Shinji Kodama

A Mathematical Model of Short-Circuiting Transfer in the High-Speed Oscillating MAG Process Development of Automatic MAG Welding Machine with Arc Sensor and its Application to Field Welding of Gas Pipelines

This paper describes an arc sensor system for automatic MAG welding. Based on conventional mathematical models of spray transfer, a new arc sensor model of short-circuiting transfer in the high-speed oscillating (10 Hz–50 Hz) MAG process has been developed. The simulation results of short-circuiting transfer behaviour agree with the experimental results. An optimisation of the oscillating frequency, for the short-circuiting frequency, sustains to improve the sensitivity and reliability of the arc sensor. The arc sensor system based on this principle enables to keep practical accuracy for seam tracking at short-circuiting metal transfer condition, and the automatic welding machine with this sensor was applied to field welding of gas pipelines.

Development of Stainless Steel Welding Wire for Galvanized Steel Sheets

Galvanized steel sheets are widely-used in the construction and automobile industries to provide structural members with high corrosion resistance. When galvanized sheets are welded, zinc near a weld molten pool evaporates. As a result, the corrosion resistance is deteriorated and repair coating treatment is required after welding. The use of austenitic stainless steel welding materials with suitable ductility and high corrosion resistance appears to be beneficial. However, the conventional welding materials have such problems that zinc liquation cracking is likely to occur in the weld metal, a lot of welding spatter is generated and solidified slag is difficult to remove from the weld bead. To solve these problems, an austenitic stainless steel flux-cored wire was developed. Susceptibility to zinc liquation cracking was improved by increasing the ferrite content in the weld metal through the adjustment of Ni and Cr contents. The problems of the removal of solidified slag and the generation of welding spatter were solved by reducing the TiO2 content in flux to a level lower than that for a commercial wire. Thus, the weld appearance was improved, making repair coating treatment after welding unnecessary. The joints welded by the newly-developed welding material exhibited suitable mechanical properties and satisfactory corrosion resistance evaluated by salt spray testing.

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.