Prototype overmolding is a casting process that allows for bonding materials of different hardnesses in layers, one on top of the other.
Prototype overmolding is a quick, inexpensive alternative to production overmolding or insert molding. It allows for testing and visualizing an overmolded product before committing to production. The process of overmolding provides the ability to create parts of different materials to fine tune the feel and color of parts during the development process. The subtle variations of the part can be used for testing and choosing the best solution to move forward with to production. Many product categories use overmolding when a form needs to be easy to grip such as toothbrushes, pens, tools, and medical devices.
Creating an overmolded prototype is a two-mold process. Initially, a master of the final part shape is created and a mold is made. Then, a second master is created of the inner rigid layer or base part. The base part is used to create a second mold. Once the base part is cast, it is cleaned and finished before overmolding begins. To create the overmolded final part, the base part is placed in the first mold and low durometer resin is injected into the space around the base part. The materials are bonded together in the mold and removed as a single part with two different materials.