Compared with ordinary plate shears, most rotary plate shears adopt an oblique blade.
They are widely used due to their simple structure, low failure rate, high efficiency and the fact that the sheets do not bow, warp or distort after shearing.
In the shearing process, the blade support of the swing beam cutting machine undergoes rotary movement, which changes the cutting angle and shear clearance of the blade during the process.
However, the design of rotary shear calculates the cutting force of sheet metal based on the straight movement of the blade holder, which leads to inaccurate calculations and results in size deviation from the design, affecting the normal performance of the machine.
Cutting force calculation
The calculation of cutting force of inclined blade shear with blade support in straight motion mainly uses the former Soviet scholar's Norshari Formula:
In the cutting force formula:
- σ b – Plate tensile strength limit,N/mm;
- δ x — Plate elongation ratio;
- h—Plate Thickness, mm;
- α— Cutting angle, °;
- X、Y、Z – Refer respectively to the bending force coefficient, relative value of the side clearance of the cutting blade, pressing material coefficient.
Clearly, the change of shear relief angle during the shearing process is not taken into account in the formula, and the shear clearance is also considered as a fixed value.
Therefore, the formula is only applicable to scissors with a blade holder that moves in a straight line.
The relief angle in the shearing process can change within the range of γ±β during complete cutting. The quality and shear strength of the plate are very sensitive to the shear gap.
In the shear process, both shear and tensile functions coexist, and the larger the shear gap, the greater the proportion of tensile function, and correspondingly, the worse the shear quality.
For cutting medium thickness plates, the shear gap should be controlled between 8% to 12% based on experience.
However, it is challenging to achieve the required γ±β for rotary cutting machines that use a simplified blade installation process.
When the shear gap exceeds the experienced value, it will inevitably lead to a change in shear force.
According to formula (1), an increase in shear clearance will result in an increase in the relative value of lateral shear clearance, ultimately leading to an increase in the force required for the shearing process.
During the cutting process with prominent traction function, it not only increases the shear force and power loss, but also causes plastic deformation of the plate, increases the friction between the blade and the plate, increases the force required by the cutting machine cutting and reduces the life of the cutter.
Therefore, when calculating the cutting force of rotary cutting machines using the above formula, it is recommended to choose a higher relative value of shear blade side clearance and a higher blade bluntness coefficient to take these factors into account.
In simple terms, the shear force calculation for a cutting machine is a technical formula.
Most calculations are based on common Q235 steel plates, with a conversion factor of 1.4 for Q345 steel plates in millimeters and 2 for 304 stainless steel.
For example, if you cut a Q235 steel plate that is 10 mm thick and 6,000 mm long, the shear force would be 10 x 6,000 x 23.5 = 1,410,000 N = 141 tons.
If it were a Q345 steel plate, the shear force would be 141 x 1.4 = 197.4 tons, and if it were 304 steel, the shear force would be 141 x 2 = 282 tons.
