Warping on a flat part after it is finished

[helmut92 1]

Hi,

 

i could use some help. I try to print an open relatively large mold at work. The problem is that the part is always warping after it is finished and cooled. 

Its not the usual warping problem at the corners. its more like the part warping in the middle of the part. During printing, everything seems nice and flat, but after printing, when the bed cools, it warps.

 

I have attached a photo where you can see it. The warping is not only at the bottom of the part, it is rather the whole part that is deformed.

 

i think it's because the part is unevenly thick and it cools unevenly as the plate cools. 
Does anyone have a suggestion on what adjustment i can make to correct the problem. Constructively, the only thing I can think of is to reduce the thickness of the surrounding rim. 

I print with Colorfabb PLA, but have also tried Ultimaker PLA and tough PLA. 

Print speed all settings 15m/s; 15% infill, 4 walls, ironing, 0.2 layerheight. I usually print directly onto the glass, but have also tried PrintaFix. 

 

Thanks for your help,

Jan

 

Edited April 29, 2021 by helmut92

[GregValiant 1,251]

It's PLA and typically the shrink % is pretty low, but it isn't 0.  The shrinkage is affected by cross-section, variations in thickness, uneven cooling, moisture content, and other factors.  

PLA suffers from cold flow deformation at fairly low temps.  Maybe you could use that to "anneal" it.

 

It would require some experimentation but If you were to put one of your finished parts on a flat hot plate, cover it, and bring it up to say 120°C(?) slow enough so that it heats evenly, and then turn the temperature down over the course of some period of time (an hour?) so that it cools evenly, you may get the part to "relax" onto the flat plate.

 

Be advised that starting at too high of a temperature could turn your nice part into a puddle of PLA possibly causing you some personal embarrassment among your co-workers.

[helmut92 1]

thank you for your answer, I will certainly try that.

 

can i adjust the gcode in cura so that the print bed cools down very slowly after printing?

[GregValiant 1,251]

19 hours ago, helmut92 said:

can i adjust the gcode in cura so that the print bed cools down very slowly after printing?

You didn't mention your printer.  My Creality machine has an End G-Code that Cura inserts at the end of any gcode file.  I would make an adjustment there.  If you have an Ultimaker printer you might still get it to work.  An option would be to add it manually to the end of a gcode file.

There will be a line "M140 S0" that turns the bed off.  Comment that out and put the following at the end where it will execute last.  I'm assuming a bed temperature of 60°.

 

;M140 S0  ;Add a semi-colon to make the line a comment

 

M190 R60

G4 S3000

M190 R50

G4 S3000

M190 R40

G4 S3000

M190 R30

G4 S3000

M140 S0

The M190 R tells the printer to wait until the bed cools to the indicated temperature.  The G4 command is "dwell" and the S is in seconds.  The above snippet sets the bed to 60 and waits for it to get there, then pauses for 5 minutes, sets the bed to 50, waits to get there, and then pauses for 5 minutes, etc.  It shows 10° steps and 5 minute dwells.  You could adjust the number of steps, the degrees / step that the temp falls, and/or the dwell time between steps.

Don't allow drafts on the part.  I would still consider a cover because the top of the part will want to cool first.  The plan is to allow any stresses to relax at the same rate so no one area will pull at another area.

 

 

 

Edited April 30, 2021 by GregValiant

[helmut92 1]

Oh yeah i forgot to mention, that i use an Ultimaker 3. 

so these are the last few lines of the g-code. there is the command 140 in there twice, which one do i need to replace?

 

;TIME_ELAPSED:10207.757117
G1 F1500 E712.09729
M140 S0
M107
G91 ;Relative movement
G0 F15000 X8.0 Z0.5 E-4.5 ;Wiping+material retraction
G0 F10000 Z1.5 E4.5 ;Compensation for the retraction
G90 ;Disable relative movement
M82 ;absolute extrusion mode
M104 S0
;End of Gcode
;SETTING_3 {"extruder_quality": ["[general]\\nversion = 4\\nname = Ultimaker Tou
;SETTING_3 gh PLA fine 0,2\\ndefinition = ultimaker3\\n\\n[metadata]\\ntype = qu
;SETTING_3 ality_changes\\nsetting_version = 16\\nintent_category = default\\nqu
;SETTING_3 ality_type = draft\\nposition = 0\\n\\n[values]\\nbottom_layers = 4\\
;SETTING_3 ncool_min_layer_time = 20\\nfill_outline_gaps = True\\nfill_perimeter
;SETTING_3 _gaps = nowhere\\ninfill_line_width = 0.4\\ninfill_overlap = 10\\ninf
;SETTING_3 ill_pattern = gyroid\\ninfill_sparse_density = 10\\ninfill_sparse_thi
;SETTING_3 ckness = 0.2\\nironing_inset = =(0.3) + skin_line_width * (1.0 - iron
;SETTING_3 ing_flow / 100) / 2\\nironing_line_spacing = 0.15\\nline_width = 0.4\
;SETTING_3 \nmaterial_initial_print_temperature = 200\\nmaterial_print_temperatu
;SETTING_3 re = 224\\noptimize_wall_printing_order = True\\nouter_inset_first = 
;SETTING_3 True\\nretract_at_layer_change = True\\nretraction_count_max = 10\\nr
;SETTING_3 etraction_hop = 1\\nskirt_brim_minimal_length = 30\\nspeed_infill = 2
;SETTING_3 5\\nspeed_ironing = 12\\nspeed_layer_0 = 15\\nspeed_print = 70\\nspee
;SETTING_3 d_topbottom = 20\\nspeed_wall_0 = 15\\nspeed_wall_x = 20\\ntop_layers
;SETTING_3  = 4\\ntravel_avoid_supports = True\\nwall_line_count = 3\\nwall_line
;SETTING_3 _width_0 = 0.4\\nwall_line_width_x = 0.4\\nxy_offset_layer_0 = -0.15\
;SETTING_3 \nz_seam_type = back\\nz_seam_x = 0\\nz_seam_y = 0\\n\\n", "[general]
;SETTING_3 \\nversion = 4\\nname = Ultimaker Tough PLA fine 0,2\\ndefinition = u
;SETTING_3 ltimaker3\\n\\n[metadata]\\ntype = quality_changes\\nsetting_version 
;SETTING_3 = 16\\nintent_category = default\\nquality_type = draft\\nposition = 
;SETTING_3 1\\n\\n[values]\\nbrim_line_count = 5\\nskirt_brim_speed = 15\\nspeed
;SETTING_3 _support = 20\\nsupport_angle = 60\\nsupport_infill_rate = 30\\nsuppo
;SETTING_3 rt_infill_sparse_thickness = 0.24\\nsupport_offset = 0.2\\nsupport_xy
;SETTING_3 _distance = 0.4\\n\\n"], "global_quality": "[general]\\nversion = 4\\
;SETTING_3 nname = Ultimaker Tough PLA fine 0,2\\ndefinition = ultimaker3\\n\\n[
;SETTING_3 metadata]\\ntype = quality_changes\\nsetting_version = 16\\nintent_ca
;SETTING_3 tegory = default\\nquality_type = draft\\n\\n[values]\\nacceleration_
;SETTING_3 enabled = False\\nadhesion_extruder_nr = 1\\njerk_enabled = False\\nl
;SETTING_3 ayer_height = 0.2\\nlayer_height_0 = 0.2\\nprime_tower_enable = True\
;SETTING_3 \nprime_tower_position_x = 200\\nprime_tower_position_y = 180\\nsuppo
;SETTING_3 rt_enable = False\\nsupport_extruder_nr = 1\\nsupport_type = everywhe
;SETTING_3 re\\n\\n"}

 

Thanks for your help!

 

EDIT:

Oh forget it, its M140 and M104.🙈 

Edited May 3, 2021 by helmut92

[GregValiant 1,251]

I looks like the Ultimaker adds the line from within Cura (rather than as an ending Gcode script).

 

There are two ways to do it.  If you think you would use the cool-down script all the time you could put it at the end of your "End Gcode" script in the printer Machine Settings in Cura.  The M140 S0 line would still be there but the code will execute so fast in the printer that the bed won't have time to cool down before it hits the first M190 line.

 

If it's a one-shot deal then open the gcode file and insert the cool-down code between the "M104 S0" line and the ";End of Gcode" line and also comment out the "M140 S0" line with a semi-colon in front.  That will allow the print to complete, the hot end to turn off, and the bed will slowly cool over time.  M190 with the R parameter should be enabled in your firmware (I'm not an Ultimaker guy).

 

M140 S0  ; existing line that will turn off the bed.  If you edit the gcode file this would become a comment.

.... ;  some already existing end-of-print-code 

M104 S0  ;existing line that turns off the hot end

M190 R60  ; first new line that will turn the bed back on

G4 S3000

M190 R50

G4 S3000

M190 R40

G4 S3000

M190 R30

G4 S3000

M140 S0 ; turn the bed off - is the last line of your cool down code.

;End of gcode

You definitely want the hot end off so it doesn't ooze while the bed is cooling down.  I still think a cover would be a good idea.  Don't let your significant other know that you stole a pot lid for the printer.

 

[geert_2 557]

Maybe 15% infill isn't enough? For moulds, I use 25%, and to me that already feels like the minimum. After printing, my moulds are totally flat, but they are much smaller, about 10cm long.

 

Did you post-process the thing? I found that chemical smoothing with dichloromethane tends to make moulds warp slightly too. Especially since I only smooth the inside (=casting side), not the outside of the shell, so it is uneven. Probably the chemicals go deep into the material, and into the hollows of the infill, and keep working there. Acetone smoothing tends to make them crack after some time.

 

Also, I would be carefull with annealing: it might destroy your parts, or change their dimensions too much to be acceptable. I found that ruler-like parts shrink severely in length, but expand in height. A bit similar to a thin piece of plastic that you overheat above a fire or with a hot gun. Also, my test parts tended to warp severely. Some first warp upwards, and after a while change direction and start warping downwards.

 

If your parts do stick well to the glass, maybe try a slightly lower bed temp? Stay below glass transition temp, instead of at it or above it? And indeed, I would also recommend very slow cooling, as described above. That should never hurt. I did the tests in a controlled lab-oven, but you could also cover the model in the printer with a simple box, so it gets a smooth even temperature.

 

Fridge box for slow cooling or annealing on the printer:

 

Warped and shrunk severely after annealing test (PLA, up to 70°C or so, don't exactly remember):

 

Annealing tests: some parts warp upwards, some up first, then downwards later on:

 

 

 

[GregValiant 1,251]

@geert were your tests done before the part had cooled(?) or did you bring them back up after they had been to room temp?  Now I'm curious is there would be a difference.  I know PLA parts will flow in a hot car (so much for the wife's phone holder - it looked like something from a Salvador Dali painting).

[helmut92 1]

Hi, 

thanks for the code.

I took it directly and started a test print. Since the printed parts adhere quite well to the glass plate, I have lowered the print bed temperature to 45°. let's see if this works. If necessary, I still have Printafix there. 

 

I will print the form again over night. I will adjust the infill to 40%. The print should be ready tomorrow morning, shortly after I start working. Then I can directly put a microwave cover over the printed part, which I stole from the kitchen. 

 

I currently rework the parts only with some sandpaper, but not chemically. 

 

I tried the annealing, but after that my mold looked like on geert_2 second picture. 

 

I will keep you updated, thanks for your help.

[GregValiant 1,251]

"Then I can directly put a microwave cover over the printed part, which I stole from the kitchen."

Make sure your supervisor knows how cost conscious you are.  His/her acknowledgement will give you some comfort when your wife berates you for using that lid.

[helmut92 1]

😄 😄

 

i think the command M190 R60 does not work with the UM3. as soon as the print is "ready", the UM shows the error ER24. Can I somehow unlock the command?
The good thing is that the print bed temperature stays on and then I can theoretically turn it down manually. 

[GregValiant 1,251]

If it doesn't work then it isn't enabled in the firmware.  You can try it with an S instead of the R as M190 S50.  That will set the temp and then the dwell command should still take effect.  The R parameter would keep the buffer from reading a bunch of following commands but it may not be necessary if the Dwell works to keep commands from executing until the dwell ends.

[helmut92 1]

Unfortunately, this doesn't quite work either. Although there is no more error, the printer simply stops after the end of printing. The print head cools down, but remains about 5 mm above the print part. The print bed does not lower completely and remains at 45°C, but does not cool down after the specified time.

 

i post times the changed end of the gcode. maybe i took over something wrong.  

 

;TIME_ELAPSED:70029.768827
G1 F1500 E113.80183
;M140 S0
M107
G91 ;Relative movement
G0 F15000 X8.0 Z0.5 E-4.5 ;Wiping+material retraction
G0 F10000 Z1.5 E4.5 ;Compensation for the retraction
G90 ;Disable relative movement
M82 ;absolute extrusion mode
M104 S0
M190 S45  ; first new line that will turn the bed back on
G4 S4500
M190 S400
G4 S4500
M190 S35
G4 S4500
M190 S30
G4 S4500
M190 S25
G4 S4500
M140 S0 ; turn the bed off - is the last line of your cool down code.
;End of Gcode
;SETTING_3 {"extruder_quality": ["[general]\\nversion = 4\\nname = Ultimaker PLA
;SETTING_3  fine\\ndefinition = ultimaker3\\n\\n[metadata]\\nintent_category = d
;SETTING_3 efault\\nsetting_version = 16\\nposition = 0\\ntype = quality_changes
;SETTING_3 \\nquality_type = draft\\n\\n[values]\\nbottom_layers = 4\\ncool_min_
;SETTING_3 layer_time = 20\\nfill_outline_gaps = False\\nfill_perimeter_gaps = n
;SETTING_3 owhere\\ninfill_line_width = 0.4\\ninfill_overlap = 10\\ninfill_patte
;SETTING_3 rn = gyroid\\ninfill_sparse_density = 40\\ninfill_sparse_thickness = 
;SETTING_3 0.2\\nironing_enabled = False\\nironing_flow = 5\\nironing_inset = 0.
;SETTING_3 3\\nironing_line_spacing = 0.2\\nline_width = 0.4\\nmaterial_flow = 1
;SETTING_3 02\\nmaterial_initial_print_temperature = 200\\nmaterial_print_temper
;SETTING_3 ature = 205\\noptimize_wall_printing_order = True\\nouter_inset_first
;SETTING_3  = True\\nretraction_count_max = 10\\nretraction_hop = 1\\nskirt_brim
;SETTING_3 _minimal_length = 30\\nspeed_infill = 15\\nspeed_ironing = 13\\nspeed
;SETTING_3 _layer_0 = 15\\nspeed_print = 15\\nspeed_topbottom = 15\\nspeed_wall_
;SETTING_3 0 = 15\\nspeed_wall_x = 15\\ntop_layers = 5\\ntravel_avoid_supports =
;SETTING_3  True\\nwall_line_count = 3\\nwall_line_width_x = 0.4\\nxy_offset_lay
;SETTING_3 er_0 = -0.1\\nz_seam_type = back\\nz_seam_x = 0\\nz_seam_y = 0\\n\\n"
;SETTING_3 , "[general]\\nversion = 4\\nname = Ultimaker PLA fine\\ndefinition =
;SETTING_3  ultimaker3\\n\\n[metadata]\\nintent_category = default\\nsetting_ver
;SETTING_3 sion = 16\\nposition = 1\\ntype = quality_changes\\nquality_type = dr
;SETTING_3 aft\\n\\n[values]\\nbrim_line_count = 5\\nspeed_support = 15\\nsuppor
;SETTING_3 t_angle = 40\\nsupport_infill_rate = 30\\nsupport_offset = 1\\nsuppor
;SETTING_3 t_xy_distance = 0.6\\n\\n"], "global_quality": "[general]\\nversion =
;SETTING_3  4\\nname = Ultimaker PLA fine\\ndefinition = ultimaker3\\n\\n[metada
;SETTING_3 ta]\\nintent_category = default\\nsetting_version = 16\\ntype = quali
;SETTING_3 ty_changes\\nquality_type = draft\\n\\n[values]\\nacceleration_enable
;SETTING_3 d = False\\nadhesion_extruder_nr = 1\\ninfill_extruder_nr = 0\\njerk_
;SETTING_3 enabled = False\\nlayer_height = 0.2\\nlayer_height_0 = 0.2\\nmateria
;SETTING_3 l_bed_temperature = 45\\nprime_tower_enable = True\\nprime_tower_posi
;SETTING_3 tion_x = 110\\nprime_tower_position_y = 190\\nsupport_enable = True\\
;SETTING_3 nsupport_extruder_nr = 1\\nsupport_type = buildplate\\n\\n"}

 

Edit: what is also strange is that I can not cancel the print in the state. I have to turn the printer off and on again to do anything. 

Edited May 6, 2021 by helmut92

[helmut92 1]

I think I have found my mistake. 
M4 S4500 means that the program waits 4500 seconds until it continues, is that right? that would be 75 minutes, I did not want to wait that long 😄
I should have rather taken 10 minutes, so S6000, per step. 

But why I can not cancel the print, I still do not understand.

[GregValiant 1,251]

The G4 command is "Dwell" and yes, "S" is in seconds.

When the printer is in "Dwell" mode it won't accept any other commands.

M0/M1 can be interrupted with a button click, but there is no timer and consequently the temperature would not continue to drop until a button click.  It would simply sit on the last temp it was told.

[helmut92 1]

Well, it worked.

 

40% infill, 45 degree bed temp, and letting the bed cool slowly seems to help.  

 

Now there is very little warpage. I may try putting a lid over the print next time it's done. The only thing I need to figure out for this is why the z axis isn't moving down. i've been reading a bit about gcode commands. Maybe i'll try manually setting a g28 or a g0/g1 command in gcode and lower the z-axis. 

 

Thanks again for your help. 

[GregValiant 1,251]

A G0/G1 could be done as a final move in the Gcode file before the cooling routine.  The G28 is not a good idea as it would raise the Build Plate and occasionally a part might be in the way.  

G0 X0 Yqqq Zqqq   ;change the qqq's to what's appropriate for your printer.  Your Max Y and Max Z would work.

 

If you were to put a move into your End Gcode it would always show up in gcode files, but you could use Cura keywords.

G0 X0 Y{machine_depth} Z{machine_height} which for my printer is entered into the gcode as Y230 Z250.

[geert_2 557]

On 5/3/2021 at 9:16 PM, GregValiant said:

@geert were your tests done before the part had cooled(?) or did you bring them back up after they had been to room temp?  Now I'm curious is there would be a difference.  I know PLA parts will flow in a hot car (so much for the wife's phone holder - it looked like something from a Salvador Dali painting).

 

They were cooled, required to get them off the glass, and then put in my electronic lab oven and warmed-up again. Actually it is an incubator with range up to 99°C, very well controlled, but I only use it for this sort of 3D-printing stuff now.

 

Maybe there is a difference if you would put a box on top of the part, directly in the printer immediately after completion, so it would not go through that extra cycle? I don't know, never thought of it. The photo with the fridge box above was just a quick one-time experiment.

 

And yes, I also had lots of PLA-parts warping in the car, even in a mild spring or autumn sun, here in "rainland" Belgium. We are not yet talking about summer or equatorial deserts.  :-)  Even forgetting them in the trunk for a few hours can destroy them. And I had them warping in both directions too, first upwards and then after a few days downwards, as in the photos. Very weird. Now I print parts for the car in PET or NGEN: I haven't had issues since then.

 

Annealing PLA parts with less critical dimensions (since the annealing itself changes dimensions) for later use in the car, did not work: they kept deforming and failing anyway in the car: hooks and clamps would lose their tension and bend. So, my suggestion is to go for a higher temp material from the beginning, and not waste time annealing.

[GregValiant 1,251]

Hi @geert.  I switched it to PETG and it's been fine.  It does have hooks that go into the dash vents and yes, that was the main failure point.  It's here in sunny Florida where it will be 90F° again today.

 

Thinking more on the topic of annealing (which we used to call "normalizing")...

3d printing involves so many disciplines it's amazing.  Mechanical engineering, electrical engineering, thermodynamics, computer engineering, software design, material science, geometry, trigonometry, physics, (I'm sure there are more) and a firm users knowledge of a few different pieces of complicated software.  They all come together in a little rectangle measured as LineWidth x LayerHeight which in a lot of cases is just .08mm².  There sure is a lot going on in that little area.

 

I have an aluminum heating plate, a glass plate that floats on it (it's edge located so no clips), and a plastic part that may be made from a few different materials and that is bonded to the glass plate (at least for a while) and each has it's own coefficient of expansion.  Once the aluminum and glass are up to temperature (admittedly not very high for those materials) the plastic gets put down at 210° to 240°, sometimes with a fan running across it and sometimes without.  So it goes through a quick freeze.  The bottom layers are at the build plate temp and as the model grows, the point source of 210-240 travels around but the build plate temp doesn't get through the plastic very well (poor thermal conductivity) and the part is cooler at higher layers.  So where is the stress and why does it build up?  Is it a function of part geometry as different mass areas (10% infill vs @helmut92's 40% infill) have local areas of thermal inertia?  Is it affected by height off the build plate?  Do large horizontal holes affect it?  "Maybe", "Could be", "Possibly" and "I don't know" are all good answers.

 

I tell ya, Everything affects Everything and 3d printing involves almost everything.

[geert_2 557]

Also, a big hot bed causes a lot of upwards airflow, cooling the sides of the model differently. And the nozzle-coolers also cool very unevenly, where they happen to be.

 

If prints are removed from the bed too early, before being cold, I could imagine that they would also be more prone to warping. It seems that molecular structure of PLA also keeps changing for some time after printing, becoming more and more crystalline. It becomes more brittle, but I don't know if this changes stresses and dimensions? I always let parts cool in the printer on the bed slowly, before attempting to remove them. I never remove the bed from the printer, I just pick up the parts as soon as the bed is at room temperature.

 

You can make stresses visible in transparent plastics and glues. I did that long ago in cast epoxies. But I have never tried it in 3D-prints; and I don't think it is easily possible due to the "sausages" and layers.

 

The setup for making stresses visible: light-source - polarising filter - transparent object under test - polarising filter - camera. Rotate the second filter for best effects.

 

Block of plexiglass with a tiny steel ball, under high load:

 

Stresses around air bubbles in a cast epoxy (fully transparant and colorless parts, the blue is from the polarising filters):

 

Stresses in dental applyances, especially around the steel wires:

 

The colored stress lines are like height-lines on a map: when closer together, the gradient is steeper, thus higher stresses. Once you can see the stresses, you can guestimate if they are a factor - or could be - in deformations, cracks or other failures.