Hole Flanging Coefficients: Your Guide to Accurate Calculations

The degree of deformation in flanging or flanging operations is commonly represented by the flanging coefficient, which is calculated using the following formula:

In the formula:

• K-the flanging coefficient;
• D₀ – the pre-punched hole diameter in millimeters (mm);
• d – the average diameter of the straight edge after flanging (mm).

The higher the value of K, the less deformation occurs; conversely, the lower the value of K, the greater the deformation.

The primary factors affecting the flanging coefficient are as follows:

1. The properties of the material; the better the plasticity, the smaller the K value can be.

2. The relative diameter of the pre-punched hole, t/D₀; the smaller the t/D₀ value, the larger the K value.

3. The method of hole processing; drilled holes, due to the absence of a tear surface, are less likely to crack during flanging. Punched holes, having some tear surfaces, are prone to cracking, thus requiring a larger K value. If the material is annealed after punching or if the hole is finished, a flanging ratio close to that of drilled holes can be achieved.

Additionally, reversing the direction of the punching relative to the flanging direction, with the burrs located on the inside of the flange, can reduce cracking, as shown in Figure 5-4.

4. When using a spherical, parabolic, or conical punch for piercing, the edges of the hole are smoothly and gradually flared, reducing the K-factor and increasing the degree of deformation. The limit piercing coefficient for low carbon steel is shown in Table 5-1, and the piercing coefficients for various materials are listed in Table 5-2.

5-1 The ultimate piercing coefficient for low-carbon steel.

5-2 Various Materials’ Flanging Ratios