Yoshihiro Tsujimura

Dynamic Behavior of Metal Vapor in Arc Plasma during TIG Welding

In the present paper, the mechanism of metal vapour in arc plasma is discussed through the dynamic observation of spectra of helium, chromium, manganese and iron during stationary TIG welding of stainless steel. Wavelengths from 400 nm to 700 nm are observed by a monochromator with a diffraction grating. Radiation from the arc is sent to the monochromator through optical lens and spectroscopic images are captured with 500 fps by a high-speed digital video camera. Spectra of metal elements exist locally in the arc plasma due to the dependence on plasma temperature, and also the intensive region of each metal spectrum depends on the kinds of metal elements. Most part of metal vapour produced from the weld pool surface is carried on the cathode jet and then swept away towards surroundings of the arc. However, if the driving force like diffusion in plasma is large, some metal elements can get across the cathode jet and then can be carried on the circulation flow towards the tungsten electrode.

A Numerical Model with arc length variation of welding arc with constant voltage power source

In the present paper, Tungsten Inert Gas (TIG) arc with Constant Voltage (CV) power source is modelled if arc length changes. And TIG arc with Constant Current (CC) power source is also modelled if arc length changes. The TIG arc is assumed on base material of water-cooled copper. For the CV power source, maximum temperature of arc plasma and arc current increase with decrease of arc length. For the CC power source, arc voltage changes but maximum temperature of arc plasma is almost constant in spite of change of arc length. Arc power increases with decrease of arc length for the CV power source. On the other hand, arc power decreases with decrease of arc length for the CC power source. For the CV power source, arc power changes largely if arc length changes. However, for the CC power source, arc power changes little if arc length changes. Heat input from welding power source is more stable using a CC power source than a CV power source at TIG welding with a change of arc length.

Nitrogen absorption phenomenon of GTA welding with nitrogen-mixed shielding gases: effect of plasma characteristics on nitrogen content in GTA welded metal

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapour, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.

Influence of plasma characteristics on nitrogen mixing into shielding gas in helium gas tungsten arc welding

The influence of welding condition on the mixing of atmospheric nitrogen into the arc plasma in helium gas tungsten arc welding was analysed by numerical simulations. In order to evaluate the effects of the convection flow and the diffusion on the nitrogen mixing phenomenon, the distributions of the Peclet number were used. Elongation of the electrode length has low impact on the decrease of shielding gas concentration because the convection flow becomes dominant in this area, which indicates higher Peclet numbers. Meanwhile, nitrogen diffusion increases in the plasma area with a temperature of about 10,000 K, so that elongation of the arc length leads to a remarkable decrease of shielding gas concentration. Additionally, the impact of convection flow increases in the arc centre area where high-velocity plasma jet exists, and the shielding gas concentration tends to rise owing to higher welding current in the condition of sufficient shielding gas flow rate.