Engineers have many factors to consider when it comes to plastic injection mold designs, including cam action and the ejection system. Once a mold designer has evaluated all geometric tolerances on the part print, they will typically create a CAD (Computer Aided Design) drawing of the part to aid in the design of the tool. While reviewing part requirements and the tooling necessary to mold the part, it will become apparent if any Cam Action, or specialized ejection system is necessary.
What is Cam Action
Cam action refers to the mechanics necessary to create an undercut feature, a hole in a part would be an example. Cam action occurs on sliding plates that would slide in when the plastic is molding around it to create the feature such as a hole, then it must slide back out in order for the part to eject properly. If the pins or mechanics that molded the feature like a hole did not slide out of the way, the part would be lodged on that pin and would not fall out. A cam device will pull the side-action mold surface out of the way to allow ejection from the mold.
Pictured is an example of cam action; the sliding plates have barrel like rods attached to move in during the molding process creating holes in the part. They slide back out when finished for proper ejection.
This photo shows cams in a closed position, while molding the hollow geometrical shape of the part.
Lifters and the Ejection System
The ejection system is what pushes the part out of the mold after a fully formed plastic part has been molded. In some instances, some help might be required for proper ejection. This is where lifters would be included as a mechanism in the ejector system. A lifter is an angled feature that is part of the ejector plate system, and is activated upon ejection.
The ejection system has several considerations during the injection mold design. The ejection pattern and stroke of the press must correspond with the mold design. Proper location of ejection pics is crucial to properly eject the mold without damaging the finished part. In some instances, lifters are the only option to ensure proper ejection.
An example of lifters assisting with ejection
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