Through the report 1, it was revealed that humping bead formation was caused by the instability of capillary liquid metal at the weld surface. In this report, effect of beam current on humping bead formation was investigated. And the formation mechanism of unstable capillary liquid metal was discussed. The obtained results were as follows.
1) Humping bead formation ranges were classified into high and low beam current ranges according to the formation mechanism.
2) In high beam current range, the formation of humping bead was cuased by the large amounts of liquid metal that formed the unstable capillary liquid mead above surface.
3) In low beam current range, the formation of humping bead was caused by the undercut that formed unstable caipllary liquid metal.
4) Undercut was formed by the reduction of the wetting between liquid metal and the wall of electron beam gouge.
5) In low beam current range, the increase of beam current was apt to form the humping bead due to the formation of undercut.
6) In high beam current range, welding with a suitable depth of groove prevented from humping bead formation due to the reduction of liquid metal above surface.
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