Showing papers on "Shielding gas published in 1995"

Thermal efficiency of arc welding processes

Abstract: A study was conducted on the arc and melting efficiency of the plasma arc, gas tungsten arc, gas metal arc, and submerged arc welding processes The results of this work are extended to develop a quantitative method for estimating weld metal dilution in a companion paper Arc efficiency was determined as a function of current for each process using A36 steel base metal Melting efficiency was evaluated with variations in arc power and travel speed during deposition of austenitic stainless steel filler metal onto A36 steel substrates The arc efficiency did not vary significantly within a given process over the range of currents investigated The consumable electrode processes exhibited the highest arc efficiency (084), followed by the gas tungsten arc (067) and plasma arc (047) processes Resistive heating of the consumable GMAW electrode was calculated to account for a significant difference in arc efficiency between the gas metal arc and gas tungsten arc processes A semi-empirical relation was developed for the melting efficiency as a function of net arc power and travel speed, which described the experimental data well An interaction was observed between the arc and melting efficiency A low arc efficiency factor limits the power delivered to the substrate which, in turn, limits the maximum travel speed for a given set of conditions High melting efficiency is favored by high arc powers and travel speeds As a result, a low arc efficiency can limit the maximum obtainable melting efficiency

The effect of plasma formation on beam focusing in deep penetration welding with CO2 lasers

Abstract: This paper deals with the absorption and defocusing of a CO2 laser beam by the laser-induced plasma plume in deep penetration welding. To derive the `effective` intensity distribution in the focal plane theoretically, the laser beam propagation through the plasma plume is calculated by solving the paraxial wave equation with a finite-difference scheme. Corresponding to experimental results, documented in the literature, the properties of the plasma plume (spatial temperature distribution and shielding gas content) are pre-set within the calculation. Parametric studies demonstrate that the intensity at the focus is reduced due to the defocusing effect of the plasma plume, mainly, and only to a minor extent due to absorption within the plume. Because of refraction within the plume, the intensity distribution in the focal plane is dependent on the plasma`s size, position and temperature. On studying the dependency of the optical properties on plasma temperature and shielding gas composition, it is found that, by applying a shielding gas mixture of He and Ar in the ratio 3:1, the variation of the focal diameter with plasma temperature can be significantly reduced. This shielding gas mixture, therefore, is recommended for enhancing process stability when welding with high-power CO2 lasers.

Heat and metal transfer in gas metal arc welding using argon and helium

Abstract: This article describes a theoretical investigation on the arc parameters and metal transfer in gas metal arc welding (GMAW) of mild steel using argon and helium shielding gases. Major differences in the predicted arc parameters were determined to be due to large differences in thermophysical properties. Various findings from the study include that an arc cannot be struck in a pure helium atmosphere without the assistance of metal vapor, that a strong electromagnetic cathode force affects the fluid flow and heat transfer in the helium arc, providing a possible explanation for the experimentally observed globular transfer mode and that the tapering of the electrode in an argon arc is caused by electron condensation on the side of the electrode.

Infrared Sensing for On-Line Weld Geometry Monitoring and Control

Abstract: This paper describes a method for on-line weld geometry monitoring and control using a single front-side infrared sensor. Variations in plate thickness, shielding gas composition and minor element content are known to cause weld geometry changes. These changes in the weld geometry can be distinctly detected from an analysis of temperature gradients computed from infrared data. Deviations in temperature gradients were used to control the bead width and depth of penetration during the welding process. The analytical techniques described in this paper have been used to control gas tungsten arc and gas metal arc welding processes.

Gas metal arc welding fume generation using pulsed current

Abstract: While the fume generation rate of gas metal arc welding (GMAW) is lower than some other arc welding processes, the further reduction of welding fumes is of interest to companies using GMAW. Several researchers have reported lower fume generation rates for pulsed welding current compared to steady current. However, the range of welding parameters where these reduced fume levels can be expected has not been well documented. This paper describes a study of the effects of pulsed welding current on the amount of welding fume and ozone produced during GMAW using a range of welding parameters. Fume generation rates were measured for steady current and pulsed current GMAW of mild steel using copper-coated ER70S-3 welding wire and 95%Ar-5% CO 2 and 85% Ar-15% CO 2 shielding gases. The amount of fume generated during welding was determined by drawing fume through a fiberglass filter using the standard procedures contained in ANSI/AWS F1.2. Results of these measurements show that pulsed welding current can reduce fume generation rates compared to steady current. There is a range of welding voltage that produces the minimum fume generation rate for each wire feed speed with both pulsed and steady current. The data also show that using pulsed current does not guarantee lower fume generation compared to steady current. Welding parameters must be correctly controlled if pulsed current is to be used to reduce fume levels. Fillet welds were made to demonstrate that the pulsed current welding parameters that reduce fume also produce acceptable welds. No significant difference was found in the chemical composition of fumes from pulsed current compared to steady current. Fumes generated by both types of current are mixtures of iron, manganese and silicon oxides. Measurements of ozone generation rates show that the pulsed current welding parameters that reduce fume also increase ozone generation compared to steady current welding

The effects of the use of different shielding gas mixtures in laser welding of metals

Abstract: The paper makes use of the solution of the system of Saha equations derived for any mixture of ionized monatomic gases. This solution is specifically applied to the case of two-component mixtures of the gases used as shields in the process of laser welding, namely Ar plus He, Ar plus O2, Ar plus N2 and Ar plus H2. The number densities of electrons and ions, the degrees of ionization of the plasma as well as the refractive indices and the inverse Bremsstrahlung absorption coefficients are presented as functions of temperature for a variety of volume ratios of the gases in the mixtures. The properties of the mixture of helium and argon change dramatically as the volume ratio of the two gases is altered. This mixture is also most interesting insofar as laser welding is concerned because it causes only very slight defocusing of the laser light above the keyhole.

Method of welding a carbon steel and an austenitic stainless steel together and resultant structure

Abstract: Method of welding a carbon steel and a austenitic stainless steel involves using high density energy beam like a laser beam or electron beam Welding using high density energy beam is effective to obtain a high precision welding For the purpose of obtaining both high precision and no cracks, and no deformation, the method of the invention controls the structure of a weld portion to be a mixed structure of an austenitic structure and not greater than 20 wt % of a ferritic structure

Flux cored arc welding : arc signals, processing and metal transfer characterization

Abstract: Metal droplet transfer in flux cored arc welding (FCAW) was studied using electrical arc signals and droplets collected from the welding process. A large number of metal droplets from the FCAW experiments was collected. According to the size distribution of the droplets, several metal transfer modes could be identified amongst which spray transfer predominated. The electrical arc signals, in particular, voltage, were processed using the fast Fourier transform (FFT) technique. Characteristic spectral frequencies corresponding to different metal transfer modes were identified. The size distribution of the collected droplets correlated extremely well with these characteristic frequencies. The electrode melt rate, calculated using the characteristic frequencies identified from the FFT analysis, agreed closely with the measured melt rate. Results from the arc signal analysis and the FFT analysis showed that both arc voltage fluctuations (Δu) and characteristic frequencies of the FFT spectra were adequate to distinguish the different kinds of metal transfer modes in FCAW. Metal transfer mode maps, constructed using the two sets of results, were used to determine the optimal parameters for E71T-1, 1/16-in.-diameter electrode, and Ar-25%CO 2 shielding gas.

The Influence of Oxygen Additions on Argon-Shielded Gas Metal Arc Welding Processes

Abstract: It has been observed experi- mentally that small additions of oxygen to the argon shielding gas affect the gen- eral operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxy- gen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophys- ical transport and thermodynamic prop- erties caused by the oxygen addition. Therefore, it is concluded that the addi- tion of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxides initiates arc- ing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the elec- trode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.

Nitride Precipitation in Duplex Stainless Steel Weld Metal

Abstract: Duplex stainless steel base material was welded using gas tungsten arc welding with an Ar-10%H2 shielding gas and laboratory-made filler wires were employed to deposit duplex and fully ferritic weld metals having different nitrogen contents. Weld metal slow extension rate tensile (WM-SERT) testing was used to examine the hydrogen-induced cracking susceptibility and fractography of the weld metals. An increase in nitrogen content in fully ferritic stainless steel weld metal increased the density of precipitates and the hydrogen-induced cracking susceptibility. The facets on the quasi-cleavage fracture surfaces of broken WM-SERT test specimens were parallel to the {100} plane in ferrite. Scanning and transmission electron microscope observations revealed the crystallographic features and morphology of the precipitates. The precipitates were rod-like Cr2N nitrides. Many of them had directions and were parallel to the cleavage {100} plane in ferrite. An orientation relationship shown between Cr2N precipitates and ferrite suggested that the axes of the Cr2N precipitates were parallel to direction in ferrite and that they were more coherent along their long faces than at their tips. As a result, the tip of these Cr2N precipitates could act as sinks for hydrogen and may be preferential sites for initiation of hydrogen cracking; this could promote crack propagation on {001} cleavage planes in ferrite on which Cr2N precipitates are located. Higher densities of Cr2N precipitates were nucleated at solidification boundaries and at oxide inclusions in ferrite.

Surface treatment techniques

Abstract: Energy, such as from a UV excimer laser (712), an infrared Nd:YAG laser (714) and an infrared CO2 laser (716) is directed through a nozzle (722) at the surface of a substrate (702) to mobilize and vaporize a carbon constituent (e.g., carbide) within the substrate (e.g., steel). An additional secondary source (e.g., a carbon-containing gas, such as CO2) (720) and an inert shielding gas (e.g., N2) are also delivered through the nozzle. The vaporized constituent element is reacted by the energy to alter its physical structure (e.g., from carbon to diamond) to that of a composite material which is diffused back into the substrate as a composite material.

A theoretical study of a gas metal arc welding system

Abstract: A theoretical model of a gas metal arc welding system has been developed to make predictions of the anode temperature profile, welding arc length and arc current. The model incorporates a one-dimensional thermal model of the moving consumable anode and a two-dimensional model for the arc plasma. The model makes possible the calculation of the relationship between the welding arc current, wire feed rate and the supply voltages, for various wire diameters and shielding gases. The predicted welding current for a given wire feed rate shows good agreement with our experimental observation for operation in the spray transfer mode, for steel wire of two different diameters, assuming a workpiece sheath voltage of 15 V.

Process and device for cooling the area of a weld during laser welding

Abstract: A process and device are disclosed for cooling the area of a weld when laser welding metal sheets or metal strips, in particular for building car bodies in the automobile industry. The invention shows how to supply coolant and to create an inert gas veil between the focus and the liquid coolant so that the liquid coolant may not reach the area of the weld and negatively affect it.

Apparatus for controlling a consumable electrode pulsed-arc welding power source

Abstract: In a consumable electrode type pulsed arc welder using a CO 2 shielding gas a voltage detected by a detector (13) is given to a comparator (14) to which a reference voltage of a voltage setting circuit (15) is also inputted. When the detected voltage exceeds the reference voltage, a droplet detachment detection signal is issued. Then, an output adjusting circuit (16) lowers the welder output to a level I r lower than the ordinary current I p .

Effect of hydrogen in an argon GTAW shielding gas: Arc characteristics and bead morphology

Abstract: The influence of hydrogen additions to an argon shielding gas on the heat input and weld bead morphology was investigated using the gas tungsten arc welding process. Variations in weld bead size and shape with hydrogen additions were related to changes in the ability of the arc to generate heat and not to generate perturbations in the weld pool caused by Marangoni fluid flow

Particle-reinforced metal matrix composite as a weld deposit

Abstract: Weld metal consisting of particulate-reinforced metal matrix composite structure was produced with ceramic or refractory metal powder filled cored wire. Results are presented for both gas tungsten arc and gas metal arc weldments on Type 304 stainless steel. The effect of powder particle density and size distribution on the dispersion of particulates in the weld deposit was investigated. The motion and final distribution of particulates in the weld pool were evaluated with a fluid mechanics-based model, and critical welding criteria for the production of uniform particle distributions were identified. With particulates of optimum size and density in powder-filled cored wire it was possible to produce arc welding particulate-reinforced metal matrix weld deposits having uniform spatial particle distributions.

High current plasma arc welding electrode and method of making the same

Abstract: The elongated welding electrode is for plasma arc welding. It has a welding flux material coated on an elongated metal core. Gaps are formed in the flux coating and located at even intervals along the entire length of the electrode. The ratio of the melting points of the flux coating material and the metal core is in the range of 0.9 to 1.05. The ratio of the weights of the flux coating material and the metal core is in the range of 1.1 to 2.5. The electrode may be used with a simple welding gun and a large welding current to produce the plasma effect for welding without having to use an additional supply of gas for shielding the molten weld metal and for cooling the slag.

Nozzle for a welding torch having sputter build-up reducing configuration

Abstract: A nozzle 22 is used for a torch 5 which effects arc welding in a shield gas atmosphere using welding wire 26 that is continuously supplied from a wire support 23 that extends in one direction. The nozzle main body is disposed around and is separated by a space from the wire support 23. Air blow adapters 24 are fixed to the outer side of the nozzle main body and serve to supply into the nozzle main body fluid for removing sputter, and they have air introduction passages 33 that are directed to the central tip end.

A comparison of pulsed and conventional welding with basic flux cored and metal cored welding wires

Abstract: The results of a comparison between the use of a programmable pulsed power supply and a conventional (constant voltage) power supply with both basic flux cored and metal cored welding wires are described. Investigations were made of welding behavior and bead characteristics for both horizontal and uphill fillet welds for each combination of wire and power supply. In addition, all-weld-metal tensile and low-temperature impact properties, as well as weld composition and metallographic features are reported for each wire and power supply combination. The results for the basic flux cored wires indicate that the use of pulsed welding allows a major extension to the usable range of welding currents and some positional welding capability, without significant changes to deposition rates, weld metal mechanical properties, composition or microstructure. With metal cored wires, the use of pulsed welding not only resulted in a major extension to the range of usable welding currents and improved positional welding capability, but also in improved weld metal mechanical properties.

Fume formation rate at globular to spray mode transition during welding

Abstract: The decrease in the fume formation rate at the transition from globular to spray mode during welding has been investigated. A physical model describing this phenomenon has been developed. The essence of the consideration is that the model takes into account the different heating of droplets of the liquid metal by the are plasma in the two welding modes. New experimental results have been obtained for welding of stainless steel in a shielding gas containing oxygen. The decrease of the fume formation rate estimated on the basis of the model is in agreement with experimental data obtained and in the literature.

A mathematical model of the arc in electric arc welding including shielding gas flow and cathode spot location

Abstract: A mathematical model of a free-burning TIG electric arc with non-consumable electrodes using a flat anode and argon shielding gas is presented. Differential equations describing the conservation of mass, momentum and energy are solved together with Maxwell's equations describing the electromagnetic field. The dependence of transport coefficients on temperature is taken into account. The gas flow is assumed to be laminar and the partially ionized plasma is assumed to be in local thermodynamic equilibrium. The mathematical model can cope with a broad range of operating conditions. The model is used to demonstrate the strong influence that the velocity and temperature of the flow of gas entering the top of the electric arc in the region of the cathode can have on the arc column. In particular, it is shown that cathode flows of strength sufficient to produce a significant constriction of the electric arc need to be assumed in order to account for experimentally measured electric fields in the arc column as well as the total voltage drop for 10 mm arcs. The use of this model also shows the part played by the cathode spot and its location in the nature of the electric arc column. In particular, two complementary techniques for studying the arc column are highlighted. In the first, a strictly stable static arc is needed in order to employ the spectroscopic technique of temperature measurement. In contrast, when the position of the arc is less stable, a rapid measurement with an electric probe is indicated in order to measure the electric field. The arc model described by Ducharme et al (1993) will then yield the temperature field. The model presented here produces the results for the temperature distribution and for the electric field based on the use of appropriate boundary conditions.

Oxygen Absorption in Iron and Steel Weld Metal

Abstract: The authors have been engaged in an extensive program of fundamental and systematic research intended to clarify the effects of alloying elements on the oxygen absorption during arc welding process. In this report, the outline of an oxygen absorption behavior in iron and steel weld metal during Gas-Metal-Arc welding process is described on the basis of the authors group's data. Initially the oxygen absorption behavior of the pure iron weld metal is thermodynamically analyzed. The similar investigations are carried out for Fe-Si, Fe-Mn, Fe-Al, Fe-Ti, Fe-Cr and Fe- Ni weld metat, and the results are analyzed. Finally, the oxygen absorption behavior of the mild steel is also described.

Nd:YAG laser welding process monitoring by non-intrusive optical detection in the fibre optic delivery system

Abstract: This paper describes a non-intrusive optical sensing technique for Nd:YAG laser welding monitoring. The cladding power monitor (CPM) detects the light returned through the cladding of the delivery fibre optic, and appropriate spectral filtering isolates the light radiated from the plume of hot gas which forms above the weld. The successful detection of welding faults using this optical signal is described, including laser focus errors and shield gas interruption.

Laser welding method for aluminum alloy without exposing molten metal on the rear surface

Abstract: PROBLEM TO BE SOLVED: To obtain through laser welding a sound weld zone with blowhole defects suppressed. SOLUTION: In the laser welding of an aluminum alloy in which molten metal is unexposed in the rear surface in a weld zone, a weld bead is formed which has a penetration depth ratio (aspect ratio) of 0.9 or less against the bead width. In welding a material having a large thickness, an upper plate is used which is provided with a groove that enlarges a penetration depth. Residual foams are reduced by minimizing the aspect ratio to 0.9 or less, enabling a weld zone to be obtained with a satisfactory mechanical characteristics.

Mag-pulse arc welding method for galvanized steel sheet

Abstract: (57) [Summary] [Purpose] It is possible to extremely reduce the occurrence of pore defects such as pits and blowholes, and it is also possible to obtain a good appearance with no bead dripping even in difficult position welding such as vertical welding or horizontal welding. Make it possible to obtain weld beads. [Composition] When performing galvanized arc welding of a galvanized steel sheet, C: 0.02 to 0.10 wt%, Si: 0.3 0.7 wt% and Mn: 1.5 to 3.0 wt% and solid wire for galvanized steel welding which comprises, as a basic alloy components, consists of a mixture of Ar gas and CO 2 gas CO 2 A shield gas having a gas mixture ratio of 5 to 10% by volume is used, a peak current value is 450 to 600 A, a peak current period is 1.0 to 2.0 ms, and a value of a short circuit migration rate r is r = 0. The welding voltage is set so as to be in the range of 7 to 1.0 to cause droplet transfer due to a short circuit during the base current period, and the galvanized steel sheet is subjected to mag pulse arc welding.

Laser welding device

Abstract: PROBLEM TO BE SOLVED: To surely shield a welding part by providing an opening with a clean air filled in a beam transmission line and blowing a shield gas against the laser beam converged from the opening and the welding part through a special shield gas feedling section. SOLUTION: The clean air is fed from an air feeding port 8 into the beam transmission line 3 and discharged from the opening 18 under a converging mirror 2. The clean air is filled in the beam transmission line 3 to keep cleanliness in the beam transmission line 3. Furthermore, the shield gas is blown against the weld zone 4 from a shield gas nozzle 6. The weld zone 4 is separated from the atmosphere with an inert gas such as Ar, He or the like used as the shield gas to prevent the generation of welding defects such as oxidation in the weld zone and voids owing to the air entrupment or the like. In addition, the reduction of the generating laser inductive plasma in the weld zone is restrained with the function of the inert gas, whereby the generation of a burn through is prevented.

Tig welding wire for high-strength cr-mo steel

Abstract: PURPOSE:To obtain a welding metal having excellent strength at high temperature and toughness, etc., by specifying composition of a TIG welding wire for a specially composed high-strength CrMo steel, in specified wt.%, C, Si, Mn, Cr, Mo, V, Nb and balance Fe. CONSTITUTION:The high-strength Cr-Mo steel having composition of, by wt.%, 2 to 3.25% Cr, 0.90 to 1.2O% Mo, 0.18 to 0.35% V and one or more of Nb, Ti and B is TIG welded with inert shield gas such as Ar or Ar+He. The TIG welding wire is composed as 0.07 to 0.15% C, 0.05 to 0.40% Si, 0.20 to 0.80% Mn, <=0.01% P and S, 2 to 3.2% Cr, 0.90 to 1.20% Mo, 0.10 to 0.50% V, 0.01 to 0.05% Nb and balance Fe with inevitable impurities. TE in the formular I is <=11.0. Thus, the welding metal excellent in creep strength, anti tempering brittle characteristic, anti high temperature crack characteristic and low temperature cracking characteristic is obtained.

Output control method of power source for consumable electrode gas shielded pulse arc welding

Abstract: PURPOSE: To reduce generation of spatter and to improve welding efficiency by setting a droplet forming energy set value to a specific range in gas shielded pulse arc welding. CONSTITUTION: An output control method of power source for pulse arc welding, in which CO 2 gas or a mixed gas containing CO 2 as principal component is used for shield gas, is executed so that a first pulse period, in which a first pulse current is supplied for detaching droplet at the tip of welding wire and a second pulse period, in which at detecting that droplet is detached from the tip of welding wire during the first pulse period, in following the first pulse period, a second pulse current smaller than the first pulse current and for forming droplet is supplied up to reaching the droplet forming energy set value ER shown by 0.4K(IP 2 )≤E≤0.8K, here K(IP 2 ) is (pulse current value)×(pulse current supply time), subsequently, a base period to supply base current. These are repeated in sequence. COPYRIGHT: (C)1996,JPO

Effects of shielding gas on metal transfer

Abstract: (1995). Effects of shielding gas on metal transfer. Welding International: Vol. 9, No. 6, pp. 462-466.

Method for decompression laser beam machining

Abstract: PURPOSE:To eliminate the defect of porosity or the like of a weld zone by reducing the pressure of the atmosphere of a part to be irradiated with the laser beam to the prescribed pressure or less, and feeding the shield gas to deepen the penetration of the laser beam welding. CONSTITUTION:A work 5 is set on a machining table 7 of a decompression chamber 6, and the laser beam 1 is made incident from the top of the decompression chamber 6 and shut off from the atmosphere by a converging lens 4. The decompression chamber 6 is evacuated to the pressure of <=50Torr by a rotary pump or the like, and the inert gas of He, Ar or the like is flowed as a small amount of shield gas to form the inert gas atmosphere in the decompression chamber. Penetration is generated in the part irradiated with the laser beam in the work 5, and the laser beam plasma is generated in the penetration zone. When the pressure is <=50Torr, the penetration 1.5 times that in the atmosphere is obtained, and generation of the porosity can be suppressed.