Showing papers on "Arc welding published in 1989"

Comparison of the microstructures and abrasive wear properties of stellite hardfacing alloys deposited by arc welding and laser cladding

Abstract: The microstructure of cobalt-based hardfacing alloys deposited by manual metal arc (MMA) welding, tungsten inert gas (TIG) welding, and laser cladding has been investigated as part of a study attempting to establish the relationship between microstructure and abrasive wear properties. For typical deposition conditions, the differences in freezing rates associated with the three processes are found to give rise to large differences in microstructure. The MMA process is found to lead to the largest degree of dilution of the hardfacing deposit; the TIG and laser deposits exhibited much lower levels of mixing with the base plate. For the deposition conditions used in this study and for the alloys examined, the scale of the microstructure decreases in the order MMA, TIG, and laser cladding, leading to an increase in the deposit hardness in the same order. It is found that with alumina as an abrasive, the wear rate persistently is higher with the MMA deposits (which have the coarsest microstructure with the lowest starting hardness), the weight loss being approximately linear with time. The laser and TIG deposits, which have more refined microstructures and slightly higher carbon concentrations, both are found to exhibit significantly lower wear rates. Initially, the TIG samples are the most resistant to abrasion, even though their microstructure compares with that of the laser samples; this is a consequence of their higher ductility associated with a lower rate of strain hardening. The laser samples, which contain a lower matrix iron concentration, strain harden more rapidly; consequently, they exhibit an initial decrease in wear rate. With the much harder silicon carbide abrasive, all samples show similar wear rates which do not decrease with time. The wear data are found to correlate with scanning and transmission electron microscopy observations, and it is possible to rationalize the interaction among microstructure, abrasive, and alloy deposition processes.

Apparatus and method of short circuiting arc welding

Abstract: Apparatus and method to reduce spatter and allow better semi-automatic welding in short circuiting arc welding of the type using a single D.C. power supply for causing a welding current to pass through a welding wire extending variable distances from a holder and between the welding wire and a workpiece at a molten metal pool on the workpiece. The welding current flows in response to an arc voltage while the welding wire is fed from the holder toward the workpiece whereby the welding wire is subjected to a succession of welding cycles each of which include an arcing condition during which the wire is spaced from the pool and a short circuit condition during which a molten metal ball formed on the end of the wire contacts the metal pool and then transfers from the wire to the workpiece by a necking action. In this type of welding operation, the invention involves the application of a preselected amount of energy into the wire during the arcing condition for each welding cycle, which preselected amount of energy slightly exceeds the known value of energy necessary to melt a given volume of metal to form a consistent molten metal ball onto the end of the wire. This constant energy is divided between the resistance heating of the wire extending from the wire holder and the anode heating caused by the arc during each arcing condition of a cycle. Consequently, constant energy is inputted to the end of the wire irrespective of changes in the amount of wire extension or stick-out.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part I - theoretical analysis

Abstract: A computational and experimental study was carried out to quantitatively understand the influence of the heat flow and the fluid flow in the transient development of the weld pool during gas tungsten arc (GTA) and laser beam welding of Type 304 stainless steel. Stationary gas tungsten arc and laser beam welds were made on two heats of Type 304 austenitic stainless steels containing 90 ppm sulfur and 240 ppm sulfur. A transient heat transfer model was utilized to simulate the heat flow and fluid flow in the weld pool. In this paper, the results of the heat flow and fluid flow analysis are presented.

Three-dimensional transient model for arc welding process

Abstract: A direct computer simulation technique, discrete element analysis (DEA), was utilized in the development of a transient multidimensional (2-D and 3-D) mathematical model for investi-gating coupled conduction and convection heat transfer problems associated with stationary and moving arc welding processes. The mathematical formulation considers buoyancy, electro-magnetic, and surface tension driving forces in the solution of the overall heat transfer conditions in the specimen. Furthermore, the formulation of the model allows realistic consideration of the geometrical variations in the workpiece. The model treats the -weld pool surface as a truly deformable free surface, allowing for the prediction of the weld surface deformations such as the “weld crown.≓ A marked element formulation was employed to monitor the transient de-velopment of the weld pool as determined by the latent heat considerations and the calculated velocities in the weld pool. The model was utilized to simulate the heat and fluid flows in the weld pool that occur during stationary (spot) and moving (linear) gas tungsten-arc welding. Also, the present analysis considers a simple rectangular specimen and a geometrically complex specimen to demonstrate the capability of the model to simulate realistic 3-D arc welding prob-lems. The results of the present investigation clearly demonstrate the significant influence of the heat and fluid flows and the specimen geometry on the development of the weld. Comparison of the predicted and the experimentally observed fusion zone and heat-affected zone (HAZ) geometries indicate good agreement.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part II-experimental correlation

Abstract: In part I of the paper, the results of the heat flow and the fluid flow analysis were presented. Here, in Part II of the paper, predictions of the computational model are verified by comparing the numerically predicted and experimentally observed fusion zone size and shape. Stationary gas tungsten arc and laser beam welds were made on Type 304 stainless steel for different times to provide a variety of solidification conditions such as cooling rate and temperature gradient. Calculated temperatures and cooling rates are correlated with the experimentally observed fusion zone structure. In addition, the effect of sulfur on GTA weld penetration was quantitatively evaluated by considering two heats of 304 stainless steel containing 90 and 240 ppm sulfur. Sulfur, as expected, increased the depth/width ratio by altering the surface tension gradient driven flow in the weld pool.

Arc-welding monitor

Abstract: The arc-welding monitor has a weld power supply, units for generating signals proportional to welding current and voltage, an audio-signal generator, welding current and voltage comparators and a monitoring sequence logic analyzer having a signal switch responsive to variations of monitored quantities, which is connected to the outputs of said welding current and voltage comparators, a signal switch responsive to incremental changes in monitored parameters, and welding current and voltage adders. One input of each adder is connected to the outputs of said units for generating signals proportional to welding current and voltage, respectively, while the second input of each adder is combined with the input of the corresponding comparator, the outputs thereof being connected to the inputs of the signal switch responsive to incremental changes in monitored parameters.

Apparatus for short circuiting arc welding

Abstract: An improvement in a short circuiting arc welding apparatus comprising a single D.C. power supply causing a welding current to pass through a welding wire extending from a holder and between said wire and workpiece at a molten metal pool on the workpiece, wherein the current flows in response to an arc voltage and the welding wire is subjected to a succession of welding cycles. Each of the welding cycles includes an arcing condition during which said wire is spaced from the pool and the energy applied to said wire exceeds a given value raising the temperature at the end of the wire to a molten temperature to form a molten metal ball on the end of the wire and a short circuit condition during which the molten metal ball on the end of the wire first contacts said molten metal pool and then transfers from the wire to the workpiece by a necking action breaking the molten metal ball from the wire to initiate an arc in a subsequent welding cycle. The welding cycles have a generally fixed frequency of repetition. The improvement comprises providing the power supply with a chopper circuit for applying a succession of input current pulses across the wire and workpiece at a pulse frequency substantially greater than the generally fixed frequency of repetition of the welding cycles and a pulse width changing circuit for adjusting current flow between the wire and the workpiece many times during each of the welding cycles.

Joint recognition and tracking for robotic arc welding

Abstract: An automatic joint guidance system was developed as part of a project to develop an expert welding robot. The apparatus consists of a servo-robot laser scanner mounted on a conventional CLOOS model ROMAT 75/76 industrial welding robot. The computer vision system is able to recognize and track the joint to be welded without external information by using range data obtained from scanning the workpiece. An approach and some experiments related to achieving this ultimate goal are discussed. Three different joint types are identified. Tracking of the joint geometry is done by building, online, a three-dimensional model of the joint during the welding process. This approach is attractive because of its complete autonomy for joint recognition and its ability to trace the geometry while at the same time avoiding an elaborate teaching pass prior to the process. The algorithms used have been tested in a simulation using real laser data. The results indicate that it is possible to recognize automatically the joint type and then to track the joint during the process of welding. >

Method and device for the loading and sealing of a double container system for the storage of radioactive material and a seal for the double container system

Abstract: A container for a radioactive material in which the cover is welded to the container by a dual weld disposed in a welding gap between the cover and the container wall, the gap having a bottom formed by opposed flanges on the cover and the wall. The root layer of the weld is formed by a tungsten electrode gas shielded arc welding process. A superimposed added layer is formed by a submerged arc welding process.

Metal Transfer in Gas Metal Arc Welding: Droplet Rate A study of droplet rates for various transfer modes verifies optimum operating parameters

Abstract: This study reports the changes in droplet-trans fer mode and rate during gas metal arc welding as the voltage is varied at a series of current levels. The droplet-transfer rate was found to be maximum (approximately 100 s_1) for the voltage/current combi­ nations that are normally suggested by the electrode manufacturers and are con­ sidered optimum in the judgment of experienced welders. At voltages above or below the TV-wide optimum range, the transfer rate decreased by about 10 s_1 per V in the vicinity of the optimum condition. Furthermore, statistical analysis of the arc current and voltage data showed that during operation outside the optimum range, the welding arc was unstable and the current output was very irregular with varying cycle time between each droplet transfer. At the maximum droplet-transfer rate, the droplet-transfer cycle time was very consistent and revealed a narrow rate range, which correlated with the high stability and lower spatter at these optimum operating conditions. The possibility of using the concept of maximum droplet-transfer rate range with minimum rate fluctuation and corresponding arc current-voltage signals as a means of short-circuiting welding process control and automation is being considered. At voltages below the optimum range, high-speed video recording confirmed that the short- circuiting transfer was very unstable and the arc reignited explosively. Above the optimum voltage, the arc became longer and the droplets became visibly larger, with mixed globular and short-circuiting transfer. The droplets, however, were no longer directed uniformly to the weld pool, resulting in increased spatter. arc (FCA), submerged arc (SA) and gas tungsten arc (GTA) welding. With the exception of GTA welding, all these pro­ cesses require a consumable electrode, which has the dual function of carrying the current that heats the weld pool and providing filler metal to complete the weld joint. This dual function has long been a topic of research. Spraragen and Lengyel (Ref. 1) reviewed the basic princi­ ples of an electric arc and summarized the development of the field of welding arc physics. In particular, they concluded that in the area of liquid metal transfer from the electrode to the weld pool, the electromagnetic pinch force, gravity, shielding gas drag force and surface ten­ sion are the major forces that act on the electrode tip. Using high-speed cinemat­ ographic techniques, Muller, Greene, and Rothschild (Ref. 2) found that large spher­ ical liquid-metal droplets in a GMA arc decreased in size with increasing current. As the electrode feed rate was continu­ ously increased, however, a sudden decrease in droplet size occurred at what was termed the transition current. In addition, they determined that with inert gas shielding, the droplet composition remained constant during the metal trans­ fer. Lesnewich (Refs. 3-5) investigated the physics of arc welding using SMA and CMA welding. Particularly, he studied the effects of welding process parameters such as current, voltage, electrode polar-

Low-resistance contacts on YBa2Cu3O7−δ ceramics prepared by direct wire bonding methods

Abstract: Wire bonding, such as electric discharge spot welding and ultrasonic bonding, has been investigated for use in simple, conventional methods of preparing low‐resistance ohmic contacts on superconducting Y1 Ba2 Cu3 O7−δ ceramics. Spot welding with thermal annealing improves the contact’s resistivity to 2×10−7 Ω cm2 , while a sample without annealing shows non‐ohmic and semiconductive characteristics. Change in the crystal structure induced by high current is analyzed. Ultrasonic bonding with annealing at 500 °C achieves 3×10−8 Ω cm2 , one of the lowest contact resistivities ever obtained in simple methods. The current‐voltage characteristics show nonlinearity, which is attributed to the superconducting state of the Ag/Y1Ba2Cu3O7−δ interface.

System and process for video monitoring a welding operation

Abstract: The invention is both a system and method for video monitoring a metal working process which involves the generation of an intense point source of light near or on a workpiece, such as an electric arc welding process. The system comprises a lens assembly for projecting an image of the point source of light and the area of the workpiece being worked onto the image sensing circuit of a television camera, a filter assembly having at least one filter element that includes both a central region of low light transmission for dimming the image of the point source of light projected onto the image sensing circuit, and a peripheral region of high light transmission for freely transmitting the image of the background surrounding the point source, and a mechanism for adjusting the apparent size of the central region of low light transmission relative to the image. In the preferred embodiment, an iris disposed within the lens assembly is used to adjust the apparent size of the central region so that it just barely covers the bright arc generated by the torch assembly so that the weld puddle and surrounding area of the workpiece is clearly visible and brightly illuminated in the resulting video image. The system provides a clear, bright and well balanced image of a welding operation without the severe and obscuring contrasts associated with prior art monitoring devices.

Weld arc simulator

Abstract: An arc voltage simulator for an arc welder permits the welder response to a variation in arc voltage to be standardized. The simulator uses a linear potentiometer connected to the electrode to provide a simulated arc voltage at the electrode that changes as a function of electrode position.

Variable polarity power supply for welding

Abstract: Disclosed is a variable polarity power supply for arc welding that quickly switches between polarities in order to more easily re-establish the arc. The variable polarity power supply includes a current-limited boost circuit for providing increased open circuit voltage to re-establish the arc, while limiting the re-establishment current. The variable polarity power supply is particularly suitable for computer-controlled welding applications because it periodically restarts the arc in either direction without using high frequency radiation, and provides quick switching times along with a low reverse current to reduce the heat in the torch, thereby increasing the longevity of the torch.

Welder's helmet and photovoltaic power transmission circuit therefor

Abstract: A welder's helmet including a panel of solar cells responsive to light generated by a welding operation to drive a fan incorporated in the helmet structure The solar cells are mounted on the helmet above the viewing window and the fan is mounted in front of the mask below the viewing window When a welding arc is struck, the light from the torch impinges on the solar panel and generates sufficient electricity to drive the fan The fan forces air from the inside of the helmet outward through the front face in a velocity controlled stream carefully directed to prevent smoke and fumes from reaching the helmet, and to also blow the smoke away from the weld site in a particular manner so that visibility of the weld remains clear while not over-oxygenating the weld site As air is exhausted from the inside of the helmet outward by the fan, fresh air is drawn in around the sides to replace that which is being exhausted to cool the welder and prevent ingestion of fumes and vapors A photovoltaic power transmission circuit is provided to process electrical energy derived from light such as that produced by the arc of an arc welder during a welding operation

Pulse arc discharge welding apparatus

Abstract: A pulse arc discharge welding apparatus comprising a pulse current waveform control circuit for periodically outputting a pulse current group consisting of a plurality of pulses, pulse arc current supplying means for outputting a pulse arc current according to an output of said pulse current waveform control circuit and an arc welding means for performing pulse arc discharge with an output of said pulse arc current supplying means, to carry out a pulse arc welding operation. In such a pulse arc discharge welding apparatus, with a discharge current waveform provided in the form of high frequency pulses, the discharge light and the gas in pulse discharge and the electrode are regulated and controlled with high accuracy.

Pulse MIG welder for welding thin-walled copper-nickel pipe

Abstract: A welding station for welding thin-walled copper-nickel pipe. An electronic welding station (10) has an output circuit (13) which provides arc welding power having the arc characteristics specified by a weld parameter selection circuit (12). A welding torch and feeder assembly (11) has a controller (20) which is responsive to a predetermined event, such as the passage of time since the start of the arc, or the average temperature of the pipe (25) as indicated by two temperature-measuring devices (30, 32). The controller (20) adjusts the wire feed speed, the pulse frequency, the pulse width, the welding voltage, the welding current and/or other parameters so as to cause the arc to have the parameters most desired for welding copper-nickel pipe. The present invention provides for a hotter arc for starting the welding operation, thereby obtaining good penetration and bonding, and a cooler arc for continuing the welding operation, thereby preventing burn-through of the pipe (25).

Flux cored wire electrode for gas shielded arc welding

Abstract: PURPOSE: To provide the subject wire which is excellent particularly in sea water corrosion resistance and low-temp. toughness and above all, COD characteristic by incorporating respectively prescribed ratios of Cu, Ni, Ti, and B into either or both of a steel sheath and filling flux contg. specific components. CONSTITUTION: The steel sheath contg., by weight %, ≤0.06% C, ≤0.012% P, ≤0.010% S, ≤0.0040% N, and ≤0.0150% O is prepd. The flux consisting, by the total weight of the wire, of 1 to 10% metal fluoride, 1 to 5% deoxidizing agent, and others including iron power, slag forming agent, arc stabilizer, and unavoidable impurities is filled at 8 to 25% of the total weight of the wire into the cavity enclosed by the above-mentioned steel sheath to constitute the flux-cored wire electrode mentioned above. In this case, 0.1 to 0.6% Cu, 0.2 to 2.5% Ni, 0.01 to 0.3% Ti, and 0.002 to 0.02% B, by the total weight of the wire, are incorporated as essential components into the steel sheath and/or flux. The flux cored wire electrode for gas shielded arc welding having the above-mentioned characteristics is obtd. in this way. COPYRIGHT: (C)1990,JPO&Japio

Computerized radiographic weld penetration control with feedback on weld pool depression

Abstract: Welding pool depression depends on plasma pressure and heat input to the pool and therefore is related to weld penetration On the basis of information on pool depression received from radiographic images in real time during welding, the possibility of using automated weld penetration control to maintain the required weld penetration has been studied The experimental system developed includes an arc welding unit, a welding manipulator, a real-time x-ray system, an image processing unit, and a system controller By analyzing the radiographic information together with metallographs of the appropriate weld cross section, the depth of the liquid metal in the pool has been determined at different levels of current and weld penetration

Welding apparatus and method for welding a joint between abutting circular workpieces

Abstract: Arc welding apparatus and method for precisely welding abutting pipe end portions defining an interface having a seam or joint to welded. The apparatus includes a roller assembly for precisely rolling the apparatus around a track circumscribing one of the pipe portions so that the seam may be suitably welded. Connected to the roller assembly is a carriage which carries an electrode housing having an electrode housed therein. A gear rack is provided on the roller assembly for engaging a pinion gear on the carriage for precisely biasing the carriage and thus the electrode housing parallel to the longitudinal center axis of the pipe portions. Connected to the carriage is a lead screw assembly for precisely biasing the electrode housing and thus the electrode perpendicularly to the longitudinal center axis of the pipe portions to be welded. Connected to the electrode housing is a manipulator arm for precisely manipulating filler wire at the weld site.

Electric welding apparatus for automatically welding heating coil fittings

Abstract: In an electric welding apparatus for automatically welding heating coil fittings substantially of plastic material a scanner (3) for scanning fitting data is connected via a converter to a first input of a controller (8) which via a power station (13) controls, for a welding period, the welding power output. In order to reach an optimal welding factor of the welding the scanner (3) and the converter (4) are provided for scanning naominal welding energy data of said fitting (1). At least a second input (at 12) of the controller (8) is connected to circuits (calculator 11) which generate signals of the actual welding energy from welding power output data as well as from the actual welding period.

Automatic arc-welding machine operating with rod electrodes and a preferred application thereof

Abstract: An automatic arc welding machine of the type which operates with rod electrodes. The electrodes (46), which are held in a welding head (28), are moved automatically with respect to the workpiece. The electrodes are moved longitudinally away from the workpiece in accordance with the arc voltage such that a certain arc length is sustained. After use they are automatically replaced with new electrodes. For this purpose there is provided an arc striking control by means of which the particular electrode (46) is placed on the workpiece with the current limited to a value below the selected welding current; the electrode is then raised from the workpiece by an amount corresponding to the predetermined arc length while the welding current is released, before the longitudinal movement of the electrode in accordance with the arc voltage begins. A precisely timed and accurately placed ignition is achieved in this manner, even if the location of the weld is covered with scale or slag.

Infrared Sensing for Adaptive Arc Welding Infrared thermography is used to sense depth of penetration

Abstract: Adaptive welding enables dy­ namic altering of the welding parameters to compensate for changing environment. Sensors providing process status informa­ tion in real time are an integral part of such an adaptive system. In this investigation, infrared thermography was used as a sen­ sor to control the position of the arc and the penetration depth of the weld. Pre­ liminary work on infrared thermography showed that variation in these parameters produces a change in the surface temper­ ature distributions of the plates being welded. Subsequently, to achieve com­ puter control of these variables, image analysis techniques have been developed to quantify the changes in the tempera­ ture distribution.

Method and apparatus for cleaning and lubricating a metal inert gas welding gun

Abstract: A method and apparatus for cleaning a metal inert gas arc welder gun of a type having a housing and a flexible conduit disposed in the housing. The flexible conduit has a first end for feeding a consumable welding wire therethrough and a second end adapted to engage with a tubular welding tip for selectively feeding the consumable wire through the flexible conduit and through the welding tip for use. The method involves removing the consumable wire from a major portion of the flexible conduit, injecting a liquid cleaner into the flexible conduit until some of the liquid exits the other end thereof, forcing the liquid cleaner out of theflexible conduit and moving the consumable welding wire back into the flexible conduit and tubular welding tip for use.

Apparatus for quick disconnect of an arc welder torch

Abstract: Apparatus for the quick connect and disconnect of a welding and a cutting torch includes a plurality of quick connectors. An outer portion of a quick connector carries electrical current which provides electrical power for an electric arc welder and an axial bore in the connector carries a liquid to provide cooling of the torch. Other quick connectors carry gas or liquid between the torch and sources of supply.