A three-plate mold has three partings – the first is between the runner plate and the cavity plate, the second between the runner plate and the top clamping plate, and the third between the cavity plate and core plate.
1. In the beginning, when the core is subjected to the pulling force of the injection molding machine, since there is a nylon lock between the core and the cavity plates while there is no connection or constraint between the runner plate and the cavity plate (in most cases, the small tie bar is also equipped with a spring), under the effect of pulling force at the moment, the runner plate is first separated from the cavity plate, and the latter moves backwards along with the core plate to the preset distance before it is blocked by the stopper of the small tie bar.
2. The cavity plate continues to move backwards with the injection molding machine, so that the small tie bar is also moved, which in turn drives the runner plate to move to the preset distance (usually 8mm), so as to remove the gates and runner. After completing the preset distance, the small tie bar and the cavity plate stop moving.
3. The injection molding machine continues moving backwards to increase the pulling force and make it exceed the clamping force of the nylon lock, so that the cavity plate is separated from the core plate for the preset distance before stopping.
4. Under the push of the molding machine ejectors, the ejector plate drives the ejecting system (ejector, sleeve and lifter, etc.) to start ejecting the finished product (removed automatically or by a mechanical arm).
5. Under the push of the injection molding machine, the core moves towards the cavity. If the ejector plate is not pulled back in advance, the return pin contacts the cavity plate first. Under the reaction force, the ejector plate is then returned by the return pin.
6. The core plate is pressed against the cavity plate and the runner plate, until the mold is tightly closed. The nozzle on the injection molding machine is in close contact with the nozzle bushing on the mold, to get ready for the next molding cycle.
So, this is the full molding cycle of a three-plate mold.
The following is an animated simulation of a three-plate mold. (In the animation, the cavity is moving, while during actual mold opening, the core moves. The relative motion of mold opening is unchanged, but the action is reversed.)