Fundamental Study of High Power Electron Beam Welding (Report 2)

Effect of Beam Oscillation on Porosity Elimination

Abstract

Electron beam welding has much advantage of thick material such as high quality, low distortion and short welding time by one side small pass welding. But one side deep penetration characteristics happen to make welding defects porosity in center of weld materials. For this porosity repair welding is sometimes difficult because of narrow melting width so that porosity free welding is required.
In this report beam oscillation technique was investigated to avoid porosity in thick steel plate (up to 100 mm).
Parameters of beam oscilaltion consist of frequency, amplitude and oscillation pattern. Welding was carried out to thick steel plates in horizontal position and one side welding.
The results can be summarized as follows;
1) Low welding speed was effective to eliminate porosity.
2) Optimum conditions of beam oscillation studied were from 500 to 2000 Hz in frequency, from 0.5 to 2.0 mm in amplitude and sine, cycle or ellipse in oscillation pattern.
3) Bead width was increased by excess amplitude to parpendicular direction to welding direction so that solidification crack occured along centerline of weld metal.
4) Beam oscillation was avilable to eliminate porosity but under optimum oscillation condition bead shape of reverse side was irregularly underfilled.
5) For thick steel plate the range of optimum welding condition to eliminate porosity by beam oscillation technique was small and beam oscillation parallel to welding direction was effective to eliminate porosity.