We’ve all built sandcastles on the beach: mighty walls, majestic towers, moats full of sharks. If you’re anything like me, you’ll be surprised how well a small amount of water sticks together—at least until your big brother shows up and kicks it in a burst of destructive joy.
Entrepreneur Dan Gelbart also uses water to bond materials, although his design is far more durable than a weekend beach spectacle.
As president and founder of Rapidia Tech Inc., a supplier of metal 3D printing systems in Vancouver, British Columbia, and Libertyville, Illinois, Gelbart has developed a part manufacturing method that eliminates the time-consuming steps inherent in competing technologies while greatly simplifying support removal. .
It also makes joining multiple parts no more difficult than just soaking them in a bit of water and gluing them together—even for parts made with traditional manufacturing methods.
Gelbart discusses some fundamental differences between his water based systems and those using metal powders containing 20% to 30% wax and polymer (by volume). Rapidia double-headed metal 3D printers produce a paste from metal powder, water and a resin binder in amounts ranging from 0.3 to 0.4%.
Because of this, he explained, the debinding process required by competing technologies, which often takes several days, is eliminated and the part can be sent straight to the sintering oven.
The other processes are mostly in the “long-standing injection molding (MIM) industry that requires unsintered unsintered parts to contain relatively high proportions of polymer to facilitate their release from the mold,” Gelbart said. “However, the amount of polymer needed to bond parts for 3D printing is actually very small—one tenth of a percent is sufficient in most cases.”
So why drink water? As with our sandcastle example used to make paste (metal paste in this case), the polymer holds the pieces together as they dry. The result is a part with the consistency and hardness of sidewalk chalk, strong enough to withstand post-assembly machining, gentle machining (although Gelbart recommends post-sinter machining), assembly with water with other unfinished parts, and sent to the oven.
Eliminating degreasing also allows larger, thicker-walled parts to be printed because when using metal powders impregnated with polymer, the polymer cannot “burn out” if the part walls are too thick.
Gelbart said that one equipment manufacturer required wall thicknesses of 6mm or less. “So let’s say you’re building a part about the size of a computer mouse. In that case, the interior would need to be either hollow or maybe some sort of mesh. This is great for many applications, even lightness is the goal. But if physical strength is required like a bolt or some other high-strength part, then [metal powder injection] or MIM are usually not suitable.”
A freshly printed manifold photo shows the complex internals that a Rapidia printer can produce.
Gelbart points out several other features of the printer. Cartridges containing metal paste are refillable and users returning them to Rapidia for refilling will receive points for any unused material.
A variety of materials are available, including 316 and 17-4PH stainless steel, INCONEL 625, ceramic and zirconia, as well as copper, tungsten carbide and several other materials in development. Support materials – the secret ingredient in many metal printers – are designed to print substrates that can be removed or “evaporated” by hand, opening the door to otherwise unreproducible interiors.
Rapidia has been in business for four years and is, admittedly, just getting started. “The company is taking its time to fix things,” Gelbart said.
To date, he and his team have deployed five systems, including one at the Selkirk Technology Access Center (STAC) in British Columbia. Researcher Jason Taylor has been using the machine since the end of January and has seen many advantages over several existing STAC 3D printers.
He noted that the ability to “glue together with water” raw parts before sintering has great potential. He is also knowledgeable about the issues associated with degreasing, including the use and disposal of chemicals. While non-disclosure agreements prevent Taylor from sharing details of much of his work there, his first test project is something that many of us might think of: a 3D printed stick.
“It turned out perfect,” he said with a smile. “We finished the face, drilled holes for the shaft, and I’m using it now. We’re impressed with the quality of work done with the new system. As with all sintered parts, there’s some shrinkage and even a bit of misalignment, but the machine is adequate. Consistently, we can compensate for these problems in the design.
The Additive Report focuses on the use of additive manufacturing technologies in real production. Manufacturers today are using 3D printing to create tools and fixtures, and some are even using AM for high volume production. Their stories will be featured here.