RepRap: Blog

I've been printing little green targets from PLA and white(ish) ones from IMPLA. The IMPLA needs an extra 10C heating, layers thinner than 0.4 and inter-layer cooling. In other words it is no fun to print with.

So, frustrated I took the whole lot outside, lined them up against the wall:




and shot them:



You can see in the aftermath, both green PLA targets have chunks missing from them. One white IMPLA target is split but holding together. The 3 BBs embedded in the wood on the left show the level of impact.




Useful stuff, but I'm not sure if it's worth offering for sale as it is so tricky to print with.

Vik :v)

Labels: filament, impact, modified, pla, plastic, reprap

One of the problems with PLA is that it shatters when stressed, rather than bending gracefully. This problem is solved in ABS by adding impact modifiers - basically synthetic rubber blends - to give some flexibility under stress. Luckily, I found an impact modifier that is compatible with PLA and does not significantly alter the melting point. At about 1/3 it makes PLA this flexible without fracturing:

I've got to run a few more printing tests on it, but it's looking promising as a material that offers the durability of ABS with the reduced environmental footprint and ease of extrusion of PLA. Oh, I suppose I'd better figure out what it'll cost me too :)

Update: I flexed some back & forth 100+ times and got bored trying to break it.

Printing with it is much trickier than plain PLA. It wants to coalesce into one lump, and you really need cooling between layers.

Vik :v)

Labels: ABS, filament, impact, modifier, pla, plastic

For those interested, here's what can happen when you use 10mm PTFE rod for your extruder insulator with plastics that melt at a higher temperature than the original CAPA. This image shows a 3mm PLA filament extracted after a jam - the PTFE insulator is now useless. The ridges on the right are from where the thread of the screw drive forces the filament in. You can see that it fades out towards the centre indicating that at this point in the PTFE, the filament is just becoming plastic enough to conform to the walls. Only the cloudy last 6mm of the rod on the left were in the heater barrel itself, and they are only cloudy because I stress-fractured the rod at that point to get it out.


You can clearly see that a significant bulge is forming in the PTFE shortly before this, expanding the filament to nearly 4mm diameter. The PLA has very little plasticity at this point and so effectively plugs itself into any developing bulge and forces it open wider. This is why the PTFE barrel is now scrap, and may explain why some users are finding that their extruder has inexplicably developed a tendency to jam solid. This extruder had always been operated with a tight hose-clamp over the join between the PTFE insulator and the heater barrel proper.

I'm reaming out the extruder clamp/base to 16mm to take the recommended, stouter PTFE insulator that I machined up on the old new lathe (or is that new old lathe) at the Wellington MakerSpace last week. The insulator's in the suitcase somewhere...

Vik :v)

Labels: bulge, filament, pla, PTFE

Back at the start of the year, plastics suppliers Claraint were kind enough to donate 10kg of polylactic acid (PLA) granules to the RepRap Project. Alan from Imagin Plastics - a welding rod and extrusion specialist in Henderson, New Zealand - then ran these granules through an extruder to produce 800m of 3mm diameter filament which I picked up on Friday. It was dried overnight at 60C and then extruded using a 180C die and 170C feed. Here's there wondrous extrusion machine:




And here's the batch of filament I picked up. It's actually quite transparent.




By running an unmodified Mk2 extruder at 155C and increasing the pressure on the filament - it's much harder than CAPA - I managed to run it well enough to produce this shotglass:




This material definitiely has some artistic possibilities.

Further experimentation is needed, but it does look like it will be possible to make watertight containers with a reasonable degree of strength from PLA in a Darwin. A straight-through extruder would probably have an easier time feeding filament, as the stuff is rather stiff.

Vik :v)

Labels: clariant, extrusion, filament, henderson, imagin plastics, pla, polylactic acid, reprap, zaphod