PVA on PLA adhesion? (stacking prints)

[peteruithoven 4]

With the Ultimaker's PVA we where experimenting with stacking multiple similar models on top of each other. This could highly decrease the amount of manual intervention when doing bigger productions.

This is possible after disabling the following behavior in the Preferences:

- Ensure models are kept apart

- Automatically drop models to the build plate

For easy separation and good prints we where thinking of adding a thin pva support (possibly interface) layer in between them.

But the pva has a really hard time adhering to the pla, even though the Z distance is 0.

What does work is setting the horizontal expansion to something like 1, which creates a pva ring around the model to which the thin in between layer adheres. But this takes a lot more time to print because now it has to switch nozzles every layer. See:

We had a similar problem when printing the following model, here we also needed the pva to touch the buildplate for it to print properly on the flat surface.

Any tips / ideas on how this could be done without having pva on almost every layer?

Edited December 6, 2016 by Guest

[nallath 1,120]

It's also possible if you group objects, ctrl click the object you want to put above the rest and translate it.

You could also try not printing it as support, but an object sandwich of sorts (you put another circle in between and mark it as print with PVA nozzle)

[peteruithoven 4]

It's also possible if you group objects, ctrl click the object you want to put above the rest and translate it.

 

I'm not quite sure what this fixes?

 

You could also try not printing it as support, but an object sandwich of sorts (you put another circle in between and mark it as print with PVA nozzle)

 

That sounds like a very interesting solution to the following issue, but doesn't affect the adhesion?

https://github.com/Ultimaker/Cura/issues/1220

[nallath 1,120]

 

It's also possible if you group objects, ctrl click the object you want to put above the rest and translate it.

 

I'm not quite sure what this fixes?

 

That you don't need to disable any settings in preferences.

[ultiarjan 1,223]

I think the best way to improve adhesion between PLA and PVA is to try different brands and colors to find which combinations stick the best.

We should probably all document and report on the combinations we tried....

And maybe we should make some sort of standardized test for this....

@sandervG do you know if UM materials people have a test method / print for this?

[peteruithoven 4]

 

 

It's also possible if you group objects, ctrl click the object you want to put above the rest and translate it.

 

I'm not quite sure what this fixes?

 

That you don't need to disable any settings in preferences.

 

Ah! Nice, thanks! I didn't realize there was a difference between shift and ctrl. Very useful.

[SandervG 1,521]

I think the best way to improve adhesion between PLA and PVA is to try different brands and colors to find which combinations stick the best.

We should probably all document and report on the combinations we tried....

And maybe we should make some sort of standardized test for this....

@sandervG do you know if UM materials people have a test method / print for this?

 

A test method which is specifically aimed at testing adhesion?

[ultiarjan 1,223]

Exactly, I'm thinking if you always print the same model in PVA/PLA and test adhesion (ofc best by measuring the force, but overcomplicated) by pulling it appart you get an idea...

I'm just assuming UM materials people tested a lot of PVA and materials combinations, if only when selecting supplier(s).

Did they find f.e. differences in adhesion between the UM PLA colors?

[ultimoose 0]

I have experienced the same problems with PLA and PVA both Ultimaker brand as supplied with the UM3 (see picture).

For me creating support structures with PVA was THE ONE AND ONLY reason to buy the UM3 so this result is both disappointing and unacceptable!

Note that the base PLA layer of my print is 72 x 104 mm so that the area where the PVA is printed on is probably relatively cold; not sure if this could be causing this behavior.

(off topic) The cap that protects the two print heads does not remain in position so I have to keep it in place with an elastic band!?

Both issues unacceptable for a printer costing almost €3700,-

[gr5 2,170]

@ultimoose - that "horizontal expansion" feature that peter used is critical. Did you try that? Will that get the pva to go over the edges of the pla and touch the glass bed?

An alternative is to use PVA with NYLON which seems to stick much better.

I have printed many PLA/PVA prints and they are tricky. Some parts have a shape such that it works great. Some not so great.

[gr5 2,170]

 

@ultimoose - another option is to flip that part over so that the PVA is underneath the part. PLA on *top* of PVA works quite well. It's the other way around that's tricky and mostly needs that "horizontal expansion" feature in cura.

[peteruithoven 4]

Looks like Cura 2.4 contains improvements that should improve pva on pla adhesion (tweaked jerk and acceleration).

https://ultimaker.com/en/blog/35482-cura-24-beta-is-here

Haven't tried this myself yet.

[tomnagel 126]

Results with Ultimaker PLA and PVA are amazing. Really. It is vital to use the quality profiles that come with Cura. Don't play around with the settings until you have gotten good results with the default profiles.

Yesterday I have been busy making spare parts for a marble track.

The part is pretty small, 25*13*12mm. The shape of this part makes it impossible to print without support. Perfect job for my UM3, with PVA support.

The next picture shows layer 51, which is about halfway in the part. You see the PVA structure.

A few layers later (layer59) , the PVA gets a roof, where the PLA will sit on:

And in layer 60, you see the PLA is deposited on the PVA:

In reality, this looks like this:

In the final picture, you see on the left side 1 layer of PLA on the PVA, and on the right already 2 layers have been deposited.

As stated above by ultiarjan, the horizontal expansion feature is crucial. But you get that automatically when using the default. To save a little bit of printing time, I set horizontal expansion to 0 one time, resulting in a print I had to stop halfway