FOCUS ON WELDING
Self-fixturing friction stir technique
The backing plate and the hydraulic actuator that provides force. The self-fixturing friction stir attachment, shown here, eliminates the need for a separate anvil and can be attached to the end of a robotic arm.
Enter the new method: self-fixturing friction stir welding.
“ We started by saying:‘ OK, let’ s get rid of the anvil,’” Blocher explained.“ Of course, it wasn’ t that simple …..”
Friction stir tools have been attached to robotic arms in the past, but they always required a separate anvil. Self-fixturing friction stir, however, uses an attachment for a robotic arm that includes both the friction stir tool and a miniature backing plate. If the old approach was an arm holding a pencil, the new approach is an arm holding both a pencil and a clipboard.
The new attachment essentially pinches the target material between the friction stir tool and the backing plate, exerting the necessary force and eliminating the need for a separate, custom-shaped anvil. The goal: freely moving, manoeuvrable friction stir welding that is deployable on the robotic arms used on typical commercial assembly lines.
However, there remains the issue of the thousands of pounds of force exerted by the friction stir tool. Because self-fixturing friction stir uses a built-in backing plate, rather than an anvil, the system must not only exert, but also withstand, that force. There’ s just one problem: most assembly lines do not employ welding robots that are strong enough to handle that.
“ Most of the welding in vehicle manufacturing requires very minimal force, since the material is melted in the process. Friction stir doesn’ t melt the material, so pushing into and across the material requires a significant amount of force,” Upadhyay said.
The PNNL team is in the process of adding another capability to its self-fixturing friction stir tooling, a hydraulic system that powers
Illustration: Mitch Blocher and Derek Munson, Pacific Northwest National Laboratory.
Image: Andrea Starr, Pacific Northwest National Laboratory.
Above: The current experimental version of the self-fixturing friction stir attachment.
This robotic arm in PNNL’ s Applied Engineering Laboratory— affectionately nicknamed“ Bubba”— is used to test robotic friction stir. Here, it is shown with a standard friction stir attachment.
the attachment and creates a closed loop for the force it generates. Currently, the hydraulic system can capture the force from the tool pressing and / or tilting. The researchers are now developing new mechanisms to capture additional degrees of movement and [ creating ] a system that allows the attachment to pull material into the tool.
“ Once this is perfected, there will be no fixturing, no anvil and no force transmitted into the assembly line,” Blocher said.“ The only job of the robot will be to hold the friction stir attachment in place and to maintain the correct position.”
After that, the researchers will package self-fixturing friction stir into a more ergonomic,“ industry-hardened” form so that the technology can be applied on real-world assembly lines.
This work was supported by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy’ s Vehicle Technologies Office. n
About PNNL
Pacific Northwest National Laboratory draws on its strengths in chemistry, Earth sciences, biology and data science to advance scientific knowledge and address challenges in energy resiliency and U. S. national security. Founded in 1965, PNNL is operated by Battelle and supported by the Office of Science of the U. S. Department of Energy.
Image: Andrea Starr, Pacific Northwest National Laboratory. www. pnnl. gov
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