How Parting Line Selection Affects Die Casting Quality and Cost

The parting line in die casting is where the two halves of the mold (the “cover” and “ejector” sides) meet—and it’s one of the earliest and most important decisions made during tooling design.

A poorly placed parting line can result in flash, cosmetic issues, or even mold failure.

📐 Why Parting Line Matters

1. Affects Tool Complexity

   A simple, flat parting line often allows for easier tooling and better sealing. Irregular parting lines (needed for complex shapes) require more mold inserts, lifters, and sliders—adding cost and risk.

2. Influences Flash Formation

   Flash occurs when molten metal escapes through the parting surface. The smoother and better matched the parting line, the less flash forms—reducing secondary cleanup.

3. Impacts Surface Finish & Appearance

   On cosmetic parts, visible parting lines may need to be hidden or aligned with design features.

4. Controls Ejection Direction & Pin Placement

   Proper parting line selection ensures that undercuts are managed and ejector pins can be applied to sturdy areas—reducing sticking and part deformation.

💡 Design Tip:

Try to align the parting line with natural geometry breaks—edges, ribs, or functional transitions. This makes the line less visible and helps with metal flow balance during injection.

At LVIO Precision, parting line evaluation is part of our early-stage DFM support. We simulate fill flow, draft direction, and ejection paths to recommend parting lines that reduce tooling cost and improve long-term reliability—especially in parts with complex enclosures or asymmetric features.