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And now, material freedom via additive manufacturing

Mark Norfolk
By Mark Norfolk President & CEO, Fabrisonic

The low temperature intrinsic to solid-state printing processes allows manufacturers to weld layers of dissimilar metals without fear of metallurgical incompatibility issues.

The major selling point for additive manufacturing has always been freedom. The first revolution in 3D printing focused primarily on geometric freedom. Would you like parts with complex internal channels? Then 3D print it. Have a need for an organic structure that optimizes strength vs. weight? Then consider additive techniques.Customer demanding that every part be slightly different? Warm up the 3D printer.

These unique capabilities have empowered engineers to design parts that are lighter, more efficient and even cheaper. At this point in time, leaders in the industry understand geometric freedom and how to leverage that freedom for profit. As the rest of industry becomes more enlightened, we will see the broad application of 3D printing to allow fundamentally better geometric designs.

But what is next on the leading edge of additive manufacturing?

New 3D printing technologies based on solid-state bonding, instead of fusion-based welding, present an opportunity to extend 3D printing success into the freedom of material.

In fusion-based welding processes, mixtures of several metals in the molten state lead to complex metallurgical interactions, such as hot cracking and undesirable intermetallic compounds. The low temperature intrinsic to solid-state printing processes allows welding layers of dissimilar metals without fear of metallurgical incompatibility issues.

Ultrasonic additive manufacturing (UAM) is a hybrid 3D metal printing technology that uses ultrasonic vibration energy to weld similar and dissimilar metal foils together one layer at a time. The process operates near-room temperature and does not use heat as the bonding mechanism. Instead, the ultrasonic vibrations of the process scrub and break off surface oxides to bring metallic lattices intimately close, which, in turn, creates a metal-to-metal bond.

UAM has been widely used to build parts where the metal feedstock changes layer-by-layer, allowing engineers to print gradient metal laminates or transition joints from one metal to another. In addition to printing dissimilar metals, solid-state weld processes can enable embedding of non-metallics.

Early UAM research focused on embedding sensors, such as fiber-optic strain gauges, into a metal matrix to allow in situ health monitoring.

In addition to sensors, UAM can be used to embed ceramic fibers into 3D print metal matrix composites (MMCs).
Fabrisonic recently completed an MMC reinforcement study printing high-strength Nextel ceramic fibers in specific locations throughout a 6061 aerospace aluminum test geometry. Selective reinforcement works by incorporating strong, stiff, and potentially heavy material where needed and using lighter, more ductile materials in areas of lower stress. The team explored a variety of fiber sizes as feedstocks in the research process.

The study concluded that continuous ceramic fibers could be integrated with minimal fiber breakage due to the solid-state nature of the build process.

Further, tensile testing showed that strain could be transmitted from the matrix to the high strength fibers at loads in excess of the yield strength of the surrounding matrix.

At the end of the program, the team built two prototypes of a complex loaded geometry. One was unreinforced printed 6061 aluminum. The second was wire reinforced 6061 aluminum. The monolithic 6061 part failed completely at 177,000 cycles. The second plate, reinforced with fibers at a weight penalty of 9.4%, ran to 20,000,000 cycles before testing funds were exhausted.

This data leads to clear applications in aerospace where weight to performance is a key metric.

3D-printed MMCs could be used in high stress transition areas, such as bosses and mounts.

They can also be leveraged as a crack arrestor as an alternative to products, such as GLARE.

Material freedom will allow future designers to tailor material properties at different locations in a “single” 3D-printed part. That is exciting.

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