PLA

This is a page to document experiments and settings for PLA: Poly Lactic Acid
Many details mined/trimmed from responses on http://groups.google.com/group/makerbot. (mifga)

NB: there are many different varieties of PLA! If you add notes to this page, please be sure to indicate to the best of your knowledge what sort of PLA you're using.

Differences Between PLA and ABS

  • PLA is a solid; ABS is a gelled liquid (Spacexula)
    • When you heat ABS it slowly transitions from a gel to a liquid: does not go through a state change.
    • PLA on the other hand is like frozen water, moving straight from solid to liquid in one step (extremely energy intensive)
    • ABS (not requiring a phase change) becomes more liquid further it travels down the barrel.
    • Because there is no phase change, ABS doesn't suck heat energy out of the nozzle as aggressively.
    • With PLA, the risk of the phase change cooling the nozzle allows greater risk of clogging.

Different Approaches: describe your process for printing with PLA here.

  • Todd Fleming's approach for MakerBot 238
    • Procedure
      1. Set the temp to 240. I have a 1mm thermistor and am using the 3mm calibration table. Your setting will be different if you have a different thermistor size or a different calibration table.
      2. Wait 10 minutes.
      3. Run the motor forward. Speed = 255.
      4. Stop the motor, clean up the mess, center the extruder, and print.
    • Notes
      • An M6 nut on your heater assembly is a must! PLA is very hard on the extruder.
      • A metal insulator retainer is a must. PLA will cause the original acrylic one to shatter.
      • All my Skeinforge temp settings are at 240.
      • I print without a raft.
      • I gave up printing on bare acrylic because it bonded too well. I now print on double-sided tape.
      • I don't let the extruder cool between prints. Even if it takes me a half-hour to prepare for the next print (rotate, Skeinforge, grab a snack, write to SD card), I keep the temp at 240. A lot of PLA drips out during this period, so I run the motor forward again to get PLA back down to the nozzle before starting the next print.
  • Coasterman's approach for Sparky, makerbot 1674:
    • Run at 200C. Print on blue 3M painter's tape. MK5 is an excellent extruder since it is teflon all the way to the hot nozzle, which means no more plugging. I use MakerGear 4043D PLA, but I'm sure the MakerBot stuff should work similarly.
    • Never print with a raft, just use the blue tape.
    • The automated build platform will shine if you put blue tape on it and turn the heat way down. In fact, you probably don't even need the heat. Just unplug the heater.
    • Overall, here is your PLA procedure:
      1. Slap blue tape on the acrylic surface.
      2. Crank up the temp to 230C or about 5-10 degrees above normal ABS temp.
      3. Remove the ABS and insert PLA.
      4. Run the extruder at the high temp until the extrusion stops kicking and becomes pure PLA.
      5. Turn the temp down to 200, extrude, and now you're set for printing like you print ABS. After the material change procedure, you can print PLA like it's ABS, only that you use a PLA profile with a lower temp.
      6. You should just idle the extruder at 200 between prints, maybe take out the M104 S0 command from the end.txt or end.gcode file.
      7. Next printing session, do NOT repeat this procedure. Just fire it up and print. No special procedures, just put blue tape on the platform, and if the blue tape gets ripped up, replace it.

Steinbex's approach for Cupcake with mk6+ (Ultimachine 4043D PLA)
After testing both of the above methods, repeatedly ran into the problem that heat traveled up the barrel too far, and made the pla too soft where it enters the PEEK section. This happens fairly quick with no air motion in the bot, at 220C unless it's running continuously at a fairly quick flow rate. At 185 it takes longer, but will still jam up, reversal and stopping makes this significantly worse. To fix this I simply added an 80mm case fan pointed towards the extruder, and retuned the PID settings for the heater as the cooling rate has significantly increased and heating has decreased. With the fan added, it has completely fixed any blocking issues even if run at higher temperatures.
PLA Procedure:

  • Just run the fan directly off the power supply and pointed towards the extruder barrel, not the part.
  • Apply blue painters tape to build platform.
  • I run the extruder with a set point of 200C it worked at 185 before the fan but afterwards the nozzle ran significantly cooler so it had to run higher.
  • Run normally, don't worry about leaving the extruder on between prints.

Other Observations:

  • Todd Fleming's observations
    • The nozzle tends to clog at the temperature people have traditionally recommended for PLA. This causes many forms of damage.
    • Running the extruder at a temperature high enough to prevent the nozzle from clogging causes the melt to run up the barrel. This puts stress on the motor, on the insulator retainer, on the insulator, and on other parts, but this stress is nothing compared to the stress of a clogged nozzle.
    • PLA bonds to acrylic like crazy.
  • Coasterman's observations
    • PLA and blue tape are like butter and bread. They just belong together.
    • Running the extruder below 200 may have bad long-term effects on the motor, and my MK4's extrusion rate has slowly decreased due to running at 185. It may just be that I fed in dirty white plastic and got crap all over the nozzle interior.
    • There is definitely less friction against the delrin for the pla.
    • A small, 30mmish, fan might work better because it could be directed under the support, and only at the heater barrel(NEEDS VERIFICATION)

Disasters:

  • Todd Fleming's disasters
    • All of the following happened to MakerBot 238 while printing with PLA. The approach I have above seems to mitigate all of this.
      • Acrylic insulator retainer shattered. Fix: use a large metal washer.
      • 3 PTFE insulators ruined:
        • Threads stripped (1 insulator)
          • Fix part 1: use an M6 nut
          • Fix part 2: run at a higher temp
        • Bulged (2 insulators)
          • Fix: run at a higher temp
      • Motor gear train wore out
          • This had to be replaced
          • Fix: run at a higher temp

PLA 4042D and PLA 4043D

4042D Datasheet.
4043D Datasheet.

  • Melting point spec is 210C +/-8C

I'm running all my experiments with a Mk. V extruder head w/thermocouple for better temperature data.

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