Can a hybrid machine tool lower the cost of additive manufacturing?

Eric Brothers, Editor - Manufacturing Group

Published February 19, 2016

Could a cost-effective metal additive manufacturing technology be developed to speed adoption by U.S. industry? That question prompted America Makes – the national accelerator for additive manufacturing and 3D printing – to issue a project call to find out.

The answer may come in a proposal that adds a laser-powered 3D printer to a 20-year-old 3-axis machining center.

America Makes is funding development partners Optomec, a privately-held supplier of additive manufacturing systems; MachMotion, a systems integrator with expertise in CNC controls; and TechSolve, a not-for-profit manufacturing consulting service. Optomec has fitted one of its laser engineered net-shaping (LENS) powder-fed metal 3D print engines to a 1990s-vintage 3-axis vertical machining center. MachMotion has added the controller, drives, wiring, software, and operator console so the upgraded CNC machine can perform both additive and subtractive processes on the same part. Mark Huffman, machining systems engineer, project engineer, and program director at TechSolve Inc., is in charge of validating the hybrid system.

The medium-size, 3-axis milling machine requires the addition of a hood to accommodate the 1kW laser on a vertical stage, protective glass, four powder nozzles, and a system to ventilate the argon gas that blankets the workpiece during sintering.

Huffman wants to learn how easy the hybrid machine is to use, if the parts produced are viable, and how having both technologies in the same environment affects the machine tool.

“How does the metal powder affect the machine? Does it cause maintenance issues? What are the issues? Are they negligible or critical,” Huffman asks.

Another focus is testing the accuracy of MachMotion’s CAM system and dual-process compatibility with the conversational programming controls. For the additive tests, Huffman is using 316 stainless steel because the powder is readily available, similar across several suppliers, and relatively inexpensive. The material is built up on a part in free space – powder and laser are delivered simultaneously – and the excess powder falls away. In other tests, powder has been collected and recycled, reducing waste.

Project genesis

While hybrid machines exist, they are expensive. The National Center for Defense Manufacturing and Machining behind America Makes wants to know if retrofitting additive capabilities on an existing machining center could provide smaller manufacturers with a less costly alternative. Lockheed Martin and Benet Labs are technical advisors on the project.

Optomec, which in 1998 commercialized the LENS deposition engine developed by Sandia National Laboratories to sinter metal powder to a part, proposes to show it is possible to retrofit legacy CNC machines with its technology, combining additive and subtractive capabilities in one machine.

America Makes funds the project, which used an eBay-purchased Fadal 4020 milling machine as the test subject.

Manufacturing consultants at TechSolve under the direction of Mark Huffman agree to validate the hybrid machine. TechSolve engineers will provide secondary machining, inspection, and testing on resulting parts to define the success of the hybrid retrofit machine. They will also compare metrics to existing LENS systems on operating costs/sustainability, training requirements, and manufacturing readiness level.

Is metal deposition on a hybrid as accurate as on a standalone LENS system? “That’s one of things we’re testing,” Huffman says. “We can make a melt pool in different sizes depending on the focal length of the laser and where you focus it on the powder.” The layers produced in early testing were 0.012" thick. “We could make it thicker or thinner if we push it a bit more.”

The laser then retracts to protect it from chips, and the machine uses the same codes and control for subtractive machining. So far, researchers have used dry machining, but the plan is to study the effects using flood coolant.

Is the hybrid system ready for widespread adoption? No, more testing needs to be done. Huffman says the hybrid is at manufacturing readiness level (MRL) 6 – fully functional in a laboratory – but the goal is MRL 7, ready to be used in a production environment.

“We are making parts and some features but not production parts in repeatable runs at this point,” he adds.

Currently, researchers are testing the machine for a part repair using 316 stainless steel powder. “The test builds are complete, so the next steps are to machine our test pieces to gather data on surface finish, material hardness, and machining forces,” Huffman says.

Huffman hopes to see the hybrid technology save time by adding metal to parts and machining it to spec; to repair and restore damaged or worn parts; and to add wear surfaces to parts using stainless steels, titanium, and superalloys.

The technology is not limited to 3-axis machines, Huffman says. Adapting any 5-axis machine to a hybrid additive/subtractive machine is theoretically possible, noting, “with a vertical machining center, gravity helps deliver powder to the substrate.”

TechSolve Inc.

Optomec Inc.

MachMotion

America Makes

About the author: Eric Brothers is senior editor of AM&D and can be reached at ebrothers@gie.net or 216.393.0228.