Bringing water soluble supports to powder based additive manufacturing
Facilitating post-processing of printed parts using multi-material printing
To many, 3D-printing is still an almost magical technology that can create objects seemingly out of thin air, much like the replicators in Star Trek. And indeed, with proper design, almost ready-to-use parts can be pulled directly from a hobbyist fused deposition modeling (FDM) printer after the print run is finished. Though more often a significant amount of manual effort is needed to make the part usable, and a lot of this is support removal.
Support structures in 3D printing are used to overcome some of the technology shortcomings. For instance, in FDM supports are used when large gaps need to be bridged. In this scenario the support material is used as a base for the extruded liquid polymer and offers it the time to stiffen up before dropping. In stereolithography and laser powder bed fusion supports are also used to mitigate the stresses associated with the solidification of the material. Here the support acts as an anchor to take us these stresses, and in so doing, prevent warping of the final part. Support material can also be used to contain liquid material, as if the case in resin jetting technology in the example below. In this case the support material can also be used to increase the definition of the final parts.
As supports are an integral part of 3D printing, and the removal is a hassle, it is not surprising that in the additive manufacturing (AM) industry alternate support strategies have been devised. In industrial FDM machines, such as those of Stratasys, a secondary print head depositing water soluble polymer is a common solution to minimize manual support removal. This technology is now even available on some consumer grade machines, showing a perfect example of functional multi-material printing, and has expanded to metal printing via the FDM based Desktop Metal technology.
In other AM technologies we are still waiting for the revolution of automatic support removal through multi material printing. For those technologies engineers have instead turned to optimizing design and print orientation as these parameters play a significant role in the amount of support needed. In some cases, clever design can be used to eliminate the support all together and even minimize post machining. This often results in the self-supporting organic shapes we’ve come to love in 3D printing. But for industrial applications function often dictates large parts of the design, and support cannot be avoided. In that case engineers take support removal into account while designing parts. Even so this limits the design freedom that AM is lauded for. Even in my own limited industrial additive manufacturing experience I’ve come across way more designs that could not be printed as support removal was going to be impossible. These typically were parts where internal features were critical to their function, and design strategies could not be used to make these completely support free. In some cases, especially with parallel channels, even after printing the part successfully without support it was considered a frustrating failure as the channels could not be cleared for powder stuck internally.
Hence, one of the first things that came to mind when I joined Aerosint is that maybe, just maybe, selective powder deposition could fill this need. The selective deposition technology developed by Aerosint can easily deposit a secondary material, such as salt or polymer, in a powder bed otherwise consisting of metal.
In the most common metal AM technology, Laser powder bed fusion (L-PBF) this is not an ideal solution. Of course, polymers cannot be used here as they have no chance of withstanding the temperatures associated with liquid metal. Salts, on the other hand, have been used in the construction of water-soluble casting cores, and hence might be a potential material to fill up internal cavities to support the melt pool somewhat. Especially if this sale is mixed with ceramic powder the salt itself might be melted and form an in-situ soluble core. Though this would be limited to metals with a lower melting temperature, such as the common L-PBF aluminum alloys, and would also require some R&D as to develop parameters for the salt cores and salt supported aluminum layers.
The most interesting opportunity, however, might be in binder jetting. There you neither have the high temperatures in the powder bed as associated with L-PBF, not the high thermal stresses that cause warping. Furthermore, you typically want to remove unnecessary material before thermal processing. As with the fine internal features, where powder removal was an issue in the L-PBF parts I encountered in the past, powder removal could be an issue in binder jetting. But if this powder is water soluble, this becomes a non-issue. Likewise the selective powder deposition technology could be used in binder jetting to duplicate the support strategy Desktop Metal employs in their FDM based technology. Depositing a fine layer of ceramic or salt at strategic locations in the powder bed would result in a support structure that can be sintered along with the main part, supporting it during the thermal process, but that can be just plucked away after the part is fully densified.
In short, selective powder deposition is more than just a tool to make multi-material parts but can also bring automatic support removal to some of the more popular industrial AM technologies around.
This is the seventh article in a series of “one-pagers” that each aim to explain (as briefly as possible!) a different innovative application for our selective powder deposition technology. To read the latest, be sure to follow us here on Medium, LinkedIn, Facebook or Twitter, and don’t hesitate to contact us if you’re interested in learning more about our technology.
