片面自動溶接における終端割れ防止に関する研究(第2報)

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Recently one sided automatic welding has widely been prevailed in the assemble stage of Japanese shipyards. As one of the problems of welding procedure, as well as any other welding techniques, cracking which sometimes occurs near the end of weld, has become an important problem. The authors have proposed the calculation technique in the seam welding. The most significant feature of the method differing from the ordinary welding thermal stress analysis is that the conditions of calculation are simulated to be those of more realistic welding procedures. Then, the following assumptions are imposed in order to calculate stress and strain during welding. (1) Before welding, specimens are connected by tack welds are prepared edges and free boundaries. (2) Molten region containing arc tip is free from stress. (3) After the arc passed by, the plates are connected by solidifying of the molten pool, that is, free prepared edge changes to supported one as temperature is cooled down. (4) When the arc passed through a tack weld, it should be melted away and free from stress. In order to calculate the thermal stress analysis during welding, firstly we solved un-stationary heat conduction problems and obtained temperature distribution during welding. Based on the calculated temperature distribution, we analysed uncoupled thermal stress problems by using the finite element method, and conclusively showed that one of the main causes of end cracking is the transient tensile stresses generated near the end part of weldment when the stress re-distribution is taken place due to the melting of the last tack weld. To endorse the numerical calculation by the proposed method, experiments are carried out and it is confirmed that the method could be applicable to this kind of transient welding stress-strain state with time depending varying boundary conditions.
社団法人日本船舶海洋工学会の論文

片面自動溶接における終端割れ防止に関する研究(第2報)

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