Quality guaranteed

The average No. 2 pencil contains approximately 0.2 grams of graphite—a naturally occurring crystalline form of the element carbon.

The average graphite log at Los Alamos National Laboratory’s Sigma Complex is 16 inches in diameter and weighs more than 3,000 pounds. “They show up on semitrucks,” explains manufacturing manager Mike Schuch. “We move them around with forklifts and cranes.”

And unlike the graphite in pencils, which is typically mixed with clay, the graphite at Sigma is pure, which means it’s prone to chipping and cracking. But according to Schuch, who leads the 10-person team that uses tools, such as lathes and mills, to carefully remove graphite from a graphite log until what’s left is a very specific shape and size, these properties are part of what makes working at Sigma so gratifying. “We take a lot of pride in being able to machine graphite,” he explains. “Our specialty is materials others find difficult to work with.”

Schuch notes that in addition to graphite, Sigma’s machinists are trained to work with dozens of other elements—everything between hydrogen and uranium on the periodic table. Elements often take different forms and can even be hazardous or radioactive.

Machinists work closely with materials scientists and engineers in support of Sigma’s manufacturing science mission. Manufacturing science involves studying how raw materials are turned into finished products. Material properties and manufacturing processes must be considered in tandem. “We want to know not only that we can do things but also why we can do them,” Schuch explains. “We can tell you if something succeeded or failed and the process that led to that outcome.”

Most items manufactured at Sigma are prototypes or test hardware with national security applications. For example, a customer (typically someone at the Laboratory or at a production plant within the nuclear security enterprise) might contact Sigma with an idea for a new type of nuclear weapon component or a new way an existing component could be manufactured. “We are the manufacturing science hub for the nuclear security enterprise,” Schuch explains. “We can receive a napkin sketch and take it from design to final part to put in a test.”

Sigma researchers and machinists will iterate on a part, process, or technology, tweaking and testing it until it’s just right. “We take theory and apply engineering to make parts,” says Matthew Zappulla, a scientist in Sigma’s Fabrication Manufacturing Science group. “Since the Manhattan Project, Sigma’s mission has been to make parts efficiently, predict a part’s functionality, and guarantee a part’s quality.”

On a tour of the Sigma building, Schuch gestures to parts, some of them a little wonky or broken. “Most things you see around the building are demonstrations or things that went wrong,” he explains. “Because if they were done correctly, they’ve been blown up as part of a test.”

Under one roof

Although Sigma’s products are complicated—structurally and materially complex—manufacturing occurs rapidly. According to Sigma Division Leader David Pugmire, “Sigma delivers production-ready manufacturing technologies for the enduring and future nuclear stockpile in a timescale measured in years, not decades.”

Laser powder bed additive manufacturing systems, a plasma spray chamber, scanning electron microscopes, hydraulic forming presses, slot-die coaters, vacuum heat treatment furnaces, and multiple uranium-casting furnaces are just some of the equipment found throughout the facility. Schuch points to a flow forming machine, which is akin to a potter’s wheel for metal that “can turn a plate into a vase in two minutes.” There’s also a Manhattan Project–era rolling mill that is used to create foils out of different types of metal plates.

Of course, none of the machinery matters without qualified people behind it. “The Sigma capability is a combination of its facility and its people,” Pugmire says. “Deep subject matter expertise in essential technologies is being transferred to future leaders, modernization programs are reestablishing expertise, and investments in Sigma are attracting talented early career staff.”

What does it take to be a machinist at Sigma? “You look for someone who wants to learn, someone with the right focus and mindset,” Schuch says. Machinists also must interface well with scientists and engineers to collaboratively tackle challenging and often pressing problems.

But even with the high-impact and sometimes dangerous work, Schuch says, “it is very, very difficult to not have fun.” He points to a hand-drawn spinner (like something you might find in a board game) that hangs on the wall. If a machinist is having trouble getting a part just right, the spinner offers humorous suggestions on what to do next. “When all else fails, we turn to the Wheel of Variables,” he laughs and gives it a spin. The arrow passes over “roller angle” and “increase speed” and stops squarely on “ask the next person who walks by.”

Production agency partnerships

Once a part or a manufacturing process is perfected at Sigma, it is handed off to the customer or to a larger-scale production agency. This handoff requires careful collaboration to ensure both the technology and the knowledge behind it are transferred appropriately. 

One example of such a collaboration starts with the aforementioned graphite logs. The logs are machined into single-use molds—vessels into which molten metal is poured. As the metal cools, it hardens into precise shapes. Graphite, although difficult to machine, is the ideal material for such molds due to its ability to withstand high temperatures and its thermal conductivity.

Sigma currently manufactures the graphite molds used for plutonium pit production, which occurs nearby in the Lab’s Plutonium Facility—the only place in the United States equipped to work with significant quantities of plutonium, a complex radioactive element that is used in nuclear weapons.

Nuclear weapons also require another radioactive element, uranium. For more than 70 years, the Y-12 National Security Complex in Oak Ridge, Tennessee, has manufactured all uranium components for America’s nuclear weapons. For decades, the uranium in these components was wrought, or extruded. Finished uranium components were (and still are) shipped to the Pantex Plant in Amarillo, Texas, for assembly into nuclear weapons.

Because Y-12 is an 811-acre, full-on production facility, its research into new manufacturing techniques is limited, even if those new techniques might be beneficial—faster, safer, less expensive—down the road. But this type of rapid prototyping and experimental work is exactly where Sigma excels.

In the early 2000s, a team of Sigma metallurgists developed a concept for direct casting some uranium components made at Y-12. In direct casting, uranium is heated to high temperatures and poured into graphite molds. When the uranium cools, the molds are broken and removed, and the cast uranium is further machined.

After many years and much testing, the National Nuclear Security Administration (which oversees both Los Alamos and Y-12), decided to supplement wrought processing at Y-12 with the direct casting method developed by Sigma. Teams from Sigma began working with teams from Y-12 to implement direct casting at Y-12 at a larger scale than was demonstrated at Sigma.

“Y-12 makes their own graphite molds,” Schuch says, “but their molds are informed by our work here at Sigma.” He explains that direct casting allows for more flexibility in weapons designs. For example, if a physicist wants to make a change, now only the graphite mold (not the steel tooling) must be updated. “Direct casting makes us more agile,” he says. “We can try new things and be responsive to military needs.” He notes that Sigma and Y-12 have the same equipment—right down to the vacuum induction melting furnace used to heat the uranium—to ensure that both facilities are on the same page and that each facility can support the other’s work.

Although dozens of people were involved in this knowledge and technology transfer, the collaboration really flourished under the direction of two men: metallurgist Rob Aiken at Sigma and Jason Steward, a metallurgical engineer at Y-12.

“Rob has eagerly shared this knowledge with Jason,” says Valerie Newman, a production liaison who is employed by Los Alamos and works at Y-12. “Jason has just as readily absorbed a great deal of uranium science and processing knowledge from Rob.”

Newman notes that Aiken worked at Sigma for nearly 25 years before his retirement in September. His decades of knowledge were acquired on the job. “This stuff is not taught in college,” Newman says. “So, this relationship—lots of conversations, lots of working alongside one another—was really the primary way of transferring information.”

Steward agrees. “Although Rob was over 1,400 miles away, his technical expertise and commitment to supporting metallurgical processes at Y-12 has been felt across the site for decades,” he says. “I appreciate the time and effort Rob has provided in mentoring; this relationship has been foundational in facilitating a fluid technology transfer of direct casting technology from Sigma to Y-12.” 

Newman says the smooth transition will benefit the nation. “I personally believe that implementing this technology at Y-12 would have had many more challenges if not for the collaborations between Rob and Jason,” she says. “Sigma’s focus on manufacturing science ensures that transformative fabrication methods will continue to be investigated in partnership with Y-12 and other production agencies. This benefits our current weapons work and the nuclear security enterprise of the future.” ★