Plasma Arc Welding Research Articles

Study on the Molten Pool Fluid Behavior of PAW-Cable-Type Seven-Wire GMAW Hybrid Welding

Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of the molten pool temperature field and flow field and experimental verification were conducted on Q235 thin plate hybrid welding with cable-type wire to explore molten pool fluid behavior. The simulation results show that keyholes form in the molten pool due to the strong penetration ability of a plasma arc and then the evolved pores by the surface tension float out of the molten pool. When the GMAW welding current increases, both the length and width of the weld pool enlarge, the weld reinforcement increases and the flow rate of molten metal in the weld pool also speeds up. While the PAW current increases, the weld pool length also increases and the molten metal in the weld pool significantly flows faster, but the weld reinforcement decreases. When the welding speed increases, the weld pool length and fusion depth decrease, but the reinforcement will first increase and then decrease. The experimental results are in strong agreement with the simulation results. It shows that the numerical analysis model established in this paper is accurate, laying a certain theoretical foundation for the popularization of PAW-cable-type seven-wire GMAW hybrid welding.

Influence of the metal flow in the keyhole molten pool on the molten pool stability in continuous variable polarity plasma arc keyhole vertical-up welding

The metal flow of the keyhole molten pool affects weld pool stability and weld formation vitally during continuous variable polarity plasma arc welding (VPPAW). A novel “keyhole inside alternating oscillation” (KIAO) thermal-mechanical coupling model was developed to study the influence of keyhole molten pool metal flow on molten pool stability. This model can achieve the oscillation effect of heat-force on the molten pool during the electrode negative (EN) and electrode positive (EP) phase. A heat source, with keyhole channel backward bending, was used to create a keyhole backward deviation along the workpiece thickness. An asymmetric arc pressure source was adopted to ensure asymmetric distribution of the arc pressure. The metal flow of the stable and cut molten pool are calculated in continuous VPPAW process, and the conditions needed for the stable existence of the molten pool are obtained. The molten pool must have sufficient liquid metal which needs to flow as follows: in the front of the upper molten pool, a part of the metal flows in the form of “two-way rotating confluence” along the keyhole side wall to the rear of the lower molten pool, and part of the metal flows backwards to the rear of the upper molten pool. The metal at the rear of the lower molten pool flows upwards along the keyhole side wall. Under the combined action of these flow behaviors, the expansion speed of the leading edge of the keyhole is approximately equal to the shrinkage speed of the keyhole trailing edge, and the keyhole molten pool is stable. The stability of the bottom molten pool has a significant impact on the overall molten pool stability. The calculated fusion line and the offset distance between the central axis of the keyhole exit and the welding torch corresponded with the measured results.

Observation of Microstructure and Mechanical Properties in Heat Affected Zone of As-Welded Carbon Steel by Using Plasma MIG Welding Process

Plasma MIG welding is a hybrid welding process that combines two welding methods of conventional metal inert gas (MIG) welding with plasma arc welding. This study investigates the effect of plasma and plasma current values on the microstructure and microhardness properties of welded carbon steel plates. It was found that utilization of the plasma has resulted in a refined microstructure in the heat affected zones (HAZ), and a decrease in microhardness values as compared to conventional MIG welds. This potentially increases the ductility of the plasma MIG weldments. Furthermore, decreasing the plasma currents would result in the decrease of microhardness and grain sizes, thus further increasing the ductility of the welds.

Correlation of reflected plasma angle and weld pool thermal state in plasma arc welding process

Keyhole behavior and weld pool thermal state have a great influence on the stability of the plasma arc welding process, detection of the weld pool thermal state plays a very important role. Deviation distance of the keyhole exit was proved to be a candidate parameter to characterize weld pool thermal state. However, such a backside detection method is often limited by space. This research proposed a method to evaluate the weld pool thermal state by the front side reflected plasma angle. The correlation is verified with varying of welding current, welding speed, and plasma gas flow rate. It was found that: before the fully penetrated keyhole is formed, the reflected plasma angle increases with the increase of arc penetration ability; after the fully penetrated keyhole is formed, the reflected plasma angle decreases with the increase of arc penetration ability. In the fully penetrated keyhole welding process, the phenomenon that the reflected plasma angle is positively correlated with the deviation distance of the keyhole exit proves that the reflected plasma angle is related to the weld pool thermal state. This work proposes a new front side detection method to evaluate the weld pool thermal state and lays the foundation for the control of plasma arc welding process.

Effect of pulsed power ultrasonic vibration on keyholing/penetrating capability in waveform-controlled plasma arc welding

Effect of pulsed power ultrasonic vibration on keyholing/penetrating capability in waveform-controlled plasma arc welding

Heat Accumulation, Microstructure Evolution, and Stress Distribution of Ti–Al Alloy Manufactured by Twin‐Wire Plasma Arc Additive

Herein, the deposition of a Ti–Al(48 at%) alloy via twin‐wire arc additive manufacturing (WAAM) using plasma arc welding (PAW) and tungsten inert gas (TIG) welding arc sources is presented. The microstructure and the phase composition of different regions of the alloy are analyzed using metalloscopy and X‐ray diffraction. The transient temperature field and residual stress distribution are measured before and after the process, respectively. A transient thermostress model is established using the finite‐element method. Results show that the alloy is composed primarily of α2‐Ti3Al and γ‐TiAl phases, while the microstructure evolution during the Ti–Al(48 at%) alloy deposition process is described. The thermal conductivity in the lower region of the alloy far exceeds that in the middle and upper regions. The thermal conductivity is smaller in the upper region and the midregion, resulting in the increase in heat accumulation. Due to arc shrinkage and reduced heat input, the PAW process reduces the heat accumulation and stress distribution differences more effectively than the TIG process.

Bypass-current plasma arc welding of aluminum alloy: thermal behavior, residual stress, and distortion

Bypass-current plasma arc welding of aluminum alloy: thermal behavior, residual stress, and distortion

Mechanical properties of fusion welded ceramics in the SiC-ZrB2 and SiC-ZrB2-ZrC systems

Mechanical properties of welded SiC-ZrB2 and SiC-ZrB2-ZrC ceramics were measured up to 1700 °C. Commercial powders were hot pressed, machined into coupons, and preheated to 1600 °C before joining the ceramics using either tungsten inert gas welding or plasma arc welding. Toughness of the parent materials was 3–4 MPa*m1/2 which decreased after welding to 2–2.5 MPa*m1/2. Strength of the SiC-ZrB2-ZrC parent material was ~700 MPa at 25 °C, ~300 MPa at 1700 °C, and retained 40–60% of this strength once welded. Strength of the SiC-ZrB2 parent material was ~600 MPa at 25 °C and 1700 °C and retained 20–30% of this strength once welded. Griffith analysis indicated that the strength in the parent materials was controlled by the size of SiC clusters while strength of welds was controlled by the size of pores in fusion zones. Therefore, removal of pores in produced fusion zones should be investigated to improve strength of future ceramic welds.

Multiscale feature extraction and its application in the weld seam quality prediction for plasma arc welding

As a complex thermo-physical process, the plasma arc welding (PAW) is easy to be unstable due to external interferences. Weld quality monitoring is important for intelligent robot PAW welding. Due to the different instability mechanisms, it is difficult to obtain high adaptivity and accuracy with features extracted in a single time window. In this paper, a novel feature extraction method based on sliding multiscale windows is proposed to improve model accuracy and calculation speed. A group of windows with different time widths are established to extract multiscale information. Windows slide throughout welding process and are synchronized on the timeline for feature correlation. The welding current and arc voltage are processed to extract features inside windows, including signal denoising by discrete wavelet transform (DWT) and dimension reduction by primary components analysis (PCA). Based on the feature vectors extracted from multiscale-windows, support vector machine (SVM) with radial basis function (RBF) kernel is used. The best window width is determined automatically by model training. The proposed method is used to predict weld quality for PAW in the field of shipbuilding. The results show that the model with multiscale feature extraction is helpful to improve prediction precision and recall ratio.

Weld reliability characteristics of AISI 304L steels welded with MPAW (Micro Plasma Arc Welding)

Micro plasma arc welding for metal coils, metal diaphragms, and others is a popular procedure in the sheet metal industry. The characteristic function is discussed below. In soldering, the square ass is used and no filler cables are used. Welding is performed on all steels at values of 0.25 mm fixed input parameters. Microstructure, kernel size, rigidity, and tensile strength are referred to as the welding features. High-quality (99.99%) argon gas is used immediately after welding to mask atmospheric absorption of protective gas and trailing gas. Peak flow, background flow, pulsed frequency, pulse length, plasma gas flow rate, welding rate, and other parameters are all influenced by the sophisticated pulsed MPAW method The core welding process parameters for a microscope plasma arc weld are maximum current, background current, pulse speed, and pulse duration. Austin stainless stones, such as AISI (321, 316Ti, 316L, and 304L) have been mounted in the MPAW pulse current series The results reveal that the AISI 304L reaches the maximum welding properties of all of the materials in the study under the same welding conditions.

Effect of post welding heat treatment on the weld quality of micro plasma arc welded SS-316L thin sheet

High thermal gradient formed during the fusion welding process results in development of undesirable residual stress in the weldments. This stress is developed due to restraint by the parent metal during weld solidification. The high heat input results in non-uniform heat distribution across the weld region in other words non-uniform microstructural development across the weld region and hence the mechanical properties of the joint are often not uniform. In order to avoid inhomogeneity in the mechanical properties and also to reduce/eliminate undesirable residual stress, the welded samples are given post welding heat treatment. In this research, 500 µm thin SS-316L sheets are welded using micro plasma arc welding process and then the welded specimens are heat treated. The welding experiments are conducted by varying welding speed, welding current and stand-off distance. Weld bead microstructure, micro-hardness, ultimate tensile strength (UTS), yield strength and percentage elongation are determined before and after heat treatment. The effects of welding heat input and process parameters on the measured weld qualities are studied. Analysis of variance is also performed to estimate the influence of factors and their interaction on the weld quality. The post weld heat treatment results in an increase in the grain size of the HAZ and is found in the range of 38.96 µm to 56.22 µm whereas for as-welded samples it is in the range of 29.88 µm to 50.40 µm. The average UTS value of the heat treated samples is increased by 9.9% compared to the as-welded samples. The hardness of the fusion zone varies in the range of 175-215 HV.

Microstructure And Corrosion Behavior of Wc-Co Composite Coating on Ss 316l Fabricated by Plasma Arc Welding

Microstructure And Corrosion Behavior of Wc-Co Composite Coating on Ss 316l Fabricated by Plasma Arc Welding

Investigation of Microstructure Evolution, Mechanical and Corrosion Properties of Saf 2507 Super Duplex Stainless Steel Joints by Keyhole Plasma Arc Welding

Investigation of Microstructure Evolution, Mechanical and Corrosion Properties of Saf 2507 Super Duplex Stainless Steel Joints by Keyhole Plasma Arc Welding

Modeling of AMg6 alloy recrystallization in the forged layer during the overlay welding of a material in the process of hybrid additive manufacturing

The regularities of static recrystallization during the welding of metal layer over the face of a prismatic specimen pretreated by plastic deformation are studied. This problem is of interest in selecting the rational parameters for the process of hybrid additive manufacturing of light and high-strength linear elements of segmented structures made of aluminum-magnesium alloys via layer-by-layer forging with a pneumatic hammer. For this purpose, the two independent problems of the one-sided forging of a prismatic specimen and temperature evolution during the plasma-arc welding of a layer over the same specimen are solved numerically. The fields of accumulated deformations and the history of temperature changes in the specimen are used to calculate the volume fraction of statically recrystallized material in the work-hardened layer under the influence of a thermal cycle temperature. The forging calculation was performed based on the LS-DYNA® package, the thermal problem was solved in Comsol Multiphysics®, and the fraction of recrystallized material was calculated by making use of the Wolfram Mathematica system. In the numerical model, the impact of the pneumatic hammer was estimated by means of a strain-gauged steel target, and then was verified by evaluating the distortions of the cross-section of the forged bar made of AMg6 alloy measured in the experiment. The thermal effect was calculated taking into account the PI controller, which automatically controls the overlaying process in the hybrid additive manufacturing plant. The volume fraction of a statically recrystallized material was calculated using Avrami's law and data on the dependence of the time of 50% transformation of the material on the accumulated deformation and the temperature taken from the literature on aluminum-magnesium alloy 5083, which is similar to AMg6. The model predicts a high sensitivity of the fraction of recrystallized material to previous plastic deformation and to the maximum temperature in the thermal cycle of overlay welding, and therefore a more localized boundary layer of recrystallized material compared to the boundary layer in plastic deformation. The results of calculation demonstrate the effectiveness of layer-by-layer pressure shaping strategies for providing deep-layer plastic deformation. In terms of the degree of recrystallization, the use of rational modes of overlay welding and forging can ensure the synthesis of products with high strength and ductility characteristics in hybrid additive manufacturing processes.

Optimization of the weld characteristics of plasma-arc welded titanium alloy joints: an experimental study

ABSTRACT Titanium alloys especially Ti6Al4V have wide commercial applications in various sectors of aerospace manufacturing industries owing to their excellent physical, mechanical, and thermal characteristics. Titanium alloys are mostly welded by conventional gas tungsten arc welding process which gives compromisingly higher productivity. There are welding technologies like plasma arc welding that provide high arc energy density results in good-quality welds with higher productivity. In this present investigation, the efforts were put to study and optimize the important welding variables, such as weld current, speed, plasma gas flow rate, and constricted arc length. These parameters govern the most desired characteristics of weld bead such as weld bead width, complete penetration, fusion zone area, and prior β grain size. Optimum solutions were found through desirability-based multi-response optimization by response surface methodology. Microstructural features and mechanical properties were evaluated for the joints welded using the optimum process parameters and found that characteristics are well within the desired criteria.

Fatigue and Fracture Behavior of Cryogenic Materials Applied to LNG Fuel Storage Tanks for Coastal Ships

The aim of this study is to investigate the applicability of automatic plasma arc welding (PAW) to cryogenic materials used in liquefied natural gas (LNG) fuel storage tanks based on experimental data. The mechanical properties of the materials were tested at room and cryogenic temperatures to investigate the fatigue and fracture performances of weld joints made by PAW. In addition, the influence of welding parameters on the welded joints such as material types and temperature were considered in this experimental study. Based on the results obtained by this experimental study, it was observed that the experimental results of all materials at room and cryogenic temperatures satisfied all the requirements of each mechanical test. Finally, we propose the experimental results of PAW that can be used in the structural design of LNG fuel storage tank applications.

Relationship among Welding Defects with Convection and Material Flow Dynamic Considering Principal Forces in Plasma Arc Welding

The material flow dynamic and velocity distribution on the melted domain surface play a crucial role on the joint quality and formation of welding defects. In this study, authors investigated the effects of the low and high currents of plasma arc welding on the material flow and thermodynamics of molten pool and its relationship to the welding defects. The high-speed video camera (HSVC) was used to observe the convection of the melted domain and welded-joint appearance. Furthermore, to consider the Marangoni force activation, the temperature on the melted domain was measured by a thermal HSVC. The results revealed that the velocity distribution on the weld pool surface was higher than that inside the molten weld pool. Moreover, in the case of 80 A welding current, the convection speed of molten was faster than that in other cases (120 A and 160 A). The serious undercut and humping could be seen on the top surface (upper side) and unstable weld bead was visualized on the back side (bottom surface). In the case of 160 A welding current, the convection on the weld pool surface was much more complex in comparison with 80 A and 120 A cases. The excessive convex defect at the bottom side and the concave defect at the top surface were observed. In the case of 120 A welding current, two convection patterns with the main flow in the backward direction were seen. Almost no welding defect could be found. The interaction between the shear force and Marangoni force played a solid state on the convection and heat transportation processes in the plasma arc welding process.

Penetration/keyhole status prediction and model visualization based on deep learning algorithm in plasma arc welding

Penetration/keyhole status prediction and model visualization based on deep learning algorithm in plasma arc welding

Strain effect on microstructural properties of SUS 304L joint by PAW+GTAW

JIS SUS 304L stainless steel was joined by a combination welding process of plasma arc welding and gas tungsten arc welding (PAW+GTAW). Then pre-strain treatment on 304L welded joint of 9 % was carried out using uniaxial quasi-static tensile at room temperature. Effect of strain on microstructure evolution in joint was analyzed by field emission scanning electron microscope (FESEM) and on mechanical properties was also studied. The results indicated that the pre-strain rate of 304L joint showed inhomogeneity including 3 % in the weld metal and 13 % in the heat-affected zone (HAZ), which induced martensitic transformation occurring in HAZ. Tensile strength of the joint increased from 700 MPa as welded to 804 MPa after pre-strain treatment at room temperature, and it reached 1700 MPa from 1480 MPa as welded at low temperature of −196 °C. Impact energy in the HAZ was the least among the whole 304L weld, but it was still 94 J at −196 °C after pre-strain. The fracture morphology showed large numbered of cleavage steps with elongated parabolic dimples.

Physical mechanisms of fluid flow and joint inhomogeneity in variable-polarity plasma arc welding of thick aluminum alloy plates

A variable-polarity plasma arc (VPPA) is an effective energy source for the welding of thick aluminum alloy plates. However, the mechanisms influencing the fluid flow and the inhomogeneous distribution associated with thick-plate VPPA welding remain unclear, restricting the application of this technology in welding of thick aluminum alloys. Here, the relationship between the microstructure of the weld bead, energy transfer, and fluid flow is clarified by combining in situ three-dimensional x-ray imaging and multi-physics modeling. We find that heat conduction at the keyhole wall is the main factor influencing the morphology of the weld pool. The plasma arc pressure hinders the upward flow of liquid metal, while shear forces promote this flow. This causes the metal close to the weld pool surface to flow slowly, while that inside the weld pool has much higher velocity. It is also concluded that the large crystal size observed in the lower layer of the weld is partly caused by heat treatment from the upper layer of the thick plate. An eddy with a high flow velocity to the rear of the weld pool destroys the crystal-growth process, and this is considered to be one of the reasons for fine crystals appearing in the upper part of the weld. The mechanisms revealed here will help us to guide the use of VPPA technology in the production of stable, high-quality welding of thick aluminum alloys.