Short-circuiting Gas Metal Arc Welding 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

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.

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.

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 %.

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.

Impacts of external longitudinal magnetic field on arc plasma and droplet during short-circuit GMAW

In gas metal arc welding, electromagnetic force, plasma stream force, gravity, and surface tension are the most important factors that affect metal transfer and spatter generation rate. In this paper, different kinds of external electromagnetic fields were introduced to gas metal arc welding (GMAW). The photos of arc plasma and droplet and electric signals covering welding current and arc voltage were acquired synchronously by an analysis and evaluation system based on LabView for GMAW. It was confirmed that the metal transfer frequency was improved, and spatter generation rate was diminished under controls of external electromagnetic fields. The influencing rules of external electromagnetic fields on electromagnetic force, the gravity, the plasma stream force, and surface tension were studied by three physical models, and the mechanism of external electromagnetic fields was revealed. This paper is for the purpose of discussing these factors and will make a profit for the application of electromagnetic coupling control to short-circuit GMAW.

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.

Observation of weld pool profiles in short-circuiting gas metal arc welding

Short-circuiting gas metal arc welding (GMAW), a main joining process for light-weight steel structures, is a complex, strongly non-linear, dynamic, and multi input/output process. It is essential to implement real-time monitoring and control of this process in order to ensure product quality and service reliability of the welded structures. In this paper, a low-cost and compact vision system is developed to observe the weld pool surface profiles in short-circuiting GMAW under different levels of welding current, welding speed, and contact tube-to-workpiece distance. Appropriate technical means are employed to lower the arc light interference and to synchronize the image grabber with the short-circuiting stage. Clear and complete weld pool surface images are captured by Observation from the Front of the Pool (OFP) and Observation from the Rear of the Pool (ORP), and the weld pool shape and size are determined. The two viewing methods (OFP and ORP) can detect the pool width reliably, but the detected pool length has a larger error. A modification method is proposed. The weld pool images are captured by Observation from the Side Position (OSP), and the tilted slope of the pool surface and the reinforcement height are detected in this way. Through modification, the measurement accuracy of the pool length is improved. This lays a foundation for the process control of short-circuiting GMAW, but further investigation is still required as a next step.

Approximate entropy—a new statistic to quantify arc and welding process stability in short-circuiting gas metal arc welding

Based on the phase state reconstruction of welding current in short-circuiting gas metal arc welding using carbon dioxide as shielding gas, the approximate entropy of welding current as well as its standard deviation has been calculated and analysed to investigate their relation with the stability of electric arc and welding process. The extensive experimental and calculated results show that the approximate entropy of welding current is significantly and positively correlated with arc and welding process stability, whereas its standard deviation is correlated with them negatively. A larger approximate entropy and a smaller standard deviation imply a more stable arc and welding process, and vice versa. As a result, the approximate entropy of welding current promises well in assessing and quantifying the stability of electric arc and welding process in short-circuiting gas metal arc welding.

Fuzzy logic based quality monitoring in short-circuit gas metal arc welding

Conventional methods, e.g. destructive and non-destructive testing methods, are expensive and time-consuming; therefore, possibilities of online and automated quality control of a welding process during welding as such are investigated. The paper deals with the possibilities of application of fuzzy logic to the analysis of weld quality, particularly assessment of the weld surface condition by means of measurable electric signals emitted during welding. A simple fuzzy inference system was realised which could relatively efficiently assess the weld quality on the basis of time variations of the welding voltage and short-circuit time in a certain time window.

Achieving cost savings with innovative welding and examination techniques

In an effort to maximize quality and production in both field and shop fabrication while minimizing cost, Fluor has assessed new and innovative welding and examination technologies. Welding applications, power sources, arc transfer modes, and shielding gas mixtures using various semi-automatic processes were compared. The strategies for the selection of these welding variables, as well as the successful application of a modified short-circuiting gas metal arc welding process to carbon, alloy, and stainless steels are discussed. The optimized process combination can achieve three times the deposition rate and one-tenth of the repair rate commonly obtained with traditional processes. In weldment examinations, a modified phased array ultrasonic technique is presented. As an alternate for radiography, phased array technology allows for 10 times lower inspection times and lends itself to an ideal weld-and-check methodology. Additional cost savings and further, productivity improvements have been achieved by combining these novel welding and examination techniques. This technology has demonstrated itself with a supporting track record on several major construction projects in North America.

Intelligent monitoring and recognition of the short-circuiting gas—metal arc welding process

This paper introduces an intelligent system for monitoring and recognition of process disturbances during short-circuiting gas-metal arc welding. It is based on the measured and statistically processed data of welding electrical parameters. A 12-dimensional array of process features is designed to describe various welding conditions and is employed as input vector of the intelligent system. Three methods, such as fuzzy c-means, neural network and fuzzy Kohonen clustering network are used to conduct process monitoring and automatic recognition. The correct recognition rates of these three methods are compared.