PEEK 3D printing: how to prevent warpage?
What is warpage ?
Warpage, sometimes called warping, is a physical phenomenon that occurs during 3D printing. It consists in the part being distorted at its base, which then causes the part to detach itself from the print bed.
What are the causes of warping?
Warpage is caused by a natural shrinkage that affects plastics when they cool. The larger the part is, the stronger the phenomenon will be. When the upper layers contract due to air cooling, they pull the lower layers upwards, which lifts the part off of the printing plate.
The video below illustrates this phenomenon very well with tape:
How to prevent warping?
Several solutions are used by 3D printer manufacturers to reduce warping:
- Using perforated print beds
- Printing extra layers around the part to increase its surface area on the bed
- Using glue on the print plate
However, these solutions do not prevent mechanical stresses in the part and only allow to work around the problem, with varying degrees of success.
Is there a sustainable solution to avoid warpage?
The only viable solution is to maintain the part at a high temperature. It should be held close to its glass transition temperature for an amorphous polymer material, or to its crystallization temperature in the case of a semi-crystalline material.
Put simply, the transition temperature is the temperature at which a certain plastic begins to soften.
Take, for example, the case of an ABS part. If the printing chamber is heated and maintained at a temperature close to its glass transition temperature (e. g. 80°C or 90°C), the material will have a much more consistent and uniform behavior.
At each added layer, the material will only shrink by about 0.05% instead of 0.5%. Since tensions in the part are reduced, there is no longer any risk for the part to peel off or break.
Warping of high-performance polymers (PEEK, PEI, PEKK…)
High-performance materials such as PEEK (PolyEtherEtherKetone), PEI (PolyEtherImide), and PEKK (PolyEtherKetoneKetone) have exceptional mechanical properties and heat resistance, but are even more difficult to print than “standard” thermoplastics like PLA or ABS.
They have very high crystallization and/or glass transition temperatures (over 200°C), and some have a shrink rate of 2% (compared to about 0.5% for ABS and 0.2% for PLA). Hence, a 200-mm-long part shrinks by 4 mm at each layer if the printing chamber is not heated up to the right temperature.
Extruder, bed, and chamber
Having a high-temperature extruder (over 400°C) and high-temperature print bed (200°C) is therefore not enough to print high-performance polymers.
It’s actually impossible to print large PEEK parts with a chamber that only heats up to 90°C or even 120°C; only small parts can be successfully printed. Unfortunately, you can’t override the laws of physics!
For PEEK, it is essential to heat the chamber to a very high temperature, generally 270 – 280°C in order to limit warping.
The chemical groups that manufacture PEEK and high-performance polymers are all working on making materials more adapted to 3D printing processes but, in any case, a heated chamber will definitely improve part quality.