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Well, it's finally time to share what we've learned about printing with Polycarbonate. As we recently announced, pre-orders for Polycarbonate in both 3mm and 1.75mm diameters are available. It took us awhile to get the details sorted out, but we're all set for a ship date of January 30, 2012. There's a whole world of materials out there for that hungry printer on your desk, and we plan to dish up a feast.
We tracked down a number of material samples from our supplier and a little gem called Polycarbonate (PC) caught our eye. Having seen the success of Richrap printing with Polycarbonate we were anxious to work with it. Polycarbonate (wiki) is a strong thermoplastic with high optical clarity and (relatively) high melting temperature. Unlike PLA with a fast transition temperature, PC slowly softens when heated allowing successful (though slow) extrusion at lower than processing temperatures. This is useful when switching from a plastic with a lower extrusion temperature as you can slowly start pushing PC through at the temperature of your previous plastic until you clear the hotend. It is important to purge ALL of the previous plastic before raising the printing temperature as ABS puts off some dreadfully nasty fumes at 260C.
The sample we received was extruded to 1/8" diameter and we had let it sit out in open air for a good while before getting to it. Initial purging at 260C (Modified Makergear Stepstruder) showed extrudate that was bubbly and white; a big red flag that this plastic needed to be dried. 10 hours at 160F in an old food dehydrator showed filament that was noticeably clearer and extruded a smooth clear thread from the nozzle. Setting extruder to 260C and the Polyimide Tape covered heated bed to 120C we repurposed an ABS printing profile for PC and started printing; once flow-rate was dialed in we tried printing our Plastic T-Slot. It was by far the strongest beam we had printed and clear enough that looking straight through it you could make out objects on the other side.
It's worth noting that adjusting temperature is similar to PLA, printing at higher flow-rates will require higher extruder temperatures for a consistent melt. An indication the flow-rate is to high or temperature to low is stripping or skipping at the filament driver. Those with Bowden style extruders will need to watch for signs of excessive force where the Bowden tube meets the filament driver and hotend. For the Ultimaker I'm using this thing to keep everything secure. If you print PC near the high end of your firmwares temperature limit, PID fluctuations can send it hot enough to force a shutdown of the hotend; temperatures drop, nozzles clog, filaments strip, things get ugly. Also, for hotends that use PTFE (teflon) insulators there is the concern of dangerous fumes when temperatures approach 300C (see Polymer Fume Fever for example.) Care should be taken to avoid inhalation of dangerous fumes or, better yet, to avoid creating them.
Larger prints were prone to peeling off the print-bed if they contained too many long aligned traces; examining the datasheet revealed that this PC had a mold release additive, great for injection molding, not so great for us (the PC available for pre-order does NOT have this additive and should stick easier to print beds). Small objects printed fine with no warping but we needed to find a way to keep large prints held down; enter ABS Glue. Painting a thin coat of that on the bed before printing completely eliminated peeling and warping, we could even print without the heated bed and maybe see only the smallest of curling on the corners of large prints.
To test the effect that leaving the PC out in open air was having we split up the sample; one went in the dehydrator, another into one lucky fellow's home for a couple days. Printing with them revealed obvious difference. The dried sample printing clear and smooth without hiccups, the sample that had gone through a few days of home living printed white and would occasionally pop and bubble. Comparing prints side by side shows an obvious reduction in clarity and surface quality for the undried filament. While we haven't done any numerical testing of compared strength, the moisture laden sample felt more brittle and prints made from it break much easier. Objects printed with the dried PC are clear and strong. Returning to the T-Slot it is clear to see the differences between dry filament and filament left where humidity is not controlled.
Polycarbonate left out for a few days has clear bubbles and voids embedded in the threads. In the photo showing the full length of the beam it is possible to see the onset of saturated filament as dry filament already present in the hotend empties. Worse, is the occasional sputtering and popping from the nozzle that occurs when moisture boils out. With dry filament however it is possible to print some very clear traces.
All in all, a very simple material to start printing with. As long as it is kept relatively free of moisture and/or dried, printed objects turn out looking good, are well bonded and very strong. This is a plastic that can take a bit more of a beating and stand a little more heat, not bad if you need something close to you're hotend such as a cooling duct. Printing parameters we're using so far are:
- Extruder - Makergear Plastruder (modified directing heat closer to nozzle and further away from insulator)
- Extrusion Temperature - 260C (success at low and high flow rates)
- Bed - Heated Polyimide Tape (aka Kapton) bed at 120C OR unheated bed with ABS Glue brushed down before hand
- Stock Extruder
- Extrusion Temperature - 270C (evaluating how to safely go hotter for better inter-layer adhesion)
- Bed - Unheated BlueTape or Polyimide Tape (recommended for keeping parts flat) bed with ABS Glue brushed down before hand
- Add-on Ultimate BowdenFeeder Repair Kit to keep Bowden assembly secure