Showing papers on "Arc welding published in 1997"

Thermal plasmas

Abstract: Although many thermal plasma processes have been developed for industrial applications, the wide acceptance as a manufacturing technology is prevented due to economical and competitive reasons, and/or reproducibility and reliability aspects. This paper is devoted to an assessment of the present knowledge in the following topics: (1) plasma torch and performance of blown arc (dc or ac), transferred arc and radio frequency torches; (2) established industrial applications with special emphasis on cutting, welding, spraying, transferred arc reclamation, reheating and purification, reheating metal melts, smelting reduction, chemical operations, and waste destruction; (3) recent developments in the knowledge of fundamental processes in plasma torches with power sources, cathodes (hot and cold), anodes (static and dynamic behavior), and torch components; (4) modeling-thermodynamic and transport properties, plasma flow with and without the Maxwell's equations; (5) measurement techniques including emission and absorption spectroscopy, laser scattering, enthalpy probes, video cameras, spectral analysis, shadowgraphy, and particle diagnostics either in flight with statistical measurements and those giving characteristics of a single particle upon flattening on a substrate; and (6) plasma-processing development in the presently used industrial processes and also in prospective processes with surface hardening, ultrafine powder production, plasma-assisted CVD, and plasma-fluidized or spouted bed reactors.

Mathematical modeling of three-dimensional heat and fluid flow in a moving gas metal arc weld pool

Abstract: Mathematical models capable of accurate prediction of the weld bead and weld pool geometry in gas metal arc (GMA) welding processes would be valuable for rapid development of welding procedures and empirical equations for control algorithms in automated welding applications. This article introduces a three-dimensional (3-D) model for heat and fluid flow in a moving GMA weld pool. The model takes the mass, momentum, and heat transfer of filler metal droplets into consideration and quantitatively analyzes their effects on the weld bead shape and weld pool geometry. The algorithm for calculating the weld reinforcement and weld pool surface deformation has been proved to be effective. Difficulties associated with the irregular shape of the weld bead and weld pool surface have been successfully overcome by adopting a boundary-fitted nonorthogonal coordinate system. It is found that the size and profile of the weld pool are strongly influenced by the volume of molten wire, impact of droplets, and heat content of droplets. Good agreement is demonstrated between predicted weld dimensions and experimently measured ones for bead-on-plate GMA welds on mild steel plate.

Welding of nickel-base superalloys having a nil-ductility range

Abstract: An article made of a nickel-base superalloy having a nil-ductility range from the solidus temperature of the alloy to about 600° F. below the solidus temperature is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, adjusting the temperature of the article to a welding temperature of from about 1800° F. to about 2100° F., welding a preselected area in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected area so as to locally melt the alloy in the preselected area, providing a filler metal having the same composition as the nickel-based superalloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Effect of various driving forces on heat and mass transfer in arc welding

Abstract: In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

An analytical solution to predict the transient temperature distribution in fillet arc welds

Abstract: This paper presents an analytical solution for predicting the transient temperature distribution in fillet arc welds. The analytical solution is obtained by solving a transient, three-dimensional heat conduction equation with convection boundary conditions on the surfaces of an infinite plate with finite thickness and mapping an infinite plate onto the fillet weld geometry with an energy equation. The electric arc heat input on the fillet weld and on the infinite plate is assumed to have a traveling bivariate Gaussian distribution. To check the validity of the solution, gas tungsten arc (GTA) and flux cored arc (FCA) welding experiments were performed under various conditions. The actual isotherms of the weldment cross sections at various distances from the arc start point are compared with those of the simulation result. As the result shows satisfactory accuracy, this analytical solution can be used to predict the transient temperature distribution in fillet welds of finite thickness under a moving bivariate Gaussian distributed heat source. The simplicity and short calculation time of the analytical solution provide rationale to use the analytical solution for modeling welding control systems or for optimizing welding process parameters.

Effect of CO/sub 2/ shielding gas on metal droplet formation in arc welding

Abstract: We have developed a unified arc electrode model that enables us to make predictions of the time development of molten drops from the welding wire in gas metal arc welding. The wire is taken as the positive electrode, and the effects of surface tension, magnetic pinch forces, and convection within the drop are taken into account to predict drop detachment for any given arc current. For pure argon, we have previously predicted the sharp transition that is observed experimentally at about 300 A between globular transfer at low current, when drop diameters are larger than the wire diameter, and spray transfer, for currents above 300 A, when drop diameters are smaller than the wire diameter. In this paper, we predict that addition of 25% of CO/sub 2/ to the argon leads to an increase in the transition current to more than 325 A, also in agreement with published experimental results. For pure CO/sub 2/, we find a significantly different drop behavior due to the more constricted arc. Both small and large drops are produced, with many very small drops being produced successively between each large drop.

Intelligent seam tracking using ultrasonic sensors for robotic welding

Abstract: This paper presents a novel approach for seam tracking using ultrasonics. An ultrasonic seam tracking system has been developed for robotic welding which tracks a seam that curves freely on a two-dimensional surface. The seam is detected by scanning the area ahead of the torch and monitoring the amplitude of the waves received after reflection from the workpiece surface. Scanning is accomplished by using two ultrasonic sensors (a transmitter and a receiver) mounted on a stepper motor such that the transmitter angle is the same as the receiver angle. The motor is mounted on the end-effector just ahead of the welding torch and covers a ninety degree arc in front of the torch. If there is no seam then the receiver receives most of the transmitted waves after reflection, but if there is a seam then most of the transmitted waves are dispersed in directions other than that of the receiver. The system has been tested and is very robust in the harsh environments generated by the arc welding process. The robustness of the system stems from using various schemes such as time windowing, a waveguide, air and metal shields, and an intelligent sensor manager. This ultrasonic system offers some distinct advantages over traditional systems using vision and other sensing techniques. It can be used to weld very shiny surfaces, and is a very economical method in terms of cost as well as computational intensity. The system can be used to detect seams less than 0.5 mm wide and 0.5 mm deep.

Real-Time Sensing of Sag Geometry During GTA Welding

Abstract: Seam tracking and weld penetration control are two fundamental issues in automated welding. Although the seam tracking technique has matured, the latter still remains a unique unsolved problem. It was found that the full penetration status during GTA welding can be determined with sufficient accuracy using the sag depression. To achieve a new full penetration sensing technique, a structured-light 3D vision system is developed to extract the sag geometry behind the pool. The laser stripe, which is the intersection of the structured-light and weldment, is thinned and then used to acquire the sag geometry. To reduce possible control delay, a small distance is selected between the pool rear and laser stripe. An adaptive dynamic search for rapid thinning of the stripe and the maximum principle of slope difference for unbiased recognition of sag border were proposed to develop an effective real-time image processing algorithm for sag geometry acquisition. Experiments have shown that the proposed sensor and image algorithm can provide reliable feedback information of sag geometry for the full penetration control system.

Prediction of gas tungsten arc welding properties in mixtures of argon and hydrogen

Abstract: A theory of gas tungsten arc welding (GTAW) arcs that treats the tungsten electrode, the arc, and the workpiece as a unified system has been applied to make predictions in two dimensions of the temperature distributions in the arc, the tungsten cathode, and the workpiece, for any given arc current and gas mixture. Predictions of arc temperatures, radii, and voltages are compared for argon and mixtures of argon and hydrogen. It is found that arcs in gas mixtures containing hydrogen are more constricted and have a higher maximum temperature and arc voltage than arcs in pure argon. The addition of hydrogen also significantly increases the volume of molten material in the weld pool due to the higher thermal conductivity of argon-hydrogen mixtures at temperatures at which molecules of hydrogen dissociate. Predictions are also compared for workpieces of steel and aluminum. The volume of molten material is very much less for aluminum, despite its lower melting point, because of the higher thermal conductivity of aluminum. Predicted arc voltages as a function of current for a mixture of 10% hydrogen in argon are in good agreement with experimental results.

Plasma transferred arc repair welding of the nickel-base superalloy IN-738LC

Abstract: Plasma transferred arc welding (PTA) has been considered a promising process to restore worn areas of land-based gas turbine blades and vanes.

Method of welding wallpaper alloy and arc welder modified to practice same

Abstract: A method of and welder for welding a corrosion resistant, wallpaper alloy to the inside surface of a vessel wall formed from a corrosion susceptible steel sheet after the wallpaper alloy has been affixed to the inside to provide an exposed seam of wallpaper alloy extending in a given path wherein the method and welder comprising moving a welding wire toward the seam, melting and depositing the welding wire onto the seam along the path by a short circuit arc welding process of the type having a welding cycle with a short condition and an arcing condition, which arcing condition constitutes a plasma boost portion with a set peak current level followed by a plasma portion with a current decreasing from said peak current level toward a set background current level with a given time between the plasma boost portion and the short condition andsetting the length of time of the plasma portion of the arcing condition to a value greater than 25% of the given time or greater than 2.0 ms.

Effect of sulfur and oxygen on weld penetration of high-purity austenitic stainless steels

Abstract: Convective flow during arc welding depends upon the surface tension gradient (dy/dT, Marangoni flow), buoyancy, arc drag force, electromagnetic force, shielding gas, and the viscosity of the melt. The Marangoni and the buoyancy-driven flow are the major factors in controlling weld penetration in ferrous alloys, especially austenitic stainless steels such as 304 and 316. Small variations in the concentration of surfactants, such as sulfur and oxygen, in stainless steels cause significant changes in the weld penetration and depth/width (D/W) ratio of the fusion zone. Gas-tungsten arc (GTA) welds were done on low- and high-sulfur 304 and 316 heats using pure argon and argon/oxygen shielding gases. Also, laser beam (LB) welds were done on the 304 and 316 heats using pure argon as the shielding gas. Increase in the sulfur content decreased the D/W ratio for the GTA 304 welds using pure argon, but for the case of LB 304 welds the results were the opposite. For the GTA 316 welds and LB 316 welds, increase in sulfur increased the D/W ratio of the fusion zone. Oxygen increased the D/W ratio of both the 304 and 316 GTA welds.

CO2 laser beam welding of 6061-T6 aluminum alloy thin plate

Abstract: Laser beam welding is an attractive welding process for age-hardened aluminum alloys, because its low heat input minimizes the width of weld fusion and heat-affected zones (HAZs). In the present work, 1-mm-thick age-hardened Al-Mg-Si alloy, 6061-T6, plates were welded with full penetration using a 2.5-kW CO2 laser. Fractions of porosity in the fusion zones were less than 0.05 pct in bead-on-plate welding and less than 0.2 pct in butt welding with polishing the groove surface before welding. The width of a softened region in the-laser beam welds was less than 1/4 times that of a tungsten inert gas (TIG) weld. The softened region is caused by reversion of strengthening β″ (Mg2Si) precipitates due to weld heat input. The hardness values of the softened region in the laser beam welds were almost fully recovered to that of the base metal after an artificial aging treatment at 448 K for 28.8 ks without solution annealing, whereas those in the TIG weld were not recovered in a partly reverted region. Both the bead-on-plate weld and the butt weld after the postweld artificial aging treatment had almost equivalent tensile strengths to that of the base plate.

Sensing ARC welding process characteristics for welding process control

Abstract: A method of sensing and controlling an arc welding process employs a high equency rate of sampling of electrical signals from the welding circuit The sampled signals are operated upon by predetermined processes to determine electrical resistance, shielding gas quality, and short circuit frequency The process measurements are compared to a predetermined set of tolerance levels and evaluated using a window technique that updates the evaluation of the data samples at the sampling rate

Metal-core weld wire for welding galvanized steels

Abstract: A metal-core weld wire usable for gas shielded arc welding gapless joints on low carbon and low alloy galvanized and galvanealed steels. The metal-core weld wire includes a low carbon steel sheath surrounding a core composition. In one embodiment, the low carbon steel sheath includes, by total weight of the metal-core weld wire, between approximately 0.01-0.03% C, and the core composition includes, by total weight of the metal-core weld wire, between approximately 0.05-0.20% Ti, between approximately 0.05-1.00% Nb, Fe powder, and Mn to the extent that the metal-core weld wire includes between approximately 0.1-1.0% Mn wherein the metal-core weld wire includes between approximately 0.1-1.0% Si. The core composition is, by total weight of the metal-core weld wire, between approximately 0.001-12.0%. The metal-core weld wire provides, at weld rates up to 150 cm/min, reduced arc ionization potential and spatter, and improved arc stability and shielding. The metal-core weld wire produces, at weld rates up to 150 cm/min, weld deposits having reduced blow holes and porosity, no liquid metal embrittlement, and reduced weld pool surface tension resulting in an improved wetting characteristic.

Dual pass weld overlay method and apparatus

Abstract: A method is disclosed for applying a weld overlay to a tube Using a first weld head, a bead of overlay material is applied onto a tube by melting the overlay material In the process of applying the weld bead to the tube, a heat affected zone is created within the tube Thereafter, a second weld head is employed to apply sufficient heat to the exterior of the tube to raise the temperature within the heat-affected zone to a temperature higher than its tempering temperature but lower than its Ae1 temperature In this manner the heat affected zone is eliminated without creating a new heat affected zone in the process In the disclosed embodiment, the tube is rotated with respect to the weld heads, while the weld heads move along the longitudinal axis of the tube According to the disclosed embodiment, the first weld head employs a gas-metal arc welding process, and the second weld head employs a gas-tungsten arc welding process

Weldability and toughness assessment of Ti-microalloyed offshore steel

Abstract: The present study has been carried out to investigate the coarse-grained heat-affected zone (CGHAZ) microstructure and crack tip opening displacement (CTOD) toughness of grade StE 355 Ti-microalloyed offshore steels. Three parent plates (40-mm thick) were studied, two of which had Ti microalloying with either Nb + V or Nb also present. As a third steel, conventional StE 355 steel without Ti addition was welded for comparison purposes. Multipass tandem submerged arc weld (SAW) and manual metal arc weld (SMAW) welds were produced. Different heat-affected zone (HAZ) microstructures were simulated to ascertain the detrimental effect of welding on toughness. All HAZ microstructures were examined using optical and electron microscopy. It can be concluded that Ti addition with appropriate steel processing, which disperses fine TiN precipitates uniformly, with a fine balance of other microalloying elements and with a Ti/N weight ratio of about 2.2, is beneficial for HAZ properties of StE 355 grade steel.

Method and apparatus for welding with preheated filler material

Abstract: An integrated non-consumable electrode and filler material nozzle for use with electric arc welding (or arc brazing). The electrode and filler nozzle are preferably integrated in one or more of the following ways: mechanically, thermally or electrically. The filler nozzle may be used to feed either hot or cold wire. Electric arc power and the wire resistance-heating power may be supplied by a single arc welding power supply, which is either directly or indirectly shunted between the electrode and filler nozzle. The nozzle can be designed to feed either single or multiple filler wires. The hot-wire nozzle preferably has a movable contact element which allows the electrical extension to be adjusted. Also the curvature of the outlet end of the hot-wire nozzle can be adjusted. If the nozzle is vertical, a wire deflection device at the nozzle outlet can be used to deflect the tip of the filler wire toward the weld puddle.

The nist automated arc welding testbed

Abstract: Proceedings of 7th International Conference on Computer Technology in WeldingSan Francisco, CA, July 8-11, 1997.THE NIST AUTOMATED ARC WELDING TESTBEDW.G. Rippey*, J.A. Falco*ABSTRACTThe Automated Welding Manufacturing System (AWMS) is a research and development testbedfor automated gas metal arc welding technology. Its activities are aimed at developing andvalidating standards that will contribute to increased use of automated welding technology bymanufacturers. The National Institute of Standards and Technology (NIST) plans to work withtechnology suppliers and manufacturing users to test systems in the AWMS. Our experiments andcontrol system designs will test the feasibility of interface standards and intelligent controltechnology to increase productivity, improve quality, and reduce the cost of system integration.Further, we will explore integration techniques that make multi-vendor system solutions moreeffective and easier to build, program, and operate. Keywords: data acquisition, gas metal arc welding, open architecture, robotic arc welding,standards, welding automation, welding sensors.INTRODUCTIONA major NIST mission is to promote economic growth by working with industry to develop andapply technology, measurements, and standards. The Intelligent Systems Division (ISD) is part ofNIST’s Manufacturing Engineering Laboratory. ISD’s goals are to foster the development andimplementation of advanced manufacturing systems, processes, and equipment and to anticipateand address the needs of U.S. industry for the next generation of measurements and standards.ISD began an effort to investigate technology in automated arc welding in 1995. ISD worked withNIST’s Materials Reliability Division (MRD), a group that has experience in welding processresearch, to determine the initial approach of the project. The focus of the project is the AutomatedWelding Manufacturing System (AWMS), a testbed for automated welding research.This document describes the current testbed hardware and the initial design for the control systemand off-line planning systems. The testbed, shown in Figure 1, includes a robot, arc weldingpower source, gun and wire feed, control computers and sensors, and robot simulation software. We emphasize modular software and hardware design to investigate opportunities forstandards and to allow insertion of components and algorithms developed by others. AWMS GOALSThe three major goals of the AWMS testbed are to:• validate and test standards• incorporate new hardware and software components developed by others to investigate open-architecture concepts• develop advanced welding technology. _________________* National Institute of Standards and Technology, Gaithersburg, Md. 20899 1

Welding method and welding material

Abstract: A welding method for two members adapted to be welded and formed of a low-alloy steel for structural purposes causing the weld metal to develop martensite transformation during cooling after welding, so that the weld metal becomes expanded to a greater degree at room temperature than at a temperature at which the martensite transformation initiates. The welding material comprises a ferrous alloy containing C, Cr, Ni, Si, Mn, Mo and Nb, all of which meet substantially with the contents of the following equation (1): ##EQU1##

Welding torch apparatus

Abstract: A welding torch apparatus for use with conventional arc welding torches which have a gooseneck, a gas nozzle with an interior and a longitudinal axis, a first passageway for supplying of both a welding wire to a tip, and gas mixtures to a gas diffuser. The welding torch apparatus comprises a second passageway for selectively introducing into the interior of the gas nozzle, gas mixtures which by-pass the first passageway, so that contact is avoided between gas mixtures passing through the second passageway and gas mixtures and welding wire passing through the first passageway, until the gas mixtures and welding wire enter the interior of the gas nozzle, and wherein gas mixtures passing through the first passageway do not contain oil additions.

Arc welder and method providing use-enhancing features

Abstract: A "hot start" method for arc welding includes selecting a first weld current, setting a time interval, striking an arc, flowing a second, higher weld current through the welding rod and then, after a brief time interval, reducing the current through the rod to the value of the first weld current. Also disclosed is a new arc welder stator having two groups of slots around a core. The group of larger slots contains the weld current windings and slots in the group of smaller slots contain windings for timing, gate voltage, battery charging, auxiliary power and the like. A new cooling apparatus for an arc welder has an air duct and a "double-bladed" fan for flowing air along several paths and cooling both the welder control section and the generating section. A new method for electronically controlling engine speed in an engine-driven arc welder is also disclosed. Such method includes manipulating a current-selecting device, contacting a work piece with a welding rod, accelerating the engine to an elevated speed and then either maintaining such speed or reducing it, depending upon the value of weld current selected.

Porosity formation in laser welding - Mechanisms and suppression methods

Abstract: The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pulse shaping in spot welding and adoption of optimum pulse modulation. Also, a proper angle of beam incidence is effective to reduce porosity formation.The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pul...

Welding of gamma titanium aluminide alloys

Abstract: An article made of a gamma titanium aluminide alloy is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, cooling the entire article to a welding temperature of from about 1000° F. to about 1400° F., welding a preselected region in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected region so as to locally melt the alloy in the preselected region, providing a filler metal having the same composition as the gamma titanium aluminide alloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Heat transfer in a liquid droplet hanging at the tip of an electrode during arc welding

Abstract: The motion of melted metal in a droplet hanging at the tip of an arc electrode during arc welding is considered. The motion is induced by a surface tension gradient due to the non-uniformly heated surface of the droplet. It is shown that the melt flow is confined within a narrow boundary layer. The thickness of this layer and the melt velocity within it are estimated. The influence of the metal motion on heat transfer in the droplet is considered. A simple formula for effective thermal conductivity, which takes into account thermocapillary convection, is obtained. Estimates show that, for conditions typical for arc welding, the effective coefficient of thermal conduction exceeds the normal value by approximately tenfold. Calculated heat fluxes agree with those obtained from the observed electrode melting rates.