The metal 3D-printing space continues to grow rapidly, with one of the most recent entrants offering a form of bound-metal 3D-printing technology that may offer significant advantage of other similar technology from companies like Desktop Metal and Markforged.
To learn about Rapidia’s so-called “water-based” metal 3D-printing process, we spoke to Production Manager Artem Bylinskii, who was able to go into detail about how removing the otherwise crucial debinding step from bound-metal 3D printing can reduce costs, time and complexity from metal additive manufacturing (AM).
Debinding the Debinder from Metal AM
Rapidia was founded by Dan Gelbart, who co-founded a 2D-printing company called Creo, which focused on designing the imaging heads for large-format printers and was sold to Kodak for $1 billion in 2005. Since then, Gelbart started two medical companies in 2007 and 2011 before launching his 3D-printing endeavor in 2016.
Gelbart’s goal was to make an impact on the metal 3D-printing space and, according to Production Manager Artem Bylinskii, the company’s technology does offer some unique advantages over metal AM processes claimed to disrupt the industry.
Rapidia’s process skips this debinding step altogether, reducing the number of required machines and steps from three to two.
“In MIM, when you put the metal into a mold, it needs to solidify really rapidly, so they need the plastic [to make it cool quickly]. Then they need to debind it to get rid of the plastic before they sinter the powder particles together,” Bylinskii explained. “Since 3D printing takes considerably longer than injection molding, we realized that you don’t need to bind it with plastic. You can bind it mostly with water.”
The firm’s key innovation is in the materials themselves. Rather than combining metal with plastic as a binder, Rapidia has developed a paste that combines metal powder with water and (a fraction of 1 percent of) “flow-control additive” so that it can be extruded onto the print bed, stacking strands of paste together to create the 3D object.
“It is effectively a sandcastle,” Bylinskii said.
During the printing process, the water binder evaporates, leaving only the printed object. This brown part is ready to be placed directly into the sintering oven, skipping the need for chemically debinding a green part.
Bylinskii pointed out a number of advantages that this presents. Probably the most important is the time-savings afforded by avoiding the debinding step, which can easily take over 24 hours. Additionally, one fewer step with one fewer machine means less overall complexity associated with production. Since debinding is a chemically intensive process, there’s no need to deal with volatile materials, making the technology potentially somewhat safer for office use—a frequent selling point of MIM-based AM systems.
Metal 3D Printing with Polymer Supports
Some other MIM-type metal 3D printers (aside from HP’s MetalJet), still rely on 3D-printing metal support structures for overhangs, bridges and other features. In the case of Desktop Metal, these structures can be easily removed through the use of an interface layer that is deposited between the part and metal supports. These supports then become waste, which has both monetary and environmental costs.
According to Bylinskii, about 50 percent of the metal in a print becomes waste and, because powdered metal can cost $100-120 per kg, the material feedstock is the highest cost in the metal AM process.
Rapidia, however, has developed a “proprietary evaporative polymer” support material. This plastic easily burns out (“evaporates”) in the sintering process, leaving only the solid metal part. The company estimates that this reduces about 90 percent of the metal that would otherwise be discarded. In rare cases when metal support is necessary, a small metal structure can be printed and a polymer interface can be deposited to ensure that removal is easy.
In addition to reducing the amount of waste generated, the polymer supports allow for the ability to create complex internal geometries and closed structures, impossible with LPBF. Current systems, both laser and sintering based, cannot feature supports inside internal structures since the metal supports cannot be removed.
A Few Metal Magic Tricks
Using water as a binder opens up some very interesting possibilities unseen in other metal 3D-printing techniques that more closely resemble magic than just about anything else. One of the most interesting is the ability to “water bond” prints together. By wetting multiple brown parts and sticking them to each other, it’s possible to sinter the assembly into a single structure.
“Maybe it’s not immediately obvious what this can do, but you can eliminate printing support entirely by segmenting the part you’re trying to print,” Bylinskii said. “Then, once it’s off the printer, you rewet the surface you need to join and put them together. Thirty seconds later, it’s dried together. You put it into the sintering furnace, and it comes out as one.”
Other abilities include improving the surface finish of an internal area of a brown object and then sealing the object with a cap via water binding or sinter-welding. Post-processing can also be improved because it’s possible to use a paintbrush and some water to smooth out walls before sintering the brown part.
Ceramics and Metals
The Rapidia system features two independent extruders and four different material cartridges. The second extruder can be used to print evaporative support material, or a mirrored object out of a different (or the same) material.
So far, Rapidia has validated the use of 17-4PH stainless steel and inconel 625. It is in the process of qualifying copper, 316L stainless steel, tungsten chrome carbide, H13 tool steel, maraging steel and titanium.
The system is also capable of 3D printing with ceramics. To start, Rapidia has qualified a white alumina-silica ceramic, as well as zirconia, a hard and strong material that has high thermal insulation properties. Next on the list is alumina, which is even harder, stronger and more temperature resistant. Because these materials are extremely tough to machine, 3D printing enables a new way to manufacture parts from functional ceramics.
More obvious uses for these ceramics are dental crowns or electronics, but Bylinskii said that, with a particular formulation, ceramic brown parts printed off of the system can immediately be used for casting expensive or difficult metals, such as gold and aluminum, which may be less expensive or easier to use in billet form.
Rapidia on the Market
The company is currently taking orders in North America, aiming to make its first deliveries locally over the summer before expanding distribution through North America by the end of the year.
Though the Rapidia setup removes an entire piece of equipment from the manufacturing workflow, the technology will be priced on par with other MIM-based systems, which means that it will still be 10 times cheaper than laser powder bed fusion (LPBF) but not necessarily less expensive than some other competitors. Bylinskii justified this by highlighting the added value that Rapidia will be providing the customer.
This may be true in terms of avoiding material waste, as well as a number of the other unique abilities offered by the use of water-based metal and ceramic pastes. Additionally, the printing process is more streamlined compared to other MIM-based technologies, reducing production time and potentially making it easier to use.
To learn more about the company and its technology, visit the Rapidia website.