Avoiding warping on solid PLA prints

[r111122223333 0]

Has anyone any tips on making REALLY STRONG PLA prints, the sort of strength one gets with a solid 100% infill density but without warping and other quality horrors? I've done it before for small parts (max dimensions 4cm x 4cm x4cm) and got away with it, but when trying bigger parts they warp up horribly from the bed and also develop a ringing like effect on the walls (which I've never seen from this printer before) which may be either ringing or may be the infill grid pattern showing through the perimeter walls. 

 

The parts I'm trying to produce need to be really tough, particularly in compression where some sections get tightened between screws as part of a clamping system, so if you can't advise on how to avoid elephants foot type warping and this horrid "ringing"  on the perimeters for fully solid parts then can you suggest not-quite-solid slicing (I use Cura, v4.12.1, later versions don't seem compatible with my OS yet) settings which could give solid strength, especially for torques applied to lower layers in a part and transmitted to upper layers (or vice versa, think compound gears) and for forces caused by tightening a screw in to a nut, with both printed parts and other things being clamped between them, where the screw's axis is in the x-y plane.

 

My printer is an Ultimaker S5, I have PLA and tough PLA to hand as well as water soluble PVA support strut, I have 0.4mm nozzles in it.

 

Thank you

Edited July 26, 2022 by r111122223333

[Smithy 1,145]

A 100% infill is always a bad idea and you will not get stronger than with a lower infill in most cases. 

Depending on your specific use case, I would say 50% could be enough, maybe 75%. Use more perimeters (walls) and print with ToughPLA which is much much stronger than normal PLA.

 

Normal PLA has also the disadvantage that it get brittle with time. 

 

If ToughPLA is also not working, I would use another material, like PC.

[dsp 18]

Also keep in mind the print orientation compaired to the force direction a printed part always tent to break easier through the layer lines (so try and print with the force in the Z direction of the end part or diagonal)

 

Next to that i prefere ABS printing for stronger parts, and up the wall count a bit. 

[GregValiant 1,342]

"where some sections get tightened between screws as part of a clamping system..."

The problem isn't being "strong enough" but rather cold flow deformation that many plastics are subject to.  When you apply constant pressure the plastic will move causing the clamping pressure to drop.  The screws connection appears to come loose with no movement of the screw/nut system.

You can try putting in infill mesh support blockers at the screw holes to increase the walls.

 

You can use Grid infill at 15 or 20% and set the "Infill Line Multiplier" to 3 and set the infill structure so it is square to the walls.  Typically that would be with the "Infill Line Directions" at [0,90].

That will help prevent warping/lifting and make for a strong piece in compression.

These models are identical wiht the infill density at 20% but the right model shows the other changes described above.  The view shows just the top layer of the infill for clarity.

 

 

Edited August 1, 2022 by GregValiant

[r111122223333 0]

Thanks, I've made some progress by going to only 70% infill, but then having some layers with fully solid infill (where needed for the screw related things) based on a technique of intersecting a shape with the main model.

 

The very bottom answer at

https://3dprinting.stackexchange.com/questions/6522/different-infill-in-the-same-part

showed me how.

[GregValiant 1,342]

The Cura Marketplace has a plugin for Cylindrical Supports.  That gives you the option of adding cylindrical Mesh Modifiers at your screw connection holes.

[geert_2 558]

PLA under load, in my experience, will cause several problems:

- creep deformation, as mentioned above: the material slowly deforms under the constand load, and clamps and screws will come loose,

- micro-cracks will form in areas that are under constant tension,

- from ca. 45-50°C onwards, the part will deform due to heat, so it is not suitable for use in a car or machine for example,

 

I have seen all these effects in my own models.

 

I don't know about sand-filled or metal-filled PLA, no experience with that.

 

If it needs to be really strong, what I would do for myself is:

- print a mould in PLA, and pour a strong sand- or metal-filled composite in it.

- or print a master model in PLA, make a silicone mould of it, and then pour the sand- or metal-filled composite in that silicone mould: that will make releasing it a lot easier.

 

This method with silicone moulds is also used to make art statues in cement or filled-epoxies.

 

Thoroughly soak the mould with silicone oil prior to casting, that will make it last longer. Remember that silicone moulds are water-tight because they repell water, but they are not solvent-tight, and not oil-tight: these will penetrate the silicone. Composites will also penetrate the silicone, cure in there, and thus damage the mould over time. That is why you need to saturate the mould with oil first, so no other products can penetrate it.