Ejector Pins Properly on plastic injection molding

 Ejector Pins Properly on plastic injection molding 

Ejector pins are the "bouncers" of the plastic injection molding world. They apply a force to eject a part from the mold, and in some cases can leave marks. In Ideal Group, our goal is to design and position pins to minimize their effect on your parts, and while Ideal Group typically determines pin placement, customers get to sign off on pin locations before an order is finalized.

Pins are located in the B-side mold half, the side in which the part will stay when the mold opens. Once the mold is opened, the pins extend into the mold cavity, push the part out,and then retract, allowing the mold to close and be refilled.

Ideal Group  uses round ejector pins, and their placement depends on a number of factors. Obviously the shape of the part is one (see example in illustration). Factors like draft and texture of sidewalls and 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 wider pins to spread force and prevent puncturing or marring of the cooled plastic.

In Ideal Group' process, the ends of ejector pins are flat and perpendicular to the direction in which the pin moves. To be effective, the pins need a flat "pad" to push against, and the surface of the pad must be perpendicular to the direction of pin movement. If the part surface at that location is textured, the smooth surface of the pad will be apparent. And if the surface of the part is not parallel to the flat end of the ejector pin, the cosmetic impact will be even more obvious.