Relation between Beam Properties and Shape of Fusion Zone in Electron Beam Welding (Report I)

Abstract

It has been already reported that the locally expanded fusion zone in electron beam welding of steel, which often accompanies with vertical cracks, closely relates with the focal point of electron beam. Theree fore the properties of the electron beam were measured by an electrical method and the AB test, and relation between these results and the shape of fusion zone were investigated. The results are summarized as follows;
(1) Beam power density distribution is of trapezoid mode at the lens side from the focal point obtained by the AB test and gaussian mode at the other side.
(2) Width of the neck portion of penetration is mainly predominated by the beam diameter.
(3) The locally expanded fusion zone is formed at large ratio of the width at the surface to the neck portion of the fusion zone under large penetration depth.
(4) Observations using a high speed camera indicate that the locally expanded fusion zone is caused by the secondary melting process due to the stagnation of the molten metal flow.
(5) For prevention of the locally expanded fusion zone, sideway beam oscillation of small amplitude is usefull.