to explain the alterations in the metal transfer behavior, spatter generation, weld bead geometry and bead finish due to the different CO2 contents in the shielding gas. Carbon steel plates were welded in adequate parametric conditions for each CO2 + Ar shielding gas composition (CO2 ranging from 2 to 100 %). These parametric conditions were found by applying a metal transfer regularity index over welds carried out at different voltage settings for each gas blend. A target of 130 A was applied as base for comparison. Laser shadowgraphy with high-speed filming and current and voltage oscillograms were used as analysis tools. The results showed (and confirmed) that the increase of the CO2 content deteriorates metal transfer regularity, leading to excessive spatter generation and uneven bead appearance, but increases the penetration and the fusion area of the weld beads and improves bead convexity. In general, the CO2 content should neither be lower than 10 % (unless for thin plates) nor higher than 30 %.

Influence of Current and Shielding Gas in TiO2 Flux Activated TIG Welding on Different Graded Steels

In tungsten inert gas (TIG) welding, limited depth of penetration can be achieved during single pass welding. To achieve the desired depth of penetration, the speed of welding needs to be significantly reduced and hence, the productivity decreases. In the present work, the effect of TiO2 activated flux on penetration is evaluated for different workpieces namely AISI 1020, AISI 304, AISI 316, and Duplex 2205 steels at different currents and shielding gas compositions. The results show a significant increase in the depth of penetration and reduction in the width-to-penetration ratio using the activated flux for all the workpiece materials considered here. Current increases the depth of penetration, however, the influence of flux becomes more significant with higher welding current. Maximum of 37.8%, 44.3%, 47%, and 124% increase in depths of penetration is measured for AISI 1020, AISI 304, AISI 316, and Duplex 2205 steels, respectively, when activated flux is used. Also, maximum of 70% increase in the depth of penetration is further achieved when Ar along with 5% H2 is used as the shielding gas compared to that when pure Ar is used. The constriction of arc column increases the energy density, which increases the depth of penetration. Measurement of microhardness and metallurgical observations are carried out for samples after TIG welding and activated tungsten inert gas (ATIG) welding and compared to observe the solidification phenomenon during the process.

Comparative Investigation of Mechanical Properties in GMAW/GTAW for Various Shielding Gas Compositions

Gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) are extensively used in the areas requiring high-speed welds, higher weld quality finishes, and superior strength properties. In this experimental study, the influence of shielding gas composition on the mechanical properties of austenitic stainless steel 316L was investigated. The selection of shielding gases and current intensities is the major concern to achieve the intended properties of the weld metal. The influence of four various shielding gas compositions was studied in this work. It was carried out in both GMAW and GTAW for 3 and 6 mm thick plates. Optimization of shielding gas mixtures, current intensities, flow rates, and welding speed is required to automate the process and to improve the overall efficiency of the weld process. Mechanical properties are analyzed for GTAW and GMAW specimens. The obtained results prove that the tensile strength, hardness, and impact strength are higher for GTAW weld specimens compared to GMAW weld specimens. Further by decreasing the percentage of CO2, the tensile strength and hardness values give the superior results.

The effect of metal transfer modes and shielding gas composition on the emission of ultrafine particles in MAG steel welding

The present study aims to characterize ultrafine particles emitted during gas metal arc welding of mild steel and stainless steel, using different shielding gas mixtures, and to evaluate the effect of metal transfer modes, controlled by both processing parameters and shielding gas composition, on the quantity and morphology of the ultrafine particles. It was found that the amount of emitted ultrafine particles (measured by particle number and alveolar deposited surface area) are clearly dependent from the main welding parameters, namely the current intensity and the heat input of the welding process. The emission of airborne ultrafine particles increases with the current intensity as fume formation rate does. When comparing the shielding gas mixtures, higher emissions were observed for more oxidizing mixtures, that is, with higher CO2content, which means that these mixtures originate higher concentrations of ultrafine particles (as measured by number of particles by cubic centimeter of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more hazardous condition regarding welders exposure.

The effect of metal transfer modes and shielding gas composition on the emission of ultrafine particles in MAG steel welding

The present study aims to characterize ultrafine particles emitted during gas metal arc welding of mild steel and stainless steel, using different shielding gas mixtures, and to evaluate the effect of metal transfer modes, controlled by both processing parameters and shielding gas composition, on the quantity and morphology of the ultrafine particles. It was found that the amount of emitted ultrafine particles (measured by particle number and alveolar deposited surface area) are clearly dependent from the main welding parameters, namely the current intensity and the heat input of the welding process. The emission of airborne ultrafine particles increases with the current intensity as fume formation rate does. When comparing the shielding gas mixtures, higher emissions were observed for more oxidizing mixtures, that is, with higher CO2content, which means that these mixtures originate higher concentrations of ultrafine particles (as measured by number of particles by cubic centimeter of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more hazardous condition regarding welders exposure.

신경망 알고리즘을 이용한 차체용 강판 아크 용접 조건 도출

Famous artificial neural network (ANN) is applied to predict proper process window of arc welding. Target weldment is variously combined lap joint fillet welding of automotive steel plates. ANN's system variable such as number of hidden layers, perceptrons and transfer function are carefully selected through case by case test. Input variables are welding condition and steel plate combination, for example, welding machine type, shield gas composition, current, speed and strength, thickness of base material. The number of each input variable referred in welding experiment is counted and provided to make it possible to presume the qualitative precision and limit of prediction. One of experimental process windows is excluded for predictability estimation and the rest are applied for neural network training. As expected from basic ANN theory, experimental condition composed of frequently referred input variables showed relatively more precise prediction while rarely referred set showed poorer result. As conclusion, application of ANN to arc welding process window derivation showed comparatively practical feasibility while it still needs more training for higher precision.

Artificial neural network optimisation of shielding gas flow rate in gas metal arc welding subjected to cross drafts when using alternating shielding gases

This study implemented an iterative experimental approach in order to determine the shielding gas flow required to produce high-quality welds in the gas metal arc welding process with alternating shielding gases when subjected to varying velocities of cross drafts, thus determining the transitional zone where the weld quality deteriorates as a function of cross-draft velocity. An artificial neural network was developed using the experimental data that would predict the weld quality based primarily on shielding gas composition, alternating frequency and flow rate and cross-draft velocity, but also incorporated other important input parameters, including voltage and current. A series of weld trials were conducted to validate and test the robustness of the model generated. It was found that the alternating shielding gas process does not provide the same level of resistance to the adverse effects of cross drafts as a conventional argon/carbon dioxide mixture. The use of such a prediction tool is of benefit to industry in that it allows the adoption of a more efficient shielding gas flow rate, while removing the uncertainty of the resultant weld quality.

Quenching Heat Treatment Effects on the Mechanical and Microstructure Properties of AISI 304 Type Welded by GMAW Process Using Different Shielding Gases

As-received samples of an austenitic stainless steel AISI 304 type was welded by Gas metal arc welding (GMAW) robotic operation process using ER308L-Si filler metal wire. Two different atmospheres were used: 68% Argon plus 32% CO2, and 100% Argon. The aim of this study is investigates the influence of quenching heat treatment on the mechanical and microstructure properties of AISI 304 type which welded by GMAW under different shielding gas compositions. The fractured surfaces of the tensile test specimens examined using scanning electron microscopy (S.E.M). The results showed that the welding using shielding gas of 68% Argon plus 32% CO2 stronger than 100% Argon. After performed quenching heat treatment process, both specimens experienced a slight decreased in hardness.

The Effect of Shielding Gas Composition on Microstructure and Abrasive Wear Resistance Fabricated with PTA Alloying Technique

Abstract In this study, SAE 1020 steel surfaces were separately alloyed with preplaced high-carbon-ferro-chromium (FeCr), ferro-molybdenum (FeMo) and ferro-titanium (FeTi) powders by using plasma transferred arc (PTA) heat source. By using three different types of shielding gas compositions during the alloying process, the study investigated the effects of modified shielding gas composition on the microstructure, hardness, and abrasive wear resistance of specimens. The most homogenous microstructure and the highest wear resistance was obtained in the gaseous environment which included 3% of H2. Increasing this rate to 5 % in the shielding gaseous composition caused gaps and pores in the microstructure and caused a decrease in the wear resistance. The x-ray examinations of the specimens identified ferro-molybdenum and ferro-titanium solid solutions, ferrit, austenite and martensite phases in their microstructure as the first phase and FeC, Cr7C3, Cr3C2, Fe3C, Fe7C3, MoC and TiC phases as the second phase. As a result, it was concluded that changes in shielding gas composition in surface alloying process affected specimens’ microstructure and abrasive wear properties.

Quantitative detection of plasma-generated radicals in liquids by electron paramagnetic resonance spectroscopy

In this paper the qualitative and quantitative detection of oxygen radicals in liquids after plasma treatment with an atmospheric pressure argon plasma jet by electron paramagnetic resonance spectroscopy is investigated. Absolute values for ·OH and radical concentration and their net production rate in plasma-treated liquids are determined without the use of additional scavenging chemicals such as superoxide dismutase (SOD) or mannitol (D-MAN). The main oxygen-centred radical generation in PBS was found to originate from the superoxide radical. It is shown that hidden parameters such as the manufacturer of chemical components could have a big influence on the comparability and reproducibility of the results. Finally, the effect of a shielding gas device for the investigated plasma jet with a shielding gas composition of varying oxygen-to-nitrogen ratio on radical generation after plasma treatment of phosphate-buffered saline solution was investigated.

Influence of CO2-Ar Mixtures as Shielding Gas on Laser Welding of Al-Mg Alloys

In this study, AA5083 samples were butt welded under a conduction regime with high-power diode laser (HPDL). Various mixtures composed of Ar and CO2 were used as a shielding gas. The influence of the shielding gas composition on the microstructure and on the properties of laser welds was analyzed. The weld beads were deeply characterized by metallographic/microstructural studies, X-ray diffraction (XRD), X-ray energy dispersive spectrometry (X-EDS) chemical analyses, X-ray photoelectron spectra (XPS), microhardness, and tensile strength. The corrosion resistance of laser-remelted surfaces with different CO2/Ar ratios was also estimated by means of electrochemical tests. The addition of CO2 to the shielding gas results in a better weld penetration and oxidizes the weld pool surface. This addition also promotes the migration of Mg toward the surface of weld beads and induces the formation of magnesium aluminates spinel on the welds. The best corrosion resistance result is achieved with 20 pct CO2. The overall results indicate that the addition of small percentage of CO2 to Ar leads to improvements of the mechanical and corrosion properties of the aluminum welds.