Annealing is the controlled heating of a printed part to elevated temperature for a sustained period, is one of the most underused post-processing operations in additive manufacturing. Done correctly, it improves tensile strength by 20 to 40 per cent, lifts stiffness by similar margins and substantially improves dimensional stability across temperature. Done incorrectly, it produces warped, deformed parts that can be worse than as-printed.
The technique is worth learning, and it pairs naturally with the engineering grades available through OzFDM and the broader FDM service at Global3D.
Why annealing works
Most engineering thermoplastics, particularly the nylons (PA6, PA12, PA-CF, PA-GF), are semicrystalline. As-printed parts have a substantial amorphous fraction because the rapid cooling during printing does not allow full crystallisation. Annealing at temperatures above the glass transition but below the melting point lets crystalline regions grow, lifting the part's stiffness, strength and heat resistance.
PEEK and PEKK are particularly responsive. A properly annealed PEEK part can approach the published datasheet values, while as-printed PEEK typically falls 30 to 40 per cent short. The same logic applies, in smaller margins, to PA-CF and PA-GF parts that need to hold tolerance at elevated service temperatures.
Temperature and time by material
Treat these as starting points. Confirm the recipe for your specific filament with the manufacturer, and run witness coupons before committing production parts.
PA-CF and PA-GF: 80 to 120 degrees C for 4 to 8 hours.
PEEK and PEKK: 170 to 200 degrees C for 4 to 12 hours.
PETG-CF: 70 to 90 degrees C for 4 to 6 hours.
ABS: 90 to 100 degrees C for 2 to 4 hours, mainly stress relief.
PLA: rarely worthwhile and high distortion risk.
Running an anneal cycle in five steps
Dry the part fully before heat. Residual moisture causes bubbling and surface defects at temperature,
Place the part on a flat heat-resistant surface, sand bed or sintered alumina plate that allows uniform shrinkage without sticking,
Ramp the oven to the target temperature over 30 to 60 minutes rather than starting at full set point,
Hold at temperature for the published soak time, with active air circulation to keep the working volume within plus or minus 2 degrees C,
Cool slowly back to room temperature, ideally by holding the oven door closed and letting it ramp down naturally over several hours,
Distortion is almost always one of two causes
Either the part lacks support during heating, so it sags under its own weight at temperature, or the heating is non-uniform and creates differential expansion. Fix both at once with a flat heat-stable bed and an oven with proper air circulation.
When to anneal ?
KEY TAKEAWAYS
Anneal anything in PA, PA-CF, PA-GF, PEEK or PEKK that has a stiffness, strength or heat-resistance target,
Skip annealing for PLA, and treat ABS annealing as stress relief rather than a property uplift,
Run witness coupons on every batch and log the actual oven profile, not just the set point,
Build the shrinkage into the model rather than fighting it after the fact.