Key Points 1: Minimum bending radius
Definition: 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 requests and should be enlarged as much as possible under normal circumstances.
The following table gives a series of minimum bending radii of a series of common sheet metal materials with different thicknesses.
Table of Minimum Bending Radius
| Thickness (mm) | 1 | 2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 |
| Materials | |||||||||
| Q195 | 2 | 2 | × | × | × | × | × | × | × |
| Q235 | × | × | 5 | 5 | 5 | 10 | 10 | 10 | 15 |
| Q345 | × | × | 5 | 5 | 10 | 10 | 10 | 15 | 15 |
| Commonly used aluminum alloy sheet | 2 | 2 | 2 | 5 | 5 | 5 | × | × | × |
Key Points 2: Minimum Bending Height
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.
As shown in the left figure, when bending at a right angle the smallest bending height follows the formula: Hmin = R+2T
Special Requirements of The Bending Height: If the design needs to bend the bending height H ≤ R + 2T, the first thing that 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 the left figure.
Height of the straight edge of the bent side with beveled corners: When bending a bent piece with beveled side edges, as shown in the left figure. The minimum height of the side edges follows the formula: Hmin = (2～4) T > 3mm
Key Points 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. See the table below for the distance between the hole edge and the inner surface of the flange:
| T (mm) | S (mm) |
| ≤2 | s≥t＋r |
| ＞2 | s≥1.5t＋r |
| T (mm) | S (mm) |
| ≤25 | s≥2t＋2 |
| ＞25-50 | s≥2.5t＋2 |
| ＞50 | s≥3t＋r |
Key Points 4: Position Of The Bending Line
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. Shown in figure 1 below
Or punching process holes or grooves to separate the deformation zone from the non-deformation. Shown in figure 2\3 below
Note the size requirements: S ≥ R; slot width k ≥ t; slot depth L ≥ t + R + k / 2.
When the hole is located in the bending deformation zone, the process measures to be taken before bending are shown in the figure below:
Key Points 5: Bent parts should be designed to set the process of 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 the figure below.
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.
Further Reading
The bending length of sheet metal workpieces has nothing to do with the length of the bending machine. It is mainly related to the V-groove and the bending tool. Usually, the width of the V-groove is 5 times the thickness of the sheet, which means that the bending line to the top of the sheet must be at least 5 times. If the V-groove is too small, the bending coefficient will change. In addition, the V-groove is overstressed, which will affect life.
5 Points To Judge Whether A Sheet Metal Workpiece Can Be Bent
But whether the sheet metal workpieces can be folded is not only just to judge whether the bending length is too short, but also pay attention to the following points:
- Points 1#: Whether the longitudinal direction exceeds the longest bending limit of the rear top gauge
- Points 2#: Whether the transverse direction exceeds the longest length of the bending machine
- Points 3#: Will the U-shaped sheet metal workpiece’s second knife product hit the top of the knife or machine?
- Points 4#: Fold the two sides of the box-shaped sheet metal workpiece well, and will the product hit the top when the other two sides are folded
- Points 5#: Will the protruding part near the bending line be pressed during bending?
We can also simulate the bent sheet metal parts according to the bending sequence in the CAD drawings of the upper and lower dies shown in the figure below:
