A new 3D printing method builds structures with two metals
(Nanowerk News) Taking cues from the structural complexity of tree and bone, Washington State University engineers have created a way to 3D print two types of steel in the same circular seam using two welding machines. The resulting bimetallic material proved to be 33% to 42% stronger than the two metals themselves, thanks in part to the stresses that occur between the metals as they cool together.
This new method uses familiar tools and is relatively inexpensive, so manufacturers and repair shops will be able to use them in the near future. With further development, it could potentially be used to make high-performance medical implants or even parts for space travel, said Amit Bandyopadhyay, senior author of the study published in the journal. Nature Communications (“Radial bimetallic structure through wire arc directed energy deposition based additive manufacturing”).
“This has a very wide application as any place that does any kind of welding can now expand their design concepts or find applications where they can combine very hard materials and soft materials almost simultaneously,” said Bandyopadhyay, a professor in the School of WSU. Mechanical and Materials Engineering.
The research team borrowed ideas from nature, noting that trees and bones derive their strength from the way layered rings of various materials interact with each other. To replicate this with metal, the WSU researchers used welding equipment commonly found in automotive and machine repair shops, integrated into computer numerical control or CNC machines. The new hybrid setup fabricates components using precise computer programming and two welding heads.
In a demonstration, two welding heads act one after the other on a circular seam to cast two metals, each with a certain advantage. The corrosion-resistant stainless steel core is made inside an outer casing of less expensive “mild” steel such as that used in bridges or railroads. Because metals shrink at different rates as they cool, internal pressure is created – essentially clamping the metals together. Tests on results show greater strength than stainless steel or mild steel alone.
Currently, 3D printing with lots of metal in a welding setting requires discontinuing and replacing metal wires. The new method eliminates that lag and places two or more metals in the same layer while the metals are still hot.
“This method keeps the metal in a circle, not just in a line. By doing so, it’s basically departing from what’s possible,” said Lile Squires, a WSU mechanical engineering doctoral student and first author of the study. “Spinning in a circle essentially allows one material to hug another, which cannot happen when printing in a straight line or in sandwiched seams.”
The ability to reinforce layer-by-layer 3D printed metal components could soon give automotive repair shops a new option with the ability to quickly fabricate strong, customized steel components. Bimetallic, torque-resistant axle shafts, for example, or cost-effective, high-performance brake rotors could be developed.
In the future, the researchers see the potential for medical manufacturing processes that score joint replacements with durable titanium on the outside and magnetic steel-like inner materials with healing properties. Similarly, structures in space can have high temperature resistant materials surrounding an inner material with cooling properties to help the structure maintain a consistent temperature.
“This concept has welder molding, so we can use multiple materials in a single layer itself, creating an advantage when combined,” says Bandyopadhyay. “And it doesn’t have to stop at just two ingredients. It can be expanded.”
