Showing papers on "Gas metal arc welding published in 2002"

The welding of aluminium and its alloys

Abstract: Introduction to the Welding of Aluminium. Welding metallurgy. Material Standards, Designations and Alloys. Preparation for Welding. Welding Design. TIG Welding. MIG Welding. Other Welding Processes. Resistance Welding Processes. Welding procedure and welder approval. Weld Defects and Quality Control. Appendices.

Online monitoring system and method for a short-circuiting gas metal arc welding process

Abstract: The present invention generally relates to a useful online monitoring system and method of user thereof for monitoring a welding process to determine weld quality, weld process stability, and weld geometry for each weld formed during a welding process. More particularly, the online monitoring system has a computer having a graphical user interface (GUI); at least one welding machine; a communication interface for interfacing communication between the at least one welding machine and the computer; a data acquisition system for acquiring welding signal data, the data acquisition system having an associated memory means; a quality management database for managing and storing acquired welding signal data; and a statistical signal processing system in communication with the data acquisition system for processing welding signal data stored in the data acquisition system associated memory means, and in further communication with the communication interface for communicating processed welding signal data to the GUI.

Laser welding of aluminium alloy 5083

Abstract: There are two laser welding mechanisms, keyhole mode and conduction mode. Keyhole welding is widely used because it produces welds with high aspect ratios and narrow heat affected zones. However keyhole welding can be unstable, as the keyhole oscillates and closes intermittently. This intermittent closure causes porosity due to gas entrapment. Conduction welding, on the other hand, is more stable since vaporisation is minimal and hence there is no further absorption below the surface of the material.Conduction welds are usually produced using low-power focused laser beams. This results in shallow welds with a low aspect ratio. In this work, high-power CO2 and YAG lasers have been used to produce laser conduction welds on 2mm and 3mm gauge AA5083 respectively by means of defocused beams. Full penetration butt-welds of 2mm and 3mm gauge AA5083 using this process have been produced. It has been observed that in this regime the penetration depth increases initially up to a maximum and then decreases with increasing spot size (corresponding to increase in distance of focus above the workpiece). Results of comparison of tensile strength tests for keyhole and conduction welds are shown.This process offers an alternative method of welding aluminium alloys, which have a high thermal conductivity.There are two laser welding mechanisms, keyhole mode and conduction mode. Keyhole welding is widely used because it produces welds with high aspect ratios and narrow heat affected zones. However keyhole welding can be unstable, as the keyhole oscillates and closes intermittently. This intermittent closure causes porosity due to gas entrapment. Conduction welding, on the other hand, is more stable since vaporisation is minimal and hence there is no further absorption below the surface of the material.Conduction welds are usually produced using low-power focused laser beams. This results in shallow welds with a low aspect ratio. In this work, high-power CO2 and YAG lasers have been used to produce laser conduction welds on 2mm and 3mm gauge AA5083 respectively by means of defocused beams. Full penetration butt-welds of 2mm and 3mm gauge AA5083 using this process have been produced. It has been observed that in this regime the penetration depth increases initially up to a maximum and then decreases with incr...

A concept for the application of augmented reality in manual gas metal arc welding

Abstract: The large problem to create manual welds of constant high quality results from missing optical information during the actual welding process. Due to the extreme brightness conditions in arc welding and the use of protective glasses, even experienced welders can hardly recognizedetails of the welding process and the environment. This paper describes a new research project for the development of a support system for the welder.

Rapid prototyping of 5356-aluminum alloy based on variable polarity gas tungsten arc welding: process control and microstructure

Abstract: This paper concentrates on rapid prototyping of a 5356-aluminum alloy based on a new deposition process of variable polarity gas tungsten arc welding (VPGTAW), and describes the microstructure and ...

Comparative evaluation of tungsten inert gas and laser welding of AZ31 magnesium alloy

Abstract: Welding of AZ31 Mg alloy was conducted using various welding techniques, namely, tungsten inert gas (TIG) welding with Ar shielding gas, TIG welding with He shielding gas, CO2 laser welding, and YAG laser welding. The results were comparatively evaluated in terms of weld bead formation and microstructural characterisation. It was found that TIG welding with both Ar and He gas shielding produced good welds without major defects. The penetration capacity can be improved using He gas shielding. Owing to their high energy density, CO2 and YAG lasers can produce weld beads having high aspect ratio. Among the four techniques used, the YAG laser produced the finest weld microstructure, whereas TIG with Ar gas shielding produced the coarsest microstructure. Shielding is a key factor controlling the O contents in the welds. The more effective the shielding provided the lower the O content in the weld. Hardness reduction in the weld metals and heat affected zones was observed for all the techniques owing to...

Effects of metal vapor on electron temperature in helium gas tungsten arcs

Abstract: In order to investigate the effects of metal vapor on the thermodynamic property of arc plasma in the welding process, electron temperatures in the pure helium plasma and in the helium plasma during welding in gas tungsten arcs (GTAs) were measured by using the laser scattering method. The experimental results showed that metal vapor led to a significant decrease in the electron temperature compared with that of pure helium GTA plasma. The temperature difference reached 6000 K in the arc fringe at the maximum.

Method for joining aluminum and steel

Abstract: PROBLEM TO BE SOLVED: To efficiently obtain a sound joining part by using arc welding without forming a fragile and thick inter-metallic compound layer in joining of dissimilar materials of an aluminum member 2a and a steel member 2b. SOLUTION: The method for joining the aluminum and the steel is constituted as follows. A solid wire made of an aluminum alloy, to which at least 3-15 wt% of silicon is added, is made as a welding wire 1. The aluminum member 2a, which is made of the aluminum or the aluminum alloy, and the steel member 2b, the surface of which zinc plating or aluminum plating or zinc aluminum alloy plating is applied to, are joined by pulse MIG welding. The joining part on the aluminum member 2a side is molten and joined. The joining part on the steel member 2b side is not molten but is joined by forming a thin inter-metallic compound layer. COPYRIGHT: (C)2004,JPO&NCIPI

Laser power coupling efficiency in conduction and keyhole welding of austenitic stainless steel

Abstract: Laser welding of thin sheets of AISI 304 stainless steel was carried out with high power CW CO2 laser. The laser power utilized in the welding process was estimated using the experimental results and the dimensionless parameter model for laser welding; and also the energy balance equation model. Variation of laser welding efficiency with welding speed and mode of welding was studied. Welding efficiency was high for high-speed conduction welding of thin sheets and also in keyhole welding process at high laser powers. Effect of pre-oxidization of the surface and powder as filler material on laser power coupling is also reported. The paper also discusses effect of microstructure on the cracking susceptibility of laser welds.

Robust Control of Pulsed Gas Metal Arc Welding

Abstract: A system is developed to control the pulsed gas metal arc welding process. To achieve controlled detachment of the droplet, the welding current is switched from a peak level to a background level to induce droplet oscillation. When the droplet moves downwards, the current is switched back to peak level. The combination of downward momentum of the oscillating droplet and increased electromagnetic force guarantees detachment of the droplet. Instead of adjusting duration of the background current, the waveform of the current is adjusted to control the melting rate of the electrode wire without having to change the transfer frequency. It is found that the dynamic model of the process depends on welding operational parameters, which vary with applications, and therefore it is unrealistic for operators to provide welding machines these parameters as inputs. Hence, welding operational parameters are considered as unfixed and their ranges are used to quantify the resultant uncertainty in the dynamic model. As a result, the process is controlled using a single algorithm at different operational parameters. Experiments verified the effectiveness of the system in overcoming two common variations in welding operational parameters, wire speed and contact tube-to-work distance.

Welding Characteristics of Aluminum and Copper Plate Specimens Welded by a 19 kHz Complex Vibration Ultrasonic Seam Welding System

Abstract: The welding characteristics of aluminum and copper plate specimens welded using a 19 kHz ultrasonic welding system with a complex-vibration welding tip were studied. The welding tip part vibrates in an elliptical or circular locus. The seam welding system uses a rotating circular disk welding tip and a shifting stage for continuous welding of the metal sheets. Using the complex-vibration system, metal plates of various thicknesses can be welded continuously at multiple positions with large and uniform welded areas and large weld strengths independently of the welding position and direction. The required complex-vibration amplitude is less than one-half of that of a conventional linear-vibration system. Aluminum-aluminum, aluminum-copper and copper-copper plate specimens were welded with weld strengths almost equal to the specimen strength.

Friction stir welding method

Abstract: Disclosed is a friction stir welding method of welding a butted portion of work pieces relatively easily and firmly with an improved finish after the butted portion is tack-welded. In the method, a plurality of work pieces are placed to be butted, a plurality of V-shaped grooves are intermittently formed along the butted portion, each of the grooves is tack-welded by using a welding material by TIG welding or MIG welding, deposits in the tack-welded sections are cut and removed so as to be substantially coplanar with a surface of the work pieces, and then friction stir welding is continuously performed over the entire length of the butted portion, and thus, the work pieces are joined.

Numerical and experimental analysis for solidification and residual stress in the GMAW process for AISI 304 stainless steel

Abstract: Gas Metal Arc Welding (GMAW) process was analyzed by combining a finite element thermomechanical model for temperature and stress with solidification model. Model prediction was compared with experimental data in order to validate the model. The effects of welding process parameters on these welding fields were analyzed and reported. The effort to correlate the residual stress and solidification was initiated, yielding some valuable results. The solidification process was simulated using the formulation based on the Hunt-Trivedi model. Based on the temperature history, solidification speed and primary dendrite arm spacing were predicted at given nodes of interest. Results show that the variation during solidification is usually within an order of magnitude. The temperature gradient was generally in the range of 104–105 K/m for the given welding conditions (welding power = 6 kW and welding speed = 3.39 to 7.62 mm/sec), while solidification speed appeared to slow down from an order of 10−2 to 10−3 m/sec during solidification. SEM images revealed that the Primary Dendrite Arm Spacing (PDAS) fell in the range of 101−102 μm. The range of predicted sizes was in agreement with the experimental values. It was observed that the average size of the PDAS was dependent upon the welding speed. The PDAS fell between 7.5 to 20 μm for columnar and 10 to 30 μm for equiaxed dendrites, for welding speeds between 3.39 to 7.62 mm/sec. When the welding speed increased, it was observed that the average size of the PDAS decreased, as the model had predicted. For grain growth at the Heat Affected Zone (HAZ), Ashby's model was employed, and the prediction was in agreement with experimental results. For the residual stress calculation, the same mesh generation used in the heat transfer analysis was applied to make the simulation consistent. The analysis consisted of a transient heat analysis followed by a thermal stress analysis. An experimentally measured strain history was compared with the simulated result. The relationship between microstructure and the stress/strain field of welding was also obtained.

Magnetically Impelled Arc Butt Welding of Hollow and Solid Parts

Abstract: Magnetically Impelled Arc Butt (MIAB) welding is mainly used in the automotive industry for butt welding of tubes and tubular parts 8–100mm in diameter and 0.8–6mm wall thickness. To extend the range of MIAB welding applications research work was conducted on different hollow and solid parts, special attention being given to welding of parts, the cross section of which is commensurable with of the active spot diameter of the rotating arc.

Mechanically assisted droplet transfer process in gas metal arc welding

Abstract: Gas metal arc welding has been generally accepted as the preferred joining technique due to its advantages in high production and automated welding applications. Separate control of arc energy and arc force is an essential way to improve the welding quality and to obtain the projected metal transfer mode. One of the most eVective methods for obtaining separate control is to exert an additional force on the metal transfer process. In this paper, the droplet transfer process with additional mechanical force is studied. The welding system is composed of an oscillating wire feeder. The images of molten metal droplets are captured by a high-speed digital camera, and both the macroscopic appearance and the cross-sectional pro®les of the weld beads are analysed. It is shown that the droplet transfer process can be signi®cantly improved by wire electrode oscillation, and a projected spray transfer mode can be established at much lower currents. By increasing the oscillation frequency, the droplet transfer rate increases while the droplet size decreases. In addition, the improvement in the droplet transfer process with wire oscillation leads to an enhancement of the surface quality and a modi®cation of the geometry of the weld beads that could be of importance for overlay cladding and rapid prototyping based on deposition by welding.

Hybrid laser-arc welding method with gas flow rate adjustment

Abstract: The invention concerns a hybrid arc-laser method for welding metal parts, such as a tube or tailored blanks by producing at least a weld joint between edges to be welded and by using a laser beam and an electric arc combined with each other so as to melt and subsequently solidify the metal along said edges to be welded. Said method consists in: (a) striking at least a pilot arc between an electrode and a hybrid welding head nozzle, said electrode being powered with electric current and being contacted with a first gas input in said hybrid welding head, said first gas having a gas composition capable of promoting sparking of the pilot arc; (b) transferring the thus sparked pilot arc to the edges of the part(s) to be welded; and (c) feeding said hybrid welding head with a second gas so as to obtain a protective gaseous atmosphere consisting of a mixture of the first gas and the second gas, said protective gaseous atmosphere being evacuated towards the welding zone by said hybrid welding head and protecting at least part of the welding zone during welding of the weld joint by combining the laser beam and the electric arc, the volume flow rate of the first gas (Q1) and the volume flow rate of the second gas (Q2) being adjusted such that: 0 < Q1 < Q2, preferably, 2 < Q2/Q1 < 55.

Control of exposure to hexavalent chromium and ozone in gas metal arc welding of stainless steels by use of a secondary shield gas.

Abstract: Previous work has demonstrated that the shield gas composition in gas metal arc welding can have a considerable effect on hexavalent chromium [Cr(VI)] concentration in the fume and on ozone concentrations near the arc. Normally a single shield gas is used. This paper describes a double shroud torch that allows used of concentric shield gases of different compositions. A solid stainless steel wire was used for welding. The double shroud torch used secondary shield gases containing small amounts of the reducing agents NO and C 2 H 4 . The Cr(VI) concentration in the fume and ozone concentration at a fixed point relative to the arc were measured and compared with results when using a single shield gas. Use of the reducing agents in secondary shielding using the double shroud torch was found to offer advantages for ozone concentration reduction compared with use in a conventional torch, but this was not found to be an advantage for reducing Cr(VI) concentrations.

Theoretical and Experimental Assessment of Chloride Effects in the A-TIG Welding of Magnesium

Abstract: Active fluxes that are deposited on the TIG torch path before alloy melting can significantly increase weld penetrations. Several mechanisms (arc constriction, surface-tension-driven flow) for the active-TIG or A-TIG welding process have been postulated. The A-TIG welding of magnesium is discussed here using a simple model for the surface tension over the weld pool, real-time monitoring data, and measured characteristics from the fusion zone region. The chlorides selected for this investigation incorporated simple-metal elements from different group numbers (LiiaCl, CaiiaCl2, CdiibC12, PbivbCl2 and CeCl3) so that correlations between their chemistry and their effects during A-TIG welding could be established. Video recordings showed that chlorides intensified the visible light emission from the arc and affected its profile. Measurements during arc welding at a constant current demonstrated that all chlorides increased the arc voltage (thus the heat input) and the arc temperature. A-TIG weld cross sections revealed that chlorides increased fusion zone dimensions, as could be expected from greater heat inputs. While calculations suggested that surface tension might have altered weld pool circulation, specially designed experiments with low-energy-density laser beams were inconclusive. Among all tested chlorides, cadmium chloride was the most effective during A-TIG welding due to the high first ionization potential of cadmium, which correlated to several observations such as: low chloride melting, boiling, and dissociation temperatures, high welding voltage, augmented arc temperature, increased fusion zone penetration, and greater depth-to-width ratio.

Selecting parameters for GMAW using dimensional analysis. Regression and dimensional analysis of experimental data established relationships between welding parameters and process variables

Abstract: A method for analyzing gas metal arc welding procedures was developed to select welding parameters that lead to a desired operating condition. Analytical relationships between welding parameters and process variables were established by regression and dimensional analysis of experimental data. This data was obtained from a detailed GMA welding experiment in which the welding parameters were precisely controlled and the process variables precisely measured and correlated. Using nondimensional variables to correlate experimental data, accurate analytical relationships between welding parameters, arc process variables, and bead geometry were obtained. The analytical relationships for bead geometry extended the work of previous researchers by introducing a nondimensional mass transfer number and demonstrating the dependence of bead geometry on mass transfer as well as heat transfer. These relationships were used to identify a range of stable welding parameters and to find the welding parameters needed to ensure process constraints were met. Specific welding parameters were found by controlling arc length and weld bead geometry to ensure arc stability, adequate weld bead size, and adequate joint penetration.

Production and use of welding filler metal

Abstract: A method for welding an article includes producing welding filler metal by the steps of furnishing a powder of a welding-filler-metal composition, preferably a titanium aluminide or a nickel-base superalloy, providing a continuous casting mold having a welding-filler-metal diameter, and melting the powder into a top of the continuous casting mold, while withdrawing a continuous length of the welding filler metal from a bottom of the continuous casting mold. The melting is preferably accomplished using a laser to achieve a concentrated heating zone. The welding filler metal is used to weld an article, by applying an overlay layer or by joining articles together.

Explosion Welding of Steel with Aluminum

Abstract: An analysis is made of the main kinematic parameters that determine the beginning of weld formation near the lower boundary of the region of explosion welding. The welding of aluminum with steel is considered. The paper reports experimental results for the flow of material in the gap under oblique collision of metal plates. Key words: oblique collision, particle flow, explosion welding.