In a cavernous laboratory, a steady glow traced a path through the air, building up layer after layer of molten steel. Over eight weeks, a massive Stamp Form Die (SFD) mold emerged - 6 feet tall, 4 feet wide and weighing nearly 2 tons.
A Stamp Form Die is a punch press used to cut or shape materials. The 3D-printed metal mold was developed through a partnership between the Department of Energy's Oak Ridge National Laboratory (ORNL) and the Boeing Company to explore state-of-the-art manufacturing methods for SFD tooling in thermoplastic composite production.
The SFD will be used by Boeing to contribute to NASA's Hi-Rate Composite Aircraft Manufacturing (HiCAM) project.
"NASA and its industry partners are working to increase the production rate of composite aircraft to meet the growing demand for air travel and to reduce aircraft weight, which improves fuel efficiency, lowering costs for aircraft operators," said Richard Young, NASA HiCAM Project Manager. "Doing so is essential to maintaining U.S. competitive advantage in the commercial aircraft industry."
Boeing utilized a network of American small and large businesses to execute the 3D-printed SFD tool project, applying cutting-edge technology and engineering expertise to overcome complex technical challenges.
"It is imperative American companies continue to innovate and push technical boundaries to retain our competitive advantage in the global marketplace," said Boeing Technical Fellow Michael Matlack.
A New Way to Make a Mold
Thermoplastic aircraft doors are made by stamping hot plastic between two SFD metal molds. Think of the molds as slices of bread for a sandwich, with a sheet of hot plastic as the filling.
Normally, these molds are made through traditional metalworking such as machining, casting, forging, and drilling. Researchers at Boeing and DOE's Manufacturing Demonstration Facility (MDF) at ORNL wanted to see whether it would be faster, less costly, and easier to 3D print a thermally controlled SFD mold instead.
"Boeing wanted to explore the possibility of using wire-arc additive manufacturing (WAAM)," said William Carter, ORNL robotics engineer at the MDF. "They worked with us to evaluate the issues in making the mold."
This project relied on ORNL engineering expertise in WAAM processes and residual stress simulation, using ORNL's Arc-1 system. Arc-1 has a robotic arm and a welding torch to melt wire and build metal parts layer by layer. Unlike most WAAM systems, Arc-1 can print with more than one kind of metal, feeding in multiple wires at the same time. This increases manufacturing versatility, broadens the range of printable geometries, and allows multiple metals to be combined with greater design flexibility for tailored performance.
"Multi-material WAAM allows for the realization of completely new designs, combining fine-tuned mechanical performance with time and cost savings," said Andrzej Nycz, ORNL senior robotics engineer.
The Boeing SFD mold leverages mild steel in the structural regions for strength and stiffness, while stainless steel is deposited at the mold surface to provide corrosion resistance, dimensional stability, and a durable working interface.
Such molds usually have long, straight holes drilled into them to create channels that will carry heating and cooling fluids. With 3D printing, engineers were able to instead build in curving channels that closely follow the shape of the mold. This helps heat and cool the part more efficiently and improves mold performance.
One major challenge to 3D printing the mold was warping. As the deposited metal cooled, inherent residual stresses caused twisting and dimensional drift. To minimize this, the team added temporary ribs to the back of the mold and used computer simulations to refine the design and compensate for this warping during the printing process. After 32 simulation iterations, they produced a mold that was within a few millimeters of the intended shape.
Once the mold was successfully printed, it was sent to Baker Industries in Michigan to be annealed to remove internal stress. The support ribs were then cut away. Baker Industries completed all remaining fabrication operations to finish the SFD to achieve all Boeing requirements.
A Mold That Could Help Shape the Future
The wire-arc technology used to manufacture the tool was developed as a collaboration between ORNL and Lincoln Electric under a Cooperative Research and Development Agreement (Baker Industries is a subsidiary of Lincoln Electric). "Baker Industries values its strong partnerships with ORNL and Boeing," said Evan Bartkiewicz, Baker Industries senior project manager.
The project highlights how leveraging engineering and scientific expertise of collaboration partners can achieve the objective in a timely manner.
While not all parts of the final tool were 3D printed, the technology developed within this project can be replicated for similar tool types.
"We used this as a test case," said Ahmed Arabi Hassen, ORNL's group leader for Composites Innovation. "Its success means the technology could be used to make large thermoplastic structures for other sectors of U.S. industry, such as energy and automotive."
By proving that large, complex tools can be 3D printed faster and more efficiently than with traditional methods, ORNL and its partners are strengthening the U.S. industrial base while opening new doors to innovation.