By Emily Newton
As 3D printing has become more popular, people have become interested in enhancing the mechanical properties of their creations. One of the ways to do that is to use a 3D-printed lattice structure. Here are some tips for bringing lattice structures into your projects.
Understand how the specifics of the lattice create certain results
Various 3D lattice types exist, and you can frequently identify them by examining the lattice’s cell structure. They often appear as recognizable shapes, such as cubes, hexagons and octagons. However, some designs are nonuniform. Each lattice unit is a cell, and the combination of all of them creates the structure. The size and shape of the lattice structure affect factors such as its strength, elasticity and weight.
Moreover, people can orient the shapes inside a lattice in different ways to affect how the part performs. However, they should also be aware that printing limitations also affect cell orientation. For example, certain ones require more support structures and could increase the post-printing processing time.
The lattice material is another point of consideration. For example, soft, stretchy options are generally unsuitable for large parts because they’re likely to sag. People often match the lattice to a part’s outermost material. Although that’s a popular choice, it’s not a rigid requirement.
Consider an end user’s requirements
Succeeding with 3D-printed lattice structures means anticipating what the target audience needs and wants while using the printed item. Sneaker brand Adidas showed what’s possible with its 4DFWD products, marketed to high-performance runners.
The company chose a trademarked industrial 3D printing technique called Carbon Digital Light Synthesis (DLS). It’s a resin-based option that creates polymeric parts with oxygen-permeable optics, digital light projection and engineering-grade materials. This project involved using a brand-new elastomeric material developed by material scientists at Carbon called EPU 41.
A partnership between Adidas and Carbon resulted in making shoes with a lattice midsole structure. It improves a wearer’s shock absorption and provides them with better stability. Rather than using one of the existing 3D lattice types for this project, the shoes feature a proprietary FWD CELL shape. This approach brought a 15% decrease in the forces present when a runner slows, plus a 23% boost in cushioning.
Additionally, the lattice shape translates the vertical impact forces caused by a runner’s push from the pavement into forward momentum. This application also features software-based tuning that lets engineers customize the shape and size of the cell, as well as the strut diameter.
Investigate how to solve known problems
Some people feel compelled to see how a 3D-printed lattice structure could address problems that affect individuals in entire industries, and arguably, all of society. Some of the associated advancements could complement progress already made in targeting those issues.
For example, since the world relies so much on concrete, there’s a tremendous collective interest in making it better. In one case, researchers are working on concrete that can heal itself. They devised a mixture containing bacteria that makes limestone to fill a crack once water enters it.
That’s one solution, but people are also looking for ways to reduce the chances that concrete will crack at all. That’s where lattices could come into the picture. Researchers at UC Berkeley wanted to target a known issue where concrete is strong when compressed but weak if exposed to tension.
Their work involved creating octet polymer lattice structures and filling them with ultrahigh-performance concrete. The resulting material was four times stronger than typical concrete. The team concluded that in addition to increasing the ductility, this use of lattice structures could reduce the carbon emissions associated with concrete production. That would occur by using more polymers in the materials.
Open your mind to new possibilities
Working with a 3D-printed lattice structure may require realizing that some of the outcomes could go against some commonly accepted theories about mechanical properties. In one case, researchers developed a new lattice structure class that’s lightweight and shows high stiffness.
The achievement brought some surprises, particularly since it went against the Maxwell criterion. That’s a mechanical design theory that suggests the most efficient load-bearing structures only become deformed by stretching.
A 50% weight reduction for the lattice structures halved their stiffness, too, experiments showed. However, less-efficient items would have shown only three-quarters or seven-eighths of the original stiffness when decreasing the weight by half. They intended to use their new knowledge to make mechanical metamaterials that are both extremely lightweight and stiff.
Engineer Seth Watts, who co-led the team, explained, “We have found two trusses that have linear scaling of stiffness with density when the conventional wisdom — this Maxwell criterion rule — is not satisfied.”
He continued, “It had been believed that the Maxwell criterion was both necessary and sufficient to show that you had high stiffness at low density. We’ve shown that it is not a necessary condition. In other words, there is a larger class of trusses that have this linear scaling property. It shows that what was the previous orthodoxy is not firm. There are exceptions, and the exceptions actually can get you better properties.”
Examine the effects of using uncommon materials
Besides determining which of the 3D lattice types is most likely to provide the desired properties for your project, it’s worthwhile to explore using materials that aren’t yet widely used. That can be somewhat of a gamble, but it may pay off.
In one instance, researchers from the University of Central Florida and the U.S. Army sought to use lattice structures to tweak the compressive strength and failure modes for gear supplied to soldiers. They chose a high-strength magnesium alloy called WE43, which is not a commonly selected option for 3D printing yet. It’s a corrosion-resistant material that tolerates temperatures of nearly 600 F.
The team fabricated 24 micro-lattice structures and optimized their printing process. These choices improved the density of the produced items, too. The hope is that the combination of 3D-printed lattices and lightweight alloys will result in more manageable weapons that are not so burdensome for soldiers to carry. Further research will involve looking at the high strain rate of the 3D-printed structures and checking their ballistic properties.
Another application of lattice structures in the military comes from a company called Windpact. It used hierarchical lattice structures inside helmets to reduce a soldier’s likelihood of suffering a traumatic brain injury. Modeling tests showed that the lattice gradients made them stronger than structures without that variance. Windpact has also designed helmets for professional football players.
Lattice structures offer exciting possibilities
These examples highlight some of the many ways you could work with 3D-printed lattice structures to achieve different mechanical properties than what’s possible without them. As more research occurs in this area, you’ll undoubtedly have more use cases that could inspire future efforts.