Is 3D Printing Safe and Flightworthy?

 

           If asked about 3D printing, many people will think of the machines that can be found in school labs, in makerspaces, or on the desktops of hobbyists. This is just one place the technology can be found, however.  The aerospace industry has been using 3D printing for several decades as a tool for prototyping, creating detailed plastic models of aircraft that are not only highly accurate, but quick and economic to make.  Now, due to developments in the last decade, advancements in the field have extended its use to manufacturing components on actual aircraft; in fact, it’s likely that anyone who has flown in the last 5 years has ridden on an aircraft with 3d printed parts on it [1]. 

This new capability comes from the ability to 3D print with new materials, as well as new techniques that allow complex shapes that were previously impossible to manufacture normally [2,3]. This is both exciting and concerning to many, as both fascination as well as the question of “Is it safe?” arise to mind.  The aerospace industry must temper advancement with caution, as safety must be the first priory in aviation.

Benefits of 3D printed parts

           3D printing, also known as additive manufacturing, has many benefits, all of which are of great use in aerospace.  The first is due to the unique manner in which parts are “printed”, as they are built up layer by layer by a machine instead of manufactured from raw stock material.  This allows internal structures that are more complex, and that can be made lighter than a normally made part.  In one example, jet turbine blades 3D printed by General Electric were 50% lighter than those made conventionally, resulting in a fuel efficiency improvement of 10% when compared to jet engines made in the normal fashion [4].  This results in cheaper flights that create less pollution, a benefit to both the public and the environment

3D printing allows very complex geometry to be created, 
even from metal.  Image via Flickr by John Biehler

           In addition to being lighter, 3D printing allows the creation of components that would otherwise be difficult or impossible to create normally.  Jet engine fuel nozzles (similar to the fuel injector in most family cars) are normally complex components that are welded together from 20 different pieces.  By using 3D printing, GE is now able to manufacture these as one single piece, allowing for faster creation while also reducing the chance of manufacturing errors [5].  This capability has risen as a result of new technology that allows printing with materials other than plastics and composites, including metal alloys [2].  Some of these alloys are even stronger than those created conventionally; In one impressive example from this year, NASA was able to use 3D printing to manufacture part of a rocket motor, with material capable of withstanding temperatures of over 2,000 degrees, and a lifespan over 1,000 times longer than previously existing alloys [3] 

Challenges presented

           Of course, this advancement is pointless if these parts aren’t as safe as those made normally.  The results of a manufacturing defect in an engine part can be both spectacular and dangerous, as can be seen in the news whenever an incident occurs [6].  Additively manufactured parts must still be held to the same standards of safety as those traditionally made, including the rigorous inspection protocols that keep the public safe.

The results of an engine manufacturing defect.  
Sourced from Wikimedia Commons

           But what happens if the properties that make additively manufactured parts so attractive to aerospace are a detriment to safety?  One study found that ultrasound inspection, a standard technique used to detect cracks in metal, had difficulty finding errors in a 3D printed part that had deliberate defects for the purpose of testing.  The unique layering process that allows complicated structures created “noise” or fuzziness in the images produced in this inspection, making the cracks impossible to find [7].    While other methods of inspection may potentially offer solutions, this inspection issue demonstrates one of the risks of rapidly advancing technology, the risk of innovation outpacing caution.

           Even more concerning than the chance of undetected accidental flaws, however, is the possibility of deliberate defects.  The machines used for 3D printing are sophisticated tools that require a significant amount of computing power to create these components.  As is the case with any computer, cybersecurity is a serious concern, especially as these machines create parts that have potential public safety risk.  In one study, researchers created a virus to test whether or not 3D printed parts could be tampered with by infecting the additive manufacturing machinery [8].  While some of the defects they created were easy to spot, they discovered it was possible to make intermittent defects that would occur only occasionally, and yet significantly weakened the produced components when present.  This kind of attack would be extremely detrimental to the afore mentioned 3D printed turbine blades, if undetected, as even the smallest flaw can create a catastrophic failure.

           Unfortunately, cybercrime is not the only form of illicit activity that takes advantage of additive manufacturing capabilities.  The ease with which parts can be created also unfortunately presents a unique opportunity for counterfeiting [9].  These parts would potentially look externally identical to those created properly, but would have none of the extensive inspection or manufacturing standards required for authentic aircraft parts.

 

Addressing the challenges

           Despite these issues, the aerospace industry has made headway in safeguards along side the advancement in 3d printing.  While some old inspection techniques such as ultrasound may not be ideal for testing additively manufactured parts, others such as x-ray and infrared scanning are still effective [10].  Furthermore, new methods such as resonant acoustic testing are in development, and the results are promising [11].  Research has also been   Using this combination of old and new methods, it will be possible to create testing regimes that will ensure safety from both accidental flaws, as well as increase the ability to discover instances of sabotage that slip through.

           In addition to continued research in inspection methods, the same capabilities that enable counterfeiters also present a means of defense against fake parts.  Due to the layered process in which 3D printed parts are made, it is possible to hide verification factors such as a QR code [12] or chemical marker [13] that is not only difficult to detect, but is nearly impossible to recreate without specific knowledge.

Conclusion

While it may at first seem that 3D printing creates just as many problems as it solves, possibly the best news is that much of the challenge with 3D printed parts is simply the fact that they are new and unfamiliar.  As this manufacturing process becomes more frequently used, the aerospace industry will become more familiar with the safety standards needed, and thus will become more adept at detecting flaws and defects within components, intentional or accidental.  This will overall lead to a safer and more efficient aerospace industry, and will continue to create new developments for aerospace manufacturing.

 

 

References

[1]       The FAA Cleared the First 3D Printed Part to Fly in a Commercial Jet Engine from GE | GE News. https://www.ge.com/news/reports/the-faa-cleared-the-first-3d-printed-part-to-fly-2. Accessed Jun. 11, 2022.

[2]       3D Printing in Aerospace Is Mostly About Metals. designnews.com. https://www.designnews.com/aerospace/3d-printing-aerospace-mostly-about-metals. Accessed Jun. 9, 2022.

[3]       Sands, K. NASA’s New Material Built to Withstand Extreme Conditions. NASA. http://www.nasa.gov/feature/glenn/2022/nasa-s-new-material-built-to-withstand-extreme-conditions. Accessed Jun. 10, 2022.

[4]       The Blade Runners: This Factory Is 3D Printing Turbine Parts For The World’s Largest Jet Engine | GE News. https://www.ge.com/news/reports/future-manufacturing-take-look-inside-factory-3d-printing-jet-engine-parts. Accessed Jun. 12, 2022.

[5]       New Manufacturing Milestone: 30,000 Additive Fuel Nozzles | GE Additive. https://www.ge.com/additive/stories/new-manufacturing-milestone-30000-additive-fuel-nozzles. Accessed Jun. 29, 2022.

[6]       Gorelik, M. “Additive Manufacturing in the Context of Structural Integrity.” International Journal of Fatigue, Vol. 94, 2017, pp. 168–177. https://doi.org/10.1016/j.ijfatigue.2016.07.005.

[7]       Manufacturing and Security Challenges in 3D Printing - EBSCO. https://discovery.ebsco.com/c/3czfwv/viewer/pdf/k4go3k35hn. Accessed Jun. 24, 2022.

[8]       Pearce, H., Yanamandra, K., Gupta, N., and Karri, R. “FLAW3D: A Trojan-Based Cyber Attack on the Physical Outcomes of Additive Manufacturing.” IEEE/ASME Transactions on Mechatronics, 2022, pp. 1–10. https://doi.org/10.1109/TMECH.2022.3179713.

[9]       Cass, T. A. C., William J. 3-D Printing Will Be a Counterfeiter’s Best Friend. Scientific American. https://www.scientificamerican.com/article/3-d-printing-will-be-a-counterfeiters-best-friend/. Accessed Jun. 25, 2022.

[10]     Hassen, A. A., and Kirka, M. M. “Additive Manufacturing: The Rise of a Technology and The Need for Quality Control and Inspection Techniques.” p. 23.

[11]     Obaton, A.-F., Wang, Y., Butsch, B., and Huang, Q. “A Non-Destructive Resonant Acoustic Testing and Defect Classification of Additively Manufactured Lattice Structures.” Welding in the World, Vol. 65, No. 3, 2021, pp. 361–371. https://doi.org/10.1007/s40194-020-01034-7.

[12]     Chen, F., Yu, J. H., and Gupta, N. “Obfuscation of Embedded Codes in Additive Manufactured Components for Product Authentication.” Advanced engineering materials, Vol. 21, No. 8, 2019, p. 1900146. https://doi.org/10.1002/adem.201900146.

[13]     How Exactly Will 3D Printing Combat Counterfeiting Additive Manufactured Products? 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing. https://3dprint.com/117613/combat-counterfeiting-am/. Accessed Jun. 25, 2022.