Commander Brad Baker, assistant professor of mechanical engineering at the United States Naval Academy, recently completed a six-week stint at Lawrence Livermore National Laboratory (LLNL) as part of the Visiting Scientist Program.
Baker has conducted research in conjunction with Livermore for more than three years, including a material characterization study of nuclear materials and joining methods. This summer, a project focused on laser-assisted friction stir welding brought him to the Lab.
"This was a chance to take the Lab's laser expertise and combine it with a welding technique called friction stir welding, a technique that the Lab is interested in and that I have experience in applying," Baker said. "We are trying to merge those two technologies and create a technology called diode laser-assisted friction stir welding. If we can heat the material up first with lasers, the process may become more efficient."
Friction stir welding is a solid-state joining process used to fuse two metal surfaces. A welding tool generates heat that creates a soft border on each metal piece, allowing the two to be mechanically intermixed and fused together without melting. This expertise, paired with the Lab's long history of leadership in lasers, creates the basis for a well-executed exploration of combining the two technologies.
Increased efficiency in friction stir welding could have a big impact on the world at large. The technology is a huge driver in the automotive, aerospace and oil industries, in addition to military application. Even Apple applies the technology to its products, incorporating friction stir welding into the newest iMacs for "seamless design."
During his time at LLNL, Baker worked with Ibo Matthews, the lead scientist in a laboratory that studies laser matter interactions and laser processing of materials.
"We study a lot of laser-matter interaction problems for NIF and other applications, one of which involves using high-power lasers to process optics and repair laser-induced damage. We're also exploring laser-assisted manufacturing projects, and this project fits right into what we're doing," Matthews said. "In particular, we are interested in the material response cause by lasers -- heating, heat transport and evaporation -- that are appropriate for this project.
"We have a history of laser research and development, so Livermore is a natural fit for laser-assisted processing," he added.
Friction stir welding uses large drill bits to drive the process. These bits are expensive ($5-10K per bit) and wear out quickly. By using lasers to heat the material prior to welding, the photon-assisted process may move faster and reduce tool wear. This summer, Baker and Matthews tested the heat transfer on HY-80, a steel alloy that is often used in naval applications for submarines and ships. The experimental results matched theoretical models well, leading to increased confidence for future testing.
In the next phase of the research, Baker will work out of the Naval Surface Warfare Center -- Carderock Division to marry the laser and friction stir welding technologies and continue to prove out the models.
"We are fairly certain that this technology will work, but we want to explore the value," Baker said. "Does it reduce tool wear? Does it weld faster? If we're able to do those things, we'll look to see how the combined technology can be optimized."
This project was funded by LLNL's National Security Office andOffice of Strategic Outcomes.