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Objectives: The objective was to quantify the blue-light hazard from gas metal arc welding (GMAW) of aluminum alloys. The exposure level is expected to depend on the welding conditions. Therefore, it is important to identify the blue-light hazard under various welding conditions., Methods: We experimentally conducted GMAW of aluminum alloys under various welding conditions and measured the spectral radiance of the arcs. The effective blue-light radiance, which the American Conference of Governmental Industrial Hygienists has defined to quantify the exposure level of blue light, was calculated from the measured spectral radiance. The maximum acceptable exposure duration per 10000 s for this effective blue-light radiance was calculated., Results: The effective blue-light radiance measured in this study was in the range of 2.9-20.0 W cm-2·sr. The corresponding maximum acceptable exposure duration per 10000 s was only 5.0-34 s, so it is hazardous to view the welding arc. The effective blue-light radiance was higher at higher welding currents than at lower welding currents, when pulsed welding currents were used rather than steady welding currents, and when magnesium was included in the welding materials., Conclusions: It is very hazardous to view the arcs in GMAW of aluminum alloys. Welders and their helpers should use appropriate eye protection in arc-welding operations. They should also avoid direct light exposure when starting an arc-welding operation., (© The Author 2017. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.)

A novel methodology has been established which allows to recycle steel slag as a suitable flux for submerged arc welding. The flux produced using waste slag as a raw material has been applied to deposit beads on plates. The bead geometry is dependent on welding parameters; hence optimization of parameters is essential. In this cut throat competition, researchers are striving to minimize the cost of experimentation using various experimental and optimization techniques to reduce number of experiments for save time, money, and resources. In this article various techniques have been explored for better optimized results. The welding parameters have been optimized to obtain desired bead geometry using various optimization techniques such as genetic and teaching–learning-based optimization algorithm, and desirability. It was observed that the genetic algorithm technique provides better results having a minimum error of penetration, bead width, and reinforcement (i.e. 1.12%, 1.83%, and 2.46%, respectively), as compared with other techniques applied. It is further observed that flux manufactured from waste slag is capable to produce desired bead profile which is similar with that of the fresh flux. Recycled slag is capable to produce optimum bead geometry having maximum penetration of 11.52 mm, bead width 20.73 mm, and reinforcement 3.24 mm. [ABSTRACT FROM AUTHOR]

This experimental investigation introduced the gas metal arc welding-based additive manufacturing to deposit single-layered beads of ER70S–6 and 316 L stainless steel (SS). Different experimental conditions are generated through response surface methodology for illustrating the effect of wire electrode material and deposition parameters on bead characteristics. From parametric analysis, wire feed speed and torch speed are found to be the most controlling factors for bead width, height, deposition area, penetration depth, dilution, and contact angle. Deposition with 316 L SS wire exhibits minimal bead characteristic features than ER70S–6 because of high electrical resistivity that restricts excessive flow of arc current (low thermal energy development) and maintains the molten pool stability. Microstructural transformation from the continuous nature of δ-ferrite into an isolated core-like structure indicates the heat input's role over grain refinement. X-ray diffraction depicts α-Fe and ϒ-austenite phases (with δ-Fe) in ER70S–6 and 316 L SS deposits. [ABSTRACT FROM AUTHOR]

This paper aims to enhance the efficiency of the utilization of arc energy by adding ultrasonic and magnetic fields. A new welding method is proposed and named as ultrasonic-magnetic coaxial hybrid gas tungsten arc welding (U-M-GTAW). In this paper, the effect of tungsten extension and welding current on the arc characteristics under different welding methods and the effect of different welding methods on the 304 stainless steel weld formation were investigated. The arc shape changed significantly with increasing tungsten extension, and the addition of ultrasonic waves can increase the arc energy and stiffness. As the current increases, the arc area increases, and the degree of contraction and rotation of the arc decreases. Compared to the weld penetration of GTAW, U-GTAW and M-GTAW increased by 58.6% and 11.5%, respectively, while the weld penetration of U-M-GTAW decreased slightly. Compared with the weld width of GTAW, U-GTAW increased by 97.1%, M-GTAW increased by 44.5%, and U-M-GTAW increased the most by 123.8%. [ABSTRACT FROM AUTHOR]

The quality of welded pressure vessels joints consists in using an optimal welding regime, a parameter that has a high influence in submerged arc welding is the welding current intensity. Increasing the welding current intensity correlated with an optimal welding speed and working voltage may result in increasing productivity. This paper deals with aspects of the effect of changing only the welding current intensity parameter within a welding regime that has the rest of the parameter's constant. The study presents how the welding current intensity affects the tensile strength of the welded joints from pressure vessel steel. The main aspects that are considered: the yield strength, breaking force and breaking stress occurred in stretching of the welded joints. The test specimens were created by using the welding process realized by using a semiautomatic industrial submerged arc welding machine. The base material used is a pressure vessel steel identified under the coding P355 N. [ABSTRACT FROM AUTHOR]

The purpose of the method of AC/DC mixed gas tungsten arc welding (GTAW) is to improve the welding efficiency of aluminum alloy AC-GTAW. It is expected to make a great change in the aluminum alloy manufacturing industries. The feature of AC/DC mixed GTAW includes two parts, AC mode and DC mode, during the welding process. A comparison study between the AC/DC mixed GTAW and AC-GTAW is carried out by analyzing the arc characteristics and weld formation. The results showed that the uniformly distributed AC and DC signals were obtained in the AC/DC mixed GTAW. The front width and back reinforcement of the weld bead in the AC GTAW and the AC/DC mixed GTAW increased first and then decreased with increasing frequency. The geometrical parameters of the weld cross-section in the AC/DC mixed GTAW was increased, when the same frequency was used. For example, the frequency of 30 Hz was employed, the front width of the weld bead in the AC/DC mixed GTAW was increased to 0.3 mm compared with that of the AC-GTAW. The AC/DC mixed GTAW has a greater effective heat input compared with the AC GTAW due to introduction of the DC mode. [ABSTRACT FROM AUTHOR]

It is well known that in order to obtain a suitable quality of the products intended for industrial use, it is necessary to identify the critical points where wear defects may appear over time. In the case of pressure vessels that work under heat and pressure, these critical points are considered the welded joints of the various component elements that make up the functional assembly of the product. In most cases, pressure vessels for industrial, non-chemical and alimentary use are made of carbon steel with fine structures that are found in the form of sheet or pipe semi-finished products, they are processed by cutting and plastic deformation before being introduced into the frame welding processes carried out by submerged arc welding under a flux layer using semi-automatic or robotic equipment. In order to obtain optimal quality and productivity, it is necessary to adapt the welding regime by choosing the right values of the working parameters that define the welding regime. In this paper are treated aspects regarding the evolution of the tensile strength characteristics depending on the variation of the welding voltage parameter within the submerged arc welding processes of P355N pressure vessel low carbon steel. [ABSTRACT FROM AUTHOR]

Bypass coupling triple-wire gas indirect arc welding (TW-GIA) has been proposed to control the heat input of base metal and consequently improve the weld forming as per the requirement. The influence of the bypass current on arc behavior, welding stability, and weld forming have been investigated. Results showed that the wetting angle and reinforcement reduced gradually, and the weld bead penetration increased with the bypass current increase. The reason was that the workpiece heating mode was changed due to the bypass circuit coupling. It was observed that the heat source was composed of two indirect arcs and two direct arcs, and they were in a coupling state. When the bypass current was 280 A, the electrical parameters of arc fluctuations were at a maximum, and the coupled arc state was not conducive to obtain a stable welding process. Compared to the lack of sidewall fusion and incomplete joint penetration defects of the weld with TW-GIA, the good butt joint of 12 mm thickness steel plates was successfully obtained with bypass coupling TW-GIA under the same energy consumption. [ABSTRACT FROM AUTHOR]

Laser-assisted double-wire welding with a nontransferred arc is used for cladding workpieces. The wire material is melted by an arc and dropped onto the substrate, where a laser beam is oscillated by a galvanometer scanner to achieve bonding of the melt with good contact angles that do not result in undercuts. In this study, the galvanometer scanner was replaced by a beam shaping optics generating a line with a width of 1.2 mm and a length of 9.1 mm. Based on Design of Experiments, the laser power was varied in a range from 1500 to 2000 W and the welding speed in a range from 600 to 800 mm/min. Single weld beads of AISI 316L were welded onto a mild steel of AISI 1024 according to a full factorial design at three repetitions per parameter set. The paper examines whether the contact angles of the weld beads produced with the line optics are comparable to those obtained by oscillating the laser beam. In addition, the dilution of the material with the substrate was determined in micrographs. The results show that the bonding to the substrate can be achieved. The parameter window for the laser power with beam shaping line optics is different from that with the oscillated laser beam. The required laser power is 1.5–2 times greater. [ABSTRACT FROM AUTHOR]

The present study deals with a new technique for controlling the weld-induced distortion. This developed technique involves in-situ preheating of welding filler wire before it emerges from the contact tube. Welding filler wire preheating was carried out using an external constant current power source and a specially designed welding torch. Weld beads were deposited on 3.0 mm low carbon steel sheet using a bead on plate technique with different preheat values of welding filler wire by the submerged arc welding process. Electrical signals were recorded to analyze the effect of welding filler wire preheating on arc characteristics. Probability density distribution (PDD) curves from electrical signals indicate that with the rise in preheat value, welding current decreases and results in stable arc characteristics. An increase in preheat value also reduces the longitudinal bending distortion of the sheet. The maximum reduction in the longitudinal bending distortion of the sheet (~53%) was obtained at the maximum preheat value of 200 Ampere. [ABSTRACT FROM AUTHOR]

The results of experimental studies of some features of non-consumable electrode welding in argon steel 12X18H10T with increased speed are presented. The possibility of improving the quality of formation and resistance of seams against the formation of hot cracks by exposing the arc and metal of the weld pool by controlling the magnetic field of the current flowing through the contact conductor located above the tail section of the weld pool, perpendicular to the electrode is shown. [ABSTRACT FROM AUTHOR]

CO2 gas is being considered as one of the potential plasma forming gases in plasma arc material processes due to its thermophysical properties, cost, and easy availability. The understanding of the thermal behavior of CO2 plasma arc is essential for an effective utilization of it. However, the studies on CO2 arc characteristics are scanty. In this study, a 2-D axisymmetric model is built for the simulation of CO2 and Ar arcs with and without evaporation of anode. The thermal characteristics of CO2 arc are compared with those of Ar arc at different arc currents and anode materials. CO2 arc possesses higher temperature compared to Ar arc and the arc current strongly influences the temperature of CO2 arc. The anode flux in CO2 arc is higher compared to that of Ar arc and the effects of arc current and nature of the anode material on the same are stronger in CO2 arc. The arc heating efficiency in CO2 is higher than that in Ar and it reduces with increasing arc current. [ABSTRACT FROM AUTHOR]

The effect of laser, Hybrid Laser-Tungsten inert gas (HLT) and Hybrid Laser-Metal inert gas (HLM) welding processes on the microstructure and mechanical properties of 5.6 mm thick 316L(N) stainless steel weld joints have been studied. The differences in weld metal microstructure and mechanical properties of the weld joints were evaluated and discussed. Weld bead geometry, ferrite number (FN), solidification mode, secondary dendrite arm spacing, hardness and tensile properties are compared. Laser weld joint showed narrow weld bead profile and a higher cooling rate than the hybrid laser arc weld joints and the weld metal manifested austenitic solidification mode. HLT weld displayed coarser weld metal microstructure due to higher heat input and austenitic ferritic solidification mode. HLM process possesses moderate heat input and cooling rate. The HLM weld metal exhibited ferritic austenitic solidification mode and 2.5 FN. The hardness of weld metal was higher in hybrid welding processes due to the higher ferrite content. HLM weld joint has higher yield strength, ultimate tensile strength and ductility compared to that of the other weld joints. HLM welding process also permits higher gap tolerance with filler metal addition and is recommended for welding of type 316L(N) stainless steel. [ABSTRACT FROM AUTHOR]

The spiral structure of seven-wire is the fundamental cause of arc rotation. The arc rotation frequency decreases with the radius of twisting circle and the helix angle, and increases with the welding current. The arc presents the reciprocating rotating upward motion when welding torch oscillates along the thickness of the plate. The sidewall penetration along the thickness direction of plates is approximately the same. The rotating arc promotes the stirring of melting metal, and the stirring effect intensifies the flow of melting metal and accelerates the heat transfer from the molten pool to the sidewall, which has a positive effect on increasing the penetration of sidewall and refining the grains of weld seams. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) has advantages of high efficiency and low cost. However, different welding current processes lead to different heat input and repeated heating treatment during the deposition process, which has an influence on the forming and performance. In this study, 30 layers of reciprocating depositions for 316L stainless steel were carried out by speed cold and speed arc welding processes, and the morphology, effective deposition rate per power, microstructure, and properties of depositions were compared. The outcomes indicated that different welding current processes make different shaping appearances, and the effective deposition rate per power of speed cold welding is 15.2% higher than that of speed arc welding. The microstructures of depositions are columnar crystals; however, the higher power of speed arc welding leads to the coarse structure, and the enhanced thermal cycle and preheating effect produce a uniform hardness and 4.9% higher tensile strength, but lower toughness than those of speed cold welding. Due to the direction of deposition, the tensile strength of depositions by two processes has obvious anisotropy that can reach to 8.18% and 13.3%, respectively. [ABSTRACT FROM AUTHOR]

The influence of researches results of the welding circuit magnetic field on the seam formation at welding steel 12X18H10T by weight with a non-consumable electrode in argon are presented. The possibility of retaining the molten metal of the weld pool by the magnetic field of the current flowing along a rectilinear conductor located in the plane of the welded joint above the tail of the weld pool is shown. It is established that the efficiency of holding the molten metal of the weld pool is largely determined by the location of the current lead, the speed and rigidity of the welding mode. [ABSTRACT FROM AUTHOR]

Load-carrying capacity of weld joints could be identified by its shape and size where weld bead geometry and shape relationship parameters are of utmost importance. Heat input and preheating temperature together can control the cooling time of weld, which in turn determines the weld microstructure and its mechanical properties. To control the shape and geometry of weld bead, it is necessary to understand its relationship with cooling time. In present work, preheating temperature is used as process variable along with heat input varying parameters for understanding their effects on weld bead geometry and shape relationship parameters using submerged arc welding process on high-strength low alloy pipeline steel. The experimental investigation was then analyzed by using the mathematical modeling in context with response surface methodology. The mathematical model predicts the influential dependency of cooling time on the preheating temperature than the other weld process parameters. The associated effects in relation to the process parameters have been discussed and analyzed in the present study. [ABSTRACT FROM AUTHOR]

In this study, we have explored the influence of newly developed tri-component oxide flux (Cr2O3, FeO, and MoO3) on weldability, bead geometry, weld pool temperature variation, and mechanical strength of Inconel 718 welded joints. Moreover, the influence of used flux on weld pool, the surface morphology of electrode and penetration capability of tungsten inert gas (TIG) welding on Inconel 718 plates have been well elucidated. Results indicate that the flux mixture significantly increases the penetration depth as well as aspect ratio almost 200% as compared to conventional TIG welding. The arc constriction caused by newly developed oxide flux upsurges the heat density and the weld pool temperature of joints. The alloying effect caused by entrapped oxide particles greatly improves the hardness as well as the tensile strength of joints. The reported reinforcement in the welding performance may increase potential utility of the developed methods for real-world applications. [ABSTRACT FROM AUTHOR]

Arc travel across the surface of a weld pool melt enables a wide range of thermal impacts on the solidifying metal during the formation of a thermal and wear-resistant nickel aluminide-based alloy. The formation of a homogeneous thermal field in the weld pool at an arc oscillation frequency of 3 Hz decreases the solidification rate. Under these conditions, the structure ratio of the relatively viscous γ-solid solution (H v of 4700–4900 MPa) is highly alloyed (up to 14 wt%) with iron and other elements to nickel–aluminium martensite, and the composition of the Ni 2 Al-phase (H v of 4400–4700 MPa) is close to optimal (approximately 50/50). The metal deposited in this structure indicates higher thermal resistance during temperature cycling within a temperature range from 20 °С to 1150 °С compared to that of the γ + γ'(Ni 3 Al) alloy structures formed at low arc oscillation frequencies. When the two composite wires are separated by a distance of 12 mm, the thermal impact of the arc on the weld pool melt becomes an impulse with an arc transition frequency of 11–13 Hz between the electrodes. The thermal cycle formed under these conditions provides the highest cooling rates of the melt near the solidification front, which reduces the size of the structural components and allows for the microalloying of the deposited metal with titanium diboride. The TiB 2 particles in the structure enable the formation of strengthening phases, such as borides, with a high content of refractory elements (Cr, W, Mo, Ta). This increases the resistance of the deposited metal to gas abrasive wear at temperatures up to 1000 °С. [Display omitted] [ABSTRACT FROM AUTHOR]

In this article, effects of advanced submerged arc welding process parameters on weld bead geometry have been investigated. A novel water-cooled torch has been developed which allow a use of higher preheat current values for a continuous advanced submerged arc welding (ASAW) operation. Weld beads have been deposited on AISI 1023 steel plates by varying open circuit voltage, wire feed rate, welding speed, nozzle to plate distance, and preheat current as per central composite design. The relationships between welding parameters and weldment characteristics namely bead width, penetration, reinforcement, and dilution have been developed using multiple linear regression. The effects of individual process parameters and their interactions on response parameters were examined. Finally, single and multiobjective optimization of process parameters were performed using desirability approach and Jaya algorithm. The results reveal that a smaller bead width and lower dilution can be achieved with the developed torch by allowing the use of higher preheat current values. [ABSTRACT FROM PUBLISHER]

In gas metal arc welding, arc ignition significantly influences arc stability, droplet transfer, and the quality of welded joints. Cable-type welding wire (CWW) CO2welding is an innovative welding method. This paper analyzes the arc ignition procedure for this type of welding based on experiments with three different wire end conditions: an unsmooth wire end, a smooth wire end, and a preheated smooth wire end. Smaller contact areas between the CWW and the workpiece led to higher arc ignition currents, and higher wire tip temperatures led to shorter arc ignition times (AITs) with the same chemical composition, diameter, and extension. Based on the characteristics of the welding wire end structures and the contact resistance between the CWW and workpiece, a suitable mathematical model of the AIT was developed. The model was validated using experimental arc ignition images. The AITs for the unsmooth smooth and preheated smooth wire ends were 14, 20, and 11 ms, respectively, essentially consistent with the model calculations. [ABSTRACT FROM PUBLISHER]

In the present investigation, multi-pass gas metal arc welding (GMAW) of SA516 Gr70 carbon steel was carried out by different filler wires such as solid, metal cored and flux cored, wherein, other process parameters were kept constant. The hybrid approach of multi-pass filler wires was applied to obtain three different welds. The root pass was filled by a solid wire for all three cases while the subsequent filler pass was applied through solid, flux-cored and metal cored filler wires, respectively. Metallographic, mechanical and metallurgical analyses such as macrograph study, optical microscopy, tensile testing and hardness variations were performed to address the quality of weld. The results revealed that defect-free sound welds were produced by the hybrid approach of different filler wires in multi-pass GMAW. Overall cost and time reduction can be achieved through hybrid filler welds, without affecting their mechanical strength. Angular distortion was reported minimum at hybrid weld of solid and metal cored filler wire. Maximum reinforcement with higher penetration was observed at weld of solid and metal cored filler wire. Impact toughness was reported higher in case of hybrid weld of solid and flux cored filler wire. Higher macro hardness was reported at weld of solid and flux cored filler wire. [ABSTRACT FROM PUBLISHER]

Objectives: The objective was to quantify the blue-light hazard from gas metal arc welding (GMAW) of aluminum alloys. The exposure level is expected to depend on the welding conditions. Therefore, it is important to identify the blue-light hazard under various welding conditions. Methods: We experimentally conducted GMAW of aluminum alloys under various welding conditions and measured the spectral radiance of the arcs. The effective blue-light radiance, which the American Conference of Governmental Industrial Hygienists has defined to quantify the exposure level of blue light, was calculated from the measured spectral radiance. The maximum acceptable exposure duration per 10 000 s for this effective blue-light radiance was calculated. Results: The effective blue-light radiance measured in this study was in the range of 2.9-20.0 W cm-2⋅sr. The corresponding maximum acceptable exposure duration per 10 000 s was only 5.0-34 s, so it is hazardous to view the welding arc. The effective blue-light radiance was higher at higher welding currents than at lower welding currents, when pulsed welding currents were used rather than steady welding currents, and when magnesium was included in the welding materials. Conclusions: It is very hazardous to view the arcs in GMAW of aluminum alloys. Welders and their helpers should use appropriate eye protection in arc-welding operations. They should also avoid direct light exposure when starting an arc-welding operation. [ABSTRACT FROM AUTHOR]

Galvanized steel is widely used and its demand is growing in automotive industry due to high quality requirement for corrosion resistance. Although there are a lot of demands on using galvanized steel as automotive parts especially for outer body, it has a grave flaw in its welding process. The difficulty is low weldability due to various defects such as porosities and blow holes in weldment, which occurred during welding. A solution to prevent these defects is using hybrid welding process, with two more welding processes. One of the hybrid solutions is using Gas tungsten arc welding (GTAW) as leading position in order to remove the zinc (Zn) coating on the surface before the followed practical fusion welding process. In this research, a numerical analysis model which can predict the eliminated Zn coated layers and the area of Fusion zone (FZ). Developed numerical analysis model was validated through comparing experiment to simulation. Basically, arc heat flux, arc pressure, electromagnetic force and Marangoni flow were employed as the boundary conditions and body force terms. Governing equations such as the continuity, momentum, Volume of fluid (VOF) and energy equations were adopted as usual. In addition to previous model, concentrated arc heat flux and contact thermal conductance models are newly suggested and showed successful result. They are adopted to realize edge concentrated arc and interfacial thermal conductance in lap joint fillet arc welding. Developed numerical analysis model successfully simulated the weld pool and temperature profile therefore the predicted Zn removed area considerably coincided with experimental result. [ABSTRACT FROM AUTHOR]

This paper describes a basic mechanism of contact welding formed by bounce arc upon contact making, based on experiments and analytical simulation of thermal conduction in the contact. We measured the weld force after every contact making in a low-voltage condition (200 V ac). The arc current was set to 60–500 A using a reactor load, the arc duration was within 0.12–2.42 ms, and the contact materials were pure silver (99.99%) and copper (99.9%). In this condition, we clarified that the weld force increases depending on arc energy supplied to the contact surface. We also measured the melted area on the contact surface and clarified the area dependence on the arc energy. Considering the tensile strength of the contact material, we found that the real welded area corresponds to about 25%–40% of the melted area. We concluded that the evaporation of contact material is a significant factor in reduction of the welded area. [ABSTRACT FROM PUBLISHER]

Crystal cracking is one of the major defects when large copper structures are joined by gas tungsten arc welding (GTA welding). In order to research the mechanism of crystal cracking, the criterion for crystal cracking formation has been optimized based on Prokhorov's theory, which shows that the interior deformation rate (Δϵ) is the main factor that leads to crystal cracking. A finite element model of thick copper plates in GTA welding based on the rigid constraint experiments has been established, and the Δϵ variation of the welds is obtained. The physical model of the tendency of crystal cracking has been established, and then the mechanism of crystal cracking has been discussed systematically by comparing the variations between Δϵ obtained from numerical simulations and the weld ductility (Pmin) obtained from hot-tension experiments within the brittle temperature range (BTR). Results show that during GTA welding, the values of Δϵ andPminare varied, respectively, with the temperature descending, and the tendency of crystal cracking and expansion velocity can be controlled by the value of (Δϵ − Pmin). Then experiments with the preheated temperatures of 300°C and 500°C, verified the validity of the optimized criterion of cracking. [ABSTRACT FROM PUBLISHER]

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root. [ABSTRACT FROM PUBLISHER]

The present study is to investigate the effects of the single component oxide fluxes in the TIG process on surface appearance, weld morphology, microstructures and micro-hardness during welding of 6 mm thick low activation ferritic/martensitic (LAFM) steel. Herein, a novel variant of the autogenous TIG welding, wherein oxide powders such as CaO, CrO, FeO, MnO, TiO, and ZnO were applied through a thin layer before welding to produce a bead-on-plate joint. Experimental results indicated that activated TIG (A-TIG) process could increase the joint penetration and weld depth-to-width ratio (D/w) of LAFM steel weldment using CaO, FeO, MnO, TiO, and ZnO fluxes. However, under same welding conditions, full penetration was achieved with the use of fluxes FeO and TiO. Accordingly, it was proposed that, there might certainly be a specific dominant mechanism capable of giving superior penetration, although complete penetration was achieved through multiple mechanisms. Additionally to consider the metallurgical respects of A-TIG process, Vickers micro-hardness test was performed and microstructure characterization was carried out using optical microscopy. No noticeable change in microstructure and micro-hardness values of the TIG and A-TIG weldment was observed. A composite mixture of fine and coarse martensite was observed in weld and HAZ region. [ABSTRACT FROM AUTHOR]

Tungsten inert gas (TIG) welding is commonly used for quality joining of ferrous and non-ferrous materials. But lower depth of penetration is one major shortcoming of TIG and more numbers of passes are required for thick plate joining. Use of activated flux layer on workpiece remarkably enhances penetration. In the present work, arc and metal flow behavior are studied to revisit and validate the presence and role of governing forces responsible for higher penetration in flux activated TIG (ATIG) welding. Arc behavior, material flow patterns are studied during conventional and activated TIG welding for AISI 304 stainless steel using four different activated fluxes by carrying out welding (when arc is moving) as well as keeping the arc halted (stationary arc) for all cases. Results clearly demonstrate the presence of electromagnetic Lorentz force and surface tension induced reverse Marangoni flow (strongly centripetal). These forces also push the metal flow downward near the center region of the molten pool and in many occasions penetration reaches beyond plate thickness in ATIG welding. [ABSTRACT FROM PUBLISHER]

The urgency of this work is associated with lowering of thermal impact on base metal during welding that promotes minimizing residual thermal deformations of items being welded, for instance, railway car or ship hull. This, in its turn, simplifies or completely eliminates the complex operation of finish straightening. However, one of the welding technologies reducing the magnitude of deformations, compared to currently applied arc welding, is laser welding. Its application, however, is limited by high requirements to edge preparation. In order to lower these requirements, it is rational to use hybrid laser-arc welding with application of consumable-electrode arc. Here, lowering of arc pressure on the weld pool and heat input into the metal being welded can be achieved due to pulse modulation of arc and laser components of the hybrid process. The work shows that it is rational to apply simultaneous pulse modulation of the welding arc and laser radiation with the frequency close to that of natural vibrations of the weld pool in laser welding, in order to improve formation of weld upper bead and increase the penetration depth. Modulation frequencies can be equal to or multiple of each other, exceeding the values of arc pulse feed frequencies. [ABSTRACT FROM AUTHOR]

The arc in MIAB welding process follow two paths of motion, one along the circumference and other comprising the zigzag motion when commuting between outer diameter and inner diameter. The moving arc dissipates necessary heat such that the butt ends reach solidification followed by forging. In this study, a pivotal attempt is made to investigate the temperature distribution during the movement of arc along and across the faying surfaces using finite element method. [ABSTRACT FROM AUTHOR]

In this study, a 2D mathematical model was developed for both arc and weld pool in stationary GTA welding. In arc model, current continuity equation has been solved in both arc and cathode regions without any assumption of fixed current density on the cathode surface which was essential in most previous works. The results of arc model were presented for both copper and aluminum anodes to investigate the effect of anode material on arc properties. It was seen that aluminum anode has lower maximum anode current density and heat flux but the distributions are wider than copper anode. Furthermore, shear stress on anode surface is higher in the case of aluminum anode. Also, calculated results of this study were compared with other available theoretical and experimental results. It has been shown that the agreement between calculated and experimental results was fairly good. The necessary information to simulate the weld pool, including the anode current density and heat flux to the workpiece were taken from the arc model. In this model, due to high thermal conductivity of pure aluminum, fluid flow into the weld pool was ignored. Effects of arc variables, i.e., arc length, applied current and welding time on the shape and size of the weld pool were investigated as well. In order to check the validity of the weld pool model, a comparison between calculated results and the results of our experimental tests was conducted. Generally, these comparisons reveal an acceptable agreement between calculated results and experimental data. [ABSTRACT FROM AUTHOR]

Thermionic arc cathodes are the cathodes where thermionic emission is the main electron emission mechanism. They are used in welding (Tungsten pure or doped with rare earth oxides) and plasma arc cutting (Tungsten for cutting with inert gas or Hafnium for cutting with Oxygen plasma). There are two different sources of erosion: constant current (CC) erosion and erosion during arc initiation and termination (cycling erosion). Available experimental data for both types of cathode and both types of erosion (CC and cycling) are presented and discussed. For quite some time, it has been clear that CC erosion is due to cathode evaporation. It has been shown that as almost all the evaporated atoms return back to the cathode, the net erosion rate is much lower than the evaporation rate. The existing model allows one to calculate the ratio of these two (escape factor). It is in the range 10^-2\--10^-3. The important role of cathode geometry and plasma flow pattern in the cathode proximity is discussed. The nature of cathode erosion during arc start and arc termination is much less understood in spite the fact that the corresponding erosion could be very important and even dominate for multiple cycles. Different processes that lead to this type of erosion are considered. [ABSTRACT FROM AUTHOR]

Abstract: The laser beam submerged arc hybrid welding method originates from the knowledge that, with increasing penetration depth, the laser beam process has a tendency to pore formation in the lower weld regions. The combination with the energy efficient submerged arc process improves the degassing and reduces the tendency to pore formation. The high deposition rate of the SA process in combination with the laser beam process offers, providing the appropriate choice of weld preparation, the possibility of welding plates with a thickness larger than 20mm in a single pass, and also of welding thicker plates with the double sided single pass technique. [Copyright &y& Elsevier]

A series of fiber laser-metal inert gas (MIG) hybrid welding experiments were carried out on the commercially pure titanium (CP-Ti) sheets to investigate the effects of the welding parameters, such as MIG welding current, welding speed, laser-arc distance, defocused distance of laser beam and gap, on the bead appearance, weld shape, and tensile properties of the welded joints. The results show that fiber laser-MIG hybrid process parameters were of considerable importance for the bead appearance, weld width, and elongation of the welded joints. However, ultimate tensile strength (UTS) of the welded joints in CP-Ti was not obviously influenced by the process parameters owing to a higher microhardness in the fusion zone compared to the base metal. [ABSTRACT FROM AUTHOR]

The conditions of formation of lack of fusion defects and hot cracks in welded joints in welding steel structures with zinc coatings are investigated. The results show that the probability of formation of lack of fusion defects in the metal of the welded joints produced in CO2 mechanized welding with a consumable electrode increases with increase of the thickness of the zinc coating and is caused by the additional consumption of the heat of the welding arc for evaporation of zinc. To prevent the formation of lack of fusion defects in the metal of these welded joints, it is recommended to correct the welding conditions taking the thickness of the zinc coating into account. [ABSTRACT FROM AUTHOR]

A gas tungsten arc in helium and argon was modelled taking into account the contamination of the plasma by metal vapour from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapour. The transient two-dimensional distributions of the temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the weld penetration as a function of time for a 150 A arc current at the atmospheric pressure, both for helium and argon welding gases. It was shown that the thermal plasma in gas tungsten arcs is influenced by iron vapour from the weld pool surface and that the concentration of iron vapour in plasma is dependent on the temperature of the weld pool. [ABSTRACT FROM AUTHOR]

Abstract: A gas tungsten arc in helium is modeled taking into account the contamination of the plasma by the metal vapor from the weld pool surface. The whole region of gas tungsten arc welding, namely the tungsten cathode, arc plasma and weld pool, is treated using a unified numerical model. A viscosity approximation is used to express the diffusion coefficient in terms of the viscosities of the helium gas and the iron vapor. The time-dependent two-dimensional distributions of temperature, velocity and iron vapor concentration are predicted, together with the weld penetration as function of time for a 150 A arc current at atmospheric pressure. It is shown that the thermal plasma in gas tungsten arcs is markedly influenced by iron vapor from the weld pool surface and that the concentration of the iron vapor in the plasma is dependent on temperature of the weld pool surface. [Copyright &y& Elsevier]

Cathode spot formation is very pronounced during arc welding of titanium and titanium alloys. The dynamic behaviour of these spots was observed to interfere with metal transfer during welding, this interference being a fundamental cause of poor weld quality in these alloys. In the present work, stabilisation of the arc cathode spot with a focused Nd–YAG laser beam during pulsed gas metal arc welding of titanium was investigated. The laser beam was focused near the leading edge of the weld pool and the laser power and focus spot size were varied to determine the values required to confine the cathode spot to the laser focus position. The results showed that, for fixed welding conditions, the laser power required to prevent cathode spot motion varied as a function of focus spot size. The required laser power was minimised at 200 W for a spot size of 0.6 mm. The laser stabilised arcs had lower voltage but approximately the same current density as stabilised arcs. Increased welding speeds required marginally higher laser powers to stabilise the spot, but the minimum power was still attained with a 0.6 mm focus spot diameter. The laser power density required for stabilisation decreased as spot size was increased, varying from almost 106 W cm-2 at the smallest spot size to approximately 104 W cm-2 at the largest. Cathode spot stabilisation improved weld quality by reducing spatter generation and weld bead irregularity. [ABSTRACT FROM AUTHOR]

In light of recent research on the potential health problems associated with sub-micrometer aerosols, a study was conducted to determine the effect that droplet mass transfer mode, shield gas composition, and welding spatter had upon the aerosols generated from a Gas Metal Arc Welding (GMAW) Operation. The results revealed that the sub-micrometer aerosols produced during spray transfer resulted in markedly higher concentrations of nucleated particles than those produced during globular transfer. This probably resulted from a larger droplet surface area for vaporization of metallic species. The shield gas experiments results revealed that as the percentage of carbon dioxide increased the number of nucleated particles also increased. It appears that oxygen may have facilitated chemical reactions with the alloy constituents, thereby increasing the mass transfer rate from the evaporating metal droplets in the plasma. Finally, an attempt to characterize the spatter aerosol revealed a distinct particle size distribution with a mode particle diameter of 6.8 μm. This particle size distribution appeared to be independent of shield gas composition, and the particle number concentration was significantly smaller than the sub-micrometer aerosols formed during the GMAW process (i.e., two-orders of magnitude smaller when weighted by particle mass). [Copyright &y& Elsevier]