Enter the part, cavity count, resin and flow path to see how many tons of clamp the mold needs, the smallest catalog machine that fits and the margin left.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Force with safety factor for each cavity count, with runner area growing along. The line is the machine under review.
Average pressure estimated from the PP/PE guide value times the viscosity factor. The dashed vertical line is the current part.
Published PP/PE ranges (250–300, 300–350 and 350–400 kgf/cm²) converted and multiplied by each group’s viscosity factor. The highlighted row is the selected resin.
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It is the force the press applies to keep the mold shut while plastic is injected under pressure. If it is lower than the force the melt exerts to open the mold, the part flashes at the parting line. The calculation helps you pick the press size, decide the cavity count and check whether a new mold fits a machine you already have.
Multiply the projected area (parts plus runner) by the average cavity pressure and a safety factor. In the page example, 4 parts of 6 × 4 in plus a 2 in² runner give 98 in²; at 4,148 psi average pressure that is 203 US tons, and with a 1.2 factor 244 US tons, or about 2,170 kN.
From the 3D model: projected area is the part’s shadow seen along the mold opening direction, minus through holes. Flow length is the longest distance from the gate to the farthest point of the part, and wall thickness is the wall along that path. For an existing mold, the moldmaker has these figures.
For PP and PE, practice guide values are about 3,600 to 4,300 psi with L/t below 100, 4,300 to 5,000 psi from 100 to 200 and 5,000 to 5,700 psi above 200. Stiffer resins multiply those: about 1.3 for nylon and PBT, 1.5 for ABS and acetal and 1.8 for polycarbonate and rigid PVC. At 4,148 psi the example works out to about 2 US tons per square inch of projected area, in line with common tonnage rules of thumb; if you have a cavity pressure sensor or fill simulation, enter the real value.
The smallest press in the series above the factored force. In the example, 244 US tons calls for a 300-ton press, leaving a 23% margin and using 68% of its clamp. Many molders avoid running above 80% of rated clamp to spare tie bars and molds; also check tie bar spacing, daylight and shot size.
It uses pressure guide values, not a simulation: a cold mold, slow injection, small gates and walls under 0.03 in can need far more. It does not add side-action forces from slides and lifters. For expensive molds, thin-wall parts or a close call between two presses, ask the moldmaker for a fill analysis.
Important notice: Indus Metrics tools produce estimates and pre-sizing results from the data you enter and from published engineering methods. They do not replace design, calculations or reports signed by a licensed professional engineer (PE), nor verification against the applicable codes, standards and regulations, such as OSHA rules and the ASME codes. Material and fuel properties vary: check manufacturer data or your own process analyses before deciding. By using this site you agree to the Terms of Use.
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