A unique manufacturing program for large metal parts holds promise to help revitalize American manufacturing and return clean energy manufacturing technologies to the United States. The approach could greatly reduce waiting times for critical components and enable economic growth in the manufacturing sector for energy, according to scientists at the Department of Energy's Oak Ridge National Laboratory.
The project, Rapid Research on Universal Near Net Shape Fabrication Strategies for Expedited Runner Systems, or Rapid RUNNERS, received DOE funding of $15 million over three years to create a system to produce the large runners used in dams for hydropower. A runner is the rotating part of a hydropower turbine that enables the pressure and movement of water to be converted into electricity.
The project will produce runners using 3D printing, or additive manufacturing, combined with conventional tools, all produced domestically. The process will use robotic welders to deposit metal layer by layer to form the runners.
"This has the potential to transform forging and casting of large-scale metal components," said Adam Stevens, an R&D staff member at ORNL and technical lead for the project.
These large metal components are produced almost exclusively overseas, and when they fail, it can take years to fabricate and receive replacements. That means lost time, money and renewable energy. For every month a hydropower turbine is idled waiting for components, thousands of megawatt-hours of renewable electricity are forfeited. But automated additive manufacturing, or AM, methods can quickly produce metal components that are close to the final dimensions of the parts, known as near-net-shape. Traditional machining techniques are then used to finalize the shape, reducing waste and downtime compared to existing processes.
"Right now, it takes around 18 months to produce one of these. If you can't operate a hydropower turbine because you're waiting for a part, that's 18 months of clean energy you're not generating. This approach can fill the gap in the domestic industrial base," Stevens said.
Near-net-shape refers to the geometry of a component that is printed as close to final size and shape as possible, greatly reducing the finishing steps that traditional metal fabrication requires. Convergent manufacturing provides a path toward achieving the desired net shape by incorporating necessary machining and finishing into the AM process. Turbines used for hydropower have complex designs and are complicated to produce, currently requiring months of manual welding and finishing.
Brian Post, leader of ORNL's Disruptive Manufacturing Systems Development group, and Jay Tiley, head of the lab's Materials Structures and Processing Section, are project principal investigators for systems and materials, respectively. The Manufacturing Demonstration Facility at ORNL is providing resources and expertise. The MDF, supported by DOE's Advanced Materials and Manufacturing Technologies Office, is the hub for a nationwide consortium of collaborators working with ORNL to innovate, inspire and catalyze the transformation of U.S. manufacturing.
To demonstrate the capability of the manufacturing system, the program will fabricate three Francis runners, a particular style of large stainless-steel turbines used in dams to generate hydropower. The first runner is a prototype to be used for testing. The second, about 5 feet in diameter, is being made for potential installation in the Tennessee Valley Authority's Ocoee Dam in Parksville, Tennessee. The Ocoee Dam is an 840-foot-wide, 135-foot tall hydropower dam spanning the Ocoee River with five generating units that produce 24 megawatts of electricity.
This program offers an innovative way for us to fulfill TVA's mission summarized by three 'E's: for Energy, it improves reliability, for the Environment, it maximizes renewable energy produced, and for Economic development, it brings great jobs back to the U.S.
The third Francis runner will be manufactured for potential installation in the TVA's Wilson Dam that has 21 generating units producing 653 megawatts of electricity. The turbine will be about 15 feet in diameter, 8 feet tall and weigh more than 46 tons. The TVA, based in Knoxville, Tennessee, is the largest public power company in the nation, operating 113 power generators in 29 dams.
"We are always looking for new ways to do things better. Innovation is a part of TVA's DNA, and it's something that we focus on in all things we do," said Joe Hoagland, TVA's vice president of innovation and research. "This program offers an innovative way for us to fulfill TVA's mission summarized by three 'E's: for Energy, it improves reliability, for the Environment, it maximizes renewable energy produced, and for Economic development, it brings great jobs back to the U.S."
Central to the program is software that allows robots to produce the parts, working collectively to do AM at greater rates across larger shapes than any individual system. The envisioned system has one robot assigned to a task, such as wire arc welding, grinding, metrology and other necessary functions traditionally done by workers in large foundries and fabrication facilities. The system may have six or more robots converge on the system at the same time.
Traditional production of these runners, all overseas, takes a lot of time and is very labor intensive, said Curt Jawdy, head of R&D at TVA. "All these foundries have a pretty big backlog, and we find that it takes two years from the time we place an order to the time we get a runner," he said.
TVA expects that eventually, many of its turbines and steel components, in this case steel known as 410 stainless, will be produced domestically by AM processes, which enable unique capabilities.
Jawdy said hydro runners have cavitation-prone areas that can cause turbines to fail due to erosion of the vane surfaces under the cumulative force of millions of collapsing air bubbles. But through AM, a cavitation-resistant coating can be applied.
"You can do things with additive manufacturing that you can't do otherwise. There are shapes you can make that you would not be able to make otherwise, and you can combine materials," Jawdy said.
This program covers development of the software, hardware, robotics and manufacturing strategies necessary to produce these large components. Partnering with ORNL on development are several organizations, in addition to TVA. These include: Huntington Ingalls-Newport News Shipbuilding, where the largest Francis runner will be 3D-printed; the Electric Power Research Institute, contributing to technoeconomic analyses; Open Mind Technologies, assisting with manufacturing strategy development; ARC Specialties, providing robotic hardware and integration; and Voith Group-Hydropower, a hydro unit manufacturer.
At the end of the three-year term, the project will have created a new distributed hybrid-manufacturing platform that could be used by many industries, "that will allow for domestic production of infrastructure-scale net-shape components for energy, defense, ship building, hydropower and municipal water supply - any industry that requires a large piece of metal could benefit from this," ORNL's Stevens said. "This will increase worker productivity and provide a healthier domestic industrial base."
The DOE award consists of $13 million from the Advanced Materials and Manufacturing Technologies Office, and $2 million from DOE's Water Power Technologies Office.
UT-Battelle manages ORNL for DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE's Office of Science is working to address some of the most pressing challenges of our time. For more information, visit energy.gov/science. - Lawrence Bernard
