Finished photo first but here is a picture of my 3D printed main bypass fan for the venerable CFM-56 which is most well known as the power plant for the Boeing 737. It was a fun journey making this. First step was researching the type of turbine I wanted to make that both looked cool and fit well on one of our largest 3D printers. I’m a mechanical engineer and jet engines have always fascinated me, they are one of the most advanced objects humans have created. They are a glowing yellow hot barely subsonic ball of single crystal superalloys crafted into intricate complex hollow arrays of precisely curved blades and stators and anytime we make an even minor material breakthrough the new understanding is immediately applied to make them slightly more insane. and then we strap 2 to 4 of these hell blenders onto a pressurized tube and that is how our planet has become so small. They are massive 5-10 foot wide behemoths that run so reliably they are taken for granted. That’s good engineering!
I had initially wanted to make the JT9D or the CF6 which were the first engines (and hence smallest) to power the 747 but the impracticality of printing a 6 foot wide turbine on such a "small" printer became apparent. The GenX engines of the 787 were quickly ruled out after being larger than some planes fuselages! After researching I found a real nifty comparison guide has taken on the task of collecting all of the essentials of every engine. http://www.jet-engine.net/civtfspec.html from here I planned out what would fit on the printer after a few quick calculations the CFM-56-3 known for powering the Boeing 737 was the winner fitting very nicely.
Turns out there are not a lot of intimate technical details easily available for the engine. Sure you can find a lot of cursory information like the width of the turbine blades, thrust, etc. but I need blade profiles depth etc. Luckily there are lots of pictures of the engine and there are lots of good views from different angles. From these pictures I was able to back into the other critical information I lacked on the main bypass fan. With this information I now had all of the critical dimensions I needed and could go into modeling it myself.
The modeling was straightforward but the challenge arose on how to design the part to be both easily 3D printable and strong. I am able to take certain liberties to improve the overall manufacturability of the part and improve its overall structural characteristics. In actual turbojets for example the turbine blades are actually somewhat loose on the ground and make a wind chime effect as they lazily turn in a breeze. When under load however the outside ring actually locks together to greatly improve its rigidity. Some engines such as the JT9D actually have two locking rings in the bypass fan blades. The new GenX engines are a departure from this since even though they are much larger they can get away from needing interlocking blades due to lower speeds and using composites. I had neither of these problems so I modeled the bypass fan as giant single part greatly improving the rigidity of the model and then quartered the turbine so it would be printable on my meter by meter printer and then designed two sets of rings which would be bolted onto the top and bottom of the turbine to hold the entire part together while being low profile.
At this point print optimization played heavily. Looking at every stage of the model and how it would print I basically broke the model down into 13 different Z height sections that would each be printed with their own specific characteristics and attributes. The end result is that I cut the print time in half versus printing the entire thing with one standard print process and saved several pounds of material with the part actually looking better in the end and saving wear on the 3D printer.
Everything looked good so onto printing! One of the parts did manage to take a massive chunk out of our borosilicate print bed which was sad.
The parts looked good and the test fitting worked great. Also one of the quarter sections was dropped during one of its transits which resulted in damaging one of the blades so it became a Southwest turbine.
The fan was taken back apart and post processed. I did not want a brand new engine but wanted something that looked like it got pulled out of the boneyard. Some silver spray paint and some black & brown airbrush paint for grime and voila!
A wall ornament for a nerds dining table. The next one will make the next fan capable of rotation! While it might not be the largest or sexiest of engines out there its a workhorse and is one of the largest 3D printed engines out there!! At least for now. Just don't bolt it onto a plane as it probably won't work very well Onto the next project which is really large gears! For really large 3d printing please drop us a line at https://www.titanic.design/contact! Thanks!!
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