Showing papers on "Gas metal arc welding published in 1997"

Mobile automated pipeline welding and quality control system

Abstract: A mobile automated pipeline welding and quality control system comprising a gas metal arc welding carriage and a weld data monitor and acquisition unit The welding carriage carries a welding torch, wire feed device for feeding consumable wire to the torch, an oscillator for oscillating the torch and a motorized drive mechanism for moving the carriage about a weldment A controller for the carriage includes digital control circuitry for dosed loop control of the drive, oscillator and wire feed devices By default, the controller operates each device at one of a plurality of pre-programmed nominal speeds selected from a mode table The controller is responsive to drive, oscillation and wire feed speed variation signals under the control of an operator, and varies the speed of each device within speed ranges which are selected to ensure compliance with welding specifications The monitor has voltage and current transducers for measuring current and voltage at the welding torch The controller supplies the monitor with speed data relating to the drive, oscillator and wire feed devices All of this information can be displayed and recorded in the monitors memory In addition, the monitor can compute and display the heat input into the weld based on the detected welding parameters This information allows the operator to make minute adjustments during the welding process to ensure that a weld falls within specifications

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.

The effect of the cathode tip angle on the GTAW arc and weld pool: I. Mathematical model of the arc

Abstract: By developing mathematical models for the arc and the weld pool in the GTAW process, the effect of the electrode tip angle on both arc and weld pool was studied. The present paper is concerned with the model for the arc. By applying a variable cathode surface area, the effect of the electrode tip angle (in the range of 10 to ) on the arc properties, especially on the anode current density, heat flux and gas shear stress over the weld pool, was investigated. Comparison of the calculated results with the available experimental data for 200 A arcs of different lengths showed that the model predictions for temperatures higher than 10 000 K are in very good agreement. For temperatures less than 10 000 K, some modifications were necessary to take into account the absorption of heat by the cooler parts of the arc. It was found that by increasing the electrode tip angle, the anode spot at the weld pool surface tended to be more localized. This led to a higher maximum heat flux and anode current density. On the other hand, the gas shear stress increased on decreasing the electrode tip angle.

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.

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.

Stainless steel cladding deposited by automatic gas metal arc welding

Abstract: Weld surfacing is increasingly employed to enhance the life of and to reduce the cost of engineering components. Gas metal arc (GMA) cladding is extensively applied in its automatic mode to obtain good quality stainless steel claddings. In stainless steel cladding, the amount of dilution and the mode of solidification of claddings are vital factors affecting the quality of claddings. Developed mathematical models relating GMAW process control parameters to cladding dimensions were used to deposit 316L and 309L stainless steel on structural steel IS:2062 and obtained 12% dilution in single layer claddings. The metallurgical features, such as cladding chemistry, microstructures, modes of solidifications, ferrite content, transition zone chemistry, etc., of single and multilayer claddings were analyzed. Controlled dilution level (12%) facilitated the achievement of the required levels of alloy content meeting corrosion resistance requirements and producing crack-free claddings. The hardness of the transition zone was found to be below 400 VHN due to low-carbon levels used in stainless steel filler metals and lower dilution achieved in cladding. Cladding solidified initially with planar or cellular structure and then gradually changed to cellular-dentritic structure depending upon the heat input condition and the dilution involved. Color metallography revealed three modes of solidification of stainless steel claddings and observed modes of solidification were in good agreement with the predicted modes. Estimated ferrite contents were also in close agreement with their corresponding measured values. Two types of ferrite morphology such as vermicular and lathy were found, and, at higher ferrite content levels, lathy morphology was predominant.

Modelling and optimizing of a mig welding process—a case study using experimental designs and neural networks

Abstract: This paper describes an application of an integrated method using experimental designs and neural network technologies for modelling and optimizing a metal inert gas (MIG) welding process. To achieve optimization, the process parameters must be adjusted in such a way that the deviations from target are minimized while the robustness to noise and to process fluctuations are maximized. This new method consists of an experiment reference template for designing and collecting training data samples, and a parallel distributed computational adaptive neural network system to provide a powerful tool for data modelling and empirical investigations. The relevant data is established using experimental design methods and highlighted in the case study. An adaptive GaRBF neural network is used to approximate the stochastically non-linear dynamics of the welding process to optimize the basic welding parameters. The neural network is trained with welding experimental data, tested and compared in an actual welding environment in terms of its ability to determine weld quality. The results show that the proposed adaptive neural network is capable of mapping the complex relationships between the welding parameters and the corresponding output weld quality. The implementation for this case study was carried out using a ‘semi-automatic’ welding facility, to mass weld a 20″ × 0.438″ pin/box onto a 20″ × 0.5″ × 37′ pipe (tubular drilling products), in an actual workshop which makes oilfield equipment. The entire range of welding combinations that might be experienced during actual welding operations is included to study the weld quality. © 1997 by John Wiley & Sons, Ltd.

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.

Method of welding

Abstract: A process for buttwelding metal workpieces (12) having bevelled joint preparations using an automatic GTAW welder (20) using filler wire (32) includes preparing the bevelled workpieces (12) with bevelled joint areas having minimal land thickness at the root extremities; placing the prepared workpiece joint sections together with an open gap between their adjacent root extremities, the gap having a minimum dimension that avoids harmful compression stress between the workpieces due to weld shrinkage and a maximum dimension that avoids filler wire penetration of the gap; fusion welding the open root area of the adjacent workpieces (12) with a root pass weld using an automatic GTAW welder (20) supplied with filler wire (32) and a shield gas including 1 to 10 % hydrogen and the balance inert gas; and then promptly overlaying the root pass weld with at least one additional filler weld pass using an automatic GTAW welder (20) supplied with filler wire (32) and hydrogen-free shield gas.

A mathematical model of gas tungsten arc welding considering the cathode and the free surface of the weld pool

Abstract: A two-dimensional axisymmetric numerical model, including the influence of the cathode and the free surface of the weld pool, is developed to describe the heat transfer and fluid flow in gas tungsten arc (GTA) welding. In the model, a boundary-fitted coordinate system is adopted to precisely describe the cathode shape and deformed weld-pool surface. The current continuity equation has been solved with the combined arc plasma-cathode system, independent of the assumption of current density distribution on the cathode surface, which was essential in the previous studies of arc plasma. It has been shown that the temperature profile, the current, and the heat flux to the anode show good agreement with the experimental data. Moreover, the current and the heat-flux distributions may be affected by the shape of the cathode and the free surface of the weld pool.

The effects of welding parameters on ultra-violet light emissions, ozone and CrVI formation in MIG welding

Abstract: This paper describes the relationships between ultra-violet emission, ozone generation and CrVI production in MIG welding which were measured as a function of shield gas flow rate, welding voltage, electrode stick-out and shield gas composition using an automatic welding rig that permitted MIG welding under reproducible conditions. The experimental results are interpreted in terms of the physico-chemical processes occurring in the micro- and macro-environments of the arc as part of research into process modification to reduce occupational exposure to ozone and CrVI production rates in MIG welding. We believe the techniques described here, and in particular the use of what we have termed u.v.-ozone measurements, will prove useful in further study of ozone generation and CrVI formation and may be applied in the investigation of engineering control of occupational exposure in MIG and other welding process such as Manual Metal Arc (MMA) and Tungsten Inert Gas (TIG).

Absorption and transport of hydrogen during gas metal arc welding of low alloy steel

Abstract: Although hydrogen induced cracking remains a major problem in the welding of steels, the present methods of managing hydrogen in the weldment are mostly empirical in nature. In recent years, numerical modelling of heat transfer and fluid flow has provided detailed insight into the physical processes in welding. However, very little effort has been made in the past to use these transport phenomena based calculations to understand the dissolution of hydrogen in the weld metal and its subsequent transport in the liquid and solid regions. The aim of the present work was to address this important need. Heat transfer, fluid flow, and hydrogen transport calculations in transient, three-dimensional form are used to predict the spatial distribution of hydrogen concentration in the weld metal during gas metal arc welding of mild steels for different welding conditions. The enhanced hydrogen solubility in the weld metal above that predicted by Sieverts law was determined from a model for the partitioning of ...

Arc light sensing of droplet transfer and its analysis in pulsed GMAW process

Abstract: A new method and its principle for sensing droplet transfer in GMAW of steel and aluminum alloy have been researched in this paper. A practical arc light sensing and controlling system has been developed. The reliability of the arc light characteristic signal that indicates droplet detachment and the control accuracy of the system have been verified using high-speed photography. Based on the mathematical model established in the paper, the mechanism of the signal and relative phenomena were analyzed. The parameters that influence arc light radiation were given and the limitation of this sensing method was discussed.

Arc Light Sensing of Droplet Transfer and its Analysis in Pulsed GMAW Process A novel arc light sensing method for droplet transfer has been developed and an arc light radiant flux signal of droplet detachment is described

Abstract: A new method and its prin- ciple for sensing droplet transfer in GMAW of steel and aluminum alloy have been researched in this paper. A practical arc light sensing and controlling system has been developed. The reliability of the arc light characteristic signal that indi- cates droplet detachment and the control accuracy of the system have been ver- ified using high-speed photography. Based on the mathematical model estab- lished in the paper, the mechanism of the signal and relative phenomena were an- alyzed. The parameters that influence arc light radiation were given and the limitation of this sensing method was discussed.

Exposure of welders and other metal workers to ELF magnetic fields.

Abstract: This study assessed exposure to extremely low frequency (ELF) magnetic fields of welders and other metal workers and compared exposure from different welding processes. Exposure to ELF magnetic fields was measured for 50 workers selected from a nationwide cohort of metal workers and 15 nonrandomly selected full-time welders in a shipyard. The measurements were carried out with personal exposure meters during 3 days of work for the metal workers and 1 day of work for the shipyard welders. To record a large dynamic range of ELF magnetic field values, the measurements were carried out with ‘‘high/low’’ pairs of personal exposure meters. Additional measurements of static magnetic fields at fixed positions close to welding installations were done with a Hall-effect fluxmeter. The total time of measurement was 1273 hours. The metal workers reported welding activity for 5.8% of the time, and the median of the work-period mean exposure to ELF magnetic fields was 0.18mT. DC metal inert or active gas welding (MIG/MAG) was used 80% of the time for welding, and AC manual metal arc welding (MMA) was used 10% of the time. The shipyard welders reported welding activity for 56% of the time, and the median and maximum of the workday mean exposure to ELF magnetic fields was 4.70 and 27.5mT, respectively. For full-shift welders the average workday mean was 21.2 mT for MMA welders and 2.3 mT for MIG/MAG welders. The average exposure during the effective time of welding was estimated to be 65 mT for the MMA welding process and 7 mT for the MIG/MAG welding process. The time of exposure above 1mT was found to be a useful measure of the effective time of welding. Large differences in exposure to ELF magnetic fields were found between different groups of welders, depending on the welding process and effective time of welding. MMA (AC) welding caused roughly 10 times higher exposure to ELF magnetic fields compared with MIG/MAG (DC) welding. The measurements of static fields suggest that the combined exposure to static and ELF fields of MIG/MAG (DC) welders and the exposure to ELF fields of MMA (AC) welders are roughly of the same level.Bioelectromagnetics 18:470-477, 1997. q 1997 Wiley-Liss, Inc.

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##

Dual welding method of laser beam and consumable electrode arc

Abstract: PROBLEM TO BE SOLVED: To provide a dual welding method of laser beam and arc capable of welding a thick plate at a high speed. SOLUTION: On a welding route 6 of plates 1, 2 to be welded, a laser beam machining nozzle 3, a plasma torch 4 and an assist injection nozzle 5 are arranged. A laser beam is preceding and an arc is succeeding, a distance between a laser beam irradiating position (a) and a welding wire targeting position (b) of an arc is set to a appropriate value, a gap of the welding route of the plates 1, 2 to be welded are set to >=10% of a plate thickness and <= laser beam diameter.

Method and process gas for laser welding metal work pieces

Abstract: The invention relates to a method for laser welding metal work pieces in which the area to be welded is enclosed in a process gas. In accordance with the invention, a mixture of at least one noble gas (preferably helium) and at least 0.5 vol. % nitrogen is used as process gas. The invention improves welding joint quality specially in aluminum materials and steels with austenitic structural constituents.

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.

Mathematical model of arc in pulsed current gas tungsten arc welding

Abstract: A two-dimensional transient model is introduced to describe the heat transfer and fluid flow in pulsed gas tungsten arc (GTA) welding. The current continuity equation has been solved with the combined arc plasma - cathode system, independent of the assumption of the current density distribution on the cathode surface which was essential in previous studies of the arc plasma. The temperature distribution in pulsed GTA welding has been described, and the transition processes of temperature contours and current densities at the anode centre have been studied. Moreover, the effects of pulsed welding parameters on the dynamic process of current density at the anode centre are studied using the developed model. The results have been compared with experimental data measured by the probe method.

Method for producing laser-welded tubes and apparatus for producing the same

Abstract: In case of producing a welded tube from a metal band by using laser welding, edges of the metal band are preheated so that the temperature at the edges of the metal band before laser welding is not less than a predetermined temperature, the preheated abutting edges of the metal band are laser-welded to form a welded tube and welding beads generated on the outer and/or inner surfaces of the welded tube having been produced are eliminated by cutting. The predetermined temperature is determined depending on the thickness of the metal band and the time from the start of laser welding to the cutting of the welding beads. The edges of the metal band are preheated before welding to prevent the welding beads from being hardened by quick cooling at the welded section after laser welding.

Process for coating or welding easily oxidised materials and plasma torch for carrying out this process

Abstract: A process for coating or welding easily oxidised materials is carried out by applying weld metal powder by a plasma powder welding process with an alternating current or with a direct current and a superimposed alternating current as welding current to generate a plasma arc for the powder welding process For this purpose, one base of the plasma arc is produced in a spherical recess (34) of an electrode (32)