A novel approach to simulating the dominant dynamic processes present durin
g concentrated energy beam welding of metals is presented. A model for the
transient behaviour of the front keyhole wall is developed. It is assumed t
hat keyhole propagation is dominated by evaporation-recoil-driven melt expu
lsion from the beam interaction zone. Results from the model show keyhole i
nstabilities consistent with experimental observations of metal welding, me
tal cutting and ice welding.