Heat-Treating

[last updated: 2022-11-08]
3d printing home page

https://all3dp.com/2/annealing-pla-prints-for-strength-easy-ways/
https://www.researchgate.net/publication/355616113_Heat_treatment_of_3D_...
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• Quick take:
  Heat up the printed parts to at, or slightly above, their glass transition temperature (but for sure below their melting point), then let them cool slowly.
  For PETG suggested temp is 80C.

• Benefits:
  Increases a printed part's strength, durability, and resistance to deformation under high heat.
• What happens:
• There is some difference of opinion about what this procedure does on a microscopic, material science level. On the web it is often called "annealing," and likened to annealing of metal. However the analogy is loose, and what we might do with our plastic parts is apparently not annealing in the strict sense of that word.
• I've seen two explanations of the mechanism of the effects:
  • that the procedure relieves the stresses that are created in the models by the printing process, most notably inter-layer stresses. Relieving these stresses increases the model's stiffness, strength and overall resistance to breaking.
    IMO this is the most plausible explanation.
  • -or- that the procedure affects the crystallization of the polymer, supposedly increasing the crystal sizes, also thereby increasing strength.
    While this is the standard description of annealing in metal, IMO this is likely totally wrong for plastics, since my understanding is that polymer doesn't have crystals like metal does, though it does have variable lengths of molecular chains, though I'm skeptical that heating can affect that.
• Regardless what you call it or how it works, there's no question that it does work. It increases a part's strength, durability, and resistance to deformation under high heat.
• For PLA, according to an (link to:) article in rigid.ink, you might get 40% increase in strength and durability, and 25% better stiffness, as well as better heat resistance.
• As a result of relieving printing-induced stresses,
  dimensions along the X and Y axes will get smaller (about 5% for PLA),
  and the Z dimensions will get larger (about 2% for PLA).
• General Procedure:
• never use a gas-fired oven
• air-circulation (convection) ovens work better than standard ovens
• oven thermostats are inaccurate; get a good thermometer to be sure
• check the specs on your specific filament, because even the same type of filament (eg. PETG) from different manufacturers can have different glass transition temperatures.
• place parts on baking sheet in the oven
• when the oven reaches temperature, wait an hour or so (heat on)
  (30 min plus 15 min for each 3mm of part thickness)
  turn off oven
  wait a couple of hours for oven to cool. Do not open the door during the cooling.
• Approximate Target Temperatures:
• for PLA:
  pre-heat oven to 60-65C (144F),
  but you might need to go to 70C (158F),
  but melting point is nom. 175C (347F), so 70 is not a problem
• For PET:
  Glass transition temperature is ~ 75C (153F)
  Melting point > 250C (482F)
  Recommend set oven to 79C (175F)
• For ABS:
  Glass transition temperature is 105C (221F)
  Melting Point: ~ 225C (437F), so set your oven to 100C (212F)
• For Nylon12:
  Glass transition temperature is 98C (208F)
  Melting Point: ~ 180C (356F)
  Recommendation is to set your oven to 130-140C (275F)
• For Polycarbonate:
  Suggest using oven at 120-130C (257F)

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