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:

K=D0d

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.

Figure 5-4 Counter-direction of Piercing and Flanging
a) Piercing b) Flanging

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.

Pilot punch profileHole Machining MethodsMaterial relative thickness, d0/t
100503520151086. 5531
Spherical punchDeburr after drilling.0.700.600.520.450.400.360.330.310.300.250.20
Punch holes with a punching die.0.750.650.570.520.480.450.440.430.420.42
Cylindrical PunchDeburr after drilling.0.800.700.600.500.450.420.400.370.350.30.25
Punch holes with a punching die.0.850.750.650.600.550.520.500.500.480.47
Note: Utilizing the limit flanging coefficient from this table may result in minor cracking at the edge of the hole after flanging. If the workpiece cannot tolerate cracking, the flanging coefficient should be increased by 10% to 15%.

5-2 Various Materials’ Flanging Ratios

Annealed raw materialHole Flanging Ratio
K0Kmin
Galvanized steel sheet (white iron)0. 700. 65
Soft steelt = 0. 25 ~ 2. 0mm0. 720. 68
t =3. 0 ~ 6. 0mm0.780.75
Brass H62, thickness ranging from 0.5 to 6.0 mm0. 680. 62
Aluminum, thickness ranging from 0.5 to 5.0 mm0.70. 64
Hard aluminum alloy0. 890. 80
Titanium alloyTA1 (Cold State)0. 64 ~ 0. 680. 55
TA1 (Heated to 300-400°C)0. 40 ~ 0. 50
TA5 (Cold State)0. 85 ~ 0. 900.75
TA5 (Heated to 500-600°C)0. 70 ~ 0. 650.55
Stainless steel, high-temperature alloys0. 69 ~ 0. 650. 61 ~ 0. 57
When minor cracking is permissible in the flanging process, the minimum numerical value K may be utilized.
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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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