Undercuts in plastic molding can be used to create part features such as screw threads, locking tabs, or slots for switches. These protrusions or indentations are parallel to a mold’s parting line, the dividing line that splits the core and the cavity. Rotational molding isn’t the only plastics molding process that allows for undercuts, but it provides some important advantages over injection molding.

Rotational Molding and Undercuts

Rotational molding is a plastics manufacturing process that creates strong, hollow plastic parts in the shapes, sizes, textures, and colors that you need. In addition to undercuts, rotomolding supports features such as multiple walls and molded-in hardware. With its low tooling costs and quick tooling modifications, rotational molding is a cost-effective way to prototype parts and to produce them in low to high volumes.

During product development, rotational molding lets you design plastic parts that will shrink away from the mold walls. During the rotomolding process itself, a part that completely shrinks away from the undercut allows for simpler removal. For best results, an undercut should equal half the material shrinkage. If a larger undercut is required, molds can be designed with features that are removed along with the part. Gregstrom, an experienced rotational molder, can provide you with design assistance.

Injection Molding and Undercuts

Injection molding guidelines may recommend avoiding undercuts because of problems with part ejection. That’s because when an injection mold is released, undercuts may interfere with the separation of the core and cavity. Injection molders can use additional tooling called side actions to facilitate this separation, but that adds costs and complexity to your plastics projects.

Do you need to design molded parts with undercuts? Would you like to learn more about rotational molding, or discover other advantages that this plastic molding process has over injection molding? Gregstrom, a rotational molder with over 70 years of experience, is ready to help. To request a quote or learn more, contact us.