Metal Additive Manufacturing for Parts up to 7 Feet Tall

Sample part in Inconel 625 challenges the size constraint usually associated with powder-based metal additive manufacturing.

One of the constraints on additive manufacturing machines that make metal parts from powder has been the relatively small build envelope of these machines. Rapid City, South Dakota-based RPM Innovations is now prepared to challenge that constraint with laser deposition additive manufacturing machines that have a build envelope of 5 ×5 ×7 feet. An 83-inch-tall rocket-like part made from Inconel 625 that was grown in one of this company’s machines will be on display in the Advanced Manufacturing Center at IMTS.

Robert Mudge is president of RPM Innovations, which was spun off last year from contract manufacturing firm RPM & Associates, a company he also co-founded. The parent company has been applying laser-deposition additive manufacturing technology for 10 years. Growing interest in the technology combined with customer pressure for bigger parts led the company to build machines with part-making envelope of 5 × 5 × 7 feet. The success of these machines, and the application track record so far, gave RPM & Associates the confidence to now launch a separate company both to provide contract additive manufacturing services and to manufacture various models of this machine for other users.

The RPM machines use a blown-powder approach to applying the metal. Deposition rates reach 2 to 3 pounds per hour, which is fast for a powder-based additive machine. Small additive metal machines, such as powder bed machines, can achieve finer detail that what RPM can do, says Mr. Mudge, though thin walls and precise features are possible on RPM’s machines as well. By contrast, he says some of the strengths that make the blown-powder machine distinctive include the abilities to perform cladding on existing parts and to repair worn parts back to their new profile.

One other strength is the ease of recovery if there is a problem in the build, he says. A flaw in the build cycle with some metal additive manufacturing machines requires the entire part to be scrapped. With RPM’s machine, the part can be pulled out, machined down to where it is still good, then returned to the additive machine to resume the cycle.

Most of the additive manufacturing work previously done on RPM’s machines is covered by non-disclosure agreements, so Mr. Mudge can’t elaborate on these parts, but he says many would probably be surprised by the application history this technology has already seen. Nearly 80 percent of its applications have been related to aerospace or defense, including aircraft engine components and aircraft structural components for “companies whose names you’d recognize,” he says. Inconel 625, Inconel 718 and titanium 6-4 are among the alloys that the machines apply routinely.

The rocket-like part took around 340 hours to build is approximately 7,000 layers, he says. And to the RPM staff, that is not all that long. “We have had big parts—not as tall as this, but broader and a lot more complex—that took us 1,800 hours to build,” Mr. Mudge says.