Combating Warping

Look for guides here.

Moderator: CrazyIvan

Post Reply
User avatar
CrazyIvan
Posts: 196
Joined: Mon Jul 10, 2023 10:25 am
Has thanked: 14 times
Been thanked: 31 times

Combating Warping

Post by CrazyIvan »

Okay, this isn't so much a guide/tutorial as a discussion, but I figure it comes under the general category of education, so...

What Is Warping?

Well look, I only have a few months experience at the sharp end (hot end? :lol: ) of FDM printing, but I'm already pretty familiar with warping. It seems to affect mainly the underside of horizontal surfaces.

Depending on the geometry of the print:
  • The first layer might lift off the print bed around the edges;
  • The magnetic plate might lift (Tina2);
  • An overhang might lift off the support layers.
  • If the nozzle or proximity sensor travel crosses the edge of a warped layer, it collide and misalign the subsequent print or knock it off the plate entirely.
Here are some examples:

Image

In the above, the warped part was the other way up when printed. I cured it by re-printing with the opposite orientation, so that any warping would then be confined to surfaces which don't matter.

Image

This roller was printed with the left side downwards. The warping is in the underside (as printed) of the flanges. What really surprised me was the short scale over which this happened: the flanges are only a few millimeters.

I have also had problems with warping lifting the first few layers, which then catch on the nozzle or proximity sensor and shifts the print, and then catches again later on and shifts the print multiple times. The result is a mess of printing into free air. I now watch the first two (at least) layers going down, rather than come back after several hours and find a ruined print and wasted filament when I could have aborted it.

Granted my Tina2 printer has no volume or bed heating, but I'm only using PLA (which is supposed to suffer least) and the build area is only 100x120mm, so warping will be much worse with ABS or bigger builds.

How Does Warping Happen?

I'm open to discussion, but it seems to me this is entirely about shrinkage when the extruded filament cools. A layer goes down, and shrinks slightly as it cools. The next layer goes down and also shrinks as it cools, but it is on top of (and bonded to) a layer which has already shrunk. The consequence is to build in strain, and if the strain exceeds the grip of the layers onto the build surface or other layers below (eg a support roof), they will flex like a bimetallic strip. It only takes a very small differential contraction for this to happen.

Presuming the flexure does not obstruct the print head, subsequent layers will print on top and add further strain, but this effect eventually peters out, and as the print head is where it should be in Z rather than tracking the layer underneath, after a few layers there is no further warping.

How Can We Stop It?

When the filament comes out of the nozzle, it is liquid. There can be no strain in a liquid. The problem is between the temperature at which the filament first solidifies and the temperature it is at when subsequent layers come along. If the model was maintained at the solidification temperature until the print is finished, then the whole model could be cooled uniformly post-print... but that temperature is rather high.

Ensuring a very good adhesion for the first layer should combat warping by holding the layers in place, but only for the bottom of the print. Any overhangs are not stuck to the plate, only loosely bonded to support structures (if any).

The purpose of a heated print bed and/or heated build volume is to slow the shrinkage and therefore reduce the strain between the layers. A heated bed improves adhesion and heats the build volume indirectly. Making the temperature very high (as might be optimal) takes a lot of energy, but also is very bad for the printer mechanics and electronics.

The Tina2 has neither. I have achieved some benefit with a difficult print by applying a hot air gun while the first few layers went down, but it made me very nervous that I might be overheating the printer components.

Other Strategies

Can we design out warping? Vertical surfaces can't warp, and top surfaces tend to be flat, so the appropriate choice of orientation in the slicer should help. A cube, for example, could be printed standing on a corner, and not require much support if the overhang angles are slight enough.

Non-solid layers should cause less strain; where an internal volume is hollow or contains support, it will conform to the layer below better. But that doesn't help for the skin layers.

–––––––

Feel free to comment! I throw the floor open...

User avatar
CrazyIvan
Posts: 196
Joined: Mon Jul 10, 2023 10:25 am
Has thanked: 14 times
Been thanked: 31 times

Re: Combating Warping

Post by CrazyIvan »

This video suggests the location of the layer print start-stop point (known as the "seam") affects warping. Might be worth experimenting with:


Antipodean
Posts: 23
Joined: Thu Jul 27, 2023 11:43 am
Location: Oxfordshire, UK
Has thanked: 2 times
Been thanked: 2 times

Re: Combating Warping

Post by Antipodean »

Interesting find. Worth experimenting with. :idea:

User avatar
CrazyIvan
Posts: 196
Joined: Mon Jul 10, 2023 10:25 am
Has thanked: 14 times
Been thanked: 31 times

Re: Combating Warping

Post by CrazyIvan »

Another video suggests printing a draft shield along with the target print. The proposition is to minimise unwanted cooling:



This begs the question what we should be setting our fans to. For Tina2 owners, the hotend fan not only blows on the heatsink but is also ducted to the print-in-progress. We can't turn off cooling the print without also stop cooling the thermal break, and I'm not sure the consequences would be very good.

Antipodean
Posts: 23
Joined: Thu Jul 27, 2023 11:43 am
Location: Oxfordshire, UK
Has thanked: 2 times
Been thanked: 2 times

Re: Combating Warping

Post by Antipodean »

CrazyIvan wrote: Sat Jul 20, 2024 7:33 am Another video suggests printing a draft shield along with the target print. The proposition is to minimise unwanted cooling:
Yes, I saw that. There is also another video (from the same guy as did the first video you posted above) where he talks about what are variously known as 'lily pads' or 'mouse ears' on corners to also combat the same problem. Sorry don't have the link handy.

User avatar
CrazyIvan
Posts: 196
Joined: Mon Jul 10, 2023 10:25 am
Has thanked: 14 times
Been thanked: 31 times

Re: Combating Warping

Post by CrazyIvan »

Antipodean wrote: Sat Jul 20, 2024 6:05 pm he talks about what are variously known as 'lily pads' or 'mouse ears' on corners to also combat the same problem.
Mouse ears are (effectively) optimised brims, with the brim only being printed in critical areas – eg corners. I think they are meant to control plucking, where the first pass of the print turns a sharp corner and might pull the filament off the bed if there is nothing to give it some sideways support.

Mouse ears will increase bed adhesion, but not as much as a full brim would. Neither is adhesion the panacea to warping (at least not when it comes to our Tina2s) – I've had warping pull the grip tape off the bed, and when I stuck the tape down even more the warping has curled the magnetic rubber plate!

The only disadvantage I can see of brim over mouse ears is the extra filament and print time.

Post Reply