Under extrusion when multimaterial printing

[Xalara 6]

I've noticed slight under extrusion issues when multimaterial printing with PolySmooth on my Ultimaker 3. In particular, right after switching materials from PVA, it seems that it takes a bit for the PolySmooth to get going again. Currently I use a PLA profile at 0.1mm layer height with the temperature overridden to 220-225 Celsius and the print speed overridden to 50mm/s. 

 

Is there some other settings adjustments I can make or is this a case where I'll need to use a priming tower to get the PolySmooth flowing again after a material switch?

Edited February 7, 2018 by Xalara
Typos

[Xalara 6]

Here is a picture of the part I am trying to debug after the supports were dissolved. Notice that, especially in the areas where rapid material changes occur, there's an unevenness to the layers. Also the area where the part broke you can see that the internal fill was not being filled in.

[kmanstudios 1,120]

What two materials are you printing with? That does look a bit on the yucky side.

[Xalara 6]

The two materials are Ultimaker PVA and Polymaker PolySmooth (PVB).

[kmanstudios 1,120]

hmmmmmm, I am not familiar with polymaker's materials, but I am familiar with the UM PVA. Would it be possible to post a project file to fully check out?

[Xalara 6]

I can do that later when I get home. In terms of printing I'm not too worried about the "pimples" and stringing since they are cleaned up easily with my fingernails. It tends to happen because Polymaker PolySmooth is on the gooey side and some oozes out while PVA is printing. That said the part breaking and unevenness in the horizontal size of layers definitely is a problem.

 

 

Now that I think about it, PolySmooth's behavior when multimaterial printing is similar to Ultimaker TPU-95A, so maybe a priming tower is needed? It's definitely not as gooey as TPU-95A but it seems up there.

[kmanstudios 1,120]

Have you tried to lower the temp to see how it prints? If you do lower the temp, you may want to slow down the speed.

[yellowshark 153]

Ok I think a bit of testing would help. Beware I have never used Polysmooth! My inclination is that your speed is too fast. For now I will assume your extruder temp. is correct.

 Halve your print speed and double your layer height. ( I am thinking that will give you a similar pressure requirement and therefore the extruder temp. will be the same).

In Cura sink your model on the Z axis so that the circular area does not get printed and waste your time.

Print the leaning arms.

Does that look better? Hopefully so but even if not better, repeat the print and take 5 degrees off your extruder temp.

Maybe repeat again with another 5 degrees taken off. You will know if it is worthwhile or pointless.

 

I probably should have asked this first but when the two leaning arms are being printed I am wondering what your layer time is? Perhaps it is under your minimum layer time (10 secs?) and causing the print speed to slow down substantially and that is your problem?

Using a priming tower would help with that.

Infill failure – you do not say what you are using so difficult to understand what might be happening. Personally I would tend to go with 40% to give those arms some strength. I am thinking you need to be watching those arms as they are printed so that you can see what is happening with the infill.

[Xalara 6]

I haven't had a chance to really dig into testing since this project is on a bit of a deadline. That said, current work around was: Printing the arms as separate models, 4-% infill, use a priming tower, and printing at 0.15mm instead of 0.1mm since it's just as good and I'll be smoothing it with vapors anyway.

 

@kmanstudios: Lower temp doesn't work out so well. I used to print around 195 celsius but PolySmooth (PVB) really wants to be around 220 I've found.

 

I will be revisiting this later with more tests (ie. print at different temps/resolution/speed). I've also run into some ER18 issues which I'm contacting Ultimaker support about, so I'm currently waiting for some help from them on this.

Edited February 12, 2018 by Xalara