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kris

Managed to overcome warping

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Hi everyone,

I have been struggling with warping over large and thin ABS structures for some time. I did try out many possible countermeasures that I found on the internet or that I came up with by myself. But nothing really worked. Although I managed to reduce the effect somewhat, I started to loose hope that the problem can be totally overcome.

But yesterday I managed to make a first print that is totally warp- free.

Here are my findings:

The main problem of warping is the non uniform cooling of a part that will result in internal stresses and thus deformation. I am using the UM2 with a heated bed. I found that warping will reduce with increased bed temperature, but 100°C is a maximum for the bed. A brim will help to stick the component to the bed, but will not do anything against the cause of warping. At some point even a brim will fail and stress concentrations at corners will make them peel of.

With increasing height of the component temperature will decrease and stresses will arise.

So I covered the top of my UM2 will a simple cardboard box with a cut out for the filament hose. I also covered the front with cardboard. Increased the temperature of the bed to 100°C and turned of the two cooling fans in Cura. I also used Cura 14.03 TEST2. That didn't help initially, I just found that the gcode size reduced by 50% in size compared to 14.03. I was a bit worried that the temperature could be too much for the internals of UM2, but the bottom section keeps pretty cool. After the print I am letting it cool down for a while. For the adhesion to the glass plate I am using the glue stick supplied with UM2.

I think key is the uniform temperature (low gradient) inside the build volume.

The structure I printed is a 0.8mm thick shell and minimum 40mm high and about 200x30mm at the base. I used the black ABS from Ultimaker.

Anyway, the result: No warping at all.

I am now planning on building a plexiglas door and roof to better control the internal temperature. I think I will also install a few temperature sensors for monitoring.

I addition I reduced material flow to 86%, there was a little overextrusion. Now with 0.1mm layer height I can hardly make out the layers.

Regards,

Kris

 

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I have greate succes with more or less the opposite approach.

I brush on a decent layer of ABS slurry, let it dry and then print first layer with standard ABS settings for filament and bed.

After first layer I turn of the bed heating and drop temperature to 235deg.

No Fans at all.

I usually don't print any parts larger than 10x10x10 cm so maybe that my solution don't work with really large pieces.

Nice to know about an alternative solution if that would be the case.

 

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Thanks for sharing!

Very interesting information here.

@Kris: How is your print quality? Did you print something with overhangs, bridges, gaps...? I imagine that you may get a lot of stringing, but I noticed that ABS behaves quite differently than PLA. Printing PLA without the fan usually yields very bad results...

 

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Hi all,

 

@ Wallan: Maybe with your approach you basically achieve the same effect: You control the temperature to get an even temp distribution by simply turning off the heated bed.

I did read about the ABS 'slurry' but was hoping to find a way to set may process parameters to get the print under control.

 

@Jonny: I hope I understand stringing correctly, but I think I had that from the start. But by reducing the material flow (tried 91%-86%) I managed to completely get rid of that. Attaching an image, hope it is visible. The image shows the printed surface.

2014 04 10 21.10.56

 

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1) Are you printing an airplane?

2) A heated chamber helps immensely of course. the upper cooling layers are pulling inward which lifts the lower layers. If you graph density of ABS versus temperature it is pretty linear from 0C to 220C but the important section is once it cools to glass temperature (around 100C) down to air temperature (typically 20C but in your case hotter). The smaller the temperature range the less shrinking while printing.

3) The glue stick is great for PLA but for ABS it is simple to mix some ABS with some acetone to make the "ABS glue". This is *much* better for ABS.

 

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I wasn't able to print ABS in any combination of settings that I tried until I started blocking off the front of the printer and letting it heat up for at least 30 minutes before printing. I use hairspray over ABS goo because it seems to be less messy. I spray it on a cloth and then wipe the glass surface with it. But overall, when printing ABS I definitely have to eliminate as much of the outside air as possible. I would love to have a true heated build chamber.

 

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