Etching technology increases the absorption capacity of powders for 3D printing of metals

Researchers at Lawrence Livermore National Laboratory (LLNL) and their academic partners have developed a technique that improves the optical absorptivity of metal powders for 3D printing.

The method, known as Holographic Direct Sound Printing (HDSP), is based on the creation of nanoscale surface structures on metal powders such as copper and tungsten. These structures enable up to 70% higher absorption of laser energy during the laser powder bed fusion (LPBF) process. A special wet chemical etching process creates fine grooves and textures that optimize energy transfer without compromising the material properties of the metals.

“Currently, with standard commercial laser-based machines, high-quality pure copper metal AM is generally considered infeasible,” said co-lead author and LLNL materials scientist Philip DePond. “Our method combines the effects of traditional surface treatments [that increase absorptivity] but doesn’t compromise the purity or material properties of copper that make it desirable — namely its high thermal and electrical conductivity. More fundamentally, we showed that laser-powder interactions extend to regions beyond the melt pool. This has been shown in simulations, especially those of high-fidelity done at LLNL, but not really detailed experimentally.  We demonstrated that those interactions exist and can be beneficial to the process.”

A key advantage of the new technology is the increased printing speed and lower energy consumption. In tests, high-purity copper structures could be produced with less than 100 J/mm³ of energy consumption, which corresponds to around a third less energy than conventional processes. This not only reduces operating costs, but also minimizes the environmental footprint of production.

“In a broad sense, we are enabling the printing of copper without the risk of damaging the AM system itself,” DePond explained. “The process parameter window becomes wider as well, which allows a wider variety of scanning conditions to be explored, which often are needed when printing complex geometries. Finally, a handful of machine manufacturers have even gone the great lengths of creating entirely new machines to process copper and other highly reflective materials. These turn out to be nearly double the cost of a traditional machine, so the barrier of entry to printing these materials is prohibitively high.”

In addition, the precise control of acoustic holograms enables the simultaneous production of multiple objects at different positions in the print space. This opens up new areas of application, for example in medical technology for the production of complex fabrics or in aerospace for the repair of sensitive components.

“This method enables even commercial machines of fairly low laser power output to print copper, thus democratizing the process and providing access to a wider community,” Energy Security Program leader Dan Flowers said, adding “From heat exchange to catalysis, more efficient printing of copper supports development of many clean energy and decarbonization technologies. The LLNL community and our low-carbon energy mission stand to benefit from this capability.”

With this innovation, LLNL is once again positioning itself as a pioneer in the further development of additive manufacturing technologies by enabling more sustainable and efficient production processes.