CECIMO Additive Manufacturing committee created to advance industrialisation of AM

A new Additive Manufacturing committee created by the European Association of the Machine Tool Industries and related Manufacturing Technologies (CECIMO) has been established to improve dialogue between policy makers and the 3D printing industry. The newly created AM committee aims to formalise the position of CECIMO as an industry body representing enterprises across the AM […]

The Effect of Powder Size Distribution on Binder Jetting Steel

In a paper entitled “Effect of powder size distribution on densification and microstructural evolution of binder-jet 3D-printed alloy 625,” a team of researchers test gas-atomized alloy 625 powders of three different powder size distributions including 16–63 μm (full), 16–25 μm (fine) and 53–63 μm (coarse). The powders were 3D printed with green relative bulk densities of about 52%, 45% and 48%, respectively, followed by vacuum-sintering at temperatures between 1225°C and 1300°C for 4 hours.

“For the fine and coarse powders with narrow size distribution, printing defects with high pore coordination numbers may form during the binder jetting process which cannot be removed during the final sintering stage even during supersolidus liquid phase sintering,” the researchers state. “However, the full particle size distribution gave higher green density with fewer large, highly coordinated pores so supersolidus liquid phase sintering was able to reach near-full density. Additionally, the fine powders gave non-uniform, anisotropic linear shrinkage during sintering which is unfavorable for designing complex structures.”

The researchers, using binder jetting, 3D printed samples of each powder size distribution, and sintered three samples from each set to study densification behavior. The bulk density and mass of each sample was measured when both wet and dry. For all particle size ranges, the relative bulk density increased with increasing sintering temperature from 1225°C to 1285°C. For temperatures above 1270ºC, it was also found that the coarse powder range samples had the lowest sintered density while the fine powder range samples showed the highest density.

“In general, it is thought that wide pore size distributions and low green density associated packing defects affect microstructural evolution, in particular the grain size and diffusion distances in final stage sintering and this controls final density,” the researchers state. “Thus, it was essential to examine the effect of the PSD on the average microstructural descriptors associated with the densification process. These include the average grain and pore size.”

In the experiments, binder jet 3D printing parameters including layer thickness, binder saturation and drying time were kept constant in order to study the effect of powder size and particle size distribution on the densification behavior. The following conclusions were reached:

“During densification of parts sintered between 1225 °C and 1300 °C for 4 h, the 16–25 μm powder showed higher linear shrinkage compared to the 16–63 μm and 53–63 μm powders. This correlated with lower green density of 45% achieved from the fine powder compared to the 47% and 52% for coarse and full range powders, respectively. Additionally, it was seen that as the sintering temperature increased to 1285 °C or higher, linear shrinkage in z direction was greater than that in the x and y directions, especially in 16–25 μm powder. This is thought to be due to the effect of gravity on particle rearrangement during sintering.”

In addition, densification was faster in the 16–25 μm powder samples up to 1270°C, but at the higher sintering temperature, the 16–63 μm powder samples showed faster densification behavior and more pore elimination during the final stage supersolidus liquid phase sintering.

Authors of the paper include Amir Mostafaei, Pierangeli Rodriguez De Vecchis, Ian Nettleship and Markus Chmielus.

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Testing the Properties of Fiber-Reinforced Geopolymer 3D Printing Material

In a paper entitled “Effect of Polypropylene Fibre Addition on Properties of Geopolymers Made by 3D Printing for Digital Construction,” a group of researchers investigates the effect of polypropylene (PP) fibers on the fresh and hardened properties of 3D printed fiber-reinforced geopolymer mortars. One of the main limitations of extrusion-based concrete 3D printing techniques, the researchers point out, is the difficulty of incorporating conventional steel reinforcement.

“As a possible solution, conventional steel bars might be partly or completely substituted by short-fibre reinforcement, thus minimizing or rendering unnecessary requirements for steel reinforcement with regard to mastering issues of cracking due to shrinkage or temperature changes and, in some cases, achieving particular load-bearing capacity and deformability,” they state.

Another limitation is the limited range of printable concretes, they continue. Conventional OPC concrete is not suitable because of its setting characteristics, as well as its high energy consumption and emissions. An alternative is geopolymer, which can be made by alkaline activation of fly ash and slag. There has not been a great deal of research done to optimize the mixture proportions of 3D printable geopolymers, so the researchers dedicated their work to developing an optimized geopolymer for 3D printing.

To produce a geopolymer mortar, the researchers used fly ash, micron-scale silica sand, an alkaline solution composed of sodium silicate and sodium hydroxide solutions, and sodium carboxymethyl cellulose (CMC) powder. They tested mixtures with different proportions of each ingredient before settling on one that was both extrudable and buildable. Different percentages of PP fiber were then added to the optimized mixture, in volumes ranging from .025% to 1.00%. They tested the mortar by 3D printing it with a custom-made testing device. The printed specimens were then heat treated.

The shape retention ability test setup

Rheological behavior of the mixtures was tested, as were the mechanical properties of the hardened mortar. Tests were also run for apparent porosity and interlayer bond strength.

“Fibre addition seems to influence compressive strengths positively only when the loading is perpendicular to the interface plane,” the researchers state. “This is due to the preferential fibre alignment parallel to the direction of extrusion. The addition of fibre significantly enhanced the flexural performance of the printed samples. The use of fibre dosages of 0.75 and 1.00 vol % caused deflection-hardening behaviour of the 3D-printed geopolymers and, hence, a significantly higher fracture energy in comparison to specimens without fibre or with lower fibre content.”

An increase in fiber volume did cause some minor reduction in interlayer bond strength. Higher fiber volumes, however, caused better shape retention ability in the printed samples, as well as ductility. A strong correlation between porosity and compression strength was found in the 3D printed material, similar to that of cast concrete.

The interlayer bond strength test

“The results indicate the possibility of printing fibre-reinforced geopolymers which meet all the necessary properties in both the fresh and hardened states,” the researchers conclude.

Authors of the paper include Behzad Nematollahi, Praful Vijay, Jay Sanjayan, Ali Nazari, Ming Xia, Venkatest Naidu Nerella and Viktor Mechtcherine.

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3D printing news sliced, European Space Agency, Optomec, and Carbon

In this edition of our 3D printing news digest – Sliced, we see the latest trends in the 3D printing industry, such as the development of a 3D printed wedding, non-Earth materials, and increasing variety of UV resins. Read on to learn more about Xometry, CRP USA, European Space Agency, and more.    Expanding metal […]

The Bride 3D Printed Her Entire Wedding Including Her Bouquet #3Dprinting @ErinWinick @techreview

I 3D-printed every bit of my wedding—including my bouquet

Associate Editor at MIT Technical Review and science fashionista Erin Winick writes in a recent Review article about 3D printing all of her recent wedding accoutrements from her bouquet to the cake toppers:

So when it came to planning my wedding, the traditional route was definitely not for me. I have a mechanical engineering background and have owned a desktop 3D printer for the past three years, so the chance to combine my passion for manufacturing with a huge life milestone was too tempting to pass up. That meant infusing 3D printing into the day everywhere I could.

So harnessing models from around the web, she went about printing:

Whenever there was a choice between making and buying something, I went for the 3D-printing option. I printed my headband, the bouquets for me and my bridesmaids, all the table numbers, the cake topper, the floral cake decorations, and the flower girl’s necklace. All this was carried out on my two desktop printers, Mini and Flash (yes, I have named my printers).

And as a special tech cred accomplishment: her 3D printed bouquet glowed in the dark!

Erin Winick Wedding Bouquet Glow in the Dark

See the details in her MIT Tech Review article and on her Instagram. Congratulations to you both!

Self Repairing Cities Project Continues to Make Progress with Flying Road-Fixing 3D Printers

The holiday season is here…and so is the season for terrible roads. Snow and ice will be ruling the roads for the next few months, and when they go, they will leave behind them potholes and cracks. Time to get the road crews out, resulting in further frustration as traffic flow is disrupted to fix the damage.

It’s a cycle that most people are used to, but it may not be the case forever. The Self Repairing Cities project is working to create a future in which drones repair road damage, using attached 3D printers to deposit asphalt into cracks and holes. The University of Leeds has already created a prototype of a road repair drone, and researchers at University College London have developed the world’s first asphalt 3D printer.

“Our 2050 vision is to have zero-disruption road works,” says Richard Jackson, a research associate at UCL who developed the asphalt 3D printer. “It will be quieter, so we can do it at night and the goal is to have no human input at all.”

Before the project reaches that stage, it may be deployed in a semi-automated version of the process, which several road contractors have already expressed interest in. For example, a logistics app could direct a small repair crew to crack locations, possibly in an automated vehicle, optimizing the work schedule, timing and routes. The crew would bring a “black box” which would use computer vision technology to position a 3D printer over the crack and fill it.

Not only would using drones to repair roads be less disruptive to traffic, it would be much less expensive than using human crews, according to Jackson. The idea is to repair small cracks before they can develop into full-blown potholes. Road surfaces would be continually scanned, using devices attached to the underside of municipal vehicles such as garbage trucks, and cracks would be treated soon after being identified. Using GPS, drones could be deployed to the sites of cracks, equipped with exactly the right amount of asphalt to treat each crack.

More research is required, according to Jackson, to figure out how the crack would be prepared for repair; it would need to be cleaned out and some sort of agent applied to help form a good bond between the repair material and the road surface.

“As scientists, we like to ask questions like ‘could we put a flame thrower on a drone?’” says Jackson. “And after the asphalt has been printed, are we going to compact it, or will each function be carried out by a different drone?”

The 3D printer that Jackson designed is a three-axis system with individual stepper motors that move the printer nozzle, which is made up of an auger screw, a stepper motor to drive the screw and a pellet hopper that feeds the asphalt pellets. The pellets are warmed by heating resistors and turned into liquid as they pass through the nozzle.

When Jackson tested the 3D printer, he compared 3D printed bars of asphalt to cast ones and discovered something surprising: the printed bars had up to nine times the ductility of the cast ones, with similar fracture strengths. Under closer observation, it was discovered that the 3D printed asphalt had a stretchy brown substance throughout its cross-section, unlike the cast samples. Jackson thinks that that the brown substance is composed of a lighter saturated faction of the asphalt that formed due to the way various sizes of particles move during heating and extrusion process.

“I have done some other work involving nano-fibres and the printing process influences the fibres quite strangely too,” he said.

Jackson is now working on 3D printing asphalt mixes, and while there is some trouble printing aggregate material at a small scale, mixtures of sand and asphalt can be printed. 3D printing would allow the material to be varied over the depth of the crack, with feedstock switched out to apply a different material at the bottom and the top. Jackson is also adding nanomaterials such as titanium dioxide nano particles. This will allow for printing materials to be customized for different locations. The operating parameters of the 3D printer could also be adjusted.

“There is an argument for machine learning in the design,” said Jackson. “We need a factory to make the 3D printing robots with different properties depending on the materials used in the road.”

In a separate project, researchers at Texas A&M have been working with 3D printing to repair spall damage, which happens when lumps of concrete in concrete roads break off around cracks. Jaeheum Yeon from the university’s Department of Engineering and Technology said that he and colleagues Julian Kang from the Department of Construction Science and Wei Yan from the Department of Architecture were inspired by dental technology to 3D print concrete patches for the spall damage.

“The use of laser scanners and 3D printers to treat cavities also has implications for engineers in concrete road maintenance,” said Yeon. “This method of treating cavities using 3D printers can be used to repair spall damage on concrete roads.”

The researchers used photogrammetry software to create a computer model of the spall damage, which was then used to create a plastic formwork into which concrete was poured. The patch was then glued into the hole. This technique has been used for two holes in the university’s parking lot. The longevity of the technique still needs to be proven before using it on roads, but the researchers believe that it could be used to repair holes in two days rather than the usual seven, as well as reducing costs from $140,000 to $1,700.

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Asphalt 3D Printing Drone Repairs Roads

With the proliferation of construction and repair 3D printing, we’ve seen ones that can make bridges and even houses. Now, the same principle is proving beneficial to infrastructure and road renovations. Leeds University have developed a prototype asphalt 3D printing drone that can fill in cracks in roadways by remote control. The concept has already […]

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