Showing papers on "Shielded metal arc welding published in 2007"

Effect of pulsed current and post weld aging treatment on tensile properties of argon arc welded high strength aluminium alloy

Abstract: This paper reveals the effect of pulsed current and post weld aging treatment on tensile properties of argon arc welded AA7075 aluminium alloy. This alloy has gathered wide acceptance in the fabrication of light weight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminium alloy are frequently gas tungsten arc welding (GTAW) process and gas metal arc welding (GMAW) process due to their comparatively easier applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying pulsed current welding technique. Four different welding techniques have been used to fabricate the joints and they are: (i) continuous current GTAW (CCGTAW), (ii) pulsed current GTAW (PCGTAW), (iii) continuous current GMAW (CCGMAW) and (iv) pulsed current GMAW (PCGMAW) processes. As welded joint strength is much lower than the base metal strength and hence, a simple aging treatment has been given to improve the tensile strength of the joints. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Post weld aging treatment is accompanied by an increase in tensile strength and tensile ductility.

Mechanism and Microstructure of Oxide Fluxes for Gas Tungsten Arc Welding of Magnesium Alloy

Abstract: Five single oxide fluxes—MgO, CaO, TiO2, MnO2, and Cr2O3—were used to investigate the effect of active flux on the depth/width ratio in AZ31B magnesium alloy. The microstructure and mechanical property of the tungsten inert gas (TIG) welding seam were studied. The oxygen content in the weld seam and the arc images during the TIG welding process were analyzed. A series of emission spectroscopy of weld arc for TIG welding for magnesium with and without flux were developed. The results showed that for the five single oxide fluxes, all can increase the weld penetration effectively and grain size in the weld seam of alternating current tungsten inert gas (ACTIG) welding of the Mg alloy. The oxygen content of the welds made without flux is not very different from those produced with oxide fluxes not considering trapped oxide. However, welds that have the best penetration have a relatively higher oxygen content among those produced with flux. It was found that the arc images with the oxide fluxes were only the enlarged form of the arc images without flux; the arc constriction was not observed. The detection of arc spectroscopy showed that the metal elements in the oxides exist as the neutral atom or the first cation in the weld arc. This finding would influence the arc properties. When TIG simulation was carried out on a plate with flux applied only on one side, the arc image video showed an asymmetric arc, which deviated toward the flux free side. The thermal stability, the dissociation energy, and the electrical conductivity of oxide should be considered when studying the mechanism for increased TIG flux weld penetration.

Study of Spot Welding of Austenitic Stainless Steel Type 304

Abstract: In this study, austenitic stainless steel type 304 were welded by resistance spot welding. The relationship of nugget diameter and welding current was investigated. Hardness distribution along welding zone was also investigated. The results indicated that increasing welding current gave large nugget diameter. The welding current did not much affected the hardness distribution.

Effect of oxygen content in He–O2 shielding gas on weld shape in ultra deep penetration TIG

Abstract: The effect of the shielding gas concentration on the weld shape was studied for the moving bead on plate TIG welding of SUS304 stainless steel under He–O2 mixed shielding. The small addition of oxygen to the helium base shielding gas can precisely control the oxygen content in a liquid pool and the weld shape. Oxygen is a surface active element for stainless steel. When the oxygen content in the liquid pool is above the critical value of ∼ 70 ppm, the weld shape suddenly changes from a wide shallow type to a deep narrow one due to the change in the Marangoni convection from the outward to inward direction on the liquid pool surface. Weld shape variations influenced by the welding parameters including welding speed, welding current and electrode tip work distance under pure He and He–0.4%O2 mixed gas shielding were systematically investigated. The investigation results showed that the final shape of the TIG weld depends to a large extent on the pattern and magnitude of the Marangoni convection on t...

Variable AC polarity GTAW fusion behavior in 5083 aluminum

Abstract: Aluminum alloys are typically welded on AC with the gas tungsten arc welding (GTAW) process. Many power sources have "max penetration" indicated when more than 50% of the AC cycle is spent on electrode negative polarity and "max cleaning" when more than 50% of the cycle is on electrode positive polarity. In the work reported here, weld bead dimensions, notably penetration and bead width, increase with the percentage of electrode positive polarity during the unbalanced square wave AC welding of aluminum alloys with the GTAW process. This is in direct contradiction of conventional assumptions about the role of electrode positive and electrode negative contributions to surface cleaning and fusion behavior during AC welding. The primary source of the extra base metal melting during electrode positive operation is in the nature of cold cathode field emission of electrons from the base metal. The dielectric breakdown of surface oxide as electrons are emitted also contributes to the increased fusion, but this is not a contributory factor once the weld metal surface is completely clean. Both phenomena require extra energy to be supplied to the cathode, which results in the increased fusion. Earlier works on the gas metal arc welding (GMAW) process confirm this behavior of enhanced melting at the cathode. Positive ion bombardment, thermal convection from the plasma jet, and radiation from the plasma complete the thermal input to the cathode for metal fusion.

Process for laser-arc hybrid welding aluminized metal workpieces

Abstract: Process for laser welding at least one metal workpiece ( 1 ) by a laser beam ( 3 ), the workpiece having a surface coating ( 2 ) containing aluminum, characterized in that the laser beam ( 3 ) is combined with at least one electric arc ( 4 ) so as to melt the metal and actually weld the workpiece(s).

Effect of boron contents on weldability in high strength steel

Abstract: Three experimental flux cored wires(basic type) designed to produce systematic variations in the concentrations of boron of 32 ppm, 60 ppm and 103 ppm in the weld metal were prepared. A previous study of crack properties, morphology and microstructure in accordance with welding conditions was published in Welding Journal(Lee, 2006). Microstructure, strength and absorbed energy were studied for EH32 TMCP (Thermo-Mechanical Controlled Process) 40 mm thick plate welded with a gas-shielded flux cored arc welding. The volume fraction of acicular ferrite decreased with increasing boron contents 32 to 103 ppm. The upper bainite instead of acicular ferrite was formed in the 103 ppm boron weld metal. The hardness values welded with 32 ppm and 60 ppm boron wire welds were in the range of Hv 190~210, while those welded with 103 ppm boron wire weld were in the range of Hv 230~235. The absorbed energy slightly decreased with increasing boron contents from 32 ppm to 60 ppm, but significantly decreased with increasing boron contents from 60 ppm to 103 ppm. In the weld joint welded with 32 ppm and 60 ppm boron content electrode, no cracks were detected. However, cracks were detected the specimen welded with 103 ppm boron content electrode.

Induction heated, hot wire welding

Abstract: A hot wire welding process. An induction coil is used to preheat the filler metal wire prior to its entering the welding puddle/arc region. An induction coil is placed in close proximity to the welding arc. The filler wire is guided and supported by a delivery guide so that the filler wire passes through the center of, and is insulated from, the induction coil. The induction coil induces a current flow in the filler wire. The current produces heat as a result of the electrical resistivity of the filler wire. The heat produced raises the temperature of the filler wire just before it is fed into the weld arc region, thus reducing the energy required from the welding arc to melt the filler metal wire into the weld puddle.

Wire, flux and process for welding steel having a high nickel content

Abstract: The invention relates to a flux-cored wire for welding nickel steels, comprising a steel sheath and filling elements, and containing, relative to the weight of the wire, 2 to 15% fluorine, 8 to 13% nickel, and iron; a welding flux containing, in proportions by weight, 25 to 35% MgO, 20 to 30% CaO, 10 to 15% Si02, 10 to 30% A1203 and 5 to 20% fluorine; and a welding process in particular a submerged-arc welding process using this wire and this flux to join steel workpieces containing more than 6% nickel, preferably around 9% nickel.

Obtaining a submerged arc welding flux of the MnO–SiO2–CaO–Al2O3 – CaF2 system by fusion

Abstract: (2007). Obtaining a submerged arc welding flux of the MnO–SiO2–CaO–Al2O3 – CaF2 system by fusion. Welding International: Vol. 21, No. 7, pp. 502-511.

Influence of Nitrogen and Heat Input on Weld Metal of Gas Tungsten Arc Welded High Nitrogen Steel

Abstract: High nitrogen stainless steel (HNS) which generally contains over 0.4wt% nitrogen is considered to be a high strength, high ductility and high toughness material. In order to study the nitrogen behavior in welding of high nitrogen steel, the steel 1Cr22Mn16N was welded by gas tungsten arc welding, and the influence of the shielding gas composition and heat input on the N-content and porosity of the weld metal was investigated. The experimental results indicate that the N-content of the weld metal increases as the nitrogen in the shielding gas containing Ar and N2 is increased under the same heat input of welding. The N-content of the weld metal decreases with the increase of the heat input when pure Ar is used as the shielding gas, whereas that of the weld metal is improved with the increase of the heat input when some nitrogen is added to the shielding gas. The nitrogen pore can be avoided when the N-content of the shielding gas is lower than a critical value. When N-content exceeds the value, the tendency of porosity in the weld metal increases with the increase of the N-content of the shielding gas. The microstructure in the weld metal consists of austenite and δ-ferrite. The amount and size of δ-ferrite is reduced with the increase of nitrogen in the shielding gas composition.

Laser-Arc Hybrid Welding

Abstract: Hybrid welding of stainless steels or aluminum alloys was performed using the heat sources of YAG laser and TIG, or YAG laser and MIG, respectively. The effects of welding conditions and melt flows on penetration depth, weld bead geometry and bubble/porosity formation were investigated with X-ray transmission real-time observation method. A great effect of melt flows on penetration depth and weld geometry was consequently confirmed. Concerning porosity suppression in YAG-TIG hybrid welding of stainless steel, no bubble generation was attributed to no porosity formation. On the other hand, it was revealed that the disappearance of bubbles from the concave molten pool surface played an important role of no porosity in YAG laser-MIG hybrid welding of aluminum alloys.

Tuning PID control of an automatic arc welding system using a SMAW process.

Abstract: A new method to tune the gains of the proportional integral derivative (PID) controller for alternating current shield metal arc welding (SMAW) of automatic arc welding system using a SMAW process is presented in this paper. This method used the genetic algorithm (GA) approach to optimize the gains of the PID auto-tuner and considerably modulated the rate of an electrode feed mechanism that regulates arc current. The proposed controller was verified by simulation and experiments of the transient response in the automatic arc welding system. Finally, the performance indices of the proposed controller are compared with that based on Ziegler–Nichols tuning rules.

Welding and Deposition of Nickel Superalloys 718, Waspaloy and Single Crystal Alloy CMSX-10

Abstract: Nickel superalloys are considered extremely difficult to weld and repair because of their susceptibility to heat-affected zone (HAZ) and weld metal cracking during fabrication, postweld heat treatment (PWHT) and subsequent operation. The weldability and repairability by TIG of annealed Alloy 718 and aged Waspaloy was investigated. Alloy 718 was investigated as this alloy provides a reference aerospace grade material. Forced cooling was applied during welding to control the temperature gradient, as this is known to be able to alleviate welding residual stress in aluminium alloys and stainless steels. The level of welding residual stress is one of the main factors controlling the weldability of nickel alloys, and minimising the amount of residual stress is beneficial to cracking resistance. An investigation into the shroud sealing of single crystal nickel superalloy CMSX-10 was also performed by TIG and electro-spark deposition (ESD) techniques with no preheat applied. Application of forced cooling aged Waspaloy resulted in the reduction or elimination of HAZ microfissures due to the reduction of thermal strain, distortion and stresses. Forced cooling during welding of Alloy 718 resulted in a substantial reduction of distortion and buckling. Weld metal and HAZ hardness were almost completely recovered after PWHT of Waspaloy deposits and SEM examination showed that γ’-phase re-formed in the HAZ during PWHT. CMSX-10 showed a high susceptibility to weld metal and HAZ cracking during standard TIG welding employing a Mar-M247 consumable. HAZ cracking was associated with recrystallisation of the parent material. No cracking or microfissures were found in the HAZ of ESD deposits on single crystal CMSX-10 alloy. No recrystallisation occurred in the parent material associated with Mar-M247 deposits produced by ESD.

Flux-cored wire for gas shielded arc welding for creep-resisting steels

Abstract: A flux-cored wire for gas shielded arc welding for creep-resisting steels, in which a flux is filled in a steel sheath and which is used in DC reverse polarity, comprises, based on a total weight of the wire, 1.0 to 5.0 mass % of BaF 2 , 0.3 to 3.0 mass % of Al, 0.04 to 0.15 mass % of C, 0.005 to 0.040 mass % of N, 1.0 to 2.7 mass % of Cr, 0.4 to 1.3 mass % of Mo, 0.05 to 0.5 mass % of Si, 0.5 to 1.5 mass % of Mn and 85 to 95 mass % of Fe, Ni being controlled to be at 0.1 mass % or below. This flux-cored wire used as a welding material for creep-resisting steels enables welding in all positions with good toughness and embrittlement characteristics.

Effect of activating flux on arc shape and arc voltage in tungsten inert gas welding

Abstract: 在焊接弧上激活流动的效果被调查。water-cooling 系统和不锈钢的一个特殊集合被用作父母材料。在焊接过程期间，高速度的照相机系统和示波器被用于分别地捕获即时弧形状和弧电压。试验性的结果显示 SiO2 流动能增加弧电压。当 TiO2 没在弧电压上有这效果时。与常规钨相比焊接的惰性的气体(C-TIG ) ，焊接的 A-TIG 的弧形状与 SiO2 流动使用了，这被发现显然变化了。

Predictions of weld formation using gas tungsten arcs for various arc lengths from unified arc-electrode model

Abstract: Predictions have been made of weld formation for stationary gas tungsten arc welding by making two-dimensional (2D) calculations of temperature and fluid flow velocity of the arc and the electrodes The whole region of the arc system is modelled, including the tungsten cathode, the arc plasma and the workpiece anode, and convection within the weld pool Predicted properties of the weld shape for 150 A arcs in argon and helium, for various arc lengths, are compared with experimental results of cross-sectional area of weld Although total power to the anode increases with increasing arc length, for argon arcs the heat flux density at the axis of the anode becomes lower, with the result that the cross-sectional area of the weld becomes smaller with increasing arc length For helium arcs total power to the anode also increases with increasing arc length, but the distribution of heat flux density to the anode is approximately constant, with the result that the cross-sectional area of the weld increases

Study of mechanism of activating flux increasing weld penetration of AC A-TIG welding for aluminum alloy

Abstract: When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld penetration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc constriction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased.

Microstructure and erosive wear behavior of weld deposits of high manganese electrode

Abstract: Low carbon steel plates were surfaced with single, double and triple pass bead on-plate welds using the shielded metal arc welding technique with a high manganese electrode. After deposition, the microstructure, hardness and erosive wear behavior of the deposit layers were investigated. Erosion tests were conducted at impact angles of 30, 60 and 90° using angular erodent with particle velocity of 30 m/s. From the results of microstructural investigation and hardness measurement, when each layer was superficially processed by the same electrode, it was seen that the microstructure changed from martensite with retained austenite to austenite. Hardness values decreased as the number of layer was increased. This was related to the higher contents of Mn and C as a result of increased layer number. The erosion test results showed that the erosion rate varied as a function of the impact angle as well as the number of the layers. The highest erosive wear occurred at 90° for all layers. Taking into consideration the erosion wear resistance, it was consequently found that the deposition with single pass gave good results for a low speed erosion test.