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Showing papers on "Shielding gas published in 1999"


Journal ArticleDOI
TL;DR: In this paper, the effect of welding process shielding gas and the addition of grain refining elements on the weld zone tensile properties of a ferritic stainless steel conforming to AISI 430 has been investigated.

102 citations


Patent
14 Jul 1999
TL;DR: An arc welding torch for robotic applications having sensing capabilities to provide intelligent diagnostics monitoring of the welding process in real time is described in this article, where a plurality of modular sensors are integrated with the torch to provide real-time monitoring of wire speed, arc voltage, gas flow, seam-tracking, welding current temperature and contact tip wear.
Abstract: An arc welding torch for robotic applications having sensing capabilities to provide intelligent diagnostics monitoring of the welding process in real time. A plurality of modular sensors are integrated with the torch to provide real-time monitoring of wire speed, arc voltage, gas flow, seam-tracking, welding current temperature and contact tip wear. The torch includes a contact tip wear sensor for sensing the wearing of the tip during the welding process. The shielding gas flow is measured by a gas flow sensor mounted between the main housing and the gooseneck. A seam-tracking sensor is mounted on the outside of the housing to detect the position of the seam to be welded. The speed of the consumable electrode is measured by a wire speed sensor module. To ensure that operating temperatures of components near the arc region are within predetermined ranges for optimum performance of the torch, temperature sensors are mounted on the torch. An arc voltage sensor is located in the housing of the torch to provide a more accurate measurement of the arc voltage near the arc region. Lastly, a current sensor is located between the main housing and the gooseneck to measure the current flow through the torch. All of the above sensors may be operatively connected to a weld controller which analyze the information received from each sensor to maintain an optimum welding process.

99 citations


Journal ArticleDOI
TL;DR: In this article, a 3.0 kW CO 2 laser system was used to weld carbon and stainless steel using wire feed and a straight thin tube nozzle, attached to the laser beam nozzle, was used for delivering the wire to the weld zone.

83 citations


Journal Article
TL;DR: In this paper, a method for detecting flaws in automatic, constant-voltage gas metal arc welding using the process current and voltage signals was developed, and seven algorithms were used to give quality parameters and flags welds that are different from a baseline.
Abstract: A method for detecting flaws in automatic, constant-voltage gas metal arc welding using the process current and voltage signals was developed. Seven algorithms process the current and voltage signals to give quality parameters. A defect-detection algorithm processes the quality parameters and flags welds that are different from a baseline. The baseline is constructed from the recorded quality parameters of previously made, defect-free welds. Two series of tests were conducted to test the sensitivity of the algorithms for defects and to test the entire sensor system in production. In the first series, on a 3-mm lap joint, the algorithms detected a lack of shielding gas, oily parts and melt-through from inadequate part cross section, but could not detect off-joint welding. The algorithms showed a mixed sensitivity to melt-through from large root openings. In production tests, 520 welds were monitored. The defect detection algorithm was tuned on data from the first 82 welds. The sensot flagged five of the six defects monitored and did not flag any defect-free welds The defect not detected was a small pore, < 3 mm diameter.

67 citations


Journal ArticleDOI
TL;DR: In this paper, a two-dimensional dynamic theory for predictions of arc and electrode properties in arc welding has been used to investigate heat transfer phenomena in the welding wire in gas metal arc welding (GMAW).
Abstract: A two–dimensional dynamic theory for predictions of arc and electrode properties in arc welding has been used to investigate heat transfer phenomena in the welding wire in gas metal arc welding (GMAW). The theory is a unified treatment of the welding wire, the plasma and the workpiece and includes a free surface treatment for the welding drops, accounting for the effects of inertia, gravity, surface tension, arc pressure, magnetic forces, and viscous drag by the gas flow around the drop. Also, the theory accounts for the variation of the surface tension coefficient with temperature and includes thermal and dynamic phenomena within the solid and liquid phases of the wire, together with a detailed treatment for the electrode sheath regions. Calculations are made for arcs in argon with wires of mild steel at currents between 150 and 325 A. Results of calculations for heat fluxes within the wire suggest that evaporation from the surface of the droplet during droplet growth has an important influence on the he...

58 citations


Journal Article
TL;DR: In this article, the results from a series of experiments in which dissimilar metals welds were made using the gas tungsten arc welding process with pure argon or argon-6% hydrogen shielding gas.
Abstract: Presented here are the results from a series of experiments in which dissimilar metals welds were made using the gas tungsten arc welding process with pure argon or argon-6% hydrogen shielding gas. The objective was to determine if cracking near the fusion boundary of dissimilar metal welds could be caused by hydrogen absorbed during welding and to characterize the microstructures in which cracking occurred. Welds consisted of ER308 and ER309LSi austenitic stainless steel and ERNiCr-3-nickel-based filler metals deposited on A36 steel base metal. Cracking was observed in welds made with all three filler metals. A ferrofluid color metallography technique revealed that cracking was confined to regions in the weld metal containing martensite. Microhardness indentations indicated that martensitic regions in which cracking occurred had hardness values from 400 to 550 HV. Cracks did not extend into bulk weld metal with hardness less than 350 HV. Martensite formed near the fusion boundary in all three filler metals due to regions of locally increased base metal dilution.

56 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of nitrogen in shielding gas on the corrosion resistance of welds of a duplex stainless steel (grade U-50), obtained by gas tungsten arc (GTA) with filler wire, autogenous GTA (bead-on-plate), electron beam welding (EBW), and microplasma techniques, has been evaluated in chloride solutions at 30 °C.
Abstract: The influence of nitrogen in shielding gas on the corrosion resistance of welds of a duplex stainless steel (grade U-50), obtained by gas tungsten arc (GTA) with filler wire, autogenous GTA (bead-on-plate), electron beam welding (EBW), and microplasma techniques, has been evaluated in chloride solutions at 30 °C. Pitting attack has been observed in GTA, electron beam welding, and microplasma welds when welding has been carried out using pure argon as the shielding gas. Gas tungsten arc welding with 5 to 10% nitrogen and 90 to 95% argon, as the shielding gas, has been found to result in an improved pitting corrosion resistance of the weldments of this steel. However, the resistance to pitting of autogenous welds (bead-on-plate) obtained in pure argon as the shielding gas has been observed to remain unaffected. Microscopic examination, electron probe microanalysis (EPMA), and x-ray diffraction studies have revealed that the presence of nitrogen in the shielding gas in the GTA welds not only modifies the microstructure and the austenite to ferrite ratio but also results in a nearly uniform distribution of the various alloying elements, for example, chromium, nickel, and molybdenum among the constitutent phases, which are responsible for improved resistance to pitting corrosion.

55 citations


Journal ArticleDOI
TL;DR: In this article, feasibility in using magnetic effect as a control tool is explored in high power CO 2 laser beam welding, and the influences of the magnetic field strength, laser power, welding speed, field direction and shielding gas (e.g., helium and argon) on the penetration depth and the width of bead were also investigated.
Abstract: During high power CO 2 laser beam welding, the plasma above the keyhole has a shielding effect that it not only absorbs part of the laser energy but also defocuses the laser beam. As a result, the welding efficiency and the aspect ratio of the welds are influenced. In order to reduce the effect of plasma, helium as a plasma control gas has been used successfully and effectively. However, the cost of helium in Southeast Asia is extremely high and therefore the production cost is significantly increased when helium is used as a continuous bleeding plasma control gas. To search for an alternative plasma control technique, feasibility in using magnetic effect as a control tool is explored in this paper. The influences of the magnetic field strength, laser power, welding speed, field direction and shielding gas (e.g. helium and argon) on the penetration depth and the width of bead were also investigated. Experimental results indicated that the magnetic field can influence the shielding effect of the plasma without using plasma control gas. It was found that at a suitable magnetic field strength the penetration depth was increased by about 7%, but no significant difference on the width of bead was found. Moreover, it was shown that the plasma control effect can be achieved at low magnetic field strength and the penetration depth can be increased significantly under argon atmosphere.

51 citations


01 Jan 1999
TL;DR: In this article, the amount of oxygen and the percentage of acicular ferrite of metal weld deposits were analyzed and the impact toughness of it on different methods of arc welding processes, such as welding with coated electrodes (basic, rutile, acid, oxide electrodes), shielded arc welding process MIG/MAG, submerged arc welding (various wires, fluxes, shielded gases).
Abstract: In analogy to the classification of metal weld deposits and arc welding processes of low-carbon and low-alloy steel in terms of the amount of hydrogen in metal weld deposits, a similar classification was given in terms of the amount of oxygen. Different methods of arc welding processes were chosen, such as welding with coated electrodes (basic, rutile, acid, oxide electrodes), shielded arc welding process MIG/MAG, submerged arc welding process (various wires, fluxes, shielded gases). The amount of oxygen and the percentage of acicular ferrite of metal weld deposits were mainly analysed and the impact toughness of it. Metallographical structures and fractography tests of metal weld deposit with varied amount of acicular ferrite were presented by putting attention to non-metallic inclusions and their morphology presented in metal weld deposit. Additional inclusions observation and measurements were done using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The studies were also made on the classification of metal weld deposits and arc welding processes of low carbon and low alloy steel in terms of the amount of oxygen in metal weld deposits on the following processes: low-oxygen processes, medium-oxygen processes, high-oxygen processes.

47 citations


Journal ArticleDOI
TL;DR: In this article, the TIG pulse welding parameters of 304L stainless steel sheet of 3mm thickness in flat, vertical and overhead positions were investigated, and the weld bead aspect ratios (W / D ) were 2.7-2.8.

43 citations


01 Jan 1999
TL;DR: In this article, an improved fume chamber was constructed, and fume rates were measured with unprecedented precision for both steady and pulsed-current weld- ing of mild steel using 92% argon/8% CO 2 shielding gas.
Abstract: An improved fume chamber was constructed, and fume rates were measured with unprecedented precision for both steady- and pulsed-current weld- ing of mild steel using 92% argon/8% CO 2 shielding gas. Comprehensive fume maps were constructed depicting fume rates over a wide range of currents and voltages. Fume generation was generally lower under pulsed-current conditions. Theoretical arguments explaining this difference are presented. Accurate fume-generation data and a comprehensive fume formation model are necessary for more sophisticated fume control strategies. This paper in- cludes precise fume generation data for GMAW of mild steel using one shielding gas under steady- and pulsed-current conditions. A physical model introduced by Gray, Hewitt and Dare (Ref. 4) is em- ployed and amplified to explain our ob- servations. Although fume formation has been studied by many scientists, results are dif- ficult to reconcile from one researcher to another. Limited accuracy of some results is one problem, but interpretation and correlation are complicated because of the multitude of variables involved. Many types of welding exist with and without fluxes using a wide range of pos- sible shielding gases. Numerous different electrode and work materials or combi- nations are possible. Much of the prior work has been directed toward the solu- tion of immediate problems in the work- place. Often, fume generation studies in- volve so many variables results are almost impossible to use for theoretical purposes. Our research was designed to produce precise results for narrow con- ditions. Although limited to GMAW of mild steel with a single shielding gas, our fume typography is typical of profiles one should expect with other electrodes and shielding gases. It is hoped that similar re- sults for such systems will become avail- able in the future. Castner (Ref. 3) has provided what may be the most comprehensive study of a single system using the standard AWS fume chamber. Although a comparison of steady- and pulsed-current fume rates

Journal ArticleDOI
TL;DR: In this paper, the effects of shielding gas types on CO 2 laser weldability of low carbon automotive galvanized steel were investigated. And the welding penetration, strength and formability of laser welds were found to be strongly dependent upon the types of shielding gases used.
Abstract: This study deals with the effects of shielding gas types on CO 2 laser weldability of low carbon automotive galvanized steel. The types of shielding gas evaluated are helium, carbon dioxide, argon, nitrogen and 50% argon+50% nitrogen. The weld penetration, strength and formability (Erichsen test) of laser welds are found to be strongly dependent upon the types of shielding gas used. Further, the maximum travel speed and flow rate to form a keyhole weld are also dependent upon types of shielding gas. The ability of shielding gas in removing plasma plume, and thus increasing weld penetration, is believed to be closely related to ionization/dissociation potentials, which determine the period of plasma formation and disappearance. Further, thermal conductivity and reactivity of the gas with the molten pool also have a strong effect on penetration and porosity formation which in turn affect formability and strength.

Journal ArticleDOI
TL;DR: In this paper, a model of the depth of penetration in gas metal arc welding is presented based on the assumption that the heat and mass transfer to the weld pool and the depth-of-penetration may be correlated by a dimensionless relation.
Abstract: A model is presented of the depth of penetration in gas metal arc welding. This model is based on the assumption that the heat and mass transfer to the weld pool and the depth of penetration may be correlated by a dimensionless relation. This correlation leads to an analytical expression for depth of penetration, which involves empirical constants that are related to the efficiency of heat and mass transfer to the pool. The accuracy of the model is examined by comparing the theoretical depth of penetration and the measured depth of the weld pool for a range of processing variables encompassing short arc and free flight mass transfer. Measurements are obtained from bead on plate welds of stainless steel using a stainless steel electrode and a shielding gas that is rich in argon. The results confirm that the depth of penetration is affected by variations in the rate of mass transfer.

Journal ArticleDOI
TL;DR: In this paper, the results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view.
Abstract: The importance of light weight magnesium alloys, especially for the automotive industry, has grown significantly during the last years. To fully benefit from the whole designing potential of this material, joining processes have to be developed. Laser beam welding turns out to be very suitable to join magnesium parts. The results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view. The determination of the process window by analyzing the influence of laser type, power, welding velocity, and shielding gas, as well as the influence of the base material, leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are e...

Journal ArticleDOI
TL;DR: In this article, a mathematical model is presented to predict the plasma properties, such as its temperature and absorption coefficient, and the partitioning of laser energy between the plasma and workpiece for different process parameters.
Abstract: A plume consisting of vapour and ionized particles from the workpiece is commonly formed during various types of laser materials processing. The process parameters such as the laser power, spot diameter, scanning speed, material properties and shielding gas affect the properties of the vapour-plasma plume. A mathematical model is presented in this paper to predict the plasma properties, such as its temperature and absorption coefficient, and the partitioning of laser energy between the plasma and workpiece for different process parameters. The effect of plasma on the surface temperature of the liquid metal and the vaporization rate are modelled using the Stefan condition at the liquid-vapour interface. A new experimental technique named as the pinhole experiment is presented in this paper to measure the partitioning of laser energy between the plasma and the workpiece.

Journal ArticleDOI
TL;DR: In this paper, gas metal arc welding (GMAW) with flux-cored wires and solid wires using shielding gas has been adopted for welding stainless steel, and spatter rates, chemical compositions, tensile strength and elongation tests have been performed and are reported.
Abstract: In the present work, gas metal arc welding (GMAW) with flux-cored wires and solid wires using shielding gas has been adopted for welding stainless steel. Five different compositions of shielding gas are used with flux-cored wire and three with solid wire. Spatter rates, chemical compositions, tensile strength and elongation tests have been performed and are reported. The spotter rates of the sample made using flux-cored wires are less than that for the sample made using solid wire. The ultimate tensile strength and elongation are not influenced by the composition of the shielding gas.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this paper, the effect of shielding gas on porosity formation was investigated in terms of plasma and keyhole behavior: In the case of He shielding gas metallic plasma emanated from a keyhole, and the keyhole was always open continuously.
Abstract: Laser welding can produce a deeply penetrated bead at high Speed. However, in high power CW CO2 laser welding, the characteristic porosity is easily formed in the weld metal, but its formation mechanism has not been well understood. Therefore, the authors have conducted systematic studies of porosity formation. They have revealed that many bubbles are formed mainly from the bottom tip of a keyhole by intense evaporation of metal. It has been also revealed that the keyhole fluctuates frequently and changes its size and shape corresponding to the intermittent bubble formation. And the majority of bubbles are trapped at the solidifying front in the rear part of the molten pool. However, there are few reports that deal the simultaneous observation of keyhole and plasma dynamic behavior as well as the formation of bubbles and porosity. In this study, therefore, the interrelationship between keyhole and plasma behavior was examined by using two synchronized high-speed cameras and X-ray transmission observation system. Especially the effect of shielding gas on porosity formation was investigated in terms of plasma and keyhole behavior: In the case of He shielding gas metallic plasma emanated from a keyhole, and the keyhole was always open continuously. On the other hand, in the case of N2 shielding gas, a big gas plasma was formed above the weld bead periodically, and metallic plasma and keyhole disappeared just like in the pulsed laser welding. Such periodical interval and duty were different depending on the materials used and exerted on effect on porosity formation tendency.Laser welding can produce a deeply penetrated bead at high Speed. However, in high power CW CO2 laser welding, the characteristic porosity is easily formed in the weld metal, but its formation mechanism has not been well understood. Therefore, the authors have conducted systematic studies of porosity formation. They have revealed that many bubbles are formed mainly from the bottom tip of a keyhole by intense evaporation of metal. It has been also revealed that the keyhole fluctuates frequently and changes its size and shape corresponding to the intermittent bubble formation. And the majority of bubbles are trapped at the solidifying front in the rear part of the molten pool. However, there are few reports that deal the simultaneous observation of keyhole and plasma dynamic behavior as well as the formation of bubbles and porosity. In this study, therefore, the interrelationship between keyhole and plasma behavior was examined by using two synchronized high-speed cameras and X-ray transmission observation ...

Journal Article
TL;DR: An improved fume chamber was constructed, and fume rates were measured with unprecedented precision for both steady and pulsed-current welding of mild steel using 92% argon/8% CO2 shielding gas.
Abstract: An improved fume chamber was constructed, and fume rates were measured with unprecedented precision for both steady- and pulsed-current welding of mild steel using 92% argon/8% CO2 shielding gas. Compre- hensive fume maps were constructed de- picting fume rates over a wide range of currents and voltages. Fume generation was generally lower under pulsed-cur- rent conditions. Theoretical arguments explaining this difference are presented.

Journal Article
TL;DR: In this paper, a gas tungsten arc welding process is modified by disconnecting the workpiece form the power supply and placing a second torch on the opposite side of the work piece.
Abstract: Cracking is a major concern in welding aluminum alloys. Although weld solidification cracks can be eliminated through the addition of filler metal, the additives modify the alloy or base metal constituents and may not always be desirable. High-energy beam processes, such as electron beam welding, that result in minimal heat input reduce crack sensitivity, but their high cost limits their applications. In this study, the conventional gas tungsten arc welding process is modified by disconnecting the workpiece form the power supply and placing a second torch on the opposite side of the workpiece. Such a modification changes the direction of the current flow, improves the weld penetration and reduces the heat input. Using this modified process, 6061-T651 alloy was welded without filler metals. Analysis suggested the reduced heat input, the changed direction of the current flow and the symmetric heating were responsible for the observed reduction of the cracking sensitivity.

Journal ArticleDOI
TL;DR: In this article, conditions for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet were determined for consistent welds on 0.8 and 1.8 mm sheets.
Abstract: Conditions were determined for consistent coupling of a CO2 laser beam to weld 5182 aluminum alloy sheet. Full penetration butt and bead-on-plate welds on 0.8 and 1.8 mm sheets were performed. Process conditions examined included beam mode, spot size and irradiance, shielding gas flow, and edge quality and fitup. The observed weld quality variations with the different process parameters were consistent with physical phenomena and a threshold irradiance model. Optimal conditions were determined for obtaining consistent welds on 5182 alloy sheets. Formability and tensile tests were performed on the welded samples. All test failures occurred in the fusion zone. Reduction in formability and tensile strength of the welded samples are discussed with respect to weld profiles and process parameters.

Patent
28 Oct 1999
TL;DR: A universal shielding gas mixture containing, by volume, about 96.5% argon, 3.0% carbon dioxide, and 2.0 % oxygen was presented in this article.
Abstract: A universal shielding gas mixture contains, by volume, about 96.0% argon, 3.0% carbon dioxide, and 1.0% oxygen. This single shielding gas composition can be used for welding ferrous metals, including both carbon steel and stainless steel using a variety of gas metal arc welding (GMAW) processes including short circuit arc, pulse arc, spray arc, metal transfer modes and flux core metal arc welding (FCAW) when welding carbon steel, stainless steel, hardfacing and metal core wires. This universal shielding gas composition will not substantially alter the carbon content of the weld metal chemistry. In a second embodiment, suitable for use with carbon steel materials but not stainless steel, the shielding gas mixture contains, by volume, about 95.0% argon, 3.0% carbon dioxide, and 2.0% oxygen. Another aspect of the invention is a single tank containing the premixed universal shielding gas, and improved gas metal arc welding processes that utilize the disclosed shielding gas mixture.

Journal ArticleDOI
TL;DR: In this article, the effects of minor elements and shielding gas on the penetration of TIG welding in type 304 stainless steel have been studied, and the results show that oxygen and sulfur are beneficial in increasing a depth/width ratio because of the increased surface tension/temperature gradient.
Abstract: The effects of minor elements and shielding gas on the penetration of TIG welding in type 304 stainless steel have been studied. The bead-on-plate test was performed, then the depth and width of the weld were measured using an optical projection machine. The arc voltage was measured with an arc data monitor. In addition, the metallurgical characteristics of weld were examined using OM and SEM. The results show that oxygen and sulfur are beneficial in increasing a depth/width ratio because of the increased surface tension/temperature gradient. Elements, such as aluminum, that have a deleterious effect on the depth/width ratio will combine with oxygen and reduce the soluble oxygen content in the weld pool. On the other hand, silicon and phosphorus have a minor effect on the depth/width ratio. Shielding gas using Ar + 1% O2 or Ar + 5% H2 can significantly promote the depth/width ratio. The former contains increased soluble oxygen content in the weld pool, and the latter produces an arc that is hotter than that produced by pure argon.

Proceedings ArticleDOI
10 May 1999
TL;DR: Through-arc sensing shows promise for detecting the onset of GMAW process disturbances including variations in tip-to-work distance, insufficient shielding gas coverage, electrode feeding problems, joint fit-up problems, and contact tip wear.
Abstract: Improved sensors are needed to enable automatic GMAW to accommodate a greater range of disturbing inputs. A low-cost, non-intrusive sensing technique, known as through-arc sensing, involves collecting and analyzing welding current and voltage signals. Through-arc sensing can be used to detect various GMAW quality indicators. It is shown that through-arc sensing can detect arc-start quality, steady-state arc stability, and the mode of metal transfer. Furthermore, the technique shows promise for detecting the onset of GMAW process disturbances including variations in tip-to-work distance, insufficient shielding gas coverage, electrode feeding problems, joint fit-up problems, and contact tip wear. Additional work is needed to refine and implement these techniques into a production-worthy system.

Patent
04 Oct 1999
TL;DR: In this paper, a laser welding apparatus with a plurality of jet nozzles for welding is described, where the jet noizles are arranged at an identical angle interval on a single circumference around the welding laser beam.
Abstract: A laser welding apparatus 10 according to the present invention comprises: a laser output mechanism 1 for applying a welding laser beam from its output end to a welding position of an object to be welded; and a plurality of jet nozzles for blowing out a shield gas to the welding position for preventing oxidation of the welding position, wherein the jet nozzles are arranged at an identical angle interval on a single circumference H around the welding laser beam. This enables to perform welding into a sufficient depth and width.

Journal ArticleDOI
TL;DR: In this article, a model was derived that accounts for several of the most important welding parameters and the alloying levels of the material allowing for predictions of how the individual parameters influence the nitrogen content.
Abstract: Welding of nitrogen-alloyed stainless steels is today performed both in production and on-site However achievement of the correct nitrogen balance during welding is delicate, and when the process is disturbed, it is not always clear which corrective measures should be made. In order to make rational decisions and allow for a reliable and robust process control, the mechanisms controlling the net nitrogen content of the weld metal must be identified, understood and mastered The paper illustrates the present situation and illuminates the factors governing the nitrogen exchange between the weld pool, plasma and shielding gas in TIG welding. A factor of major importance is the nitriding capacity of plasma which is strongly enhanced compared with a gas with corresponding nitrogen content Deviations from the ideal behaviour of a molecular diatomic gas are thus observed for the plasma and the Siewerts law is consequently not obeyed Techniques applicable to the study of the nitriding capacity of plasma and the rate controlling reactions of nitrogen absorption and desorption from liquid steel in contact with plasma have been examined. Experiments using stationary TIG are and real welds with travelling are are presented. both were performed using different materials and shielding gases. A model was derived that accounts for several of the most important welding parameters and the alloying levels of the material allowing for predictions of how the individual parameters influence the nitrogen content.

Journal ArticleDOI
TL;DR: In this paper, the influence of different additives on the physical behavior of the welding arc was investigated and it was found that the addition of SiO2 resulted in a voltage increase in the range 1-3 V, depending on arc length, welding current, and travel speed.
Abstract: This paper concerns a novel approach to through the arc position sensing, which is based on the influence that certain additives have on the physical behaviour of the welding arc. The changes in the physical behaviour are reflected by changes in arc parameters, in particular arc voltage, which can be monitored during the welding process. In the first part of the paper the results of bead on plate experiments aimed at determining the influence of different additives on arc voltage are presented. Of the different additives considered, SiO2 is found to have the most pronounced effect. It appears that addition of SiO2 results in a voltage increase in the range 1–3 V, depending on arc length, welding current, and travel speed. The observed effect is ascribed to arc contraction and arc trailing. The influence of SiO2 on the weld bead geometry and the mechanical properties of the weld was also determined. It appears that the addition of SiO2 results in enhanced weld penetration, presumably as a result of...

Journal ArticleDOI
TL;DR: In this paper, the weldability of high nitrogen austenitic stainless steel was evaluated using the Schaeffler diagram and showed a good correlation with the weld microstructure and the resulting mechanical properties.
Abstract: There is no other class of metallic materials offering a similar combination of strength, toughness. corrosion resistance and non magnetic properties as nitrogen alloyed austenitic stainless steels. However, welding characteristics of these materials still have to be quantified. In the present paper recent developments on the weldability of a new high nitrogen austenitic stainless steel are presented. Due to an approximate nitrogen content of 0.6% by weight, careful welding procedures are required to retain as much nitrogen as possible in the weld. Different are welding techniques such as shielded metal are welding (SMAW), gas metal are welding (GMAW) and gas tungsten are welding (GTAW) were used. To investigate the influence on the microstructure and the resulting mechanical properties different filler materials and gas compositions were used. The welding performance tests were carried out according to EN 288-3. All weld tests were successful. For the SMAW process the microstructure showed fusion zones without pores or any other defects. In the GMA and GTA welds the addition of nitrogen to the shielding gas promotes the formation of pores. It has been shown that a content of 8 vol.-% of nitrogen in the shielding gas is too high. An optimum can be expected around 4 vol.-% of nitrogen. Hardness tests exhibited lower values in the fusion zone. Lower values could also be observed in the ultimate tensile strength with a loss in the range of 15%. These results are due to a lower nitrogen content in the weld metal. The Charpy V values in the fusion zone are high. A weighting factor of 18 for nitrogen was used in the Schaeffler diagram and showed a good correlation.

Journal Article
TL;DR: In this paper, an attempt is made to further the understanding of factors influencing the hydrogen content in duplex stainless steel gas tungsten arc and gas metal arc (GMA) welds as well as to what extent it affects hydrogeninduced cracking susceptibility.
Abstract: In this investigation, an attempt is made to further the understanding of factors influencing the hydrogen content in duplex stainless steel gas tungsten arc (GTA) and gas metal arc (GMA) welds as well as to what extent it affects hydrogen-induced cracking susceptibility. The results indicated that susceptibility to hydrogen cracking using the GTA or GMA process appears to be limited. In practice, maintaining a moisture level below 10 ppm in the shielding gas is of less importance than the choice of welding parameters. Even a moisture level of 1000 ppm in the shielding gas, in combination with the correct welding parameters, will result in a sufficient low hydrogen content in the weld. Similarly, a moisture level in the shielding gas below 10 ppm does not necessarily result in low hydrogen content in the weld metal. Although very high ferrite levels were combined with high restrain and high hydrogen content, none of the GMA and GTA welds cracked. Susceptibility to hydrogen cracking is concluded to be limited.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this paper, the dynamic behaviors of the plasma plume during laser welding were investigated using a high-speed camera at a speed of 9000 frames/second, and it was found that the plasma grew in size continuously to a maximum height and then became small with respect to the elapsed time.
Abstract: In high-power laser welding, a focused laser beam melts and vaporizes the material to form a metal vapor above the surface of a workpiece. As the focused laser beam continuously irradiates on the metal vapor, the laser beam ionizes the metal vapor and a portion of the shielding gas forming a hot and opaque plasma plume. Previous studies showed that the plasma plume was unstable during laser welding and it influenced laser energy utilization, process stability, and weld quality. In this study, dynamic behaviors of the plasma plume during laser welding were investigated using a high-speed camera at a speed of 9000 frames/second. It was found that the plasma grew in size continuously to a maximum height and then became small with respect to the elapsed time. The plasma fluctuated at an average frequency of 1.2 kHz in laser welding of steel. The plasma plume varied in dimensions dramatically in laser welding of aluminum and the average fluctuation frequency was about 1.3 kHz. The plasma fluctuation was related to the keyhole instability and this fluctuation was likely caused by the variation of the keyhole opening. Laser weld quality would be improved significantly if the keyhole instability or plasma fluctuation was suppressed during laser welding. One of the techniques of minimizing keyhole instability was the use of dual-beam laser welding technology. Experimental results indicated that the plasma plumes in dual-beam laser welding were stable and good-quality welds were produced for both steel and aluminum.In high-power laser welding, a focused laser beam melts and vaporizes the material to form a metal vapor above the surface of a workpiece. As the focused laser beam continuously irradiates on the metal vapor, the laser beam ionizes the metal vapor and a portion of the shielding gas forming a hot and opaque plasma plume. Previous studies showed that the plasma plume was unstable during laser welding and it influenced laser energy utilization, process stability, and weld quality. In this study, dynamic behaviors of the plasma plume during laser welding were investigated using a high-speed camera at a speed of 9000 frames/second. It was found that the plasma grew in size continuously to a maximum height and then became small with respect to the elapsed time. The plasma fluctuated at an average frequency of 1.2 kHz in laser welding of steel. The plasma plume varied in dimensions dramatically in laser welding of aluminum and the average fluctuation frequency was about 1.3 kHz. The plasma fluctuation was relate...

Journal ArticleDOI
TL;DR: In this article, a diamond deposition was performed using an industrial arc-heater with argon/hydrogen mixtures and a high-speed converging-diverging nozzle anode, and a special shield gas flow was used to protect the arc's negative electrode from destruction by the hydrocarbons in recirculated flow.