Injection Molding Cooling Time Calculator

In injection molding, cooling is almost always the longest part of the cycle, and it scales with the square of wall thickness — double the wall, and cooling takes roughly four times as long. This calculator uses the standard analytical solution for transient heat conduction in an infinite flat plate, the model injection molders use as the practical stand-in for real part geometry: t = (s²/(π²·α)) × ln(8(Tm−Tw)/(π²(Te−Tw))), where s is the maximum wall thickness converted to meters, α is the material's thermal diffusivity (α = k/(ρ·Cp), computed here from thermal conductivity, density, and specific heat), Tm is melt temperature, Tw is mold wall temperature, and Te is the ejection temperature at which the part is rigid enough to release without warping. The tool clamps ejection and mold temperatures into a physically sensible order (Tw < Te < Tm) before running the log, since the equation is undefined otherwise.

Cooling time then combines with injection/packing time and mold open-close time to give a total cycle time, which converts directly into a single-cavity parts-per-hour production rate. It also reports the Fourier number, a dimensionless ratio of actual cooling time to the material's characteristic diffusion time, as a sanity check on how "cooked" the model considers the part at ejection. Two things worth knowing: the flat-plate model is an approximation — cylindrical or highly ribbed geometries cool differently and would need a different shape factor — and it only estimates the *thickest* section, so a part with a heavy boss or rib may need meaningfully more cooling than this number implies.