Big things are happening in the aviation maintenance, repair and operations (MRO) market: the first industry-wide material allowables for metal additive manufacturing (AM) parts are anticipated to be released this autumn.
Some of the behemoths of both commercial aircraft manufacturing and the largest of the MRO companies that serve them have already developed internal materials data, allowing them to produce AM parts certified for flight.
FAA 14 CFR 21.1 permits airframe, engine and propeller manufacturers to do this.
For those who have applied AM, it has taken years of trial and error and huge expenditures on build-and-break manufacturing and testing to get to this point.
For everyone else, there have been few-to-no FAA-recognized specs or allowables available.
MRO providers and aviation-related companies of more modest means have encountered significant certification challenges that have held back the widespread use of 3D printing.
This year, however, MRO companies of all sizes will finally gain access to a robust data set—MMPDS Volume 2 for Additive Materials—that will enable them to embrace AM without going to such great lengths of time and expense.
MMPDS (metallic materials properties development & standardization) is an industry-based source for design allowables recognized by the FAA, DoD and NASA, and references a material spec, typically AMS (aerospace material standards), that can be used for parts and repairs.
But hold on.
Why should aviation MRO providers be so interested in this news in the first place?
Well, consider the state of the industry right now: Problems with spare parts availability are literally grounding aircraft. Casting lead times of six to 24 months are routine in the industry. The skilled-labor workforce for complex fabrications has been declining for decades.
Particularly for older aircraft, even if the right tooling still exists, it can be in such disrepair that it must be remade completely.
And minimum order sizes make the efficiencies of just-in-time strategies impossible to realize.
For every $1,000 part you have on order, there could be a multi-million-dollar asset sitting on the ground unused.
Here’s where it gets interesting: Additive manufacturing—particularly Laser-Powder Bed Fusion (L-PBF)—has finally reached the point where it can produce end-use, certifiable aircraft parts with lead times of just weeks, rather than months. Existing parts can be 3D printed with minimal redesign, allowing for on-demand manufacturing and supply chain flexibility.
What’s more, the strength and quality of L-PBF parts exceed that of castings. When printed in the most advanced systems, the density is 99.9 percent—versus around 95 percent with castings.
Alloy 718 (an Inconel), which is to be the first L-PBF material to be evaluated by MMPDS in 2021, is a high-strength, high-temperature alloy commonly used in the aerospace industry.
Its material properties are similar to 17-4 pH stainless steel, for which it’s sometimes used as an alternative.
Getting to the point of having MMPDS approval for this alloy has been a learning experience for everyone involved: government, industry, AM equipment makers and material providers.
Once Alloy 718 gets added to MMPDS, the development of data curves for other common alloys, such as aluminum and titanium, will follow.
Until now, certified AM parts have been the purview of those major OEMs and MRO providers who have had the time and money to develop their own internal specs and allowables.
The uneven evolution of 3D printing capabilities has likely hampered this progress.
Now that advanced industrial AM can produce metal parts that match the exacting specifications of newly certified materials, large and small MRO providers can, with full confidence, take advantage of the many benefits that 3D printing offers the industry.
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