It has been reported that Washington State University engineers have created a way to Additively Manufacture two types of steel in the same circular layer using two welding machines. The resulting bimetallic material was said to be between 33% and 42% stronger than either metal alone, thanks in part to pressure caused between the metals as they cooled.
Amit Bandyopadhyay, professor in WSU’s School of Mechanical and Materials Engineering and senior author of the study published in the journal Nature Communications, shared that the new method uses commonplace, relatively inexpensive tools, meaning that manufacturers and repair shops could use it in the near term. “It has very broad applications because any place that is doing any kind of welding can now expand their design concepts or find applications where they can combine a very hard material and a soft material almost simultaneously,” said Bandyopadhyay.
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The research team, consisting of Amit Bandyopadhyay, Lile Squires, a WSU mechanical engineering doctoral student and the study’s first author, and second author Ethan Roberts, a WSU undergraduate mechanical engineering student, borrowed the idea from nature, noting that trees and bones get their strength from the way layered rings of different materials interact with each other. The WSU researchers then used welding equipment commonly found in automotive and machine shops, integrated inside a computer numerical control or CNC machine, in order to mimic the structure with metals.
The two welding heads reportedly worked one after another on a circular layer to print two metals, each with specific advantages. A corrosion-resistant, stainless-steel core was created inside an outer casing of cheaper “mild” steel, often used in bridges or railroads. Since the metals shrink at different rates as they cool, internal pressure was created — essentially clamping the metals together. Tests on the result reportedly showed greater strength than either stainless steel or mild steel has on their own.
Additively manufacturing with multiple metals in a welding setup currently requires stopping and changing metal wires; this new method eliminates that pause, putting two or more metals in the same layer while the metals are still hot.
“This method deposits the metals in a circle instead of just in a line. By doing that, it fundamentally departs from what’s been possible,” said Lile Squires. “Going in a circle essentially allows one material to bear hug the other material, which can’t happen when printing in a straight line or in sandwiched layers.”
This capacity to strengthen Additively Manufactured metal parts layer-by-layer could soon give new options to automotive shops, such as the development of bimetallic, torque-resistant axle shafts, or cost-effective, high-performance brake rotors.
The researchers also see potential for medical manufacturing processes that print joint replacements with durable titanium on the outside and an inner material such as magnetic steel with healing properties in the future. Similarly, structures in space could have a high-temperature resistant material surrounding inner material with cooling properties to help the structure maintain a consistent temperature.
“This concept has both welders printing, so we can use multiple materials in the same layer itself, creating advantages as they combine,” said Bandyopadhyay. “And it doesn’t have to stop at just two materials. It can be expanded.”
The researchers and WSU have submitted a provisional patent application for this development. This research also reportedly received support from the National Science Foundation.
To read the full study, click here.