1991 Volume 9 Issue 3 Pages 348-354
This paper describes the effect of molten metal behavior on melting process and spiking phenomenon in electron beam welding. X-rays generated as a consequence of beam-metal interaction were detected at specific sites of 3 mm in length along penetration to clarify the melting process for various beam focussing conditions and welding speeds. Behavior of molten metal flow was also observed using high speed cinecamera simultaniously. JIS SM 50 A steel, Fe-10% Mn alloy and Fe-20% Mn alloy were used as base metals to investigate the effect of vapor pressure on melting process.
Results obtained were as follows.
(1) Spiking phenomenon was caused by an intermittent melting of base metal depending on the fluctuation in morphology of beam cavity.
(2) Spiking was suppressed with an increase in Mn content involved in the base metal, since the beam cavity was stable and always clear of molten metal during welding by high pressure Mn vapor.
(3) The front wall of the beam cavity was melted almost continuously for upper focussing condition, whereas it was melted intermittently for down focussing condition due to the periodical flow of the molten metal, resulting in more probable occurrence of acute spiking.
(4) Spiking was more likely to occur with a decrease in the welding speed under the same penetration depth, since the electron beam could drill the bottom deeply for low welding speed.
(5) The periodical flow was caused by natural vibration of the molten metal or high voltage power ripple depending on the amount of the molten metal around the beam cavity.
