Mechanism of Penetration and Bead Shape in Electron-Beam Welding

Studies on Electron-Beam Welding, 4

Abstract

In view of the lack of knowlege on the reason for the unique shape of bead and penetration in electron-beam welding, experimental and theoretical studies were performed on the mechanism of penetration and bead formation and the following conclusions were obtained
(1) The heat source in electron-beam welding is not a point source on the specimen surface, but a line source vertical to the specimen surface at the bead front.
(2) A wedge-shaped hole (deep crater) is formed by electron-beam in front of the molten metal and works as the heat surface. As the electron-beam passes on, this hole is filled up successively with molten metal.
(3) The wedge-shaped penetration is always directed parallel to the beam direction regardless of the inclination or position of a specimen.
(4) A wooden bowl-shaped bead top, formed near the surface of the specimen, is made by the heat flow from the molten metal which has been pulled up backward from the wedge-shaped hole.
If the beam happens to burn through the specimen with the molten metal flowing down, a wooden bowl-shaped bead top is no more seen.
(5) The width of weld bead can be predicted by the theory of heat flow. Experimental equation for the bead width (w) is given by
ω=k₁{a×30/√(C×ρ×Tm+H)-2×Tm×K/(C×ρ×Tm+H)}
(6) The penetration of wedge-shaped bead is not explained by the above equation. However, experimental equation for the penetration (p) is given by
p=k₂(C×ρ×Tm+H)^0.5×(1-K⁴)