Clamp Force Calculator

Projected Area per Cavity is the flat, two-dimensional area the part (and its runner system) presents when viewed straight down through the mold's parting line -- essentially its silhouette -- not the part's full three-dimensional surface area, which is always larger for anything but a flat shape. Clamp force calculations use projected area because that's the area the injected melt's pressure actually pushes against to try to force the mold open.

Required Clamp Force is a straight product of all four inputs, so there's no single input that dominates the other three across this calculator's full declared ranges -- Number of Cavities (1 to 128) or Cavity Pressure (1,000 to 30,000 psi) can each move the result by more than Projected Area per Cavity does, depending on where the other inputs sit. The one comparison that reliably holds: Safety Factor is deliberately confined to a narrow 1.0-2.0 multiplier, so any of the other three inputs -- Projected Area per Cavity, Cavity Pressure, or Number of Cavities -- will move Required Clamp Force far more than Safety Factor alone ever can.

Total Projected Area is a purely geometric figure -- Projected Area per Cavity multiplied by Number of Cavities -- with no dependence on how much pressure the melt reaches or what safety margin you apply on top. Cavity Pressure and Safety Factor both move Required Clamp Force, but they only come into play after Total Projected Area has already been fixed by part size and cavity count.

This calculator's helpText and default (1.1) reflect a commonly used 10% margin, with 1.1 to 1.2 (a 10-20% cushion above the bare theoretical minimum) cited as typical practice, though the right figure depends on your specific material, process stability, and mold condition. Treat the 1.0-2.0 range this calculator accepts as a planning tool, not a substitute for your press manufacturer's or process engineer's guidance on a specific job.

Recommended Machine Size rounds Required Clamp Force up to the next size in a list of standard press tonnages (25, 50, 75, 100, 150 tons, and so on up through 5,000), because presses are sold in fixed increments rather than at any arbitrary tonnage. If Required Clamp Force already lands exactly on a standard size, Recommended Machine Size shows that same figure rather than jumping to the next one up.