Showing papers on "Shielded metal arc welding published in 2000"

Investigation into arc constriction by active fluxes for tungsten inert gas welding

Abstract: Mechanisms by which active fluxes increase the penetration of conventional tungsten inert gas (TIG) welds (so called A-TIG welds) are reviewed. The most dominant mechanism for increased penetration is considered to be arc constriction rather than a change in the surface tension of the molten pool. An experimental programme of work was carried out using A-TIG flux in combination with a number of welding processes. The plasma process was investigated as it gives greater penetration than conventional TIG welding by increasing current density. The CO2 laser and electron beam processes which do not rely on a current carrying arc as the heat source for welding were also investigated. Macrosections taken from the welds made by these processes showed that the A-TIG flux was only effective when the weld pool was produced by an arc or plasma. Where there was no arc or plasma present, the flux had little effect.

Effects of activating flux on arc phenomena in gas tungsten arc welding

Abstract: Dramatic increases in the depth of weld bead penetration have been demonstrated by welding stainless steel using the gas tungsten arc (GTA) process with activating fluxes consisting of oxides and halides. However, there is no commonly agreed mechanism for the effect of flux on the process. In order to clarify the mechanism, behaviour of the arc and weld pool in the GTA process with activating flux was observed in comparison with a conventional GTA process. A constricted anode root was found in the GTA process with activating flux, while a diffuse anode root was found in the conventional process. Furthermore, it is suggested that these anode roots are strongly related to metal vapour from the weld pool, which is also related to temperature distributions on the weld pool surface.

Acute respiratory effects of exposure to stainless steel and mild steel welding fumes.

Abstract: Over the past few years, many studies, including one on our previous work, have examined the chronic effects of fumes from stainless steel (SS) welding on the health of welders. These chronic effects have been related to concentrations of chromium and nickel in SS welding fumes. The present study examined the acute respiratory effects of welding fumes in the workplace by measuring the across-shift changes in a population of 144 SS and mild steel (MS) welders and 223 controls. Manual Metal Arc, Metal Inert Gas, and Tungsten Inert Gas welding processes were studied. Pulmonary function tests were performed at the start (ante, or A) and at the end (post, or P) of the work shift. The study of sensitization to harmful respiratory effects of welding was based on the study of the (P-A)/A ratio (%) of the spirometric variations during the shift. The means of these ratios in the control subjects were used to account for the circadian effect. In SS welders we observed a significant decrease in forced vital capacity (FVC) during the shift. Significant across-shift decrements in forced expiratory volume in 1 second (FEV1) and FVC were related to the SS welding exposure compared with MS welding. Moreover, the across-shift decreases in FEV1, FVC, and peak expiratory flow (PEF) were significantly related to the Manual Metal Arc welding process, compared with Metal Inert Gas techniques (respectively, PEF = -2.7% of baseline values [SD, 11.9] vs 2.0% of baseline values [SD, 7.7] P = 0.04; FVC = -1.5% of baseline values [SD, 4.8] vs 0.2% of baseline values [SD, 4.5] P = 0.05). We also demonstrated the influence of duration of SS welding exposure on the course of lung function during the work shift. After 20 years of SS welding activity, SS welders had more significant across-shift decreases than MS welders with a similar MS exposure duration (respectively, FEV1 = -2.7% of baseline values [SD, 5.9] vs 0.7% of baseline values [SD, 4.2] P = 0.008; PEF = -3.8% of baseline values [SD, 9.6] vs 2.3% of baseline values [SD, 6.5] P = 0.04). We concluded that welding-related lung function responses are seen in SS compared with MS welders and in those with a longer lifetime welding history.

Welding of ship structural steel A36 using a Nd:YAG laser and gas–metal arc welding

Abstract: Laser welding has the potential of offering both technical and economical advantages in many applications in the shipbuilding industry. A limiting factor is currently the power level available with commercial lasers, since steel plates of more than 5 mm in thickness are used in almost every shipbuilding application. In addition, the high hardness of the welds produced using laser welding is a disadvantage compared with the requirements of existing classification society standards. It has been reported that by using a hybrid welding method in which a laser beam and a gas–metal arc weld (GMAW) arc are combined it is possible to weld thicker sections, because the penetration is increased. Hardness values are correspondingly lower than those using the laser process because of the increased energy input. Results of a study of hybrid high power Nd:YAG laser and GMA welding are reported. All plates were welded in a butt joint configuration. When laser and GMAW were combined into a single process, I grooves were used. The air gaps between the welded plates varied. Some tests were made using a partially grooved V joint. In these cases, the root faces were welded by a Nd:YAG laser, and the upper part of the joint was welded by GMAW. It was seen that it is possible to produce defect-free welds using these processes. Macrosections of the welds, hardness values and parameters are presented and discussed.

A quality and cost approach for welding process selection

Abstract: The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.

Welding method and welded joint structure

Abstract: The invention provides a welding system capable of freely controlling the dispersion and concentration of arc heat over the groove face with an extreamly narrow gap and a high strength and high quality welded joint structure which is formed by this welding system and which is capable of preventing softening/hardening of the structure, the lowering of the toughness thereof and the generation of a crack. According to the welding system, the melting rate of a welding wire is controlled relative to the welding wire feeding rate by changing the characteristic of an arc current so that the range of behavior and the transfer rate of the arc pole (the arc generating main point at a groove surface) are controlled. Further, the welded joint structure consists of a high strength steel having a superfine grain structure with a carbon equivalent of as low as less than 0.38 and a crystal grain size of less than 7 μm and is welded by a consumable electrode type arc welding method so as to control the arc heat distribution on the groove face of the joint.

Nitrogen Absorption by Iron and Stainless Steels during YAG Laser Welding

Abstract: The nitrogen absorption by iron, Fe-20Cr-10Ni and SUS329J1 stainless steel YAG laser welding in the atmosphere of Ar-N2 mixture gas was investigated in comparison with those during arc welding using the same materials as in this experiment and equilibrium data. Although the nitrogen contents of YAG laser weld metal increase with the nitrogen partial pressure were as well as those of arc weld metal of arc welding, the nitrogen content during YAG laser welding were quite less than those during arc welding. Blowholes can not be observed in Fe-20Cr-10Ni and SUS329J1 stainless steel and can only be found in iron at lower nitrogen partial pressure during YAG laser welding. A discussion on the difference in nitrogen absorption between YAG Laser and arc welding has suggested that small amount of nitrogen absorption results from less opportunity of nitrogen to touch the surface of molten metal due to the active evaporation of metal which covers the major surface of molten metal during laser welding metal. Additionally, the short-time thermal cycle compared with arc welding may bring insufficient nitrogen absorption in the weld metal during cooling. It can be considered that the nitrogen absorption during YAG laser welding is basically different from that during arc welding.

Experimental investigation of gas tungsten arc welding and comparison with theoretical predictions

Abstract: An experimental investigation in gas tungsten arc welding with the hydrogen addition to argon was made. The hydrogen addition to argon makes the arc constrict and the energy concentrate in the arc, which produces increase in arc power. Experimental welding was carried out on three base metals, i.e., low-alloy steel, high-alloy stainless steel, and an aluminum alloy, using no filler material and in argon with the addition of 0.5-20% hydrogen. In welding of stainless steel with the addition of 20% hydrogen to argon, the quantity of the base metal melted increases by three to five times, with the other parameters remaining the same, in welding of low-alloy steel by three times, and in welding of aluminum by six to nine times. The experimentally obtained results were compared with the theoretical ones. With both steels, the experimental and theoretical results agreed well, but with aluminum, they differed very much.

Flux-containing wire for gas shield arc welding

Abstract: PROBLEM TO BE SOLVED: To provide a flux-containing wire for gas shield arc welding capable of obtained weld metal having good welding operability and excellent low temperature toughness even in the case gaseous CO2 is particularly used as shield gas in a CaF2 series flux-containing wire. SOLUTION: In this flux-containing wire for gas shield arc welding, the inside of the outer surface made of steel is filled with flux containing CaF2 of 1.0 to 5.0%, one or two kinds of the multiple oxide of alkali metal and/or alkaline-earth metal and Ti and the multiple oxide of alkali metal and/or alkaline-earth metal, Ti and Si (hereinafter referred generically as alkali TiO2 multiple oxide) of 0.3 to 3.5% and TiO2 of 0.5 to 3.0% (inclusive of the value expressed in terms of TiO2 of Ti in the alkali TiO2 multiple oxide), to the total weight of the wire, and, in the flux-containing wire, CaF2/ alkali TiO2 multiple oxide=1.0 to 5.0, and CaF2/TiO2=1.0 to 5.0 are satisfied, moreover, the total content of hydrogen in the wire is 90 ppm or less, and furthermore, carbonate is contained in 2% or less.

Solidification behavior of Al-Mg aluminum alloy using double-sided arc welding process

Abstract: As popular aluminum alloys, the 5xxx Al-Mg series, such as 5050 and 5052, etc., are widely used in applications such as automobile, pressure vessels, armor plate, and components for marine and cryogenic service. In this, as in all non-heat-treatable aluminum alloys, the weld metal zone is considered to be the weakest part of the joint and is the location of failure when the joint is loaded in tension during welding [1]. Solidification behavior of the weld pool, which controls the microstructure of the weld metal zone, plays a critical role in determining the ultimate strength of the joint.

Shielding gas mixture for gas-metal arc welding

Abstract: A shielding gas mixture for gas-metal arc welding of austenitic stainless steel is provided in which the gas mixture comprises from about 2 to about 5% carbon dioxide, from about 1 to about 4% nitrogen, and the balance being argon. Also, a process for welding austenitic stainless steel is provided by forming an electric arc between a nonconsumable electrode and the workpiece and in which the gas mixture is used.

Gas shielded-system arc welding method

Abstract: PROBLEM TO BE SOLVED: To improve properties such as wear resistance, corrosion resistance, etc., by making small the dilution of overlaying metal by a base metal 3. SOLUTION: When performing overlaying by gas shielded-system arc welding using an electrode wire 1, by emitting a laser beam 7 to the rearward of molten metal 5 and by introducing an arc 4 backward, the zone overlaying is made by penetration by the only heat of the molten metal 5, the dilution of the overlaying metal by the base metal 3 is made small, and the properties such as the wear resistance, the corrosion resistance, etc., are improved.

Numerical modelling of temperature distribution during multipass welding of plates

Abstract: Welding is a reliable, cost effective, and efficient metal joining process. Manual metal arc welding (MMAW) is a widely used welding process in industry and multipass welding is very frequently use...

Torch for consumable electrode type gas shielded metal arc welding

Abstract: PROBLEM TO BE SOLVED: To provide a torch for the consumable electrode type gas shielded metal arc welding which is fitted to a wrist part of an industrial robot SOLUTION: In this torch for the consumable electrode type gas shielded metal arc welding in which a wire passing hole is formed in a center part in the axial direction of the welding torch, and a wire is brought into contact with a power supply chip to supply the power to the wire, a conventional power supply chip 14 is split into an outer chip 19 or 23 and an inner chip 24 or 37 and a chip case 25 in an attachable/detachable manner, a compression spring 27 having the wire passing hole in the center in the axial direction and the inner chip 24 or 37 are disposed inside the outer chip 19 or 23 and the chip case 25, and the compression spring 27 presses the inner chip 24 or 37 to allow the inner chip 24 or 37 to be inscribed with the outer chip 19 or 23

Laser lap welding method for steel sheet

Abstract: PROBLEM TO BE SOLVED: To provide a laser lap welding method for steel sheet members including cold rolled and galvanized steel sheets, a method in which an inter-sheet gap tolerance incident to superior welding can be expanded in comparison with conventional laser lap welding. SOLUTION: In the laser lap welding method for members consisting of steel sheets, laser welding 4 as well as arc welding 8 which is aimed at the rearside 10 of a laser machining point 9 are performed, and also, the current/ voltage range of the arc welding 8 is defined as a short circuiting transfer area. Molten metal is supplied to the laser machining point 9 through the arc welding 8, to fill a gap formed between steel sheets 1, 2. By using both the laser welding 4 and the arc welding 8, high speed welding is performed by using the arc welding 8 as a short arc. In addition, as a result of using the arc welding 8 as a short arc, a thin part on a steel sheet surface which is due to excessive widening of arc is no longer produced, and an excellent weld zone without spatters is produced.

Reproducibility of pop-ins in laboratory testing of welded joints

Abstract: The pop-in phenomenon, quite common in fracture mechanics tests of welded joints, corresponds to a brittle crack initiation grown from a local brittle zone (LBZ) that is arrested in reaching the higher toughness material that surrounds this LBZ. A methodology to obtain a high percentage of pop-in occurrence in laboratory testing is necessary to study the pop-in significance. Such a method is introduced in this work and includes the consumable combination and welding procedures for the SMAW welding process to generate artificial LBZ. In order to find out the influence of the loading state upon the pop-in phenomenon, laboratory CTOD tests were performed using two specimen configurations: some single edge-notched specimens were loaded on a three-point bending (SE(B)) fixture while others were tested in tensile load (SE(T)). A higher frequency of pop-in occurrence was observed in the SE(B) geometry.

Weld Repair of Aged Cr-Mo Steel Piping—A Review of Literature

Abstract: Power plant piping operating at elevated temperatures is subject to several types of service aging-related degradation, such as softening, spheroidization, embrittlement, and creep. When cracks are found in these components, weld repair is often employed to ensure continued operation. The efficacy of the weld repairs in terms of extending the life of the aged components has, however, not been documented quantitatively. The Electric Power Research Institute (EPRI) has recently undertaken a comprehensive study to evaluate weld repairs performed to aged piping. In connection with this study, results from other worldwide activities have been reviewed, leading to significant conclusions regarding weld repair. This review of results from several worldwide studies has confirmed that aged high-temperature piping can be successfully weld repaired to gain additional lives in excess of several decades. The key aspects of successful weld repair include excavation and removal of all prior creep cavitation damage, elimination of external bending stresses, and implementation of good welding practice. From merely a creep rupture point of view, postweld heat treatment (PWHT) has been concluded to be superfluous by several authors. Temperbead repairs appear to offer a promising alternative to PWHT repairs from a creep, tensile, and toughness standpoint. Choice of the repair process ultimately is dictated by many considerations such as toughness, notch sensitivity, residual stresses and hydrogen embrittlement susceptibility. Several reports suggest that gas tungsten arc welding (GTAW) repairs may outperform shielded metal arc welding (SMAW) repairs with or without PWHT.

Al-Mg-Si系合金レーザ溶接部における凝固割れ防止に関する検討

Abstract: Al-Mg-Si alloys are widely used for industrial components because of those excellent extrudability, high corrosion resistance, and relatively high strength within the various aluminium alloys. However, welds of Al-Mg-Si alloys are known to have high crack susceptibility and to be softened due to weld heat input.Laser welding process has significant advantages in terms of low heat input, low distortion, high welding speed, and ease to automation compared with the conventional welding process. In particular, there is considerable interest in welding heat treated alloy, such as Al-Mg-Si alloy, since low heat input makes softened region of welds minimize.This paper describes the results of welding efforts of Al-Mg-Si alloys, mainly A6063-T5 with 5 kW CO2 laser. Wel-dabilities, solidification crack susceptibilities were studied in bead-on plate tests. Solidification crack susceptibilities were estimated by using a crater cracking test and a self-restraint cracking test, a modified form of Houldcroft test. After that, welding with filler materials were performed in order to prevent the solidification cracking in weld metal. Microstructure, alloying element distributions, and mechanical properties were studied. Effects of groove geometry and Si contents of weld metals on properties have been established. Solidification cracking in weld metal has been prevented by using high Si content Al-Si alloy, such as A4047, and getting Si content of all the weld metal more than 2%.

Method of welding overlapped plates plated with zinc or zinc-based metal and the welded plates

Abstract: PROBLEM TO BE SOLVED: To provide a method for preventing as many blowholes as possible even when the gap is zero between overlapped steel plates plated with zinc or zinc-based metal and to obtain favorable beads by using both laser and arc in welding overlapped steel plates plated with zinc or zinc-based metal. SOLUTION: The welding method comprises a first manufacturing step to weld a specified part by YAG laser and a second step to weld by gas metal arc. In the second step, the width of the bead made by the gas metal arc is not more than 2.0 times that made by the YAG laser.

Method of composite welding by laser arc and welding equipment

Abstract: PROBLEM TO BE SOLVED: To provide a method of a composite welding by a laser and arc where the laser and the arc are used jointly with which method an arc is stable even when the welding is carried out at high speed, a welding bead having an excellent form is available and the efficiency of the welding work is remarkably improved, and to provide a composite welding equipment using the laser and arc. SOLUTION: The front and the rear sides of an arc electrode 5 with respect to the advancing direction of a welding work are irradiated with a guide beam B1 and a following beam B2, respectively.

Welding method of an Si-based material

Abstract: The heat of arc plasma generated in arc welding is used to provide a welding method for a Si-based material. The method of the present invention is capable of welding a Si-based material, which is difficult to weld by conventional methods due to its brittle nature and high electric resistance. In an argon gas atmosphere, a tungsten electrode is used as a cathode. A water cooling copper sheet and plate is used as an anode. An arc is generated between this pair of electrodes. The arc length is gradually extended, and a pair of Si-based materials are near an arc column. Fusion welding of a weld zone is carried out while rotating the Si-based materials around an axis.

A welding electrode, a welded article, and a steel weldable with the welding electrode

Abstract: The invention concerns a welding electrode consisting of a core and a coating. The core wire consists of an austenitic stainless steel, which contains in weight %: 0.001-0.03 C, 0.01-0.3 Si, 0.5-2.5 Mn, 19-21 Cr, 9-12 Ni, 0.01-0.2 N. The coating contains in weight %: 6-10 CaCO3, 2-5 F, 10-30 SiO2, 4-10 Al2O3, 25-35 TiO2, 7-12 Fe, max 5 CrN, max 5 Ni, max 10 Cr, max 5 Mn, balance essentially only sodium- and potassium compounds existing as components and natural minerals; binding agents; and unavoidable impurities. The invention also relates to a welded article of an austenitic stainless steel, a new austenitic stainless steel and a welding wire made of such steel.

Microstructure and Toughness of 950 MPa High Strength Weld Metals.

Abstract: The effects of both microstructure and oxygen content on the toughness of weld metals of a 950 MPa high strength steel have been investigated. The weld metals were prepared by SMAW (shielded metal arc welding), SAW (submerged arc welding), GMAW (gas metal arc welding) and GTAW (gas tungsten arc welding) processes. The microstructures of the weld metals were characterized with optical microscopy, SEM (scanning electron microscopy) and TEM (transmission electron microscopy) as well as continuous cooling transformation (CCT) diagram. The oxygen content was measured with a non-dispersive infrared absorption analyzer.The microstructures of all weld metals in as-welded state prepared by SMAW, SAW, GMAW and GTAW processes were martensitic structures, although slight differences in their morphologies were observed. The microstructures of the reheated weld metals in multi-pass weldment depended on both reheating temperatures TP and welding process. When TP≥Ac3, the reheated microstructures of SAW and GMAW weld metals consisted of fine martensitic structures, while that of SMAW was martensite with coarsened laths. The microstructure of the reheated weld metal of GTAW was lath martensite with a large amount of carbide precipitates. When TP≥Ac3, especially when Tp-Ac1, a large amount of precipitation were observed in the reheated weld metals of SAW, GMAW and GTAW, while the precipitation in that of SMAW was only slight. The toughness of the weld metals was closely related to their microstructures and oxygen contents. In particular, superior toughness could be associated with the formation of fine martensitic structures. Furthermore, the toughness of the weld metal was increased with the decrease in oxygen content, when the microstructure consisted primarily of martensite.