NASA JPL team shows results of porous metal printing PBF process

Scott Roberts, Materials Technologist IV at JPL (NASA’s Jet Propulsion Laboratory) and Co-Founder at Metallic Glass Consulting, LLC, and other colleagues at NASA JPL have published their first of several papers on a very interesting additive manufacturing process that they’ve been working on for the past five years: porous metal printing. The results in terms of controlled part porosity for various alloys were just published in a paper titled “Experimental and analytical investigations of AlSi10Mg, stainless steel, Inconel 625 and Ti-6Al-4V porous materials printed via powder bed fusion“.

“It’s great to finally be able to start talking about this technology because we’ve now spent several years developing new applications,” Douglas Hoffman said on LinkedIn. “The current paper gives an overview of how to de-optimize the laser in powder bed fusion to create custom porosity, which can be printed alone or embedded in solid metal.”

As explained in the study, for each metal alloy, there is a zone where the porous metal is both rigid and permeable, allowing the creation of mechanically robust structures from a single powder. The work was originally developed to create pumped two-phase heat exchangers but has since been used for loop heat pipes, catalysts, filters, capillary-driven plant watering in microgravity, isothermalizing printed optics, fluid wicking samplers, ice anchors, and even drilling bits that can sample gasses in-situ.

“It’s such a neat technique that we’ve found all sorts of applications where strategically adding internal porosity to a part has benefits,” continued Hofmann. “JPL has numerous patents filed with interesting applications for this technology.” Demos shown include the front and back of the NASA/JPL coaster printed with solid and porous metal that wicks away all moisture from your cup (image below).

It is particularly interesting that in this study on porous metal printing porosity represents a significant asset while for two decades it has been considered primarily a challenge to deal with in order to ensure PBF printed parts that would be “as dense as traditionally manufactured ones”. Binder jetting, a process that by its very definition produces porous parts has evolved to deal with porosity through infiltrations and subsequently through the use of specific binders. However, it had already shown some potential for leveraging controlled part porosity, especially in ceramic and sand binder jetting processes. Until now, however, controlled porosity has never been explored in depth in an L-PBF process but this study gives a very clear indication of how engineers need to rethink the way parts are made to fully exploit the possibilities of AM.

Porous metal printing also enables patterns of porous and solid material, demonstrating multifunctionality in a single print. More papers on heat exchangers will be coming soon. “What I find appealing about this method is that the parts are totally unique from a property and function perspective and they can’t be put through the standard qualification process for AM. The parts are multifunctional and can’t be replicated with other techniques,” Hofmann concluded.

Authors of the study also include Ryohei Gotoh, Ben Furst, Scott Roberts, Stefano Cappucci, Takuro Daimaru, and Eric Sunada.