Core pins are used primarily in the plastic molding and die casting applications. In most cases core pin are fixed in the plastic mold and are used to create a desired shape in the molded or cast part. Unlike the purpose of a an ejector pin which is pushed or extended by the ejector plate to eject the cooled molded or cast part from the cavity/core. It is often easier to machine a core pin as a separate element and add it to the A-side or B-side of the mold as needed. Core pins are sometimes used in aluminum molds to create tall, thin cores that might be too fragile if machined out of the bulk aluminum of the mold. In some applications core pins are also used for part ejection from a casting die.
There are many types of pins with in mold bases and die casting molds. Each are designed (based on material type, core and surface hardness, and coatings) for different applications within the molding or casting process. Many factors need to be considered to choose the correct pin for the application. Factors like the draft and texture of sidewalls, depth of walls and ribs can increase the likelihood that areas of the part will cling to the mold. Resin choice can also affect pin placement or size. Some resins are “stickier,” requiring more force for release from the mold. Softer resins may also require the use of more or bigger pins to spread the force and prevent puncturing or marring of the cooled plastic.