Short-circuiting Gas Metal Arc Research Articles

Multi-objective Optimization of Short-Circuit Gas Metal Arc Welding for Overhang Structures by Grey Relational Analysis Integrated Taguchi Method

Multi-objective Optimization of Short-Circuit Gas Metal Arc Welding for Overhang Structures by Grey Relational Analysis Integrated Taguchi Method

Characterization of cold metal transfer and conventional short-circuit gas metal arc welding processes for depositing tungsten carbide-reinforced metal matrix composite overlays

This paper compares the processing characteristics of advanced CMT (cold metal transfer) and conventional GMAW-S (gas metal arc welding with short-circuit metal transfer) processes for depositing Ni-WC MMC (nickel-based metal matrix composites reinforced with WC) overlays. In contrast to common expectations, advanced CMT technology with mechanically assisted droplet transfer could not demonstrate significant advantages over the GMAW-S process; on the contrary, CMT exhibits marginal disadvantages in terms of carbide transfer efficiency, volume fraction of retained WC, and deposition rate. Some carbides originally contained in the core of the feed wire are blown away and expelled out of the processing zone leading to physical losses of WC particles during the deposition processes, which is more significant for the CMT process owing to much higher waveform cycle frequency and cyclic feed wire retractions. CMT exhibits superior waveform stability, better control over penetration depth, marginally lower dilution level, and exceptional arc stability. The main parameters affecting carbide transfer efficiency and volume fraction of retained WC are wire feed speed and travel speed for both processes; increased wire feed speed and travel speed generally lead to decreased carbide transfer efficiency and reduced volume fraction of retained WC. Shielding gas may have different effects on the outcomes for the CMT and GMAW-S processes. CMT overlays show comparatively higher W and lower Fe concentration in the matrix, while GMAW-S overlays show a higher concentration of Fe in the matrix (due to elevated dilution level) with marginally higher matrix microhardness and more herringbone-like secondary carbide precipitates.

Development and evaluation of a closed-loop z-axis control strategy for wire-and-arc-additive manufacturing using the process signal

Wire-and-arc-additive manufacturing (WAAM) is an additive manufacturing technology with a high deposition rate. WAAM usually employs a layer wise build-up strategy. This makes it necessary to know the height of each deposited layer to determine the height the z-axis has to travel after each layer. Current bead geometry models (BGM) lead to variations, which can gradually accumulate over the layers. The present study focuses on the development of a closed-loop control system capable of keeping the contact tube working distance (CTWD) constant during short-circuit gas metal arc welding (GMAW) based WAAM. The algorithm calculates the CTWD based on the resistance during the short circuit. The closed-loop strategy is compared to an open-loop control strategy, which moves along a predefined height step after each layer. Using the proposed control strategy, WAAM becomes a fully automated process without the need for preliminary experiments to determine the height step. Only a short calibration slope is necessary for a complete closed-loop additive build-up. To study the influence of the control strategy on the workpiece the energy input, mechanical strength, microhardness, porosity, and microstructure were analyzed. It is shown that the CTWD of the open-loop deposited component increases slowly. Due to the novel control approach, this is prevented by the closed-loop control, while the mechanical strength and microhardness remain.

Study on the Oscillating Phenomenon of Welding Pool with Different Penetration States in Short-Circuiting GMAW

The oscillating phenomenon of the weld pool has a direct physical correspondence with its penetration state, which has broad application prospects in the monitoring of weld penetration states. This article studied the characteristics of the oscillating phenomenon of the weld pool in short-circuiting gas metal arc welding (S-GMAW) with different penetration states based on a welding high-speed photography system. The results show that the form of the liquid bridge electric explosion impact on the weld pool is “surface impact” in S-GMAW. The oscillation frequency of the weld pool decreases as the size of the weld pool increases. Compared with the partially penetrated weld pool, the boundary conditions of the fully penetrated weld pool had different boundary conditions, resulting in higher oscillation amplitude and lower oscillation frequency. In S-GMAW, no difference in welding voltage signal, caused by the difference in amplitude of the weld pool oscillation with different penetration states, was observed.

Assessment of weld bead geometry in modified shortcircuiting gas metal arc welding process for low alloy steel

ABSTRACT Ever-growing needs in pipeline welding relating to quality, frequent usage of advanced, heat-sensitive, and corrosion-resistant materials alongside high production costs encourage the evaluation of a welding process thoroughly. The only way to overcome those problems is the adaptation of technically evolved welding methods that combine the goodness of cutting-edge power supply sources and advanced software configuration. One such technique is Regulated Metal Deposition (RMDTM) welding. In this context, the current study explores the influence of the regulated metal deposition (RMDTM) welding variables on ASME SA387-11-2 steels. Current (A), voltage (V), and gas flow rate (GFR) are preferred regulated metal deposition (RMD™) welding variables, and at the same time the depth of penetration (DOP), heat-affected zone (HAZ), bead height (BH), and bead width (BW) are incorporated as performance evaluation attributes. Furthermore, the exploration of Rao algorithms is presented to evaluate the optimal welding settings. The obtained optimal welding settings is current = 92 A, voltage = 13 V, and gas flow rate = 21 litre/min. The results are also compared with the JAYA, and teaching learning-based optimization (TLBO) approaches to show the efficacy of the intended approach.

Study of parametric influence and welding performance optimization during regulated metal deposition (RMD™) using grey integrated with fuzzy taguchi approach

Regulated Metal Deposition (RMD™) welding process is fundamentally a modified short-circuit gas metal arc welding (GMAW) process wherein a precisely-controlled metal transfer provides uniform droplet deposition, making it easier for the welder to control the puddle and hence achieve an enhanced quality of welded joints. RMD technique was experimented and implemented on a variety of steels such as stainless steel, carbon steels, etc. However, obtaining satisfactory welding performance is indeed a challenging task during RMD. Hence, this study aims to assess the favorable parameters settings in order to optimize welding performance characteristics such as Heat affected zone (HAZ), depth of penetration (DOP) and bead width (BW) of Regulated Metal Deposited arc weldment using grey relation analysis integrated with fuzzy inference system with Taguchi approach. From the adopted methodology the optimal parameter settings for current (135 A), voltage (14 V), and gas flow rate (13 L/min) have been achieved. The study also tells that the voltage is the most influencing parameter during RMD welding.

Study on Short-Circuiting GMAW Pool Behavior and Microstructure of the Weld with Different Waveform Control Methods

In order to study internal relation among the behavior of the weld pool, the microstructure of weld bead and the waveform of short-circuiting gas metal arc welding (S-GMAW), a high speed photograph-images analysis system was formed to extract characteristics of weld pool behavior. Three representative waveform control methods were used to provide partly and fully penetrated weld pools and beads. It was found that the behavior of the weld pool was related to the instantaneous power density of the liquid bridge at the break-up time. Weld pool oscillation was triggered by the explosion of the liquid bridge, the natural oscillation frequencies were derived by the continuous wavelet transform. The change of weld pool state caused the transition of oscillation mode, and it led to different nature oscillation frequencies between partial and full penetration. Slags flow pattern could be an indication of the weld pool flow. Compared with the scattered slags on fully penetrated weld pool, slag particles accumulated on partially penetrated weld pools. The oscillating promoted the convection of the welding pool and resulted in larger melting width and depth, the grain size, and the content of pro-eutectoid ferrite in the weld microstructure of S235JR increased, the content of acicular ferrite decreased.

A new model to distinguish welds performed by short-circuit GMAW based on FRESH algorithm and MLP ANN

The short-circuit gas metal arc welding has been continuously studied over the years, due to its important role in manufacturing processes. Concerning the process, many kinds of research are carried out aiming to understand the influence of the shielding gas in welds quality. In this context, this work treats the voltage and current welding signals as time series and applies a feature extraction based on scalable hypothesis tests, which is called FRESH algorithm, in order to obtain the signal features. After that, these features are applied in a multilayer perceptron artificial neural network, trained by the scaled conjugate gradient method, which classifies the welds according to the flow rate and type of shielding gas used in the process. The model presented excellent performance, which shows that the proposal is suitable to be used in welding quality monitoring.

Review of current waveform control effects on weld geometry in gas metal arc welding process

Control of welding parameters is an important factor in gas metal arc welding (GMAW) because these parameters determine the heat input, cooling conditions, and time during which the microstructure and the geometry of the weld are formed. It is therefore essential that sufficient heat is transferred to highly conductive metals like aluminum and appropriate heat input used with very sensitive metals such as stainless steel and high-strength steels or when welding dissimilar metals. The objective of this study is to identify parameters of current, voltage waveforms, and electrode feeding motion that directly contribute to improvement in metal and heat transfer conditions from the electrode to the base metals. The effects of these parameters on welded joint geometry are determined. The work critically reviews research on the effect on welded joints of control of current waveform, voltage, and the alternating electrode and analyzes the different parameters that promote forces acting during metal transfer. Experiments and case studies based on controlled waveforms are discussed. The analysis shows that in controlled short-circuit gas metal arc welding (CS-GMAW), all identified parameters contribute to control of heat input and reduction in the amount of spatter and fumes generated. Variable polarity gas metal arc welding (VP-GMAW) is found to be particularly effective for aluminum welding because of its good control of mass metal transfer and weld penetration. Mixed waveform approaches (i.e., 20 pulses/controlled short circuit) improve weldability in difficult welding positions.

Modified Short Arc Gas Metal Arc Welding Process for Root Pass Welding Applications

It is well known that, the major limitation of conventional short circuiting gas metal arc welding process (GMAW) for welding of various ferrous and non-ferrous materials is poor bridgeability and generation of large number of spatters. To overcome these difficulties, in recent years, waveform controlled technology has been introduced in GMAW process for specific application to meet required quality and productivity. However, the specific advantage of the process for various welding application primarily depends on the waveform parameters such as peak current, background current, time and voltage. It is often found that, irregular control of waveform leads defects like porosity, undercut and burn through etc. which impairs the weld joint quality. Thus, it is very important to study the effect of different waveform on bead geometry and microstructure. In this regard, in the present investigation aimed to carry out various waveforms on root pass welding of carbon and alloy steels. The bead appearance, soundness, macro and micro structure analysis has been carried out. Based on the results the optimum range of waveform has been derived and appropriately correlated with process parameters.

Feature extraction for gas metal arc welding based on EMD and time–frequency entropy

Hilbert–Huang transform (HHT) and time–frequency entropy were used to estimate the stability of short-circuiting gas metal arc welding (GMAW). First, the current signals were divided by empirical mode decomposition (EMD) into several intrinsic mode functions (IMFs). Then the IMFs were converted by Hilbert transform to Hilbert–Huang spectrum which describes the instantaneous time–frequency distribution of welding current signals. Since the uniformity of energy amplitude distribution with time–frequency reflects the stability, we introduced time–frequency entropy to quantify the energy distribution with time–frequency range in the HHT spectrum. We found HHT can effectively depict the amplitude with time and frequency distribution of welding current signals, and the welding was more stable when the time–frequency entropy was larger. Thus, this is a new way to assess and quantify the stability of short-circuiting GMAW.

Stability evaluation of short-circuiting gas metal arc welding based on ensemble empirical mode decomposition

The arc of gas metal arc welding (GMAW) contains abundant information about its stability and droplet transition, which can be effectively characterized by extracting the arc electrical signals. In this study, ensemble empirical mode decomposition (EEMD) was used to evaluate the stability of electrical current signals. The welding electrical signals were first decomposed by EEMD, and then transformed to a Hilbert–Huang spectrum and a marginal spectrum. The marginal spectrum is an approximate distribution of amplitude with frequency of signals, and can be described by a marginal index. Analysis of various welding process parameters showed that the marginal index of current signals increased when the welding process was more stable, and vice versa. Thus EEMD combined with the marginal index can effectively uncover the stability and droplet transition of GMAW.

Metallurgical characterization of the 5083H116 aluminum alloy welded with the cold metal transfer process and two different wire-electrodes (5183 and 5087)

Aluminum-magnesium alloys have great prominence in the naval sector as they represented structural materials with low specific weight and excellent corrosion resistance in marine environments. Such benefits are also seen in other maritime structures, as oil platforms. Welding is the main manufacturing process in this sector. However, there are substantial technological challenges when welding these alloys. The work undertaken in this paper aimed at the development of welding science and technology in the specific framework of the construction project of an oceanographic sailboat of naval aluminum alloy 5083. This paper presents a technical and scientific contribution for the short-circuiting gas metal arc welding (GMAW) process version designated as cold metal transfer (CMT). As to the CMT mode, work intended to verify the compatibility of existing synergic programs in the welding equipment with the investigated wire-electrodes 5183 and 5087 and perform needed adaptations, as there are no programs designed specifically for these materials. The focus was on obtaining root and fill pass on 6.0-mm-thick plates. The work also examined the influence of this process on metallurgical effects for the distinct wires and compared the properties between them. Welding procedure development and mechanical performance tests, destructive and non-destructive, were conducted. The results show excellent performance of welded joints with both wires, and a slightly higher mechanical performance with 5087 wire-electrode.

Joining of galvannealed steel and aluminium alloy using controlled short circuiting gas metal arc welding process

Controlling the Fe–Al intermetallic layer thickness along the joint interface has remained a critical challenge in gas metal arc welding of galvanised steel and aluminium alloys. An attempt is presented here to join galvannealed steel and aluminium alloy sheets using a novel gas metal arc welding process that allows controlled short circuiting to reduce the rate of heat input significantly. The real time current and voltage transients during the process are monitored to estimate the rate of heat input and its influence on the formation of intermetallic phases and layer thickness. The results show that the intermetallic layer thickness can be controlled and good joint strengths can be achieved when the rate of heat input remains lesser than 130 J mm− 1 for the typical lap joint configuration considered here.

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 %.

Microstructural investigation of controlled short circuiting gas metal arc welding deposited aluminium–lithium alloy

Controlled short circuiting gas metal arc welding (CSC-GMAW) was investigated as a potential solid freeform fabrication (SFF) process for AA2199. The low heat input of the CSC-GMAW process resulted in a cooling rate on the order of 840–3500°C s−1 being realised during deposition. The solidification time was then calculated to range between 2–5 ms depending on the location within the weldment. The deposited material displayed a fine (4·3±1 μm) cellular structure, comparable to that previously reported for electron beam welding. Through comparison with the Kurz–Giovanola–Trivedi (KGT) model for microstructural development during solidification, the solidification front velocity (SFV) of the CSC-GMAW process was estimated to be ∼2–4·5×10−4 m s−1. Chemical analysis revealed lateral segregation of copper to the cell walls. TOF-SIMS revealed a homogeneous lateral lithium distribution, however depth profiling displayed some extent of lithium enrichment at the surface of the deposited material.On a examiné le soudage à l’arc sous protection gazeuse à court-circuit contrôlé (CSC-GMAW) comme processus potentiel de fabrication en forme libre solide (SFF) pour l’AA2199. Le faible débit de chaleur du processus de CSC-GMAW produisait une vitesse de refroidissement de l’ordre de 840 à 3500°C/s lors du dépôt. On a ensuite calculé que le temps de solidification variait de 2 à 5 ms, dépendant de l’emplacement dans la soudure. Le dépôt montrait une structure cellulaire fine (4·3±1 μm), comparable à la structure rapportée antérieurement pour le soudage par faisceau d’électrons. Par comparaison avec le modèle de Kurz–Giavanola–Trivedi (KGT) de développement de la microstructure lors de la solidification, on a estimé que la vélocité du front de solidification (SFV) du processus de CSC-GMAW était de ∼2 à 4·5×10−4 m s−1. L’analyse chimique a révélé une ségrégation latérale du cuivre sur les parois de la cellule. TOF-SIMS a révélé une distribution latérale homogène du lithium, cependant le profilage en profondeur a exposé une certaine zone d’enrichissement en lithium à la surface du matériel déposé.

Weld pool temperatures of steel S235 while applying a controlled short-circuit gas metal arc welding process and various shielding gases

The temperature determination of liquid metals is difficult and depends strongly on the emissivity. However, the surface temperature distribution of the weld pool is an important characteristic of an arc weld process. As an example, short-arc welding of steel with a cold metal transfer (CMT) process is considered. With optical emission spectroscopy in the spectral region between 660 and 840 nm and absolute calibrated high-speed camera images the relation between temperature and emissivity of the weld pool is determined. This method is used to obtain two-dimensional temperature profiles in the pictures. Results are presented for welding materials (wire G3Si1 on base material S235) using different welding CMT processes with CO2 (100%), Corgon 18 (18% CO2 + 82% Ar), VarigonH6 (93.5% Ar + 6.5% H2) and He (100%) as shielding gases. The different gases are used to study their influence on the weld pool temperature.

Effect of Current Waveform on Metal Transfer in Controlled Short Circuiting Gas Metal Arc Welding

With high-speed welding inverter and precisely controlling the welding current with arc-bridge state, advanced pulse current waveforms can be produced to optimize the transfer characteristics of short circuiting transfer welding. In this paper, the images of droplet/wire, and the transient data of welding current and arc voltage were simultaneously recorded to study the influence of peak arcing current, background arcing current and tail-out time on the stability of short circuiting transfer process. It was found that maximum short circuiting transfer stability is reached under specific welding conditions. Any deviation from these conditions will cause abnormal rises in arc voltage indicating instantaneous arc extinguishing and greater spatter. Optimal welding conditions were obtained to achieve the maximum stability of short circuiting metal transfer process.

Probing current, voltage and metal transfer characteristics in pulsed arc and in conventional and a novel low energy input short arc GMAW

An accurate control over the rate of heat input and material deposition is essential in gas metal arc welding for its greater use in joining of sheet metals. Although pulsed current gas metal arc welding facilitates excellent control over the rate of material deposition, greater rate of heat input due to high peak pulses remains critical. Gas metal arc welding with conventional short-circuiting mode of metal transfer provides a significant reduction in the rate of heat input while an uninterrupted and spatter-free material deposition is too difficult to achieve. A novel low energy input short-circuiting gas metal arc welding is proposed here that facilitates short-circuiting mode of metal transfer with a very low power detachment phase. Here we present an investigation on the current, voltage and consequent metal transfer sequences in pulsed current, and the conventional and the novel low energy input short-circuiting gas metal arc welding processes of high strength automotive steel sheets. It is realized that the low energy input short-circuiting process could provide uninterrupted and nearly spatter-free metal transfer at significantly reduced electrical power in comparison to both pulsed current and conventional short-circuiting gas metal arc welding. The low energy input short-circuiting process could also facilitate fairly small angular distortion of weld joints.

Process Characteristics of Inverter Type GMAW Power Source Under Static and Dynamic Operating Conditions

The process characteristics of inverter type gas metal arc welding (GMAW) power source under static and dynamic operating conditions of welding have been studied during weld bead on plate deposition of 12 mm thick mild steel plate by using 80%Ar + 20%CO2 gas shielding. The power source characteristics considered in the present investigation is response to voltage and current variation under different modes of the power source operations as conventional GMAW, pulsed gas metal arc welding (P-GMAW), dual pulse gas metal arc welding (DP-GMAW), and modified short circuit (waveform controlled metal transfer) gas metal arc welding (MS-GMAW) processes. It is observed that in all the modes of power source operations under different conditions of welding, the increase of wire feed rate (WFR) linearly enhances the welding/mean current and arc voltage. It is further observed that using MS-GMAW process provides better weld quality with respect to less spatter generation than those of the GMAW, P-GMAW, and DP-GMAW processes.