Sheet metal bending is a stamping process that uses pressure to force the material to produce plastic deformation, thereby forming a shape with a certain angle and curvature. Commonly used bending includes V-shaped bending, Z-shaped bending, and anti-bending pressure equalization.
The bending height is at least 2 times the thickness of the sheet metal plus the bending radius, that is, H≥2t+R, as shown in the figure. If the bending height is too low, the sheet metal is easily deformed and twisted when bending, and it is not easy to obtain the ideal part shape and ideal dimensional accuracy.
When the bend is a hypotenuse, it is most prone to bend distortion due to too small a bending height. As shown in the figure, in the original design, because the leftmost bending height is too small, it is easy to be twisted and deformed during bending, resulting in low bending quality. In the improved design, the left bending height can be increased or remove the part with a smaller bending height.
In order to ensure the bending strength, the bending radius of the sheet metal should be greater than the minimum bending radius of the material. The minimum bending radius R of various commonly used sheet metal materials is shown in the table, where t is the thickness of the sheet metal.
|Low carbon steel |
Low alloy steel
Of course, the bending radius of sheet metal is not as big as possible. The larger the bending radius, the greater the bending rebound, and the harder it is to control the bending angle and bending height. Therefore, the sheet metal bending radius needs to be reasonably valued.
Sheet metal mold manufacturers tend to have a bending radius of 0 so that the radius is not easy to rebound after bending, and the size of the bending height and the bending angle is easier to control.
However, bending with a bending radius of zero can easily cause external cracking or even breaking of the sheet metal bending. At the same time, the sheet metal bending strength is relatively low, especially for harder sheet metal materials, and the mold on the mold after a period of production The right angle will gradually become smoother, and the bending size will become difficult to control.
In order to reduce the bending force and ensure the bending size, another method adopted by the sheet metal mold manufacturer is to increase the crimping process before the bending process. Of course, such a design will cause the sheet metal bending strength to be relatively low and easy to break and other defects.
When the sheet metal is bent, it should be as perpendicular to the fiber direction of the metal material as possible. When the sheet metal is bent parallel to the fiber direction of the metal material, cracks are easily generated at the sheet metal bending, and the bending strength is low, and cracks are prone to occur.
Avoid Bending Failure Due to Inability to Press The Material at The Root
When the sheet metal is bent, it is often because other features are too close to the sheet metal part, which results in the inability to press the material and cannot be bent or the bending is severely deformed. Generally speaking, at least 2 times the thickness of the sheet metal must be guaranteed above the root of the sheet metal bending. In addition to the distance of the bending radius, there are no other features that block the pressing of the sheet metal during bending.
In the original design, as shown in the figure below, the reflexed flattening position is too close to the root of the sheet metal bending, causing the sheet metal to be bent and the material cannot be pressed and the bending fails; in the original design, as shown in the lower part of the figure, the sheet metal is pulled too close Bending the roots makes the bending impossible.
At this time, you can move the extraction to a position far away from the sheet metal root. If the extraction and bending positions cannot be moved due to design requirements, you can bend the root corresponding to the extraction Add a process cut to ensure smooth bend.
Ensure Bending Gap 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 motion of sheet metal bending to avoid interference during bending and cause bending failure. See below.
As shown in the above figure, the bending sequence of the parts is that the upper side is bent first, and the right side is bent second. In the original design, there is no gap between the two bends. When the upper side is bent, the right side is bent again, Due to the existence of sheet metal bending tolerances, it is likely that the right side will interfere with the upper side during the bending process. In the improved design, at least a 0.2mm gap between the right side and the upper side can be effectively avoided.
Ensure Bending Strength
Sheet metal bending needs to ensure bending strength. The long and narrow bending strength is low, and the short and wide bending strength is high. Therefore, the sheet metal bending should be attached to the longer side as much as possible, as shown in the figure, the same function. For bending, in the original design, the bending strength is low because the bending is attached to the shorter side, and the improved design is bending attached to the longer side and the bending strength is high.
Reduce Sheet Metal Bending Process
The more sheet metal bending processes, the higher the mold cost, and the lower the bending accuracy. Therefore, the sheet metal design should minimize the bending process. As shown in the figure, the sheet metal in the original design requires two bending processes. In the improved design, Sheet metal only needs one bending process to complete two bends at the same time.
- Short side first, long side first: Generally speaking, when all four sides are bent, folding the short side first and then the long side is beneficial to the processing of the workpiece and the assembly of the bending mold.
- Peripheral first, then middle: Under normal circumstances, it is usually bent from the periphery of the workpiece to the center of the workpiece.
- Partial first and then whole: If there are structures inside or outside the workpiece that are different from other bending structures, generally these structures are bent first and then other parts are bent.
- Consider the interference situation and arrange the bending sequence reasonably: the bending sequence is not static, and the processing sequence should be adjusted appropriately according to the bending shape or obstacles on the workpiece.
Avoid Complicated Bends
Similarly, the more complex the sheet metal bending process, the higher the mold cost, the lower the bending accuracy, and the complex mold bending may cause a waste of parts and materials. Therefore, when the sheet metal part has a complex structure, it can be considered to split the complex bending part into multiple parts, which will help the cost and improve the product quality.
How to Avoid The Deviation of Sheet Metal Bending Angle And Size
- The left and right molds are not aligned with each other, which will cause deviations in the bending dimensions. Before bending, the centering adjustment of the left and right molds’ CNC blades must be carried out.
- After the upper and lower parts of the back stop are moved, the relative position of the plate and the upper die is likely to change, which will damage the bending size. The distance between the back stop parts must be measured again before bending.
- Insufficient flatness of the product workpiece and the upper die will cause the bending resilience and endanger the bending angle. The flatness must be accurately measured and adjusted before bending.
- When the primary bending angle is not enough, the secondary bending will also suffer damage. The accumulation of bending deviation will increase the forming size and angle deviation of the product workpiece. Therefore, it is very important to ensure the accuracy of single-sided bending.
- When bending, the size of the upper die V port is inversely proportional to the bending working pressure. When producing and processing different thin and thick metal sheet materials, you must select a suitable down die V groove according to the regulations, generally choosing the thickness of 6~8 Times more suitable.
- When bending the product workpiece after grooving, in order to better avoid knife clamping, the angle of the lower die is controlled at 84.
How to Avoid Sheet Metal Bending Indentation
- Causes of indentation
Most bending machines use V-shaped molds, the left picture is before bending, the right picture is in bending.
Points A and B are the stress points of the sheet, and creases usually appear at points A and B. When bending, the upper die falls, and the plate slides along two points A and B. L is the sliding range, which is also the place where indentation is most likely to occur. If the manufacturer adopts a coating method to avoid indentation, the protective film is easy to rupture as the bending pressure changes. Once the protective film is broken, the indentation will occur.
Roller type V mold
The main working principle of this kind of mold is that the upper mold falls, the rotating shaft rotates, and the flip plate is turned over. It is precise because of the turning plate that the workpiece is in full contact with the lower mold without any sliding range, which avoids indentation.
Replaceable rubber strip V mold
The principle of the mold is to open a gap on both sides of the common V-shaped mold and insert a rubber strip in this gap. During the bending process, the sheet is in contact with the rubber strip. The hardness of the rubber strip is much lower than that of the ordinary lower mold, so as to avoid indentation.
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