Gas Shielded Metal Arc Welding Research Articles

Optimizing of gas-shielded metal arc welding parameters for 10.5-12.5% chromium steel using 3o8L electrodes

The 10.5-12.5% chromium, titanium-stabilized ferritic stainless steel (FSS) plates used to fabricate coal line jumbo wagons is susceptible to undesirable chromium depletion during welding with 309L electrodes. In this work, non-stabilized FSS plates were welded using 308L welding electrodes. The objective was to weld non-stabilized FSSs using gas-shielded metal arc welding without causing sensitization. The welding process was optimized by lowering the heat input. Sensitization was assessed by rigorous etching techniques and anodic polarization scans. In addition, the welds were subjected to tensile testing, and their fracture surfaces were examined for intergranular cracking. Non-stabilized FSS plates were successfully welded using gas metal arc welding.

Influence of arc mode on the microstructure and mechanical properties of 5356 aluminum alloy fabricated by wire arc additive manufacturing

In this paper, two arc modes of gas shielded metal arc welding (GMAW), a new pulsed mode (microMIG) and a non-pulsed mode (microMIG-CC), were used to melt ER5356 aluminum alloy wire for thin-wall fabrication. The influence of both arc modes on the melt–drop transition pattern, thin–wall properties, porosity, microstructure and mechanical properties was investigated at the same heat input. The microMIG mode adds SKS-based current time based on conventional pulsed GMAW for short-circuiting the transition, which leads to a faster spread of melt pool temperature. The rapid cooling of the melt pool contributed to the increase of grain nucleation rate and inhibited grain growth, resulting in smaller grain size in the microMIG mode specimens. In addition, the low porosity of microMIG specimens is attributed to the high voltage of the micro-MIG mode resulting in an unfocused heat source, which leads to a shallow penetration depth of the specimens and a reduced hydrogen escape distance. Compared with the microMIG-CC mode, the microMIG mode specimens have smaller grain size and lower porosity, therefore higher tensile strength is obtained. The isotropic property of thin walls is due to the existence of equiaxed grains and the random distribution of grain orientation. However, the aggregation of dislocations and the increase of precipitates make microMIG-CC have higher hardness. Overall, the mechanical properties of the thin wall specimens of WAAM 5356 aluminum alloy are higher than those of the as-cast specimens.

Additive manufacturing of a bridge in situ

AbstractNominated for Eurosteel 2021 Best Paper AwardAdditive manufacturing (AM) is playing an increasing role in the production of complex steel structures. Robot‐ or machine‐guided gas‐shielded metal arc welding (GMAW), known as wire and arc additive manufacturing (WAAM), is suitable for this purpose. A small footbridge was designed in shell form at TU Darmstadt. It was completely additively manufactured over a stream on site using a welding robot. The work called for cantilevered manufacturing without support structures, which poses special challenges in manufacturing. This paper describes selected aspects of this project: the preliminary strength studies, the manufacturing strategy to ensure homogeneous manufacturing and the findings from on‐site manufacturing. In addition, investigations were carried out which led to a notable increase in the deposition rate with the right choice of gas and wire.

Application of magnetic fields to weld overlay cladding to improve its performance in the oil & gas industry

Abstract There are increasingly more aggressive hydrocarbons, as they have high contents of hydrogen sulfide/carbon dioxide, under conditions of high pressure/high temperature (HP/HT). For driving these aggressive hydrocarbons, one of the most cost-effective solutions is the coating and cladding on conventional carbon steel using a corrosion-resistant alloy (CRA). The overlay is one of the methods used for the application of this cladding. However, among the main problems of this method is the dilution and microsegregation, which causes a decrease in corrosion resistance and its subsequent failure. In this work, the application of the gas-shielded metal arc welding process (GMAW) with the interaction of magnetic fields of low intensity is proposed to reduce these problems. API X60 was used as base material and 316L as overlay. The interaction of the magnetic field with the molten metal causes the temperature to become homogeneous, induces grain refinement, reduces the extend of the heat-affected zone (HAZ), leads to a decrement in microhardness, a decrease in dilution and, micro-segregation, as well as the elimination of the magnetic blow, stabilizing the arc. This coating technique can be applied to pipelines and fittings as the trim of submarine equipment used for driving aggressive hydrocarbon.

3D numerical simulation of GMAW Cold Metal Transfer using response surface methodology

This work presents a fast methodology to adjust heat source model parameters that reproduce the evolution of temperatures and distortions of a welded joint. This joint is obtained by the Cold Metal Transfer (CMT) process, a variant of the most frequently used gas-shielded metal arc welding (GMAW) process. The proposed methodology combines Response Surface Method (RSM) and Finite Element Method (FEM). The thermal simulation is tackled by a 3D transient FEM-model with a Goldak heat flux; and the mechanical behaviour is addressed by a 3D elastic-plastic FEM-model. A Design of Experiments (DoE) is applied to simulate a set of thermal and mechanical FEM-models varying the heat source parameters. Then, the temperatures and distortions of all simulations are gathered and used to build polynomial regression models that are able to predict temperatures and distortions as functions of the heat flux parameters. Finally, best parameters are found using RSM. The method is based on automation of pre and post processes that replaces the trial and error process, which involves large amount of engineering time.

Experimental tests on built-up cold-formed steel section laced compression members

This paper presents the detailed results of the first experimental tests investigating the behaviour and strength of axially loaded built-up cold-formed steel laced compression members, wholly assembled using Gas-Shielded Metal Arc Welding. The built-up laced test specimens consisted of two longitudinal cold-formed carbon steel channels (chords) placed back-to-back with an internal gap and connected using end batten plates and two parallel planes of single lacing systems. The compression tests were performed using built-up laced members with similar lengths but with various back-to-back gap distance. The compressive strengths, modes of failure and deformed shapes at failure were observed in the tests and reported in this paper. In addition, the load-axial shortening, load-lateral displacement, and load-axial strain relationships were also measured and reported. Overall, the new tests on built-up laced members compensated the lack of data on this form of construction and provided valuable experimental information in terms of buckling behaviour and compressive strength which may be powerfully used to develop nonlinear 3-D finite element models. The compressive strengths measured experimentally were compared against the design strengths determined using the North American Specification, Australian/New Zealand Standard and European Code for the design of cold-formed steel structures. Generally, it is shown that the specifications were accurate for the built-up cold-formed steel section laced compression members except for those failing mainly by overall buckling, where the specifications were considerably conservative.

Influence of classified pore contents on the quasi-static and cyclic strength properties of the welded joint in gas-shielded metal arc welding of galvanized, high-strength steels

High-strength steel sheets are used in the automotive industry to save weight. In particularly, in the chassis area, high-strength steels are constantly replacing the previously used strength classes of 440–590 MPa. In body in white construction, galvanized sheet steel has had long been established use due to its anti-corrosive effect. In chassis production, steel materials are usually processed without galvanizing. In the automotive industry, demand for galvanized steel sheets for chassis production is increasing. Gas-shielded metal arc welding is an established joining process for chassis components. The zinc layer poses difficulties as it evaporates during the welding process and leads to pores in the resulting weld seam. A pore-filled weld seam can reduce the strength of the welded joint. When designing chassis parts, the influence of the pores in the weld seam on the strength properties is an important finding. It has been shown that the resulting pore content of the weld seam can be influenced by the heat input and the welding process used. The following article presents the findings of a low-energy Cold Metal Transfer (CMT) process and a high-energy pulse process on a hot-dip galvanized high-strength steel of strength class 760 MPa in a sheet thickness of 2.5 mm at the lap joint without a gap.

3D‐Printing with Steel: Additive Manufacturing of a Bridge in situ

AbstractAdditive manufacturing (AM) plays an increasing role in the production of complex structures in steel construction. Robot‐guided Gas Shielded Metal Arc Welding (GMAW), known as Wire and Arc Additive Manufacturing (WAAM), is suitable for this purpose. At TU Darmstadt, a small pedestrian bridge in shell form was designed. It was completely additively manufactured on site with a welding robot over a creek. This paper presents selected aspects of this project. The focus is particularly on the preliminary strength investigations carried out and the process sequences required for homogenous manufacturing. The paper concludes with a consideration of the implementation on site.

High variability in toxicity of welding fume nanoparticles from stainless steel in lung cells and reporter cell lines: the role of particle reactivity and solubility

Millions of people in the world perform welding as their primary occupation resulting in exposure to metal-containing nanoparticles in the fumes generated. Even though health effects including airway diseases are well-known, there is currently a lack of studies investigating how different welding set-ups and conditions affect the toxicity of generated nanoparticles of the welding fume. The aim of this study was to investigate the toxicity of nine types of welding fume particles generated via active gas shielded metal arc welding (GMAW) of chromium-containing stainless steel under different conditions and, furthermore, to correlate the toxicity to the particle characteristics. Toxicological endpoints investigated were generation of reactive oxygen species (ROS), cytotoxicity, genotoxicity and activation of ToxTracker reporter cell lines. The results clearly underline that the choice of filler material has a large influence on the toxic potential. Fume particles generated by welding with the tested flux-cored wire (FCW) were found to be more cytotoxic compared to particles generated by welding with solid wire or metal-cored wire (MCW). FCW fume particles were also the most potent in causing ROS and DNA damage and they furthermore activated reporters related to DNA double- strand breaks and p53 signaling. Interestingly, the FCW fume particles were the most soluble in PBS, releasing more chromium in the hexavalent form and manganese compared to the other fumes. These results emphasize the importance of solubility of different metal constituents of the fume particles, rather than the total metal content, for their acute toxic potential.

Assessment of Technologies for Measuring Exposure to NO2 during Welding on Aluminum Alloys

Arc welding is a complex process that results in many air contaminants of health significance to humans. As a result, regulators worldwide require employers to determine exposure of welders and other workers to these contaminants. The very small Exposure Limit for NO2 limits the technology available for assessing exposure. Bias caused by ozone, a known interferent in the measurement of NO2, is a major concern. This investigation involved side-by-side comparison of results provided by handheld instruments containing electrochemical sensors for NO2 to those produced by an air pollution analyzer specific to NO2 using bag samples of plumes collected during production welding (Gas Shielded Metal Arc Welding [GMAW] commonly known as Metal Inert Gas [MIG welding]) on aluminum alloys. The shield gas was argon. Monitoring to confirm utility of the method was performed on welders. Results from all instruments were similar despite differences in measurement technology and instrument and sensor manufacturer. Levels experienced during confirmatory testing on welders to determine exposures of short duration and long intermittency as occur during real-world activity were comparable to the Threshold Limit Value for NO2 of 0.2ppm (parts per million) expressed as a Time-Weighted Average over 8 hours, and were less than the Ceiling Limit of 1ppm used by some jurisdictions. Hand-held instruments containing electrochemical sensors for NO2 and datalogging capability are suitable for use in this application. The ability to draw the sample to the instrument by a pump is an important consideration in providing welder safety and protecting the instrument.

Mathematical Modeling of Optical Radiation Emission as a Function of Welding Power during Gas Shielded Metal Arc Welding.

Arc welding is accompanied by intense optical radiation emission that can be detrimental not only for the welder himself but also for people working nearby or for passersby. Technological progress advances continuously in the field of joining, so an up-to-date radiation database is necessary. Additionally, many literature irradiance data have been measured for a few welding currents or for parts of the optical spectral region only. Within this paper, a comprehensive study of contemporary metal active gas, metal inert gas, and cold metal transfer welding is presented covering optical radiation emission from 200 up to 2,700 nm by means of (spectro-) radiometric measurements. The investigated welding currents range from 70 to 350 A, reflecting values usually applied in industry. Based upon these new irradiance data, three mathematical models were derived in order to describe optical radiation emission as a function of welding power. The linear, exponential, and sigmoidal emission models depend on the process variant (standard or pulsed) as well as on the welding material (mild and stainless steel, aluminum). In conjunction with the corresponding exposure limit values for incoherent optical radiation maximum permissible exposure durations were calculated as a function of welding power. Typical times are shorter than 1 s for the ultraviolet spectral region and range from 1 to 10 s for visible radiation. For the infrared regime, exposure durations are of the order of minutes to hours. Finally, a validation of the metal active gas emission models was carried out with manual arc welding.

The research of technological and environmental conditions during low-energetic gas-shielded metal arc welding of aluminium alloys

In this paper, two trends of research conducted at the Welding Institute have been presented, namely the study of material and technological welding conditions of different aluminium alloys using CMT and ColdArc methods and the influence of selected technological parameters on emission rate to the working environment. The properties of welded joints as well as the application fields of modern low-energy welding devices for joining thin aluminium sheets have been discussed. The relationships between the welding method, base and filler material type, and emission rate have also been presented.

Droplet Transfer on Three Phase Relations at Four-Wire Welding Robot

Based on the high-speed photography, the effect of phase relations on droplet transfer and welding seam was analyzed. To each TCGMAW (Twin-wire Co-pool Gas-shielded Metal Arc Welding) torch at four-wire welding robot, under the descriptive welding parameters, when the phase relation of the front wire and the back wire was alternate, the arcs of the two wires had no effect on each other basically; the welding seam shaped very well. When the phase relation was synchronized, the arcs attracted each other and the two arcs centralized to the middle of the two wires; the humping bead was formed. When the phase relation was random, now and then the arcs synchronized and attracted each other, and at times the arcs changed alternately and had no effect on each other; the appearance quality of the welding seam was moderate.

GMA溶接の溶滴移行現象に及ぼすシールドガスとワイヤの影響

In this paper, metal transfer modes of mild steel wire of 1.2 mm in diameter, which were observed for welding variables of current, voltage and polarity in Gas shielded Metal Arc Welding process with four kinds of shielding gases (Ar, He, CO2 and mixture gas of Ar+20%CO2) are described. In electrode positive polarity, metal transfer transition from globular to spray occurs with use of shielding gas of Ar or Ar+20%CO2. But with shielding gas of He or CO2 only globular transfer was observed. In electrode negative polarity, mild steel wire added by a very small amount of Rare Earth Metal, which promotes electron emission at the cathode, makes globular to spray transition possible with shielding gas of CO2 or Ar+20%CO2. Other combinations of shielding gas and electrode wire result in globular transfer in the current range up to 400 A. In spray transfer mode, current density was estimated to be higher than 1×108 A/m2 at the surface of metal drop onto detachment.

English

Welding technique is one of the widely used permanent fastener techniques, where in different types of welding are used for different applications. Welding creates property changes in the welded location, so it is important to investigate the core mechanical properties after welding to create better designs using welding techniques. In this project the effect of the welding process of Shielded Metal Arc Welding (SMAW) and the relatively Tungsten inert gas welding (TIG) process on 304 Austenitic Stainless steel is studied. The welding process was carried out on 6mm thick plate of 304 Stainless Steel using SMAW and TIG welding processes The two set of plates having the single plate size of 200mmX150mmX6mm were welded using Tungsten Inert Gas welding And Shielded metal arc welding process. This project focuses on tensile property, toughness; micro hardness and micro structure of the each welding process of weld joints are studied and compared with those properties of each process related to the base metal, which shows the better welding process on Stainless Steel. The output variables of SMAW and TIG welding process on 6mm weld plate tensile strengths are compared. The studies indicated that the TIG joints were having better tensile strength than SMAW welded joints on 304stainless steel.

Status and Perspectives in Overlaying under Particular Consideration of Sophisticated Welding Processes

Surfacing is an indispensable measure both to conserve as well as to generate worth. Different welding methods have been created over the time, were established and have found their long-term utilization in numerous specific industrial applications. This paper is intended to basically focus on some of the most important overlay welding processes and an evaluation of most recent process developments and advancements respectively, standing for remarkable improvements in terms of weld quality and reproducibility. The emphasis should thereby being laid upon the fully mechanized Gas Shielded Tungsten Arc (Hot wire) Welding (GTAW) and the Gas Shielded Metal Arc Welding (GMAW). Especially the usage of the highly advanced Cold Metal Transfer Process (CMT) enables the user to achieve new levels in process stability and quality, also in the field of overlaying.

1－2 ミグ／マグ溶接

1－2 ミグ／マグ溶接

Modeling of Molten Drop Oscillation in Gas Shielded Metal Arc Welding

In Gas shielded Metal Arc Welding process, the molten drop at the electrode wire tip is detached and transferred into the weld pool by various driving forces, which have been discussed mainly focusing on gravity force, electro-magnetic force, surface tension force and plasma drag force. In this paper the oscillation phenomena of metal drop and their numerical model are described. The numerical model developed is an axial symmetrical 2D model which enables to calculate and visualize time-change of the drop shape and the flow in the drop using VOF-CSF method. The validity of the model is verified through the comparison between calculations and experiments using waterdrop. It is shown that the natural frequency of the pendant drop decreases with increase of the drop size. And the numerical simulation predicts that it is possible to detach the molten drop from the electrode wire by exciting the forced oscillation around the natural frequency with pulsed current.

溶滴振動現象のモデル解析

In Gas shielded Metal Arc Welding process, the molten drop at the electrode wire tip is detached and transferred into the weld pool by various driving forces, which have been discussed mainly focusing on gravity force, electro-magnetic force, surface tension force and plasma drag force. In this paper modeling of the oscillation phenomena of molten drop at the wire tip are described. An analytical model evaluating natural frequency of liquid pendant drop was proposed on the basis of mass-spring model. The numerical model developed is an axial symmetrical 2D model which enables to calculate and visualize time-change of the drop shape and the flow in the drop using VOF-CSF method. It is shown that the natural frequency of the pendant drop decreases with increase of the drop size by both analytical and numerical models. And the natural frequency evaluated by analytical model is shown to be little higher than that by numerical model because of neglecting viscous resistance of liquid flow.

Dissimilar welds between unreinforced AA6082 and AA6092/SiC/25p composite by pulsed-MIG arc welding using unreinforced filler alloys (Al–5Mg and Al–5Si)

Weldability between an unreinforced aluminium alloy (AA6082) and an AA6092/SiC/25p composite, using as filler metals both Al–5Mg (ER5356) and Al–5Si (ER4043) unreinforced alloys, has been studied in the present work. One of the main requirements considered to obtain metallurgical weldability was to reduce at maximum the heat input to limit the possible interfacial reaction among molten aluminium matrix and SiC particles which produces aluminium carbide (Al 4C 3) inside the weld pool and fusion line. For it, welding procedure selected was a gas shielded metal arc welding, working in pulsed current mode (MIG-P), to obtain an improved control of the metal transfer to the molten pool. Three kind of joint designs were used: “I”, “V” and “X”, working with one and two filler metal runs. Mechanical tests of welded joints showed that tensile strengths, for all these welding conditions, were very similar and close to 223 MPa, which is approximately the 65% of the AA6082-T6 one. In all cases, failure was located through the HAZ of the unreinforced alloy. The application of a postwelding heat treatment made possible to recover the 100% of the parent unreinforced alloy tensile strength.