During Cooling, the injection molded part shrinks onto the mold components.
For ejection of the part, draft angles are used.
If they are missing, it might lead to no ejection of the part, or visible scratches or scoring arise during ejection.
Dependent on material and surface, different draft angles are chosen:
Amorphous materials need larger draft angles on a rib than semi-crystalline materials.
On the other hand, if the part shrinks to a core, it is vice versa.
The higher shrinkage of semi-crystalline materials is the reason for this.