How to Do Sheet Metal Bending Well

1. Bending height

The Bending height of the sheet metal should be at least twice the thickness of the sheet metal plus the bending radius, i.e. H>2t R. The bending height of sheet metal is too low, and it is easy to deform and deform during bending, making it difficult to obtain the ideal shape and size.

When the bending is inclined, it is most likely to cause bending deformation due to the small bending height. As shown in the figure, in the original design, due to the small height of the leftmost bend, distortion and deformation are prone to occur during bending, resulting in low bending quality. In the improved design, the left bending height can be increased or the smaller part of the bending height can be removed, so that the sheet metal will not deform during bending and the bending quality is high.

2. Bending radius

To ensure bending strength, the bending radius should be greater than the minimum bending radius of the material, as shown in the following figure:

The original improved bending radius design of sheet metal is shown in the following figure:

The larger the bending radius of sheet metal, the better. The larger the bending rebound, the more difficult it is to control the bending angle and height. Therefore, a reasonable value is required for the bending radius of sheet metal.

Sheet metal mold manufacturers tend to have a bending radius of 0, so it is not easy to rebound after bending, and the dimensions of bending height and angle are easier to control. However, zero bending radius can easily lead to external cracking or even fracture of sheet metal bending, and the bending strength of sheet metal is relatively low, especially for hard sheet metal materials. After a period of time, the right angles on the mold gradually become smooth, making it difficult to control the bending size.

Another method adopted by sheet metal mold manufacturers to reduce bending force and ensure bending dimensions is to add a pressing process before the bending process. Of course, this design will result in relatively low bending strength of sheet metal and easy fracture.

The wire pressing process is a Stamping process that forces local extrusion of materials, extruding grooves on sheet metal, which is beneficial for bending and ensures bending accuracy.

3. Bending direction

The bending of sheet metal should be as perpendicular as possible to the direction of the metal fibers. When the bending of the sheet metal is parallel to the direction of the metal fibers, cracks are prone to occur at the bending point of the sheet metal, resulting in low strength and easy fracture.

4. Avoid bending failure due to no pressure at the root of the bend

When bending sheet metal, due to other characteristics that are too close to the root of the sheet metal bending, the material is often unable to be compressed, bent or severely deformed. Generally speaking, at least twice the thickness of the metal plate should be ensured above the bending root, and there are no other characteristics between the bending radii to prevent the metal plate from bending.

As shown in the figure below, in the original design, the reverse bending position was too close to the bending root of the sheet metal, resulting in the failure of the sheet metal bending. As shown in the figure below, the sheet metal teeth were too close to the bending root, causing bending. The teeth can be moved away from the sheet metal root. If due to design requirements, the teeth and bending position cannot be moved, a process incision can be added at the corresponding bending root to ensure smooth bending.

5. Ensure bending clearance and avoid bending interference

Due to the existence of sheet metal bending tolerances, it is necessary to ensure a certain bending gap in the direction of movement of sheet metal bending to avoid bending failure caused by interference during the bending process.

As shown in the above figure, the bending sequence of the parts is to first bend on the upper side and then bend on the right side. In the original design, there was no gap between the two bends. When the upper side bending is completed and the right side bending is completed, due to the existence of sheet metal bending tolerance, it is likely to interfere with the right and upper sides during the bending process. In the improved design, at least a 0.2mm gap between the right and upper sides is retained to effectively avoid interference.

6. Ensure bending strength

Sheet metal bending needs to ensure bending strength. The bending strength of the long and narrow parts is low, while the bending strength of the short and wide parts is high. Therefore, sheet metal bending should adhere to the longer edges as much as possible, as shown in the figure. The bending function is the same. The original design has low bending strength because the bending adheres to the shorter edges. The improved design has high bending strength because the bending adheres to the longer edges.

7. Reduce bending process

The more sheet metal bending processes there are, the higher the mold cost and the lower the bending accuracy. Therefore, sheet metal design should minimize the bending process as much as possible. As shown in the figure, sheet metal requires two bending processes in the original design. In the improved design, sheet metal only requires one bending process to complete two bends simultaneously.

8. Avoid complex bending

The more complex the sheet metal bending process, the higher the mold cost, and the lower the bending accuracy. Complex bending may cause waste of part materials. Therefore, when sheet metal bending is complex, it can be considered to divide the complex bending into two parts through rivets, self riveting, or spot welding.

9. Multiple bending holes are difficult to align

Sheet metal bending has a large tolerance, especially in multiple bends where the accumulation of tolerance makes it difficult to align holes.

The more times the sheet metal is bent, the greater the bending tolerance. The multiple bending of sheet metal makes it difficult to ensure dimensional accuracy, which is also the reason why the screw holes, rivet holes, and self riveting holes on sheet metal bending are difficult to align.

Solution:

Design the holes on the bend as large or elongated holes to increase the tolerance.

Add two internal positioning holes, add internal positioning to the mold, reduce the tolerance during sheet metal bending, and ensure the alignment of the two bending holes.

Bending before punching can ensure the dimensional accuracy of the two holes, but it is generally not recommended to increase the complexity and cost of the Stamping mold.