2012 Volume 30 Issue 2 Pages 116-124
In fusion welding, gravity makes molten metal flow downward and it sometimes causes irregular shaped weld bead and weld defects such as undercut and overlap. This problem makes high-quality and high-deposition rate welding difficult especially in horizontal and overhead positions.
To solve this problem, Dr. Manabe and others have proposed the basic concept of "Electromagnetic Controlled Molten Pool Welding Process (ECMP)", which controls the molten metal flow and the bead shape by using upward electromagnetic force, which is generated by giving the magnetic field perpendicular to the unidirectional current in the molten pool. Based on this concept, the ECMP method which uses magnetic field coaxially to the welding torch was already put into practical use in horizontal and vertical position welding with a high deposition-rate.
To expanding the application of ECMP process, we have paid attention to a penetration welding without backing material represented by pipe welding, gravity causes a serious influence on the penetration bead shape which determines the weld joint quality in many cases. For this reason, if the penetration bead shape can be controlled by ECMP process, the industrial application will be expanded. So, we propose a new ECMP method using the opposed magnetic poles straddling the weld line, and the possibility of this ECMP method was examined for overhead and flat position welding.
As a result, in flat position welding even under excessive heat input condition which molten metal hangs down and undercut occurs, the molten metal was lifted up by the upward electromagnetic force and the penetration bead shape was improved remarkably by adjusting the conditions of magnetic field and wire heating current, etc. Furthermore, in the most difficult overhead position welding, we could prevent undercut defect by adjusting the above-mentioned conditions and welding torch angle, and we could obtain proper penetration bead shape.