6 ms·

Media loves talking about 3D Printing primarily due to its click ratio and viewership. As an mechanical engineer, I've had experience developing aircraft stages

Media loves talking about 3D Printing primarily due to its click ratio and viewership. As an mechanical engineer, I've had experience developing aircraft stages and frames - the whole premise of 3D printed parts going into an aircraft from airworthiness perspective is flat out insane.

ethagknight 6y ago
I believe you, but please go on and tell us why
- systemvoltage 6y ago
  This was 10+ years ago but the process is roughly as follows: Requirements of loads and flight envelopes are first provided to us (I was employed in a stress analysis group). The parts that I worked on weren't "new" per se, these were modifications to existing parts to comply to new loads or new materials, fasteners etc. Once envelopes + safety factors are set, we literally sketch out basic FBD (free body diagrams) along with shear-moment diagrams depending on the type of the part. You know the kind of diagrams you had to do in Statics class in University. Most of us knew the appendix formulas and many other empirical results by heart, and some of the guys at work were total nerds. They knew every possible cross sectional moment of inertia formulas, etc. It was really humbling. You'd think that aircraft industry some slow moving folks, but it couldn't be more false. The discipline was astounding. Then we consult existing parts directory, fastener books and materials for conceptual design. During the first conceptual design review (CDR), Principal engineers (depending on how critical this part is) get involved and provide us feedback. Post CDR, we send out parts to our FEA dept (mostly part time workers, some of them even commercial pilots) that get the models from the drafting department (Catia V4 at the time) and run some discretization scripts, they are pretty versed on how fine the mesh should be, but everything must be documented. Sensitivity study against mesh size needs to be proven. Converged models are sent back to us, we test it against intuition, and theoretical predictions (but not always). Detail design: Flange thickeness to thread pitch is set in stone, about 1800 fastener choices are narrowed down to a few, cost implications are non-existent, so most of the times weight is king. Coatings if any are specified. Prototypes are made by our supplier, GD&T red marks are fixed. Goodman diagram is consulted for fatigue studies, and sometimes even simulated in the FEA model. Same with creep and crack propagation studies. Detail Design review takes place and we are blessed by principal engineer. If it is an external part with any sort of interaction with the airflow, flutter dynamics to CFD guys are called, I honestly never worked on any farrings or anything affecting flight dynamics. Then comes the guaging (where to put rosette and stress gauges) and ground test certification process. Prototypes are tested against real world conditions and failures. Depending on the part, various tensile strength tests are conducted and sometimes with simulated internal cabin pressure. Not all parts were tested though. All in all, it takes forever to make a part in an airplane. My memory is fading so I can't recall everything. It was a lot of paperwork and documentation. We took that seriously. Having designed parts in an airplane, I just can't take 3D printing seriously. You wouldn't believe the kind of work that goes into designing parts from composites - that was a new thing at the time when I was in the industry.
  - redis_mlc 6y ago
    Consumer 3D printing results in bathtub toys. An Apache helicopter is not made of bathtub toys. Metal is awesome compared to filaments and composites: Mike Busch - "Making Metal Behave" https://www.youtube.com/watch?v=m1jl6IlywAk https://www.youtube.com/watch?v=m1jl6IlywAk
  - tantalor 6y ago
    I don't think you have answered the question even remotely. What about 3d printing prohibits using parts in aircrafts? Are you aware "3d printing" can produce many types of materials, including metal, and not just plastic?
    - wlesieutre 6y ago
      It’s been used for several rocket engines
      - WalterBright 6y ago
        Interesting. Are they man-rated engines? Which parts? Since rocket engines tend to be single-use only, fatigue strength wouldn't be much of an issue.
        wlesieutre 6y ago
        SuperDraco on SpaceX’s crew dragon capsule aren’t used in the launch, but it’s the launch escape system. [1] SpaceX also apparently prints the main oxidizer valve in Falcon 9’s Merlin 1D, which isn’t a single use vehicle, but who knows what components get replaced between launches. [2] As of 2016, the Raptor engine being developed for ITS (now Starship) was 40% printed by mass, but I have no idea how much of that was for faster prototyping and if they might be using less in later production. [3] Rocket Lab’s Rutherford engine for their Electron rocket. [4] More in the works from Relativity Space, Launcher, NASA, and others I’m sure. We’ll see what pans out. [1] https://en.wikipedia.org/wiki/SuperDraco https://en.wikipedia.org/wiki/SuperDraco [2] https://3dprint.com/10830/spacex-3d-print-oxidizer-valve/ https://3dprint.com/10830/spacex-3d-print-oxidizer-valve/ [3] https://www.nasaspaceflight.com/2016/10/its-propulsion-evolution-raptor-engine/ https://www.nasaspaceflight.com/2016/10/its-propulsion-evolu... [4] https://en.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)
- tpmx 6y ago
  The article does cover that, in a very brief manner: > So far, he said, they’ve evaluated 31 percent of the parts – over 30,000 items – and found 252 that are “potential candidates for additive manufacturing.” That’s less than one percent.
  - robocat 6y ago
    I think that was for a prototype for the Lower Tier Air and Missile Defense Sensor radar. For the helicopter: “We expect to probably get about 20,000 structural parts, -ish, out of that,” Royar said. “We’ll take a look at it and evaluate every one” to see whether it can be safely and economically replaced with a 3D-printed version. So I am guessing they might find say 100 suitable non-critical parts (say plastic covers). 3D scans of critical parts could still be very useful for rigs, emergency field use, or other non-flight purposes. > [GP]: the whole premise of 3D printed parts going into an aircraft from airworthiness perspective is flat out insane. The article responds that observation very well IMHO.
starpilot 6y ago
I was a structural engineer for Sikorsky. I think it's obvious we will not be replacing a machined titanium main rotor hub with a 3D printed part soon. The article touches on this. It will probably be non-structural components like buttons on an MFD.
- monocasa 6y ago
  The super draco combustion chambers made by space x are 3d printed. I'm not saying they're the best fit for everything, but saying they'll be relegated to button on an MFD is probably too far on the other end of the spectrum.
  - icegreentea2 6y ago
    Form is function in high performance manufacturing (including most of aerospace). Just switch materials is a huge deal. If you set out with "use additive manufacturing" as one of your requirements/design goals, you can probably use additive manufacturing in a lot of aero. Using additive manufacturing to drop in replace existing parts that were made with different materials and techniques is very unlikely however.
    - monocasa 6y ago
      Oh absolutely. There's no way you can just drop a scan in to solid works, send it to the printer and call it a day. Some serious engineering needs to occur to change manufacturing processes. That's probably not a deal breaker in the grand scheme of things is all I'm saying.
- kbenson 6y ago
  I was going to write a reply saying that I don't see why we can't use it in many places as long as we understand the parameters of the product, but as so often happens I found an excellent source that actually explains your stance in details.[1] The TL;DR is that there are lots of imperfections in 3D printed parts, which means they typically fail at much lower stresses. It actually includes some pretty good video illustrating this at a microscopic level. That said, there are apparently new techniques being researched and discovered that have promise to increase the quality of 3D printed parts. One way to thing of it is that we have hundreds to thousands of years of experience in material science with forming metals in other manners, and we've just started with additive engineering, so there's a lot of room for improvement. 1: https://www.youtube.com/watch?v=fzBRYsiyxjI https://www.youtube.com/watch?v=fzBRYsiyxjI
d_silin 6y ago
I know a bit about turbofan engines in aircraft. 3D-printed parts are already going into them right now, as we speak: https://www.ge.com/news/reports/airbus-gets-1st-production-jet-engines-with-3d-printed-parts-from-cfm https://www.ge.com/news/reports/airbus-gets-1st-production-j...
- d_silin 6y ago
  Also, to elaborate on which parts can be 3D-printed. The latest and greatest breakthrough is using EBM (electron beam melting) for 3D printing second stage turbine blades from titanium aluminide in GE9X engine. Those parts are continuously experiencing mechanical and thermal loads far in excess of forged or machined parts in any airframe. There is no added safety barrier for them unlike for fan blades. If turbine stage flies apart, its parts will go straight through everything in their path, including passengers.
- d_silin 6y ago
  To further explain my point but also support the root comment. Aluminium/steel/titanium airframe parts are usualy machined or forged. It is not possible to replace them with 3D printed parts just yet. But! All of jet engine turbine blades are cast, not machined. Those parts can be safely 3D printed, as various metal sintering/remelting methods produce similar or better structural quality. Same goes for those magnesium castings used in aircraft landing gear - can be replaced with 3D printed ones. Parts that only under hydrostatic load like fuel nozzles can be 3D printed. Fatigue is not an issue there. Parts that do not experience significant structural loads, but high thermal loads (combustors) can be also 3D printed. I believe that's a better answer to the topmost comment.
  - systemvoltage 6y ago
    I also worked on Turbine blades. Specifically did studies on trailing edge dump and pressure side bleeding holes, the air is bled from 7-10th compressor stage for cooling. 3D printing would massively benefit it because more than structural loads, the part is at its thermal limits and structurally it becomes weak as a result. If they can just cool it by 200 degrees, it would be groundbreaking. The trailing edge of the blade is by far the most critical - thicker and aerodynamic efficiency will take a toll; make it razor sharp and it will just melt away.
paulmooreparks 6y ago
In civilian aviation, or in military training and peacetime operations, sure, but in a fly-or-die situation, like the one described in the article where supply lines are compromised, the ability to print and use a part for emergency use could be a literal lifesaver. It's analogous to replacing fuses with copper bars before entering combat (in some scenarios).
DarthGhandi 6y ago
Incredibly strange view, because additive 3d metal printed parts are being used in high powered automotive and aviation right now. Perhaps check out some of the leading contenders in the field and reconsider that appeal-to-authority stance? https://www.ge.com/additive/industry/aerospace https://www.ge.com/additive/industry/aerospace https://youtube.com/watch?v=NKr_zCCkEKs https://youtube.com/watch?v=NKr_zCCkEKs https://youtube.com/watch?v=a6SSw7FGky0 https://youtube.com/watch?v=a6SSw7FGky0 https://youtube.com/watch?v=cGGLSN6CTwI https://youtube.com/watch?v=cGGLSN6CTwI
lmilcin 6y ago
Exactly. The issue of developing aircraft parts is how to make it as light as possible and still perform reliably. Machining the part is least of the problem. Any other method will be inferior if it produces heavier part to get same reliability or will be less reliable for the same weight.
mensetmanusman 6y ago
It might be now, but metal composites with electron beam sintered 3d printing will get us there eventually.

ethagknight 6y ago

I believe you, but please go on and tell us why

systemvoltage 6y ago
This was 10+ years ago but the process is roughly as follows: Requirements of loads and flight envelopes are first provided to us (I was employed in a stress analysis group). The parts that I worked on weren't "new" per se, these were modifications to existing parts to comply to new loads or new materials, fasteners etc. Once envelopes + safety factors are set, we literally sketch out basic FBD (free body diagrams) along with shear-moment diagrams depending on the type of the part. You know the kind of diagrams you had to do in Statics class in University. Most of us knew the appendix formulas and many other empirical results by heart, and some of the guys at work were total nerds. They knew every possible cross sectional moment of inertia formulas, etc. It was really humbling. You'd think that aircraft industry some slow moving folks, but it couldn't be more false. The discipline was astounding. Then we consult existing parts directory, fastener books and materials for conceptual design. During the first conceptual design review (CDR), Principal engineers (depending on how critical this part is) get involved and provide us feedback. Post CDR, we send out parts to our FEA dept (mostly part time workers, some of them even commercial pilots) that get the models from the drafting department (Catia V4 at the time) and run some discretization scripts, they are pretty versed on how fine the mesh should be, but everything must be documented. Sensitivity study against mesh size needs to be proven. Converged models are sent back to us, we test it against intuition, and theoretical predictions (but not always). Detail design: Flange thickeness to thread pitch is set in stone, about 1800 fastener choices are narrowed down to a few, cost implications are non-existent, so most of the times weight is king. Coatings if any are specified. Prototypes are made by our supplier, GD&T red marks are fixed. Goodman diagram is consulted for fatigue studies, and sometimes even simulated in the FEA model. Same with creep and crack propagation studies. Detail Design review takes place and we are blessed by principal engineer. If it is an external part with any sort of interaction with the airflow, flutter dynamics to CFD guys are called, I honestly never worked on any farrings or anything affecting flight dynamics. Then comes the guaging (where to put rosette and stress gauges) and ground test certification process. Prototypes are tested against real world conditions and failures. Depending on the part, various tensile strength tests are conducted and sometimes with simulated internal cabin pressure. Not all parts were tested though. All in all, it takes forever to make a part in an airplane. My memory is fading so I can't recall everything. It was a lot of paperwork and documentation. We took that seriously. Having designed parts in an airplane, I just can't take 3D printing seriously. You wouldn't believe the kind of work that goes into designing parts from composites - that was a new thing at the time when I was in the industry.
- redis_mlc 6y ago
  Consumer 3D printing results in bathtub toys. An Apache helicopter is not made of bathtub toys. Metal is awesome compared to filaments and composites: Mike Busch - "Making Metal Behave" https://www.youtube.com/watch?v=m1jl6IlywAk https://www.youtube.com/watch?v=m1jl6IlywAk
- tantalor 6y ago
  I don't think you have answered the question even remotely. What about 3d printing prohibits using parts in aircrafts? Are you aware "3d printing" can produce many types of materials, including metal, and not just plastic?
  - wlesieutre 6y ago
    It’s been used for several rocket engines
    - WalterBright 6y ago
      Interesting. Are they man-rated engines? Which parts? Since rocket engines tend to be single-use only, fatigue strength wouldn't be much of an issue.
      - wlesieutre 6y ago
        SuperDraco on SpaceX’s crew dragon capsule aren’t used in the launch, but it’s the launch escape system. [1] SpaceX also apparently prints the main oxidizer valve in Falcon 9’s Merlin 1D, which isn’t a single use vehicle, but who knows what components get replaced between launches. [2] As of 2016, the Raptor engine being developed for ITS (now Starship) was 40% printed by mass, but I have no idea how much of that was for faster prototyping and if they might be using less in later production. [3] Rocket Lab’s Rutherford engine for their Electron rocket. [4] More in the works from Relativity Space, Launcher, NASA, and others I’m sure. We’ll see what pans out. [1] https://en.wikipedia.org/wiki/SuperDraco https://en.wikipedia.org/wiki/SuperDraco [2] https://3dprint.com/10830/spacex-3d-print-oxidizer-valve/ https://3dprint.com/10830/spacex-3d-print-oxidizer-valve/ [3] https://www.nasaspaceflight.com/2016/10/its-propulsion-evolution-raptor-engine/ https://www.nasaspaceflight.com/2016/10/its-propulsion-evolu... [4] https://en.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)
tpmx 6y ago
The article does cover that, in a very brief manner: > So far, he said, they’ve evaluated 31 percent of the parts – over 30,000 items – and found 252 that are “potential candidates for additive manufacturing.” That’s less than one percent.
- robocat 6y ago
  I think that was for a prototype for the Lower Tier Air and Missile Defense Sensor radar. For the helicopter: “We expect to probably get about 20,000 structural parts, -ish, out of that,” Royar said. “We’ll take a look at it and evaluate every one” to see whether it can be safely and economically replaced with a 3D-printed version. So I am guessing they might find say 100 suitable non-critical parts (say plastic covers). 3D scans of critical parts could still be very useful for rigs, emergency field use, or other non-flight purposes. > [GP]: the whole premise of 3D printed parts going into an aircraft from airworthiness perspective is flat out insane. The article responds that observation very well IMHO.

starpilot 6y ago

I was a structural engineer for Sikorsky. I think it's obvious we will not be replacing a machined titanium main rotor hub with a 3D printed part soon. The article touches on this. It will probably be non-structural components like buttons on an MFD.

monocasa 6y ago
The super draco combustion chambers made by space x are 3d printed. I'm not saying they're the best fit for everything, but saying they'll be relegated to button on an MFD is probably too far on the other end of the spectrum.
- icegreentea2 6y ago
  Form is function in high performance manufacturing (including most of aerospace). Just switch materials is a huge deal. If you set out with "use additive manufacturing" as one of your requirements/design goals, you can probably use additive manufacturing in a lot of aero. Using additive manufacturing to drop in replace existing parts that were made with different materials and techniques is very unlikely however.
  - monocasa 6y ago
    Oh absolutely. There's no way you can just drop a scan in to solid works, send it to the printer and call it a day. Some serious engineering needs to occur to change manufacturing processes. That's probably not a deal breaker in the grand scheme of things is all I'm saying.
kbenson 6y ago
I was going to write a reply saying that I don't see why we can't use it in many places as long as we understand the parameters of the product, but as so often happens I found an excellent source that actually explains your stance in details.[1] The TL;DR is that there are lots of imperfections in 3D printed parts, which means they typically fail at much lower stresses. It actually includes some pretty good video illustrating this at a microscopic level. That said, there are apparently new techniques being researched and discovered that have promise to increase the quality of 3D printed parts. One way to thing of it is that we have hundreds to thousands of years of experience in material science with forming metals in other manners, and we've just started with additive engineering, so there's a lot of room for improvement. 1: https://www.youtube.com/watch?v=fzBRYsiyxjI https://www.youtube.com/watch?v=fzBRYsiyxjI

d_silin 6y ago

I know a bit about turbofan engines in aircraft. 3D-printed parts are already going into them right now, as we speak: https://www.ge.com/news/reports/airbus-gets-1st-production-jet-engines-with-3d-printed-parts-from-cfm https://www.ge.com/news/reports/airbus-gets-1st-production-j...

d_silin 6y ago
Also, to elaborate on which parts can be 3D-printed. The latest and greatest breakthrough is using EBM (electron beam melting) for 3D printing second stage turbine blades from titanium aluminide in GE9X engine. Those parts are continuously experiencing mechanical and thermal loads far in excess of forged or machined parts in any airframe. There is no added safety barrier for them unlike for fan blades. If turbine stage flies apart, its parts will go straight through everything in their path, including passengers.
d_silin 6y ago
To further explain my point but also support the root comment. Aluminium/steel/titanium airframe parts are usualy machined or forged. It is not possible to replace them with 3D printed parts just yet. But! All of jet engine turbine blades are cast, not machined. Those parts can be safely 3D printed, as various metal sintering/remelting methods produce similar or better structural quality. Same goes for those magnesium castings used in aircraft landing gear - can be replaced with 3D printed ones. Parts that only under hydrostatic load like fuel nozzles can be 3D printed. Fatigue is not an issue there. Parts that do not experience significant structural loads, but high thermal loads (combustors) can be also 3D printed. I believe that's a better answer to the topmost comment.
- systemvoltage 6y ago
  I also worked on Turbine blades. Specifically did studies on trailing edge dump and pressure side bleeding holes, the air is bled from 7-10th compressor stage for cooling. 3D printing would massively benefit it because more than structural loads, the part is at its thermal limits and structurally it becomes weak as a result. If they can just cool it by 200 degrees, it would be groundbreaking. The trailing edge of the blade is by far the most critical - thicker and aerodynamic efficiency will take a toll; make it razor sharp and it will just melt away.

paulmooreparks 6y ago

In civilian aviation, or in military training and peacetime operations, sure, but in a fly-or-die situation, like the one described in the article where supply lines are compromised, the ability to print and use a part for emergency use could be a literal lifesaver. It's analogous to replacing fuses with copper bars before entering combat (in some scenarios).

DarthGhandi 6y ago

Incredibly strange view, because additive 3d metal printed parts are being used in high powered automotive and aviation right now. Perhaps check out some of the leading contenders in the field and reconsider that appeal-to-authority stance? https://www.ge.com/additive/industry/aerospace https://www.ge.com/additive/industry/aerospace https://youtube.com/watch?v=NKr_zCCkEKs https://youtube.com/watch?v=NKr_zCCkEKs https://youtube.com/watch?v=a6SSw7FGky0 https://youtube.com/watch?v=a6SSw7FGky0 https://youtube.com/watch?v=cGGLSN6CTwI https://youtube.com/watch?v=cGGLSN6CTwI

lmilcin 6y ago

Exactly. The issue of developing aircraft parts is how to make it as light as possible and still perform reliably. Machining the part is least of the problem. Any other method will be inferior if it produces heavier part to get same reliability or will be less reliable for the same weight.

mensetmanusman 6y ago

It might be now, but metal composites with electron beam sintered 3d printing will get us there eventually.