Injection Molding Clamp Tonnage & Cooling Time Calculator

How it works

clamp (US tons) = projected area (in²) × material factor (1.5–5 t/in²), +10% margin · cooling t = h² ÷ (π² α) × ln( (4 ÷ π) × (T_melt − T_mold) ÷ (T_eject − T_mold) ) · cycle = fill + pack + cool + open/eject · parts/h = 3,600 ÷ cycle × cavities

Molten plastic injected at hundreds of bar pushes the two mold halves apart with a force equal to cavity pressure times the area the part presents to the parting plane, so clamp tonnage is that area — parts, runners and sprue together — multiplied by a factor that rises with the viscosity of the material, from under two tons per square inch for polyethylene to five for polycarbonate. Once filled, the part must cool until its core is stiff enough to eject, and heat has to conduct out through the wall, so cooling time grows with the square of the thickest section and dominates the cycle; the logarithmic term is the one-dimensional conduction solution for a slab between two cold plates. Cycle time then sets output, and shot weight sets the barrel size.

Worked example

Four ABS parts of 80 cm² each with 15% runner area present 368 cm² (57 in²), needing about 200 US tons of clamp — a 220-ton press. A 2.5 mm wall cools in about 11.4 s (240 °C melt, 90 °C eject, 50 °C mold), giving a cycle near 19 s and roughly 750 parts an hour; a 3.5 mm wall would take 22 s to cool — nearly double.

Frequently asked questions