UC Davis

Additively manufacturing metal parts through laser powder bed fusion (LPBF) is of growing interest to many welds, ranging from medical to aerospace. Typical LPBF systems use a single laser to weld the metal powder, which leads to sharp temperature gradients as metal rapidly melts and solidifies. However, due to the extreme heating and cooling cycles experienced during LPBF, the resulting parts are often plagued with internal residual stresses which can cause warping and a deviation from the original design specifications. This work explores an in situ method of mitigating residual stress by using a dual laser systemwhere a secondary diode laser projects uniformly over a large area to heat the current top layer. With the ability to determine the timing, duration, intensity, and periodicity of the secondary laser projection, the user is allowed full control of the thermal history of their part throughout the build. This selective heating of the welded surface pattern reduces the temperature gradient between layers, thus reducing the residual stress. The capability to control grain growth in LPBF using the secondary surface-heating laser is also explored in this work. Such a system allows the user to control the solidication time, thus controlling the transition through various phases and ultimately the resulting microstructure. This secondary surface heating source provides an alternative to other heat treatment methods such as post annealing and build plate heating. Directly heating the topmost layer allows for temperature control within the region most affected by the welding.