Delamination: why the layers of a 3D print separate

Why layers fail to bond

In FDM a new layer bonds to the one below only if the lower one is still warm enough. If the plastic is too cold, the layer merely rests on it and the bond is weak. See also delamination in general.

Common causes are a low nozzle temperature, draughts and too strong a fan, damp filament, or a layer height that is too large for the nozzle diameter. That is why a part's strength is always weakest in the direction of the layers.

It shows up as a fine crack along a layer or as complete separation when bent. On decorative parts it does not matter, but on functional ones such as brackets, hooks or latches it is the main reason for failure.

The direction of the layers decides strength

A part is strong along the layers and weaker across them. When force acts perpendicular to the layers, the pull leads straight to separation. That is why the way a part lies on the plate matters, see model orientation.

A hanging hook printed standing up cracks easily, because the load pulls the layers apart. A hook printed lying down holds up far better.

How to design a strong part

• Let the loaded areas run along the layers, not across them.
• Choose 40 % strength for loaded parts, see infill and walls.
• Add a fillet to sharp transitions, where stress concentrates.
• With PETG the bonds between layers are usually better than with PLA, see PLA or PETG.

For your order

For functional parts, write in the note how they will be loaded, and choose the strong option and the material. We do not guarantee that a part will withstand a certain load, as strength depends on the shape. We photograph the batch before dispatch, but we do not measure the strength of individual parts.