How to calculate the projected area of an injection mold?

Calculating the Projected Area of an Injection Mold

The projected area is the area of the molded part (and runners/gates) as seen from the direction of the clamping force — essentially the shadow the part casts when viewed from above (along the mold opening axis).

The Basic Formula

A_projected = Length × Width

of the part's silhouette perpendicular to the parting line direction.

What to Include in the Projected Area

Why It Matters — Clamping Force

The projected area is used to calculate the required clamping force:

F_clamp = A_projected × P_cavity

• F_clamp = clamping force (tonnes or kN)

• A_projected = total projected area (cm² or in²)

• P_cavity = cavity pressure (typically 300–500 kg/cm² or 4,000–7,000 psi depending on material)

Step-by-Step Example

Part: 200mm × 150mm rectangle, 4-cavity mold, with a runner system adding ~30 cm²

1. Single cavity area: 20 cm × 15 cm = 300 cm²

2. 4 cavities: 300 × 4 = 1,200 cm²

3. Add runners: 1,200 + 30 = 1,230 cm²

4. Clamping force (using 400 kg/cm² for ABS):

• 1,230 × 400 = 492,000 kg ≈ 492 tonnes

• So you'd select a machine rated at least 550 tonnes (add ~10–15% safety margin)

Tips

• Complex shapes: Use CAD software to extract the projected area accurately — don't estimate for irregular geometries

• Safety margin: Always add 10–20% to your calculated clamping force

• Material matters: Higher-viscosity materials (PC, POM) need higher cavity pressures than polyethylene or polypropylene

• Thin walls: Increase assumed cavity pressure as thin walls require higher injection pressure

For critical tooling decisions, always validate with mold flow simulation software (e.g., Moldex3D, Autodesk Moldflow).