Clamping force calculator
The clamping force (also called closing force) of an injection moulding machine has to hold back the melt pressure in the mould. With the free calculator you work it out from projected area, cavity pressure and number of cavities, in kN and tonnes. The Resinovo app uses the same formula.
The clamping force formula
Clamping force
F = A × p × 0.1 × n × (1 + S)
A projected area in mm², p mean cavity pressure in bar, n cavities, S safety margin (default 15 %). 1 bar equals 0.1 N/mm², 1 t equals 9.81 kN.
Worked example: ABS housing
F = 12,500 mm² × 525 bar × 0.1 × 1 × 1.15 ≈ 754.7 kN
125 cm² projected area per cavity (12,500 mm²), one cavity, 525 bar cavity pressure (typical value for ABS), 15 % safety margin. Result: about 755 kN, roughly 77 t. The machine should therefore provide at least this clamping force.
Projected area and cavity pressure
The projected area is the shadow of the moulded part in the clamping direction, taken per cavity; the formula multiplies it by the number of cavities n. The projected area of a cold runner is added to A where relevant, a hot runner adds nothing. The area acts like a piston: the larger it is, the greater the force with which the melt tries to push the mould open.
The mean cavity pressure depends on the material and the flow length. Mean values of the typical ranges in the material guide: PP 350 bar, ABS 525 bar, PA6 605 bar, PC 750 bar. Thin-walled parts with long flow paths need more, simple thick-walled parts less.
What happens with too little clamping force?
If the clamping force is too low, the parting line opens slightly and melt escapes, which causes flash. An excessive safety margin wastes machine capacity and loads the mould and tie bars.
More on the defect and its remedies: Injection moulding defects: causes and remedies.
Frequently asked questions
How do you calculate the clamping force?
Clamping force = projected area × mean cavity pressure × number of cavities, plus a safety margin. With the area in mm² and the pressure in bar, multiply by 0.1 to get the force in N.
What is the projected area?
The area of one moulded part seen in the clamping direction, that is perpendicular to the parting plane. It is entered per cavity and multiplied by the number of cavities; a cold runner is added to A where relevant.
How do I convert kN to tonnes?
1 t of clamping force equals about 9.81 kN, so 1,000 kN is roughly 102 t. The calculator shows both units.
How large should the safety margin be?
The calculator starts with 15 %. In practice the margin depends on the mould, the sealing area and the process; change the value in the calculator to suit your case.
Which machine suits the mould?
Besides clamping force, shot weight, tie-bar spacing, mould height and cycle time matter. ResiCheck in the app checks everything together and creates a PDF report.
Every calculator in your pocket.
The calculators are free. Everything else with Resinovo Basic: try it free for a week, then from €2.99 a month. On iPhone, iPad and Android.