Novel materials for 3D printing enabling high-performance parts optimized for strength, stiffness, and damage tolerance.

Rajesh Uppal December 2, 2021 Manufacturing, Material Comments Off on Novel materials for 3D printing enabling high-performance parts optimized for strength, stiffness, and damage tolerance. 818 Views

3D printing or additive manufacturing is ongoing revolution in manufacturing with its potential to fabricate any complex object and is being utilized from aerospace components to human organs, textiles, metals, buildings and even food. 3D printing is also revolutionizing defence by printing small components to full drones on naval vessels, replacement parts for fighter aircrafts to printing ammunition.

With the constant technology inventions, more materials are used for 3D printing. No longer is the 3D printing market limited to polymers as there are various materials to tap into. Substantial improvements have been made in 3D printing with the fabrication of 3D objects from metals, ceramics, plastics, and even multi-material capabilities.

Common 3D printing materials

Nylon is a synthetic thermoplastic polyamide and is the most popular plastic substance used for 3D printing. What makes it an ideal choice for 3D prints is its flexibility, low friction, and durability. This material is also a common choice for textiles and making accessories. Nylon filament is an ideal option for complicated or delicate geometries. It’s majorly used as a filament material in Fused Filament Fabrication or Fused Deposition Modeling 3D printers. It’s inexpensive and one of the sturdiest plastic materials.

ABS Plastic: This thermoplastic filament material is a top choice for use as a 3D printer filament. ABS is also one of the most commonly used materials for household and personal 3D printing. ABS is a good option for engineers and manufacturers who need high-quality prototype products.

Resin: Here is another common choice for 3D printing. Resin materials are typically used in DLP, SLA, CLIP, and Multijet technologies. Several kinds are compatible with 3D printing, including tough resin, castable resin, flexible resin, and more.

Gold and Silver: These metal filaments get processed in powder form and are some of the sturdiest for use in 3D printing. They are mostly used to make jewelry. Printing processes used with these metal filaments include Direct Metal Laser Sintering and Selective Laser Melting.

Stainless Steel: Fusion and laser sintering are the methods used when printing with stainless steel. This material works with two types of technologies: DMLS and SLM. Given stainless steel is good for constructing sturdy materials and detailed work, it’s ideal for things like key chains, bolts, and miniatures, among others.

Titanium: This is the lightest and strongest 3D printing material and has a moderate surface roughness. Titanium gets printed via Direct Metal Laser Sintering. The main application of titanium filaments is in high-tech fields like medicine, space exploration, and the aerospace industry.

Ceramics: Ceramics can withstand extreme pressure and temperature without warping or breaking. It’s less likely to get corroded and doesn’t easily wear away. Therefore, it’s more long-lasting than metals and plastics. Ceramics are typically used with Binder Jetting technology, Stereolithography, and DLP (Digital Light Processing).

Novel Materials

Now 3D printing is being used to print novel high-performance materials. An engineering physics professor at the University of Wisconsin–Madison has created new materials that behave in an unusual way that defies the standard theory engineers use for designing things like buildings, airplanes, bridges and electronic devices.

A team of researchers has demonstrated a novel 3-D printing method that yields unprecedented control of the arrangement of short fibers embedded in polymer matrices. They used this additive manufacturing technique to program fiber orientation within epoxy composites in specified locations, enabling the creation of structural materials that are optimized for strength, stiffness, and damage tolerance.

German Researchers have developed and manufactured a family of architectures that maximizes the stiffness of porous lightweight materials. It’s practically impossible to develop stiffer designs. Virginia Tech researchers have created a novel way to 3-D print the type of high-temperature polymeric materials commonly used to insulate space craft and satellites from extreme heat and cold. Previously, the polyimide could previously be made only in sheets.

Researchers Invent Technology To Remedy 3D Printing’s ‘Weak Spot’

Allowing users to create objects from simple toys to custom prosthetic parts, plastics are a popular 3D printing material. But these printed parts are mechanically weak — a flaw caused by the imperfect bonding between the individual printed layers that make up the 3D part. Researchers at Texas A&M University, in collaboration with scientists in the company Essentium, Inc. have now developed the technology needed to overcome 3D printing’s “weak spot.” By integrating plasma science and carbon nanotube technology into standard 3D printing, the researchers welded adjacent printed layers more effectively, increasing the overall reliability of the final part.

“Finding a way to remedy the inadequate bonding between printed layers has been an ongoing quest in the 3D printing field,” said Micah Green, associate professor in the Artie McFerrin Department of Chemical Engineering. “We have now developed a sophisticated technology that can bolster welding between these layers all while printing the 3D part.” Their findings were published in the February 2020 issue of the journal Nano Letters. Plastics are commonly used for extrusion 3D printing, known technically as fused-deposition modeling. In this technique, molten plastic is squeezed out of a nozzle that prints parts layer by layer. As the printed layers cool, they fuse to one another to create the final 3D part.

However, studies show that these layers join imperfectly; printed parts are weaker than identical parts made by injection molding where melted plastics simply assume the shape of a preset mold upon cooling. To join these interfaces more thoroughly, additional heating is required, but heating printed parts using something akin to an oven has a major drawback. “If you put something in an oven, it’s going to heat everything, so a 3D-printed part can warp and melt, losing its shape,” Green said. “What we really needed was some way to heat only the interfaces between printed layers and not the whole part.”

To promote inter-layer bonding, the team turned to carbon nanotubes. Since these carbon particles heat in response to electrical currents, the researchers coated the surface of each printed layer with these nanomaterials. Similar to the heating effect of microwaves on food, the team found that these carbon nanotube coatings can be heated using electric currents, allowing the printed layers to bond together. To apply electricity as the object is being printed, the currents must overcome a tiny space of air between the printhead and the 3D part. One option to bridge this air gap is to use metal electrodes that directly touch the printed part, but Green said this contact can introduce inadvertent damage to the part.

The team collaborated with David Staack, associate professor in the J. Mike Walker ‘66 Department of Mechanical Engineering, to generate a beam of charged air particles, or plasma, that could carry an electrical charge to the surface of the printed part. This technique allowed electric currents to pass through the printed part, heating the nanotubes and welding the layers together. With the plasma technology and the carbon nanotube-coated thermoplastic material in place, Texas A&M and Essentium researchers added both these components to conventional 3D printers. When the researchers tested the strength of 3D printed parts using their new technology, they found that their strength was comparable to injection-molded parts.

“The holy grail of 3D printing has been to get the strength of the 3D-printed part to match that of a molded part,” Green said. “In this study, we have successfully used localized heating to strengthen 3D-printed parts so that their mechanical properties now rival those of molded parts. With our technology, users can now print a custom part, like an individually tailored prosthetic, and this heat-treated part will be much stronger than before.” The primary author of the research is C. Brandon Sweeney, a former Texas A&M materials science and engineering student in Green’s laboratory. He is the head of research and development and co-founder at Essentium.

US Army adapts military-grade steel alloy for 3D printing ultra-strong parts

Researchers from the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory have adapted a specialized steel alloy for Powder Bed Fusion 3D printing. The new material, along with specific process parameters, can produce parts that are roughly 50% stronger than commercially available materials.

The ability to produce ultra-strong metal components from the military-grade steel, however, could be a game changer. “You can really reduce your logistics footprint,” said Dr. Brandon McWilliams, a team lead in the lab’s manufacturing science and technology branch. “Instead of worrying about carrying a whole truckload, or convoys loads of spares, as long as you have raw materials and a printer, you can potentially make anything you need.”

The material in question is AF96, a steel alloy originally developed by the U.S. Air Force for bunker-busting bomb applications. Researchers from the army laboratory adapted the material, which boasts high strength and hardness, into powder form so it can be used with Powder Bed Fusion technology. The researchers have successfully 3D printed complex components using the steel powder that would have been impossible to produce using more traditional manufacturing processes.

“The nice thing about that for the Army is that it has wide ranging applications,” McWilliams added. “We have interest from the ground combat vehicle community, so [AF96] could be used for replacement parts. A lot of our parts in ground vehicles now are steel. So this could be dropped in as a replacement not having to worry about material properties because you know it’s going to be better.”

“We’ve printed some empeller fans for the M1 Abrams [Main Battle Tank] turbine engine and we can deliver that part—they can use it, and it works,” he said. “But it’s not a qualified part. In terms of a battlefield scenario, that may be good enough to be able to get your tank running again for hours or days if that’s important to the mission, but on the other hand, we still need to be able to answer, does this perform as good as the OEM part? Does this perform better?”

With that in mind, the army researchers are pursuing two strategies: one for battlefield sustainment, involving the production of replacement parts on demand; and one for futures systems. In the latter strategy, the researchers are working with OEMs and industry partners to see how additive manufacturing can be adopted and certified more broadly across the military. Presently, the lab is working with its various industry and academic partners to model new alloy designs and perform computational thermodynamics. Ultimately, the aim is to deploy new, better performing alloys to soldiers in the field for 3D printing.

McWilliams concluded: “We’ve developed a road map and that’s an integrated plan that’s now focused on supporting our modernization priorities, but we’re also tied closely to the ground combat vehicle community.”

The stiffest porous lightweight materials ever

A research team from ETH Zurich and MIT led by Dirk Mohr, Professor of Computational Modeling of Materials in Manufacturing, has developed and fabricated material architectures that are equally strong in all three dimensions, and that are simultaneously extremely stiff. It is possible to determine mathematically just how stiff materials with internal voids can theoretically become; Mohr’s structures have been shown to come extremely close to this theoretical maximum stiffness. Put another way, it’s practically impossible to develop other material structures that are stiffer for the given weight.

Plates replacing trusses

A characteristic feature of the design is that the stiffness in the material’s interior is achieved through plate-lattices rather than trusses. “The truss principle is very old; it has long been used for half-timbered houses, steel bridges and steel towers, such as the Eiffel Tower. We can see through truss lattices, so they are often perceived as ideal lightweight structures,” says Professor Mohr. “However, using computer calculations, theory and experimental measurements, we have now established a new family of plate-lattice structures that are up to three times stiffer than truss-lattices of the same weight and volume.” And it is not just the stiffness (resistance to elastic deformation) of these structures that approaches theoretical maximum values: their strength (resistance to irreversible deformation) does, too.

The ETH researchers initially developed these lattices on the computer, calculating their properties in the process. Then they produced them at the micrometre scale from plastic through 3D printing. Mohr emphasises, however, that the advantages of this design are universally applicable — for all constituent materials and also on all length scales, from the very small (nanometre-sized) to the very large.

Lightweight construction, the current cost of which limits its practical use to aircraft manufacturing and space applications, could then also be used for a wide array of applications in which weight plays a role.” In addition to making structures lighter, the numerous voids also reduce the amount of raw materials needed, and thus also the material costs. There’s no limit to the potential applications, Mohr says. Medical implants, laptop casings and ultralight vehicle structures are just three of many possible examples. “When the time is right, as soon as lightweight materials are being manufactured on a large scale,” Mohr says, “these periodic plate lattices will be the design of choice.”

Novel 3-D printing technique yields high-performance composites

Nature has produced exquisite composite materials — wood, bone, teeth, and shells, for example — that combine light weight and density with desirable mechanical properties such as stiffness, strength and damage tolerance.

Now, a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has demonstrated a novel 3D printing method that yields unprecedented control of the arrangement of short fibers embedded in polymer matrices. They used this additive manufacturing technique to program fiber orientation within epoxy composites in specified locations, enabling the creation of structural materials that are optimized for strength, stiffness, and damage tolerance.

Their method, referred to as “rotational 3D printing,” could have broad ranging applications. Given the modular nature of their ink designs, many different filler and matrix combinations can be implemented to tailor electrical, optical, or thermal properties of the printed objects.

“Being able to locally control fiber orientation within engineered composites has been a grand challenge,” said the study’s senior author, Jennifer A. Lewis, Hansjorg Wyss Professor of Biologically Inspired Engineering at Harvard SEAS. “We can now pattern materials in a hierarchical manner, akin to the way that nature builds.” Lewis is also a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard.

3-D printing to make their new polymer lattice materials

Roderic Lakes and graduate student Zachariah Rueger of University of Wisconsin–Madison used 3-D printing to make their new polymer lattice materials. Their design—the pattern in which the materials’ polymer strips are arranged—is a repeating crisscross structure. When it’s twisted or bent, a bar of this polymer lattice is about 30 times stiffer than would be expected based on classical elasticity theory.

The classical elasticity theory works well for predicting the behavior of most ordinary materials, including steel, aluminum and concrete, and ensuring structures can withstand mechanical forces without breaking or deforming too much. But for some materials, the theory is limiting.

Performing measurements in the lab, Lakes determined that the materials’ behavior was consistent with Cosserat elasticity, a more descriptive theory of elasticity that takes into consideration the size of the underlying structure in a material. “When you have a material with substructure in it, such as some foams, lattices and fiber-reinforced materials, there’s more freedom in it than classical elasticity theory can handle,” Lakes says. “So we’re studying the freedom of materials to behave in ways not anticipated by the standard theory.”

This increased freedom offers a potential path to creating novel materials that are immune to stress concentration; in other words, materials with improved toughness. Such materials would be useful for a variety of applications, including making airplane wings more resistant to cracks.

If a crack forms in an airplane wing, stress is concentrated around the crack, making the wing weaker. “You need a certain amount of stress to break something, but if there’s a crack in it, you can break it with less stress,” Lakes says.

Using the Cosserat theory of elasticity to inform materials design will yield tougher materials in which stresses are distributed throughout the materials differently, according to Lakes.

These same effects are present in materials such as bone and certain types of foams. However, when engineers make foam for a seat cushion, for example, they don’t have much control over the foam’s substructure—the tiny bubbles that form and make up the cells inside the foam. As a result, they have limited ability to tailor the Cosserat effects.

In contrast to foam, the UW–Madison researchers can tune the Cosserat effects in their lattice materials and make them very strong.

“We developed a material in which we have exceptionally detailed control over the fine structure of our lattice, and that enabled us to achieve very strong effects when bending and twisting the material,” Lakes says.

Novel 3D-printed high-performance polymer could be used in space

The material, formally known as Kapton, is an aromatic polymer composed of carbons and hydrogens inside benzene rings, which provides exceptional thermal and chemical stability. But because of this molecular structure, the material is notoriously difficult to produce in any format other than thin sheets. Kapton often is used in the multi-layer insulation that forms the outer wrapping of spacecraft, satellites, and planetary rovers to protect them from extreme heat and cold. It often is mistaken for “gold foil.”

Researchers from the College of Engineering and College of Science were able to synthesize the macromolecules, allowing them to remain stable and maintain their thermal properties for processing in 3-D printing. The high-performance polymer now could theoretically be used in any shape, size, or structure, with small chess pieces and lattice bricks already produced inside Virginia Tech labs. Possible future uses are not limited to the aerospace industry. The same material can be found in scores of electronic devices, including cell phones and televisions.

Materials currently used in 3-D printing do not have the high strength and stiffness across broad hot-cold temperature ranges necessary for the extremes of space. Typically, printable polymers start to lose their mechanical strength at about 300 degrees Fahrenheit.

This new polymer maintains its properties above 680 degrees Fahrenheit, the research team said. “We are now able to print the highest temperature polymer ever – about 285 degrees Fahrenheit higher in deflection temperature than any other existing printable polymer. Additionally, our 3-D printed material has equivalent strength to the conventionally processed thin-film Kapton material,” Williams said.

(The material’s heat-resistant ceiling before degradation is 1,020 degrees Fahrenheit.)

CRP Technology launches new carbon fibre filled polyamide material for powder bed fusion 3D printing reported in June 2021

RP Technology has announced the launch of a new polyamide-based carbon fibre filled composite for powder bed fusion 3D printing processes. Windform RS is the tenth material of CRP’s Windform TOP-LINE range of composite materials developed for powder bed fusion and is said to boast ‘exceptional’ mechanical characteristics.

The material has high resistance to damage, shock, vibrations, deformations and high temperatures, as well as water and liquid absorption. It has been successfully tested at -40°C and down to just 1 millimetre part thickness, rated HB according to the flammability UL 94 test. Windform RS also has a tensile strength of 85.25 MPa, elongation at break of 9.46% and low density of 1,10 g/cc.

Offering ‘enhanced functionality’ and good printability, CRP says Windform RS is able to provide designers and engineers with greater flexibility and speed when developing parts that have to meet requirements around fatigue, shocks and high and low temperatures. The company expects Windform RS to be of interest to customers in the aerospace, military, robotics, motorsports, automotive and marine sectors, where it can be leveraged to produce functional prototypes and heavy-duty end-use applications that are deployed in harsh environments.