Modulated Nd : YAG laser welding of Ti-6Al-4V

Modulating the output of Nd : YAG laser sources has been evaluated as a technique for producing high quality welds in titanium alloys. Welds with high internal quality were produced when a square wave form was used with a modulation frequency >= 125 Hz and a duty cycle of 50%. Undercut present in the weld profile can be reduced if the correct combination of modulation amplitude and laser beam focal plane position are used. High speed observation and subsequent Fourier analysis of the vapour plume and keyhole behaviour have shown that they both exhibit the same periodic tendencies. With the correct parameters, an oscillating wave can be set up in the weld pool, which appears to manipulate the vapour plume behaviour and hence reduce porosity formation.