Showing papers on "Gas metal arc welding published in 2001"

Weld metal composition change during conduction mode laser welding of aluminum alloy 5182

Abstract: Selective vaporization of volatile elements during laser welding of automotive aluminum alloys affects weld metal composition and properties. An experimental and theoretical study was carried out to seek a quantitative understanding of the influences of various welding variables on vaporization and composition change during conduction mode laser welding of aluminum alloy 5182. A comprehensive model for the calculation of vaporization rate and weld metal composition change was developed based on the principles of transport phenomena, kinetics, and thermodynamics. The calculations showed that the vaporization was concentrated in a small high-temperature region under the laser beam where the local vapor pressure exceeded the ambient pressure. The convective vapor flux driven by the pressure gradient was much higher than the diffusive vapor flux driven by the concentration gradient. The computed weld pool geometry, vaporization rates, and composition changes for different welding conditions agreed well with the corresponding experimental data. The good agreement demonstrates that the comprehensive model can serve as a basis for the quantitative understanding of the influences of various welding variables on the heat transfer, fluid flow, and vaporization occurring during conduction mode laser welding of automotive aluminum alloys.

Effect of vacuum on penetration and defects in laser welding

Abstract: The effect of vacuum on weld penetration and porosity formation was investigated in high-power cw CO2 and YAG laser welding. It was consequently confirmed in welding with both lasers that the penetration was slightly deeper in aluminum alloys and austenitic stainless steel with a decrease in the ambient pressure. It was also revealed that no porosity was present in the materials welded at lower pressures. The reason for no porosity formation in vacuum was examined by observing keyhole behavior, bubble and porosity formation situation, and liquid flow in the molten pool during high-power YAG laser welding under various conditions through the microfocused x-ray real-time observation system. It was confirmed in the coaxial Ar or He shielding gas that a lot of bubbles were generated near the bottom part of the molten pool from the tip of a fluctuated keyhole and resulted in large pores. On the other hand, under the vacuum conditions, no bubbles were formed in the melt pool from the keyhole, although the middl...

Recent developments in underwater wet welding

Abstract: Developments in underwater wet welding processes over the past 25 years are reviewed. Shielded metal arc welding with rutile base coated electrodes is still by far the most common wet welding process in use. Research and development of wet welding electrodes has led to improvements in the control of hydrogen content, porosity, chemical composition, and microstructure of the weld metal. Additional work is required to develop welding consumables with improved control over diffusible hydrogen and porosity. Development of techniques such as temper bead welding has allowed successful wet welding repairs on steels having carbon equivalents greater than the traditional limit of 0.40. Alternative wet welding processes such as flux cored arc welding and friction welding are under development, but have yet to become widely accepted.

Effects of surface active elements on weld pool fluid flow and weld penetration in gas metal arc welding

Abstract: This article presents a mathematical model simulating the effects of surface tension (Maragoni effect) on weld pool fluid flow and weld penetration in spot gas metal arc welding (GMAW). Filler droplets driven by gravity, electromagnetic force, and plasma arc drag force, carrying mass, thermal energy, and momentum, periodically impinge onto the weld pool. Complicated fluid flow in the weld pool is influenced by the droplet impinging momentum, electromagnetic force, and natural convection due to temperature and concentration gradients, and by surface tension, which is a function of both temperature and concentration of a surface active element (sulfur in the present study). Although the droplet impinging momentum creates a complex fluid flow near the weld pool surface, the momentum is damped out by an “up-and-down” fluid motion. A numerical study has shown that, depending upon the droplet’s sulfur content, which is different from that in the base metal, an inward or outward surface flow of the weld pool may be created, leading to deep or shallow weld penetration. In other words, it is primarily the Marangoni effect that contributes to weld penetration in spot GMAW.

Fuel cell operated welder

Abstract: An electric arc welder powered by a plurality of liquid organic fuel cells The fuel cells use a methanol/water mixture as the organic feed The fuel cells produce carbon dioxide as a reactive product which is used an a shielding gas during the arc welding process The fuel cells are stacked together to produce the desired arc voltage and current between an electrode and the workpiece The arc welder includes a welding current to control the current wave shape through the electrode and to control or increase the voltage through the electrode

Metal transfer measurements in gas metal arc welding

Abstract: The present work reports results obtained using combined laser shadowing and cross correlation techniques to investigate the metal transfer process. Experimental results of the droplet size and velocity of 0.9 mm and 1.2 mm wires from the globular region to the spray transfer region are presented. The results indicate that the droplet size is not continuous in the narrow region of mode transition, and also preferred bands of droplet size exist. Droplet velocity measurements show good agreement with a simple model based only on the electromagnetic pinch force.

Quality and productivity improvement in aluminium alloy thin sheet welding using alternating current pulsed metal inert gas welding system

Abstract: An alternating current (ac) pulsed metal inert gas (MIG) welding power source has been developed for welding thin sheets of aluminium alloys and the process features are investigated. Advantages such as high wire melting coefficient, low heat input, shallow penetration, and increased reinforcement height are obtained at high values of electrode negative ratio (ratio of electrode negative current integration to electrode negative plus electrode positive current integration over one pulse cycle). These features successfully counteract the problem of burnthrough in welding of thin sheet joints and greatly improve the bridging ability for wide gap joints. Thin sheet joints can be welded at high speed and with low distortion. By integrating the present welding power source with a welding robot, welding process and current waveform parameters can be defined by key operations in the teach pendant. It is possible to switch between welding processes such as ac pulsed MIG, direct current (dc) pulsed MIG, lo...

Laser welding with activating flux

Abstract: The effect on laser welding of activating flux, originally developed to improve penetration depth for tungsten inert gas welding, was investigated. Both mild and stainless steels were tested. Results show that weld penetration capability relates closely to the laser power level and welding speed of the process. Significant improvement in penetration was only observed when laser welding was performed in the conduction mode (i.e. weld aspect ratio <1). For the range of parameters studied, the best penetration capability improvements achievable for mild steel, type 304 stainless steel, and duplex stainless steel were found to be 41, 53, and 63% respectively. These data are of use in the selection of parameters for laser welding with activating flux.

Simulation of dynamic behavior in a GMAW system

Abstract: A model is developed to predict variations in welding parameters due to surface tension and electromagnetic force.

Method and system for hot wire welding

Abstract: A hot wire welding method and system rely upon a welding torch with a non-melting electrode, a melting metal filler wire that is fed into a weld puddle created by welding arc, a microprocessor controller for controlling (i) current of the main welding arc, (ii) filler wire feed speed, and (iii) hot wire current for heating the filler wire. The method and system also rely upon a main welding power supply for supplying the main welding arc and a secondary DC supply for supplying the hot wire current. The hot wire current is automatically controlled by the microprocessor to supply the correct amount of current to the filler wire in response to changes in wire feed speed.

Weldability of thin sheet metals by small-scale resistance spot welding using high-frequency inverter and capacitor-discharge power supplies

Abstract: An investigation has been conducted of the weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding using a high-frequency inverter and a capacitor-discharge power supply. The results have been compared to those of previous investigations using a line-frequency alternating current power supply. The effects of electrode materials and process parameters on joint strength, nugget diameter, weld-metal expulsion and electrode-sheet sticking were studied. This work has also provided practical guidelines for selection of power supplies, process parameters (welding current/pulse energy, welding time/pulse width, electrode forces, etc.) and electrode materials for small-scale resistance spot welding of thin sheet aluminum, brass and copper.

Rapid prototyping based on variable polarity gas tungsten arc welding for a 5356 aluminium alloy

Abstract: This paper presents a new deposition process for directly building cylindrical parts of the 5356 aluminium alloy with variable polarity gas tungsten arc welding (VPGTAW). The relationship between the geometric sizes of the deposited layer and the welding parameters is investigated. A machine vision sensor is used to monitor and control the arc length that is a key welding parameter in the achievement of a uniform deposition. By optimizing the depositing speed and the thickness of the depositing layer, there is no need for a cooling system to cool the part. Three-dimensional parts with diVerent wall thicknesses and diVerent shapes are successfully obtained. The surfaces of the deposited parts are smooth and uniform.

Laser/arc hybrid welding process with appropriate gas mixture

Abstract: Process for welding one or more metal workpieces to be joined together by producing at least one welded joint between the edges to be welded of the said metal workpiece or workpieces, the said welded joint being obtained by using at least one laser beam and at least one electric arc, in which process, during welding of the joint, at least one part of the welding zone comprising at least one part of said welded joint is shielded during the operation with at least one shielding atmosphere formed by a gas mixture consisting of argon and/or helium with a content greater than or equal to 70% by volume; and at least one additional compound chosen from H 2 , O 2 , CO 2 and N 2 with a content of 0 to 30% by volume.

A model for prediction of fume formation rate in gas metal arc welding (GMAW), globular and spray modes, DC electrode positive

Abstract: Prediction of fume formation rate during metal arc welding and the composition of the fume are of interest to occupational hygienists concerned with risk assessment and to manufacturers of welding consumables. A model for GMAW (DC electrode positive) is described based on the welder determined process parameters (current, wire feed rate and wire composition), on the surface area of molten metal in the arc and on the partial vapour pressures of the component metals of the alloy wire. The model is applicable to globular and spray welding transfer modes but not to dip mode. Metal evaporation from a droplet is evaluated for short time increments and total evaporation obtained by summation over the life of the droplet. The contribution of fume derived from the weld pool and spatter (particles of metal ejected from the arc) is discussed, as are limitations of the model. Calculated droplet temperatures are similar to values determined by other workers. A degree of relationship between predicted and measured fume formation rates is demonstrated but the model does not at this stage provide a reliable predictive tool.

A fuzzy logic system for process monitoring and quality evaluation in GMAW: Monitoring weld quality in real time is proposed using voltage and current for raw data to develop graphic histograms

Abstract: This paper introduces a fuzzy logic system that is able to recognize common disturbances during automatic gas metal arc welding (GMAW) using measured welding voltage and current signals. A statistical method was employed to process the captured transient raw data, and the probability density distributions (PDDs) and the class frequency distributions (CFDs) were obtained. Based on the processed data (PDD values of welding voltage and current and CFD values of the short-circuiting timel, the system automatically generates fuzzy rules and membership functions of linguistic variables, conducts inference and defuzzification, and completes the evaluation process without further expert knowledge.

Welding electrode and method for reducing manganese in fume

Abstract: A cored electrode for arc welding, said electrode having a core in which the fill material incudes a manganese-containing composite particle.

Keyhole gas tungsten arc welding: a new process variant

Abstract: The topic of this thesis is the discovery and development of a robust 'keyhole mode' of the Gas Tungsten Arc Welding ( G T A W ) process. This process variant represents a significant departure from conventional fusion welding processes, and is not explicable by traditional models of keyhole formation and behaviour. To be specific, the well-known keyhole processes of plasma, laser and electron beam welding are dependent on the generation of significance ablation (or 'recoil') pressure. Furthermore, there has been an acceptance that this is an essential characteristic of all keyholes. The power densities associated with G T A W are known to be too low to achieve significant ablation, and consequently this process is regarded as incapable of conventional keyhole operation, unless the circumstances are exceptional. This thesis therefore challenges the established views on two counts: • Keyholes welding is practical with existing GTAW technology; and • Keyholes can be stable even in the absence of significant surface ablation. Defence of these claims necessarily raises discussions ranging from the very practical aspects of work-place applications through to theoretical considerations such as the geometry of surfaces. While this work has endeavoured to address the various issues as they have arisen, emphasis has been placed on the development of a broad appreciation of the topic. It is acknowledged that in doing so it has failed to fully explore many of the areas that have been presented. For example, the relationship between G T A W keyhole surfaces and minimal surfaces may lead to fresh insights in weld pool mechanics. In practical terms such a study might lead to a much better appreciation of various forms of porosity, or potential control strategies based on the detection and interpretation of plasma or surface oscillations. The work begins with an experimentally based exploration of the process before addressing the questions of keyhole stability, formation and the process dependencies. It is hoped this approach will provide an efficient means of presentation, and might provide fresh insights into the physics of gas tungsten arc welding.

Assessing metal transfer stability and spatter severity in flux cored arc welding

Abstract: Five experimental basic type flux cored arc welding consumable wire electrodes were manufactured from the same base formulation. The composition of these electrodes was adjusted in an attempt to improve the operating performance. This involved additions of various ratios of alkali oxides, namely, lithium, magnesium, sodium, and potassium containing ingredients, in the flux formulations. The operating behaviours of these experimental electrodes and two reference products (i.e. one commercial basic T–5 and one commercial rutile T–1 electrode) were thoroughly investigated by recording welding arc signals using a high speed data acquisition system. By comparing these electrodes among themselves, the experimental electrodes were reported to exhibit extremely stable arcs, some showing electrical arc signals even smoother than those for the reference rutile grade electrode. Despite their improved metal transfer consistency, however, basic electrodes were characterised by somewhat higher spatter levels.

Welding of austenitic stainless steel using double sided arc welding process

Abstract: This study explores an improved method of welding austenitic stainless steel. The method uses two series connected arcs to weld the workpiece simultaneously from opposite sides. Owing to this arc configuration, the welding current is forced to flow from one arc to the other through the workpiece. It is known that such current flow concentrates the arcs and thus improves the penetration capability. Also, the current flowing through the workpiece generates fluid flow within the weld pool. In addition, owing to the use of the two opposite arcs, the heating tends to be symmetric. In addition to the increased penetration, the use of this method for welding austenitic stainless steel results in improved microstructure in the resultant welds because of an increased columnar to equiaxed transition and a decreased angular distortion, which sometimes induces solidification cracking.

Keyhole Double-Sided Arc Welding Process

Abstract: In the proposed method, the current/arc is guided through the keyhole so that the energy of the plasma jet is compensated while it is consumed in heating the workpiece along the keyhole. As a result, deep narrow penetration has been achieved on 12.7 mm (1/2") thick stainless steel plates using 70 A welding current.

Laser-assisted gas metal arc welding of 25-mm-thick HY-80 plate

Abstract: Laser-assisted gas metal arc welding of HY-80 steel was investigated. The effect of welding parameters was studied and optimum welding conditions were identified. Welding using Lincoln LA-100 wire on 25-mm-thick HY-80 plate with a four-pass technique, a double 45-deg groove preparation, 9.5 mm deep with no root opening, a heat input of 1.6 kJ/mm and a 50% Ar-50% He gas shield produced a predominately martensitic weld metal microstructure. An acicular ferrite weld metal microstructure could not be produced for any set of processing conditions investigated. This is believed to be a result of the high levels of dilution. The toughness of the laser-assisted gas metal arc welds was assessed with dynamic tear testing and explosion bulge testing. Toughness was found to be low but highly variable. Optimum electrode chemistry would probably allow the toughness to be improved.

Pore formation during laser beam welding of die-cast magnesium alloy AM60B: Mechanism and remedy controlled remelting of the fusion zone led to removal of gas bubbles, reducing porosity

Abstract: Weld metal porosity is a major concern during laser beam welding of magnesium alloys. This study seeks to identify both the mechanism of pore formation and a remedy for this problem during continuous-wave Nd:YAG laser beam welding of die-cast magnesium alloy AM60B. Preexisting pores in the base metal coalesced and expanded during welding of this alloy and, as a result, large pores were commonly present in the weld metal. Unlike laser beam welding of aluminum alloys, the stability of the keyhole was not a major factor in pore formation during laser beam welding of alloy AM60B. The porosity in the fusion zone increased with the increase in heat input, i.e., increase in the laser power and decrease in the welding speed. It was found that well-controlled remelting of the fusion zone led to removal of gas bubbles and reduced porosity in the fusion zone.

Modeling of transport phenomena in a gas metal arc welding process

Abstract: A numerical study of three-dimensional heat transfer and fluid flow in a moving gas metal are welding (GMA IV) process is performed by considering various driving forces of fluid flow such as buoyancy, Lorentz force, and surface tension. The computation of the current density distribution and the resulting Lorentz force field is performed by solving the Max-well equations numerically in the domain of the workpiece. The phase change process during melting and solidification is modeled using the enthalpy-porosity technique. Mass and energy transports by droplet transfer are also considered through a thermal analysis of the electrode. The droplet heat addition to the molten pool is considered to be a volumetric heat source distributed in an imaginary cylindrical cavity within the weld pool ("cavity" model). This nature of the heat source distributed due to the failing droplets takes into account the momentum and thermal energy of the droplets. The numerical model is able to capture the well-known "finger" penetration commonly observed in the GMAW process. Numerical prediction regarding the weld pool shape and size is compared with the corresponding experimental results, showing good qualitative agreement between the two. The weld pool geometry is also found to be dependant on some key parameters of welding, such as the torch speed and power input to the workpiece.

Welding method, filler metal composition and article made therefrom

Abstract: A weld filler metal alloy composition and a method for welding stainless steel components into a final assembly includes the steps of: austenitizing the stainless steel components to be welded at a temperature of 1800°F-2000°F; applying, using conventional arc welding techniques a solid wire of the filler metal alloy comprising in % by weight: up to 0.02% carbon; up to 0.8% manganese; up to 0.02% phosphorus; up to 0.015% sulfur; up to 0.6% silicon; 4.5-5.5% nickel; 0.4-0.7% molybdenum; 10-12.5% chromium; up to 0.1% copper; balance essentially iron and incidental impurities; and tempering the welded assembly welded at a temperature of 930°F -1300°F. A second tempering step conducted at a temperature of 1095°F-1145°F may follow. The welding method can be used to make compressor impellers (6). The compressor impeller components comprise 13Cr-4Ni stainless steel.