Blanking force is the load required to shear material around a cut perimeter. A first estimate can help compare a part with press capacity, but the estimate depends on the perimeter, sheet thickness, material strength, and how the die engages the sheet. The coefficient shown below is a source-specific approximation for cases where shear resistance is not known. It is not a universal constant for every alloy or die condition.

Sheet Metal Blanking Force Coefficients

Choose the correct equation

MISUMI gives the direct relationship P = L × t × S, where P is force in kilogram-force, L is the forming circumference in millimetres, t is plate thickness in millimetres, and S is shear resistance in kilogram-force per square millimetre. If the shear resistance is difficult to obtain, its tutorial substitutes 80% of tensile strength and writes the estimate as P = K × L × t × Ts, with K = 0.8. Preserve the units as written or convert the complete calculation consistently.

The coefficient connects an assumed shear resistance to tensile strength. It does not change the geometry terms. A longer cut perimeter increases estimated force directly; doubling thickness or the assumed tensile strength also doubles the estimate. This linear relationship is useful for a first screening calculation, but actual peak load depends on the punch and die, edge condition, material, and position through the stroke.

Read the example as an estimate

The table uses an illustrative 100 mm perimeter, 1 mm sheet, and 30 kgf/mm² tensile-strength assumption for SPCC. Applying 0.8 gives 2,400 kgf, or about 23.54 kN. The perimeter is a stated example input, not a value from a production drawing. Replace it with the actual total cut length and use a tensile-strength value supported by the material specification. If the material is supplied with a range, evaluate the appropriate upper bound for preliminary equipment checks.

Do not confuse perimeter with the width or diameter of a feature. For a profile containing several cutouts, include each sheared edge that is engaged at the same time. Where the die uses staged cutting, the load distribution may differ from a single simultaneous cut. The die designer should establish which perimeter contributes to the peak load for the actual operation.

Shear angle and press capacity

MISUMI notes that a shearing angle can reduce blanking force, and its tutorial describes about a 30% reduction when the angle height is approximately equal to sheet thickness. Treat that as source guidance for the illustrated arrangement, not a guaranteed reduction for every die. A shear angle may also affect part flatness, scrap behavior, side thrust, tool loading, and the timing of the peak force.

Press selection requires more than comparing one force number with the rated tonnage. Check where in the slide stroke the press delivers its rated force, the energy available, eccentric loading, shut height, bed and bolster limits, stripping and return forces, and the die’s structural capacity. Include a suitable design allowance according to the press and tooling supplier’s method. A calculated blanking force does not establish that the operation is safe or suitable for a particular machine.

Confirm the production inputs

Before using an estimate, confirm the material grade and condition, thickness tolerance, tensile data, cut perimeter, clearance, punch condition, and whether the cut is blanking or piercing. Evaluate the most demanding sheet and tool condition expected in production. Record the source and assumptions alongside the result so another engineer can reproduce the estimate.

If the job includes multiple stations, consider whether several cuts occur at once and whether their loads overlap. For a progressive die, a station-by-station load estimate can reveal the total slide load and possible imbalance. If the estimate is close to a machine limit, consult the press manufacturer and die designer rather than relying on a rounded conversion or a generic coefficient.

References

• MISUMI Press Dies Tutorial #124: Blanking Force

This reference is a preliminary force-estimation aid. Validate the material properties, complete die load, press rating at the operating position, and tooling design for the real operation.