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Making a material difference

High-tech additive manufacturing, or 3D printing, takes the guesswork out of making a hollow metal object, while tweaking and fine-tuning the properties of the material composing it. These components were fabricated at the Signma Complex at Los Alamos National Laboratory. (Courtesy of LANL)

Making a vessel by building it up from a base material is at least as old as the art of pottery. To create a vase, a potter starts by mixing clay with sand, other minerals – perhaps mica for a glittery shine – and water. Then the clay is kneaded to the desired consistency and coiled into thick ropes of moist clay that lie on top of each other to form the desired shape.

That ancient process has a lot in common with high-tech additive manufacturing, or 3D printing. It is a good way to take the guesswork out of precisely fabricating a hollow metal object, while tweaking and fine-tuning the properties of the material composing it.

Additive manufacturing starts with a design file from a computer. That file controls an electron beam or laser that fuses successive layers of metal alloy or other material to build an object. The laser traces the shape of the part by melting the raw material with a bright flash, and then the machine’s platform shifts down almost imperceptibly and a wiper spreads another layer of powder. This process might repeat thousands of times over several hours or days.

This highly controlled manufacturing process lets you build a part relatively quickly and easily, test and analyze it, redesign it based on what you learn, create an improved version, and then repeat the process in ongoing refinement.

Additive manufacturing is a potential way to solve the performance challenges a component faces with hard use in harsh environments where failure isn’t an option, such as aerospace or drilling. Researchers at Los Alamos National Laboratory’s Sigma Complex apply fundamental science and research to take this advanced manufacturing to an even higher level.

Sometimes, the solution is to make new components in a new way – no easy task. Traditional fabrication methods lean heavily on trial and error, which is a slow, laborious and imprecise method of crafting a part. That’s not good enough for the work at Los Alamos, so material scientists are overcoming these challenges by making new parts with predictable performance by pioneering an approach called science-based qualification.

In one recent project, researchers at the Sigma Complex at Los Alamos, in collaboration with a team from other Department of Energy laboratories, set out to make a metal pressure vessel for energy applications via additive manufacturing. Traditionally, this part – the size and shape of an aluminum can – was forged, machined and welded. Could additive manufacturing make the vessel more efficiently and with equal or better properties?

How well a component performs depends on the properties of its materials. Will it twist or bend under a force, burst under pressure, corrode in humidity, weaken in extreme heat, or break down in high radiation? The part’s reliability also depends on how well the manufacturing process has been controlled.

The team needed just the right properties of stainless steel in the sweet spot between brittle and soft. To hit that sweet spot, they first modeled the vessel using computer codes describing the physics and properties of the materials and drawing on real-world data about the compounds making up the steel. In this way, they designed a specific microstructure for the alloy with predictable material properties matching the performance requirements for the part.

The team also used sensors and diagnostics during the build to understand what the process was doing, and then tore the finished piece apart to analyze it through destructive testing.

From all this analysis, the researchers were able to improve the manufacturing-physics models and continue refining the design. When they were done, they not only established a significantly better way to make this pressure vessel, but also laid the foundation for improving fabrication of other metal components.

Additive manufacturing won’t solve every materials-related manufacturing challenge. In many cases, the tried-and-true methods of casting and forging metal will do the job just fine. The most challenging situations, though, depend on an intimate understanding of the materials and how the parts are made.

Manufacturing technology is always evolving and manufacturing science helps us understand new methods, as well as old. Advances in computer modeling allow scientists to penetrate deeper into the mysteries of how twisting the knobs and dials in the process can alter the structure at the molecular level and improve the performance of a part – like a pressure vessel – for a specific purpose. New technology will make a material difference in our world as it helps bring new ideas into reality, with applications ranging from space and ocean exploration to sustainable energy development and aeronautics, plus a hundred applications we haven’t even thought of yet.

Deniece Korzekwa is an expert in casting and fabrication, and serves as senior engineer of Sigma division at Los Alamos National Laboratory.

 

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