Double-electrode Gas Metal Arc Welding Research Articles

Robotizing double-electrode GMAW process through learning from human welders

Gas metal arc welding (GMAW) is the most robotized arc welding process and most widely used process for wire arc additive manufacturing (WAAM). Double-electrode GMAW (DE-GMAW) is its novel modification achieved by adding a second/bypass electrode. It provides the capability to freely adjust the base metal current (heat input) without changing the wire current (mass input). However, it must be robotized in order to be adaptive to manufacturing variations and constraints. Due to the complexity of the process, we propose learning from human welders through their attempts to adjust the bypass electrode in collaboration with the robotized GMAW. To generalize human success using a follower robot/surrogate, the distance between the wire and bypass electrode is proposed as the process state to quantify human observation and operation. As such, Inertial Measurement Unit (IMU) sensors are integrated to track the wire and bypass electrode operated by both the lead robot and the human welder. To interpret human adjustments per arc observation, a Convolutional Neural Network (CNN) is employed to process arc images and calculate the distance. The automatically obtained distance labels from IMU signals are used to train the CNN; however, they are noisy and inaccurate. Thus, the CNN is finely tuned through transfer learning using manually labeled distances. With accurately automatically calculated distances from the finely tuned CNN for all the data, the demonstrations from human welders are analyzed. The generalized knowledge is implemented by a robotic surrogate, substituting for the human welder to fully automate the DE-GMAW. Experiments demonstrated the superior performance of the fully robotized, and adaptively controlled, DE-GMAW process.

Microstructures and Electrical Resistivity of Aluminum–Copper Joints

Using pulsed double electrode-gas metal arc welding, aluminum wires are joined to copper plates with fillers of different fractions of silicon. Two layers of different microstructures are formed near the Al-Cu interface: one consists of a hypoeutectic microstructure of α (Al) + Al2Cu, and the other consists of an intermetallic compound (IMC) of Al2Cu. Increasing the heat input causes increases in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. Si suppresses the growth of the IMC layer and assists the growth of the layer of the hypoeutectic microstructure. The effects of the interface microstructures and chemical compositions on the electric resistivity of the joints are analyzed. The electric resistivity of the joints increases with the increase in the thicknesses of the IMC layer and the layer of the hypoeutectic microstructure. The law of mixture is used to calculate the electric resistivity of the joints, which is in accordance with the experimental results.

Effect of Different Filler Wires on Mechanical Property and Conductivity of Aluminum-Copper Joints.

The 1060 aluminum and T2 copper were joined by the pulsed double electrode gas metal arc welding (DE-GMAW) brazing method by using four types of filler wires, namely pure aluminum (Al) ER1100, aluminum-magnesium (Al–Mg) ER5356, aluminum-silicon (Al–Si) ER4043, and Al–Si ER4047, respectively. The effects of different types of filler wires on intermetallic compounds, microhardness tensile strength, and conductivity of joints were investigated. The results showed that a lot of brittle intermetallic compounds laying in the copper side brazing interface zone were generated using pure Al, Al–Mg, and Al–Si filler wires, which caused the change of microhardness, tensile strength, and the conductivity of joints. Meanwhile, with the increase in Si elements contents for Al–Sifiller wires, the thickness of the intermetallic compound layers decreased obviously, which was only up to 3 µm and the conductivity of the joints decreased. In addition, the microhardness, tensile strength, and the conductivity of the joints, when using Al–Sifiller wires, was higher than that using pure Al and Al–Mg filler wires. Hence, in comparison to the pure filler wires and Al–Mg filler wires, the Al–Si filler wires were more suitable for Al–Cu joints by DE-GMAW as Si element content was lower.

Microstructures and mechanical behavior of aluminum-copper lap joints

5052 aluminum alloy and pure copper (T2) are joined, using a low heat input pulsed double-electrode gas metal arc welding (DE-GMAW)-brazing method with AlSi12 filler metal. The effects of welding current (heat input) on the microstructure and mechanical behavior of the joints, which consist of Al-Al welding zone and Al-Cu brazing zone, are investigated. The Al-Cu welding zone mainly consists of α-Al solid solution and Al-Cu eutectic phase in coral-like shape. There exists a layer of Al2Cu intermetallic compound (IMC) in the Al-Cu brazing zone. Using the theory of thermal activation process, a quadratic relation between the thickness of the IMC layer and welding current intensity is derived. The experimental result supports this relationship. The shear strength of the Al-Cu joints first increases with the increase of the welding current (heat input), reaches a maximum of 17.66MPa, and then decreases with the increase of the welding current due to the dispersion of the Al2Cu IMCs of large sizes in the Al alloy. Fracture of the Al-Cu lap joints occurs at three different positions, and the corresponding failure mechanisms are discussed according to the morphologies of fracture surfaces.

Microscopic structure and property of double-electrode gas metal arc welding of AZ31B magnesium alloy

This paper focuses on the research on double-electrode gas metal arc welding (DE-GMAW) of AZ31B magnesium alloy sheet with 2mm thickness. During the welding process, stable hybrid arc of metal inert gas (MIG) and tungsten inert gas (TIG) is employed as welding heat source. Optical and electron microscopes are used to observe the microstructures of the weld joint. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are employed to identify the components in fusion zone. Microhardness is also tested. When the MIG current is 80A, the perfect weld joint is obtained, though figures of fish scales are observed in all joints in the research. The fusion zone is formed by dendrites, where β-Mg17(Al, Zn)12 is dispersed. The hardness in fusion zone and heat affected zone (HAZ) is lower than that in base metal (BM). The average Vickers hardness of fusion zone and HAZ is about 58 and 56 respectively, while the Vickers hardness of BM is about 63.

Deposition Time and Thermal Cycles of Fabricating Thin-wall Steel Parts by Double Electrode GMAW Based Additive Manufacturing

The deposition time for fabricating the thin-wall part as well as the peak temperature of the substrate during the process was analyzed in the double electrode gas metal arc welding (DE-GMAW) based additive manufacturing (AM). The total deposition time and the interlayer idle time of the manufacturing process decreased with the increasing of the bypass current under the same interlayer temperature and the same deposition rate. The thermal cycling curves illustrated that the peak temperature of the substrate was lower in the DE-GMAW base AM under the same conditions. When depositing the thin-wall parts, the DE-GMAW based AM can reduce the heat input to the substrate and improve the fabrication efficiency, compared with the GMAW based AM.

Modeling and control of consumable DE-GMAW process

A novel and highly efficient consumable double-electrode gas metal arc welding (consumable DE-GMAW) method was introduced. A non-linear mathematical model for the dynamic DE-GMAW process was developed by adopting the method of equivalent current path, according to the dynamic characteristics of coupled arc and the rule of wire melting. A multi-input multi-output (MIMO) control scheme was proposed and simulated because coupled welding parameters are complicated and the high welding current of DE-GMAW can lead to welding defects. This scheme controlled the bypass arc by adjusting the bypass wire feed speed and controlled the base metal current by adjusting the bypass current. To test the effectiveness of the MIMO control scheme, a welding experiment was conducted. Results showed that the MIMO control scheme was effective. The base metal current was controlled at a nearly constant level, the welding process was stable, and a good weld appearance was obtained.

Numerical simulation of the effects of bypass current on droplet transfer during AZ31B magnesium alloy DE-GMAW process based on FLUENT

A modified Gaussian current density is put forward, which is used to simulate the dynamic process of AZ31B magnesium alloy double-electrode gas metal arc welding (DE-GMAW) droplet transfer. The process of droplet transfer in the AZ31B magnesium alloy DE-GMAW was simulated using FLUENT software. The influence of different bypass welding currents was investigated with a constant total current. The simulated results revealed that when the bypass current was 0 A, the process was the globular transfer type, the droplet transfer with a bypass current of 80 A was a projected transfer type and the droplet transfer at a bypass current of 170 A was a spray transfer type. The critical current is decreased so that spray transfer would occur at a lower current level in the DE-GMAW process. As the bypass current was increased, the shape of droplet changed from oval to round and the transition frequency of the droplet increased in a stepwise fashion. To confirm the accuracy of the simulated results, welding experiments were performed and the image processing method was used to obtain the droplet size. The simulated and experimental results were found to be in good agreement.

Forming characteristics of thin-wall steel parts by double electrode GMAW based additive manufacturing

A novel additive manufacturing (AM) system using double electrode gas metal arc welding (DE-GMAW) was developed to fabricate metallic products. The width of the deposited multi-layer parts decreased with the increasing of the bypass current and the deposited height increased in proportion to the bypass current under the same deposition rate. The height difference between arc striking point and arc extinguishing point in the deposited parts was reduced by the bypass arc. The coefficient of materials utilization increased more than 10% using DE-GMAW for depositing thin-wall parts within a certain range of bypass current. The DE-GMAW based AM shows promise to fabricate narrower thin-wall components with high deposition rate and has higher deposition efficiency, compared with the normal GMAW based AM.

Dynamic Model of Consumable Double-Electrode Submerged Arc Welding Process

Double-electrode submerged arc welding (DE-SAW) is a new variant of the innovative double-electrode gas metal arc welding (DE-GMAW) process. In order to control this process, its dynamic model needs to be established. To this end, this paper analyzes the melting physical process of the consumable DE-SAW to derive its dynamic model. To identify the parameters in the dynamic model, a series of experiments are designed and performed. Least-squares technique has been used to identify the parameters from the experimental data.

Analysis and Improvement of Metal Transfer Behaviors in Consumable Double-Electrode GMAW Process

Consumable double-electrode gas metal arc welding (consumable DE-GMAW) is the efficient improvement of DE-GMAW. Due to the variety of coupled arc and metal transfer behaviors, this paper applies static force balance theory to analyze the changes in the forces acting on the main and bypass droplets separately. For main torch, the bypass arc changes the forces affecting on the main droplet, and the main metal transfer becomes more desirable. For bypass torch, with direct current electrode negative (DCEN) polarity, the volume of droplet is big and not easily transfers to the weld pool. In order to improve the bypass metal transfer, a method has been proposed which adds CO2 to pure argon shielding gas to change the forces affecting on the bypass droplet. Then, the welding experiment is carried out to test the effectiveness of this method. It is found that bypass droplet transfers easily and the diameter of bypass droplet is decreased significantly. Also a good weld appearance is acquired.

Numerical simulation of AZ31B magnesium alloy in DE-GMAW welding process

The prerequisite to predict the welding temperature field accurately is to select the thermal efficiency η correctly. In this paper, the AZ31B magnesium alloy was used to study the thermal efficiency η of the bypass arc in double-electrode gas metal arc welding (DE-GMAW) process. The experimen- tal molten pool images were captured using a charge-coupled device (CCD) camera. Then, the molten pool size was extracted using an image-processing algorithm. A finite element model capturing the features of DE-GMAW welding was established by using ANSYS software. The simulated values of the molten pool size were obtained according to the numerical simulation results of the tem- perature field in DE-GMAW welding. By comparing the simulated molten pool sizes with the experimentally mea- sured values, it was found that the best match is obtained when η=0.28∼0.32. In addition, the simulation results show that when only the bypass current decreases, the weld width and the weld penetration depth, as well as the heat input of the base metal, increase. These results are in good accordance with the experimental observations.

Study on the Force Analysis of Droplet in Pulsed Double-electrode Gas Metal Arc Welding and Design Current Waveform

A method for high efficiency and low heat input, pulsed double-electrode gas metal arc welding(DE-GMAW), joining of aluminium to steel is presented. In order to achieve the droplet steadily transfer at the process of welding, analyzing the bypass arc influence factors of the current density. The electromagnetic force action mechanism of the Pulsed DE-GMAW droplet transfer is established. Under the circumstance of the base metal is pulse current, studying on designing three forms of the bypass waveform and the base metal matching forms for constant current, alternate pulse current and synchronous pulse current, respectively. Use a high speed camera to capture the droplet transfer image for experiment comparison and verification. The results show that the different welding current waveform and the matching form would lead to the change of the forces exerted on the welding droplet, thus the welding process stability and weld quality is found changing. The pulsed DE-GMAW welding process is stability, the droplet transfer is uniform and the weld shape is smooth and beautiful by using of synchronous pulse current.

Welding process of consumable double electrode with a single arc GMAW

Double-electrode gas metal arc welding (DE-GMAW) was recently developed to control the current through the workpiece at a desired level when the welding productivity was increased. A novel welding method entitled consumable double electrode with a single arc GMAW (consumable DESA-GMAW) was proposed to further enhance the welding productivity by replacing the non-consumable electrode in DE-GMAW with a consumable electrode. The consumable DESA-GMAW system can work stably with appropriate welding parameters. In this paper, the effects of control variables including the voltage of the main power source and slave power source as well as the wire feed speed of the main wire and bypass wire on the current distribution between the workpiece and bypass wire were studied. The effects of the variables on arc behavior and metal transfer process were also studied. The ratio of the current through the bypass wire to the main wire can be increased by decreasing the main power source voltage, increasing the slave power source, or increasing the main wire feed speed. However, a higher ratio obtained by modifying a single control parameter may negatively influence the regular metal transfer process.The ratio of the current through the workpiece to the main filler wire can be most effectively decreased with a combination of relatively lower main power source voltage and higher slave power source voltage.

Numerical and Experimental Study of Temperature Field for Double Electrode Gas Metal Arc Welding

Based on the features of double electrode gas metal arc welding (DE-GMAW), a new hybrid heat-source model for DE-GMAW was proposed. Using this heat-source model, the temperature fields of DE-GMAW with different welding parameters were simulated. According to the simulation results with different welding parameters, the influence of welding parameters to the heat input to base metal in DE-GMAW were analyzed. To verify the rationality of the hybrid heat-source model of DE-GMAW, the simulation results of the temperature field were compared with the experimental results with same welding parameters. The research results indicate that under the same total current, the heat input to base metal decrease gradually with the increase of by-pass current. In addition, the closer to the welding line from the measured point the greater decrease rate of the heat input to base metal. By the study and comparison of the thermal cycle curve of measured points, the simulation results were in good agreement with the experimental results. These results indicate that the calculated temperature field is accurate and the hybrid heat-source model is rational.

Double-electrode arc welding process: Principle, variants, control and developments

Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100A base current for 1.2mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment.

Metal Transfer Behavior of Consumable DE-GMAW

Consumable double-electrode gas metal arc welding (consumable DE-GMAW) is a novel and high efficient welding method. According to the different polarity of two electrodes in consumable DE-GMAW, the metal transfer behaviors are analyzed by using the state force balance theory. For main torch with direct current electrode positive polarity, the arc root area is enlarged by bypass arc and increased electromagnetic force promotes main metal transfer. For bypass torch with direct current electrode negative polarity, the electromagnetic force does not work on the melting area. Only gravity force is major detaching force. The volume of bypass droplet is large and not easily detache to the weld pool.

Multi-Input Multi-Output Control of Consumable DE-GMAW

A novel and high efficient consumable double-electrode gas metal arc welding (consumable DE-GMAW) method has been introduced. Because of the coupled welding parameters, a multi-input multi-output (MIMO) control scheme was proposed and tested, which controlled the bypass arc by adjusting the bypass wire feed speed, and controlled the base metal current by adjusting the bypass current. Then, the welding experiment has been carried out. The results showed that the MIMO control scheme was effective. The base metal current was controlled at a nearly constant level and the welding process was stable. Also a good weld appearance was obtained.

Effects of Si and Mg elements on the microstructure of aluminum–steel joints produced by pulsed DE-GMA welding–brazing

Pulsed double electrode-gas metal arc welding–brazing of aluminum alloy and galvanised steel had been conducted using Al–Si and Al–Mg filler wires, respectively. Good formation and little deformation for the lap joint design were obtained. The microstructure, composition and phase analysis of weld joints were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron probe microanalyser and X-ray diffraction. By comparing the microstructures of weld joints using different welding wires, it was found that intermetallic compound layers formed at the interface of aluminum and galvanised steel weld seam using Al–Si filler wire were composed of a needle-like shape FeAl3 layer at the weld seam side and a flat Fe2Al5 layer at the galvanised steel side, while a Fe2Al5 intermetallic compound layer was present when using Al–Mg filler wire and it was tongue-like oriented toward the galvanised steel side, and a FeAl3 zigzag-like intermetallic compound layer was also found at the aluminum side. After the weld samples were peeled down using Al–Si filler wire, the Fe0·7Al3Si0·3 phase was detected on the peeled surface of the weld joint. By comparing the intermetallic compounds formed in the weld seam using different welding wires, it indicated that Si had the effects to inhibit the formation of the Fe2Al5 intermetallic compound by reducing the diffusion rate of Fe by exhibiting the Al–Fe–Si intermetallic compound. Under the constant total current and the same bypass current, the strength of weld joints using Al–Si filler wire is larger than the strength of weld joints using Al–Mg filler wire by tension tests.

Consumable double electrode with a single arc GMAW

Double-electrode gas metal arc welding (DE-GMAW) was developed to control the heat input to the work piece when the filler wire deposition rate was increased. Consumable DE-GMAW was developed to enhance the welding productivity by replacing the non-consumable electrode in DE-GMAW with a consumable electrode. However, the process of consumable DE-GMAW was unstable without a particular control system. In order to improve the stability of the welding process on condition of keeping the main characteristics of DE-GMAW, a novel welding method named consumable double electrode with a single arc (DESA)-GMAW was proposed. In this welding system, there were two consumable electrodes but only one arc. The distance between the tips of the main wire and the bypass wire mainly determined whether the welding method was consumable DESA-GMAW or consumable DE-GMAW. The welding process could be very stable with appropriate welding parameters: one filler wire kept arcing stably with regular metal transfer process, and the other filler wire was kept short-circuited with workpiece all through the time and was fed into the welding pool stably and smoothly. The transverse section of the weld bead was analyzed, and it was found that the penetration could be effectively decreased with high metal deposition rate by using consumable DESA-GMAW.