Strengthening 3D printed parts… with Holes?..

Hello, Sunday!

 

Silence reigns as it rains down on this blog, but bear with me, for I yet persevere through my final year.

I’ve been doing a lot of 3D printing recently on my self built CoreXY “ETA”, and I had to make a case for a portable speaker I have. The speaker in question had rudimentary loops for tying it to something, but was rather insufficient for actually wearing on a belt. Having a 3D printer, I decided to print a case for it.

1.png

The blue object is the case, and the black body is a mock-up of the speaker

I quickly modeled a case for the speaker on Fusion 360, it’s a simple design where you slide the speaker into the case from the top, and a pair of clips snap onto indents on the speaker. Pretty straightforward, but during self review, I ran into a little problem. The case was 3mm thick on most sides, and as FDM/FFF 3D prints by nature are weak along the vertical Z axis, the clips looked like they would wear and break fairly quickly.

2.png

This is the orientation at which the print would be on the bed. The thin section just below the clasp is the weakest section, as repeated bending would result in it snapping off eventually.

Traditional knowledge would lead one to assume the simplest solution would be to increase the thickness of the section, or add structural elements like ribs to strengthen it.

Practical knowledge would assume that it would be unlikely that I would want to repeatedly remove the speaker from it’s case. Perhaps there could be better designs that would have eliminated the flaw entirely. However, I came up with a little trick to take full advantage of my medium, Fused Filament Fabrication, and exploit the way slicers work.

I started with making a void in my part. Yes, I plan on making it stronger by removing material. Removing material is typically used to maintain strength while keeping the weight down like with I-beams or fullers. However I use it here to induce a certain feature in the slicer. I created a side profile of the weak point in question, and hollowed out a tiny sliver, 0.1mm thick.

3.png

A sectional analysis of the case reveals the paper thin void modeled into the case

“What’s that going to change?”, you may be asking your screen, but rhetoric questions to a monitor aren’t going to get you answers, scrolling down will. This is the result when the model is sliced in Cura.

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The original shell thickness would have been 4 shell lines + the infill, but here it’s 8 shells, which should result in greater strength and bonding.

In my experience, infill has a marginal influence on strength. Around 15% is good for structural integrity, 30% for decent rigidity, and about 50-70% if you really want it as strong as possible. However, increasing shells is also an effective way to boost strength. By creating a hollow inside the weak section, the slicer prints additional shell lines in the area, and the shells fuse together to make it stronger.

5.png

Here you can see just 4 lines, infill, and 4 lines again in Cura’s Layer mode

Here is a view of the same layer in another section of the part, which is not reinforced with a void. You can see that when compared to the previous image, the number of perimeter loops is nearly doubled, effectively making the weak areas a nearly solid part.

IMG_20170806_093807_HDR.jpg

Here you can see a close-up of the part being printed. The clip on the left is nearly solid, whereas the wall on the right is hollow but for the infill.

If this case was to be injection molded, it’s strength would be vastly superior to a 3D print of the same. However, by exploiting the nature of 3D printer slicers, we are able to selectively increase the strength of our prints in areas where it is required without increasing the entire part’s material and time cost.

 

I hope this little tip aids you in your designs, please let me know your thoughts via the comments below, and if you would like more tips and tricks in 3D printing.

Thank you, and have a great week.

~Adithyaa

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2 thoughts on “Strengthening 3D printed parts… with Holes?..

  1. Great job well done- from conception, design to execution. I like this attention to details. Adithyaa is all set to take innovation, design and implementation of concepts to higher levels. Kudos. Keep it up.

    Like

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