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The Failure Series- Why are there holes in my 3D Print?

Within this series of blog posts we will be discussing how you can remedy the failures you may be spotting in your prints. Issues can occur, and understanding why they’re happening can sometimes be difficult. Within this blog we shall …

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Tom Watkins

June 16, 2020

Within this series of blog posts we will be discussing how you can remedy the failures you may be spotting in your prints. Issues can occur, and understanding why they’re happening can sometimes be difficult. Within this blog we shall be gaining an understanding as to why you may be spotting holes in your prints. These holes will generally be occurring inside the top surface of the print. A commonly used term for this issue is “pillowing”.


Why is it occurring?

There are a few potential reasons its occurring, so we shall run through these. Firstly, there’s a chance that there is a a temperature build up inside the part. If the top layers are not cooled well enough, then the layers warp around the infill pattern, causing the pillow shapes to occur.

This is an issue that can affect most FDM printers, especially when using small layer heights, and softer materials (such as TPU).

Another reason for it occurring is that the infill density is not high enough, which can also be linked with too few top layers. These two are connected as they both produce a limited amount of material to close up the top of the part. With it being too thin, it then falls through as it tries to bridge the gaps ineffectively.


How can I fix this?

There are a few simple steps you can take to fix this issue.

Increase the infill density. If you are using an infill density of 5%-10% you are greatly increasing your chance of this issue occurring. Up the infill density and give the top layers a greater chance of bridging between the infill pattern.

Increase top layers. If increasing the infill density doesn’t help we increase the top layers. Therefore we are increasing the thickness. The first top layer that’s printed may not quite bridge the infill, however the layers above will. Furthermore, if the first top layer is improperly cooled, the layers printed after will effectively cover it up.

Improve cooling. The next step to try is to increase the fan speed, or just turning them on towards the end of the print. This works with the bridging of material over the infill, as its cooled before it sags- therefore limiting the chance of pillowing occurring.

Decrease in speed/temp. The last option is to try decreasing the print speed and/or print temp. By working with units of 5 (i.e 5mm/s, 5 degrees) you are only creating slight changes, and can therefore check the effects without creating other problems.


How low infill directly correspond to pillowing/ holes in your print

The information above will help you fix these issues, however the best way to check if you are experiencing pillowing is to compare against the print below. This was created using an Ultimaker S3. Each slice of this “pillowing pie” has a different infill to test the theory. This can be achieved very easily within Ultimaker Cura. By selecting onto the individual bodies, we choose “per model settings” and then “select settings”. At this point we can add in “infill density”, and then change each slice to the appropriate infill.

how to change individual bodies to infill densities

During the print process, you can see how different the 5%, 12.5%, 17.5% and 25% infill densities are. With these variations, it will be stretching the filament to its extremes over the top layers.

infill during print

Within the resulting print its clear to see how much pillowing can occur with lower infill densities.

5% – affected with a smaller quantity of pillows. However the pillows that occur are of the largest size

12.5% – slightly smaller pillows than the 5%, however we can see the infill pattern quite clearly.

17.5% – Even with this higher infill density, the resulting issue is now that we can perfectly see the triangular infill pattern as its not quite high enough.

25% – No visible infill, smooth finish.

infill density pillowing
infill density pillowing

If you have a part that you’re looking to get printed, or would like to improve your current manufacture then drop us a call on 01926 333 777 or check out our contact us section.

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