Proper venting is critical for injection molding success. As molten plastic fills the cavity, air must escape. Inadequate venting causes burn marks, short shots, poor weld line strength, and dimensional variation.
Vent depth depends on material viscosity. Too deep and flash occurs. Too shallow and air cannot escape. General vent depth by material: ABS 0.03-0.05mm, Nylon 0.01-0.03mm, PC 0.03-0.05mm, PP 0.02-0.04mm, POM 0.01-0.02mm, PEEK 0.03-0.05mm. Vent land length: typically 0.5-1.0mm. Vent width: 3-10mm per vent channel.
Place vents at: last-fill locations (opposite the gate), along the parting line at 20-40mm intervals, at weld line locations, and at deep cavity corners where air traps form. For tall cores, place additional vents at the core bottom.