A mathematical model for deep penetration laser welding has been developed that
considers only main phenomena. A moving linesource describes the net energy
input given by the difference between laser power entering the keyhole and
evaporation loss. Energy flow continuity yields the dependence of welding speed
on the wall temperature of the keyhole. Since it is generally assumed that the
keyhole is held open by the vapour pressure, a second condition for the keyhole
wall temperature is obtained.