Shielding gas

About: Shielding gas is a research topic. Over the lifetime, 6697 publications have been published within this topic receiving 58668 citations.

Depth of penetration in gas metal arc welding

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.

Pulse arc welding method

Abstract: In pulse arc welding, a welding wire (1) is fed at a rate corresponding to a current average set value (Iar). An arc (3) is struck by passing a peak current (Ip) for a peak period (Tp) and a base current (Ib) for a base period (Tb), where the peak and base periods (Tp,Tb) make one pulse period (Tf). The arc (3) transfers a droplet (1b) from the wire (1). The peak period (Tp) includes a first peak period (Tp1) for a first peak current (Ip1) and a second peak period (Tp2) for a smaller second peak current (Ip2). The first peak period (Tp1) and current (Ip1) are determined so that an arc anode point (3a) is formed at the top of the droplet (1b) even if the shield gas mixing ratio deviates from a standard value. The second peak period (Tp2) and current (Ip2) are determined so that one droplet (1b) is transferred during every pulse period (Tf), and beads are formed with no undercuts.

Plasma plume oscillations during welding of thin metal sheets with a CW CO2 laser

Abstract: An analysis is presented of the oscillations of keyhole pressure and plasma radiation emitted during welding with a continuous wave (CW) CO2 laser. Welding was done with a CW CO2 laser, Photon Sources VFA 2500, operating at the power of 1.75 kW. The welded materials were mild and stainless steel sheets, 0.8-2 mm thick. The shielding gas was argon or helium. Oscillations of plasma radiation were registered in monochromatic or broad band radiation with the use of a photomultiplier or photodiode and pressure variations with a microphone in the frequency range of 20-2×104 Hz. It has been found that the optical signal from the plasma plume is closely connected with the acoustic signal and that the source of the acoustic signal is the pulsating movement of the plasma plume. Spectral analysis of the measured oscillations shows differences in power spectra depending on the welding conditions. Generally, two intrinsic frequency peaks in the range of 0.5-4 kHz are always present but the amplitude, frequency and width of the peaks depend on the material and welding conditions. The results show that the optical and acoustic signals emitted during the welding process can be useful for process monitoring. The behaviour of the observed oscillations is characteristic for deterministic chaos. Considerable regularization of the process was observed as an effect of modulation of the laser beam. The modulation factor (Pmax -Pmin )/Pmax was equal to 0.2 and the modulation frequency was 2 kHz. In this case, the intense peak corresponding to the modulation frequency was observed in the power spectrum together with smaller peaks corresponding to the harmonic frequencies.

Numerical Modeling of Enhanced Nitrogen Dissolution during Gas Tungsten Arc Welding

Abstract: Weld-metal nitrogen concentrations far in excess of Sieverts-law calculations during gas tungsten arc (GTA) welding of iron are investigated both experimentally and theoretically. A transient, threedimensional mathematical model has been developed to calculate the residual nitrogen concentrations during GTA welding. This model combines calculations for the plasma phase with those for nitrogen absorption and for the transport of nitrogen by convection and diffusion in the weld metal and diffusion throughout the weldment. In addition, the model takes into account the roles of turbulence and the nitrogen desorption reaction in affecting the residual nitrogen concentration in the weldment. Autogeneous GTA welding experiments in pure iron have been performed and the resulting nitrogen concentrations compared with the modeling results. Both experimental and modeled nitrogen concentrations fall in a range between 2.7 and 4.7 times higher than Sieverts-law calculations at a temperature of 2000 K. Modeled nitrogen concentrations correlate well with the experimental results, both in magnitude and in the general trends, with changes in the travel speed and nitrogen addition to the shielding gas.