3D printed components - FDM method no good ?

[airgunfans]

This is the first time I tried to make a 3D-printed component. I use the cheapest method of FDM ( sticking melted filaments of plastic together ) and the material is ABS. The silencer works quite well but after about 20 shots, it just exploded. While this is not unexpected considering the power of the rifle ( Huben K1 ), the way it breaks makes me wonder whether the FDM method can be used to print components requiring good mechanical strength or the 3D-printing service provider has not done the job properly. Around the breaking point, the plastic separates into thin layers like they are not bonded well in the printing process. Can anyone having experience in 3D printing share your thoughts ? Can I expect higher strength if the silencer is printed by other methods such as SLS ( fusing particles by laser ) ?

 

[dreuf]

ABS is a strong material but hard to print due to high room temperature requirement.

I had similar failure as you experince until I enclosed my printer and add a heater to achieve 45°C room temp.

I also had to relocate all electronic components outside for safety.



Right now I can print 100% infill parts without bending or delamination. I built an air stripper for my 457 texan and it survives.

Hope it helps

 

[addertooth]

Some thoughts on the failure. Post baking may improve fusion. Or, because all of your filaments are circular/radial to the applied force, consider something as simple as a bonded wrap of paper (glue paper on the outside). You will be amazed how much gluing paper with epoxy to the outside of your silencer tube increases strength. Consider taking higher stress components, like air strippers, and make them press fit parts out of brass. Epoxy bind the brass parts to the 3d fabricated part. If you want an all plastic part, consider making the Outer diameter of your tube slightly smaller than the Inner diameter of a hot water PVC pipe, put epoxy on the outside of your tube, then slide the Hot Water PVC pipe over your finished tube before the epoxy cures. Hot water PVC pipe is more "chewy" than the more brittle white cold water PVC pipe.

The last part falls to the 3d design itself. If the wave generated by the first stripper stage (which is moving towards the exit end of the assembly), it met by a returning wave from the last stripper (which will be moving towards the entry of the tube), meet in the middle, they will make a high dynamic pressure stress zone, and cause failure in the middle of the assembly. The force of the colliding waves with be quite high. You mitigate this by having all reflection zones with a curved radius to diffuse the sharpness of the reflected wave. If you think of the impulse as a sonic wave, which you wish to scatter, it is more intuitive. Sharp corners on the interior are the enemy, and make problems both structurally and sonically. Or, you can just make it so strong, via the methods in the previous paragraph, so that good acoustical design does not matter.

 

[Bizill]

The problem is that the print didn't have good enough layer adhesion. I tried making a roller mechanism for my Kreepy Krauly pool cleaner because it kept getting stuck on the steps. I didn't use ABS, but rather PLA but the physics are the same in this situation. I had smaller "tubes" that I printed in the manner your LDC was, concentric circle atop concentric circle and a simple bend of my fingertips and that part broke apart with very little force. Had I printed the lines "horizontally" vs circle atop circle then the part would have been many times stronger. Problem is, with FDM printing, printing that LDC horizontally would leave lots of cleanup because you'd have to print the part on top of a "raft" and your surface finish would look like crap, even after post-cycle clean up. But functionally, it would be more sound. Function over form.



Your guy who printed for you may not have known how much pressure the part would actually encounter. But then again, depending on the force, if you printed the part horizontally, then a stress fracture could still split lengthwise. But I'd bet dollars to donuts it'd be okay. But as dreuf pointed out, he may not have had his print area warm enough and adhesion suffered. Hard to say for certain.



I think SLA would be stronger, but could end up being too brittle. I believe SLA can be printed in various resins just like FDM can print more than one "plastic". I haven't played with one yet. It's a process that's more involved and costly all around. If your guy has hardened nozzles and a better setup, he could perhaps print in nylon with his FDM printer. But if he's having bad luck with ABS, then nylon will probably be a no-go. Same with carbon fiber.



Ask your guy if he printed with his layer cooling fans on as well. Have him try printing with them off. That'll cause the layers to bond with better adhesion.

 

[Bizill]

Another thing he may or may not want to try is printing with PETG.