Tool Name: Sheet Metal Bending Force & Tonnage Calculator | Provider: Hindustan Hydraulics | Application: Industrial Press Brake Tonnage Estimation
Engineering Overview: Mechanics of Bending Force Calculation
The Hindustan Hydraulics Sheet Metal Tonnage Calculator is a precision engineering tool developed for fabricators, design engineers, and shop-floor machine operators to calculate the precise bending force required to air-bend mild steel, stainless steel, and aluminium sheet metal on industrial CNC press brakes. Accurate tonnage calculation is essential to ensure that the selected press brake possesses adequate forming capacity while preventing structural overloading of press brake frames, hydraulic cylinders, and precision tooling.
The Air-Bending Tonnage Formula
In standard air bending, bending force per linear metre is calculated using the established engineering formula:
F = (k × σb × L × t²) / V
where:
- F: Required bending force in kilonewtons (kN) or metric tons (1 metric ton ≈ 9.81 kN).
- k: Empirical process and tooling coefficient, typically 1.33 to 1.42 for standard precision ground 88° or 85° air-bending punches and dies.
- σb: Ultimate tensile strength of the sheet metal in N/mm² (or MPa). Standard values include: Mild Steel IS 2062 / CRCA ≈ 420–450 N/mm²; Stainless Steel AISI 304 / 316 ≈ 600–700 N/mm²; Aluminium Alloy 5052-H32 ≈ 210–230 N/mm².
- L: Bending length in millimetres (mm) along the bend line.
- t: Sheet thickness in millimetres (mm). Note that bending force scales with thickness squared (t²), meaning doubling sheet thickness quadruples required forming tonnage.
- V: Bottom die V-opening width in millimetres (mm).
Bottom V-Die Opening Selection Guidelines
Selecting the correct bottom V-die opening width is critical for controlling both required tonnage and inside bend radius (Ri):
- Sheet thickness t ≤ 2.5 mm: Optimal die opening is
V ≈ 6 × t to 8 × t. Resulting natural inside bend radius is approximately Ri ≈ (5/32) × V ≈ 0.16 × V.
- Sheet thickness 3.0 mm ≤ t ≤ 8.0 mm: Optimal die opening is
V ≈ 8 × t to 10 × t, providing a smooth bend without surface fracturing.
- Heavy plate t ≥ 9.0 mm or High-Tensile Steels: For heavy plate formed on our Griffon Series or Hardox wear plates, V-openings must be expanded to
V ≈ 10 × t to 14 × t to reduce peak tonnage and prevent cracking along the outer tensile zone.
Tonnage Sizing Safety Margins
Continuous production operations should never operate a press brake at 100% rated tonnage. Hindustan Hydraulics recommends operating at 75% to 80% of machine rated capacity to accommodate tensile strength variances between material batches, slight sheet thickness tolerances, and work-hardening effects during multi-bend sequences.
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