Wire DED for Printing Large Metal Parts

By: Brad Kuvin

Thursday, August 22, 2019

Oak Ridge National Laboratory, in collaboration with numerous partners in industry, government and academia, including Lincoln Electric, used the DED metal-AM process, on a production cell similar to that at Lincoln Electric, to produce the first fully functional excavator using AM components, shown here. This 7-ft.-long, 400-lb. part was printed from low-cost steel weld wire in 5 days. Photos provided by Oak Ridge National Laboratory, U.S. Department of Energy.





In May of this year, Lincoln Electric penned an updated agreement with Oak Ridge National Laboratory (ORNL) to expand its large-scale additive manufacturing (AM) development work to manufacture metal components using its automated wire directed energy deposition (DED) technology at deposition rates exceeding 100 lb./hr. The work, ongoing at the ORNL Demonstration Facility and supported by the U.S. Department of Energy, aims in part to support efforts by U.S. manufacturers to apply AM technology in the development of large tools, dies and molds. The announcement came on the heels of the acquisition by Lincoln Electric of Baker Industries, Inc., Detroit, MI, a manufacturer of custom tooling, fixtures and other components, primarily for the automotive and aerospace industries. The result: the ability of Lincoln Electric to nurture and scale its new metal AM service business in Cleveland, OH.

“We are uniquely aligned to collaborate with ORNL and continue to expand the capabilities of wire DED,” explains Tom Matthews, senior vice president for technology and R&D at Lincoln Electric, during our recent visit with key members of the company’s AM team.

“We understand deposition technology and how to deposit molten metal,” adds Mark Douglass, business development manager, additive solutions. “And, our team of inhouse engineers and metallurgists will lead the development of new wire feedstocks needed to expand the capabilities of the process. We’ll be focusing on, among other variables, the thermal cycling that occurs during deposition, and the development of detailed and precise robot-motion profiles—coordinated with other automation devices—to ensure precision, even as speed and deposition rate rise.”

Developing and fine-tuning the robot path, and learning to take advantage of the free motion available during robotic DED, enables molten-metal deposition at the right orientation to leverage gravity and avoid the need for supports. That’s just one of the advancements resulting from the development of enhanced and proprietary software from Lincoln Electric.

“Other software-driven process enhancements we’re striving to achieve,” says Mike Whitehead, senior vice president, and president, global automation, cutting and additive businesses, “include modeling of how the layers of deposited metal will look like as we adjust parameters such as wire diameter, speed and amperage.”

Software Development at the Core

Much of the software development mentioned above has its foundation in Lincoln Electric’s inherent welding and metallurgy knowledge, and as the software evolves, the need for manual intervention into the high-deposition DED process will diminish. Automation then will quicken the production of prototype and production parts. “In the end,” says Whitehead, “tools and parts made as low-volume castings that can take a manufacturer months to tool up for can be printed in weeks or even days. And, we can robotically deposit part features that would be difficult or impossible to achieve in a machining environment.”

For now, Lincoln Electric Additive Solutions prints carbon and stainless steels, and will soon be printing Invar (FeNi36 nickel-iron alloy) as well as nickel and aluminum alloys. It’s using two DED processes: laser hot-wire, where an advanced power supply preheats the wire almost to the melting point, allowing for a much higher deposition rate compared to no preheat; and gas-metal-arc welding (GMAW). GMAW typically finds use for printing carbon and stainless steels; the laser hot-wire process gets the call for more complex base materials such as titanium and nickel alloys, and also can accommodate cored wires, which allow Lincoln the ability to customize the material mix. Whether using solid or cored wire, Lincoln Electric’s ability to produce wire in huge several-hundred-pound boxes, compared to the 10-lb. spools, allows uninterrupted production for days at a time.

Lincoln Electric operates its AM business with a team of 250, most of which work at Baker’s Detroit-based facilities. The Additive Solutions team in Cleveland comprises 10 individuals, and is expected to grow to 25 or 30 by year-end, as the firm looks to add more than 20 new production workcells to its dedicated 75,000-sq.-ft. plant. This is in addition to the three DED workcells at ORNL, including a three-robot workcell.

The focus: making parts, demonstrating DED capabilities to customers and prospects, and learning how to enhance and ensure quality throughout what typically are very large builds comprising hundreds of stacked layers.

“We really want to get to 100 lb./hr. per robot,” says Matthews, noting that with a single-wire process, the production rate averages around 10 lb./hr. Lincoln and ORNL intend to operate the three-arm robot setup with Lincoln’s new two-arc process (HyperFill, launched at FABTECH 2018 in Atlanta), which they expect to deposit metal at around 60 lb./hr. 3DMP


See also: Lincoln Electric Co.

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