abril 29, 2022
Prevent Warping with Draft Shields in Cura?
Anybody that has been FDM 3d printing is no stranger to a spool of filament. They come in a massive range of colors, some of them are chopped with other additives to give them unique looks or unique properties. And there's really a lot of options out there depending on what your specific use case is. With all these differences, there is one thing that they share in common and that's that they are thermoplastics. Thermoplastics are a form of plastic that are moldable at a certain temperature and they solidify when they are cooled. And it's this characteristic that makes them perfect for 3d printing. However, it's during these heating and cooling cycles that these materials will expand and then contract with. Some of them doing it more than others and it's a huge contributor to warping, which is something that anybody that 3d prints is familiar with.
3D Print Filament Shrinkage
Although the materials we put with our
thermoplastics, they all have their own
varying degrees of shrinkage, which we can see by taking a look at this chart, I found for various injection molding plastics.
The exact shrinkage amount can vary greatly based on a handful of
factors including processing method. ABS has a higher shrinkage rate than PLA, which is one of the reasons it's recommended to print inside of an enclosure. Enclosure will allow it to maintain a more uniform heat and have it shrink together, versus having it cool section by section as the hot end gets further and further away, which can cause things like splintering or warping. Due to this, I would never recommend printing ABS without an enclosure. But that's exactly what we're gonna do today.
For my testing, I started off with a motor mount that i had downloaded for the Voron switch wire, and all the parts are printed out in build series ABS on the Aquila S2 3D printer. I went with 105 celsius on the bed, and 255 celsius on the hot end. The 255 celsius on the hot end is a bit warmer than I would typically print ABS. I decided to go a little bit warmer, because again we are not using an enclosure while the part was printing.
I plugged in the ir camera to get some videos as well as some photos. One thing that i found that was really interesting was just how hot the base of the part was butting up against the bed. Now i expected it to be fairly warm but it was as warm as filament that had just been extruded out of the nozzle just a few moments ago.
The part ended up having a bit of elephant's foot on them. and you can see the heat that is contributing to that elephant's foot by looking through the camera. As for the part itself, other than that glowing base, the temperature
throughout it was fairly uniform while it was printing, which i believe is due
to the fact that the part was not very tall and that would also explain why in
the past i've been able to print some small parts in ABS or ASA that are
fairly flat without having an enclosure.
It is worth noting the place that the
printer is in is fairly tight and the temperature throughout this condo has been in the mid to even upper 70s. So it is fairly warm which is also not hurting its ability to maintain that heat.
After the part was printed i was ready to apply a draft shield in Cura. Draft shields are not visible by default. We'll need to head over to the hamburger menu in the print settings toolbar and go to "Manage Setting Visibility"
in the search bar if you type the word draf. You'll see Draft Shields if you
scroll down to "Experimental" in the print
What is a draft shield?
Cura describes “Draft Shield” as a wall around your model that traps hot air in and shields from external airflow. If you're familiar with skirt in Cura, picture a skirt but one that goes up much higher than just the first layer.
I then re-sliced the same model with the exact same settings, but i enabled the
Draft Shield. I went with a default 10mm XY distance and full for the draft shield limitation, which means it will build the wall all the way up to the top of the model.
With the two photos side by side, I could see the impact the draft shield had. Having the thermal camera set to the exact same range for all the prints, the parts in the draft shield stayed much warmer throughout the entire print.
Looking at the draft shield, you can see it's doing exactly what it's supposed to. As the outside of it is cooler, keeping some of the draft away from the part. and the heated part is able to maintain some additional heat.
After those first two prints, I ran a series of additional prints. I took a
small fan and i put it on high and one foot away roughly from the printer. I then opened the window that's next to the room so there was some cool air coming through.
My goal with that was to see if having that airflow we would be able to see any sort of temperature changes in the abs with or without the draft shell using the ir camera.
I stretched a 20mm test cube to be 40mm tall in hopes that
we'd be able to see some of the difference in temperature from the bottom to the top of the part and maybe a little bit of deviation in in between.
Once the cube got to about 30mm in height, i was able to notice some temperature difference within the cube. Although i didn't notice any warping when the part was printing or when i took it off, there was a pretty big bulge around the 15mm mark.
I then went ahead and printed the exact same cube with all the same settings but with a draft shield. Taking them side by side, you can definitely see that the cube stayed much warmer.
When i put the prints side by side i can see a slight slight bulge, maybe around the 15mm mark. but it is very very minimal compared to the part that did not have the draft shield at all.
Prior to playing around these draft shields over the past week or so, here i
had known of them for quite a long time. But I wasn't really convinced they did
much. I still 100% believe that ABS filament should just about always be printed inside of an enclosure.
My goal of this video was certainly not to fight a case against that. Because all we've done here is look as far as the visual properties go for these parts. But we haven't checked to see how they compare in terms of strength versus a part that with an enclosure. and i have no doubt that you will get much better inner layer
adhesion whether visually or not by using an enclosure. However i do think
that there are some unique cases, where maybe a draft shield could be beneficial even for materials like petg, which typically don't need an enclosure. As mentioned, i print in a fairly temperature controlled environment where
there's just not a lot of changes in temperature more than a couple degrees, but i know that's not the case for everybody. i've talked to quite a few people that 3d print in their garage and they've got snow, they've got much cooler conditions than we get. i do think that someone in a situation like that could potentially benefit from using something like a draft shield.
I don't feel that draft shields are something that are super commonly used. But if anybody does or has used them let me know what's your thoughts or what your feedback.
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