Showing papers on "Gas metal arc welding published in 2000"

Electron beam welding, laser beam welding and gas tungsten arc welding of titanium sheet

Abstract: Microstructures, properties and technical parameters of welding specimen of 0.5 mm thick sheets of commercial purity titanium (C.P. Ti) have been studied via high vacuum electron beam welding (EBW-HV), CO2 laser beam welding (LBW) and gas tungsten arc welding (TIG), as well as optical microscope (OM) observation and microhardness measuring. The results indicate that the EBW is more suitable for C.P. Ti sheets welding, and the welding seam without defects can be obtained. The tensile strength and microhardness of joints are corresponding to matrix structure. The full-penetration butt welds are obtained by TIG, but they have many defects such as wide weld-seam, big deformation and coarse grains. The LBW has many advantages such as the narrowest weld-seam, the least deformation and the finest grains. The fine grains are good for properties of weld seam, but the LBW should be studied again for the reasons of unstable welding technologies and strict condition.

Investigation into arc constriction by active fluxes for tungsten inert gas welding

Abstract: Mechanisms by which active fluxes increase the penetration of conventional tungsten inert gas (TIG) welds (so called A-TIG welds) are reviewed. The most dominant mechanism for increased penetration is considered to be arc constriction rather than a change in the surface tension of the molten pool. An experimental programme of work was carried out using A-TIG flux in combination with a number of welding processes. The plasma process was investigated as it gives greater penetration than conventional TIG welding by increasing current density. The CO2 laser and electron beam processes which do not rely on a current carrying arc as the heat source for welding were also investigated. Macrosections taken from the welds made by these processes showed that the A-TIG flux was only effective when the weld pool was produced by an arc or plasma. Where there was no arc or plasma present, the flux had little effect.

Effects of activating flux on arc phenomena in gas tungsten arc welding

Abstract: Dramatic increases in the depth of weld bead penetration have been demonstrated by welding stainless steel using the gas tungsten arc (GTA) process with activating fluxes consisting of oxides and halides. However, there is no commonly agreed mechanism for the effect of flux on the process. In order to clarify the mechanism, behaviour of the arc and weld pool in the GTA process with activating flux was observed in comparison with a conventional GTA process. A constricted anode root was found in the GTA process with activating flux, while a diffuse anode root was found in the conventional process. Furthermore, it is suggested that these anode roots are strongly related to metal vapour from the weld pool, which is also related to temperature distributions on the weld pool surface.

Continuous wave-Nd: yttrium–aluminum–garnet laser welding of AM60B magnesium alloy

Abstract: This study shows that the formation of macroporosity and overfill in the weld pool were the most pronounced problems during continuous wave Nd:yttrium–aluminum–garnet laser welding of AM60B die cast magnesium alloy. The influences of various welding parameters on the formation of porosity and overfill were investigated with particular emphasis on the mechanism and prevention of porosity formation. It was found that the macro pores in the weld pool were mainly formed by the expansion and coalescence of the preexisting pores in the base metal. The amount of macro- porosity in the weld pool could be reduced to approximately that in the base metal by reducing heat input, i.e., by increasing welding speed and decreasing laser power. Increasing the beam defocusing did not reduce porosity in the weld metal until the beam was highly defocused and a shallow weld pool, characteristic of conduction mode welding was obtained. Overfill was observed for deep penetration autogenous welds and its formation could be attributed to porosity formation and the resulting displacement of the liquid metal over the top surface of the workpiece.

Consumable electrode type arc welding method and device therefor

Abstract: A welding method capable of increasing or decreasing a welding wire feeding speed during welding, wherein, after short-circuiting is detected, a welding wire feeding speed is decreased, and, after a transfer to arcing by being freed from short-circuiting is detected, a welding wire feeding speed is increased.

Prediction of process parameters for gas metal arc welding by multiple regression analysis

Abstract: The purpose of this study is to find a prediction regression equation of the welding process parameters in order to obtain the desired geometry of the back-bead in butt welding, a form of g...

Gas metal arc welding process monitoring and quality evaluation using neural networks

Abstract: To ensure product quality, it is essential to ensure process quality. Thus, early monitoring and detection of process disturbances in welding production lines are of great significance. The present paper introduces a neural network system for process monitoring and quality evaluation in gas metal arc welding. The system is based only on the measured and statistically processed data for welding voltage and short circuiting time. It is a self-organising feature map Kohonen network which can automatically recognise and classify process disturbances occurring during welding.

A semi-empirical model of the fume formation from gas metal arc welding

Abstract: The control of exposure to welding fume is necessary to meet health and safety obligations. The work reported here examines the fundamentals of welding-fume formation. A physical chemistry model of the metal vapour mechanism for fume formation has been developed for non short-circuiting transfer gas metal arc welding (GMAW). The model includes the important contribution made by direct condensation of metal vapour onto the weldpool and workpiece, in removing a substantial fraction of the fume. The model shows that droplet size and wire feed speed control the fine fume formation rate. The understanding developed so far, indicates that the smaller the detached droplet size, the lower the total fume formation rate. The physics behind this is explained. The model gives an insight into how process modification might be used to control fume at source. Control at source is believed to be the most cost-effective and energy-efficient technique for dealing with welding fume. It is anticipated that the understanding gained from this project will be applied to determine the practical limits for the control of welding fume at its source.

Characteristics of a pulsed-current, vertical-up gas metal arc weld in steel

Abstract: The performance of the pulsed-current gas metal arc welding (GMAW) process for vertical-up weld deposition of steel has been found to be superior over the use of the short-circuiting arc GMAW process with respect to the tensile, impact, and fatigue properties of the weld joint. The microstructure, weld geometry, and mechanical properties of a pulsed-current weld joint are largely governed by the pulse parameters, and correlate well to the factor φ, defined as a summarized influence of pulse parameters such as peak current, base current, pulse-off time, and pulse frequency. The increase of φ has been found favorable to refine the microstructure and enhance the tensile strength, Cv toughness, and fatigue life of a weld joint. The fatigue life of a short-circuiting arc weld joint has been found to be markedly reduced due to the presence of an undercut at the weld toe and incomplete side-wall fusion of the base material.

A hot-cracking mitigation technique for welding high-strength aluminum alloy

Abstract: A hot-cracking mitigation technique for gas tungsten arc welding (GTAW) of high-strength aluminum alloy 2024 is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch. The development of the mitigation technique was based on both detailed welding process simulation using advanced finite element techniques and systematic laboratory experiments. The finite element methods were used to investigate the detailed thermomechanical behavior of the weld metal that undergoes the brittle temperature range (BTR) during welding. As expected, a tensile deformation zone within the material BTR region was identified behind the weld pool under conventional GTA welding process conventional GTA welding process conditions for the aluminum alloy studied. To mitigate hot cracking, the tensile zone behind the weld pool must be eliminated or reduce to a satisfactory level if the weld metal hot ductility cannot be further improved. With detailed computational modeling, it was found that by the introduction of a trailing heat sink at some distance behind the welding arc, the tensile strain rate with respect to temperature in the zone encompassing the BTR region can be significantly reduced. A series of parametric studies were also conducted to derive optimal processmore » parameters for the trailing heat sink. The experimental results confirmed the effectiveness of the trailing heat sink technique. With a proper implementation of the trailing heat sink method, hot cracking can be completely eliminated in welding aluminum alloy 2024 (AA 2024).« less

Influence of GMAW droplet size on fume formation rate

Abstract: The relationship between the fume formation rate (FFR) in gas metal arc welding (GMAW) and the droplet size that is transferred from the wire to the workpiece is explored. A strong relationship between droplet size and FFR has been found experimentally. This is in agreement with the predictions of recent modelling work. The result could be applied in the design of welding procedures using pulsed GMAW to minimize fume.

Online monitoring of weld defects for short-circuit gas metal arc welding based on the self-organizing feature map neural networks

Abstract: A method for automatic detection of weld defects of short-circuit gas metal arc welding is presented. It is based on the extraction of arc signal features as well as classification of the obtained features using self-organizing feature map (SOM) neural networks in order to get the weld quality information, for example, to determine if there is a defect in the product. This is important for the online monitoring of weld quality especially in robotic welding and lays the foundation for further real-time control of weld quality.

Welding of ship structural steel A36 using a Nd:YAG laser and gas–metal arc welding

Abstract: Laser welding has the potential of offering both technical and economical advantages in many applications in the shipbuilding industry. A limiting factor is currently the power level available with commercial lasers, since steel plates of more than 5 mm in thickness are used in almost every shipbuilding application. In addition, the high hardness of the welds produced using laser welding is a disadvantage compared with the requirements of existing classification society standards. It has been reported that by using a hybrid welding method in which a laser beam and a gas–metal arc weld (GMAW) arc are combined it is possible to weld thicker sections, because the penetration is increased. Hardness values are correspondingly lower than those using the laser process because of the increased energy input. Results of a study of hybrid high power Nd:YAG laser and GMA welding are reported. All plates were welded in a butt joint configuration. When laser and GMAW were combined into a single process, I grooves were used. The air gaps between the welded plates varied. Some tests were made using a partially grooved V joint. In these cases, the root faces were welded by a Nd:YAG laser, and the upper part of the joint was welded by GMAW. It was seen that it is possible to produce defect-free welds using these processes. Macrosections of the welds, hardness values and parameters are presented and discussed.

Plasma arc torch with coaxial wire feed

Abstract: A plasma arc welding apparatus having a coaxial wire feed. The apparatus includes a plasma arc welding torch, a wire guide disposed coaxially inside of the plasma arc welding torch, and a hollow non-consumable electrode. The coaxial wire guide feeds non-electrified filler wire through the tip of the hollow non-consumable electrode during plasma arc welding. Non-electrified filler wires as small as 0.010 inches can be used. This invention allows precision control of the positioning and feeding of the filler wire during plasma arc welding. Since the non-electrified filler wire is fed coaxially through the center of the plasma arc torch's electrode and nozzle, the wire is automatically aimed at the optimum point in the weld zone. Therefore, there is no need for additional equipment to position and feed the filler wire from the side before or during welding.

Neural networks for online prediction of quality in gas metal arc welding

Abstract: Modern welding equipment often features a rather complex operator interface that can make it somewhat difficult, even for an experienced welder, to determine optimum settings for a given welding job. For example, the joint fitup may vary, or some form of unexpected contamination may occur. In addition, in welding tasks for which a procedure has been specified, and in automated welding, changes in welding conditions may mean that some adjustment to the pre-established welding parameters is desirable. With online signal inputs from the welding process, artificial neural networks offer the possibility of providing signals that can be used for control, either indirectly by advising the operator of problems when the system conditions have deviated from satisfactory operation, or by direct feedback control of the welding equipment. This paper reports the development of a prototype which takes arc voltage data as online input, and applies the data to a neural network. The neural network has been trained ...

Torch for gas shielderd arc welding using consumable electrode

Abstract: A welding torch comprises a torch body having a wire guide cylinder for guiding a welding wire; an internal cylinder fitted to the torch body in such a manner as to surround the wire guide cylinder; and an external cylinder fitted to the internal cylinder in such a manner as to surround the internal cylinder. The primary interception of outside air is effected with a second shielding gas layer blown off from a second gas passageway on the outer side, and the complete interception of outside air is effected with a first shielding gas layer blown off from a first gas passageway on the inner side. Consequently, it is made possible thereby to sufficiently prevent outside air from reaching a molten pool and also sufficiently suppress the generation of an unfavorable surface oxide, thus enabling welding work to be satisfactorily practiced by using the above welding torch.

Some basic aspects of geometrical characteristics of pulsed current vertical-up GMA weld

Abstract: The performance of pulsed current gas metal arc welding (GMAW) in vertical-up position has been studied in reference to thermal behaviour of the droplet at the time of deposition affecting the geometrical characteristics of weld deposit. A more realistic estimation of heat generation at tip of the filler wire has been worked out by modifying its resistive heating component using effective current (RMS value) of the pulse current wave. The estimated rate of heat generation and measured burnoff rate of the filler wire are correlated to a factor o defined as summarised influence of pulse parameter such as peak current, base current, pulse duration and pulse frequency. Analysis of heat balance in between the heat generated at tip of the filler wire and heat consumed in melting the volume of filler wire fed to the arc indicates that the temperature of droplet decreases with the increase of both o and mean current. The variation in pulse parameters affects the weld geometry by maintaining a good correlation with factor o. In consideration of these correlations, a qualitative understanding over the control of pulse current G MAW process in vertical-up position, affecting weld geometry has been developed.

A quality and cost approach for welding process selection

Abstract: The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.

Method for welding the surfaces of materials

Abstract: A method for welding the surfaces of materials, of which at least one is glass, during which the energy that is required for the welding process is provided by with a laser beam, characterized by the fact that an intermediate sealing glass is applied between the surfaces that are to be welded and that the laser beam is adjusted in such a way that only the intermediate sealing glass melts.

Method for laser welding a fin and a tube

Abstract: A method of laser welding a planar metal surface to a cylindrical metal surface is provided, first placing a planar metal surface into approximate contact with a cylindrical metal surface to form a juncture area to be welded, the planar metal surface and cylindrical metal surface thereby forming an acute angle of contact. A laser beam, produced, for example, by a Nd:YAG pulsed laser, is focused through the acute angle of contact at the juncture area to be welded, with the laser beam heating the juncture area to a welding temperature to cause welding to occur between the planar metal surface and the cylindrical metal surface. Both the planar metal surface and cylindrical metal surface are made from a reflective metal, including copper, copper alloys, stainless steel alloys, aluminum, and aluminum alloys.

Regulation of GMA welding thermal characteristics via a hierarchical MIMO predictive control scheme assuring stability

Abstract: This paper deals with the regulation of the thermal characteristics of gas metal arc welding (GMAW). A complete treatment of the welding control problem requires the regulation of both the geometrical and thermal characteristics of the weld. Both classes of characteristics are of critical importance, but the thermal ones have received less attention in the majority of previous work. The present paper proposes a hierarchical predictive control scheme for the metallurgical characteristics of GMAW. A previously developed model for the regulation of the heat-affected zone, the cooling rate and the nugget cross-sectional area is used for the open-loop predictions. At the first level of the hierarchy, a parameterized generalized predictive control (GPC) algorithm is selected, among other control techniques, due to the inherited difficulty of the welding thermal process and the robustness of this algorithm against modeling errors and parameter variations. The main drawback of GPC is that it does not guarantee stability. The second level of the control hierarchy, where a coordinator specifies a set of reliable values for the parameters of GPC, so that stability is assured, and transmits them to the controller of the first level overcomes this difficulty. This paper provides a representative set of simulation results obtained by the present hierarchical GPC scheme, including a comparison with the classical linear-quadratic optimal control scheme. These results show the superiority of the GPC scheme.

Method and apparatus for hybrid welding under shielding gas

Abstract: A hybrid welding from a combination of laser beam welding with gas-shielded welding by electric arc uses at least two electrodes are used The electrodes can be flooded by a common shielding gas curtain or separately or in groups The hybrid welding increases the possibility of influencing the welding process and especially provides improved possibilities for automation

Welding method and welded joint structure

Abstract: The invention provides a welding system capable of freely controlling the dispersion and concentration of arc heat over the groove face with an extreamly narrow gap and a high strength and high quality welded joint structure which is formed by this welding system and which is capable of preventing softening/hardening of the structure, the lowering of the toughness thereof and the generation of a crack. According to the welding system, the melting rate of a welding wire is controlled relative to the welding wire feeding rate by changing the characteristic of an arc current so that the range of behavior and the transfer rate of the arc pole (the arc generating main point at a groove surface) are controlled. Further, the welded joint structure consists of a high strength steel having a superfine grain structure with a carbon equivalent of as low as less than 0.38 and a crystal grain size of less than 7 μm and is welded by a consumable electrode type arc welding method so as to control the arc heat distribution on the groove face of the joint.