Why corners lift, and how to design so they do not
Warping is shrinkage, not bad luck. Which materials suffer, which shapes cause it, and the design changes that eliminate it.
4 min read
Plastic leaves the nozzle above 200 °C and cools to room temperature. As it cools, it shrinks. The lower layers are already cold and stuck to the bed; the upper ones shrink on top of them and pull. When that pull beats the adhesion, the corner peels off and lifts. That is warping: shrinkage, not a malfunction.
Which materials suffer
| Material | Tendency | Note |
|---|---|---|
| PLA | Very low | Barely shrinks. Which is why it is the material for large flat parts. |
| PETG | Low | Behaves well except on very wide, shallow parts. |
| ABS | High | The classic offender. Needs an enclosure, and still wants careful design. |
| Carbon fibre PLA | Very low | The fibre restrains shrinkage. Even better than plain PLA. |
The geometry that causes it
Warping does not depend on the material alone. A large, flat part with sharp corners is the worst possible combination: a lot of shrinking area, little height to spread the stress, and corners where all that force concentrates on one point. The same part with rounded corners behaves far better.
Five design changes
- 1Round the corners of the base. A 3 mm radius spreads the stress a sharp corner concentrates. Best effort-to-result change there is.
- 2Reduce continuous contact area. A solid 200 × 200 mm plate warps; the same plate lightened with cut-outs warps far less.
- 3Avoid abrupt section changes. Where a thick wall meets a thin one, the thick one shrinks more and pulls. Transition with a chamfer.
- 4If the part is tall and narrow, so much the better: warping is a problem of wide, shallow parts.
- 5Change material if you can. If the part does not need ABS’s 95 °C, in PETG the problem simply goes away.