Showing papers on "Arc welding published in 1996"

Predictions of metal droplet formation in arc welding

Abstract: A two-dimensional time-dependent model has been developed for the prediction of droplet formation in gas metal arc welding. The model is a unified treatment of the arc, the welding wire, taken as the anode, and the workpiece, taken as a plane cathode. Predictions are made of the formation and shape of the welding droplets as a function of time, accounting for effects of surface tension, gravity, inertia and magnetic pinch forces. The wire feed rate and gas flow rates are also incorporated into the model. Calculations are made of current densities, electric potentials, temperatures, pressures and velocities in two dimensions both in the arc and also within the molten drop and solid electrodes. For an arc in argon with a mild steel wire of 1.6 mm diameter and a current of 325 A or more, we predict the formation of small drops of diameter 1.2 mm or less and large drop frequencies consistent with the spray transfer mode observed in welding. At currents of less than 275 A, we predict large drop sizes of about 3.8 mm in diameter or more, consistent with the globular transfer mode in welding. At a current of 300 A, in a transition zone between the two modes, we predict the presence of both small and large drops.

Adaptive control of full penetration gas tungsten arc welding

Abstract: This application paper addresses the control of a nonminimum-phase plant with variable large orders and delays. The process concerned is full penetration gas tungsten arc welding. Based on an analysis of accepted adaptive algorithms, the generalized predictive control algorithm presented by Clarke et al., is selected as the principal control strategy. An adaptive generalized predictive decoupling control scheme is constructed. To decouple the authors' nonminimum-phase multivariable plant, a predictive decoupling algorithm is also proposed. Simulations are performed to determine the default parameters of the algorithms. The performance has been tested by both simulations and experiments.

Structural stability of super duplex stainless weld metals and its dependence on tungsten and copper

Abstract: Three different superduplex stainless weld metals have been produced using manual metal arc welding under identical welding conditions. The concentration of the alloying elements tungsten and copper corresponded to the concentrations in commercial superduplex stainless steels (SDSS). Aging experiments in the temperature range 700 °C to 1110 °C showed that the formation of intermetallic phase was enhanced in tungsten-rich weld metal and also dissolved at higher temperatures compared with tungsten-poor and tungsten-free weld metals. It could be inferred from time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams produced in the present investigation that the critical cooling rate to avoid 1 wt pct of intermetallic phase was 2 times faster for tungsten-rich weld metal. Microanalysis in combination with thermodynamic calculations showed that tungsten was accommodated in χ phase, thereby decreasing the free energy. Experimental evidence supports the view that the formation of intermetallic phase is enhanced in tungsten-rich weld metal, owing to easier nucleation of nonequilibrium χ phase compared with σ phase. The formation of secondary austenite (γ2) during welding was modeled using the thermodynamic computer program Thermo-Calc. Satisfactory agreement between theory and practice was obtained. Thermo-Calc was capable of predicting observed lower concentrations of chromium and nitrogen in γ2 compared with primary austenite. The volume fraction of γ2 was found to be significantly higher in tungsten-rich and tungsten + copper containing weld metal. The results could be explained by a higher driving force for precipitation of γ2 in these.

Finite element analysis of thermal tensioning techniques mitigating weld buckling distortion

Abstract: The use of welding in fabricating large structures offers advantages over mechanical joining methods in flexibility of design, weight and cost savings, and enhanced structural performance. However, in large structures made of relatively thin section components, welding can cause buckling, which can lead to loss of dimensional control and structural integrity. Weld distortion in thin section structures is usually caused by buckling due to the residual stresses. In addition to conventional techniques, such as reduction of weld size and design modifications, new techniques such as thermal tensioning can be used to minimize welding induced buckling. This paper presents a finite element analysis model of the thermal tensioning technique. A series of finite element simulations and corresponding experiments are performed to demonstrate the technique. Thermocouple measurements are performed to verify the transient thermal analyses and blind hole drilling measurements to verify the predicted residual stresses. Implementing the thermal tensioning conditions determined by the finite element simulations, the residual stresses of large size and high heat input welds are reduced below the critical buckling level.

Dilution in single pass arc welds

Abstract: A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.

Measurement and prediction of energy transfer efficiency in laser beam welding

Abstract: The absorption of laser energy by the workpiece during laserbeam welding (LBW) has been studied through direct measurements of heat input obtained with a Seebeck envelope calorimeter. The experiment compared workpiece materials with contrasting thermal properties (304 stainless steel, 1018 steel, tin), and varied the laser power, travel speed, and focus spot size in order to determine their effects on two figures of merit : the energy transfer efficiency and the melting efficiency. An uncertainty analysis of the experimental measurements and calculated parameters has been included. The energy transfer efficiency during laser beam welding was found to increase with beam intensity from 0.20 to 0.90 and to stabilize at a high value at intensities greater than 30 kW/cm. No correlation with energy transfer efficiency was found for either the fusion zone depth-to-width ratio or the travel speed. Measured melting efficiencies for laser welding were found to be no higher than the theoretical maximum value of 0.48 which can be obtained with conventional arc welding processes. However, improved melting efficiency over conventional processes was obtained due to the shapes of laser welds that create two-dimensional heat flow in nominally three-dimensional heat flow applications. A mathematical model for laser welding has been developed using dimensionless parameters that relate the size of a laser weld to the net heat absorbed by the workpiece. Through application of this model, the energy transfer efficiency for continuous wave laser welding processes can be calculated after measurements of weld cross-sectional area have been made. Use of this model is expected to assist in optimization of laser welding for any type of material when it is used to select processing regimes that maximize melting efficiency and energy transfer efficiency.

Automatic welding condition setting device

Abstract: A welding condition setting device that allows even a beginner to easily set a work process and welding conditions for a target welding, comprising a welding information recording unit (12) recording therein welding working information on welding working such as information on a welding machine for use in arc welding, information on shield gas and information on welding wires, welding information inputting and outputting means (11) for inputting and outputting the welding working information, welding working information setting means (15) for setting the welding working information, retrieving means (13) for retrieving relevant information from the information stored in the welding information storing unit (12) based on information so set, and information control means (14) for giving the retrieving means (13) a retrieving requirement instruction in retrieving information in the information storing unit (12) and outputting the relevant welding information.

The wear behavior between hardfacing materials

Abstract: Hardface weld cladding in industry most commonly uses cobalt-based STELLITE nos. 6 and 12 and nickel-based Colmonoy nos. 56, 83, and 88 for plasma transferred arc (PTA) welding of 4140 steel. Frictional and abrasion wear of weld layers are compared with that of the widely used nitridized, low-level SKD61, SACM1 steel alloys and with centrifugal-cast nickel-based Colmonoy No. 68 bimetal. Experimental results show that cobalt alloys are not suitable for low-alloy steel frictional wear. However, nickel alloys are quite compatible. Resistance to abrasive wear increased in the experimental materials according to the level of hardness. Wear resistance was compromised in experimental materials when the hard phase was too dispersed.

Dynamic Analysis and Identification of Gas Tungsten Arc Welding Process for Weld Penetration Control

Abstract: In this study, gas tungsten arc welding is analyzed and modeled as a 2-input (welding current and arc length) 2-output (weld depression and width) multivariable process. Experiments under a number of typical welding conditions are performed to excite and identify the process characteristics and variations. It is observed that the model parameters vary in a large range with the experimental conditions. A real-time model frame with only a few parameters to be identified on-line is proposed. Based on the obtained models, the process characteristics in terms of inertia, delay, nonminimum phase, and coupling are given. These characteristics suggest an adaptive predictive decoupling control algorithm. By designing and implementing the suggested control algorithm with the real-time model, excellent results have been achieved for both simulation and practical control. This shows that the dynamic analysis and identification provide sufficient process information for design of the control system.

Method for developing residual compressive stress in stainless steel and nickel base superalloys

Abstract: Compressive residual stresses can be developed by underwater plasma transferred arc welding. The development of these compressive stresses act to prevent hot cracking and He embrittlement that can develop during welding or stress corrosion cracking that can develop subsequent to the welding operation.

Mathematical models for control of weld bead penetration in the GMAW process

Abstract: This paper presents the effects of welding process parameters on weld bead penetration for the gas metal arc welding (GMAW) process. Welding process parameters included wire diameter, gas flow rate, welding speed, arc current and welding voltage. The experimental results have shown that weld bead penetration increased as wire diameter, arc current and welding voltage increased, whereas an increase in welding speed was found to decrease the weld bead penetration. However, the weld bead penetration is not affected significantly by gas flow rate changes. Mathematical equations for study of the relationship between welding process parameters and weld bead penetration have also been computed by employing a standard statistical package program, SAS.

Stress corrosion crack repair by plasma arc welding underwater welding

Abstract: Stress corrosion cracking damage to stainless steels and nickel base superalloys is repaired by underwater plasma transferred arc welding which under conditions which reduce residual tensile stresses in the weld and adjacent portions of the repaired structure.

TIG welding method and welding torch therefor

Abstract: A TIG welding method is usually carried out in a manner that a tungsten electrode is inserted into a weld groove portion of a member to be welded, an electric voltage is applied to a current conducting portion provided for the tungsten electrode while flowing a shield gas means to thereby generate an arc between the tungsten electrode and the member to be welded to form a molten pool of the member, a welding wire is inserted into the molten pool, and a welding torch is then operated to perform a welding process In the improvement of the TIG welding method, the shield gas means is composed of an inner shield gas (13) flowing from a periphery of the tungsten electrode (3) to a front end thereof inserted into the weld groove portion (2a) of the member (1a) to be welded and an outer shield gas (14) flowing towards the weld groove angle from an outside of the inner shield gas (13) to prevent the molten pool from being oxidized and to prevent oxygen in air from being involved The TIG welding torch for carrying out the method is specifically provided with the inner and outer shield gas flow means, and further provided with a central shield gas flow means

Sliding mode control of a heat equation with application to arc welding

Abstract: This paper considers the use of sliding mode control to perform robotic welding The arc welding model is considered as a distributed parameter system described by partial differential equations with unknown boundary conditions Simulations with temperature distribution surface plots are also included

Optimisation of submerged arc welding process parameters in hardfacing

Abstract: In this paper, a feedforward neural network is used to model submerged arc welding (SAW) processes in hardfacing. The relationships between process parameters (arc current, arc voltage, welding speed, electrode protrusion, and preheat temperature) and welding performance (deposition rate, hardness, and dilution) are established, based on the neural network. A simulated annealing (SA) optimisation algorithm with a performance index is then applied to the neural network for searching the optimal process parameters. Experimental results have shown that welding performance can be enhanced by using this new approach.

Reduction of hexavalent chromium concentration in fumes from metal cored arc welding by addition of reactive metals

Abstract: Previous work has demonstrated that both the mass and composition of fumes produced during metal arc welding can be influenced by changes in the welding wire composition, the flux or gas shielding used and by changes in the process parameters, including voltage, adopted. The present paper describes modifications directed at reducing the concentration of hexavalent chromium [Cr(VI)] in welding fume by the addition of active metals—zinc, magnesium and aluminium to metal cored arc welding wires containing 10% Cr. There were marked changes in both the Cr(VI) concentration in the fume and the fume formation rate and hence in the Cr(VI) formation rate over the range of voltages used (18–24 V). Fume from wires containing the addition of 1% zinc contained Cr(VI) concentrations in the fume below those in the control and in wires with 1% magnesium and wires with 1% aluminium additions. Also, at 18 V, the Cr(VI) formation rate was at a minimum compared to the other wires. This advantage was not sustained as the voltage was increased and above 21 V the Cr(VI) formation rate for all the three wires containing active metal additions was higher than the control. These results demonstrate that at 18 V a significant reduction of Cr(VI) in welding fume can be produced by the addition of 1% zinc to the welding wire.

Electric arc welding

Abstract: Methods and apparatus for the electric arc welding of metal workpieces utilize a current comprised of squared waveform high-amplitude current pulse groups alternated with squared waveform low-amplitude current pulse groups, the current pulse groups being developed or developed and algorithmically varied in response to detected welding arc voltage/current condition changes and with respect to pulse group periods, pulse group peak current amplitudes, pulse group repetition frequencies, and pulse group current rise/fall rates for particular applications.

Pulsed arc welding method and apparatus

Abstract: A pulsed arc welding apparatus includes a short circuit detecting circuit for detecting a time during which a short circuit is being produced by melting a consumable electrode across a consumable electrode and a base metal, a comparison circuit for comparing an integrated value or a mean value of short circuit generating time detected by the short circuit detecting circuit with an optional set value, and a control circuit for controlling either one of the supply time of the pulse current and the base current supply time in accordance with the result of comparison by this comparison circuit, thereby to control the arc length.

Finite element analysis of temperature distribution during arc welding using adaptive grid technique

Abstract: Analysis of temperature and the cooling rates during the welding process is essential to determine the deformation and residual stresses, and hence, the load-carrying capacity of the weldments. Numerical methods with nonlinear temperature-dependent mechanical properties with latent heat effects have been developed in recent years. The accuracy and computational efficiency of these methods depend on the input mesh used in the analysis. In this paper, a transient adaptive mesh, which gives a fine mesh around the arc source where temperature gradients are too high and a coarse mesh in other places, is developed. The computed values of temperature for a sample problem are compared with the experimental results available in the literature. The mesh and temperature plots at different times are presented.

Advanced consumable electrodes for gas metal arc (GMA) welding of high strength low alloy (HSLA) steels

Abstract: This invention relates to solid, bare, consumable wire electrodes for gas metal arc (GMA) welding of high strength low alloy (HSLA) steels. The electrodes require little or no preheat, interpass and post soak temperature controls. The invention also relates to the method of welding and weld deposits produced therefrom.

Plasma cutting or arc welding power supply with phase staggered secondary switchers

Abstract: A power supply, such as a plasma cutting power supply or a welding power supply, that provides an output to a pair of output terminals is disclosed. The power supply includes a source of voltage and a plurality of choppers. The choppers are connected in parallel between the voltage source output terminals. A controller controls the choppers so that they are out-of-phase with respect to each of the other of the plurality of choppers. The choppers preferably include a freewheeling diode, an inductor and a switch. The number of choppers is approximately equal to the ratio of the open circuit voltage to the output load voltage.

High speed rotating automatic arc welding device

Abstract: PROBLEM TO BE SOLVED: To provide a high speed rotating automatic arc welding device having suitability to the welding on-site at a high position and high welding efficiency in high welding quality. SOLUTION: This device is composed of rail 5 parallel fitted with a welding line 201 extended in the perpendicular direction in a work 200 with plural magnet devices 6, an automatic welder 10 vertically welding downward by the high speed rotating arc welding with a rotation welding torch 1 through an arc sensor while travelling on the rail 5, a welding condition setting panel of a welding control device having handles for setting the welding condition and an operational pendant for finely adjusting the welding condition at an operator side. Then, a semi-automatic welding torch 20 is inserted into a connecting metallic tool at the base end side of the rotation welding torch so as to be freely attached/detached and commonly supply a welding electric source, shield gas and welding wire.

Contact tip for welding

Abstract: A contact tip for arc welding is split into a tip main body (1) and a tip distal end portion (2), and is removably fitted by a screw method or a taper press-in method. The tip main body (1) is made of brass, copper, aluminum, chromium copper, zirconium copper, zirconium chromium copper or phosphor bronze, and the tip distal end portion (2) is made of copper, chromium copper, zirconium chromium copper, silver tungsten, copper tungsten, alumina dispersed copper, beryllium copper or nickel beryllium copper, in order to extend life of the contact tip and to reduce the total cost. In this instance, brass is a particularly suitable material for the tip main body, and chromium copper or zirconium chromium copper is a suitable material for the tip distal end portion (2). Of the wire passage of the tip main body (1), the passage diameter of at least the tip distal end portion side is within the range of 1.03 to 1.50 times the wire diameter, and the wire passage diameter of the tip distal end portion (2) is within the range of 1.03 to1.25 times the wire diameter. According to this arrangement, the wire can be smoothly inserted, electric current can be reliably supplied, and positioning error of arc welding can be prevented.

Occupational Health in Metal Arc Welding

Abstract: The physical and often acute effects associated with metal arc welding, such as death by electrocution or physical injuries in the workplace are well recog nised. Increasingly today, attention is focused upon chronic effects, in particu lar cancer risks in welders. This review aims to address these concerns; put the risks into perspective and direct the reader to the means of assessment and control. Attention is drawn to the activities of Commission VIII International Institute of Welding which, through its various working groups, is charged with reviewing world-wide publications on health and safety in welding and with the issue of authoritative statements. The mechanism of gas and fume generation from welding processes is described. Fume particle size and mor phology in relation to inhalation and effects within the body are addressed. Epidemiology studies on cancer and other risks are reviewed. Strategies for the assessment and control of risks from metal arc welding are considered, taking due note of i...

Welding process for drawn ARC stud welding

Abstract: The invention relates to a welding process for drawn arc stud welding wherein after ignition of the main current electric arc, the latter's voltage (U) is measured and, depending upon the measured voltage, the current flow of the continued main current electric arc and/or the dipping movement of the parts which are to be welded together, is regulated or controlled.

Quality monitoring in robotised welding using sequential probability ratio test

Abstract: This paper addresses the problem of automatic monitoring the weld quality produced by robotised short arc welding. A simple statistical change detection algorithm for the weld quality, recursive sequential probability ratio test (SPRT), is used. The algorithm may equivalently be viewed as a cumulative sum (CUSUM) type test. The test statistics is based upon the variance of the amplitude of the weld voltage. It is shown that the variance of the weld voltage amplitude decreases when the welding process is not operating under optimal condition. The performance of the algorithm is evaluated using experimental data. The results obtained from the algorithm indicate that it is possible to detect changes in the weld quality automatically and on-line.

Method for joining two parts by heterogeneous welding and use thereof

Abstract: The machined ends of two parts (2, 4) are arranged in facing positions to form a welding bevel (6) between the parts (2, 4). A series of layers of filler metal are deposited one on top of the other in the welding bevel (6) in a direction thereof corresponding to the width of the parts (2, 4), by melting a wire (14) supplied at a predetermined feed rate to an electric arc between the parts to be welded and an electrode (13) supplied with a predetermined welding current and voltage. Each layer of filler metal essentially consists of a single weld bead across the full width of the bevel (6). The electric welding current and voltage and the feed rate of the wire (14) are predetermined in accordance with the width of the bevel (6).