Showing papers on "Arc welding published in 1988"

Welding Metallurgy of Stainless Steels

Abstract: Contents: Significance of Constitution Diagrams for the Understanding of Welding Phenomena * Metallurgical Processes During Solidification and Cooling in Stainless Steel Weld Metal * Metallurgical Phenomena in Secondary Crystallization of Stainless Steels and Weld Metals * Precipitation Phenomena in Stainless Steel and Weld Metals * Hot Cracking Resistance During the Welding of Austenitic Stainless Steels * Welding Metallurgy of Ferritic Stainless Chromium Steels with Carbon Contents Below 0.15 per cent * Welding Metallurgy of Low Carbon Chromium-Nickel Martensitic Stainless Steels (Soft Martensitic Steels) * Welding Metallurgy of Duplex Austenitic-Ferritic Stainless Steels * Welding Metallurgy of Austenitic Stainless Steels * General Instructions for the Welding and Post-Weld Surface Treatments of Fabrications and Welded Components Made from Austenitic Stainless Steel * Welding Metallurgy of Heat Resisting Steels * Welding Metallurgy of Austenitic-Ferritic Dissimilar Joints * Appendix: Abbreviations and Short Designations * References * Author Index * Subject Index.

Welding parameters and the grain structure of weld metal — A thermodynamic consideration

Abstract: The grain structure of the weld metal can significantly affect its resistance to solidification cracking during welding and its mechanical properties after welding. An experimental study was conducted to investigate the effect of two basic welding parameters,i.e., the heat input and the welding speed, on the grain structure of aluminum-alloy welds. Gas-tungsten arc welding was performed under various heat inputs and welding speeds, with thermal measurements in the weld pool being carried out during welding and the amounts and nuclei of equiaxed grains in the resultant welds being examined using optical and electron microscopy. The experimentally measuredG/R ratios and the clearly revealed heterogeneous nuclei together demonstrated the thermodynamic effect of the heat input and welding speed on the weld metal grain structure.

Ultrasonic sensing of weld pool penetration

Abstract: This paper reports how the geometry of the sidewall as it is penetrated by the weld pool during gas metal arc welding (GMAW) can be detected by high-frequency sound waves. The penetration geometry is detected using a piezoelectric transducer, operating in the pulse-echo mode, to generate shear sound waves that travel through the base metal to the weld region. The received echoes contain information that can be related to the sidewall penetration and thus to the quality of the weld. Different geometries can be discriminated using expert system methods, thus providing the potential of sending information on sidewall penetration to a closed-loop welding system for real-time feedback control to assure adequate sidewall penetration.

Retinal burns caused by exposure to MIG-welding arcs: report of two cases.

Abstract: A new generation of arc welder has recently become widely available at a price which is within reach of most amateurs and part-time mechanics, known as the MIG welder (metal-arc inert gas welder). In MIG welding the arc is ensheathed in a stream of inert gas which prevents the molten metal from oxidising. The stream of gas changes the character of the emitted radiation, and it is possible that this type of welder poses a greater threat to sight than previously recognised. Radiation in the ultraviolet range emitted by arc welders is absorbed by the unprotected cornea and lens, giving rise to a keratoconjunctivitis, or 'arc-eye,' which, though intensely painful, is not considered a threat to sight. Radiation in the visible and near infrared spectrum, however, penetrates the eye to be absorbed by the retina and may cause thermal or photochemical damage which may be permanent and sight-threatening. Retinal injuries resulting from exposure to ordinary electric welding arcs have been reported, but such injuries are uncommon. Two cases of retinal burns resulting from exposure to MIG welder emissions which presented on consecutive days to the Leicester Royal Infirmary are presented. This is the first report of such injuries relating specifically to MIG welding.

Apparatus for the televisual monitoring of an arc welding operation

Abstract: The televisual monitoring apparatus incorporates at least one camera (10) fastened to the support of the welding machine. The camera (10) incorporates, interposed on the path of the light rays coming from the welding zone and upstream of a device (22) for conversion of the light rays into video signals, a filter (24) composed of a plate of ceramic material having light rotatory properties and electrodes disposed in contact with each of the two faces of the plate in accordance with a determined network. The monitoring device also incorporates, associated with the camera 10, an electronic video signal analysis and electrode potential control arrangement.

Twin pulsed arc welding system

Abstract: The invention provides a gas-shielded arc welding system using two side-by-side electrodes each of which is provided with current pulses superimposed on a respective background current level to maintain the desired controlled spray transfer mode of the weld metal without overheating effects. The pulses are supplied to the two arcs out of phase with one another to minimize interaction of their magnetic fields, but this alone is not sufficient to assure stability of the two arcs. In the system of the invention, one arc is designated as the master arc and the other as the slave arc. The master arc is stabilized by means of a feedback loop controlling its master pulse frequency. Each master pulse triggers a respective slave pulse after a preset time delay, in this way keeping corresponding master and slave pulses in synchronism. This is not necessarily sufficient to stabilize the slave arc and independent stabilization is therefore provided for it by a feedback loop controlling its pulse duration or its background current, but preferably by controlling both simultaneously.

Laser-arc apparatus and method for controlling plasma cloud

Abstract: A pulsed laser arc welding method and apparatus whereby a pulsed input laser beam is generated by a laser pulse generator to cause an ionized plasma cloud to be generated at a worksite. A power supply supplies energy to an arc welding device, which is stored in a capacitor therein. This energy is drawn out of the storage capacitor once the ionized plasma cloud is sufficiently conductive. Control circuitry is provided to control the pulse repetition frequency of the laser pulse generator and to control the energy dissipation from the storage capacitor in the arc welding device.

Ac tig welding apparatus using hot wire

Abstract: An unconsumable electrode such as tungsten is opposingly arranged with a base metal to be welded. An AC arc welding power supply is connected between the base metal and the unconsumable electrode. A filler wire such as of aluminum is fed by a wire feeder toward an arc-generated part between the base metal and the unconsumable electrode. Also included is a wire-heating power supply for producing a pulsed current. The wire heating power supply heats the filler wire by supplying thereto a pulsed current in accordance with a sync signal from the AC arc welding power supply or a detection signal of an arc current i A or an arc voltage of the AC arc power supply. The filler wire is thus heated by being supplied with a heating current i W in pulse form while the unconsumable electrode is kept negative by an AC arc formed between the unconsumable electrode and the base metal. During the period when the unconsumable electrode is kept positive by the AC arc, the filler wire is not supplied with any current or is heated by being supplied only with a sufficiently small current not to cause any substantial magnetic flow. Accordingly, even if a large current flows through the wire, arc interruptions can be eliminated, thereby improving the welding process of aluminum by using an AC TIG arc.

Reduced-spatter pulse arc welding machine for use with a consumable electrode

Abstract: A consumable electrode arc welding machine in which if a short circuit does not lasts beyond a predetermined first time limit, pulse current and base current outputs for the arc are alternated with each other in a basic pulse period. If a short circuit lasts beyond the first time limit, the welding output during the subsequent short circuit period is subjected to constant-current control along a predetermined first trace, and a second time limit begins from the start of arc regeneration. The welding output is controlled to be different from both the pulse current and base current during the second time limit to restore the operation of the welding within the basic pulse period.

Inverter controlled-type power source for arc welding

Abstract: An arc welding power source supplies a high voltage for the reignition of an arc after the polarity reversal of a welding current to prevent the destruction of circuit elements and ensure the stable and positive polarity reversal despite its reduced size, and also the occurrence of a spike voltage in a main circuit during the polarity reversal of a large current or alternatively the welding current during the polarity reversal is controlled to suppress a spike voltage during the current reversal.

Tig or mig arc augmented laser welding of thick mild steel plate

Abstract: Effects of various operating parameters on penetration depth were investigated in laser +TIG and laser +MIG welding of steel plate. In laser +TIG welding (of C-Mn-Nb-V steel), DCEN TIG welding at 100-300A was closely followed by laser welding with 1-5kW beam power. Effects of welding speed, distance between TIG electrode and laser beam, focal position of laser and TIG welding current were determined. In laser +MIG welding (of C-Mn-Ni-Mo steel), DCEP helium-MIG welding at 400A was followed by laser welding at up to 5kW. Effects of arc-beam distance, focal position, joint preparation and laser beam power were determined.

An approach to an expert robot welding system

Abstract: Adaptive control and sensory processing techniques in robotic arc welding are discussed. The gas metal arc welding and gas tungsten arc welding processes are considered, along with a literature review of aspects of welding automation. Topics covered include process modeling, detection and measurement of process features, real-time control, and implementation considerations. An approach for an adaptive welding system is presented. The proposed architecture fits within the scope of an ambitious project to develop an expert welding robot. Different levels of automation are discussed, from the decision level to the closed-loop control of process variables and torch trajectory. >

Automatic arc-welding method

Abstract: An automatic arc-welding method, which comprises, when welding two objects to be welded together by means of a welding wire along a first groove formed between the objects to be welded on a first side thereof, continuously determining by calculation a target welding current, with which a depth of penetration agrees with a target value thereof, on the basis of the root gap, the material of the welding wire and the like; continuously determining by calculation a target feeding rate of the welding wire, at which an extension length of the welding wire agrees with a target value thereof, on the basis of the welding current, the material of the welding wire and the like; continuously determining by calculation a target welding speed, at which a height of the weld bead agrees with a target value thereof, on the basis of the feeding rate of the welding wire, the material of the welding wire, the root gap and the like; and on the other hand, when welding the objects to be welded together by means of the welding wire along a second groove formed on a second side of the objects to be welded, opposite to the first groove, continuously determining by calculation a target welding current and a target welding speed while taking into consideration the depth of penetration and the weld bead in the first groove; thereby automatically controlling the welding current, the feeding rate of the welding wire and the welding speed on the basis of the respective target values thus determined.

Theoretical Analysis of Weld Pool Behavior in the Pulsed Current GTAW Process

Abstract: A general three-dimensional, closed-form welding heat-flow solution, which is capable of analyzing thermal behavior of the weldment in its transient state and/or under time-dependent power change during welding, is presented. The analytical model utilizes the finite heat source theory with a Gaussian distribution and also considers the effects of finite plate thickness. The numerical values of the solution are calculated using the computational schemes on a minicomputer. In this paper the welding parameters of the pulsed current Gas Tungsten Arc Welding (GTAW) were studied using the solution. Two sets of pulsation parameters were analyzed and their sensitivity to the heat input control were evaluated.

Power and current distributions in gas tungsten arcs

Abstract: The power- and current-density distributions in a welding arc can significantly affect heat and fluid flow in the weld pool during arc welding, which in turn affects important weld characteristics such as weld penetration, segregation, gas porosity and solidification structure. In order to provide quantitative information for studying heat and fluid flow in the weld pool, an experimental study was carried out to measure the power- and current-density distributions from the experimental data generated by the split-anode technique is rather critical. A new, improved method developed in the present study, as well as four other previous previous methods, were employed to determine the power- and current-density distributions from the experimental data. The validity of the approximation of the Gaussian distribution was examined, and the effects of the arc length, arc current and electrode diameter were observed.

Arc welder with improved arc striking capability

Abstract: A pulse type arc welder with improved arc starting characteristics. An output voltage level sensor (2017) monitors the output voltage to determine whether the arc has been struck. If the arc has not been struck, a first oscillator (2000) gates a second, higher frequency oscillator (2002) so that the input to the driver (2010) is a chopped, pulsed, high duty cycle waveform. Also, the bandwidth of the output current level sensor (2012) is reduced so that the high value, short lived arc starting transient current does not cause the output current level sensor (2012) to improperly shut down the driver (2010). Additional current limiting protection is provided during this period since the high chopping frequency causes the reactor (2010a) to have a high impedance. After the arc has been struck, the output voltage will drop to the arc sustaining voltage and the output voltage level sensor (2017) will de-energize relay (2003). The first oscillator (2000) then provides the driver (2010) with an input signal having the characteristics selected for the particular welding operation. Also, the bandwidth of the output current level sensor (2012) is restored to its full value.

Method for controlling and synchronizing a welding power supply

Abstract: A microprocessor-controlled arc welding power supply is disclosed. An silicon controlled rectifier ("SCR") bank is used to generate a direct current arc welding current under program control. Positive sychronization is provided by the microprocessor using a phase locked loop and a polarity detector, so that the gating signals applied to the SCRs are correctly timed. Optimum tradeoffs between hardware and software are accomplished by using look up tables to store correction factors that can be quickly accessed during execution, and by using timers as smart interface chips to fire the SCRs at the same angle during each cycle until changed or updated by the microprocessor. The arc welding power supply is capable of operating in a constant current or constant voltage mode without rewiring the circuit.

Constant arc voltage gas metal arc welding process

Abstract: A gas metal arc welding process employing a shielding gas mixture consisting essentially of (A) 2 to 12 volume percent carbon dioxide, (B) 20 to 45 volume percent helium and (C) the balance argon.

Power supply system for consumable electrode arc welding and method of controlling the same

Abstract: A power supply system for consumable electrode arc welding alternately switches between the reverse polarity and the straight polarity. The formation of an arc is detected. A polarity change control signal is generated when the arc duration reaches a predetermined time or when the quantity of charge reaches a predetermined value. The predetermined value of the welding current or voltage is reduced either immediately before or after the change in polarity.

Consumable electrode type arc welding contact tip

Abstract: A welding contact tip for use on a consumable electrode type welder has a core part (1) having a bore (3) for guiding a consumable electrode (4) and capable of supplying welding current to the consumable electrode (4), and a main part (2) which embraces and supports the core part (1). The core part (1) is made of a heat- and wear-resistant conductive metallic material such as a chromium-copper alloy, while the main part (2) is made from a less-expensive material such as copper, a copper alloy, aluminum or an aluminum alloy.

Gas tungsten arc welding machine with infinite rotating welding head and torch tilt

Abstract: This invention relates to a machine for practicing the gas tungsten arc welding process which includes means (5) for rotating the welding torch (28) continuously while welding. Means are provided for feeding the shielding gases, feed wire and electric current to the rotating torch while welding. Means (23) and (24) are also provided for tilting the torch about the point of welding. This invention makes it possible to weld continuously along a spiral path about a cylindrical object or on a flat or irregular surface.

Stud welding apparatus

Abstract: Control circuit for arc welding components to workpieces, in which a component is placed on to a workpiece by a weld gun and after a welding stroke is lifted from the workpiece in a return stroke by igniting a pre-current arc and is brought up to the workpiece again in a forward stroke during the burning of an interconnected welding arc, in which a sequencing control determines the tripping moments of return stroke and forward stroke as well as of the welding arc and a monitoring voltage is bypassed from the pre-current arc ignited at the welding point, characterized in that the monitoring voltage (V) is converted into a correction voltage (line 27) by means of a set-point comparator (25) and is superposed on a control voltage (line 18) for principally controlling a high-frequency modulated switching mode power supply unit (15) and said switching mode power supply unit (15), in accordance with the thus corrected control voltage, adjusts its output current (lines 13,14) during the respective welding operation to the resistance value of the pre-current arc established by the monitoring voltage (V) representing the respective welding data.

Process and device for short circuit arc welding

Abstract: Process and device for short-circuit arc welding in which a continuously fed welding wire alternately passes into an arc phase and a short-circuit phase, the wire being at a distance from the molten pool of the workpiece during the arc phase, and the molten metal at the end of the welding wire touching the pool of molten metal during the short-circuit phase and then passing to the workpiece by pinch effect, which tears the molten metal from the wire. The improvement consists in the fact that a first current-control circuit (22) with high inductance is provided which continuously conducts a background current of low intensity between the welding wire and the workpiece, which background current supports the arc, and that a second current-control circuit (24) is provided which controls the current flow during the arc phase of the melting process. This second current-control circuit (24) has time-delay means which allow the arc at the start of the arc phase to occupy an area which is primarily determined by the background current for a preselected time during which the molten metal on the tip of the welding wire and in the molten metal pool is drawn by surface tension against the wire and/or into the welding pool, the latter essentially being pressed down, and means being provided which then allow a high current surge to run with preselected energy through the arc between the wire and the welding pool in order to melt a relatively constant volume of metal at the end of the wire and at a distance from the molten pool. This high energy pulse takes place near the start of the arc phase and generally ends before the centre of the arc phase so that the wire is first melted and then directed into the molten metal pool after the pool has essentially been pressed down or has steadied.

Trailer shield assembly for a welding torch

Abstract: A trailer shield assembly (10) having a housing (24) with an open lower side and a welding torch (12) mounted so that a welding tip portion (48) of the torch (12) extends through the lower side of the housing (24). A flexible gas guide (76) is affixed to a rear wall (74) of the housing (24) and has an interior (116) in communicating relation with a welding region (34) of the housing (24). A flexible shield gas manifold (90) having a plurality of spaced openings (92) therein is disposed in an upper region (110) of the gas guide (76) and is connectible to a source (11) of shield gas. A diffuser (112) surrounds the flexible manifold and serves to distribute shield gas in an even layer downwardly to cover a hot weld. A pair of openings (96) in the flexible manifold (90) communicates with a second gas manifold (32) disposed in an upper region of the housing (24), with this second gas manifold (32) being provided with an aluminum gas diffuser (30). Diffuser (30) distributes shield gas ahead of torch (12) to cover metal preheated by this welding operation.