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Foam extrusion

Posted by jason.fisher 
Foam extrusion
November 14, 2011 01:37PM
It seems that extruding a plastic foam could be a useful way to fill objects more quickly, using less material. Extrude the walls normally and fill with a PLA foam.

Depending of the properties/mixture of the foam, you could conceivably fill an object that was larger than your build area. Print snap-together wall pieces, construct and fill through a hole in the top of the object. Sort of like a sealant..

The foam should have reasonable insulation capabilities also. My dream application would be two tall hexapod bots with a hanging delta arm. One bot would walk the perimeter of a foundation and extrude hollow walls, the other bot would follow and fill with a plastic foam.

I see a design that uses two high-temp (260 C) silicone hoses, one feeding the starch (+water or glycerin) mixture and the other feeding plastic. I believe that we will only need 100-140 C and the appropriate mechanical action to achieve the reaction we are looking for. Perhaps a brass tube that has a drill bit inside.. use a metal pinion/set screw adapter like we use to connect the Z axis motors to threaded rods -- a few of these will allow different bolts and bit sizes inside the tube to be connected, allowing flow characteristics to be adjusted.



Edited 1 time(s). Last edit at 11/14/2011 01:38PM by jason.fisher.
Re: Foam extrusion
November 16, 2011 10:40PM
It would seem to me that controlling your fill volume would be quite difficult, as the amount that the foam expanded would undoubtedly be temperature dependent. I would also expect that any foam which happened to make its way onto the top of an extruded layer would affect layer adhesion.
Re: Foam extrusion
November 17, 2011 07:19PM
I am thinking of a PLA cap off of the walls to form a ceiling. Designs would certainly need to take a new set of structural problems into account..

If we could see 5% below the fill line, we might be able to gradually dial the water/starch mixture out and raise the temperature until we are just shy of the top. I have no idea if it would work, of course. Ideally let the 90-95% fill set a bit to keep the heavier layers above from collapsing down.

For fill detection..

The least expensive would be a whisker of sorts. Think of a thin hard wire hanging through the center of a washer--the washer would complete the circuit when the wire was disturbed by the foam as it filled. You would calibrate the length of the wire for your machine and attach it to the head. Attach a small plastic bead to the foot of the wire..

That's the simplest design I can think of.. I would like to avoid complex software. I am a developer by day and find it sometimes tiresome to write (debug) more code at night.

But a CMOS/photo sensor and a fixed LED light source would allow you to compare pixels before/after. Edge detection to find the boundaries of the container and then watch the color of the inside edge. However, you would still need a way to dynamically locate Z.. mount the camera at an angle and count the pixels between a marker on the head and the color of the bed/material. You are looking to measure the 'nothing' space in the distance. If the LED angle relative to the camera were fixed, you might measure/detect shadows or volumes. If you have a laser point light, you might measure the size of the point to determine distance.. a photo senor brings many potential advantages (and complexities)..

Of course, nothing is worthy of being called a solution until it works in practice.. I will play around with this whisker thing and an LED light though. winking smiley
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