Sheet Metal Cutting Force Calculation (Based on Hydraulic Guillotine)

Comparison of Rotary Plate Shears and Ordinary Plate Shears

Blade Design and Shearing Process

Compared to ordinary plate shears, most rotary plate shears adopt an oblique blade design. This design is advantageous because it allows for a more efficient shearing process. The oblique blade reduces the shearing force required and minimizes the deformation of the sheet metal.

Advantages of Rotary Plate Shears

Rotary plate shears are widely used in the industry due to several key benefits:

• Simple Structure: The design of rotary plate shears is straightforward, which simplifies maintenance and operation.
• Low Failure Rate: The simplicity of the structure contributes to a lower likelihood of mechanical failure.
• High Efficiency: The oblique blade design enhances the efficiency of the shearing process.
• Minimal Sheet Deformation: Sheets processed by rotary plate shears do not experience bowing, warping, or distortion, which is crucial for maintaining the quality of the final product.

Shearing Mechanism

In the shearing process, the blade support of the swing beam shearing machine undergoes a rotary motion. This rotary motion is essential as it changes the cutting angle and shear clearance of the blade during the process. The varying cutting angle and shear clearance help in achieving a clean and precise cut.

Design Considerations and Challenges

One of the challenges in the design of rotary shears is the calculation of the sheet metal cutting force. The current design methodology often calculates the cutting force based on the assumption of straight motion of the blade support. However, in reality, the blade support undergoes rotary motion. This discrepancy can lead to inaccurate calculations of cutting force, resulting in design size deviations and potentially affecting the normal performance of the machine.

Cutting Force Calculation

The cutting force calculation for inclined blade shear with blade support in straight motion primarily uses the Norshari Formula, developed by a former Soviet scholar. This formula is crucial for determining the force required in the shearing process, particularly for machines with straight-moving blade supports.

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 – Respectively refer to bending force coefficient, cutting blade sidewise clearance relative value, press material coefficient.

Limitations of the Norshari Formula

The Norshari Formula does not account for the changing shear relief angle during the shearing process and assumes a fixed shear clearance. Consequently, it is only applicable to shears with blade support that moves in a straight motion.

Shear Relief Angle and Shear Clearance

During the shearing process, the relief angle can vary within the range of γ±β. The quality of the plate shear and the force required are highly sensitive to the shear clearance. A larger shear gap increases the proportion of the pulling function, leading to poorer shear quality. For medium thickness plate cutting, the shear clearance should ideally be controlled between 8% to 12%.

Rotary Shearing Machines

For rotary shearing machines, achieving the required γ±β is challenging due to the simplified blade installation process. When the shear gap exceeds the experienced value, it leads to a change in shear force. An increase in shear clearance results in a higher relative value of shear sidewise clearance, thereby increasing the force required for shearing.

Impact of Pulling Function

A prominent pulling function during the cutting process increases shear force and power loss, causes plastic deformation of the plate, increases friction between the blade and plate, and reduces the cutter’s service life. Therefore, when calculating the cutting force for rotary shearing machines, it is recommended to choose a higher relative value of shear blade sidewise clearance and a higher blade dulling coefficient.

Practical Calculation Example

The calculation of shear force for a shearing machine typically uses a technical formula. Most calculations are based on ordinary Q235 steel plates, with conversion factors for different materials:

• Q235 Steel Plate: Conversion factor = 1
• Q345 Steel Plate: Conversion factor = 1.4
• 304 Stainless Steel: Conversion factor = 2

Example Calculation

For a 10mm thick and 6000mm long Q235 steel plate:
Shear Force=10×6000×23.5=1410000 N=141 Tons

For a Q345 steel plate:
Shear Force=141×1.4=197.4 Tons

For a 304 stainless steel plate:
Shear Force=141×2=282 Tons