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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. Its advantages include less waste and an ability to print custom designs, such as intricate lattice structures, that are otherwise hard to create. 3D printing is also revolutionizing defence by printing small components to full drones on naval vessels, replacement parts for fighter aircrafts to printing ammunition.
Not only is 3D printing becoming faster and producing larger products, but scientists are coming up with innovative ways to print and are creating stronger materials, sometimes mixing multiple materials in the same product. Substantial improvements have been made in 3D printing with the fabrication of 3D objects from metals, ceramics, plastics, and even multi-material capabilities.
Military requires new type of 3D printers with high speed so that they can rapidly adapt to new missions such as during conflicts or after natural disasters. NASA and the US military used 3D printed components to successfully test advanced prototype airplanes, spacecraft and even ground vehicles. In March 2016, the Navy successfully test launched three Trident II D5 Fleet Ballistic Missiles made by Bethesda, Maryland-based Lockheed Martin. The one-inch wide aluminum alloy connector backshell component protects vital cable connectors in the missile. The backshell component was designed and fabricated entirely using 3D design and 3D printing, a process that allowed Lockheed Martin engineers to produce the part in half the time it would take traditional methods. Considerable investments are being made worldwide to develop, qualify and certify 3D printed parts for the military.
3D printers are also required to print strategic materials like synthetic diamonds and carbon fibers.
According to John Burrow, deputy assistant secretary of the Navy for Research, Development, Test and Evaluation, additive manufacturing is at the core of the Pentagon’s Third Offset Strategy. “I will tell you, frankly…AM is the foundation for the Third Offset,” Marotto said. “Levering the technology as agnostic as it is…is really the key if you’re going to operate as a Marine Corps in a distributed ops environment. Everything from being able to print your own parts in stream…to printing your own UAVs for ISR, for weaponization, on site, custom made, with sensors to do that exact mission that you need at that exact moment.”
3D Printer evolution
Early printers were slow, small-scale and prone to producing layered, imperfect and weak structures. These found a niche in rapid prototyping, making plastic model parts as mock-ups for later production by conventional methods. As an area of research, this kind of printing wasn’t thrilling, says Timothy Scott, a polymer scientist at Monash University in Melbourne, Australia: “Basically making trinkets and knick-knacks. For a polymer chemist, it was pretty dull.”
In 2015 by a team led by Joseph DeSimone, a chemist and materials scientist at the University of North Carolina at Chapel Hil unveiled a way to print light-sensitive resin up to 100 times faster than conventional printers. It uses a stage submerged in a vat of resin. A digital projector shines a pre-programmed image up at the stage through a transparent window in the floor of the vat. The light cures an entire resin layer at once. DeSimone’s advance was to make the window permeable to oxygen. This kills the curing reaction and creates a thin buffer layer, or ‘dead zone’, just above the window’s surface so that the resin doesn’t stick to the bottom of the vat each time a layer is printed. The stage rises continually, pulling the completed part up through the liquid as new layers are added at the bottom.
Other labs were working on similar concepts at the time, says Lewis. But perhaps most impressive about DeSimone’s resins was that they could undergo a second reaction in a post-print heat treatment to strengthen the finished product. “It opens up a much broader array of materials,” says Lewis.
Inventions in 3D printing often have rapid commercial potential: some researchers start forming companies before they publish their advances. On the same day DeSimone’s paper was published, for instance, he showcased it at a TED talk in Vancouver, Canada, and officially launched his start-up firm Carbon 3D in Redwood City, California. The firm is now one of the biggest start-ups in 3D printing; it has already raised US$680 million in publicly disclosed funding rounds, and is reportedly valued at $2.4 billion. It has high-profile contracts with Adidas to make rubber-like midsoles for athletic shoes, and with sports-gear firm Riddell to manufacture customized helmet padding for American-football players.
MarkForged founded by MIT aerospace engineer Greg Mark, has introduced revolutionary Mark One 3D printer, the world’s first 3D printer designed to print parts from continuous carbon fibers. Its Composite Filament Fabrication (CFF) process overcomes the strength limitations of traditional 3D printed materials, and enable 3D printing of continuous carbon fiber parts that are up to 20 times stiffer and five times stronger, than ABS plastic, the commonly 3D-printed material, and have a higher strength-to-weight ratio than CNC-machined 6061-T6 aluminum. Designers can choose between lightweight carbon fiber, low-cost fiberglass, abrasion resistant Kevlar or low cost and biodegradable PLA to print parts, tooling, and fixtures and can serve many applications from medical prosthetics to hobbyist drone manufacture.
3D Printing 100 Times Faster With Light
3D printing could change the game for relatively small manufacturing jobs, producing fewer than 10,000 identical items, because it would mean that the objects could be made without the need for a mold costing upwards of $10,000. But the most familiar form of 3D printing, which is sort of like building 3D objects with a series of 1D lines, hasn’t been able to fill that gap on typical production timescales of a week or two.
Rather than building up plastic filaments layer by layer, a new approach to 3D printing lifts complex shapes from a vat of liquid at up to 100 times faster than conventional 3D printing processes, University of Michigan researchers have shown. Their method solidifies the liquid resin using two lights to control where the resin hardens—and where it stays fluid. This enables the team to solidify the resin in more sophisticated patterns. They can make a 3D bas-relief in a single shot rather than in a series of 1D lines or 2D cross-sections. Their printing demonstrations include a lattice, a toy boat and a block M.
Using conventional approaches, that’s not really attainable unless you have hundreds of machines,” said Timothy Scott, U-M associate professor of chemical engineering who co-led the development of the new 3D printing approach with Mark Burns, the T.C. Chang Professor of Engineering at U-M. “It’s one of the first true 3D printers ever made,” said Burns, professor of chemical engineering and biomedical engineering.
They faced one challenge namely, the resin tends to solidify on the window that the light shines through, stopping the print job just as it gets started. By creating a relatively large region where no solidification occurs, thicker resins—potentially with strengthening powder additives—can be used to produce more durable objects. The method also bests the structural integrity of filament 3D printing, as those objects have weak points at the interfaces between layers.
“You can get much tougher, much more wear-resistant materials,” Scott said. An earlier solution to the solidification-on-window problem was a window that lets oxygen through. The oxygen penetrates into the resin and halts the solidification near the window, leaving a film of fluid that will allow the newly printed surface to be pulled away.
But because this gap is only about as thick as a piece of transparent tape, the resin must be very runny to flow fast enough into the tiny gap between the newly solidified object and the window as the part is pulled up. This has limited vat printing to small, customized products that will be treated relatively gently, such as dental devices and shoe insoles. By replacing the oxygen with a second light to halt solidification, the Michigan team can produce a much larger gap between the object and the window—millimeters thick—allowing resin to flow in thousands of times faster.
The key to success is the chemistry of the resin. In conventional systems, there is only one reaction. A photoactivator hardens the resin wherever light shines. In the Michigan system, there is also a photoinhibitor, which responds to a different wavelength of light. Rather than merely controlling solidification in a 2D plane, as current vat-printing techniques do, the Michigan team can pattern the two kinds of light to harden the resin at essentially any 3D place near the illumination window.
U-M has filed three patent applications to protect the multiple inventive aspects of the approach, and Scott is preparing to launch a startup company. A paper describing this research will be published in Science Advances, titled, “Rapid, continuous additive manufacturing by volumetric polymerization inhibition patterning.”
The world’s first 3D-printed concrete pedestrian bridge was made by researchers at the Institute for Advanced Architecture of Catalonia in Barcelona, Spain, and installed in a park in Alcobendas, near Madrid, in 2016. Twelve metres long, the bridge features a lattice structure designed with algorithms that maximize strength and reduce the amount of material needed. Other teams have made similar structures, including a 26-metre-long bridge in Shanghai, China, produced by engineers at Tsinghua University in Beijing. And teams and companies in China and the Netherlands have 3D printed demonstration houses.
Those structures aren’t constructed in one print job, however: separate segments are printed and then connected. By producing bridges and houses more cheaply and efficiently, 3D printing could reduce concrete’s carbon footprint — but it could also just encourage engineers to build more. It’s not just concrete that is going big: Amsterdam firm MX3D has printed a bridge from stainless steel. First displayed publicly in 2018, the bridge is now being tested and having sensors installed ahead of a planned installation over an Amsterdam canal.
Manufacturing Breakthrough Towards Eliminating Waste in 3D Printing
With Laser Sintering, the second most commonly used 3D printing technology, up to 50% of the powder becomes waste. The potential to recycle used powder is limited and 3D printing with only used powder creates surface problems that make the 3D printed object unsuitable for most applications. Now, Materialise announces Bluesint PA12, a manufacturing innovation that makes it possible to print with up to 100% re-used powder, drastically increasing the resource efficiency of Laser Sintering.
With Bluesint PA12, powder that would normally be wasted can be given a second life to make new parts. Parts printed with Bluesint PA12 have similar mechanical properties, allowing users to make a choice not only based on technical specifications but also on the environmental impact. “With Bluesint PA12 we are able to significantly reduce powder waste,” says Jurgen Laudus, VP and General Manager of Materialise Manufacturing. “Bluesint PA12 represents a major step towards making 3D printing more sustainable and is an example of how we empower our customers to make a choice for sustainability.”
The problem with Laser Sintering is that 3D printing with only used powder – residual powder from a previous 3D print process – creates a surface texture problem called the “orange peel” effect, which makes the printed object largely unusable. The orange peel effect is caused by shrinking that occurs when the powder cools down between two consecutive sintering processes. The existing solution is to mix used powder with fresh powder, which is clearly not sustainable.
By using a 3D printer with multiple lasers, Materialise engineers were able use one laser for sintering the powder and a second laser to keep the powder above a certain temperature threshold. By preventing the powder from cooling down between two layers, they prevented the shrinking process that causes the orange peel effect. The result is a printed object with similar mechanical and visual properties but printed with 100% recycled powder, drastically reducing waste.
BAAM (Big Area Additive Manufacturing)
BAAM (Big Area Additive Manufacturing) is an industrial sized, additive machine. The machine uses the proven design and technology from our laser platform, including the machine frame, motion system, and control, and has been adapted with an extruder and feeding system. BAAM was designed to allow 3-D printing to be used for production manufacturing. The size and speed allow large parts to be made quickly. The ability to use commodity thermoplastic materials means that the cost per part will be reasonable. By designing a system with an open architecture for material vendors, material costs will be kept lower and with more options.
With the demand for maritime surveillance on the increase, navies use manned and unmanned submersibles to deploy sensors and to provide logistics capabilities. When no two missions are identical, there’s a need to build these vessels faster and incorporate new design features.
Big Area Additive Manufacturing (BAAM), a large-scale 3D printing technology developed by Oak Ridge National Laboratory’s Manufacturing Demonstration Facility and Cincinnati Inc., was used to fabricate a 34’ catamaran boat hull mold. The goal of this project was to explore the feasibility of using BAAM to directly manufacture the mold without the need for thick coatings.
The catamaran boat hull mold was designed with an additional 0.15” thickness of material on the mold surfaces. After printing, the mold was immediately machined and assembled. Alliance MG, LLC (AMG), the industry partner of this project, experimented with mold release agents on the carbon-fiber reinforced acrylonitrile butadiene styrene (CF ABS) to verify that the material can be directly used as a mold. A steel subframe was manufactured to provide structural integrity. The mold was printed in twelve individual sections. Each section was about six feet long, and three sections were printed simultaneously in approximately twelve-hour builds. All mold sections were printed over a five-day period, and the total amount of material used was 5,500 pounds of CF ABS. The success of this project will significantly reduce the time and cost necessary for manufacturing large resin infusion molds using the BAAM process.
Metal 3D printing
Metal 3D printing is considered the apex of all 3D printing. When it comes to strength and durability, there’s nothing quite like metal. Metal 3D printed parts have excellent mechanical properties and can be manufactured from a wide range of engineering materials, including metal superalloys.
Metal 3D printing is most suitable for complex, bespoke parts that are difficult or very costly to manufacture with traditional methods. Metal 3D printed parts can be topologically optimized to maximize their performance while minimizing their weight and the total number of components in an assembly. Topology optimization is essential for maximizing the added benefits of using metal printing.
The material and manufacturing costs connected with metal 3D printing is high, so these technologies are not suitable for parts that can be easily manufactured with traditional methods. The build size of the metal 3D printing systems is limited, as precise manufacturing conditions and process control are required. Already existing designs may not be suitable for metal 3D printing and may need to be altered. Minimizing the need for support structures will greatly reduce the cost of metal printing.
And California start-up firm Relativity Space in Los Angeles says it is constructing a nearly fully 3D-printed rocket. The rocket is designed to lift 1,250 kilograms into low Earth orbit, and its first test launch is slated for 2021. Printed metal doesn’t always have the same heat-dissipating performance as non-printed metal, says Relativity Space’s chief executive, Tim Ellis, but the printing process can add cooling channels in geometries that can’t usually be manufactured. Because rockets are used only once or perhaps a few times, they don’t have to be as strong in the long term as do alloys in aeroplane parts, which must resist failure over tens of thousands of pressure cycles, Ellis says.
These large-scale metal-printed projects are built with robot arms that feed a thin metal wire to a laser that welds the material into place. Other established ways to print metal use a laser or a beam of electrons to melt or fuse a bed of powder into layers of finished product. Another technique binds a bed of powder with liquid glue, then sinters the structure in a furnace. And printers designed in the past few years extrude molten metals through nozzles, in much the same way as in FDM.
Aviation firms such as Boeing, Rolls Royce and Pratt & Whitney are using 3D printing to make metal parts, mainly for jet engines. It can be cheaper than milling metal blocks, and the intricate components often weigh less than their conventionally made counterparts. But 3D-printed metals are prone to defects that can weaken the final products. Spadaccini and others are trying to use arrays of sensors and high-speed cameras to watch for irregularities such as hotspots of heat or strain — and then make adjustments in real time, he says.
Many scientists are also hoping to improve the intrinsic strength of printed metals, sometimes by controlling the microstructures of the materials. For instance, in October 2017, a US team reported that the intense heat and rapid cooling used in 3D-printing stainless steel could alter the metal’s microstructure such that the product is stronger than those cast conventionally. In 2020, researchers in Australia and the United States reported a titanium–copper alloy with similar strength advantages. As they solidified, previous 3D-printed titanium alloys tended to form grains that grew in column-like structures. The copper helps to speed up the solidification process, which results in grains that are smaller and sprout in all directions, strengthening the overall structure.
In 2016, Xjet introduceed ceramic nanoparticle
XJet introduced their unprecedented NanoParticle Jetting Technology which is dramatically different than other metal 3D printing technologies, using liquid instead of powder to build metal parts as easily as any inkjet printing system. The liquid, which contains metal nanoparticles or support nanoparticles, is loaded into the printer as a cartridge and jetted onto the build tray in extremely thin layers of droplets. High temperatures inside the build envelope cause the liquid to evaporate, leaving behind metal parts with almost identical properties to traditionally manufactured metal parts.
NanoParticle Jetting Technology prints ceramic materials in the same way as metals. A liquid dispersion containing ceramic nanoparticles, contained in sealed cartridges, is loaded into the printer, where it is then jetted onto the build platform, just like any inkjet printer. The high temperatures inside the build envelope cause the liquid to evaporate, leaving layers of ceramic behind to form parts with the same mechanical properties as traditionally manufactured ceramics.
The advantages of NanoParticle Jetting, according to XJet, can be summed up as three major points: Details, dispersion and design freedom. The small size of the metal particles and the thinness of the layers allow for smaller details and thinner walls than other metal additive manufacturing technologies, and the cartridge delivery system provides safe and simple handling. Meanwhile, the unique support materials require no pre-design and are easily removed afterwards, enabling parts of almost any geometry to be printed.
“The expansion of NanoParticle Jetting to include ceramics will allow XJet to address an even wider range of applications, such as dental, medical and specific industrial applications,” said Dror Danai, Chief Business Officer, XJet. “At formnext we will demonstrate how the usage of ink-jet technology, and it’s very large tray, will encourage more industries to look at Ceramic Additive Manufacturing as an option for both customized parts and relatively large scale manufacturing of small parts.”
Lockheed Martin files patent for a synthetic diamond 3D printer in 2016
Inventor David G. Findley of Lockheed Martin, the aerospace company, have filed a patent for a new kind of 3D printer. The patent, describes a new way of 3D printing which would heating pre-ceramic polymer and nanoparticle filler to create synthetic diamond objects of pretty much any shape you can dream up.
Synthetic diamond is emerging as most versatile super material for defence that shall have significant effect in a variety of applications as diverse as high power radars, communications and electronic warfare systems, Directed Energy Weapons, MEMS applications, Aerospace applications and Quantum science among many others.
“[The] method includes depositing alternating layers of a ceramic powder and a pre-ceramic polymer dissolved in a solvent. Each layer of the pre-ceramic polymer is deposited in a shape corresponding to a cross section of an object. The alternating layers of the ceramic powder and the pre-ceramic polymer are deposited until the layers of the pre-ceramic polymer form the shape of the object. The method includes heating the deposited ceramic powder and pre-ceramic polymer to at least a decomposition temperature of the pre-ceramic polymer. The decomposition temperature of the pre-ceramic polymer is less than a sintering temperature of the ceramic powder. The method further includes removing excess ceramic powder that the pre-ceramic polymer was not deposited onto.”
In Oct 2020, it was reported that Lockheed Martin has enlisted the help of California-based rocket-building firm Relativity Space to 3D print projectiles for an upcoming experimental NASA mission. The contract, which has been awarded as part of NASA’s Tipping Point program for advancing new technologies, will see several different cryogenic fluid management systems launched into orbit and tested. Utilizing Relativity’s 3D printing technology, Lockheed aims to construct complex rockets to carry the potentially-dangerous cargo with reduced lead times, for a launch date in 2023.
Tim Ellis, Relativity’s Founder and CEO, explained that the company’s top-to-bottom additive manufacturing approach is an ideal fit for the NASA mission: “We’re building a custom payload fairing that has the specific payload loading interfaces that they need, as well as custom fittings and adapters,” said Ellis. “It still needs to be smooth of course, and to a lay person it will look like a normal rocket.”
Russian scientists improve 3D printing technology for aerospace composites using oil waste reported in Nov 2020
Scientists from NUST MISIS have improved the technology of 3D printing from aluminum, having achieved an increase in the hardness of products by 1,5 times. The nanocarbon additive to aluminum powder, which they have developed, obtained from the products of processing associated petroleum gas, will improve the quality of 3D printed aerospace composites. The research results are published in the international scientific journal Composites Communications
Today, the main field of application for aluminum 3D printing is the creation of high-tech parts for the aviation and space industries. The presence of even the slightest defects in printed structures is critical to the safety of the technology being created. According to NUST MISIS scientists, the main risk of such defects is the high porosity of the material, caused, among other reasons, by the qualities of the original aluminum powder. To ensure a uniform and dense microstructure of printed products, scientists from the MISIS Catalis Lab proposed adding carbon nanofibers to the aluminum powder. The use of this modifying additive makes it possible to ensure a low porosity of the material and an increase in its hardness by 1.5 times.
“Changing the chemical and phase composition of the powder for printing by introducing additional components into the main matrix allows improving its properties. In particular, carbon nanofibers have high thermal conductivity, which helps to minimize temperature gradients between printed layers during product synthesis, at the stage of selective laser melting. Thanks to this, the microstructure of the material can be almost completely eliminated from inhomogeneities,” said the head of the laboratory, professor at NUST MISIS, Ph.D. Alexander Gromov.
The technology for the synthesis of nanocarbon additives developed by the research team includes methods of chemical deposition, ultrasonic treatment, and IR heat treatment. The used carbon nanofibers must be a by-product of associated petroleum gas processing. During its catalytic decomposition, carbon accumulates in the form of nanofibers on dispersed metal particles of the catalyst. Usually, at present, associated gases are simply burned in the fields, which harms the environment. Therefore, the application of the new method also has a serious environmental significance, — said Professor Gromov. The study has been carried out jointly with specialists from the Boreskov Institute of Catalysis SB RAS. In the future, the research team plans to determine the optimal conditions for selective laser melting of new composite powders, as well as to develop a technology for post-processing and industrial use of synthesized products.
Future trends
Lewis and her lab described a printer that can rapidly switch between different polymer inks or mix them as it prints a single object. This means objects can be printed with both flexible and rigid parts. Lewis has spun off previous work on multi-material printers into a firm called Voxel8, a start-up in Somerville, Massachusetts. Her multi-material printer could help with the athletics wear that Voxel is developing, says Lewis. Wearable devices need to be flexible around joints while also having rigid parts to house electronics. Saiz calls the printer “beautiful work”, adding wistfully: “There’s nothing like that for ceramics or metal.”
And in March 2018, a team led by Jerry Qi, a materials engineer at Georgia Institute of Technology in Atlanta, unveiled a four-in-one printer. This combines a nozzle that extrudes molten polymer with one that prints light-sensitive resin, ready to be cured by ultraviolet lamps or lasers, and two that print wires and circuitry from tiny dots of metal. The print heads work together to make integrated devices with circuits embedded on a rigid board or inside a flexible polymer enclosure. Qi says his group is now collaborating with electronics companies interested in printing circuit-board prototypes faster than conventional methods. It wasn’t as simple as bolting four different printers into one platform: the researchers also needed to develop software that would allow each print head to communicate with the others and keep track of the progress.
The field’s future could also lie in ‘4D printing’ — 3D-printed objects that also have the ability to perform some mechanical action, akin to artificial muscles. Often, these incorporate shape-memory polymers, materials that can react to changes in their environment such as heat or moisture. In May 2018, researchers at the Swiss Federal Institute of Technology (ETH) in Zurich and the California Institute of Technology in Pasadena reported printing a submarine that propels itself forward using paddles that snap backwards when placed in warm water9. The work could lead to microrobots that can explore the oceans autonomously. But for the moment, the paddles must be reset after each stroke. Such devices could use battery power to reset themselves, but that makes the machine less efficient than one made conventionally, says Geoff Spinks, a materials engineer at the University of Wollongong in Australia. “There are still some big challenges with 4D printing,” he says.
Another approach to 4D-printed devices involves triggering the action with a changing external magnetic field. US researchers have 3D-printed lattice structures filled with a liquid that changes stiffness in response to a magnetic field10 — which could perhaps be used to help car seats stiffen on impact.
Other, more passive potential 4D printing applications include stents, which could be compressed to be implanted then expanded on reaching the desired site in a blood vessel to prop it open. Last July, researchers in Switzerland and Italy described a 4D-printed stent that is just 50 micrometres wide11, much smaller than conventional ones. The devices are so small, the team says, they could one day be used to treat complications in fetuses, such as strictures in the urinary tract, which can sometimes be fatal.
Perhaps the most ambitious example of 4D printing is matter that not only moves, but is alive. Currently, techniques for such bioprinting can print tissue, such as human skin, that is suitable for lab research, as well as patches of tissue for livers and other organs that have been successfully implanted in rats. But such techniques are still far from ready to integrate into a human body. Researchers dream of printing fully functioning organs that could alleviate long wait lists for organ donors. “I personally feel we’re a decade-plus away from that, at least, if ever,” says Lewis.
References and Resources also include:
https://www.nature.com/articles/d41586-020-00271-6
