Showing papers on "Gas metal arc welding published in 1995"

Physical processes in fusion welding

Abstract: In recent years, major advances have taken place in our understanding of welding processes and welded materials Because of the complexity of fusion welding processes, solution of many important contemporary problems in fusion welding requires an interdisciplinary approach Current problems and issues in fusion welding are reviewed Solution of these problems, apart from being a contribution to the advancement of science, is also necessary for science-based tailoring of composition, structure, and properties of the welded materials

Thermal efficiency of arc welding processes

Abstract: A study was conducted on the arc and melting efficiency of the plasma arc, gas tungsten arc, gas metal arc, and submerged arc welding processes The results of this work are extended to develop a quantitative method for estimating weld metal dilution in a companion paper Arc efficiency was determined as a function of current for each process using A36 steel base metal Melting efficiency was evaluated with variations in arc power and travel speed during deposition of austenitic stainless steel filler metal onto A36 steel substrates The arc efficiency did not vary significantly within a given process over the range of currents investigated The consumable electrode processes exhibited the highest arc efficiency (084), followed by the gas tungsten arc (067) and plasma arc (047) processes Resistive heating of the consumable GMAW electrode was calculated to account for a significant difference in arc efficiency between the gas metal arc and gas tungsten arc processes A semi-empirical relation was developed for the melting efficiency as a function of net arc power and travel speed, which described the experimental data well An interaction was observed between the arc and melting efficiency A low arc efficiency factor limits the power delivered to the substrate which, in turn, limits the maximum travel speed for a given set of conditions High melting efficiency is favored by high arc powers and travel speeds As a result, a low arc efficiency can limit the maximum obtainable melting efficiency

Heat and metal transfer in gas metal arc welding using argon and helium

Abstract: This article describes a theoretical investigation on the arc parameters and metal transfer in gas metal arc welding (GMAW) of mild steel using argon and helium shielding gases. Major differences in the predicted arc parameters were determined to be due to large differences in thermophysical properties. Various findings from the study include that an arc cannot be struck in a pure helium atmosphere without the assistance of metal vapor, that a strong electromagnetic cathode force affects the fluid flow and heat transfer in the helium arc, providing a possible explanation for the experimentally observed globular transfer mode and that the tapering of the electrode in an argon arc is caused by electron condensation on the side of the electrode.

The particle size distribution, density, and specific surface area of welding fumes from SMAW and GMAW mild and stainless steel consumables

Abstract: Particle size distributions were measured for fumes from mild steel (MS) and stainless steel (SS); shielded metal arc welding (SMAW)and gas metal arc welding (GMAW) consumables. Up to six samples of each type of fume were collected in a test chamber using a micro-orifice uniform deposit (cascade) impactor. Bulk samples were collected for bulk fume density and specific surface area analysis. Additional impactor samples were collected using polycarbonate substrates and analyzed for elemental content. The parameters of the underlying mass distributions were estimated using a nonlinear least squares analysis method that fits a smooth curve to the mass fraction distribution histograms of all samples for each type of fume. The mass distributions for all four consumables were unimodal and well described by a lognormal distribution; with the exception of the GMAW-MS and GMAW-SS comparison, they were statistically different. The estimated mass distribution geometric means for the SMAW-MS and SMAW-SS consumables we...

Infrared Sensing for On-Line Weld Geometry Monitoring and Control

Abstract: This paper describes a method for on-line weld geometry monitoring and control using a single front-side infrared sensor. Variations in plate thickness, shielding gas composition and minor element content are known to cause weld geometry changes. These changes in the weld geometry can be distinctly detected from an analysis of temperature gradients computed from infrared data. Deviations in temperature gradients were used to control the bead width and depth of penetration during the welding process. The analytical techniques described in this paper have been used to control gas tungsten arc and gas metal arc welding processes.

Thermal modeling of gas tungsten arc welding process with nonaxisymmetric boundary conditions

Abstract: A numerical study of three-dimensional heat transfer and fluid flow in a moving gas tungsten arc welding (GTAW) process is performed by considering nonaxisymmetric boundary conditions. The current density distribution and the resulting Lorentz force field are evaluated by numerically solving Maxwell's equations in the domain of the workpiece. The numerical modeling of the melting/solidification process is done by appropriately applying the enthalpy-porosity approach to the GTAW process. Numerical computations of the heat transfer and flow characteristics are carried out by including the effects of buoyancy, surface tension, and electromagnetic forces. The weld-pool dynamics is found to be strongly dependent on the relative locations of the clamp and electrode.

A study on the effect of contact tube-to-workpiece distance on weld pool shape in gas metal arc welding

Abstract: Computer simulations of the three-dimensional heat transfer and fluid flow in gas metal arc (GMA) welding have been studied for analyzing the effect of contact tube-to-workpiece distance on the weld pool shape by considering the driving forces for weld pool convection, the electromagnetic force, the buoyancy force and the surface tension force at the weld pool surface, and also the effect of molten electrode droplets In the numerical simulation, difficulties associated with the irregular shape of the weld bead have been successfully overcome by adopting a boundary-fitted coordinate system that eliminates the analytical complexity at the weld pool and bead surface boundary The method used in this paper has the capacity to determine the weld bead and penetration profile by solving the surface equation and convection equations simultaneously The experiments are performed to show the variation of the weld bead geometry due to the change of the contact tube-to-workpiece distance The calculated weld shapes correspond well with those of experiments, and both these resu Its demonstrate that the contact of tube-to-workpiece distance exerts a considerable influence on the formation of the weld pool and the resulting weld shape by affecting the arc length and welding current

Method of joining metal parts by fusion welding

Abstract: A method of joining metal parts by fusion arc welding in a weld of small volume includes the steps of providing the metal parts to be joined having a first side which accessible to a welding operation and a second side opposite the first side. The metal parts have welding surfaces shaped to have a first flank adjacent the first side and a second flank adjacent the second side, a step joining the flanks. Each part has a relief bulge formed in the second side adjacent the second flank, and a centering offset at the second flank to position the metal parts relative to one another for welding. The relief bulge is provided to ensure that the centering offsets melt during welding, and is shaped to have a sufficient size so that a predetermined melt-through point develops for melting of the centering offset during welding. The metal parts are positioned for welding by abutting the second flanks at the centering offset, the parts being positioned so that the first flanks define therebetween a first gap and the second flanks define therebetween a second gap, the second gap being narrower than the first gap. In a first welding step, the metal parts are joined at the second flanks by one of a fully automatic tungsten inert-gas welding process (GTAW) or gas metal-arc welding process (GMAW) to form multi-pass welding beads which extend over the entire width of the second gap, and thereafter, the first flanks are joined with a submerged-arc welding process by forming a plurality of welding beads bearing alternately against one and an opposite flank.

Gas metal arc welding fume generation using pulsed current

Abstract: While the fume generation rate of gas metal arc welding (GMAW) is lower than some other arc welding processes, the further reduction of welding fumes is of interest to companies using GMAW. Several researchers have reported lower fume generation rates for pulsed welding current compared to steady current. However, the range of welding parameters where these reduced fume levels can be expected has not been well documented. This paper describes a study of the effects of pulsed welding current on the amount of welding fume and ozone produced during GMAW using a range of welding parameters. Fume generation rates were measured for steady current and pulsed current GMAW of mild steel using copper-coated ER70S-3 welding wire and 95%Ar-5% CO 2 and 85% Ar-15% CO 2 shielding gases. The amount of fume generated during welding was determined by drawing fume through a fiberglass filter using the standard procedures contained in ANSI/AWS F1.2. Results of these measurements show that pulsed welding current can reduce fume generation rates compared to steady current. There is a range of welding voltage that produces the minimum fume generation rate for each wire feed speed with both pulsed and steady current. The data also show that using pulsed current does not guarantee lower fume generation compared to steady current. Welding parameters must be correctly controlled if pulsed current is to be used to reduce fume levels. Fillet welds were made to demonstrate that the pulsed current welding parameters that reduce fume also produce acceptable welds. No significant difference was found in the chemical composition of fumes from pulsed current compared to steady current. Fumes generated by both types of current are mixtures of iron, manganese and silicon oxides. Measurements of ozone generation rates show that the pulsed current welding parameters that reduce fume also increase ozone generation compared to steady current welding

Formation of molten droplets at a consumable anode in an electric welding arc

Abstract: A theoretical dynamic model has been developed to predict the formation of molten droplets on a moving wire electrode in a gas metal welding arc. Calculations have been made of the droplet shape and size as a function of the welding current by accounting for the electromagnetic pinch effect, surface tension, gravitation and momentum transfer due to motion of the solid wire electrode. Our calculations start with an artificial cylindrical liquid column which, for low currents, develops into a droplet which is close to spherical. However, for currents above about 250 A, the magnetic pinch constricts the column such that a smaller elongated droplet is formed.

Hybrid laser and arc process for welding workpieces

Abstract: A welding process in which laser radiation is trained on the seam area fod between two sheet-metal workpieces, one of which has an edge projecting above the other In addition, the arc is guided along this edge to melt the edge and contribute molten metal to the pool formed by the laser

MAG arc welding apparatus

Abstract: An MAG arc welding method and apparatus is capable of achieving a welding bead in a regular ripple pattern or in a suitable sectional form The welding power source generates the first welding current I1 and a second welding current I2 larger than the first welding current The wire melting speed is changed by switching between the first and the second welding currents The welding method or apparatus according to the invention generates the first arc length more than 2 mm and the second arc length more than the first arc length and switches between both arc length at a switching frequency F of 05 to 25 Hz The ratio of the second to the first welding currents is made to be in 103 to 120 In addition to a welding method to change the arc length by switching the first and the second welding currents at a constant wire feeding rate, the present welding method makes it possible to carry out the lap welding or butt welding even when there is a large gap The large gap requires a large amount of molten metal which is prepared by increasing the wire melting speed caused by an increase in the wire feeding rate by 5 to 20% The resultant reinforcement has a beautiful appearance

Method of welding a carbon steel and an austenitic stainless steel together and resultant structure

Abstract: Method of welding a carbon steel and a austenitic stainless steel involves using high density energy beam like a laser beam or electron beam Welding using high density energy beam is effective to obtain a high precision welding For the purpose of obtaining both high precision and no cracks, and no deformation, the method of the invention controls the structure of a weld portion to be a mixed structure of an austenitic structure and not greater than 20 wt % of a ferritic structure

Welding torch assembly and method

Abstract: A welding system includes a feeder with a reel rotatably mounted therein for supplying welding wire; and a torch having a cable extending therefrom connected to the feeder for receiving wire therefrom and a pair of opposing conductive drive rolls connected to a source of charging power and mounted for powered rotation on the torch. The rolls engage, charge and deliver the wire to the work piece. Opposing rollers driven by a motor through a clutch also pull the wire from the reel in the feeder and push it through the cable. The torch is equipped with a nozzle on the torch is fitted with a nonconductive delivery tube to guidingly receive the welding wire without sparking. A unique method of delivering a charged wire electrode in a MIG welding torch assembly is disclosed. Also disclosed is a special configuration for the groove for engaging the wire electrode between the rolls or rollers.

The Influence of Oxygen Additions on Argon-Shielded Gas Metal Arc Welding Processes

Abstract: It has been observed experi- mentally that small additions of oxygen to the argon shielding gas affect the gen- eral operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxy- gen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophys- ical transport and thermodynamic prop- erties caused by the oxygen addition. Therefore, it is concluded that the addi- tion of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxides initiates arc- ing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the elec- trode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.

Occupational asthma due to gas metal arc welding on mild steel.

Abstract: Occupational asthma has been documented in electric arc welders exposed to manual metal arc welding on stainless steel. A subject is described who developed late and dual asthmatic reactions after occupational-type challenge exposure to gas metal arc welding on uncoated mild steel.

Estimation of regional pulmonary deposition and exposure for fumes from SMAW and GMAW mild and stainless steel consumables

Abstract: The particle size distributions and bulk fume densities for mild steel and stainless steel welding fumes generated using two welding processes (shielded metal arc welding [SMAW] and gas metal arc welding [GMAW]) were used in mathematical models to estimate regional pulmonary deposition (the fraction of each fume expected to deposit in each region of the pulmonary system) and regional pulmonary exposure (the fraction of each fume expected to penetrate to each pulmonary region and would be collected by a particle size-selective sampling device) Total lung deposition for GMAW fumes was estimated at 60% greater than that of SMAW fumes Considering both the potential for deposition and the fume specific surface areas, it is likely that for equal exposure concentrations GMAW fumes deliver nearly three times the particle surface area to the lungs as SMAW fumes This leads to the hypothesis that exposure to GMAW fumes constitutes a greater pulmonary hazard than equal exposure to SMAW fumes The implications of t

Theoretical investigation of penetration characteristics in gas metal-arc welding using finite element method

Abstract: In the modeling of the gas metal-arc (GMA) welding process, heat inputs to the workpiece by the arc and the metal transfers have been considered separately. The heat energy delivered due to the metal transfer has been approximated in the form of a cylindrical volumetric heat source, whose dimensions of the radius and the height are dependent on the molten metal droplet characteristics. The pinch instability theory (PIT) and the static force balance theory (SFBT) of drop detachment have independently been used to obtain the expressions for various characteristics of the drop,i.e., the drop radius, the drop velocity, and the drop frequency at various welding parameters. The occurrence or the nonoccurrence of finger penetration, routinely found in the GMA welding at high welding currents, has been satisfactorily explained by the cylindrical heat source model. The effect of various welding parameters,e.g., the welding current, the wire radiusetc., on the weld bead penetration characteristics has been investigated. In this modeling effort, the heat conduction equation has been solved in three dimensions.

A theoretical study of a gas metal arc welding system

Abstract: A theoretical model of a gas metal arc welding system has been developed to make predictions of the anode temperature profile, welding arc length and arc current. The model incorporates a one-dimensional thermal model of the moving consumable anode and a two-dimensional model for the arc plasma. The model makes possible the calculation of the relationship between the welding arc current, wire feed rate and the supply voltages, for various wire diameters and shielding gases. The predicted welding current for a given wire feed rate shows good agreement with our experimental observation for operation in the spray transfer mode, for steel wire of two different diameters, assuming a workpiece sheath voltage of 15 V.

Process and device for cooling the area of a weld during laser welding

Abstract: A process and device are disclosed for cooling the area of a weld when laser welding metal sheets or metal strips, in particular for building car bodies in the automobile industry. The invention shows how to supply coolant and to create an inert gas veil between the focus and the liquid coolant so that the liquid coolant may not reach the area of the weld and negatively affect it.

Building tomorrow`s automobiles

Abstract: Detroit is awhirl these days with speculation about the next generation of automobile. Pressures are clamping down on the industry to produce cars that are free from emissions, much more fuel efficient, and, through it all, salable. Right now, a great deal of attention is being paid to the body-in-white or that part of the automobile represented by the frame and the body parts. Will it be high-strength steel, aluminum, plastic, composite, or a combination of different materials? Will resistance spot welding and gas metal arc welding still be used? What role will the laser play in all of this activity? Can welding expect severe competition from other joining processes, like adhesive bonding and riveting? The best answers to the above questions are yes, maybe, and no. Whatever happens, it seems the jury is still out. Nevertheless, the verdicts will be critical to the welding industry because the automotive industry is the largest single market for welding. Competitively, welding technology has its hands full. A number of Fortune 500 companies are developing improved adhesives. There is also a quasi-riveting process popular in Europe that is being introduced here in the States. And there is a rivet bonding version of thatmore » process. Also, weld bonding or the technique of making resistance spot welds through adhesives is gaining ground among the designers of the next generation of automobile. Over the years, the number one market for arc welding and resistance welding has been the automotive industry. Changes in the designs of automobiles have required adjustments on the part of welding technologies, but there has not been anything unusual in that respect. For the most part, the requirements have been met.« less

Power characteristics in GMAW: experimental and numerical investigation

Abstract: The voltage and power distributions in gas metal arc welding (GMAW) were studied both experimentally and numerically. The principal voltage drop takes place in the arc, which also constitutes the dominant power contribution. Within the arc, the dominating voltage contributions are from the arc column and the cathode fall, while the anode fall and the electrode regions are less significant. The power input to the arc column increases with both increasing current and increasing arc length. These results indicate that it is critical to control the arc length in order to control the power input to the system.

Effect of hydrogen in an argon GTAW shielding gas: Arc characteristics and bead morphology

Abstract: The influence of hydrogen additions to an argon shielding gas on the heat input and weld bead morphology was investigated using the gas tungsten arc welding process. Variations in weld bead size and shape with hydrogen additions were related to changes in the ability of the arc to generate heat and not to generate perturbations in the weld pool caused by Marangoni fluid flow

Particle-reinforced metal matrix composite as a weld deposit

Abstract: Weld metal consisting of particulate-reinforced metal matrix composite structure was produced with ceramic or refractory metal powder filled cored wire. Results are presented for both gas tungsten arc and gas metal arc weldments on Type 304 stainless steel. The effect of powder particle density and size distribution on the dispersion of particulates in the weld deposit was investigated. The motion and final distribution of particulates in the weld pool were evaluated with a fluid mechanics-based model, and critical welding criteria for the production of uniform particle distributions were identified. With particulates of optimum size and density in powder-filled cored wire it was possible to produce arc welding particulate-reinforced metal matrix weld deposits having uniform spatial particle distributions.

Method and apparatus for gas tungsten arc welding tailored aluminum blanks

Abstract: Tailored aluminum blanks, such as structural automotive components, are formed by gas tungsten arc welding a plurality of aluminum or aluminum-alloy sections. Preferably, a backup plate having a shallow longitudinal groove or a plurality of longitudinal grooves and a beveled electrode are employed. A preferred embodiment comprises the use of a multi-torch assembly for initial cleaning and subsequent smoothing of the resulting weld.

High current plasma arc welding electrode and method of making the same

Abstract: The elongated welding electrode is for plasma arc welding. It has a welding flux material coated on an elongated metal core. Gaps are formed in the flux coating and located at even intervals along the entire length of the electrode. The ratio of the melting points of the flux coating material and the metal core is in the range of 0.9 to 1.05. The ratio of the weights of the flux coating material and the metal core is in the range of 1.1 to 2.5. The electrode may be used with a simple welding gun and a large welding current to produce the plasma effect for welding without having to use an additional supply of gas for shielding the molten weld metal and for cooling the slag.

Flexible elongated welding electrode

Abstract: The elongated welding electrode has a flexible welding flux material coated on the outside surface of a flexible welding metal core The flux material is provided in short equal length segments with slots formed between adjacent segments to expose the metal core therein The welding current can be applied to the weld through the core in a plurality of the exposed slots so that a large current with relatively no current loss can be used in the welding operation The slots also serve as means to facilitate the automatic advancement of the electrode through the welding equipment The welding flux coating over the metal core of the electrode is covered with flexible protective coatings so that it is extremely flexible such that the flux coating will not break off from the metal core during winding on and unwinding from the carrier reel

A comparison of pulsed and conventional welding with basic flux cored and metal cored welding wires

Abstract: The results of a comparison between the use of a programmable pulsed power supply and a conventional (constant voltage) power supply with both basic flux cored and metal cored welding wires are described. Investigations were made of welding behavior and bead characteristics for both horizontal and uphill fillet welds for each combination of wire and power supply. In addition, all-weld-metal tensile and low-temperature impact properties, as well as weld composition and metallographic features are reported for each wire and power supply combination. The results for the basic flux cored wires indicate that the use of pulsed welding allows a major extension to the usable range of welding currents and some positional welding capability, without significant changes to deposition rates, weld metal mechanical properties, composition or microstructure. With metal cored wires, the use of pulsed welding not only resulted in a major extension to the range of usable welding currents and improved positional welding capability, but also in improved weld metal mechanical properties.