In molding, an undercut is an indentation or protrusion in a shape that will prevent its withdrawal from a one-piece mold. Undercuts on molded parts are features that prevent the part from being directly ejected from an

injection molding machine An injection molding machine (also spelled as injection moulding machine in BrE), also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, an ''injectio ...

. They are categorized into ''internal'' and ''external'' undercuts, where external undercuts are on the exterior of the part and interior undercuts are on the inside of the part. Undercuts can still be molded, but require a ''

side action Side or Sides may refer to: Geometry * Edge (geometry) of a polygon (two-dimensional shape) * Face (geometry) of a polyhedron (three-dimensional shape) Places * Side (Ainis), a town of Ainis, ancient Thessaly, Greece * Side (Caria), a town of ...

'' or ''side pull''. This is an extra part of the mold that moves separately from the two halves. These can increase the cost of the molded part due to an added 15 to 30% cost of the mold itself and added complexity of the molding machine... If the size of the undercut is small enough and the material is flexible enough a side action is not always required. In these cases the undercut is stripped or snapped out of the mold. When this is done usually a stripping plate or ring is used instead of

ejector pins Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

so that the part is not damaged. This technique can be used on internal and external undercuts.

References

Bibliography

*. *{{Citation , last = Rosato , first = Dominick V. , last2 =

Plastics Institute of America Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

, last3 = Schott , first3 = Nick R. , last4 = Rosato , first4 = Marlene G. , title = Plastics Engineering, Manufacturing & Data Handbook , publisher = Springer , year = 2001 , url = https://books.google.com/books?id=2KSbTcdYv9QC , isbn = 978-0-7923-7316-2. Forming processes