Effect of inter-layer dwell time on distortion and residual stress in additive manufacturing of titanium and nickel alloys

In situ measurements of the accumulation of distortion during additive manufacturing (AM) of titanium and nickel base alloys are made as a function of changes in dwell time between the deposition of individual layers. The inclusion of dwell times between individual layers to allow for additional cooling during the deposition process is a common technique utilized in AM processes. Experimental observations made here in Inconel^® 625 laser deposited builds show that the accumulation of distortion occurs with a consistent trend over the course of the builds and both distortion and residual stress levels decrease with increasing dwell times from 0 to 40 s. On the other hand, changes in dwell time for the Ti-6Al-4V laser deposited builds have a significant impact on the accumulation of distortion, with shorter and no dwell times minimizing the distortion accumulation and even reducing it over a range of build heights. These shorter dwell times also produce builds with significantly lower residual stress and distortion levels, particularly when no dwell time is applied. Based on these results, the materials to be deposited should be considered when developing appropriate path planning schedules.