A new 3D printing technique uses a nozzle that can change its size and shape during the printing process.

The new nozzle overcomes the speed-resolution tradeoff inherent to traditional 3D printers with fixed-nozzle diameters.

The researchers say that the new nozzle, also known as AN3DP, promises to improve the printing of everything from aerospace components and soft electronic devices to structural beams and walls.

The team’s work appears in Science Advances.

“Traditional 3D printers use fixed nozzles, which limit either resolution or speed. Smaller nozzles improve resolution but slow down printing, while larger nozzles increase speed but reduce detail. AN3DP’s design overcomes this by adjusting to the specific requirements of each feature being printed, allowing for both high resolution and faster printing,” says corresponding author Jochen Mueller, assistant professor in the Whiting School of Engineering’s civil and systems engineering department, who worked with Seok Won Kang, a postdoctoral fellow, on the project.

Inspired by the mechanisms of retractable grabber tools and tendons in humans and animals, AN3DP uses eight movable pins controlled by motors to change its shape and size. Connecting the pins is an elastic membrane that allows the material emerging from the nozzle to maintain a smooth shape. The movable pins and elastic membrane together allow for the accurate production of highly complex structures, the engineers say.

“One of the major benefits of this adaptive nozzle is its ability to reduce the ‘stair-stepping’ effect, which is common in traditional 3D printing,” says Mueller.

“This effect, reminiscent of the blocky figures in the popular game Minecraft, occurs when sloped or curved surfaces are printed using fixed nozzle sizes, resulting in a series of small, visible steps rather than a smooth surface. By adjusting the nozzle shape and size during the printing process, we can create smoother, continuous surfaces, enhancing the overall quality of printed objects.”

While AN3DP solves two primary challenges in 3D printing—accuracy and speed—it has shortcomings of its own, the team says. For instance, the current nozzle design requires manual assembly and cleaning and can only be used for a single type of fabrication process.

Mueller and Kang plan to address these limitations by refining the design to make it more practical for widespread use. They also aim to adapt AN3DP for Fused Filament Fabrication, a common 3D printing process, which would broaden its application to include more every day and industrial uses.

“I’m really excited about AN3DP and its future applications. Its flexibility is going to improve the structural integrity and functionality of printed objects, making them more suitable for complex engineering applications,” says Mueller.

Source: Johns Hopkins University

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Researchers have developed a fully biodegradable, reusable, and recyclable material to replace the wasteful concrete formwork traditionally used across the construction industry.

The base of this material is upcycled sawdust. Millions of tons of sawdust waste are created each year from the 15 billion cut trees and often burned or dumped in landfills left to contribute to environmental pollution.

The BioMatters team at the Taubman College of Architecture and Urban Planning and Digital Architecture Research & Technology (DART) Laboratory at the University of Michigan is making productive use of this readily available resource. Currently, they are using sawdust created at the Fabrication Laboratory at Taubman.

“We have made a recyclable, all natural biomaterial which is made out of sawdust. Other sawdust-based solutions are using other petroleum-based polymers—we use biopolymers which are completely decomposable,” says Muhammad Dayyem Khan, researcher at the DART laboratory. “And the biggest thing is it’s very easy to recycle and reuse.”

Led by DART director Mania Aghaei Meibodi, along with researchers Tharanesh Varadharajan, Zachary Keller, and Khan, the team proposes a novel method that couples robotic 3D printing of the wood-based material with incremental set-on-demand concrete casting to create zero-waste freeform concrete structures. The 3D-printed wood formwork shapes the concrete during casting, and the concrete stabilizes the wood to prevent deformation.

Once the concrete cures, the formwork is removed and fully recycled by grinding and rehydrating the material with water, resulting in a nearly zero-waste formwork solution.

“When the sawdust decomposes, it is producing fatty acids, lignin, which causes toxicity in water. And once it starts contaminating water, it has its effects on smaller wildlife, microbes, and a broad range of organisms. And with sawdust being extremely flammable, its potential contribution to wildfires is very high,” Khan says.

This solution directly addresses significant waste and pollution contributions of the concrete industry where formwork constitutes 40% of concrete construction expenses. Traditionally made from wood and discarded once deformed, formwork adds to the negative environmental impact of concrete construction.

“The amount of sawdust that is being produced out there—it is a huge chunk of material that is just being dumped or burned,” Khan says. “So rather than burning it up and generating more CO2 emissions, it is so much better that we make it into a material that is actually capable of being used again and again.”

This research is paving the way for sustainable construction practices that reduce waste, pollution, and resource consumption in the concrete industry. By upcycling this unused byproduct of the wood industry, the project represents a significant step toward environmentally friendly and efficient concrete construction methods.

Source: University of Michigan

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Knitted shell holds up 5-ton curved concrete structure

Researchers have created a knitted textile that serves as the shaping element for curved concrete shells. They’ve used the new technology to create a five-ton concrete structure for an exhibition in Mexico City.

The heart of the 13-foot tall curved concrete shell is a knitted formwork textile that a steel cable-net supports. The prototype, called KnitCandela, marks the first architectural-scale application of this technology. The structure is an homage to Spanish-Mexican architect Felix Candela (1910–1997).

Following a digitally generated pattern, an industrial knitting machine produced the shuttering of the formwork for the shell structure: in 36 hours, it knitted a fully shaped, double-layered 3D textile consisting of four long strips.

The lower layer forms the visible ceiling—a designed surface with a colorful pattern. The upper layer contains sleeves for the cables of the formwork system and pockets for simple balloons, which, after the entire structure is coated in concrete, become hollow spaces that help save on materials and on weight.

Manufacturing a formwork for such a geometrically complex structure using conventional methods would cost substantially more in both time and material.

In the museum’s inner courtyard, researchers had the knitted formwork tensioned between a temporary boundary frame and sprayed with a specially formulated cement mixture. This initial layer was just a fraction of an inch thick, but sufficient to create a rigid mold; once it hardened, a team applied conventional fiber-reinforced concrete.

The researchers brought the knitted fabric to Mexico City inside two suitcases—as normal checked baggage. The knit weighs only 55 pounds (25 kilograms) and the cable net around 66 pounds (30 kilograms). Taut in between the boundary frame, they supported over 5 ton of concrete curves.

Mariana Popescu and Lex Reiter developed the technology behind KnitCandela as part of Switzerland’s National Centre of Competence in Research (NCCR) in Digital Fabrication research project. Mariana Popescu is a doctoral student with Philippe Block, professor of architecture and structure at ETH Zurich, while doctoral student Lex Reiter studies with Robert Flatt, professor of physical chemistry of building materials.

Popescu’s research shows that employing knitted textiles in architectural applications cuts down on material, labor, and waste, and simplifies the construction process for complex shapes.

“It took only five weeks from the initial work until completion—much less time than if we were using conventional technology,” says Matthias Rippmann, project manager for KnitCandela and senior researcher in the Block Research Group.

KnitCandela also represents an evolution of the flexible forming system researchers developed for the HiLo roof: a doubly curved, thin-shell concrete structure the Block Research Group developed for Empa’s research and innovation building NEST in 2017. For KnitCandela, the researchers produced the knitted shell in one go, whereas they created HiLo’s shell with a network of steel cables and a sewn textile.

“Knitting offers a key advantage that we no longer need to create 3D shapes by assembling various parts. With the right knitting pattern, we can produce a flexible formwork for any and all kinds of shell structures, pockets and channels just by pressing a button,” Popescu says.

For the construction industry, 3D printing is a major topic. Philippe Block says that, to a certain extent, his group’s pioneering method is a new form of 3D printing, “only it doesn’t require a completely new kind of machine. A conventional knitting machine will do just fine.”

The researchers collaborated on the project with Zaha Hadid Architects Computation and Design Group (ZHCODE) and Architecture Extrapolated (R-Ex).

Source: Michael Walther for ETH Zurich

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