Simplify geometry: Reduce undercuts, deep ribs, and thin walls where possible. Favor uniform wall thickness to prevent sink marks and warpage.
Draft angles: Provide draft on all vertical faces for ejection—typically 0.5°–2° depending on texture and part height.
Wall thickness: Use the minimum consistent thickness required for strength; typical ranges: 0.75–3.0 mm depending on material. Avoid abrupt thickness changes—use ribs or gussets instead of thick sections.
Ribs and bosses: Design ribs ≤60% of nominal wall thickness and with fillets at the base; bosses should have relief holes or ribs to avoid sink and add support.
Fillets and radii: Use generous radii at corners to improve flow and reduce stress concentration.
If you design a vertical wall (0° draft), the part will weld itself to the steel. As plastic cools, it shrinks onto the core. Without draft, ejector pins will push through the part (ejector pin push-through) or the mold will seize.
Two-Plate Mold: Simplest design. The runner is ejected with the part.
Three-Plate Mold: The runner is on a separate plate. Allows center gating on parts without automated removal.