A well-designed ejection system is essential for producing quality parts consistently. The ejection system must overcome shrinkage-induced grip force on the mold core without damaging the part.
The most common and cost-effective ejection method. Standard pin diameters range from 1mm to 20mm. Pin placement should be on stiff part features (ribs, bosses) or on flat surfaces where witness marks are acceptable. General guidelines: place pins at corners first, then along edges at 25-50mm spacing. Minimum 6mm pin diameter for unsupported pins.
Sleeves are hollow pins that eject around a fixed core. Used for circular features, bosses, and through-holes where a standard pin would leave an unacceptable mark. Sleeves are more expensive and more prone to contamination than solid pins.
A stripper plate contacts the entire part periphery, providing uniform ejection force. Ideal for thin-wall parts, large flat parts, and parts with minimal draft. Stripper plates eliminate ejector pin witness marks on the part surface.
Used for parts with internal undercuts. The lifter moves both vertically (ejection direction) and laterally (to clear the undercut). Lifter design requires careful calculation of travel distance, angle, and clearance. Maximum recommended lifter angle is 12-15 degrees.
Compressed air is directed between the part and the mold surface to break the vacuum and push the part off. Used for thin-wall containers, cup-shaped parts, and in combination with mechanical ejectors to reduce pin marks.