Print long thin pieces

[Curven 28]

Hello,

At work we need to print long plastic rails for an magnetic field mesuring system. (can't use metal part because it would interfer with it).

these rails look like this white piece.

We print it as shown on the image, problem is, once print finished and heated bed cooled down it lifts in the middle...

We tough it was because of the rail profil and tested tu print the same size but juste a big rectangle, it lifts as well. (maybe a little less)

Tried PLA and ABS, both behave the same, tried 100% infill and 40% Cubic. always the same...

Do you have any tips and tricks to print this flat? 

Small design modification are possible.

 

Thank you very much.

[NickB 2]

What kind of adhesion are you using? Mabye put a bit more down in the middle.
I use 3Dlac from lay3rs and dont have any 'warping'.

also what temperature are you using for what material?

[Curven 28]

Hello thanks for your reply. I use the UHU glue stick.

For PLA I print at 200-210 °C with buildplate at 60°C. (It's from colorfabb, PLA/PHA)

For the ABS I print at 250°C with the buildplate at 95°C (Ultimaker ABS)

 

I'm not sure it is really warping, the corners stick well to the build plate during the print and I don't think it lifts during the print, but either after, when it cools down.

[NickB 2]

Temperature seem good, that wont be the problem.

Are you using an Ultimaker and/or is your printer enclosed?

I dont know where and in what kind of enviroment you are printing but mabye there is a gust/stream of wind that blows over the part and cools it down(to quickly).

 

Mabye if you remove some surface area on the bottom in the middle it will 'warp' less there because there is less matieral that is in contact with the build plate.
I have drawn a quick cross section view of your part (looking at the image i thought it looked like this🤔) In red is what I mean with less surface area:

 

[NickB 2]

Mabye there is a easyer solution😉(I always think of the hard ones first🤦‍♂️). have you tried printing with a (bigger) brim or a raft. If it still bends with these options then you could start looking into modifying the part.

[Curven 28]

It is printed on an UM2+ with a front window to reduce warping problems. I did not try to print it with a raft until now... I may give that a try.

 

You got the cross section well, the design modification seems tu be a good idea too!

[gr5 2,265]

I've never heard of a long thin shape lifting off the bed in the middle.  Usually it's the ends.  Do you mean "the middle" vertically?  Or half way between the two ends of the part?

 

I guess I would reheat the part above it's softening temp (for pla dunk it in water that is around 80C (pour boiling water into a pan or dish) for about 1 minute - for ABS leave on heated bed at 110C under a towel for about 1 minute) then put it on something flat and hold it in position for 2 minutes while it cools back down into the right shape.

 

So the layers adhere well?

 

By the way I would never print  ABS on a 95C print bed.  100C minimum.  You want to be above the softening temp of ABS but if it's sticking well then 95C is fine.

 

 

[geert_2 558]

I have seen this problem too in long prints: while printing, the model sticks to the glass very well: no lifting/warping at all. But after removal, it starts to deform slightly. And indeed, for PLA usually the center "lifts" half a mm, if you put it on a flat table. So this must be due to residual cooling stresses in the material, which are not enough to pull the part off the glass, but enough to slightly bend it.

 

However, I don't have a good solution: warming it up again to release the stresses, tends to make things worse, far worse. I have had models warp upwards on the edges. Or others warping upwards at first, but then after some time reverting and severely warping in the other direction, very weird. And they shrink in length, but expand in width and height with several percent.

 

Maybe, if you could clamp the model between heavy metal plates, and gently warm it up to around its glass transition temp, and very slowly cool down, you could remove some of these stresses? Or let it sit for a night on the warm glass bed of the printer, before removing it (and cover the bed with a box, so temp is uniform)?

 

Edit: the photo shows some of the warped test models. In this case they were subjected to way more elevated temperatures after printing, to try the effects of annealing. Thus way above glass transition temp. But the bending upwards in the center shown in the second model, is also very lightly present in 20cm long models, immediately after removing from the glass (although far less than shown here, only ca. 0.5mm).

 

 

Edited November 2, 2019 by geert_2

[Curven 28]

First of all I want to thank you all for your replies, suggestions and ideas. It is really great tu have many people sharing their experience.

 

On 11/1/2019 at 2:49 AM, gr5 said:

I've never heard of a long thin shape lifting off the bed in the middle. 

... Or half way between the two ends of the part?...

Its half way between the two ends, but as Geert_2 says, it sticks well during the print and bends after when the part is cold.

Here is an image were bending is better shown, holding to pieces together. So the "gap" is double.

 

I have the feeling that layers do adhere well, part is printed in black ABS so it is hard to get a nice image of it but here is my attempt.

 

 

I will give NickB idea a try, but for now this job has been put as low priority, so I won't have much time for it... I'll try to do tests as soon as possible!