Showing papers on "Arc welding published in 1998"

Optimisation of the weld bead geometry in gas tungsten arc welding by the Taguchi method

Abstract: In this paper, determination of the welding process parameters for obtaining an optimal weld bead geometry in gas tungsten arc welding is presented. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each welding process parameter on the weld bead geometry, and to predict the optimal setting for each welding process parameter. Experimental results are presented to explain the proposed approach.

A theoretical model for gas metal arc welding and gas tungsten arc welding. I.

Abstract: A recently developed theory for predicting arc and electrode properties in gas metal arc welding (GMAW) has been generalized to include arc–electrode interfaces, variation of surface tension pressure with temperature, Marangoni forces and handling of weld pool development in stationary gas tungsten arc welding (GTAW). The new theory is a unified treatment of the arc, the anode, and the cathode, and includes a detailed account of sheath effects near the electrodes. The electrodes are included as dynamic entities and the volume of fluid method is used to handle the movement of the free surface of the molten metal at one electrode. Predictions can be made of the formation and shape of the welding droplets as a function of time in GMAW and also of weld pool development in GTAW, accounting for effects of surface tension, inertia, gravity, arc pressure, viscous drag force of the plasma, Marangoni effect and magnetic forces, and also for wire feed rate in GMAW. Calculations are made of current densities, electric potential, temperatures, pressures and velocities in two dimensions, both in the arc and also within the molten metal and solid electrodes. Calculations are presented for GMAW and GTAW for an arc in argon and the results are compared with experimental temperature measurements for the plasma and the electrodes.

The dynamic analysis of metal transfer in pulsed current gas metal arc welding

Abstract: The dynamic characteristics of metal transfer in the pulsed current gas metal arc welding are analysed using the volume of fluid method incorporating the electromagnetic force. The surface profile and the velocity distribution of fluid in the drop are computed numerically. The viscous flow and inertial force of a molten metal generated by the peak current are found to have significant effects on the metal transfer and drop detachment. The ranges of the pulsing frequency for which one drop is detached per current pulse are predicted and calculated results are in good agreement with the experimental data with some discrepancy for low load duty cycles.

Arc welding monitoring device

Abstract: An arc welding monitoring device which can easily recognize the correspondence between the operating path of a robot, namely, the weld line information of a work to be welded and detected data such as welding voltages and currents. The monitoring device is provided with means (4 and 5) which detect at least either welding currents or welding voltages, a means (14) which retains the detected data of the means (4 and 5), a means (14) which stores the operating path of the robot, and a means (12) which displays at least either the welding currents or welding voltages detected by means of the detecting means (4 and 5) and the operating path of the robot stored by means of the storing means (14) on a display, sets an extent on the operating path displayed on the display, and makes arc welding monitoring displays within the set extent.

Chromium, nickel and manganese in shipyard welding fumes

Abstract: Tests were conducted to determine the effects of base metal and welding electrode composition on welding fume. Materials included HY-100 and HSLA-100 high-strength, low-alloy steels. Shielded metal arc welding (SMAW) was performed with E1 1018-M electrodes and gas metal arc welding (GMAW) with MIL-100S-1 electrode wire. These tests included measurement of fume composition, fume generation rates and worker breathing zone fume. Sampling of welding fume also was conducted in a shipyard. This study concludes that some shipyard welding and cutting operations, materials and processes will be impacted by the recent and anticipated reductions in exposure limits. Additional controls will be required to comply with these reductions. Results indicate: . Exposure to hexavalent chromium can be expected when welding or cutting materials that contain chromium or chromates. These materials include stainless steels, high-chromium nickel alloys and some low-alloy steels. . The highest nickel levels occurred during SMAW and GMAW of stainless steels and nickel alloys. However, only the samples in enclosed spaces exceeded the proposed limit for nickel. . SMAW, GMAW and flux cored arc welding (FCAW) of stainless steels, carbon steels and low-alloy steels produced the highest manganese levels. . Eight-hour TWA levels of hexavalent chromium of up to 1-2 μg/m 3 were found during shipyard and laboratory sampling of SMAW of HY-100 using E11018-M and E12018-M electrodes. Similar levels also may be possible when welding with these electrodes on other materials.

An analysis of the formation of metal droplets in arc welding

Abstract: A dynamic two-dimensional arc model has been used to investigate the effects of the various forces acting on the droplet in gas metal arc welding (GMAW). The model is based on the equations of conservation of mass, energy, momentum and current, Ohm's law and a Maxwell equation. The model treats the welding wire, the plasma and the workpiece. For molten metal droplets at the tip of the welding wire, we account for effects of inertia, gravity, surface tension, magnetic force, viscous drag force and arc pressure. Calculations are presented for a 1.6 mm diameter wire of mild steel for arcs in argon to determine the separate effects of these forces on droplet formation. It is found that, for arcs in pure argon at currents around the transition from the globular transfer mode to the spray transfer mode, viscous drag and arc pressure effects are approximately self-cancelling. It is also found that forces have a much larger effect than do forces on the transition from globular to spray modes of metal transfer.

Method and system for gas metal arc welding

Abstract: An improved method of gas metal arc welding (GMAW) is disclosed. The method includes utilizing a pulsed current having a variable waveform to ensure the detachment of one-droplet-per-pulse of current. During the welding process, the current is sufficient to produce a droplet at the end of a consumable electrode wire. After the droplet reaches a desired size, the current is lowered to induce an oscillation in the droplet. The current is then increased which, in combination with the momentum created by the oscillation, effects droplet detachment. The oscillation may be monitored by observing the arc voltage to determine a preferred detachment instant. A computer implemented method allows for the adaptive control of the current waveform to accommodate for anticipatable variations in the welding conditions, while maintaining ODPP transfer and a constant pulse period. An accompanying system is disclosed for implementing the method of adaptive welding.

Investigation into properties of laser welded similar and dissimilar steel joints

Abstract: Laser beam welding is currently used in the welding of steels, aluminium alloys, thin sheets, and dissimilar materials. This high power density welding process has unique advantages of cost effectiveness, deep penetration, narrow bead and heat affected zone (HAZ) widths, and low distortion compared to other conventional welding processes. However, the metallurgical and mechanical properties of laser welds and the response of conventional materials to this new process are not yet fully established. The welding process may lead to drastic changes in the microstructure with accompanying effects on the mechanical properties and, hence, on the performance of the joint. The thermal cycles associated with laser beam welding are generally much faster than those involved in the conventional arc welding processes. This leads to the formation of a rather small weld zone that exhibits locally a high hardness in the case of C–Mn structural steels owing to the formation of martensite. It is currently difficult ...

Arc welding power supply

Abstract: A dual stage power supply for creating a D.C. welding current through an arc welding gap, the power supply comprising an input inverter stage with a full wave rectified A.C. voltage source and an output capacitor; and, an output chopper stage connected across the output capacitor, with the chopper including output leads connected across the arc welding gap, a switch for gating the output current of the inverter stage at a controlled rate through the leads and through the arc welding gap, an output inductor in one of the leads between the switch and the arc welding gap and a free wheeling diode across the leads between the switch and the output inductor.

Apparatus and method for controlling an arc welding robot

Abstract: An apparatus and method controls an arc welding robot. During robot teaching, an allowable width for a command value (central value) is entered via an input. The robot is taught, and operated according to data stored in a memory, and a CPU judges if an actual welding value taken from an external interface during actual welding is within the allowable width corresponding to the entered welding condition command value, and when the actual welding value is outside of the allowable width, operation information of the robot can be immediately displayed by an information noticing device, or stored in the memory, and displayed in batch at the end of one welding stroke. An arc welding condition is monitored only during regular welding, and can be ignored during crater treatment, or a section of unstable welding right after the start of welding can be excluded from the welding condition monitoring object section. As required, depending on characteristics of a wire feeder, the conditions of crater treatment can be changed.

Predictions of metal droplet formation in gas metal arc welding. II.

Abstract: Predictions of metal droplet formation in gas metal arc welding (GMAW) are made for mild steel wires with argon as a shielding gas, using a generalized theory for predictions of arc and electrode properties in arc welding The theory is a unified treatment of the arc and the electrodes and includes a detailed analysis of the anode sheath region, together with a free surface treatment for the molten metal at the tip of the welding wire Results of calculations made for a mild steel wire of 012 and 016 cm diameters are in good agreement with experimental measurements of droplet diameter and droplet detachment frequency at currents between 150 and 330 A The results indicate that the anode sheath region and the effects due to variation of surface tension with temperature have an important influence on the dynamics of droplet growth at the tip of the wire in GMAW Predictions are made for the transition from the globular to the spray mode of metal transfer, in agreement with experimental observations in arc welding

Rotor repair system and technique

Abstract: A system for repairing worn, distorted, cracked, or degraded portions of high temperature rotors such as those used in high-pressure and reheat steam turbines is disclosed. The repairs are applicable to low alloy steels generally described in ASTM Specification A-470 classes 3, 7, and 8. Explicit controls on the welding process, the welding consumables, and the placement of the weld fusion line are disclosed. For the welding process, a novel staging of the "relative heat input" for applying the initial cold wire gas tungsten arc weld (GTAW) buttering layer is disclosed. Significantly, the optimum weldment properties are achieved in the cold wire GTAW by utilizing a lower heat input for the crucial second layer relative to the first layer. Faster deposition or weld build-up is achieved over the buttering layer by applying the balance of welding through utilization of the hot-wire GTAW process. Hot-wire weld integrity is assured by control of a helium-argon cover gas mixture, application of a trailing gas shroud, weld-head oscillation, and control of the wire insertion point into the molten puddle. For the weld deposit, a specially modified 9Cr-1Mo filler metal based on the "Grade 91" alloy developed by the Oak Ridge National Laboratory is selected. Additional stringent controls are placed on the chemical composition of the weld wire. Finally, judicious placement of the weld fusion line to insure long service is achieved by a detailed finite-element stress analysis. Near the fusion line, the stresses are limited to values below the minimum stress-rupture strength of the base metal as described by a correlation using the Larson-Miller time-temperature parameter.

Elevated-temperature, plasma-transferred arc welding of nickel-base superalloy articles

Abstract: A nickel-base superalloy article which is susceptible to strain-age cracking and has a directionally oriented, single crystal, or equiaxed grain structure is repaired with minimal welding heat input into the article. The article is first heated to a welding temperature of from about 1650° F. to about 2000° F. in an inert atmosphere. A damaged area of the article is weld repaired using a plasma-transferred arc welder which vaporizes a filler metal in a plasma arc and deposited the vaporized metal onto the article to form a weld overlay. Minimal additional heat is added to the article during welding, as the weldment metal is vaporized remotely from the article.

Method of arc welding using dual serial opposed torches

Abstract: An improved method of arc welding uses a single power supply connected to opposed welding torches placed on both sides of a workpiece Each torch is connected to a different polarity lead of the power supply and forms a separate arc with the workpiece When a current is supplied to the first torch, it is guided from the first electrode, through the first arc, the workpiece, the second arc, and to the electrode of the second torch This guiding function improves the penetration, concentration, as well as the directional stability of the arc This permits the effective and efficient welding of relatively thick workpieces using existing equipment at low current levels

Short circuit pipe welding

Abstract: An apparatus and method of short circuiting arc welding two spaced ends of two pipe sections at a groove between the two pipe sections. The method and apparatus include the use of a cored metal electrode and moving the electrode toward the groove as the electrode is moved along the groove and about the outer peripheral surface of the pipe sections during the welding operation. The cored electrode is melted by an electric wave which comprises a transfer portion and a controlled melting portion. The melting portion is controlled to bridge the gap between the pipe sections for laying a root bead along the groove. The cored electrode is preferably a self-shielding electrode and includes alloying components in the core to form a root bead having a substantially similar composition as the composition of the two pipe sections.

Remote operator viewing and measurement system for arc welding

Abstract: Arc welding control apparatus includes a laser (10) for projecting a first reference mark (24) along a first axis onto the line of a weld (26) and a video camera (12) arranged to view the work piece along a second axis to generate a video image including the first reference mark. The apparatus is mounted on a welding torch for movement therewith, the first and second axes intersecting at a predetermined point relative to the video camera. Sensor control means (30) receives the video signal from the video camera, and generates a composite video signal representing the original image with an image of a second mark superimposed therein. The position of the second mark is adjustable within the image frame. The position of the welding torch is set such that the welding electrode is positioned with the first mark projected onto the line of the weld ahead of the torch. The location of the second mark is adjusted within the image frame such that it is aligned with the first mark. During welding, the position of the second mark is monitored and the vertical and/or horizontal position of the welding torch is adjusted so as to maintain the first and second reference marks in alignment. The invention may be adapted to enable remote dimensional measurements of the workpiece.

Double-sided arc welding increases weld joint penetration : Aluminium welding

Abstract: Connecting two torches to the two terminals of a single power supply achieves more concentrated arcs that increase weld joint penetration.

Electromagnetic interference and ICD discharge related to chiropractic treatment.

Abstract: Electromagnetic interference is well known to cause false sensing in ICDs. Sources may include instrumentation involved with acupuncture, arc welding, electrocautery, diathermy, electrolysis, and transcutaneous electric nerve stimulator units as well as power lines. Patients with ICDs are cautioned to avoid exposure to these sources.

Weld quality measurement

Abstract: This invention concerns weld quality measurement. In particular it concerns an apparatus and a process for measuring on-line, while the welding process is under way, the quality of the resulting weldment. The invention is applicable to spray-transfer gas-metal arc welding, short-circuiting transfer gas-metal arc welding, pulse welding, radio-frequency resistance welding and submerged arc welding. It involves the measurement of voltage or current and the generation of an artificial signal for the other. A two dimensional signal analysis then produces data for comparison with data obtained from a high quality weld.

Cathodic cleaning and heat input in variable polarity plasma arc welding of aluminum

Abstract: For variable polarity plasma arc welding (VPPAW) of 1,100 Al, it was found that the net heat input to the aluminum workpiece did not decrease as independent changes in polarity balance enabled the tungsten electrode to become the predominant anode in the alternating current arc. For the thin sheet edge welds made in this study, the independent parameters used to vary the arc current polarity balance were very effective in delivering a wide range of actual arc power polarity balance. The ratio of electrode positive polarity arc energy to the total arc energy ranged from as little as 0.03 to as high as 0.99. Despite this pronounced difference in arc polarity, no significant variation in the average arc efficiency (net heat input/arc energy) of 0.51 was found. Substantial heating of the workpiece during electrode positive polarity was attributed to field type emission of electrons from the low boiling point aluminum cathode. Unlike thermionic emission at the tungsten, field emission electrons do not cool the cathode. While the actual arc efficiency were relatively constant, there were significant differences in the measured heat input, the weld size, and the effectiveness of the cathodic cleaning.

Solid wire for gas shielded arc welding

Abstract: PROBLEM TO BE SOLVED: To provide a solid wire for gas shielded arc welding, the solid wire that is highly efficient and provides excellent mechanical performance in a weld zone when carbon dioxide gas shielded arc welding is applied to a carbon steel whose strength is not higher than 520 N/mm 2 class. SOLUTION: The solid wire for gas shielded arc welding has the composition containing, by mass%, 0.70-1.00% Si, 1.50-1.90% Mn, 0.005-0.025% S, 0.19-0.25% Ti, 0.12-0.35% Mo, 0.020-0.100% C, ≤0.0050% B, and ≤0.45% Cu, wherein P and O is regulated to, by mass%, ≤0.020% and ≤0.0160%, respectively, and Si/Mn is controlled to ≥0.385, total contents of Mn and Mo is controlled to ≤2.20 mass%, and total contents of S and O is controlled to ≤0.034 mass%, and wherein when C content (mass%) is [C] and B content (mass%) is [B], the following expressions are satisfied. When 0.020≤[C]≤0.05, [B]≥0.0015; when 0.050<[C]<0.060, [B]≥0.009-0.15×[C]; and when 0.080≤[C]≤0.100, [B]≤0.013-0.10×[C]. COPYRIGHT: (C)2006,JPO&NCIPI

Arc welding apparatus

Abstract: The present invention is directed to an arc welding apparatus constructed of: a welding transformer 1, wherein a first tap T1 is provided at a point of half N/2 of the total number of turns N of the secondary winding of the transformer 1, the first tap T1 is connected to the electrification section 9 of a manual welding holder 8, a second tap T2 is provided at a point of N1 turns from the start Ts of the secondary winding, the second tap T2 is connected to a second thyristor 3, a first thyristor 2 and a third thyristor 4 are connected across both ends of the secondary winding, a third tap T3 is provided at a point of half N1/2 of N1 turns of the secondary winding and the third tap T3 is connected to a CO2 arc welding torch 10; a control circuit 6 for controlling these thyristors 2-4, a gate signal switchover circuit 5 for executing switchover between gate signals of the thyristors 2-4; and a reactor 7 for smoothing a welding current. The arc welding apparatus executes switchover between manual welding and CO2 welding by means of thyristors, thereby manufacturing the apparatus at low cost and achieving improved reliability.

Consumable electrode type AC pulse arc welding apparatus

Abstract: The consumable electrode type AC pulse arc welding apparatus is configured so that the pulse width setting circuit 16 includes the pulse width setting device 16a for hard wire, the pulse width setting device 16b for soft wire and the switch SW2 for switching the pulse width setting device. Further, the frequency setting device 20 includes the frequency setting device 20a for hard wire, the frequency setting device 20b for soft wire and the switch SW3 for switching the frequency setting device. By switching the switch SW1 when switching wire type, within the pulse width setting devices and the frequency setting devices, the selection between the hard wire side and the soft wire side can be simultaneously switched, thereby welding can be implemented with a suitable welding condition according to the wire type.

An electronic welder control circuit

Abstract: This paper presents a 6 kW electronic welder control circuit. The DC welding current is controlled with a simple and robust control circuit. Fast dynamic performance and low current ripple are achieved. Paralleled IGBTs are used with a switching frequency of 50 kHz. The welder machine with this control stage can be applied to shielded metal arc welding and gas tungsten arc welding processes. The welding DC voltage is also controlled with an outer controller acting in the current reference value. Fast dynamic is also obtained for the DC voltage control without steady state error. With this control level, gas metal arc welding and flux-cored arc welding can be applied. The current control and the DC voltage control can also be applied in different cycles depending on a external signal. In the peak and background current cycles. the current control and DC voltage control are applied, respectively, enabling the use of the electronic welder for pulsed gas metal arc welding. In the paper, the system modelling is also realised. Some modelling and experimental results are presented. The annoying problems caused by this type of equipment in low voltage networks are also shown.

Penetration in spot GTA welds during centrifugation

Abstract: Convective flow during arc welding processes mainly depends on electromagnetic force, Marangoni force, and buoyancy force. The Marangoni flow (caused by surface tension gradient,dγ/dT)and the buoyancy driven flow are the major factors in controlling weld penetration in austenitic stainless steels, such as types 304 and 316. Alloys 304 and 316 were subjected to a 7 s spot gas-tungsten arc (SGTA) welding at 1 g (g = 9.8 m/s2)and 5 g accelerations. The welds at 5 g were performed on Clarkson University’s multigravity research welding system (MGRWS). The cross sections of the fusion zones were polished/etched, and their depth (D)and width (W)were measured to ± 0.025 mm. It was determined that the depth/width ratio (D/W)of the welds decreased as the acceleration increased from 1 to 5 g. This result indicates that increase in buoyancy driven flow will produce wider but shallower welds during SGTA welding.

Hybrid welding apparatus

Abstract: A hybrid welding apparatus for subjecting a base metal to gas-shielded arc welding and laser welding comprises a laser generator for emitting a laser beam and a condenser optical system for condensing the laser beam to laser weld the base metal. The condenser optical system includes a plurality of lenses, each having a hole portion in the center thereof. A tubular supply holder for supplying a welding wire is passed through these respective hole portions of the lenses and located substantially coaxially with the axis of the condenser optical system. The laser beam and welding wire to be applied to the base metal are arranged coaxially, so that laser-welding and arc-shielded welding can be simultaneously performed with a wide angle between the welding head and a bevel of the base metal, thereby deepening penetration of the weld at an increased welding speed.