Tuesday, April 07, 2009
PP Printing Pt.2
The photos show the complete set of parts printed in PP, the ones on the left I showed in my last note the ones on the right are the last ones off the machine.
Gradual changes were made to the settings going from left to right.
The first two prints were done at 235 and 220DegC, a slight improvement was seen in the reduction in temperature, further reduction did help a little but it made the material hard to extrude, the minimum pratical temperature being around 208-210DegC, layer adhesion was poor at this temperature so this was taken as the raft interface temperature.
I commented last time on the elasticity of the material, it pulls back from the edges on infill given the least opportunity. Note the effect either side of the hole on the top face of the foot. I thought that a reduction in speed would give the filament time to relax a little. The third reasonable looking foot was printed at 8mm/sec the best parts on the right printed at 6mm/sec. (220DegC with a little fan cooling)
The parts are incredibly tough and reasonably accurate. Across the width the cross brace is +0.05mm, in Z its +0.7mm, the holes are -0.5 to -0.2mm.
Where did you get the PP filement? Is it the same as for ABS/HDPE? (ie. 3mm diameter rod)
Thanks for the comments, the parts are not in the same class as prints done with PLA or ABS but they are usable. There is scope for much further development on this material, I have only scratched the surface. Speeds temperatures and cooling strategies all need to be fully explored before I can say that my settings are somewhere near the optimum.
The filament was provided by Ian from BfB, it is in the regular 3mm stock same as ABS/HDPE
I know he has this in stock so if you want to give it a go you can contact him.
(I think the new stock Ian has is beige not black but it is the same stuff.)
Could you upload the little feet (if that's what they are) to thingiverse.com? Or mail me the STL ( reprap at erikdebruijn.nl ) and I'll do it and attribute you for it.
Thanks again for your kind words.
I think PP and PCL have been the worst for warping. ABS not so bad and PLA seems to show very little at all.
PP is very elastic as it is printed, if printed quickly, and it sticks, then the object builds with a lot of built in stress. One or two of the first prints warped so much they were able to distort the base material I had stuck down with heavy duty double sided tape.
The only way I have found to control the amount of warping is by printing at a slightly higher temperature and running very slowly. The hypothesis being that this will keep the molten filament soft long enough for the long polymer chains to relax. It does not cure the problem but it seems to greatly reduce the effect. A possible alternative may be the print in a bag solution where it may well be possible to run faster with the object held at a high enough temperature for the stress relief to occur.
Getting the heat into the plastic is one side of the equation I think how you get the heat back out is equally important. The best objects in the photos benefited from some cooling.
In this case quality and speed were improved with carefully applied cooling. I am not talking about a 90mm fan pointing directly at the nozzle at short range, this will almost certainly freeze the material in the nozzle. The cooling of most benefit seems to be very light and indirect. When experimenting with this I mount the fan on the side of the machine, maybe 2-300mm away from the print area, often the fan is pointing down at the table rather than at the object. The result is a very light waft of cool air over the object. The benefit of this light cooling is that you can run elevated temperatures without the object turning into a molten mess. I am guessing that running higher temperatures at slower speeds does the stress relief while the light cooling controls the heat build up in the object.
I may have the theory completely wrong but the set-up seems to work.
PP and PCL are the two materials that seem to benefit most from cooling, the almost waxy nature of these materials seems to hold on to the heat. If you don't deal with the heat build up during the print it will be seen in the print quality.
ABS also responds to light cooling especially where slender features would otherwise cause the object to sag.
I have only run quick test on HDPE. This seems to have similar properties to PP when printing I guess this would respond well to slow running and a light cooling strategy. Any feedback would be appreciated.
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