1. Minimum bending radius
The minimum bending radius is the radius of the inner corner of the bend, under the condition that the outer fibers of the sheet are bent without cracking.
The minimum bending radius is only required on special request and should be enlarged as much as possible under normal circumstances.
The minimum bending radii for different thickness series of commonly used sheet metal materials are given in Table 1.
Table 1 Minimum bending radius
|Commonly used aluminum alloy sheet||2||2||2||5||5||5||×||×||×|
2. Minimum bending height
2.1 In order to ensure the quality of the workpiece bending, the straight edge of the bent parts should be not less than the minimum bending height.
When bending a right angle as in Figure 1, the minimum bending height as in formula (1).
hmin = r+2t·····················(1)
2.2 special requirements of the bending height:
If the design needs to bend the bending height h ≤ r + 2t, the first thing needs to do is to increase the height of the bending, then bend and process it to the required size.
After processing shallow arc grooves in the bending deformation zone, bend again, as shown in Figure 2.
2.3 Height of the straight edge of the bent side with beveled corners.
When bending a bent piece with beveled side edges, as shown in Figure 3.
The minimum height of the side edges is as in equation (2).
hmin = (2～4) t > 3mm···············(2)
3. Minimum hole margins
When there is a bending requirement after punching, the hole should be positioned outside the bending deformation zone to avoid deformation of the hole when bending.
The distance of the hole edge from the inner surface of the bent edge is shown in Table 2.
Table 2: Minimum hole margins
|t (mm)||s (mm)|
|t (mm)||s (mm)||≤25||s≥2t＋2|
4. Position of the bending line
4.1 When partially bending a section, the bending line should not be at the location of the dimensional abruptness in order to prevent bending cracks resulting from stress concentrations at the sharp corners of the dimensional abruptness.
The distance S from the mutation should be greater than the bending radius r, see Figure 4a.
Or punching process holes or grooves to separate the deformation zone from the non-deformation, see Figure 4b, 4c.
Note the size requirements of the figure: S ≥ R; slot width k ≥ t; slot depth L ≥ t + R + k / 2.
4.2 When the hole is located in the bending deformation zone, the process measures to be taken before bending is shown in Figure 5.
5. Bent parts should be designed to set the process positioning holes
In order to ensure the accurate positioning of the sheet in the die and prevent the sheet from moving during bending and waste products, the bent parts should be designed with process positioning holes, as shown in Figure 6.
Especially for the parts formed by multiple bending, the process hole must be used as the positioning reference to reduce the cumulative error and ensure product quality.