Key principles.
Mold split
Where mold halves separate for ejection.
Slight ridge
Plastic squeeze creates visible parting ridge or flash.
Hidden seam
Place on edges, hidden surfaces, or matched seams.
Affects gating
Parting line position affects gate locations, weld lines.
Undercut features
Side action mold pieces enable undercut features.
Angled retract
Angled mold pieces lift past undercut during opening.
FAQ
At the geometric split between male/female mold halves. Visible as ridge/flash on part.
Cannot fully eliminate. Can hide in textures, edges, or seam patterns.
Two-shot molds have two parting positions. Each requires careful design.
Avoid. Move mold split or add side actions. Sometimes two-piece molded + assembled.
Sub-mm parting flash typical. Painted or textured parts hide most.
Mold flow analysis predicts. Specify acceptable flash on drawing.
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