Published on 22 January 2013
In the early seventies, during the now historic Skylab flights, electron beam welding experiments were carried out to establish the effect of a zero gravitational welding environment on weld quality and microstructure. Back on earth identical welds were made with exactly the same equipment. NASA wanted to compare them.
TWI has many years' experience in the study of weld solidification structures and was one of the few overseas organisations invited by NASA to be consultant in the Skylab experiments.
In Skylab the chamber was vented to the space environment and welding carried out at a pressure of 10-4 torr. So in the absence of terrestrial gravitational forces convection was suppressed. A comparison of welds made in Skylab and on earth allowed deductions to be made on the role of convection in weld solidification.
Segments of partial and full penetration welds in three materials were received by TWI for metallographic examination. Bead shape, surface rippling, grain size, dendrite size and segregation comparisons were performed. Small differences in structure were noted but these may have been attributable to an astigmatic beam in the Skylab. The tests revealed that no outstanding differences in solidification pattern were evident between the space and earth welds.
This allowed NASA to conclude that convection does not play a major role in weld pool mixing and that welding in conditions of zero gravitational force posed no difficulties for the future.
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