Annealing is a post-processing heat treatment used to improve the mechanical properties of FDM 3D printed parts. By heating a part to a temperature above its Glass Transition Temperature but below its melting point, you allow the polymer chains to relax and re-crystallize.
Key Benefits:
Increased Heat Resistance: Prevents parts from warping in hot environments (e.g., inside a car).
Enhanced Strength: Improves interlayer bonding and structural integrity.
Stress Relief: Eliminates internal tensions created during the rapid cooling of the printing process.
"Annealing is a double-edged sword. Before proceeding, you must be aware of the following risks:"
Loss of Dimensional Accuracy: Annealing causes polymer chains to contract. Typically, PLA shrinks by approximately 2% in the XY plane and expands by about 1% along the Z-axis. This means precision-engineered parts (such as screw holes, gears, or snap-fits) may fail to assemble post-annealing.
Irreversible Deformation: If heating is uneven or if the part lacks sufficient support, the model may suffer from twisting, collapsing, or base warping. Once these structural failures occur, the model cannot be repaired.
Surface Degradation: High temperatures can alter the gloss or finish of certain filaments. Additionally, support structures may fuse more tightly to the model’s surface, making them significantly harder to remove.
If your project requires high dimensional precision, it is strongly recommended to print a small test sample (e.g., a 20mm calibration cube) first. Perform a trial bake to calculate the exact shrinkage rate of your specific filament before processing the final part.
Step-by-Step Instructions
Annealing causes the plastic to shrink as it densifies.
Typical Shrinkage: PLA usually shrinks by 2% in the XY plane and expands by 1% in the Z-axis.
Tip: Scale your model in your slicer (e.g., 102% for X/Y) before printing if precision is required.
Electric Oven: Use a convection oven for stable airflow. Avoid gas ovens as they have localized "hot spots" that can melt the model.
The Sand Bath Method (Pro Tip): Bury your part in a container of fine sand and pack it tightly. The sand acts as a mold, providing physical support to prevent the part from warping or collapsing while it is in its soft state.
Preheat the oven to the target temperature.
Place the part inside and start the timer once the temperature stabilizes.
Crucial Step: Once the time is up, do not remove the part. Turn off the oven and let the part cool down slowly inside the oven until it reaches room temperature. Rapid cooling can re-introduce internal stresses.
Keep Supports Attached: Do not remove support structures before annealing; they prevent the model from sagging under its own weight.
Infill Density: Use a higher infill (50% or more) for better results. Hollow parts are much more likely to deform.
Wall Count: Increasing the wall thickness (3-5 perimeters) provides more material to resist warping.
Annealing is a "trade-off" process. While it makes your parts significantly more durable and heat-resistant, you sacrifice a degree of dimensional accuracy. It is highly recommended for functional mechanical parts but unnecessary for aesthetic models.