Showing papers on "Shielding gas published in 1997"

Spectroscopic characterization of laser-induced plasma created during welding with a pulsed Nd:YAG laser

Abstract: A spectroscopic study of a laser-induced plume created during the welding of stainless steel and other materials (iron and chromium) has been carried out A pulsed Nd:YAG laser of 1000 W average power is used The evolutions of the electron temperature and electron density have been studied for several welding parameters We use working powers from 300 to 900 W and pulse durations between 15 and 5 ms The influence of shielding gases like nitrogen and argon has been taken into account Temperature and density calculations are based on the observation of the relative intensities and shapes of the emission peaks We assume that the plasma is in local thermal equilibrium The temperature is calculated with the Boltzmann plot method and the density with the Stark broadening of an iron line The electron temperatures vary in the range of 4500–7100 K, electron density between 3×1022 and 65×1022 m−3 The absorption of the laser beam in the plasma is calculated using the Inverse Bremsstrahlung theory

Welding of nickel-base superalloys having a nil-ductility range

Abstract: An article made of a nickel-base superalloy having a nil-ductility range from the solidus temperature of the alloy to about 600° F. below the solidus temperature is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, adjusting the temperature of the article to a welding temperature of from about 1800° F. to about 2100° F., welding a preselected area in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected area so as to locally melt the alloy in the preselected area, providing a filler metal having the same composition as the nickel-based superalloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Effect of various driving forces on heat and mass transfer in arc welding

Abstract: In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

The spectroscopy of the plasma plume induced during laser welding of stainless steel and titanium

Abstract: Results of spectroscopic measurements of laser-induced plasmas under welding conditions are presented and discussed. The metals welded were stainless steel and titanium. It is shown that the intensities of the atomic lines of metals give information on the peripheral region of the plasma plume. The plasma-plume parameters are found to be similar for these two metals. The ratios of intensities of the ionic and atomic lines of the metals give maximum temperatures of about 11 000 K. These temperatures are several thousand kelvins higher than the temperatures determined from the atomic lines. The plasma plumes over the keyhole consist of metal vapours diluted by argon used as the shielding gas. The electron densities determined from the Stark broadening of the argon lines are about . The average partial pressure of the metal vapours is found to be 0.2 atm, the argon partial pressure 0.6 atm and the remaining pressure is due to electrons. Equilibrium conditions have been examined and it has been found that the plasma is in local thermal equilibrium.

High power laser welding in hyperbaric gas and water environments

Abstract: A hyperbaric laser welding facility has been constructed and the feasibility of high power CO2 and Nd:YAG laser welding in both high pressure gas and water environments, to simulated water depths of 500 m, has been established. From initial trials on welding through water at atmospheric pressure, it was found that the different absorption characteristics of water to 10.6 μm (CO2 laser) and 1.06 μm (Nd:YAG laser) radiation proved crucial. The Nd:YAG laser was totally unsuitable as the beam was largely diffused in the water, whereas the CO2 beam was readily absorbed and, using high speed video equipment, was found to form a high irradiance channel and a dry region around the weld area. Welding under a high pressure gas environment produced a highly energized plume which prevented keyhole welding at pressures over 1 × 106 Pa. An investigation carried out into the efficacy of a gas jet delivery system to alleviate the extent of the plume showed that argon blown horizontally across the weld was the optimum configuration, extending the welding range up to 5 × 106 Pa. A limited investigation into high pressure underwater welding showed porosity to be a problem although sound welds were produced at pressures up to 2 × 106 Pa.

Effect of CO/sub 2/ shielding gas on metal droplet formation in arc welding

Abstract: We have developed a unified arc electrode model that enables us to make predictions of the time development of molten drops from the welding wire in gas metal arc welding. The wire is taken as the positive electrode, and the effects of surface tension, magnetic pinch forces, and convection within the drop are taken into account to predict drop detachment for any given arc current. For pure argon, we have previously predicted the sharp transition that is observed experimentally at about 300 A between globular transfer at low current, when drop diameters are larger than the wire diameter, and spray transfer, for currents above 300 A, when drop diameters are smaller than the wire diameter. In this paper, we predict that addition of 25% of CO/sub 2/ to the argon leads to an increase in the transition current to more than 325 A, also in agreement with published experimental results. For pure CO/sub 2/, we find a significantly different drop behavior due to the more constricted arc. Both small and large drops are produced, with many very small drops being produced successively between each large drop.

Prediction of gas tungsten arc welding properties in mixtures of argon and hydrogen

Abstract: A theory of gas tungsten arc welding (GTAW) arcs that treats the tungsten electrode, the arc, and the workpiece as a unified system has been applied to make predictions in two dimensions of the temperature distributions in the arc, the tungsten cathode, and the workpiece, for any given arc current and gas mixture. Predictions of arc temperatures, radii, and voltages are compared for argon and mixtures of argon and hydrogen. It is found that arcs in gas mixtures containing hydrogen are more constricted and have a higher maximum temperature and arc voltage than arcs in pure argon. The addition of hydrogen also significantly increases the volume of molten material in the weld pool due to the higher thermal conductivity of argon-hydrogen mixtures at temperatures at which molecules of hydrogen dissociate. Predictions are also compared for workpieces of steel and aluminum. The volume of molten material is very much less for aluminum, despite its lower melting point, because of the higher thermal conductivity of aluminum. Predicted arc voltages as a function of current for a mixture of 10% hydrogen in argon are in good agreement with experimental results.

Effect of sulfur and oxygen on weld penetration of high-purity austenitic stainless steels

Abstract: Convective flow during arc welding depends upon the surface tension gradient (dy/dT, Marangoni flow), buoyancy, arc drag force, electromagnetic force, shielding gas, and the viscosity of the melt. The Marangoni and the buoyancy-driven flow are the major factors in controlling weld penetration in ferrous alloys, especially austenitic stainless steels such as 304 and 316. Small variations in the concentration of surfactants, such as sulfur and oxygen, in stainless steels cause significant changes in the weld penetration and depth/width (D/W) ratio of the fusion zone. Gas-tungsten arc (GTA) welds were done on low- and high-sulfur 304 and 316 heats using pure argon and argon/oxygen shielding gases. Also, laser beam (LB) welds were done on the 304 and 316 heats using pure argon as the shielding gas. Increase in the sulfur content decreased the D/W ratio for the GTA 304 welds using pure argon, but for the case of LB 304 welds the results were the opposite. For the GTA 316 welds and LB 316 welds, increase in sulfur increased the D/W ratio of the fusion zone. Oxygen increased the D/W ratio of both the 304 and 316 GTA welds.

Sensing ARC welding process characteristics for welding process control

Abstract: A method of sensing and controlling an arc welding process employs a high equency rate of sampling of electrical signals from the welding circuit The sampled signals are operated upon by predetermined processes to determine electrical resistance, shielding gas quality, and short circuit frequency The process measurements are compared to a predetermined set of tolerance levels and evaluated using a window technique that updates the evaluation of the data samples at the sampling rate

Formation mechanism and reduction method of porosity in laser welding of stainless steel

Abstract: It is generally acknowledged in any steels or alloys that porosity is liable to be formed in a keyhole type of deeply penetrated fusion zones made with a high power laser. Therefore, this investigation was carried out with the objectives of elucidating the formation mechanism of porosity and developing preventive procedure of pores in high power laser welding.The formation behavior of keyhole, bubbles and porosity was observed during butt-joint or bead-on-plate CO2 laser welding of stainless steel by microfocused X-ray transmission insitu imaging system with high speed video camera. The influence of various laser welding conditions on porosity formation was investigated. As a result, it was observed that many bubbles were predominantly frequently formed at the bottom of a molten pool from the tip part of a deep keyhole in consequence of its dynamic motion due to intense evaporation, and some bubbles were formed from the middle part of the keyhole in the case of focal point under the plate surface or high power laser irradiation. It was also seen that most of the bubbles were soon captured or trapped into pores by the solidifying solid-liquid interface during floating up in a stainless steel. SEM observation result of a fractured surface demonstrated traces that liquid was penetrated and solidified inside pores, probably because evaporated materials trapped in the bubble solidified and/or the temperature dropped to render their inside pressure lower. According to Q mass-spectroscopic analysis of gas content of porosity, it was revealed that He shielding gas and H2 gas were included inside a pore near the bottom of the weld fusion zone. It was observed to be feasible to produce a sound full-penetration weld bead without porosity in steel plates of 10 mm thickness, since no bubbles were formed from the bottom part of the fully penetrated keyhole. Bubbles, porosity or pores were confirmed to be reduced by utilizing N2 shielding gas and forward keyhole-inclination welding in He shielding gas even in the case of partially penetrated weld.It is generally acknowledged in any steels or alloys that porosity is liable to be formed in a keyhole type of deeply penetrated fusion zones made with a high power laser. Therefore, this investigation was carried out with the objectives of elucidating the formation mechanism of porosity and developing preventive procedure of pores in high power laser welding.The formation behavior of keyhole, bubbles and porosity was observed during butt-joint or bead-on-plate CO2 laser welding of stainless steel by microfocused X-ray transmission insitu imaging system with high speed video camera. The influence of various laser welding conditions on porosity formation was investigated. As a result, it was observed that many bubbles were predominantly frequently formed at the bottom of a molten pool from the tip part of a deep keyhole in consequence of its dynamic motion due to intense evaporation, and some bubbles were formed from the middle part of the keyhole in the case of focal point under the plate surface or high ...

Metal-core weld wire for welding galvanized steels

Abstract: A metal-core weld wire usable for gas shielded arc welding gapless joints on low carbon and low alloy galvanized and galvanealed steels. The metal-core weld wire includes a low carbon steel sheath surrounding a core composition. In one embodiment, the low carbon steel sheath includes, by total weight of the metal-core weld wire, between approximately 0.01-0.03% C, and the core composition includes, by total weight of the metal-core weld wire, between approximately 0.05-0.20% Ti, between approximately 0.05-1.00% Nb, Fe powder, and Mn to the extent that the metal-core weld wire includes between approximately 0.1-1.0% Mn wherein the metal-core weld wire includes between approximately 0.1-1.0% Si. The core composition is, by total weight of the metal-core weld wire, between approximately 0.001-12.0%. The metal-core weld wire provides, at weld rates up to 150 cm/min, reduced arc ionization potential and spatter, and improved arc stability and shielding. The metal-core weld wire produces, at weld rates up to 150 cm/min, weld deposits having reduced blow holes and porosity, no liquid metal embrittlement, and reduced weld pool surface tension resulting in an improved wetting characteristic.

Method of welding

Abstract: A process for buttwelding metal workpieces (12) having bevelled joint preparations using an automatic GTAW welder (20) using filler wire (32) includes preparing the bevelled workpieces (12) with bevelled joint areas having minimal land thickness at the root extremities; placing the prepared workpiece joint sections together with an open gap between their adjacent root extremities, the gap having a minimum dimension that avoids harmful compression stress between the workpieces due to weld shrinkage and a maximum dimension that avoids filler wire penetration of the gap; fusion welding the open root area of the adjacent workpieces (12) with a root pass weld using an automatic GTAW welder (20) supplied with filler wire (32) and a shield gas including 1 to 10 % hydrogen and the balance inert gas; and then promptly overlaying the root pass weld with at least one additional filler weld pass using an automatic GTAW welder (20) supplied with filler wire (32) and hydrogen-free shield gas.

The effects of welding parameters on ultra-violet light emissions, ozone and CrVI formation in MIG welding

Abstract: This paper describes the relationships between ultra-violet emission, ozone generation and CrVI production in MIG welding which were measured as a function of shield gas flow rate, welding voltage, electrode stick-out and shield gas composition using an automatic welding rig that permitted MIG welding under reproducible conditions. The experimental results are interpreted in terms of the physico-chemical processes occurring in the micro- and macro-environments of the arc as part of research into process modification to reduce occupational exposure to ozone and CrVI production rates in MIG welding. We believe the techniques described here, and in particular the use of what we have termed u.v.-ozone measurements, will prove useful in further study of ozone generation and CrVI formation and may be applied in the investigation of engineering control of occupational exposure in MIG and other welding process such as Manual Metal Arc (MMA) and Tungsten Inert Gas (TIG).

Absorption and transport of hydrogen during gas metal arc welding of low alloy steel

Abstract: Although hydrogen induced cracking remains a major problem in the welding of steels, the present methods of managing hydrogen in the weldment are mostly empirical in nature. In recent years, numerical modelling of heat transfer and fluid flow has provided detailed insight into the physical processes in welding. However, very little effort has been made in the past to use these transport phenomena based calculations to understand the dissolution of hydrogen in the weld metal and its subsequent transport in the liquid and solid regions. The aim of the present work was to address this important need. Heat transfer, fluid flow, and hydrogen transport calculations in transient, three-dimensional form are used to predict the spatial distribution of hydrogen concentration in the weld metal during gas metal arc welding of mild steels for different welding conditions. The enhanced hydrogen solubility in the weld metal above that predicted by Sieverts law was determined from a model for the partitioning of ...

Semi-automatic tig welding apparatus

Abstract: A semi-automatic TIG welding apparatus including a torch handle, a wire-feeding curved nozzle which is disposed within the torch handle and is curved at a point slightly extended from the torch handle, and a TIG torch supporting arm which is fixed to a TIG torch having a shielding gas hose and center gas hose. An inside portion of the TIG torch supporting arm is formed of an electroconductive material. The apparatus further includes water-cooling welding cable hoses which are attached to a water tank, extend through the inner side of the torch handle, and are attached to the TIG torch. The water-cooling welding cable hoses being formed with electroconductive cables provided therein. The apparatus may additionally include a TIG torch rotation block which is rotatably mounted to the wire-feeding curved nozzle and fixed to the TIG torch supporting arm. Thus, a semi-automatic TIG welding apparatus is provided wherein a TIG welder can freely adjust the position of the welding wire, and wherein the welding wire can be inserted to an ideal position, and also wherein the wire-feeding curved nozzle and thus the wire do not fluctuate in position, resulting in great savings in the expense and time related to TIG welding, and also in the amount of labor on the part of the welder.

Method and process gas for laser welding metal work pieces

Abstract: The invention relates to a method for laser welding metal work pieces in which the area to be welded is enclosed in a process gas. In accordance with the invention, a mixture of at least one noble gas (preferably helium) and at least 0.5 vol. % nitrogen is used as process gas. The invention improves welding joint quality specially in aluminum materials and steels with austenitic structural constituents.

Welding of gamma titanium aluminide alloys

Abstract: An article made of a gamma titanium aluminide alloy is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, cooling the entire article to a welding temperature of from about 1000° F. to about 1400° F., welding a preselected region in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected region so as to locally melt the alloy in the preselected region, providing a filler metal having the same composition as the gamma titanium aluminide alloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Flux-cored wire for gas shielded metal-arc welding

Abstract: PROBLEM TO BE SOLVED: To extend the range of the welding condition and to improve the welding work efficiency by adding water glass as an arc stabilizer in a wire and kneading the mixture, and adding fired sodium titanate and potassium titanate of a specified quantity. SOLUTION: Water glass is added as an arc stabilizer to the composition of a flux-cored wire for the gas shield metal arc welding having a butted part, the mixture is kneaded, and one or two of fired sodium titanate and potassium titanate is added by 0.2-2% to the total wt.% of the wire. Excellent moisture absorption resistance is ensured thereby. In addition, the total amount of hydrogen is regulated to be <=70 ppm. In this flux-cored wire, the arc condition is stable also in the CO2 gas shield gas welding, spatters are small and generated only in a small amount. Firing after adding water glass and kneading is preferably performed at 150 deg.C or over. The outer steel shell is preferably formed of mild steel from the viewpoint of the drawability after the flux is filled.

Apparatus and method for centering a laser welding probe within a tube using gas pressure

Abstract: An apparatus for welding the interior surface of a tube includes a laser welding probe body configured for positioning within an interior surface of a tube. A centering mechanism relying upon fluid pressure is used to substantially center the laser welding probe body within an annular void defined between the laser welding probe body and the interior surface of the tube. In one embodiment, the centering mechanism is implemented with a set of seals. In another embodiment, the centering mechanism is implemented with a set of centering balls that respond to the fluid pressure and thereby operate to center the laser welding probe body within the annular void. The fluid pressure may be created with shielding gas used during the laser welding operation.

Reduction of blowholes in high-speed arc welding of hot-dip galvanised steel sheets

Abstract: Summary This paper describes an investigation of the blowhole formation mechanism and the substances causing blowholes during high-speed arc welding of galvannealed steel sheets extensively used in the chassis components of motor vehicles Based on these results, it clarifies the effect of the shielding gas composition on suppression of zinc vaporisation and also examines suitable preventive measures The results obtained may be summarised as follows: Provided the organic substances adhering to the base material amount to around 1 mg/cm2, they are not the main cause of blowhole formation Even after thorough degreasing in such a way that the amount of organic substances present is equivalent to less than 1 in 500 parts of the zinc coating weight, numerous blowholes are formed to much the same extent as those found in the base material before degreasing The gas collected through the blowhole zone being broken apart reveals its main components to be hydrogen and hydrocarbons, including methane Hydrogen is

Method to eliminate weld solidification cracking of 312 stainless steel overlay and to minimize the overlay's thermal expansion mismatch with carbon steel or low alloy steel substrate

Abstract: A method for applying a stainless steel weld overlay on a substrate, e.g., a carbon steel or low alloy steel, uses an arc welding process. The process includes welding a stainless steel weld overlay onto the substrate using a shielding gas mixture including greater than 2% nitrogen by volume with balance being an inert gas or a mixture of inert gases. The nitrogen is of a sufficient concentration so as to eliminate solidification cracking in the weld overlay. In addition, the nitrogen may help to eliminate a mismatch in me coefficient of thermal expansion between the weld overlay and the substrate. Furthermore, if the weld overlay comprises only a single layer, the nitrogen concentration in the shielding gas mixture may be less than 2%.

Plasma arc spot welding of car body steels containing vaporizable ingredients

Abstract: Method of one side spot welding of a metallic auto body construction containing vaporizable coatings or ingredients, the construction having overlapping metal plys, comprising: impinging a plasma column on a selected spot of one side of the construction, the plasma column being generated by passing a plasma gas at a predetermined flow rate through an electrical arc created by a predetermined electrical current path; shielding the plasma column in an inert gas containing at least 5-35% by volume of oxygen, the shielded plasma column melting at least the metal on one ply at the spot while the oxygen increases the fluidity and wetablility of the melted metal and reduce its surface tension allowing any vaporization of the ingredients to quiescently escape through the molten metal; and ceasing plasma arc impingement for allowing the molten metal to solidify and complete the spot weld.

Multi-purpose, multi-transfer, multi-position shielding gas for arc welding

Abstract: A shielding gas composition and method of using the shielding gas in gas metal arc welding of flux cored are welding, or composite cored arc welding The gas is a mixture of argon, helium and carbon dioxide blended to facilitate metal transfer in any position for all the named processes

A numerical analysis of molten pool convection considering geometric parameters of cathode and anode

Abstract: The heat transfer and fluid flow in the molten pool during stationary gas tungsten arc welding (GTAW) using Ar shielding gas have been studied with an emphasis on the impact of geometric parameters on the welding arc, such as electrode bevel angle, arc length and surface depression due to arc pressure acting on the molten pool surface. Driving forces responsible for weld pool convection, i.e., self-induced electromagnetic force, surface tension due to the temperature gradient at the surface of the molten pool and shear stress acting on the molten pool surface by the arc plasma flow, were considered. The numerical model was applied to type 304L stainless steel plate with 30 ppm sulfur. As the welding current increased, the discrepancy of penetration at the weld center between the calculation and experiment increased because of the strong flow along the molten pool surface. As the electrode bevel angle decreased, the shear stress acting on the molten pool surface increased. Therefore, the fusion width increased and the fusion depth decreased. Changing the arc length did not influence the fusion shape because variation in shear stress, which determined the surface flow along the molten pool surface, was minor. From the simulation, considering the depression of the molten pool surface, the effects of the increased arc length and elevated anode temperature resulted in a more accurate fusion width.

Consumable electrode type gas shielded metal arc welding method

Abstract: PROBLEM TO BE SOLVED: To provide a joined part having the performance of a sound weld joint free from blow holes SOLUTION: In a method to perform the consumable electrode type gas shielded metal-arc welding using the high-nitrogen stainless steel welding material, nitrogen gas, argon gas or helium gas up to 98vol%, or the mixture gas of argon gas, helium gas and nitrogen gas is used as the shield gas The stainless steel welding material is preferably the austenitic stainless steel welding material containing, by weight, 60-300% Ni, 160-300% Cr, and 015-045% N as the main alloy composition, or the two-phase stainless steel welding material containing, by weight, 30-90% Ni, 160-300% Cr, 015-045% N as the main alloy composition COPYRIGHT: (C)1998,JPO

Laser welding or coating method

Abstract: A laser welding or cladding method for metal workpieces, comprises flushing the welding point by a process gas mixture of at least one inert gas and hydrogen.

Process and apparatus for reducing the emission of ozone produced during a gas shielded arc welding operation

Abstract: Reducing the emission of ozone products during an electric arc welding operation under a protective gas (F1,26) comprises using a gas (F2,38) sheathing the electric arc, the gas being at a temperature greater than 100 degrees C immediately upstream of the root of the electric arc. Also claimed is the device for the above process.

Laser beam welding method

Abstract: PROBLEM TO BE SOLVED: To prevent burn-through by feeding the side shield gas parallel to a surface of a work to be welded from the upstream side to the downstream side in the welding advancing direction, and setting the gas flow velocity V (m/s) immediately above the molten pool to be >=22 times (t) where (t) is the thickness (mm) of the work SOLUTION: A side shield nozzle 4 is arranged parallel to the surface 2a of a work 2 to be welded immediately above the weld seam on the upstream side in the advancing direction of a center shield nozzle 3 to form the side shield gas flow 6 horizontal to the molten pool 8 The force to push the molten metal in the molten pool 8 in the downstream side, ie, the force to raise the molten metal in the vicinity of the back surface side of the work 2 to be welded over a preceding solidified part 9' is applied The molten pool 8 is held by the raising force and the surface tension of the molten metal, and is not sagged from the surface 2b The flow velocity of the side shield gas flow 6 is >=22 times the thickness (t) (mm) of the work A sound weld joint can be obtained thereby