Guide - Injection Mold Design

| Parameter | Formula / rule | |-----------|----------------| | Projected area | Part + runner area on parting line | | Clamp force (tons) | (Projected area in cm² × injection pressure in tons/cm²) × safety factor (1.2–1.5) | | Ejector pin stress | F_push / (n × pin_cross_section) < 300 MPa for steel | | Cooling time estimate | (thickness² × constant) / thermal diffusivity (empirical) | | Shrinkage compensation | Multiply part dims by (1 + shrinkage %) – use moldflow to refine |

The primary entry point into the mold. It must be tapered (typically 2 to 4 degrees) to allow clean extraction and must have a cold slug well at its base to catch the initial, colder plastic drop. Runner Systems Runners distribute plastic from the sprue to the gates. injection mold design guide