Start with the parting-plane projection
Projected area is the “shadow” of every cavity and runner on the plane normal to mold opening. Include every cavity and runner layout, not merely the nominal part footprint. KEYENCE describes total projection area as the cavities and runners in relation to the parting surface.
Clamp force = total projected area × estimated cavity pressure
Use cavity pressure, not a controller reading
Machine hydraulic or nozzle pressure is not automatically the pressure acting across the cavity projection. Flow restriction, material viscosity, gate geometry, fill rate, venting, and packing conditions change the result. Use measured cavity pressure where available; otherwise label the input as an estimate and add an explicit margin.
A practical validation sequence
- Obtain CAD projection for the complete shot, including cold-runner projection.
- Document the pressure basis, material, melt/mold temperatures, and fill/pack profile.
- Check the calculated requirement against the machine’s rated clamp force and platen/tie-bar limits.
- During trials, watch for flash, parting-line separation, and process changes; validate with cavity-pressure data where appropriate.
Why a simple rule of thumb is not enough
Rule-of-thumb tons per area can be useful for early quoting, but it cannot account for a thin flow path, a high-viscosity grade, a cosmetic fill requirement, or a changed runner layout. Treat it as a screening value and retain engineering margin.
FAQ
Should I enter machine injection pressure?
No. Use a justified cavity-pressure estimate or measured cavity pressure; controller pressure is not automatically pressure at the parting plane.
What should be included in projected area?
Every cavity and the runner projection on the parting plane. Use CAD projection for complex geometry.