Bend radius and K factor calculation
Flux calculates K factor and actual radius (RA) for a bend line with thickness of 1.5mm and design radius at 90° (RD) of 2.1mm as below:
Interior angle in ° |
Inner bend radius (RA) in mm |
K-Factor |
90 |
1.92 |
0.394 |
60 |
1.46 |
0.38 |
135 |
4.45 |
0.498 |
Let us see how we arrive at the above values.
For a given dxf file, V width is suggested based on thickness, radius (RD) and interior angle.
Deciding V width if not specified
First for given thickness, V width range is selected
Up to thickness in mm |
V width range in mm |
0.875 |
4 - 14 |
1.125 |
5 - 18 |
1.375 |
6 - 22 |
1.625 |
7 - 22 |
1.875 |
7 - 27 |
2.25 |
9 - 27 |
2.75 |
11 - 35 |
3.25 |
15 - 45 |
3.75 |
15 - 55 |
4.25 |
19 - 65 |
4.75 |
19 - 75 |
5.5 |
28 - 85 |
6.5 |
28 - 95 |
7.5 |
37 - 110 |
9 |
47 - 120 |
11 |
57 - 120 |
1e99 |
67 - 120 |
After the V width range is decided, V width is fine-tuned based on radius using table below.
Bend radius (RD) at 90° in mm |
V width in mm |
1 |
6 |
1.3 |
8 |
1.6 |
10 |
1.9 |
12 |
2.6 |
16 |
3.2 |
20 |
3.8 |
24 |
4.8 |
30 |
6.4 |
40 |
8 |
50 |
9.6 |
60 |
11 |
70 |
13 |
80 |
14 |
90 |
16 |
100 |
19 |
120 |
Example
Let us take the example, where thickness is 1.5mm, desired radius (RD) is 2.1mm and interior angle of 90°.
From the table, V width range is 7-22mm and desired V width based on RD(2.1mm) is 12mm.
Note: If die is suggested in geo file, above step is skipped.
Now, based on thickness, V width and interior angle, bend radius and deduction are computed.
Bend radius computation
For Trumpf machines, TBS is used to compute bend radius (RA).
From given V width, actual radius at 90° (RA) is computed by multiplying constant 0.16 with V width.
So, for the given Example,
RA = 0.16 * 12 = 1.92mm
For angles other than 90°, radius is computed as below.
Angle less than 90°
For a given angle 45° radius factor is computed using interpolation.
radius factor = interpolated radius (RI) / calculated radius at 90° (RC90)
RI = interpolation between the punch tip radius and the effective radius at 90° (RC90)
= Punch tip radius * (1 - interpolation lie) + calculated radius at 90° * interpolation lie
Punch tip radius is 1mm for the given thickness 1.5mm, calculated using below table.
For angle 45°, the interpolation lie between 30° and 90° is
interpolation lie = (45 - 30) / (90 - 30) = 0.25
RC90 = 1.92,
so applying these,
RI = 1 * (1 - 0.25) + 1.92 * 0.25 = 1.23
∴ radius factor = 1.23 / 1.92 = 0.640625
∴ actual radius at 45° (RA) = RA90 * radius factor
= 1.92 * 0.640625
= 1.23
Punch radius calculation based on thickness
Up to Thickness in mm |
Punch tip radius in mm |
0.95 |
0.5 |
6.34 |
1 |
1e99 |
4 |
Calculated radius (RC90) based on thickness
From the thickness, V width is computed from the table below:
Thickness in mm |
V width in mm |
0.75 |
6 |
1 |
8 |
1.25 |
10 |
1.5 |
12 |
1.75 |
12 |
2 |
16 |
2.5 |
20 |
3 |
24 |
3.5 |
30 |
4 |
30 |
4.5 |
40 |
5 |
40 |
6 |
50 |
7 |
60 |
8 |
70 |
10 |
80 |
12 |
90 |
Then, for the Example,
calculated radius (RC90) = 0.16 * V width = 0.16 * 12 = 1.92mm
Angle greater than 90°
Based on angle, a radius factor is decided from the table below:
Angle in degree |
Factor |
90 |
1 |
105 |
1.25 |
120 |
1.93 |
135 |
2.32 |
150 |
3.98 |
157 |
5.22 |
169 |
11.19 |
175 |
25 |
In the above Example, if the interior angle is 135°, inner bend radius (RA) is calculated by multiplying radius factor 2.32 with actual radius at 90° (RA90). Thus,
RA = radius factor * RA90 = 2.32 * 1.92 = 4.45mm
K factor computation
For Trumpf machines, TBS is used to compute bend deduction and from that K factor is calculated.
Based on K factor table in Material settings (Database → Material)
K factor is computed and from that bend deduction is computed.
See below for sample table:
Ratio (Inner radius / Thickness) |
K-Factor |
1 |
0.38 |
2 |
0.43 |
3 |
0.5 |
In the Example, inner radius for 90° is 1.92mm and thickness is 1.5mm. So the ratio is 1.28.
We have to now compute K factor for 1.28 by interpolation.
Let the required intervals of K factor be Ka = 0.38 and Kb = 0.43 and the intervals of ratio be Ratioa = 1 and Ratiob = 2.
K factor = Ka * (1 - lie of the ratio) + Kb * lie of the ratio
lie of the ratio between Ratioa and Ratiob = (1.28 - Ratioa) / (Ratiob - Ratioa) = 1.28 - 1 / 2 - 1 = 0.28
∴ K factor = 0.38 * (1 - 0.28) + 0.43 * 0.28 = 0.394