Showing papers on "Shielded metal arc welding published in 2005"

Effects of torch configuration and welding current on weld bead formation in high speed tandem pulsed gas metal arc welding of steel sheets

Abstract: Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13° , which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow ...

Effect of stainless steel manual metal arc welding fume on free radical production, DNA damage, and apoptosis induction.

Abstract: Questions exist concerning the potential carcinogenic effects after welding fume exposure. Welding processes that use stainless steel (SS) materials can produce fumes that may contain metals (e.g., Cr, Ni) known to be carcinogenic to humans. The objective was to determine the effect of in vitro and in vivo welding fume treatment on free radical generation, DNA damage, cytotoxicity and apoptosis induction, all factors possibly involved with the pathogenesis of lung cancer. SS welding fume was collected during manual metal arc welding (MMA). Elemental analysis indicated that the MMA-SS sample was highly soluble in water, and a majority (87%) of the soluble metal was Cr. Using electron spin resonance (ESR), the SS welding fume had the ability to produce the biologically reactive hydroxyl radical (•OH), likely as a result of the reduction of Cr(VI) to Cr(V). In vitro treatment with the MMA-SS sample caused a concentration-dependent increase in DNA damage and lung macrophage death. In addition, a time-dependent increase in the number of apoptotic cells in lung tissue was observed after in vivo treatment with the welding fume. In summary, a soluble MMA-SS welding fume was found to generate reactive oxygen species and cause DNA damage, lung macrophage cytotoxicity and in vivo lung cell apoptosis. These responses have been shown to be involved in various toxicological and carcinogenic processes. The effects observed appear to be related to the soluble component of the MMA-SS sample that is predominately Cr. A more comprehensive in vivo animal study is ongoing in the laboratory that is continuing these experiments to try to elucidate the potential mechanisms that may be involved with welding fume-induced lung disease.

Manganese Exposures During Shielded Metal Arc Welding (SMAW) in an Enclosed Space

Abstract: The work reported here evaluates the effectiveness of various rates of dilution ventilation in controlling welder exposures to manganese in shielded metal arc welding (SMAW) fume when working in enclosed or restricted spaces. Personal and area monitoring using total and respirable sampling techniques, along with multiple analytical techniques, was conducted during the welding operations. With 2000 cubic feet per minute (CFM) (56.63 m 3 /min) dilution ventilation, personal breathing zone concentrations for the welder using 1/8″ (3.18 mm) E6010 and E7018 mild steel electrodes were within 75% of the existing threshold limit value (TLV® of 0.2 mg/m 3 for total manganese and were five times greater than the 2001–2003 proposed respirable manganese TLV of 0.03 mg/m 3 . Manganese concentrations using high manganese content electrodes were five times greater than those for E6010 and E7018 electrodes. Area samples upstream and downstream of the welder using E6010 and E7018 electrodes exceeded 0.2 mg/m3 manganese. C...

Effects of Nb on the microstructure and corrosive property in the Alloy 690–SUS 304L weldment

Abstract: A study of the microstructure and corrosion of dissimilar weldments of Alloy 690 and SUS 304L with various additions of niobium (Nb) (0.1, 1.03, 2.49, and 3.35% by weight) in the flux of coated electrodes is presented. With identical welding parameters and procedures, the weldments were butt-welded in three layers by shielding metal arc welding (SMAW), with each layer being deposited in a single pass. The results show that the dendritic microstructure in the fusion zone changed from a cellular to columnar dendrite and equiaxed dendrite with increasing Nb addition. Furthermore, the interdendritic phase increased in volume and changed in composition from an Al–Ti oxide to a mixture of Nb–Si phase and Nb-rich phase. Nevertheless, it was clearly observed that Cr 7 C 3 precipitated at the grain boundaries of the low Nb weldment root pass. Finally, the results revealed that corrosion occurs primarily at the grain boundaries and within the interdendritic regions of the weldements irrespective of the level of Nb addition. For the region of abundant formation of Nb-rich phase, the high-Nb weldment had a relatively low corrosion resistance.

Occupational asthma due to manual metal-arc welding of special stainless steels

Abstract: Occupational asthma (OA) can be induced by fumes of manual metal-arc welding on stainless steel. In recent years, the use of special stainless steels (SSS) with high chromium content has increased. This study presents two cases of OA caused by manual metal-arc welding on SSS. In both cases, the diagnosis of OA was based on respiratory symptoms, occupational exposure and positive findings in the specific challenge tests. In the first case, a 46-yr-old welder had experienced severe dyspnoea while welding SSS (SMO steel), but not in other situations. Challenge tests with both mild steel and stainless steel using a common electrode were negative. Welding SSS with a special electrode caused a delayed 37% drop in forced expiratory volume in one second (FEV1). In the second case, a 34-yr-old male had started to experience dyspnoea during the past few years, while welding especially SSS (Duplex steel). The workplace peak expiratory flow monitoring was suggestive of OA. Challenge tests with both mild steel and stainless steel using a common electrode did not cause bronchial obstruction. Welding SSS with a special electrode caused a delayed 31% drop in FEV1. In conclusion, exposure to manual metal-arc welding fumes of special stainless steel should be considered as a new cause of occupational asthma.

Arc power and efficiency in gas tungsten arc welding of aluminium

Abstract: A calorimetric study of gas tungsten arc welding of aluminium is described. The present study comprised experiments in which autogenous welding runs were each made on a block of electrical conductor grade aluminium. The blocks were all approximately cubic in shape which, when combined with the high thermal conductivity of aluminium, ensured that their temperature equalised soon after the completion of a run. Each sample was immersed in insulating material before welding so that heat losses to the surroundings were minimised. Thermocouples were attached to the block in each experiment and the bulk temperature rise was related to the energy input associated with the welding run. The effects of arc polarity, alternating current balance, shielding gas composition, arc length and welding current on the arc power and arc efficiency were investigated. The results obtained with alternating current are compared to those for direct current, and the differences are explained.

Laser Hybrid Welding Method and Laser Hybrid Welding Torch Using a Zinc and/or Carbon and/or Aluminum-Containing Rod

Abstract: The invention relates to a method for welding coated sheet metal (3) by way of a laser hybrid welding method, whereby at least one laser method and one shielded arc-welding method are carried out, and a weld metal (12) is supplied to the weld by way of the shielded arc-welding method. The invention also relates to a laser hybrid welding torch for welding coated sheet metal (3), which comprises at least one laser (13) and at least one shielded arc unit (5) and a rod feeding device (11) for a welding rod (12). The aim of the invention is to provide a method or a device of the aforementioned kind which allows for reducing or completely avoiding inclusions such as are e.g. caused by the evaporation of the coating of the metal sheet (3). For this purpose, a clamping device (6) is used for positioning the coated metal sheet (3) without substantial gaps between the individual sheets. A material having a zinc and/or carbon and/or aluminum content is used as the weld metal or welding rod (12).

Pipe seam tack welding methods and apparatus using modified series arc welding

Abstract: Welders and methods are presented for short-circuit arc welding a workpiece using a modified series arc welding configuration with two electrodes via a sequence of welding cycles, in which each cycle includes an arc condition a short-circuit condition, wherein one or both electrode currents are selectively reversed during a reverse boost portion of the welding cycle to transfer molten metal from the second electrode to the first electrode prior to a short-circuit condition of a subsequent welding cycle.

Nitrogen desorption by high-nitrogen steel weld metal during CO2 laser welding

Abstract: Nitrogen desorption by high-nitrogen steels (HNSs) containing 0.32 and 0.53 pct nitrogen during CO2 laser welding in an Ar-N2 gas mixture was investigated and the obtained data were compared with those for arc welding and at the equilibrium state predicted by Sieverts’ Law. Although the nitrogen content in the weld metal during CO2 laser welding was lower than that in the as-received base material in all conditions, the nitrogen desorption was larger in the top part of the weld metal than in the keyhole region. The nitrogen desorption in the Ar atmosphere was less during CO2 laser welding than during arc welding. With the increase in nitrogen partial pressure, the nitrogen content in the weld metal sharply increased during arc welding, but only slightly increased during CO2 laser welding. The nitrogen absorption and desorption of the HNS weld metal were much smaller during CO2 laser welding than during arc welding.

Laser/arc hybrid welding process for ferritic steels

Abstract: A method and an apparatus for a hybrid laser beam and electric arc welding process. A laser beam, an electric arc, a shielding gas and a consumable welding wire are used to create a weld on a steel work piece by melting the welding wire. The weld contains 30 to 1000 ppm titanium by weight, at least 0.7% manganese by weight, 50 to 1000 ppm oxygen by weight, and less than 10% nickel. The welding wire is either solid welding wire or cored welding wire, and may contain, in varying percentages: titanium, manganese, iron, nickel, boron, molybdenum, carbon or chromium.

Composite welding method of laser beam and metal argon gas (mag) arc

Abstract: PROBLEM TO BE SOLVED: To provide a composite welding method of a laser beam and an MAG arc, which method is excellent in the gap resistance and can improve the welding quality even if the welding has been performed at a high speed. SOLUTION: In the composite welding method of the laser beam and the MAG arc, the laser beam welding and a consumable electrode type arc welding are used together. In this case, the laser beam and the arc are arranged on the same welding line, and the arc welding precedes and the laser beam welding follows. COPYRIGHT: (C)2006,JPO&NCIPI

Microstructures of gas metal arc weld metal of 950 MPa class steel

Abstract: The effects of shielding gas composition on the properties and microstructure of single pass weld metals produced by GMA (gas metal arc) groove welding of 950 MPa class steel plates have been investigated. The shielding gas employed was a mixture of argon (Ar) and carbon dioxide (CO2) (0–25%), and the weld heat input was ∼3 kJ mm. With increasing CO2 content, the hardness of the weld metal decreased from 380 HV to 280 HV, and the absorbed energy of the Charpy impact test decreased from 130 J to 90 J. The microstructures of the weld metal, consisting primarily of low carbon martensite and carbide free bainite, became more bainitic as the CO2 content of the shielding gas was increased. It was also found that the MA constituent, embrittling microstructure, was formed in the granular bainitic area, the volume fraction of which increased with the CO2 content of the shielding gas.

High-Speed Welding of Steel Sheets by the Tandem Pulsed Gas Metal Arc Welding System †

Abstract: In tandem gas metal arc (GMA) welding, it is important to prevent adverse effects caused by electromagnetic interference between the two adjacent arcs to create good metal transfer. In the tandem pulsed GMA welding system, newly developed by the authors, pulse peak currents are fed simultaneously to the leading and trailing electrodes in principle and a unique pulse timing control is employed in which the end of a pulse peak current for the trailing wire is delayed by 0.5 ms from that for the leading wire to prevent the arc extinguishing By using the tandem pulsed GMA welding system, the effects of the inter-wire distance, inclination angle and welding current (wire feed rate) ratio between the two wires have been investigated to study the essential requirements for the welding torch configuration and the allocation of welding currents to obtain sound weld beads with the absence of undercut and humping in the high speed welding of steel sheets. When the welding speed was 3 m/min, a sound weld bead with uniform width was obtained with the trailing wire set at 9-degree push angle regardless of the inclination angle of the leading wire. The inter-wire distance greatly affected the weld bead formation in high speed welding. That is, the maximum welding speed was improved with the proper inter-wire distance in the range 9 to 12 mm. In the proper range of welding current ratio, IT/IL=0.31 to 0.5, the maximum welding speed achieved was 4 to 4.5 m/min, which is 275% higher at the maximum when compared with single wire pulsed GMA welding (at a maximum welding speed of 1.2 m/min).

Welding of magnesium alloys with activating flux

Abstract: The effects of an activating flux on AZ31B alloy welding were investigated. Alternating current tungsten inert gas (ACTIG) welding was used to weld 5·0 mm thick AZ31B alloy plates with CdCl2, AlF3 and TiO2 activating flux. Applying the activating flux on the AZ31B alloy surface led to an increase in weld penetration depth. Various welding conditions, such as welding current, welding arc length, welding shielding gas flowrate, welding speed and flux thickness, influenced to different extents the ability of the activating flux to increase weld penetration. Furthermore, a high speed camera was used to monitor the arc images during welding. It was found that the brightest region of the arc was broader when CdCl2 and AlF3 were used, while the stability of the arc was increased when TiO2 was used, especially in the positive electrode period. In summary, it is important that a uniform flux layer is present at the alloy plate surface and suitable welding parameters are selected.

Chromium-free welding consumable

Abstract: A chromium-free welding consumable and a method of welding stainless steel to reduce the presence of chromium emissions. The consumable is made from an alloy that reduces the emission of chromium during a welding process, and include predominantly nickel, with between approximately five and twenty five percent by weight copper, up to approximately five percent by weight of palladium, up to approximately ten percent by weight of molybdenum and up to five percent non-copper alloying ingredients. Welding consumables made from the alloy are particularly well-suited for welding austenitic stainless steels, such as type 304 stainless steel. The method involves using chromium-free weld filler material with a stainless steel base material.

Numerical Simulation of the Welding Process — Distortion and Residual Stress Prediction, Heat Source Model Determination

Abstract: The paper presents the results of our recent developments. Studies for detailed understanding of the behaviour of a steel structure during welding operations have been carried out. Mainly the distortion of the steel structure has been observed. Several welding experiments have been prepared and carried out. The results from the welding experiments have been used as the input and output parameters during the numerical simulations. Measurements were also carried out on the material properties needed for numerical analysis. Numerical simulations have been made according to experiments. The calculated results were compared with the measured results. Based on the comparison parameters have been determined, which have an influence on the final distortion of the steel structure. The following input parameters have been observed: model of the temperature source, constraint condition, and material models. A good correlation has been obtained for temperature (mainly for shape and size of the molten zone) as well as distortion prediction between experimental and numerical approaches. The double ellipsoid heat source model has been used and modified to fit the measured parameters. The modified double ellipsoid heat source was used for MMAW and GTAW welding technology.

Investigations on Laser-TIG Hybrid Welding of Magnesium Alloys

Abstract: This paper presents results of recent investigations on the weldability of several wrought (AZ31, AZ61) and cast magnesium-based alloys (AZ91) by laser-TIG welding process. The investigations showed that magnesium alloys can be easily welded by laser-TIG welding. The grain of the fusion zone was finer than that of in base metal. The width of the heat-affected zone welded by laser-TIG welding process was obviously narrower than that of welded by TIG. Besides, with the Al content of magnesium alloys increasing, the width of the heat-affected zone (HAZ) was increased，as well as the content of β phase(Mg17Al12). The hardness in the fusion zone (FZ) and in HAZ of AZ61 and AZ91 has a large change to the base metal due to the existing of β phase, while no change relative for AZ31. It results from above discussing that laser-TIG welding is an excellent welding process for magnesium alloys.

Pulsed gas metal arc welding of Al-Cu-Li alloy

Abstract: An experimental Al–Cu–Li–Mg–Ag–Zr type alloy in the form of 13.7 mm thick plates was studied for its fusion characteristics using gas metal arc welding (GMAW) and pulsed gas metal arc welding (P-GMAW). High copper 2319 filler of 1.6 mm diameter was used. The burn-off characteristics of 2319 filler wire in GMAW and P-GMAW were experimentally determined, including the relation between pulse current and pulse duration for the desired one-drop detachment per pulse (ODPP) condition and feasible range of pulse parameters. The effect of welding parameters on bead geometry and shape relationships was investigated through beadon-plate experiments in the welding current range above the spray transition current. Reasonably good weld beads were obtained in P-GMAW at currents as low as 194 A and welding speeds of 45 cm min–1. P-GMAW yielded significantly higher weld penetration compared to GMAW.

Determination of GTA and GMA welding arc temperatures

Abstract: The welding arc has been successfully used in the welding industry for many years. However, not all physical phenomena assciated with it have, as yet, been fully understood and explained. Consequently, there arises a need to investigate the work of the arc during GTA and GMA processing. Models of the welding arc are being constructed with a view to gaining a better insight into the occurring phenomena1–5 including arc temperature since this is the parameter which influences all of the changes taking place.6 Investigations into the welding arc temperature lead to a better understanding of its working, The temperature of the welding arc varies from 5 000 to 30 000 K depending on the welding parameters and the type of shielding gas. After the introduction into the arc's plasma of easily ionized atoms of sodium or potassium, a maximum temperature of the order of 6 000 K can be reached.7

Cold Cracking in Weldments of Steel S 690 QT

Abstract: The cold cracking process in shielded metal arc and gas metal arc welding of steel S 690 QT is investigated by Tekken test. The conditions for cold cracking are varied by changing the specimens’ thickness, heat input, initial weld metal hydrogen concentration and preheating temperature. The kinetics of initiation and propagation of cracking is monitored by acoustic emission equipment. It is found out that the crack’s propagation path shifts from weld metal to fusion line and HAZ with decreasing initial weld metal hydrogen concentration and increasing hardness of HAZ. In the investigated range of cold cracking conditions the magnitude of cracking is mainly controlled by the preheating temperature and heat input. The acoustic emission signal provides valuable information about the factors controlling the kinetics of crack initiation and propagation and the intensity of cold cracking. The initial hydrogen concentration in weld metal controls the incubation period’s duration and affects the cracking intensity at higher heat inputs. The preheating temperature does not influence the incubation period, but significantly affects the kinetics of crack propagation. The heat input has a complex influence on the cracking kinetics and intensity. This is related to the contradictive effects of heat input on the initial hydrogen concentration per unit length of weld metal and on the behaviour of hydrogen during cooling. The obtained results provide a basis for combined experimental — modelling investigations on the cold cracking phenomenon in weldments of higher strength structural steels, aiming at quantitative evaluation of the influence of the main controlling factors.

Influence of procedure variables on C-Mn-Ni-Mo metal cored wire ferritic all-weld metal

Abstract: Different shielding gases, welding position, number of weld passes, and arc energy were all studied to assess their influence on the all-weld-metal properties of a metal cored filler metal.

Plasma ARC weld repair of IN100 material

Abstract: A method for weld repairing airfoils made from nickel based super alloy material is provided. The method includes removing a damaged portion of the airfoil by machining the airfoil to a relatively smooth surface. Powdered alloy material, such as IN-100 material is then fed to a plasma arc welding device. A plurality of weld beads are deposited along the damaged portion of the airfoil in a continuous bi-directional pattern by the welding device to eliminate abrupt thermal transients at the ends of the weld, thereby reducing the thermal stresses that cause cracking in susceptible alloys such as IN-100.

Online Infrared Detection of Inclusions and Lack of Penetration during Welding

Abstract: Thermographic imaging using infrared sensors has been a natural choice for sensing and weld process monitoring. The basis for using infrared imaging lies in the fact that an ideal welding condition would produce surface temperature distributions that show a regular and repeatable pattern. Any variation or perturbation would result in discernible change in the thermal profiles. This paper focuses on the application of infrared imaging for online detection of lack of penetration and tungsten inclusions formed during manual metal arc welding. Both lack of penetration and tungsten inclusions could be distinctly detected with good confidence levels. Wavelet transform based image processing tools could be successfully applied for the extraction of the required features and determination of the dimensions of the discontinuities from the thermal images and radiographs. These studies form the basis for online discontinuity detection and control.