In recent years, press brakes have been widely used in various industries, and the range of their applications is expanding. However, there has not been a systematic discussion on the calculation of bending force. In this article, we will start with the original calculation formula for bending force and provide a detailed explanation.
Calculation of Bending Force in Press Brakes
Bending Force Calculation Formula:
F: Bending force, in Newtons (N)
Rm: Material tensile strength, in Newtons per square millimeter (N/mm²)
t: Material thickness, referring to the thickness of the sheet metal to be bent, in millimeters (mm)
V: Die opening, in millimeters (mm)
L: Length of the material to be bent, in millimeters (mm)
Common material tensile strengths:
Tensile strength is the critical value at which a metal transitions from uniform plastic deformation to localized plastic deformation. It represents the maximum load-bearing capacity of the metal under static tensile conditions. Tensile strength reflects the resistance of the material to maximum uniform plastic deformation. Before reaching the maximum tensile stress, the deformation of the tensile specimen is uniform and consistent. However, beyond this point, the metal begins to exhibit necking, which indicates localized deformation. For brittle materials with little or no uniform plastic deformation, tensile strength reflects the material's resistance to fracture. It can also be understood as the maximum stress value before the steel fractures under tension, known as ultimate strength or tensile strength. The symbol for tensile strength is Rm (in the old national standard GB/T228-1987, the symbol for tensile strength is σb), and the unit is Megapascals (MPa) (Note: N/mm² = MPa).
Aluminum (AL): 200-300 N/mm²
Q235: 370-500 N/mm² (low carbon steel, typically 450 N/mm²)
Q345B: 450-630 N/mm² (carbon alloy steel)
Stainless Steel (SS): 650-700 N/mm²
Rules for Die Opening Selection:
Die opening refers to the width of the die slot in the press brake tooling. It is generally related to the material thickness. Based on market requirements, the following data has been summarized: for sheet thicknesses of 0-3mm, the die opening width (V) of the press brake tooling is V = t * 6, and for precision bending, it can be narrowed down to 4 times the material thickness. For sheet thicknesses of 3-10mm, the die opening width (V) is V = t * 8. For sheet thicknesses above 10mm, the die opening width (V) is V = t * 12, as shown in the table below.
Rules for Die Opening Selection
Minimum Allowed Bend Length:
During the bending deformation process, the material on the inner side of the bending radius is compressed, while the material on the outer side is stretched. The material that maintains its original length forms an arc distribution, which represents the neutral line in the material mechanics. This line is used to calculate the flat length. It cannot exceed half of the geometric shape of the plate thickness.
Minimum Allowed Bend Length
Example Calculation:
Material: Q345B, Material Thickness: 20mm, Bending Length: 7500mm.
Example Calculation
Common Simplified Formulas:
In practical production, most bending materials are low carbon steel (420MPa) with a thickness of 3-8mm. Therefore, we can simplify the formulas as follows:
Common Simplified Formulas
After simplification, the value of t is taken in millimeters (mm), and the value of L is taken in meters (m). The result is given in tons.
For example, if we need to bend a 2.8mm thick low carbon steel plate with a length of 2.5m, how many tons of force are required?
F = 8 * 2.8 * 2.5 = 56 tons
Note: The above formulas are only suitable for rough estimation.
Comparison Table of Bending Forces in Free Bending:
The data in this table is calculated based on a 90° bend, material tensile strength (Rm) of 420MPa, and a bending length of 1m.
Comparison Table of Bending Forces in Free Bending
