Showing papers on "Shielding gas published in 2017"

Material properties of CMT—metal additive manufactured duplex stainless steel blade-like geometries

Abstract: Impeller blades are often individual and complex-shaped components made of challenging metals. As the manufacturing of such blades is highly sophisticated, only a few companies worldwide possess the necessary processing knowledge and that is why long production times have to be accepted by customers. To overcome this economic disadvantage, manufacturing technologies are permanent under supervision and it seems that metal additive manufacturing could thereby play an important role in future. In this paper, wire arc additive manufacturing (WAAM) based on gas metal arc welding (GMAW) is considered. Shape-giving GMAW is well known in industrial manufacturing, but its application is limited due to restrictions by the welding process itself: For thinner wall thicknesses, a significant reduction of the weld process energy is required which increases the risk of process instabilities and spatter formation. Extensive welding process-related efforts have been undertaken to overcome this fact and a new GMAW process, called CMT (Cold Metal Transfer) was introduced. CMT is based on a high-frequency forward and backward movement of the welding wire electrode and provides an almost spatter-free and absolute precise, periodic detachment of accurately defined droplets from the filler wire at very low process energies. In combination with an accurate robotic movement of the CMT welding torch, geometries with minimum thicknesses in the range of 2–4 mm can be build up layer by layer. Additionally, a broad range of different, well established and third party-approved GMAW filler metals for joining is available. In this work, an impeller blade-like geometry out of duplex stainless steel has been manufactured by CMT using a filler wire type G 22 9 3 N L. The investigations have shown that the achieved surface roughness is comparable to sand casting and the microstructure is without any evidence for porosity and lack of fusion. Furthermore, an austenite/δ-ferrite weld microstructure with partly preferred grain orientations and a δ-ferrite content of around 30FN exists. The measured mechanical properties, especially strength and toughness, are comparable to data provided by the filler metal data sheet.

Effect of A-TIG Welding Process on the Weld Attributes of Type 304LN and 316LN Stainless Steels

Abstract: The specific activated flux has been developed for enhancing the penetration performance of TIG welding process for autogenous welding of type 304LN and 316LN stainless steels through systematic study. Initially single-component fluxes were used to study their effect on depth of penetration and tensile properties. Then multi-component activated flux was developed which was found to produce a significant increase in penetration of 10-12 mm in single-pass TIG welding of type 304LN and 316LN stainless steels. The significant improvement in penetration achieved using the activated flux developed in the present work has been attributed to the constriction of the arc and as well as reversal of Marangoni flow in the molten weld pool. The use of activated flux has been found to overcome the variable weld penetration observed in 316LN stainless steel with <50 ppm of sulfur. There was no degradation in the microstructure and mechanical properties of the A-TIG welds compared to that of the welds produced by conventional TIG welding on the contrary the transverse strength properties of the 304LN and 316LN stainless steel welds produced by A-TIG welding exceeded the minimum specified strength values of the base metals. Improvement in toughness values were observed in 316LN stainless steel produced by A-TIG welding due to refinement in the weld microstructure in the region close to the weld center. Thus, activated flux developed in the present work has greater potential for use during the TIG welding of structural components made of type 304LN and 316LN stainless steels.

Effects of shielding gas control: welded joint properties in GMAW process optimization

Abstract: One function of shielding gases used in welding processes, such as hydrogen (H2), oxygen (O2), carbon dioxide (CO2), nitrogen (N2), helium (He), argon (Ar) and their mixtures, is protection of the weld pool against harmful contamination that could generate defects. In addition to this primary function, shielding gases significantly affect the shape of the weld, weld geometry, seam appearance, metallurgical and mechanical properties, welding speed, metal transfer, arc stability or beam and fume emissions. The shielding gas is thus a key factor in determining weld joint properties and welding process efficiency. As welding processes have become enhanced and welding research has advanced, different combinations of shielding gas mixtures have become available under a wide variety of trademarks, each claiming to offer the best efficiency. The shielding gas flow rate in GMAW welding is usually set according to empirical experiment. The flow generally remains unchanged throughout the entire welding process and is set at maximum values of the welding parameters so that there is sufficient gas cover. This setting means, however, that unnecessarily large quantities of shielding gas may be consumed in other phases of the welding process. In view of constantly increasing prices and shortfalls in helium supply, there is a need to optimize the use of shielding gas. Consequently, an ability to closely monitor the shielding gas blend and reduce waste can provide valuable cost savings. This paper examines the effects of shielding gas mixtures and their components, presents a cross-comparison of shielding effects in fusion welding and suggests guidelines for adaptive controllability of shielding gas in advanced adaptive fusion welding. The study reviews scientific case studies and experiments from the point of view of the effect of the shielding gas on the process efficiency and process outcome. The study considers shielding gases for welding of both ferrous metals (i.e. carbon steels, stainless steels, high-strength steels) and non-ferrous metals (i.e. aluminium and its alloys, nickel and its alloys and copper and its alloys). Appropriate choice of shielding gas and use of an optimum flow rate results in better quality in terms of increased productivity, reduced gas consumption and improved weld geometry properties, microstructure and mechanical properties. Although some blends can be used effectively in many different processes, other blends appear process-dependent; they produce far poorer results when utilized in non-appropriate processes. Particle image velocimetry (PIV) and Schlieren techniques can be used for visual sensing of gas flow during fusing welding. Moreover, an adaptive alternative gas supply can improve welding performance and weld quality and reduce harmful fume emission.

Additive Manufacturing Based on Welding Arc: A low-Cost Method

Abstract: The objective of this paper is to present a review of a new developing manufacturing technology based on welding of metallic materials. Additive manufacturing (AM) is based on robot welding and it has showed the high flexibility, efficiency, fast output, good quality and low cost. This paper explores several common welding materials and manufacturing technologies include the shield gas, materials engineering, processes and most concerned commercial interests. AM has the potential to revolutionize the global parts manufacturing and industrial tendencies with the rapid development of increasing material manufacturing technology. AM based on arc welding has the big advantages of high efficiency and low cost, which makes it possible to use in many industries although it has a little bit poor surface qualities compare to AM based on laser and electron beam manufacturing.

Microstructure, Mechanical and Intergranular Corrosion Behavior of Dissimilar DSS 2205 and ASS 316L Shielded Metal Arc Welds

Abstract: There are many industrial situations particularly in petro-chemical, marine, power plant and other such industries where the use of dissimilar metal weldments is necessary, mainly due to economic benefits and also sometimes to improve the performance of the component. Both austenitic stainless steels and duplex stainless steels have received much attention in recent days due to their superior anti-corrosive and mechanical properties. Further, the use of shielded metal arc welding (SMAW) process is inevitable in engineering industries. In the present work, microstructure, mechanical and intergranular corrosion behavior of dissimilar 2205 duplex stainless steel and 316L austenitic stainless steel fabricated by SMAW process using E2209 electrode by taking two different heat input (0.45–0.60 kJ/mm) was investigated. The microstructures were characterized by using optical microscopy and scanning electron microscopy (SEM), while the localized chemical information was obtained by an energy dispersive spectrometer attached to the SEM. Double loop electrochemical potentiokinetic reactivation test was performed to quantitatively assessing the intergranular corrosion based on degree of sensitization. The effect of weld dilution on mechanical properties (i.e. tensile/hardness properties) was also studied. The ferrite content was experimentally measured by using ferritoscope and it was observed that the weld joint achieved the required ferrite content for both the heat inputs. Higher ferrite content (results of faster cooling rate) increased the hardness and tensile strength of low heat input as compared to high heat input. While, high heat input improved the corrosion resistance due to formation of higher austenitic phases. Higher impact energy was observed in E2209 weld metal than that of the base metals. No welding defects were observed and recommended for industrial use.

Effect of Continuous and Pulsed Current Gas Tungsten Arc Welding on Dissimilar Weldments Between Hastelloy C-276/AISI 321 Austenitic Stainless Steel

Abstract: In the present investigation, an attempt has been made to join Hastelloy C-276 nickel-based superalloy and AISI 321 austenitic stainless steel using ERNiCrMo-4 filler. The joints were fabricated by continuous and pulsed current gas tungsten arc welding processes. Experimental studies to ascertain the structure-property co-relationship with or without pulsed current mode were carried out using an optical microscope and scanning electron microscope. Further, the energy-dispersive spectroscope was used to evaluate the extent of microsegregation. The microstructure of fusion zone was obtained as finer cellular dendritic structure for pulsed current mode, whereas columnar structure was formed with small amount of cellular structure for continuous current mode. The scanning electron microscope examination witnessed the existence of migrated grain boundaries at the weld interfaces. Moreover, the presence of secondary phases such as P and μ was observed in continuous current weld joints, whereas they were absent in pulsed current weld joints, which needs to be further characterized. Moreover, pulsed current joints resulted in narrower weld bead, refined morphology, reduced elemental segregation and improved strength of the welded joints. The outcomes of the present investigation would help in obtaining good quality dissimilar joints for industrial applications and AISI 321 ASS being cheaper consequently led to cost-effective design also.

Comparative study of hybrid laser–MIG leading configuration on porosity in aluminum alloy bead-on-plate welding

Abstract: Laser–metal inert gas (MIG) welding is a promising welding technology, which presents many attractive properties. However, porosity still remains a serious problem in laser–MIG welding of aluminum. In this experimental study, the effect of leading configuration on porosity formation and distribution in laser–MIG bead-on-plate welding of A7N01 alloy was investigated. Experiments on arc current, welding speed, and arc configuration were performed comparatively for two leading configurations, respectively. The welds were analyzed with X-ray photographs and cross-section observations. Pores in laser–MIG-welded samples were mainly keyhole-induced. The concept of porosity area fraction was used to evaluate the severity of pore defect. The maximum porosity area fraction presented at different arc currents in the two leading configurations (in laser leading welding, it is 150 A, while in arc leading welding, it is 110 A). With welding speed increasing, porosity area fraction decreased. Bubble escape condition was deduced and used to discuss the probable mechanism of the effect of leading configuration on pore formation. The results showed that leading configuration was considerable in porosity minimization and prevention.

Effects of Pulsed Nd:YAG Laser Welding Parameters on Penetration and Microstructure Characterization of a DP1000 Steel Butt Joint

Abstract: Of particular importance and interest are the effects of pulsed Nd:YAG laser beam welding parameters on penetration and microstructure characterization of DP1000 butt joint, which is widely used in the automotive industry nowadays. Some key experimental technologies including pre-welding sample preparation and optimization design of sample fixture for a sufficient shielding gas flow are performed to ensure consistent and stable testing. The weld quality can be influenced by several process factors, such as laser beam power, pulse duration, overlap, spot diameter, pulse type, and welding velocity. The results indicate that these key process parameters have a significant effect on the weld penetration. Meanwhile, the fusion zone of butt joints exhibits obviously greater hardness than the base metal and heat affected zone of butt joints. Additionally, the volume fraction of martensite of dual-phase steel plays a considerable effect on the hardness and the change of microstructure characterization of the weld joint.

Study of hybrid additive manufacturing based on pulse laser wire depositing and milling

Abstract: The hybrid additive manufacturing which involves direct metal deposition and high-speed milling has been considered as an effective process to make high performance products with well surface finish. Research that have been reported indicate that continuous energy sources can lead to intolerable residual stress and distortion even after the parts are processed by machine tools. Therefore, a hybrid additive manufacturing machine tool based on pulse laser wire depositing is established taking advantage of its intensive exposure. The designed work area of the hybrid AM machine tool is 50 mm × 50 mm × 100 mm. On this basis, a set of preliminary experiments are carried out to study the performance of the proposed hybrid AM process. Both the substrate and the wire are stainless steel (SUS304), and the wire diameter is 0.6 mm. Depositing trails were kept by oxide film since shield gas is not used during the deposition. Results show that stabilization of the process has a strong impact on both the surface finish and the microstructure. Moreover, experiment results indicate that wire feeding performance is the critical factor influencing the product performance due to the small weld pool size and the rapid melting and solidifying. Typical macrodefects of the fused welding and the exclusive flaw of additive manufacturing are detected. Microstructures show that column grains less than 1 μm dominate the deposition zone, where the column grains grew in the direction of depositing on the middle layers and along the curvature direction on the top surface. A thin wall about 0.5 mm wide is milled, and the result shows that the surface of the bead is greatly improved and no defects are detected after the thin wall is cut. However, the trapezoid cross section indicates that a further study on cutting is still demanded.

Optimizing the Parameters of TIG-MIG/MAG Hybrid Welding on the Geometry of Bead Welding Using the Taguchi Method

Abstract: The main aim of this work was to evaluate the influence and optimize the factors of the TIG-MIG/MAG hybrid welding process on the geometry of the weld bead. An experimental design using the Taguchi methodology (robust design method) was used to conduct the experiments. The experiments were carried out according to an orthogonal matrix with 27 experiments, with three replicates each, totaling 81 test specimens. The factors (MIG/MAG shielding gas type, MIG/MAG voltage, MIG/MAG wire feed, gas flow rate of TIG, electric current intensity of TIG and welding speed) were varied with three levels each. Penetration, heat-affected zone (HAZ), bead width and bead height were the response variables analyzed. The results showed that the penetration was significantly influenced by the MIG/MAG wire feed, MIG/MAG shielding gas type, MIG/MAG voltage and welding speed. The HAZ has been influenced by MIG/MAG voltage, MIG/MAG shielding gas type, welding speed and electric current intensity of TIG. All factors had effects on the width, except the MIG/MAG wire feed. The bead height was significantly influenced by the MIG/MAG wire feed and by the electric current intensity of TIG. Optimizing the process was performed, so that for each output variable, the values of the factors that should be used were indicated, and the optimization was confirmed by welding test specimens.

Erratum to: Mechanisms of weld pool flow and slag formation location in cold metal transfer (CMT) gas metal arc welding (GMAW)

Abstract: This work investigates the weld pool flow behavior by observing the flow pattern of floating slag particles for cold metal transfer (CMT) gas metal arc welding (GMAW) using three different welding wires. These wires contain different amount of deoxidizers in the form of silicon and manganese. In situ high-speed videography shows that for the wire containing a high amount of deoxidizer, the weld pool flows from the center towards the toe. With the presence of a lower amount of deoxidizers, it flows from the toe towards the center. Besides, a higher amount of CO2 in the shielding gas changes the amount and location of slag formation. Chemical composition analysis of weld metals relates the weld pool flow behavior with the amount of dissolved oxygen (surface active element). The presence of adequate amount of oxygen in the weld pool can alter the weld pool flow pattern, which changes with the amount of deoxidizers present in the materials and the amount of oxygen supplied through the shielding gas. Based on this concept, the mechanisms involved in weld pool flow pattern and slag formation location for different composition of the consumables are disclosed to improve weld quality and productivity through the selection of the proper welding consumables in CMT-GMAW.

Effects of shielding gas composition on arc behaviors and weld formation in narrow gap tandem GMAW

Abstract: In narrow gap gas metal arc welding (GMAW), it is useful to understand the arc behaviors to ensure the weld quality. Arc behaviors are strongly affected by the shielding gas composition. In this study, a three-component shielding gas mixture was used in tandem narrow gap pulsed GMAW, and the effect of its composition on arc behaviors and weld formation were investigated. The shielding gas included argon, carbon dioxide, and helium. The arc behaviors and electrical characteristics were recorded by a high-speed camera and an electrical signal acquisition system. The results show that the arc behaviors in different shielding gas are different. The arc expands and the arc length decreases with the increase of CO2 content or helium content. The arc is the widest when the shielding gas is 80%Ar10%CO210%He. The weld shape was observed, and it was found that the weld width increases first and then decreases with increasing of the CO2 content. When the helium content is below 15%, the weld width increases as the helium content increases, but when the helium is 15%, the weld width drops due to the decrease of arc length. When the helium content is above 15%, the weld width continues to increase as the helium content increases. The largest weld width can be obtained in 80%Ar10%CO210%He.

Residual stresses in cold-wire gas metal arc welding

Abstract: This work compares the welding residual stresses of the cold-wire gas metal arc welding and conventional gas metal arc welding processes. Two techniques were used to measure the residual stresses: X-ray diffraction and acoustic birefringence. The base metal used was carbon manganese steel plates of 9.5- mm thickness. The results showed that the introduction of the cold-wire tends to decrease the residual stresses, suggesting that the introduction of the cold wire decreases the amount of heat given to the base metal, and consequently lowers residual stresses.

Effect of multipass TIG welding on the corrosion resistance and microstructure of a super duplex stainless steel

Abstract: This is a study of the effect of repetitive TIG (tungsten inert gas) welding passes, melting and remelting the same material volume on microstructure and corrosion resistance of 2507 (EN 1.4410) su ...

Microstructure and Mechanical Properties of Cryogenic High-manganese Steel Weld Metal

Abstract: Extant studies have focused on the development of high-manganese austenitic steel, which is a potential cost-effective alternative to commercial cryogenic materials such as 9% Ni steels, 304 stainless steels, and Al5083 alloys. The development of suitable welding consumables is of significant importance in the commercial application of this new material for cryogenic applications. Specifically, flux-cored arc welding consumables that allow all-positional welding for high-Mn steel are required to fabricate liquefied natural gas (LNG) tanks. Hence, a welding wire alloyed with austenite-stabilizing elements (e.g., C, Mn, and Ni) was developed for cryogenic toughness. The microstructure and mechanical properties were evaluated as a function of the alloy composition. This unique combination of strength and toughness demonstrated the potential of this newly developed high-Mn steel for cryogenic services.