NIF laser diodes reduce stress in metal 3D parts

This image shows the process of building and annealing a rectangular block of 316L stainless steel. The first and second panels are the focused scanning laser melting the powder layer into the underlying part. The third panel is the diode turning on and illuminating the surface of the part to heat and anneal it. The last panel is right after the diode turns off, showing the block is at high temperature (more than 950°C).

In 3-D printing, residual stress can build up in parts during the printing process due to the expansion of heated material and contraction of cold material. This can generate forces that can distort the part and cause cracks that can weaken or even tear it to pieces, especially in metals.

Researchers at LLNL and the University of California are addressing the problem by using laser diodes to rapidly heat the printed layers during a build.

The new technique, described in a paper released online by the journal Additive Manufacturing, resulted in the reduction of effective residual stress in metal 3D-printed test parts by 90%. The technique enabled researchers to reduce temperature gradients and control cooling rates.

The approach is an offshoot of a previous project in which laser diodes, developed to smooth out lasers in NIF, were used to 3D-print entire metal layers in one shot. It bests other common methods for reducing residual stress in metal parts, such as altering the scanning strategy or using a heated build plate.

The project was funded through the Laboratory Directed Research and Development (LDRD) program.