One parting line is not enough to eject complex geometries of injection molded parts.
Undercuts in the direction of ejection are the main difficulty.
So called slider are used to build an additional parting line.
The movement of the slider diagonally to the opening direction of the mold frees the undercuts and allows the ejection of the part.
Slider can be placed inside the fixed as well as the movable side of the mold.
The angle of the slider compared to the other parts of the mold should be between 83° and 97° to avoid a blocking of the slider.
The buoyancy inside the mold needs to be considered for the correct size of the slider.
It need to be ensured that the sliders are adequately locked.

Slider in Injection Molding

Opening of a simple mold with sliders

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.