Showing papers on "Shielding gas published in 2006"

Evaluation of cold metal transfer (CMT) process for welding aluminium alloy

Abstract: Cold metal transfer (CMT) is an automated welding process based on dip transfer welding, characterised by controlled material deposition during the short circuit of the wire electrode to the workpiece. Preliminary results are presented examining the suitability of this process for welding aluminium alloy. Trials show that in comparison with pulsed metal inert gas (MIG) welding, CMT exhibits a higher electrode melting coefficient. By adjusting the short circuit duration penetration can be controlled with only a small change in electrode deposition. Furthermore, by mixing pulsed MIG welding with CMT welding the working envelope of the process is greatly extended allowing thicker material sections to be welded with improved weld bead aesthetics.

The Investigation of Gravity-Driven Metal Powder Flow in Coaxial Nozzle for Laser-Aided Direct Metal Deposition Process

Abstract: The quality and efficiency of laser-aided direct metal deposition largely depends on the powder stream structure below the nozzle. Numerical modeling of the powder concentration distribution is complex due to the complex phenomena involved in the two-phase turbulence flow. In this paper, the gravity-driven powder flow is studied along with powder properties, nozzle geometries, and shielding gas settings. A 3-D numerical model is introduced to quantitatively predict the powder stream concentration variation in order to facilitate coaxial nozzle design optimizations. Effects of outer shielding gas directions, inner/outer shielding gas flow rate, powder passage directions, and opening width on the structure of the powder stream are systematically studied. An experimental setup is designed to quantitatively measure the particle concentration directly for this process. The numerical simulation results are compared with the experimental data using prototyped coaxial nozzles. The results are found to match and then validate the simulation. This study shows that the particle concentration mode is influenced significantly by nozzle geometries and gas settings.

The influence of seeding conditions and shielding gas atmosphere on the synthesis of silver nanowires through the polyol process

Abstract: The polyol process including the introduction of preformed seeds and the inducement of poly(vinyl pyrrolidone) (PVP) has been developed as a powerful approach for synthesizing silver nanowires. Here, silver nanowires without other metal elements as impurities were synthesized through a silver seeding polyol process in a shielding gas atmosphere. It is demonstrated that the first seeding step is critical in obtaining silver nanowires as the principal product, and we also observe that the shielding gas atmosphere not only improves the repeatability of experiments but also affects the morphology of the final product. We obtained nanocubes with hydrogen gas shielding in a short reaction time; these would scarcely appear with argon or air shielding. Our work supplies new evidence to explain the actual growth mechanism of silver nanowires.

Fume emissions during gas metal arc welding

Abstract: The control of exposure to welding fumes is of increasing importance in promoting a healthy, safe and productive work environment. This article describes the effects of shielding gas composition on the amount and composition of welding fumes produced during gas metal arc welding (GMAW). The amount of fumes generated during welding was measured for steady current over a range of wire-feed speeds and arc voltages using the standard procedures contained in ANSI/AWS F1.2 [American Welding Society. ANSI/AWS F1.2. Laboratory method for measuring fume generation rates and total fume emission of welding and allied processes. Miami, Florida; 1992]. Results of these measurements show that the fume formation rates (FFRs) increase with CO2 and O2 in the shielding gas mixture. The lowest FFRs were obtained with the mixtures of Ar + 2%CO2 and Ar + 3%CO2 + 1%O2. The highest FFRs were obtained with the mixtures of Ar + 18%CO2 and Ar + 5%CO2 + 4%O2. The welding fumes contains mainly iron, manganese, silicon, titanium and ...

Effect of oxide fluxes on activation mechanisms of tungsten inert gas process

Abstract: Activated tungsten inert gas (TIG) welding, which involves the deposition of an inorganic powder on the metal surface prior welding, improves TIG welding performances in terms of weld bead penetration. Most common commercial fluxes contain halides and oxides. The present paper focuses on fluxes made of oxides. It appears that oxides have two different effects: one on the fusion zone chemistry and the other on the electric arc behaviour. First, oxygen reverses the Marangoni convection movements that become centripetal, contributing thus to increase 'D' penetration. On the other hand, oxides may cause an increase in the energy flux density transferred by the arc to the metal. The characterisation of the arc plasma by optical emission spectroscopy suggests that oxides do not increase the arc temperature. It is established that the oxide effects by Marangoni convection appear for a critical value of the welding energy, whereas the oxide effects on the electrical arc exist irrespective of the welding e...

Liquid metal expulsion during laser spot welding of 304 stainless steel

Abstract: During laser spot welding of many metals and alloys, the peak temperatures on the weld pool surface are very high and often exceed the boiling points of materials. In such situations, the equilibrium pressure on the weld pool surface is higher than the atmospheric pressure and the escaping vapour exerts a large recoil force on the weld pool surface. As a consequence, the molten metal may be expelled from the weld pool surface. The liquid metal expulsion has been examined both experimentally and theoretically for the laser spot welding of 304 stainless steel. The ejected metal droplets were collected on the inner surface of an open ended quartz tube which was mounted perpendicular to the sample surface and co-axial with the laser beam. The size range of the ejected particles was determined by examining the interior surface of the tube after the experiments. The temperature distribution, free surface profile of the weld pool and the initiation time for liquid metal expulsion were computed based on a three-dimensional transient heat transfer and fluid flow model. By comparing the vapour recoil force with the surface tension force at the periphery of the liquid pool, the model predicted whether liquid metal expulsion would take place under different welding conditions. Expulsion of the weld metal was also correlated with the depression of the liquid metal in the middle of the weld pool due to the recoil force of the vapourized material. Higher laser power density and longer pulse duration significantly increased liquid metal expulsion during spot welding.

Real-time arc welding defect detection technique by means of plasma spectrum optical analysis

Abstract: An optimized technique for real-time spectral analysis of thermal plasmas, with application in the monitoring and defect detection of industrial welding processes, particularly arc-welding, is presented in this paper. The calculation of the plasma electronic temperature by means of a sub-pixel algorithm permits on-line quality assessment of the welds, allowing the detection of common defects to be found in the welding seam, such as oxidation due to insufficient shielding gas flux or lack of penetration caused by current fluctuations of the welding power source. The proposed technique has been successfully checked in a real-time arc-welding monitoring system, and experimental results of stainless-steel welds are also reported.

Effect of fluxes containing oxides on tungsten inert gas welding process

Abstract: The use of an inorganic powder, termed activating flux, is a technique that can be used to improve the tungsten inert gas welding process. The activated tunsten inert gas (ATIG) process greatly increases single pass depth penetration. In the present work the activating effect of different oxides on 304L stainless steel was studied, to determine the main relationships between the oxide propertie(s) and the weld bead geometry variation and consequently to determine the mechanism(s) occurring during the ATIG welding process. The results show that oxide melting point T m, the liquid state (T b–T m), the lattice energy E L, and the quantity of oxygen that can be liberated seem to play an important role, even though T m is the main property. Moreover, for some oxides, the hygrometry rate is another property that can increase the activating effect.

Effect of shielding gas mixture on gas metal arc welding of HSLA steel using solid and flux-cored wires

Abstract: In this work, gas metal arc welding of high strength-low alloy (HSLA) steel with solid- and flux-cored arc welding wires using different shielding gas compositions was performed. The composition of filler wire and shielding gas in gas metal arc welds of HSLA steel determines the inclusion characteristics, microstructure and mechanical properties. Thus, acceptable weld metal properties in HSLA steel using gas metal arc welding (GMAW) process could be achieved with the proper combination of filler wire and shielding gas composition.

Magnetic stirring during laser welding of aluminum

Abstract: The use of magnetic fields to influence melt flow is a well-established method, e.g., in foundry technology. For arc welding processes (especially tungsten inert gas welding), a process called magnetic stirring was first proposed, patented, and investigated in the 1970s. The central aim was to improve (by the help of an alternating magnetic field coaxial with the arc axis) weld quality especially in aluminum by the combined effects of arc current and magnetic field. It was established that such fields are indeed capable of influencing weld bead appearance, of increasing the degree of dilution, of decreasing pore formation and of producing a finer grain structure. However, the process never gained wide industrial acceptance. In the late 1990s, some efforts have been taken to apply constant magnetic fields to laser welding processes, aiming at influencing weld geometry, reducing porosity, and potentially increasing welding speed. However, neither have any detailed statements been made on possibilities to in...

Automatic gas control for a plasma arc torch

Abstract: A method and apparatus for controlling a gas supply to a plasma arc torch uses a proportional control solenoid valve positioned adjacent the torch to manipulate the gas flow to the torch, thereby extending electrode life during arc transfer and shutdown. Swirl ring design can be simplified and gas supply and distribution systems become less complicated. The invention also allows manipulation of shield gas flow to reduce divot formation when making interior cuts. The system can be controlled with a digital signal processor utilizing a feedback loop from a sensor.

Physical Phenomena and Porosity Prevention Mechanism in Laser-Arc Hybrid Welding

Abstract: Hybrid welding of stainless steels or aluminium alloys was performed with 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, geometry and porosity formation were investigated with the X-ray transmission real-time observation method. Melt flows on penetration depth and geometry were consequently confirmed. Concerning porosity suppression, in TIG-YAG hybrid welding of stainless steel, no formation of bubbles was attributed to the absence of pores. On the other hand, disappearance of bubbles from the concave molten pool surface due to the arc pressure played an important role in reducing porosity in YAG-MIG hybrid welding of aluminium alloys at high arc currents.

MIG Welding Guide

Abstract: Part 1 Technologies: The MIG welding process Equipment for MIG welding Shielding gases in MIG welding Consumables in MIG welding Flux cored arc welding Pulsed MIG welding MIG brazing. Part 2 Quality and safety issues: Improving productivity in MIG/MAG welding Assessing weld quality in MIG welding Occupational health and safety in MIG welding Reducing costs in MIG welding. Part 3 Applications: MIG welding of uncoated and surface coated steel MIG welding of stainless steel MIG welding of aluminium and aluminium alloys Robotic equipment for MIG welding Optimising the use of robotic MIG welding Automotive applications of robotic MIG welding Heavy vehicle applications of robotic MIG welding.

Welding flash protection apparatus

Abstract: A welding flash protection apparatus for use with a welding machine with gas shielding is disclosed, the apparatus providing for delay of the welding flash thereby preventing the typically inherent fraction of a second delay between flash and lens darkening, hence protecting the eyes. The apparatus provides a complete helmet or apparatus components for fitment to an existing helmet. The apparatus provides a unique transmitter antenna mount for the shielding gas tank.

Plasma arc torch providing angular shield flow injection

Abstract: Plasma arc torches described herein include a torch tip with an improved nozzle that provides angular shield flow injection. In particular, the nozzle provides angular/conical impingement of a fluid (e.g., a shield gas) on an ionized plasma gas flowing through a plasma arc torch. Some of the torch tips described herein include a nozzle with a conical external shape combined with a shield with complementing internal geometry to form the angular fluid flow. As a result, a plasma arc torch including the improved nozzle have the benefits of a stabilized ionized plasma gas flow together with enhanced nozzle cooling and protection from reflecting slag during torch use.

Toward a unified model to prevent humping defects in gas tungsten arc welding

Abstract: During gas tungsten arc (GTA) welding, high welding speed and current can lead to a serious weld defect with a bead-like appearance known as humping. Currently, there is no unified model to predict the formation of humping defects in GTA welding. Here we propose and test a new comprehensive computational model that can predict and prevent the formation of humping defects considering the values of arc current, welding speed, nature of the shielding gas, electrode geometry, ambient pressure, torch angle, and external magnetic field during gas tungsten arc (GTA) welding. The model considers stability of the waves on the weld pool surface due to relative motion between the shielding gas and the liquid metal based on the Kelvin-Helmholtz instability theory. The main factors for the instability were found to be the velocities of the shielding gas and the weld metal, densities of the molten metal and shielding gas, weld pool size, and surface tension of the molten weld metal. The weld pool size and weld metal velocities were calculated by a numerical heat transfer and fluid flow model, and the shielding gas velocity was calculated from an analytical relation. Good agreement between the model predictions of humping and the independent experimental results from various sources show that the model can be used to prevent humping considering the effects of arc current, welding speed, nature of the shielding gas, electrode geometry, ambient pressure, torch angle, and external magnetic field during GTA welding. Recommendations are provided for the use of special electrodes and an external magnetic field and, where practical, controlled pressure and careful selection of shielding gas to prevent humping under conditions when high welding speed and current are needed to sustain productivity goals.

Prediction of ferrite number of duplex stainless steel clad metals using RSM : Response surface methodology (RSM) was used to establish a relationship between process parameters and ferrite number for duplex stainless steel clad metals

Abstract: Duplex stainless steel clad metals contain delta ferrite, which is expressed in terms of Ferrite Number (FN). The amount of ferrite present in the deposit is a function of chemical composition of the filler and base metals, welding process, type of shielding gas, welding procedure, and heat input during cladding. Excessive ferrite in duplex stainless steel claddings can result in poor ductility, toughness, and corrosion resistance. Likewise, insufficient ferrite can also produce inferior mechanical and corrosion resistance properties. Hence, control of ferrite in duplex stainless steel cladding is essential to obtain the required mechanical and corrosion-resistant properties. This paper highlights the application of response surface methodology to develop mathematical models and to analyze various effects of flux cored arc welding (FCAW) process parameters on the FN of duplex stainless steel clad metals. The experiments were conducted based on four-factor, five-level, central composite rotatable design with full replications technique and mathematical models developed using multiple regression technique. The developed mathematical models are very useful for predicting and controlling the FN in duplex stainless steel cladding. The main and interaction effects of input process parameters on calculated FN (by WRC-1992 diagram) and measured FN have been presented in graphic form, which helps in selecting FCAW process parameters to achieve the required FN.

MIG Brazing of Galvanized Thin Sheet Joints for Automotive Industry

Abstract: MIG welding of zinc-coated thin plates in the automotive industry leads to major issues, mainly zinc evaporation followed by a decrease of corrosion resistance, as well as residual strains and stresses difficult to minimize. The use of a lower heat input technique for joining galvanized steels would bring significant benefit, if the final overall mechanical properties of the joints are adequate for the application. The use of MIG brazing (MIGB) with the recently commercialized alloyed copper-based filler metal is an alternative worth considering. The present paper addresses the MIGB processes, describing the influence of the different shielding gases and the process parameters on the mechanical, corrosion, and metallurgical properties of the joint, when lower heat input procedures are targeted. The paper describes the influence of the gases on the mechanical properties of the brazed joint, both in normal conditions after joining and after corrosion in a salt water environment. Microstructural features of the different zones are discussed. Results of corrosion and tensile tests are presented and interpreted.

Effect of oxygen in ambient atmosphere on penetration characteristics in single yttrium aluminum garnet laser and hybrid welding

Abstract: Welding with a yttrium–aluminum–garnet (YAG) laser only or with hybrid source combined with a YAG laser and a TIG arc was carried out on Type 304 stainless steel plate with low S content in the air or in the chamber with Ar gas including 0%–15% oxygen gas. It was confirmed in both laser and hybrid welding that the penetration and geometry of welds depended upon the volume of the oxygen in the ambient atmosphere, and that a pronounced “nail head” disappeared in a weld metal containing a higher content of oxygen. An x-ray transmission real-time imaging apparatus revealed that melt flows depended on the volume ratio of oxygen in the atmosphere and there was a strong melt flow from the keyhole inlet to the surrounding pool near the top surface in pure Ar atmosphere. It is therefore considered that the melt flows induced by surface tension produces the “nail head” in pure Ar shielding atmosphere and the resulting weld becomes a wine glass shape. During YAG laser and hybrid welding in the air or in the Ar gas with the oxygen gas increased, the downward melt flows along the keyhole wall was more dominant to produce slightly deeper welds with narrower surface bead widths due to the effect of the surface tension with the positive gradient. On the other hand, the formation of shallower YAG-TIG weld beads produced in air was attributed to the mechanism that the Marangoni convection and electromagnetic convection induced by TIG arc constriction in the central part of the molten pool prevented downward melt flows from a keyhole tip resulting in deeper penetration than the tip. It was moreover confirmed that the porosity reduction in hybrid welding at a high current was due to the reduced formation of bubbles.

Reactive gas shielding during laser surface alloying for production of hard coatings

Abstract: The effects of nitrogen addition to shielding gas during laser surface alloying with a mixture of 80 wt.% 431-type stainless steel and 20 wt.% titanium carbide powders were investigated. Microstructural characterization of the laser deposits indicated that titanium carbide melted and re-precipitated as fine carbides from the liquid melt during cooling. With 100% nitrogen shielding and the same powder mixtures, a deposition with increased hardness was obtained. The microstructural evolution in the deposit was calculated with equilibrium thermodynamic calculations.

Modelling of plasma plume induced during laser welding

Abstract: A theoretical modelling of the plasma plume induced during welding of iron sheets with CO2 laser is presented. The set of equations consists of the equations of conservation of mass, energy, momentum and the diffusion equation and is solved with the use of the commercially available program Fluent 6.1. The computations are made for a laser power of 1700?W and for two shielding gases?argon and helium. The results show a significant difference between these two cases. When helium is used as the shielding gas, the plasma is much smaller and burns only where the metal vapour is slightly diluted by helium. In the case when argon is the shielding gas, there are actually two plasmas: argon plasma and metal plasma. The flowfield shows that the velocity increases in the hot region but only part of the mass flux enters the plasma core. In the case when argon is used as the shielding gas, the total absorption of the laser radiation amounts to 18?33% of the laser power depending on argon and iron vapour velocities. In the case of helium the total absorption is much lower and amounts to ~5% of the laser power.

Penetration enhancing flux formulation for tungsten inert gas (TIG) welding of austenitic stainless steel and its application

Abstract: A Penetration Enhancing Activating Flux (PEAF) in paste form for autogenous TIG welding of austenitic stainless steels adapted for ready application with a brush on top weld surface prior to conducting autogenous TIG welding to favour single weld pass, of austenitic stainless steels of AISI 304LN and AISI 316LN varieties with weld bead penetration up to a section thickness of 12 mm. Importantly, the above (PEAF) paste based TIG welding of the invention achieves an increase in weld bead penetration of about 300% over the conventional TIG process without activating flux. The PEAF paste based TIG welding also favours higher productivity and high quality apart from being cost-effective due to less requirement of consumables and controlled heat input to arrest distortion, making it widely acceptable for variety of industrial applications for welding of austenitic stainless steel.

Direct metal deposition using laser radiation and electric arc

Abstract: A direct metal deposition process using a laser/arc hybrid process to manufacture complex three-dimensional shapes comprising the steps of providing a substrate and depositing a first molten metal layer on the substrate from a metal feedstock using laser radiation and an electric arc is disclosed. The electric arc can be provided by gas metal arc welding using the metal feedstock as an electrode. The use of laser radiation in combination with gas metal arc welding stabilizes the arc and provides higher processing rates.

Gas-shielded arc welding method

Abstract: PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method where the generation of spatters can be suppressed even in high speed welding without depending on welding speed, further, the uniformization of the shape of toes is satisfactory, a wide and flat bead shape can be obtained, and cracking resistance, blow hole resistance or the like are excellent as well. SOLUTION: In the gas shielded arc welding method where pulse welding is performed using a solid wire, the solid wire comprises S, Si, Mn, C and P each by prescribed quantity, and the balance Fe with inevitable impurities, and in which pulse peak current (Ip) in a pulse P of pulse welding is ≥350 A, a pulse peak period (Tp) is 0.5 to 2.0 msec, and further, as a shielding gas, a gaseous mixture composed of, by volume, 75 to 98% Ar, and the balance one or more selected from CO 2 and O 2 is used. COPYRIGHT: (C)2008,JPO&INPIT

The effect of shielding gas composition on welding performance and weld properties in hybrid CO2 laser–gas metal arc welding of carbon manganese steel

Abstract: Metals industries producing large structures currently have a particular interest in hybrid laser welding processes, which possess advantages compared with conventional methods of welding. One major benefit is a reduction in deformation that enables the amount of postweld finishing work to be reduced. Assembly then also becomes simpler because of the greater accuracy that may be achieved. Larger joint tolerances may be accommodated compared with laser welding alone. By using appropriate filler metal, the weld metal composition may be controlled to meet metallurgical criteria. The hybrid CO2 laser–gas metal arc (GMA) welding process was investigated in this study; the aim being to clarify the effects of process gas composition on welding performance, weld cross section, quality, and mechanical properties, when welding carbon manganese steel. Helium, argon, and carbon dioxide were used in varying proportions as shielding gases for welding I-butt and T-butt joints. The composition of the shielding gas was fo...