Ejector pin marks.
Mold release.
Hidden surfaces.
Ejector pin design for injection molded parts. Pin placement, size, mark visibility considerations. Plan ejector marks on non-cosmetic surfaces.
Key principles.
Hidden surface
Place ejector pins on non-cosmetic surface (B-side).
3-6 mm typical
Standard ejector pin diameter. Matches force needed.
Distribute force
Even ejector force distribution prevents part distortion.
Slight depression
Ejector pins leave 0.05-0.2 mm depression. Hidden = OK.
Avoid weak spots
Don't place ejector pins where material weak (gates, weld lines).
Through smaller
Through-hole ejection cleanest. Surface depression unavoidable on flat areas.
FAQ
Where to place ejector pins?
Non-cosmetic surface (back, hidden side). Discuss with tooling engineer.
Visible mark severity?
0.05-0.2 mm depression typical. Visible if cosmetic surface, hidden if back.
Pin size selection?
3-6 mm standard. Large parts use larger pins for sufficient force.
Pin marking elimination?
Cannot eliminate completely on most parts. Choose location to hide.
Sleeve ejection?
Cylindrical features ejected by sleeve, no pin marks on visible surface.
Cost impact?
Standard ejector pin design, no premium. Custom ejection (sleeve, stripper) adds 20-50% mold cost.
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