Parting Line

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Injection mold halves separated showing the parting line interface

Definition of Parting Line

The parting line is the plane or contour where the moving and fixed mold halves separate to eject the part. It appears as a visible seam on many molded products and is where the mold designer splits geometry for draft and undercut management.

Projected area at the parting line (everything the cavity pressure pushes against) is used to estimate required clamp force. Poor alignment, wear, or contamination at the parting line increases flash risk.

Why It Matters for Plastic Injection Molding

Tooling design choices

Parting-line placement affects cosmetics, tool cost, and side-action requirements. AMP mold designers try to hide the line on non-show surfaces while keeping fill and ejection practical.

Maintenance and quality

Nicks, debris, or polish loss at the parting line show up immediately as flash or dimension drift. Regular inspection during preventive maintenance keeps high-cavity programs stable.

Related Terms

Clamp ForceFlashVenting
On some cosmetic parts the line is placed on hidden edges or softened with texture, but every two-plate mold has a physical split. Zero visible line usually requires design compromise or multi-stage tooling.