Print the impossible / Larry Greenmeyer

Will XNUMXD printing change the face of traditional production?

The robotic prosthetic hand created at the US National Laboratory in Oak Ridge looks like an artifact created in the Middle Ages: a hand covered in chain mail, better suited to holding a heavy sword than a cup of coffee. Both the internal skeleton and the thin, mesh-like skin are made of titanium, so that the hand is durable, easy to move and light in weight. The tiny and powerful hydraulic mechanisms that move the fingers rely on a network of hollow channels integrated into the structure of the prosthetic hand itself, without the need for drilling holes, pipes or couplings.

However, what makes this robotic hand special is not what it can do, but how it was created and what it represents. The hand was developed on a computer and assembled from several dozen parts, which were printed in a process called "additive manufacturing", or by its more familiar name, "XNUMXD printing". Oak Ridge's invention provides a glimpse into the future of manufacturing, a future where it will be possible to produce in a few hours tailor-made content that was never possible before.

"We have a very complex structure here, with internal hydraulic mechanisms capable of withstanding a very high load," says Craig Blue, director of the energy materials program at Oak Ridge. "There is a mesh structure here that makes the hand lightweight, because material is only found in the necessary places. Today, there is no technology, except for layered production, that can do something like that."

With the maturation of XNUMXD printing to the level of creating complex machines, which cannot be produced in any other way, giant companies such as Boeing and General Electric are starting to implement this technology in their advanced production lines. Instead of the old approach, where useful parts were carved from large blocks of material, layered manufacturing builds objects layer by layer. This change in thinking may affect all aspects of manufacturing, from prototype design to mass production of products.

However, XNUMXD printing still faces technical challenges. Compared to conventional production based on the removal of excess material, it can be slow, and the fit and finish of materials can be inconsistent. Also, XNUMXD printers have difficulty creating objects from multiple materials, and are unable to integrate electronics into them without burning the electrical circuits.

Researchers are working hard to overcome these limitations, and there is no doubt that for dedicated small-scale applications, layered manufacturing has a huge advantage. When this technology expands into the mass production market, it may bring about a general revolution in the industry.

Advantages upon advantages

The history of 80D printing begins in the late 175,000s, when start-up companies and academic institutions, mainly the University of Texas at Austin, invented machines that could build XNUMXD models of digital content in minutes. For decades, such and other systems, which initially cost about $XNUMX, have gained a reputation for their ability to help inventors and engineers produce prototypes quickly and at relatively low cost.

Since then, XNUMXD printing has progressed along two paths. At one end, hobbyists and budding entrepreneurs can easily produce plastic models with machines that cost $XNUMX or less. These home devices allow users to invent new objects, a technology that has drawn comparisons between XNUMXD printing and personal computers. "Just as the Internet, cloud services and open source software allowed small teams to survive on "hot dishes" for six months, build applications, publish them and see if anyone is interested, so we are beginning to see a similar phenomenon of building products," says Thomas Kalil, VP Technology and Innovation in the Office of Science and Technology Policy at the White House.

At the other end, large manufacturers are cultivating sustainable and advanced approaches to the production of aircraft parts and biomedical devices, such as hip replacement joints. The machines required for this cost at least $30,000, and can reach up to laser-based devices that produce high-quality metal products and cost about a million dollars. Such printers can use polymers, metals and other materials in liquid or powder form. The objects begin as digital files, which allow designers to make small changes to the work before actual construction begins, with a minimal impact on costs.

According to the report "Global Trends 2030: Alternative Worlds", produced in November 2012 by the US National Intelligence Council, a team of analysts that assists the US Director of National Intelligence, 2030D printing could replace certain mass production processes such as casting, molds and machining by 20,000, especially In limited scale production or among manufacturers of more specialized products. At the forefront of this trend are the aerospace companies. The jet engine division of General Electric, GE Aviation, which has been producing aircraft engines for almost a century, recently acquired two suppliers that specialize in creating aircraft parts using layered manufacturing processes. Boeing already uses XNUMXD printers for more than XNUMX parts used in its civilian and military aircraft.

Such companies are discovering that 80D printing can also be more efficient than conventional manufacturing, both in terms of the energy invested and in terms of materials. "When you're machining something, often 90% to XNUMX% of the block [of material] you had initially becomes chips or scraps on the floor," says Terry Wohlers, principal consultant and president of Wohlers Associates, a Fort Collins, Colo.-based layer manufacturing consulting firm.

break the mold

Despite the advantages, many manufacturers still see XNUMXD printing as a means of creating prototypes only, and not industrial-level products. There are three reasons for this: slow speeds, inconsistent quality, and the difficulty of creating complex objects.

First of all, layering processes are relatively slow, according to the level of detail required. Engineers at Oak Ridge, led by lead designer Lonnie Love, spent 24 hours creating the parts of the robotic hand that weighs about 600 grams, and another 16 hours assembling it (they are developing hardware that will print the entire prosthetic hand at once). "If you're building something the size of a tennis ball and you're interested in fine, high-definition detail, you can imagine that it will take 6 to 8 hours to build," says Richard Martoknitz, director of the Center for Innovative Materials Processing by Direct Digital Lamination at Pennsylvania State University. At this rate, producing thousands of units on XNUMXD printers will take years.

However, there are layered production systems that work faster. These are systems that were developed for the US Navy and are able to layer about nine to eighteen kilograms of material every hour. But, the speed here comes at the expense of the ability to separate, which is not impressive. Also, Martoknitz says, the printed parts need additional machining. To improve the speed, the researchers are developing systems that will print at a variable speed - they will quickly laminate large pieces, but will slow down when the part needs a high level of detail. "This issue is getting a lot of attention now because people are looking at the limitations of the layering process from a manufacturing efficiency standpoint," he says.

Another option to improve speed is to spread the workload over several production facilities, but this approach requires a higher level of regulation than is currently the case. A vital component in a GE jet engine must look the same and behave exactly the same, regardless of how and where GE or any of its suppliers manufacture it. One organization working on developing standards for XNUMXD printing is ASTM International, formerly the American Society for Testing and Materials, although this work is in its early stages.

Scientists are also trying to develop self-monitoring XNUMXD printers that can quickly print consistent content. The system, Blue says, will analyze high-speed video footage of the object while printing, or use infrared thermal imaging to locate defects and fix them immediately without stopping the printing process. "You can download the part plans to the printer, and you will get a perfect result every time," he says.

The increasing complexity of the products, which combine more and more different materials alongside electronic components, poses another challenge to the XNUMXD printers. One approach is to develop printers with multiple print heads, each of which will laminate a different material. One of these heads could be used to embed electric wires directly inside the device while it is being printed.

Researchers in Oak Ridge, at the V. M. Keck Center for XNUMXD Innovation at the University of Texas at El Paso and elsewhere are designing XNUMXD printers that can also print electrical circuits. The challenge is to avoid overheating and damaging the electrical components, and to add layers of plastic or metal around them. The researchers are looking at ways to print insulating material around the electrical components to protect them. "In the next ten years you will see a combination of printed electronics with other materials," says Blue.

A combination of all these developments predicts a bright future for the Oak Ridge robotic arm, and it goes without saying who will use it. The scientists envision an era in which doctors will be able to scan a person's healthy hand, create a mirror image of it electronically, and print a new, assembled, ready-to-use prosthetic hand.

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About the author

Larry Greenmeyer is an editor at Scientific American

How It Works

The foundation fund

The Oak Ridge researchers used an electron beam melting (EBM) machine to build their robotic prosthetic hand. The process, which is carried out under intense heat, melts powders of metal alloys, such as titanium or chromium-cobalt, and creates from them durable and ready-to-use metal parts. No additional heat treatment is required to stabilize these materials.