New 3D Printing Tool Replicates Nature's Use of Multiple Materials

May 2017
Topics: Electronics Manufacturing, Technological Innovations, Computing Methodologies
Can fabricated objects ever match the complexity and adaptability of the natural world? Researchers at MITRE believe they're on track to do just that, using innovative concepts in advanced manufacturing, such as 3D printing and additive manufacturing.
Employees looking at 3D printer

Nature has some incredibly sophisticated manufacturing tricks up her sleeve.

Take the human knee for example. The cartilage is soft and flexible enough to allow the joint to bend and absorb impact. Yet the bone is tough and durable enough to support our weight. Two materials with completely different properties melded into a single entity to optimize efficiency, comfort, and use.

Biological systems routinely transition between diverse material properties in a single "product." They also optimize for both form and material composition—meaning the bone and cartilage are also perfectly shaped for their task.

So far no human manufacturing processes come close to this level of sophistication. Traditional manufacturing processes focus on shape, rather than composition. They use uniform materials, such as aluminum, plastic, or steel to create individual parts. The parts are then assembled into a large, complex product, such as an engine. But these complex assemblages tend to be heavy, expensive, and prone to performance issues.

Even cutting-edge materials have limitations to their heterogeneity. Composites are typically layered, with little variation along each layer. Nanomaterials may vary three-dimensionally, but are frequently constrained to complex geometries and discrete subcomponents. They generally cannot vary in material composition on a voxel-by-voxel basis. Producing larger items with such methods can often be a challenge.

The key to replicating nature may ultimately lie in the realm of advanced manufacturing (AM), specifically with additive manufacturing or 3D printing. These technologies use a computer program to direct the build-up of successive layers of material into a desired object. Advanced 3D printers exist now that can manufacture objects consisting of multiple materials—but only if the designer knows exactly where to put each material beforehand. Few tools or techniques exist to guide that process—until now.

Optimizing for Both Shape and Material Composition

MITRE mechanical engineers Jared Ahern and Anthony DiCarlo are getting ahead of the curve by developing technology to support state-of-the-art AM. They've developed a technique called Computationally Engineered Advanced Manufacturing of Parts (CEAMP), which is based on a set of algorithms for computing the optimal multi-material configurations for a single part. In other words, they can determine the best place for certain materials to be positioned within a single shape to improve performance. Ahern and DiCarlo co-lead the project for MITRE's internal research program.

"With CEAMP, we can optimize both the material and the topology," Ahern says. "That means we can put the stronger materials where we need them—such as at a stress point or a location where rigidity is needed—but use something lighter everywhere else. That will result in size and weight reductions and increased performance. It's really the beginning of a paradigm shift in design."

An example of future designs is a backpack frame that has the strongest (and typically heaviest) materials near the attachment points, but is light everywhere else. That could save a foot soldier several pounds on his or her back. Or it could be used to create a next-generation prosthetic leg that exactly matches the more durable materials against the weight distribution of the wearer. And what about a phone case with rubber built into the areas most apt to get thwacked if it's dropped?

Ahern and DiCarlo launched CEAMP in 2015, funded by MITRE's Technology Futures Program. In 2016, they delivered a conference paper at the IEEE Aerospace Conference about their work. They initially focused on proving their concept in load-bearing experiments, which they conducted at the MITRE Mechanical and Reliability Engineering test laboratory in Bedford, Massachusetts.

The experiments showed that the heterogeneous material configuration they manufactured using MITRE's multi-material 3D printer performed better than the uniform stiffness design.

Navy Aircraft Test Is Important First Step

Their goal now is to advance these techniques to address issues of thermal conduction and electromagnetism. This could ultimately lead to devices such as improved heat sinks and radomes.

The researchers realize their technology is about five to seven years ahead of real-world application. But for there to be demand for material optimization tools, AM must first make it to the factory floor as a viable, affordable alternative to current machinery.

As DiCarlo explains, industries from automotive to electronics have millions of dollars invested in existing production lines. They don't want to take cost write-offs until AM has proven to be totally reliable and repeatable. In other words, there's little point in improving the technology until the technology has been widely accepted. And while AM software exists today with the ability to optimize shape, the ability to create multi-material parts is still in its infancy.

Our sponsors are already interested in using AM in innovative ways. For example, with the support of MITRE and the Penn State Applied Research Lab, the Naval Air Systems Command took an important step last summer with its first successful flight demonstration of a critical aircraft component built using 3D printing techniques. A military aircraft completed a test flight using a titanium, 3D-printed rod to secure the engine to the wing. It was the first time a U.S. Navy aircraft flew with an AM part deemed essential to safe flight.

"AM is a game changer," Liz McMichael, Naval Air Systems Command AM Integrated Product Team lead said at the time. "It will revolutionize how we repair our aircraft and develop new capabilities."

That’s certainly a promising step to DiCarlo and Ahern. Now, they would like government and industry to push the envelope further and use the unique capabilities of AM to not just replace traditionally manufactured parts, but improve upon them. In addition to CEAMP, MITRE works in other areas of AM. The Sensors and Electromagnetics Systems department has developed a phased-array antenna based on small, interlocking 3D features. These projects were recently highlighted in a YouTube video.

"This is why companies like MITRE exist—to nudge them along, to prove a concept and make it absolutely clear what the advantages are and that they are within their reach," DiCarlo says. 

—by Twig Mowatt

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