Idea for dealing with HDPE warping
April 09, 2008 06:11PM
Okay well I would love to test this myself but it will be a bit before I can even get started on my own Darwin. So I figured I might as well post the idea here so that it could be tested now instead of a year from now. Alright enough of my excuses and on the the good part.

The biggest/only? problem from what I have seen and read is that the HDPE shrinks to much from layer to layer. This is cause the stresses to increase as the layers increase, and eventually warp the object. So why not try and compensate for this shrinking by making the next layer slightly "larger". So in order to make a "perfect" and square rectangle you print something that is more like a trapezoid. The picture I attached is an exaggeration of what I am thinking but that is because the angles that are probably require might be less than 1 degree. So there you have it an idea that even if it does work might be to hard to implement
open | download - Trapazoid.jpg (60.6 KB)
Re: Idea for dealing with HDPE warping
April 09, 2008 06:38PM
Making the next layer bigger than the one below will not reduce the stress pulling inwards that it exerts on the layer below when it shrinks. That stress causes the corners to curl upwards and the sides inwards. You would compensate for the sides coming in but not help with the base curling upwards.

Re: Idea for dealing with HDPE warping
April 09, 2008 07:58PM
OH dam that is a good point. I forgot about the interior material messing with the structure. If any thing this might just make the internal stress increase.
I have worked on a 3d wax plastic printing machine used to build 3d,
After each layer of buildup the surface is planed (milled) to get it flat for the next layer.
milling each layers is ofcourse the perfect solution, but without the milling toolhead one must find alternative solution. wouldnt the shrinking lessen considerably if the printing enviroment is taken to near melting point of the material. that way the entire object will cool down later equally. i hear that soulution is used in commercial solutions. one would have to build a closed enviroment and put a hairdrier in it for example to achive this
Re: Idea for dealing with HDPE warping
April 10, 2008 08:04AM
Milling can increase the accuracy of the outline and the top surface but it does not help with warping of the base, or the warping that occurs after the object has been removed from the table.

Wax is not far from room temp when it becomes hard so it will give low warping like PLA and PCL do for the same reason.

Yes extruding in an oven will unadoubtably reduce warping but you have to make all the head parts high temperature which prevents self replication.

I think putting the object in an oven after it has been extruded but while still attached to the base will help a lot and is much easier to do.

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