How to Calculate Bending Springback?

When designing a bending die with an internal arc, precision and material behavior are critical factors often overlooked in conventional approaches. Many designers either neglect springback entirely by using the same radius (R) as the finished product or apply a rudimentary reduction factor to the R value without considering the complexities of material properties and geometries.

For instance, a common practice for a product with an original R value of 1 mm involves reducing the convex mold radius by a factor of 0.8 for harder materials or 0.9 for softer materials. This simplistic approach, while sometimes effective for basic applications, lacks the nuance required for more demanding specifications.

The limitations of this method become particularly apparent when dealing with thin materials and large radii. Consider a product with a thickness of 0.5 mm and an internal radius of 200 mm. In such cases, accurately predicting springback becomes challenging due to the complex interplay between material properties, thickness-to-radius ratio, and bending angle.

To address these limitations and improve precision in die design, a more sophisticated approach is necessary. The following section introduces a universal springback formula that accounts for various material and geometric parameters, allowing for more accurate calculations based on numerical inputs. This method provides a robust foundation for die design across a wide range of applications and materials.

In the formula:

• r – workpiece fillet radius (mm):
• r1 – punch radius (mm);
• a – the central angle of the arc length of the workpiece fillet;
• a1 – the central angle of the arc length of the punch fillet;
• t – material thickness;
• E – elastic modulus of material;
• σ_s – yield point of the material.

Assuming 3σ_s/E=A as the simplification coefficient, with values listed in Table 2-27. The calculation formula for the convex die corner radius during the bending of circular section bars is as follows:

The value of A is shown in the table below.

If the necessary materials are not available above, you can also refer to the table below to find the modulus of elasticity and yield strength of the material, and then substitute them into the formula above for calculation.

It is best to establish a commonly used material database and obtain missing physical parameters from suppliers. If the parameters for elastic modulus and yield strength are correct, the bending and rebound of general spring terminals, appearance parts, and profiles are more precise.