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The purpose of this study was to optimize the conditions of the gas–metal arc welding using CO2 shield gas (CO2 arc welding) with hot-wire feeding technology. A high-speed camera was used to investigate welding phenomena of a butt joint of 36-mm-thick steel plates. The optimum parameters were determined under combinations of the welding current (300 or 400 A) and hot-wire feeding speed (0 to 12.5 m/min) to avoid molten metal precedence. A sound joint was achieved with only four weld passes using optimum conditions. Adequate joint properties, including tensile strength and toughness, were obtained. The optimum conditions provided a welding process with both high efficiency and low heat input.

This fundamental research aims to analyse the effect of heat transfer coefficients, plasticity model of evolved material properties and simplified meshing strategy on substrate deformation induced by wire arc additive manufacturing (WAAM) process with dissimilar materials based on experiment and numerical simulation. Throughout the experiment, stainless steel wire SS316L was used as feedstock to build a five-layer and three-string component on an 8-mm-thick low carbon steel S235 as substrate plate by means of a robotic GMAW system with pure argon as shielding gas and diagonal clamping. In order to define heat transfer coefficients by adjusting simulation to experimental results, the transient thermal distribution was to be measured at specific points located in the component layer using Type K thermocouple inserted during the process and on the substrate implanted beforehand. For modelling and simulation, a non-linear thermo-mechanical method was applied in which the component was modelled using rectangular element shape with optimized hexagonal mesh size obtained through sensitivity analysis in accordance to actual specimen geometry and clamping condition. Non-linear isotropic hardening rule with von Mises yield criterion and temperature-dependent material properties was implemented into the simulation which were generated by means of advanced material modelling software based on elemental composition of evolved component characterized using SEM/EDX. For numerical and experimental validation purpose, substrate deformation was measured using coordinate measurement machine before and after the process. It can be concluded that the result of the computed substrate deformation showed an acceptable agreement compared to experiment within the range of error between 0.5 and 27.5% at each specific measurement points and 10.1% as average single error. This basic investigation can be enhanced in the case where cost-effective WAAM application with dissimilar materials towards single-piece substrate component is concerned.

Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components; however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. It is known that Ar gas is not suitable for welding steel because it cannot provide the desired arc stability and weld bead characteristics. The results reveal that the arc is stable in the multilayer deposition of the WAAM process, and the short-circuit of the metal transfer at the heat input of 1.17 kJ/cm enables smoothing of the fabricated surface with large irregularities. Better arc stability under Ar gas is achieved when the oxygen content of the fabricated surface is 22 wt%. Furthermore, the short-circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. The results indicate that proper use of Ar gas can improve the surface quality when depositing on rough surfaces.

This study investigated the microstructures and properties of deposits protected by seven different proportions of N2 and Ar by performing wire-arc additive manufacturing of the 5356 aluminium alloy. The results show that when the proportion of N2 in the shielding gas was larger than and equal to 50%, flaky nitrides were generated in the deposits. With an increase in the proportion of N2 in the shielding gas, the number and size of nitrides in the deposits as well as the fluctuation frequency and amplitude of the microhardness of the deposits all increase. The existence of flaky nitrides incurs a low ultimate tensile strength of additively manufactured parts protected by a mixed gas containing N2. The presence of large-size flaky nitrides between layers in the deposits leads to a large difference in tensile properties in the horizontal and vertical directions of the deposit. Tensile fracture shows that the deposits were fractured in the mixed mode of ductile and brittle fracture.

The use of pulsed gas metal arc welding (P-GMAW) is fundamental to applications were versatility and control of heat input are required during deposition. However, when welding using pure argon shielding gas, a drawback is the instability derived from wandering of the cathode spots on the weld pool. This work investigates an alternative to weld steels using pure argon shielding gas with cold wire pulsed gas metal arc welding (CW-P-GMAW). A mechanism for enhanced stability is revealed in CW-P-GMAW, related to the migration of cathode spots to the cold wire which prevents the cathode spots from wandering around the weld pool. The migration of cathode spots is likely related to charging of oxides on the cold wire surface by ions formed in the arc plasma. The enhanced arc stability smooths the shape of bead profile, since wandering of the arc due to cathode motion is suppressed.

Automated robotic laser welding is commonly used for the joining of thin-gauge sheet metals for automotive applications due to the precision and speed of the welding process. Without proper process optimization, high-speed laser welding for automotive applications is known to have defects such as porosity, weld concavity, and cyclic humping. Several welding parameters can be adjusted to optimize the laser welding process: decreasing the laser power and the welding speed, changing the intensity distribution of the laser on the surface of the substrate, or by changing the type and flow rate of shielding gas used during welding. However, decreasing the laser power and welding speed leads to a loss in productivity which can be costly in large-scale manufacturing endeavors. This study presents the effect of beam defocusing on the weld pool geometry while holding other parameters constant as the welding mode transitions from full penetration or open keyhole mode (OKM) when the beam is fully focused to partial penetration or closed keyhole mode (CKM) as the beam is defocused. It has been shown that by defocusing the laser beam and controlling the weld pool geometry, the welding process can be stabilized to eliminate defects such as severe concavity without decreasing the laser power or slowing down the welding process. A numerical solution is presented that uses three-dimensional (3D) transient finite element (FE) analysis to calculate the temperature fields and predict the molten weld pool geometry in both the full and partial penetration welding modes using a double conical-Gaussian (DCG) volumetric heat source derived from the classical 3D conical-Gaussian (CG) heat source. The model was calibrated using video imaging of the welding process and known experimental data, and it was validated using an extensive experimental study. The results of this work show that the model can be used to predict the molten weld pool geometry that stabilizes the liquid flow in the melt pool during high-speed laser welding whereby allowing faster speeds to be used in the manufacturing of laser-welded components.

Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technology that uses a high-energy–density laser to scan through a powder bed and completely melts the metal powder. The environment inside the printer chamber, including the flow field of the shielding gas and the spatter particles induced by laser–powder interactions, is essential for product quality. For the first time, this work built a full-size model of printer chamber, and numerically investigated the interaction between the shielding argon flow and the laser induced spatter particles with considering laser temperature. A full-size geometric model of a commercial L-PBF printer with a Gaussian heat source was constructed, as well as a movable particle-release source model for particle injection. The distribution of the argon flow field, the temperature field, and the trajectory and deposition of spatter particles, particularly above the workbench during the L-PBF process were quantitatively analyzed. The results show that the gas flow within 30 mm above the workbench is uniform, and in the upper region of the printer chamber, the flow field is disorderly. The laser can only induce high temperature and upward gas flow in a small region close to the workbench (the height less than 1.6 mm), and the laser induced velocity disturbance in rest regions of the L-PBF printer is negligible. Particles injected towards the outlet (ID4) are mostly blown into the outlet, and in the other four injection directions, more than 90% of spatter particles are deposited inside the printer chamber, especially more than 50% deposited on the workbench. Increasing the laser power (from 100 to 200 W) has little effect on particle deposition on the workbench. Results will be helpful for improving the L-PBF product quality.

The MCAW with rotating electrode process (MCAW-RE) is a variation of the conventional MCAW (metal-cored arc welding) process, where reduced costs and superior productivity are obtained due to narrow gap welding, since the rotational motion of the electrode allows the electric arc to reach peripheral regions of the groove, preventing lack of fusion on the sidewall. Although there is some information about the operational characteristics of this process, the literature studying the mechanical properties is very limited. This work evaluates the mechanical and microstructural properties of high strength steel weld metals obtained by the MCAW-RE using two different mixtures of Ar-CO2 as shielding gas. Multipass welding by MCAW-RE was performed with preheating of 100 °C, in 500 × 150 × 10 mm steel plates. Weld metals were obtained by the MCAW-RE process using a consumable of the class 700 MPa and two mixtures of Ar-CO2 (5% CO2 and 25% CO2) as shielding gas. The results obtained from mechanical tests (hardness and impact Charpy-V) and metallographic examination (optical microscopy, scanning electron microscopy, and electron backscattering diffraction) carried out in samples removed transversally to the weld bead showed equivalent results for all weld metals. These results evidenced that the MCAW-RE process can provide weld metals with satisfactory behavior with different shielding gases. This process has a high potential for replacement of the conventional GMAW process because the weld metals achieved the requirements for several industrial applications.

Gas Metal Arc Welding (GMAW) is a welding process in which an electric arc is formed between a wire electrode and a metal work piece alongside a shielding gas to protect the arc from contaminants. There are several ways in which the molten electrode droplet can be transferred to the weld pool known as metal transfer modes. Identifying the metal transfer mode automatically is essential to monitor and control the welding process, especially in automated processes employed in modern Industry 4.0 manufacturing lines. However, limited research on this topic has been found in literature. This paper explores automatic classification of metal transfer modes in GMAW based on machine learning techniques with various signals from the welding process, including acoustics, current, voltage, and gas flow rate signals. Time and frequency domain features are first extracted from these signals and are used in a support vector machine classifier to detect the metal transfer modes. A feature selection algorithm is proposed to improve the prediction rate from 80% to 99% when all the four signals are utilized. When only the non-intrusive acoustic signal is used, the prediction rates with and without the proposed feature selection algorithm are approximately 96% and 81%, respectively. The high prediction rate demonstrates the feasibility and promising accuracy of the acoustic signal based classification method for future smart welding technology with real-time adaptive feedback control of the welding process.

High nitrogen stainless steel with nitrogen content of 0.75% was welded by gas metal arc welding with Ar–N2-O2 ternary shielding gas. The effect of the ternary shielding gas on the retention and improvement of nitrogen content in the weld was identified. Surfacing test was conducted first to compare the ability of O2 and CO2 in prompting nitrogen dissolution. The nitrogen content of the surfacing metal with O2 is slightly higher than CO2. And then Ar–N2-O2 shielding gas was applied to weld high nitrogen stainless steel. After using N2-containing shielding gas, the nitrogen content of the weld was improved by 0.1 wt%. As N2 continued to increase, the increment of nitrogen content was not obvious, but the ferrite decreased from the top to the bottom. When the proportion of N2 reached 20%, a full austenitic weld was obtained and the tensile strength was improved by 8.7%. Combined with the results of surfacing test and welding test, it is concluded that the main effect of N2 is to inhibit the escape of nitrogen and suppress the nitrogen diffusion from bottom to the top in the molten pool.

Grade 2, the most widely used pure titanium in the industry, has high corrosion resistance, excellent ductility, good weldability and is easily machinable. If titanium is exposed to temperatures above 500 °C due to moisture or hydrocarbons in the air, it is susceptible to taking up oxygen, nitrogen, carbon and hydrogen. This can cause cracks, especially after welding. Therefore, protection of the welding zone from external factors is of great importance during welding. For these reasons, TIG welding is the most widely used method for titanium welding. In this study, Grade 2 pure titanium plates are joined by TIG welding at three (40 A, 60 A and 80 A) current values under the same conditions. For the welding process, 2 wt.-% cerium addition Tungsten tip and high purity (99.99 vol.-%) argon was used as a shielding gas. After a visual inspection of the welded samples, microstructure inspections, macrostructure inspections, hardness measurements, bending tests and tensile tests were performed in accordance with the standards. As a result of the investigations, it was determined that the most suitable current value for the joining of Grade 2 titanium by TIG welding was 60 A.

This work investigates the effects of Ar-based shielding gases on the microstructure and phase balance of duplex stainless steel (DSS) depositions. The results are then used for fabrication of DSS walls using wire arc additive manufacturing (WAAM), and the microstructural characteristics and mechanical performance of the products are assessed. WAAM currently poses as one of the most interesting methods of manufacturing by enabling joining of materials to fabricate structures layer by layer. However, the extreme conditions imposed by the process, such as high heat inputs and re-melt and solidification of the deposited layers, could compromise the performance of the products. A detailed microstructural analysis is conducted on single layer and double layer depositions of DSS to assess the effects of different shielding gases on the ferrite/austenite phase balance in the specimens. The results show that the depositions shielded with a small fraction of carbon dioxide (CO2) present better microstructural features in comparison to depositions shielded with the other selected gases. A mixture of 98%Ar + 2%CO2 was employed for fabrication of a 60-layer DSS WAAM-made wall and some mechanical characteristics were studied. The mechanical examinations demonstrate that the properties of the parts fabricated using WAAM are comparable with their wrought counterparts.

Gas protection is very important in arc welding processes and several factors influence its effectiveness. This paper provides a discussion of the applicability of the Schlieren technique to arc welding processes. Tests were performed with different types of shielding gas and with GMAW and GTAW torches, in order to highlight differences associated with the various conditions. The results obtained in conjunction with a review of results reported in the literature allowed an evaluation of the limitations associated with the use of the Schlieren technique in the arc welding processes. The most important limitation is that the visualization is inherently difficult when using pure Ar gas, meaning that in most situations it is not possible to adequately visualize the flow interface with atmospheric air, which is the main region of interest in this type of analysis. However, visualization is possible in regions where pure Ar is heated, or when mixtures with other gases are used. In addition, the results obtained with different sources of light were compared and the test was performed by filming the arc welding or with the gas flowing through the torch without the arc. The differences observed in the results obtained are discussed herein.

Metal matrix composites enhance the wear and corrosion properties of components in heavy-duty industries. This work reports the preliminary effects of process parameters such as current, linear speed, powder flow rate, nozzle angle, powder gas, shield gas, and center gas at the macro-scale and micro-scale of single-track multiple-layer depositions. The use of plasma transferred arc as an additive manufacturing system yields enough energy for a fast solidification rate of the matrix without compromising the carbide in the composite. The results show that the bead height is mainly affected by the powder flow rate, the powder gas, and the travel speed at the macro-scale. The bead width has a close relationship with powder flow rate, powder gas, and current, the latter contributing to the formation of a slumping phenomenon due to heat accumulation. The volumetric deposition is affected by similar parameters to the bead height. At the micro-scale, the process parameters did not show significant carbide changes but demonstrate its homogeneous distribution. The electron microscope observation exhibited the composite’s high quality due to the fast solidification of the process. The results demonstrate that the porosity is mainly affected by the powder flow rate. By understanding the preliminary contribution of process parameters, this manufacturing process can print near net-shaped parts minimizing the post-processing of metal additive manufacturing components. Therefore, this work contributes to implementing a preliminary experimental methodology to understand the deposition process of WC-reinforced composites in plasma transferred arc additive manufacturing.

In the automotive industry, it is essential to reduce the weight of the car body to improve fuel efficiency and reduce CO2 gas emissions. As such, the application of advanced high-strength steels is rapidly increasing. However, in the case of gas metal arc (GMA) welding of advanced high-strength steels (AHSS), slag particles are observed to form on the weld surface resulting in poor corrosion resistance. The presence of slag particles on the weld also affects mechanical performance. This paper focuses on the degradation of corrosion resistance due to these slag particles. Current methods to decrease slag islands are costly as they attempt (1) to better protect the weld pool by decreasing the content of oxygen-containing ingredients or increasing argon in the shielding gas and (2) to mechanically clean the weld surface using processes such as shot blasting after gas metal arc welding (GMAW). In this study, the amount of slag was reduced by adjusting the chemical composition of welding consumables. Silicon was decreased to minimize silica/silicate formation, and sulfur was adjusted to affect the surface tension balance of the molten pool. Slag particles were observed to flow along the welding direction to solidify into a large particle in the weld crater that could be removed easily. In a separate consumable, Si and Mn contents were adjusted to form Mn3O4 and SiO2 slag. The use of these two welding consumables reduced the amount of slags, which improved the corrosion resistance. It is not the intent of this paper to compare the performance of these two experimental consumables, however.

Argon–helium mixtures in gas tungsten arc welding of an iron workpiece are investigated using an axisymmetric computational model that includes the cathode, workpiece, and arc plasma in the computational domain. The three-gas combined diffusion coefficient method is used to treat diffusion of helium, argon, and iron vapour. Calculations for argon–helium mixtures without metal vapour are performed; good agreement with previous numerical results is found. A transition from a helium-like to an argon-like arc occurs when the argon mole fraction increases above about 0.3. Calculations for a wide range of argon–helium mixtures including iron vapour are then performed. Adding helium to argon alters the arc properties and affects the weld geometry. Iron vapour cools the arc for all argon–helium mixtures. Iron vapour is present above the workpiece, near the cathode and in the arc fringes for very low argon mole fractions. As the argon mole fraction increases, the iron vapour becomes increasingly confined to the region above the workpiece, with small amounts near the cathode tip. Emission spectroscopy measurements of arcs in argon–helium mixtures with water-cooled copper and uncooled iron workpieces were performed. The measured distributions of atomic helium and iron emission show good agreement with the predictions of the model.

The quality of welded joints depends on the most optimal welding parameters and the selection of shielding gas type. The shielding gas was selected for joining stainless steels through gas metal arc welding methods by considering properties such as chemical-metallurgical interaction of shielding gas and the molten weld metal during the welding process, heat transmission capability of the gas and cost. In this study, the effect of different shielding gas combinations on the mechanical and microstructural properties of 316 austenitic stainless steel joined by the metal inert gas (MIG) welding method was investigated. In the welding process, pure argon (100 % Ar), 98.5 % Ar + 1.5 % H2and 95 % Ar + 5 % H2were used as shielding gases. Tensile, hardness, and bending tests were conducted to determine mechanical properties of the welded samples. In addition, metallographic examinations were carried out to detect the macrostructural and microstructural properties of weld zones. According to the results obtained from the study, the highest tensile strength was obtained from the joints welded using 100 % Ar shielding gas. When the addition of H2into the Ar gas increased, the tensile strength of the welded samples decreased. As a result of the tensile test, fractures occurred in the base metal in all welded samples. In all welding parameters, the hardness of the weld metal was lower as compared to the heat affected zone (HAZ) and the base metal. As a result of the bending test, crack and tearing defects were found in the weld zone.

The effect of shielding gas on the mechanical and microstructural characteristics of ER410NiMo martensitic stainless steel weldments was investigated. Three weldments with various inclusion contents were manufactured using different shielding gas compositions and welding processes: gas metal arc welding (GMAW) with 100% argon (Ar), GMAW 85% Ar/15% carbon dioxide (CO2), and flux cored arc welding (FCAW) 75% Ar/25% CO2. The inclusions in each weldment were characterized by means of scanning electron microscope observations and energy-dispersive spectroscopy analysis. The weldments underwent postweld heat treatment, after which the chemical composition and reformed austenite proportion were measured to account for microstructural effects. Hardness measurements, tensile tests, and impact toughness tests using the Charpy method were performed. The results showed that the Charpy V-notch (CVN) absorbed energy decreases with increasing inclusion content. The highest CVN absorbed energy, 195 J, was obtained for the GMAW 100% Ar weld, which had the lowest inclusion content. GMAW 85% Ar/15% CO2, with four times more inclusions than the former, had a CVN absorbed energy of 63 J. The current manufacturing process, FCAW 75% Ar/25% CO2, was found to have an inclusion content three times higher than the GMAW 100% Ar weld but a CVN absorbed energy of 66 J, which is close to the GMAW 85% Ar/15% CO2 weld. The results showed that using GMAW 100% Ar as a replacement to FCAW 75% Ar/25 % CO2 would lead to a three-fold improvement in terms of absorbed impact energy. The effect of inclusions on tensile properties, which was not clearly identified as several factors, in addition to inclusion content, affects the weld strength and elongation. Overall, the yield and ultimate tensile strengths differed slightly: 724 and 918 MPa for GMAW 100% Ar, 746 and 927 MPa for GMAW 85% Ar/15% CO2, and 711 and 864 MPa for FCAW 75% Ar/25% CO2, respectively.

This research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components.

It has been well known that, in GMA welding, various welding phenomena are largely affected by the type of shielding gas used. However, up to the present time, almost no attempt has been made to ut...

An inert gas environment is required during the laser metal deposition of titanium alloys due to oxidation. A nozzle with local shielding device is more flexible than the inert gas chamber, and size of the components produced is not restricted. In this study, a coaxial double-deck gas shielding nozzle was designed to provide a local shielding for the laser metal deposition of Ti-6Al-4V alloy. Numerical simulation of flow field under four different gas flow rates was carried out, and the corresponding Ti-6Al-4V single clads as well as components were produced. Experimental results revealed that the effective protection length increased and then became steady with the gas rate getting larger. Every component showed significant change in the degree of surface discoloration. Among that when the gas flow rate exceeded 30 L/min, surface of the formed bulk components showed yellowish and shiny silver and the internal oxygen content was below 2000 ppm, which had a minimal raise from the powder. In addition, the microhardness of the components showed little increase compared with the rolled substrate.

Purpose The purpose of this paper is to find a theoretical reference to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition in wire arc additive manufacturing (WAAM) and ensure the effect of the gas shielding and stable heat and mass transfer in deposition process. The multiphysical numerical simulation and physical experiment are used for validation. Design/methodology/approach In this study, welding torch tilt deposition and external parallel magnetic field–assisted deposition are presented to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition, and a three-dimensional numerical model is developed to simulate the arc of torch tilt overlapping deposition and external parallel magnetic field–assisted overlapping deposition. Findings The comparison of simulated results indicate that the angle of welding torch tilt equal to 20° and the magnetic flux density of external transverse magnetic field equal to 0.001 Tesla are capable of balancing the electric arc and shielding gas effectively, respectively. The arc profiles captured by a high-speed camera match well with simulated results. Originality/value These studies of this paper can provide a theoretical basis and reference for the calibration and optimization of WAAM process parameters.

The surface modification of Ti6Al4V alloy using a TIG re-melting process with a non-consumable electrode under Ar and Ar + N2 shielding gases has been investigated. The re-melted layers were characterized using optical and scanning electron microscopy and x-ray diffraction. The corrosion behavior of samples was also examined by potentiostat analysis. Based on the results, the TIG surface re-melting process of Ti6Al4V alloy under Ar shielding gas has negative effects on hardness and corrosion behavior of coatings. In contrast, Ti6Al4V/TiN composite coatings were successfully formed during TIG re-melting process in the presence of N2 in shielding gas. The prepared coatings showed the hardness value of about 890-910 Hv which was over four times higher than the substrate (220 Hv). The hardness showed an increasing tendency by increasing the TIG current up to 115 A. By annealing the produced coatings, the metastable TiN phase was transformed into a stable Ti2AlN phase, and the hardness value increased to about 980 Hv. Moreover, the corrosion resistance of re-melted coatings was improved during the annealing process.

CO2 gas-shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, its characteristic repelled transfer pro...

Aluminum alloys AA5754 and AA6013 were joined using gas metal arc welding (GMAW) and the mechanical, microstructure and corrosion properties of the joints were investigated. The welding process was performed using argon as shielding gas with three different wire feed speeds and welding speeds. Metal wire (ER5356 filler) with a diameter of 1.2 mm was used in the welding process. In order to determine the mechanical properties of the joints, the welded specimens were subjected to tensile and hardness tests. In addition, an electrochemical corrosion test was conducted to determine the corrosion resistance of the specimens. The welding zone of the specimens was characterized via microstructure examination. In the tensile tests, fractures occurred in the weld metal and the heat affected zone (HAZ). However, tensile strength performance of the joints exceeded 90% under the appropriate welding parameters. The corrosion test results showed that the samples with joint defects (insufficient melting) were exposed to corrosion more rapidly than the others. Hardness test results revealed that maximum hardness values were measured at the HAZ of the AA6013 specimen, followed by the weld metal and HAZ of the AA5754 specimen, respectively. Microstructure inspections showed the structures of all the weld metals to be dendritic. © 2019 Karabuk University

This paper presents the influence of welding current, electrode-workpiece distance, electrode composition, electrode diameter, electrode tip angle, shielding gas composition, and pulsed current frequency over the arc stagnation pressure of gas tungsten arc welding (GTAW). In this study, arc application tests were carried out over a 1-mm diameter hole on a non-melting water-cooled copper plate. The hole was connected to a differential pressure sensor through an extension tube. As a result, the welding arc pressure was observed to be directly proportional to the square of the welding current and to the tungsten electrode diameter. Moreover, the pressure increases as the electrode-workpiece distance is reduced, and it is inversely proportional to the electrode tip angle, for angles greater than 45°. Also, the electrode composition, the pulsed current frequency, and the gas composition influence the welding arc stagnation pressure.

Wire arc additive manufacturing (AM) is the process by which a large, metallic structure is built layer-by-layer using a welding arc to melt a wire feedstock. A novel opportunity exists to alter the shielding gas composition to fabricate distinct geometrical features without altering the other AM parameters. In the following study, shielding gases with varied concentrations of Argon (Ar) and CO2 was used to deposit three distinct geometric shapes (walls, infill, and overhang) using a wire-based additive manufacturing system utilizing the gas metal arc welding (GMAW) surface tension transfer (STT) process. Computer-aided design (CAD) models were sliced with a custom-built slicer, and the sliced algorithm was converted into optimal robotic toolpaths. A custom virtual instrument (VI) was built in LabVIEW to compare the temperature profiles on the surface during each deposition process. After each deposition, the geometric features were scanned, and the surface waviness value was evaluated. Tensile and Charpy impact coupons were extracted from the wall geometries in the longitudinal and transverse directions and tested. The results indicated that a higher CO2 content produced higher melt pool temperatures to an extent, while lower contents of CO2 resulted in a dimensionally accurate geometry. The data also indicated that the 2%/98% CO2/Ar blend produced scatter in tensile strength and the analysis of variance (ANOVA) shows significant difference. However, the intermediate range of CO2 (5–10%) resulted in uniform tensile properties. Altogether, these results indicate that a 5%/95% CO2/Ar blend is the ideal shielding gas for lowering process temperatures and improving mechanical properties in wire arc additive manufacturing using the gas metal arc welding surface tension transfer process. Additionally, varying concentrations of Ar/CO2 can be used within the same part in order to modify the local properties or process parameters such as strength, toughness, temperature, or dimensional features. This may improve overall manufacturing quality without sacrificing specific properties.

The flow behavior of the shielding gas has been a key factor to improve the quality of products manufactured by the selective laser melting (SLM) technology as it is a major mechanism to remove the ejected metal particles away from the working plane. In this study, to obtain a proper flow field, computational fluid dynamics (CFD) with the application of the Taguchi method was employed to investigate the flow field across the working chamber, with the variations in the geometries of the blowing nozzle, the widths of the suction tunnel, the suction-to-plane distances, and the Reynolds numbers of the blowing flow. The simulation was first verified with experimental measurements. The ejecting motions of the metal powders were also taken into consideration to study the interactions between the shielding gas and the ejected particles. The results demonstrated that axis switching as well as the suction-to-plane distance are the important factors for improving the particle removal efficiency during the SLM operation.

The arc physical properties of the plate-butt welding and narrow gap welding were simulated. The narrow gap groove affects the arc properties, and the narrow gap welding arc has its special properties. The shielding gas flows along the longitudinal direction in the narrow gap groove, and the arc temperature field constricts transversely but expands longitudinally. The high-temperature region expands and the welding heat efficiency increases. The current density is larger for narrow gap welding, which induces the larger Lorentz force to accelerate the plasma flow. The axial and radial plasma flow velocities are both larger for narrow gap welding, which leads to the larger arc pressure and shear stress. The results have good agreements with the experiments results.

To reduce the consumption of gas metal arc welding shielding gas and improve welding quality, three spiral-diffusion nozzles with different structures were designed in this study. The four evaluation indexes of the flow field quality of shielding gas were determined by analyzing the protective airflow field with the computational fluid dynamics simulation method. Isight software was used to optimize the multi-objective parameters of the three spiral-diffusion nozzles with the self-adaptive mutation genetic algorithm. Combined with the computational fluid dynamic simulation results, the optimized value of each nozzle and the percentage of parameters such as gas reduction were obtained. Three new double-helical spiral-diffusion stainless nozzles were created using 3D printing, and the gas metal arc welding of the Q235 and A36 steel plates was performed using 80% Ar + 20% CO2 mixed shielding gas with three nozzles. The tensile test and impact test were conducted to inspect tensile strength and impact toughness, and the hardness and average grain grade of microstructures in the weld seam were analyzed. The experimental results were consistent with the optimization simulation results. In terms of welding quality, compared with the shielding gas consumption of the conventional nozzle, that of the optimized spiral-diffusion nozzles I, II, and III could be reduced by 29.22%, 33.19%, and 27.31%, and the effective protection range could be increased by 34.53%, 19.79%, and 19.69%, respectively.

Welding of ferritic steel tube material T91 (9Cr-1Mo), was used because of high temperature withstanding, mechanical properties, compatibility with chemicals and adequate weldability. The main objective of this project is to find out near optimum welding parameters with appropriate shielding gas in gas tungsten inert gas welding (GTAW) of T91 tube. The quality and productivity of the weld joint strongly depends on welding parameters. The perfect arc during welding is produced when the welder uses the optimum welding parameters. The composition of shielding gas plays an important role ensuring sound quality of welds. The composition of shielding gas with the molten pool has a marginal influence in the depth of penetration. The optimized parameters with three samples were prepared with different purging gases Viz. 100% helium, 100% Argon, Argon 50% plus Helium 50% for welding of 2.9 mm thick T91 tube with ER 505 filler wire.

Laser welding has been increasingly adopted into the automotive sector due to its competitive processing speed, less restrictive single-sided access requirements and improved process flexibility. These benefits notwithstanding, laser welding still remains susceptible to the weld cracking especially for 6xxx high strength aluminium extrusions, which are widely used in the automotive industry for body-in-white and battery tray manufacturing. This paper reviews current challenges and opportunities for construction of battery tray using aluminium alloys with laser welding process. It aims to provide a view on the selection of welding equipment in terms of beam oscillation, power modulation, beam shaping, filler wire and shielding gas, and analyze their impact on joint integrity for 6xxx grades aluminium extrusions. The driving idea is to control the thermal history in and around the molten pool and to modify the chemical composition in the fusion zone to reduce the formation of solidification cracks. Results of the study have shown that the modification of chemical composition by the use of filler wire is currently the most efficient approach to improve joint strength. Further results evidences also showed that beam shaping with adjustable ring mode laser helps to stabilize the keyhole and achieve a wider molten pool and weld interface width. Manufacturing implications are reviewed and discussed throughout the paper.

Optimization techniques are widely used tools in the engineering sector and suitable to all the fields of mechanical engineering. Welding is an important manufacturing process and its parameter optimization is highly focused on getting optimal results. Gas Tungsten Arc Welding (GTAW) is the suitable arc welding process joining variety of the engineering materials. This process has various parameters like welding current, speed, arc length, shielding gas and gas type etc. A lot of attempts were made by the researchers to get an optimal outcome like the appearance of the weld bead and tensile strength etc… In this article, various optimization techniques used in GTAW process are discussed. The widely used optimization methods, GTAW parameters and the outcomes are discussed from the literature. These result will help the researchers to avoid selecting same techniques and parameters. This paper will give guidelines to the researchers to focus on new studies.

Thin AISI 430 ferritic stainless steel sheets containing 18% Cr were hardened by continuous-wave laser beams under different conditions. A symmetric double laser treatment platform was developed to operate two lasers simultaneously in order to achieve a homogenous microstructure through the specimen and avoid the overheating associated with single laser treatments on one surface. The influence of linear energy density and shielding gas on microstructure and hardness is investigated for both single and double laser treatments. Tensile behavior and oxidation effect during treatment are also studied. With a peak temperature around Tm, the single-track laser yields local microhardness that is 90% higher than the base material, while samples completely treated by the multi-track laser present a 60% increase in yield stress and 45.8% in ultimate tensile stress. These improvements in mechanical behaviors are driven by the formation of martensite and chromium carbides upon rapid cooling despite poor carbon content and dramatic grain coarsening. These results could be useful in order to locally modify the behavior of medium chrome ferritic stainless steel to meet industrial requirements. ANR JCJC SCOLASTIC 16-CE08-0009

The use of shielding gases in laser beam welding is of particular interest for materials interacting with ambient oxygen, e.g., copper, titanium or high-alloy steels. These materials are often processed by remote laser beam welding where short welds (e.g., up to 40 mm seam length) are commonly used. Such setups prevent gas nozzles from being carried along on the optics due to the scanner application and a small area needs to be served locally with inert gas. The article provides systematic investigations into the interaction of laser beam processes and parameters of inert gas supply based on a modular flat jet nozzle. Based on the characterization of the developed nozzle by means of high-speed Schlieren imaging and constant temperature anemometry, investigations with heat conduction welding and deep penetration welding were performed. Bead-on-plate welds were carried out on stainless steel AISI 304 for this purpose using a disc laser and a remote welding system. Argon was used as shielding gas. The interaction between Reynolds number, geometrical parameters and welding/flow direction was considered. The findings were proved by transferring the results to a complex weld seam geometry (C-shape).

Gas tungsten arc welding (GTAW) is a common joining method for austenitic stainless steel sheets. Edge joint is frequently used configuration when the aim is to produce weldments e.g., between the tube sheets and the tubes and to other hollow structures needing tight sealing welds and sound joints. In those applications all positions for welding is usually needed. Robotized welding is utilized, when manual welding is not possible, e.g., in maintenance for nuclear power applications. In automatic welding a strict control of location of arc and welding parameters are extremely important. In this work the aim was to find suitable welding parameters, as pulse parameters, welding speed and shielding gas composition and study their effects on weld joint penetration and weld quality in different welding positions. In addition, the inaccuracy in the alignment of the arc and its effects was tested in different cases. It was found that it was possible to find the optimal parameters in different positions, flat (PA), overhead (PE), and vertical-up position (PF). However, the vertical-down position (PG) was giving a lower joint penetration in the cases which allow sound welds. Therefore, it was considered that the fabrication of the circumferential joint was best done in two steps to avoid the PG position, which ensures that a sound weld with the set 2.6 mm penetration requirement is achieved over the entire circumference. The use of a shielding gas mixture containing argon and 2% hydrogen showed significant advantages over the other three shielding gas compositions tested, which was observed as deeper penetration of the welds. Post-print / Final draft

Samples of AA5086 aluminium alloy were welded by gas tungsten arc welding (GTAW) with alternating current using three different shielding gases. The samples were welded with pure argon (Ar), a mixture of argon and helium (Ar + He) and a new mixture composed of argon, nitrous oxide and oxygen (Ar + N2O + O2). The effect of the shielding gas on the residual stresses and on the mechanical and microstructural properties of the welded joints was evaluated and compared with the base metal. The new gas mixture produced compressive residual stresses in the longitudinal and transverse directions in the weld metal. Tensile test of welded joints indicated similar values for yield strength and ultimate tensile strength; however, these values were lower compared to the base metal. The new gas mixture provided a welded joint with hardness values in the weld metal and heat affected zone close to the base metal values and with greater magnitude compared to samples welded using pure argon and mixture of argon and helium. Microstructural characterisation performed by optical and scanning electron microscopy showed that the new mixture produced welded joints with lower porosity.

Tungsten inert gas (TIG) welding of austenitic stainless steels is a critical process used in industries. Several properties of the welds must be controlled depending on the application. These properties, which include the geometrical, mechanical and microstructural features, can be modified through an appropriate composition of shielding gas. Researchers have studied the effects of the addition of nitrogen through the shielding gas, however, due to limited amount of experimental data, many of the interaction effects are not yet reported. In this study, welds were made homogeneously as well as heterogeneously with various concentrations of nitrogen added through the shielding gas. The gas compositions used were 99.99%Ar (pure), 2.5% N2 + Ar, 5% N2 + Ar and 10% N2 + Ar. Additionally, the welding process parameters were varied to understand different interaction effects between the shielding gas chemistry and the process variables such as filler wire feed rate, welding current, etc. Strong interactions were observed in the case of heterogeneous welds between the gas composition and the filler wire feed rate, with the penetration depth increasing by nearly 30% with the addition of 10% nitrogen in the shielding gas. The interactions were found to influence the bead geometry, which, in turn, had an effect on the mechanical properties as well as the fatigue life of the welds. A nearly 15% increase in the tensile strength of the samples was observed when using 10% nitrogen in the shielding gas, which also translated to a similar increase in the fatigue life.

Powder interlayer bonding (PIB) is a novel joining technique, which has been developed to facilitate high-integrity repairs of aerospace components, manufactured from commonly used titanium alloys. The PIB technique utilises an interlayer between complex geometric components which are mated under pressure and a highly localised heating source. In this study, induction heating enabled bonding in an inert fusion zone by use of an oxygen-displacing shielding gas, with particular attention to the initial heating and pressure application. These early stages proved crucial to the elimination of pores and consolidation of the alloy powder, with porosity volume fraction reduced to just 0.5% after just 20 sec at the bonding force. The technique has produced high-integrity bonds in alloys such as Ti-6Al-4V, retaining approximately 90% of the alloy strength in previous studies, offering advantages over established joining methods such as tungsten inert gas (TIG) and plasma arc (PA) welding due to a more highly localised heating and fusion zone. It is believed that powder interlayer bonding can compete against these techniques, providing a more time and cost-effective repair route for net shape components manufactured from a range of alloys with minimal post-processing.

As a widely used additive manufacturing technique, the laser metal deposition process (LMD) also known as direct energy deposition (DED) is often used to manufacture large-scale parts. Advantages of the LMD process are the high build-up rate as well as its nearly limitless build-up volume. To manufacture large-scale parts in lightweight design with high strength aluminium alloy EN AW-7075, the LMD process has a disadvantage that must be considered. During the process, the aluminium alloy is melted and has therefore a high solubility for hydrogen. As soon as the melt pool solidifies again, the hydrogen cannot escape the melt and hydrogen pores are formed which weakens the mechanical properties of the manufactured part. To counter this disadvantage, the hydrogen must be successfully kept away from the process zone. Therefore, the covering of the process zone with shielding gas can be improved by an additional shielding gas shroud. Furthermore, the process parameters energy input per unit length as well as the horizontal overlapping between two single tracks can be varied to minimize the pore volume. Best results can be achieved in single tracks with an elevated energy input per unit length from 3000 to 6000 J/cm. To manufacture layers, a minimal horizontal overlapping will lead to lowest pore volume, although this results in a very wavy surface, as a compromise of low pore volume and a nearly even surface a horizontal overlapping of 30 to 37% leads to a pore volume of 0.95% ± 0.50%.

Statistical models were developed to study the effect of gas metal arc welding process parameters (i.e., wire feed speed, voltage, travel speed, and shielding gas chemistry) on the resultant weld bead width, penetration, and reinforcement height, using a factorial design of experiment. Analysis of variance (ANOVA) indicated that the weld width depended on voltage, travel speed, gas type, and the interactions between these factors. The weld penetration depended only on wire feed speed and gas type, as well as the two-way interactions of wire feed speed with travel speed and gas type. Reinforcement height depended on travel speed, wire feed speed, and their two-way interactions with gas type. Residual analysis revealed that all assumptions inherent in the regression analysis were satisfied over the range of welding parameters considered in this study. The predictive power of the statistical models was validated using intermediate process parameter values in the experimental design, and it was found that predicted values were mainly in agreement with the measured values for a 95% prediction interval.

Exposures to airborne particles and toxic gases generated by welding fabrication activities will potentially lead to various diseases. Accurate information on the transport and deposition of such aerosols in the respiratory system is critically needed for precise health risk assessments. To address the data demand mentioned above, a multiscale computational fluid-particle dynamics (CFPD) model was developed in this study. Specifically, a virtual fabrication shop was integrated with a virtual human in the numerical model to evaluate the effects of ventilation condition, particle size, and gas species on the lung uptakes of those welding fume particles and gases. Welding fume particle and gases transmission, transport, and deposition have been simulated and analyzed starting from the emission source to the subject-specific human respiratory system via oral inhalation. Spherical iron particles with diameters of 100, 190, and 830 nm were simulated. The transport and absorption of NOx and CO were predicted too. Steady-state inhalation with 11.87 L/min was applied with two different air filter ventilation conditions. The numerical results indicate that the ventilation condition can significantly influence welding gas transport and deposition. The pulmonary gas absorption rate is much higher at poor ventilation conditions. The air-tissue absorption coefficient is another crucial factor that can impact pulmonary gas absorption. The total particle deposition fractions (TDFs) from mouth/nose to generation 6 (G6) are less than 18.0%, and particles mostly deposit in the oral cavity. Regional and local particle deposition data demonstrate that particles tend to enter the two upper lobes more than the other three lobes. In summary, this study paves the way to build a personalized in silico tool based on CFPD models for noninvasive precise health risk assessments associated with different welding activities.

Dissimilar welding of 3mm thickness of AISI 304L austenitic stainless steel plate and AISI 430 ferritic stainless steel plates were performed by Tungsten Inert Gas welding without any filler material by using argon as shielding gas. Welding is carried out according to set of combinations of welding parameters such as welding current (levels of 135,140,145 Ampere), welding speed (levels of 105, 110, 115 mm/min) and shielding gas flow rate (of levels 5,10,15 Litre/min) obtained through Taguchi L9 orthogonal approach for maximizing the ultimate tensile strength by using MiniTab software . Radiography test was performed to know the soundness of the welds. Tensile specimens are fabricated as per ASTM E8 standard for tensile testing. Microstructural observations of the weld are performed. Correlations have been obtained to know the effect of welding speed, welding current and shielding gas flow rate on tensile strength and an optimum level of parameter is obtained at welding current of 145 Ampere, welding speed of 115 mm/min and shielding gas flow rate of 5 Litre/min.

Several case studies have shown that welding of stainless steel to galvanized steel leads to evolution of zinc which can penetrate through the steel and result in cracking, the present study focuses on determination of the effect of zinc on the mechanical behaviour of such weld joints. Welding was carried out using two shielding gas combinations. The other variations in parameters were heat input and presence or absence of zinc coating at the weld location. Tensile tests showed that the ductility of weld specimen improved when the coating was stripped off the samples prior to welding. Impact strength of weld specimens also followed similar trend. The impact strength was found to be improved when welding was done using Ar+2%He+2%O2 as shielding gas. The compressive strength was found to be similar. To explain the mechanical behaviour of the welded specimen, microstructural characterization of the weld region was carried out.

Laser welding experiments are performed on Ti-6Al-4V alloy sheets by adopting fiber laser. A special kind of workpiece fixture is designed and fabricated for providing shielding gas. After experiments, penetration depth, fusion zone width and heat-affected zone size at different locations within weld bead are measured and discussed in detail. Influence of line energies on the formation of non-uniform microstructure within weld bead is explored by conducting microstructural analysis. Various kinds of microstructural morphology of martensitic structure such as α′ martensite, blocky α, massive α and basket-weave microstructure are found in fusion zone. Experimentally, it is found that beam power is the key parameter for controlling penetration depth. Higher hardness is noticed within fusion zone due to the existence of large volume of α′ martensite. Tensile strength and hardness of welded specimens are increased with decreasing line energy. Small amount of micropores are also found in solidified weld bead. However, its sizes are in acceptable range as per BSEN:4678 standard. Most favorable welding condition is identified as a combination of beam power of 800 W and welding speed of 1000 mm/min which yields full penetration, narrower bead width, small heat-affected zone, minimal defects and acceptable mechanical properties.