3D printed nut fails under axial force

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1

Hi there!

Thanks in advance for your replies!

My goal is to print a nut for a bolt that can withstand as much axial force as possible. The filament i choose is the arnite id 3040 PET-P, as it has a very low friction coeficient with steal and does wear out much either and has decent stats when it comes to mechanical properties. I printed the nut on the H2D with the following parameters:

For the filament (used generic PETG and modified it):

  • Flow ratio - 1.05
  • Nozzle temperature - 275°C for all layers
  • Plate temperature (textured PEI plate) - 73°C
  • Fan speed - 0%
  • Force cooling for overhangs and bridges - checked
  • Fan speed for overhangs - 40%
  • I also dried it in the AMS 2 pro for 20 hours at 65°C

For the quality:

  • Layer height - 0.12mm
  • Layer height for first three layers - 0.2mm
  • Layer height where the threads are - 0.08mm
  • Wall generator - Arachne
  • Detect overhang walls - checked

For the strength:

  • Wall loops - 3
  • Sparse infill density - 80% / 100%

For the speed:

  • Outer wall - 200 mm/s
  • Inner wall - 300 mm/s

This is the file i printed:

Nut.3mf (235,3 KB)

For the one print with 80% infill, i reached 108kg of force in the one direction and 139.3kg of force in the other direction. With 100% infill, i reached 136.7 in the one and 190 in the other direction.

My nut failed like this:

Broken nut (1)
Broken nut (1)1920×1440 267 KB

As we can see, it didnt break the way the lines are what we can see clearly in the picture bellow.

Broken nut layers
Broken nut layers1920×1440 212 KB

And here we can also see the infill.

Brocken nut infill
Brocken nut infill1920×1440 275 KB

This is what it looked like with 100% infill.

Broken nut 100 infill
Broken nut 100 infill1920×1440 260 KB

I wonder if anyone knows, how to improve the strength of my 3d printed nut. Or did i simply hit the boundaries of 3d printed PET-P?

2

The failure looks like maybe it was caused by “low” interlayer adhesion. Can’t say anything about if it is out of spec though. Could be as good as it gets or maybe not.

Things that affect interlayer adhesion are filament moisture, extrude speed, extrude temperature, and chamber temperature at least from what I’ve read.

No expert on that though but if you need more strength it might be a place to look and maybe others who have looked deeper can add better info.

3

Thank you very much for your quick response!

Unfortunately, that doesn’t seem to be the problem here. Under the microscope, it looks like the crack goes straight througth all of the layers and not between.

Thank you anyway!

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4

There are tricks you can do with interleaved layers or brick layers (they are different things) that increase the strength of parts printed this way.

Makers Muse has a video on interleaved layers, which he used to print spinning blades for combat robots (battlebots).

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5

Thanks!

Seems very interesting, let me print it that way real quick.

6

Did you also try a different print orientation? Depending on tolerance needed, you can just about print the overhangs in a sideways nut.

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7

Have you checked the threads on the mating pieces match and have some tolerance? Also, have you calibrated the filament for dimensional accuracy?

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8

This video demonstrates, once again, why, for myself and many more other users, OrcaSlicer is considered to be way better slicer than Bambu Studio.

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