A sample part-printed from bulk metallic glass via the TPF-based FFF process

3D printing of metal made simpler with metallic glass fusion

Image credit: The authors

New research has demonstrated a new approach to 3D printing, which fuses metallic filaments made from metallic glass into metallic objects.

While the 3D printing of plastics has largely come of age in the last decade, solving many of the engineering challenges in the process, the 3D printing of metal objects has proved more problematic.

Now, a team of scientists, led by Jan Schroers, professor of mechanical engineering and materials science at Yale University, in conjunction with Desktop Metal Inc., Burlington, Massachusetts, USA, has addressed the issue of how and why 3D printing of metals is still limited.

Professor Schroers started by considering the conundrum that while the 3D printing of thermoplastics is highly advanced, metals generally don’t exist in such a similar state that they can be readily extruded.

The approach taken by Prof. Schroers and colleagues simplifies the additive manufacturing of metallic components by exploiting a softening behavior unique amongst metal of bulk metallic glasses (BMGs). As well as exhibiting plastic-like characteristics, BMGs also have high strength and elastic limits, high fracture toughness and high corrosion resistance.

The team focused on a BMG made from zirconium, titanium, copper, nickel and beryllium, with a unique alloy formula. This is a well-characterised and readily available BMG material.

The team used amorphous rods 1mm in diameter and 700mm long. An extrusion temperate of 460°C was used and an extrusion force of 10 to 1,000 Newtons to force the softened fibres through a 0.5mm diameter nozzle. The fibres were then extruded into a 400°C stainless steel mesh, where crystallisation does not occur until at least a day has passed. A robotically controlled extrusion can then be enacted to create the desired object.

“We have shown theoretically in this work that we can use a range of other bulk metallic glasses and are working on making the process more practical - and commercially-usable - to make 3D printing of metals as easy and practical as the 3D printing of thermoplastics,” said Schroers.

Unlike conventional metals, bulk metallic glasses (BMGs) have a super-cooled liquid region in their thermodynamic profile and are able to undergo continuous softening upon heating - a phenomenon that is present in thermoplastics, but not conventional metals. Schroers and colleagues have shown that BMGs can be used in 3D printing to generate solid, high-strength metal components under ambient conditions of the kind used in thermoplastic 3D printing.

This work could side-step certain compromises in choosing thermoplastic components over metal components, or vice-versa, for a range of materials and engineering applications. Additive manufacturing of metal components has already been developed, where a powder-bed fusion process is used. However, this approach requires a highly localised heating source and then solidification of a powdered metal shaped into the desired structure. This approach is both costly and complicated.

When asked what challenges remain toward making BMG 3D printing a widespread technique, Schroers said, “In order to widely use BMG 3D printing, practical BMG feedstock available for a broad range of BMGs has to be made available. To use the fused filament fabrication commercially, layer-to-layer bonding has to be more reliable and consistent.”

The team’s research has been published in the journal Materials Today.

3D printing is evolving rapidly, enabling the exploration and manufacture of objects as diverse as bionic eyes, aircraft parts, concrete and peat houses, as well as - more regrettably - handguns.

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