2014 Volume 32 Issue 3 Pages 156-163
The high frequency electric resistance welding (hereinafter referred to as the HFW) pipes and tubes are being used for high-grade line pipes. To cope with high need for weld seam reliability, the clarification of welding phenomena is important. To clarify the HFW phenomena, at first, we have developed HFW simulation system by using electro magnetic, heat conductive and elastic plastic finite element analysis (FEA) methods. A continuous electromagnetic and heat conduction analysis was conducted by subdividing the cross section containing the electrode and the welding point into a large number of two-dimensional models. The temperature distribution in the HFW pipe welding procedure can be successfully simulated by this system. The deformation behaviour in which a portion of the weld rises to the inner and outer surfaces as the result of pressurisation from welding rolls can be analysed with this system. Secondly, HFW phenomena have been visualized dynamically using high-speed video camera technique. The high-intensity part visualized by high-speed images has a good accordance with the temperature distribution of FEA result. High-speed images have visualized the dynamic phenomena of molten metal flow and sputtering of molten steel. Very rapid movement of molten metal in the forming direction along the welding line was observed at V-convergence point with a speed of 2m/s∼50m/s, which was far faster than welding speed. This rapidly-moved molten metal generated the peculiar sputtering which spread the molten metal particles as describing an arc perpendicular to the welding line. These phenomena were assumed to be caused by the electromagnetic force concerning the molten steel at V-convergence point.