Materials:
Non-uniformity of molding materials.

Molding process:
1. The operating process conditions change.
2. Control accuracy error of molding equipment.

Mold status:
1. Manufacturing tolerance of mold dimensions.
2. Mold wear.
3. The matching position error between the movable parts of the mold.
4. Temperature fluctuation of mold:.
5. The elastic deformation of the mold under molding pressure.