Understanding materials is crucial to new processes for weapon parts
Sandia researchers are exploring how to use additive manufacturing, familiar to most people as 3-D printing, to make parts for nuclear weapons and other national security needs, saving time and money and simplifying the manufacturing process.
The target of much of its research is an advanced metal additive process that uses a laser to melt successive layers of metal powder to build up shapes. The technique lets engineers design in ways that aren’t possible with standard manufacturing methods and could make components that perform better and weigh less. But researchers must answer hard questions before they can certify that parts made in non-traditional ways can meet high-consequence requirements.
President Barack Obama has pushed for ways to strengthen US manufacturing. Last year, Sandia joined America Makes, the federally backed National Additive Manufacturing Institute, which aims to reduce the cost of 3-D printing, offer new opportunities to businesses, and train American workers in sophisticated technologies. Ultimately, a robust additive manufacturing industry could make the nation more competitive in a global market.
Additive manufacturing opens up seemingly limitless possibilities. It can make shapes with complicated geometries that traditional machining can’t handle. It offers the potential to integrate parts or assemblies, reducing the number of joints and other interfaces that could be points of failure. In the future, designers might be able to custom-tailor the properties of additive materials to make components better. All of those opportunities could save both time and money.
Understanding properties of new materials
The biggest barrier to using new materials is understanding their properties well enough to certify that they meet rigorous requirements for high-consequence applications. Materials assurance, a key to certification and qualification, is “the first, most immediate obstacle that we need to overcome,” says manager Andre Claudet (2617).
Parts must meet multiple requirements for mechanical, thermal, or vibration performance — particularly crucial when something is intended for a nuclear weapon, a satellite, or an airplane. “How do you actually verify the material is what you want? For some applications it’s not a big deal. For high-consequence hardware it’s a very big deal,” says Bradley Jared (1832).
The path to certification requires conducting experiments using instruments to understand what’s happening and performing sophisticated computations to verify that material properties meet specifications.
Sandia is well-suited to tackle the problem because of its expertise in computational mechanics and analysis, high-performance computers, and modeling tools it developed. Sandia also has experience in handling large amounts of data, people who know how to write and adjust codes, skill in materials science, and a history of inventing additive manufacturing techniques. In the 1990s, Sandia developed both Laser Engineered Net Shaping (LENS), a process to print complex metal parts from powders, and robocasting, a 3-D ceramic process that forces ceramic slurry through a pressurized needle to create a part that is fired in a furnace to harden it. Both processes have been commercialized.
Most metal additive techniques involve melting a feedstock material that then re-solidifies into its final shape. However, the process alters a material’s microstructure, which can dramatically affect its properties and how parts perform. Researchers need to understand how the extreme temperatures and heating and cooling rates affect material properties.
Metal parts historically have been made from ingots, rods, bars, or plates whose properties can be verified. “You can cut some samples and check the chemistry and the microstructure and mechanical properties and say, ‘Yea verily, this is a good piece of material and anything you make out of it will be fine,’” says Senior Manager Mark Smith (1830). “With additive you build material at the same time you build the part. So the question is, does it have the right microstructure and chemical composition and are there defects like voids or unmelted particles that will affect its performance?”
Strength, other characteristics affected by how materials are processed
Important material characteristics such as strength or ability to withstand stress depend on many things, including how a material’s internal structure is affected by phase changes — for a simple analogy, think ice melting into water, then refreezing into ice again. In the laser metal powder bed process, for example, feedstock powder is random in the way it’s laid down and in its distribution of particle sizes. As the laser scans the surface and melts some particles, they coalesce.
“The behavior of the final part depends on the metallic microstructure of the material from which it is built,” says manager Anthony Geller (1516), whose department does modeling and simulation for fluid and multiphase flows. “The microstructure depends on the temperature history that the metal experienced while it was cooling, and the temperature history the metal experienced while it was cooling depends on the temperature and flow history of the particles as they were heated, melted, and flowed together, which in turn depends on that first step, how the particles were laid down.”
Anthony says researchers must acknowledge the inherent variability of additive materials, and design according to probabilities for internal stress.
Embracing material variability is the broader goal of Sandia’s Engineering of Materials Reliability Research Challenge, which is developing a framework to understand how variability impacts the reliability of engineering components. The research challenge is using the metal additive process for its initial study.
Additive manufacturing allows designers to create complex geometries that can’t be made by traditional manufacturing. Given the triple constraints of cost, schedule, and performance, a complex part can be preferable: it’s cheaper because you use less material and faster because you’re printing less, and it performs better because optimization tools are used, Andre says. Sandia is developing computational tools incorporating technologies such as topology optimization (see story on next page) to take advantage of this aspect of additive manufacturing, he adds.
But it’s very difficult to characterize complicated additive manufacturing parts such as a bar engineered for rigidity that resembles the skeleton of a cholla cactus. “From a production standpoint that’s the part I want to make because it’s faster and uses less material,” Bradley says. “From a measurement standpoint, however, that part is a greater challenge.”
Research must measure temperatures as structures form
For accurate simulations, researchers must know what happens as layers are put down, but it’s difficult to measure temperatures in layers that become hidden as other layers form on top. “We can’t embed anything in those lower layers because that would change the behavior,” Anthony says.
Simulations, aimed at calculating real-world results using large computers, can predict temperatures in inaccessible layers, while experiments can validate the model. Simulations can study parameters such as particle size distribution that would be difficult and costly to study by experiments alone.
Diagnostics for the LENS process included a thermal camera to learn about the melting process and metallurgy, and Bradley suggests something similar for the powder bed process. Some studies have used optical cameras to see how the powder disperses on a layer and to study the powder laydown process. Some diagnostics might be able to use these types of sensors.
“Right now we don’t have a whole lot of information coming off the machine and off the process,” Bradley says. “We don’t know what we don’t know.”
Understanding how materials form might eventually mean custom-tailoring microstructure properties.
“So you can have different material, different microstructures, different properties in different regions that can be incorporated as part of the design process if we can understand it well enough,” Mark says. “That’s sort of the long-term vision: You would not only design the geometry, but actually design the microstructure of the part as you build it.”
Additive manufacturing is a tool, not a panacea, and won’t replace traditional manufacturing for everything, he says. “We’re not going to print a complex mechanical assembly with precision moving part anytime in the near future,” he says. “But there may be some applications where it offers unique advantages for us.”
Bradley expects it to complement current techniques. “Where you need it, you’ll use it, and where you don’t, you’ll use traditional methods.”
-- Sue Major Holmes
Topology optimization: Creating the best design for the purpose
Imagine a table with sinuous legs resembling the organic shapes of tree branches rather than straight table legs. Those flowing legs might make the table stronger, better able to handle whatever someone piles on it.
Sandia researchers believe such designs, achieved through a technology called topology optimization, could enable better parts for nuclear weapons, satellites, and other vital uses. Along with advanced additive manufacturing (AM) it opens possibilities for complex shapes that conventional manufacturing methods can’t handle. Partnering the techniques also offers the potential to combine parts to save time and money, reduce the number of joints or other interfaces, and embed sensors or wiring within a structure as it’s formed.
Before the technologies can be widely employed in high-reliability, high-consequence uses, however, researchers must understand how to create the best shapes for parts and guarantee material properties.
“There are aspects of this marriage between additive manufacturing and topology optimization that are going to be critical for us to address if we’re really going to do this well,” says manager Ted Blacker (1543). “If all you do is make the same old parts a new way, it’s taking advantage of only a fraction of what is possible in additive manufacturing. And if you make these new optimal parts but you can’t ensure material quality, they’re of no use.”
Sandia’s expertise in computational mechanics, analysis tools it developed in engineering codes such as Sierra and Alegra, and geometry tools such as Cubit are advantages for working on those critical problems. Sandia also has experts in materials science and computational simulation of materials, experience in handling large amounts of data, and know-how in writing codes for high-performance computers.
Additive manufacturing, typically synonymous with 3-D printing, encompasses techniques to make parts or whole assemblies in plastic, ceramic, or metal.
Additive manufacturing handles complex shapes
New AM technologies, particularly those that produce metal, open possibilities for designs that previously were not realistic because they were too complex for conventional manufacturing. “We need to develop computational tools that will enable us to make the leap to new types of designs; tools that will make modern computer-aided design systems seem as quaint as drafting tables and T-squares,” says manager Andre Claudet (2617).
Sandia is interested in additive manufacturing for nuclear weapons components because the technique can handle complex geometries and is particularly efficient for low-volume production. It’s especially compelling early in product development, when frequent design changes can be quickly evaluated, says Bradley Jared (1832).
Additive manufacturing and topology optimization together could combine several pieces into one, eliminating possible weak points, saving material, and removing the need to model what could happen at those interfaces, Bradley says. “If you can combine interfaces, suddenly you’ve simplified a part for simulation, for testing, and for qualification,” he says.
With topology optimization, engineers start with an allowable space — the area where the part fits — then specify functional requirements, “how heavy they will allow it to be, what material they want to use, the loads, and the constraints,” Ted says. “They allow the optimization calculations to determine where the material is needed, placing material only where it will be used most effectively to meet design demands.”
Thus, a designer no longer focuses on creating a shape, but is free to drive the design by the functions required. For example, a designer might choose tradeoffs between device rigidity and ability to conduct heat. Prioritizing stiffness produces a shell-like structure, with material pushed outward to maximize rigidity. If thermal transfer is more important, the optimization produces a structure with more massive legs, natural paths for heat. If stiffness and heat transfer are equally important, the result is a truss-like structure that adds stiffness but still has material in the legs.
Designers use computer-aided design programs to envision useful shapes for a function. But with topology optimization, that’s reversed. They tell the program, “‘Here are my engineering requirements; you create my geometry for me,’ a major revolution in how we do design,” Ted says.
He displayed a black plastic table and chair, inches in scale, an additive manufacturing example project that demonstrates how topology optimization works. The table top and chair seat are flat, but the organic-looking legs twist in shapes reminiscent of the inverted trunk of a swamp cypress.
Topology optimization program works from specifications
The project defined an allowable volume for the table and chair, fixed positions on the floor for legs, and stipulated flat surfaces for the tabletop and chair seat, along with uniform loads — the weight they bear — then let the topology optimization program do its thing.
It requires engineering judgment and carefully specifying the entire problem. Parameters such as feature size control whether you get a tree trunk or a more spider web structure holding up the tabletop. If you don’t tell the program to secure the legs so the table doesn’t move, it adds cross members along the floor to increase strength, even though that also prevents a chair from sliding under the table. “With topology optimization, you get what you asked for, whether that’s what you wanted or not,” Ted says.
Thus, topology optimization requires what he calls interactive steering. If engineers watching a shape form on a computer screen realize they didn’t put in enough information, they can stop the program. “Where we stopped we say, ‘Add this additional constraint,’ and let it continue,” Ted says. “Even though the calculations are being done in batch mode on very large machines, we can still have an interactive design environment on those machines. We think it’s a very powerful addition.”
Interactive steering paid off in a test problem to design a bicycle frame. The engineer identified requirements for a seat, handlebars, and pedals, something to hold the tires, and loads to simulate a rider standing on the pedals rather than sitting on the seat. But as the shape evolved on the screen, he realized the specified load on the handlebars was in the wrong direction. He stopped, made adjustments, and finished the design.
Engineering analysis to predict optimal shapes takes full advantage of AM, but poses an extremely difficult computational problem. Static loads, something sitting on top of a table, are easy to include. Dynamic loads, someone jumping on the table, are not.
Optimization requires not only high-performance computing capacity but also expertise in modeling to include as much physics as possible. “If you want a really good optimization, you’ve got to include every possible physical environment that a part will see,” Ted says.
Simulating physics saves time, money
Manager Anthony Geller (1516) says it would be extremely expensive to use only experiments to understand the physics of how something works, and simulations save time and money. “If we need 100 tests, maybe we would do 90 of them through simulation and 10 of them experimentally for validation purposes. Also, the simulation gives us access to certain data points that would be difficult if not impossible to acquire through actual physical experiments,” he says.
A program assumes certain materials properties as it follows specifications for a design. But sometimes engineers overbuild because they’re uncertain about the properties. “The optimization says that if we have that tiny curved strut that’s very thin, that’s all the material you really need to carry the load,” Anthony says. “But if we have to make it thicker because of our uncertainty, we’re losing that benefit.”
Ted says Sandia is working on “robust optimization,” letting calculations derive a shape that will meet requirements with point-by-point uncertainties in material properties or in loading conditions. Such uncertainty quantification determines the likelihood of outcomes when some aspects of a problem aren’t known, and predicts results in a statistical sense.
Senior manager Mark Smith (1830) says that in the near term, additive manufacturing could save time and money in tooling, fixtures, and jigs used in manufacturing components since those items don’t have to be certified like an actual part. “We’re already making very extensive use of additive in those areas,” he says.
He believes Sandia can make significant progress in three to five years but says it could take a decade or more to reach the ultimate goal of design optimization, tying materials assurance and topology optimization together.
Researchers must balance what can be accomplished now with how much work is still needed to qualify parts for the stockpile. “I don’t want to minimize the potential benefit but I also don’t want to minimize that there’s still a lot of work to be done,” Anthony says.
-- Sue Major Holmes
Small NM businesses get a scientific leg up, and prosper
by Nancy Salem
Ski bums need fuel to schuss down mountains day in and day out. Their go-to snack is an energy bar, a backpack staple. “We need something that is quick, healthy, sustaining, and cheap,” says Kyle Hawari of Taos.
But taste matters, too. “We humans crave something that is enjoyable to eat,” Hawari says. “Simply put, we wanted something healthy that delivered in the taste department.”
Hawari says the bars he tried were chalky and dry, and some had fillers and preservatives. Others were just plain bad. “There were many choices when it came to bars but none lived up to the fancy packaging or the hyped-up story on the back,” he says. “We saw the same tired flavors, bad textures, and poor ingredients over and over again.”
Hawari and his longtime friend and fellow outdoorsman Brooks Thostenson thought they could do better and in 2010 set out to craft a line of artisan energy bars using premium, organic ingredients. “There’s a legend in Taos that if the mountain calls you there to make art, you have little choice but to surrender,” he says. “Well, we heard it calling.”
Hawari and Thostenson founded Taos Mountain Energy Foods LLC using the community kitchen at the Taos Food Center. Their first sales were in New Mexico but distribution quickly expanded throughout the United States. Hawari and Thostenson were overwhelmed.
They turned to the New Mexico Small Business Assistance (NMSBA) program for help streamlining production and were paired with the New Mexico Manufacturing Extension Partnership, which contracts with NMSBA. It helped the company reduce cooking times, automate manual processes, and improve how products flowed from customer order to receipt and fulfillment.
Taos Mountain Energy Foods cut costs by $120,000 and, along with a Los Alamos Venture Acceleration Fund award, expanded to a 10,000-square-foot manufacturing center in Questa. The company employs 17 people.
“NMSBA helped me tap into high-level resources and expertise,” Hawari says. “Our company has grown into a national outdoor lifestyle brand. I couldn’t be happier with how it all panned out.”
Millions of dollars’ worth of expertise
Taos Mountain Energy Foods was among 352 small businesses in 31 counties that participated during 2014 in NMSBA, a public-private partnership among Sandia, Los Alamos National Laboratory, and the state of New Mexico that connects small business owners with scientists and engineers who provide technical assistance. The program also contracts with the New Mexico Manufacturing Extension Partnership, University of New Mexico Management of Technology program at the Anderson School of Management, Arrowhead Center at New Mexico State University, and the New Mexico Tech Department of Management. NMSBA provided $4.7 million worth of assistance to New Mexico small businesses last year.
Ten projects that achieved outstanding innovations through the program in 2014 were honored in a series of six events held statewide through August 18. Taos Mountain Energy Foods received the Honorable Speaker Ben Luján Award for Small Business Excellence as the honoree that demonstrated the most economic impact. The award was presented by the late New Mexico House speaker’s son, US Rep. Ben Ray Luján.
“NMSBA is a partnership that generates jobs and economic wealth in our state. It has created and retained more than 4,000 jobs,” says Jackie Kerby Moore, manager of Technology and Economic Development Dept. 7933. “We are grateful to the principal investigators who work with New Mexico’s small businesses. Together they are implementing innovative ideas and stimulating our state’s economy. It is a powerful tool.”
On the road
The six NMSBA events brought together small businesses, local economic development representatives, elected officials, and community leaders. Panel discussions with past NMSBA participants let company owners share their experiences and encourage others to join. And laboratory project managers were on hand to answer questions.
“Instead of a single awards ceremony, we decided to do it differently this year and take the event on the road,” Jackie says. “We wanted to celebrate with the businesses in their back yards with their community leaders. It was more personal.”
The first gathering was May 6 at the Taos County Economic Development Corp. Taos Mountain Energy Foods was recognized as a 2014 NMSBA success story with Mayor Dan Barrone, State Sen. Carlos Cisneros, and State Rep. Bobby Gonzales on hand.
The next stop was May 27 at the Arrowhead Center at NMSU. Fundamentalist Flowerchild Productions, a Mimbres Valley film animation company, was named a success story. Las Cruces Mayor Pro Tem Greg Smith and State Rep. Doreen Gallegos attended.
On July 22, KemKey LLC, which makes transfer fittings for the chemical industry, was recognized as a success story at an event at Katrina’s East Mountain Grill in Edgewood attended by State Sen. Sue Wilson Beffort and State Rep. Matthew McQueen. The company worked with Sandia’s Juan Romero (1832) on three-dimensional modeling to develop prototypes and designs.
A gathering Aug. 5 in Santa Fe honored three companies that participated together in what is known as an NMSBA leveraged project: Earth System Sciences LLC, Geo-Risk, and Terramar Inc., which are developing a software tool to evaluate geothermal resources. The lighting company iBeam Materials Inc. and Pharma Connect Express, which created software linking pharmaceutical reps and physicians, also were named success stories.
‘The state should be proud’
On Aug. 12, Sisneros Brothers Manufacturing LLC, which makes prefabricated ductwork, was honored in Belen. Mayor Jerah Cordova, State Sen. Michael Sanchez, and State Rep. Don Tripp were on hand. Sisneros Brothers worked with Sandia PIs John Robert Laing (1851) and Thomas Bosiljevac (1558) on tensile and lateral testing.
“NMSBA is a major benefit offered by the national laboratories,” Tripp, the House Speaker, said. “Scientists provide a level of expertise most small businesses cannot afford. The state really gets its money’s worth.”
Sanchez, the Senate Majority Leader, said the program not only helps small businesses but the communities where they are based. “These businesses thrive and support the area with jobs and other economic stimulus,” he said. “This is one of the most successful programs New Mexico has ever started. The state should be proud.”
Three NMSBA participants were honored at the final event Aug. 18 in Albuquerque, which was attended by State Rep. Gail Chasey: Facility Facts, which makes emergency-response software; IC Tech Inc., which developed automated water-flow monitoring systems and worked with Sandians Don Small (5348) and Michael Holzrichter (5335); and the leveraged program group TriLumina Corp., Dynamic Photonics Inc., 3D Glass Solutions, Theta Plate Inc., and Ideium Inc., which produce laser arrays. They worked with Sandia PI Robert Brocato (1751) on a laser-array submount assembly.
“There’s a great synergy to NMSBA,” State Sen. Gerard Ortiz y Pino said at the Albuquerque event. “The resources of a place like Sandia are applied to real-world problems. How will we break the cycle of poverty in New Mexico? We need everything we can get. NMSBA is an example of how government can provide a tremendous shot in the arm for entrepreneurs in the private sector.”
NMSBA was created in 2000 by the state legislature to bring national laboratory technology and expertise to small businesses in New Mexico, promoting economic development with an emphasis on rural areas. The program has provided more than 2,300 small businesses in all 33 New Mexico counties with $43.7 million worth of research hours and materials. It has helped create and retain 4,086 New Mexico jobs at an average salary of $38,488, increase small companies’ revenues by $200 million, and decrease their operating costs by $85 million. These companies have invested $68.3 million in other New Mexico goods and services and received $77.1 million in new funding and financing.
For further information about NMSBA, call Genaro Montoya at (505) 284-0625 or visit www.NMSBAprogram.org.-- Nancy Salem