Author:Site Editor Publish Time: 2020-07-13 Origin:Site
Bending is a stamping process that uses pressure to force the material to plastically deform to form a certain angle and curvature shape. Commonly used bending includes V-shaped bending, Z-shaped bending, and the opposite pressure equalization.
The bending height of the sheet metal is at least twice the thickness of the sheet metal plus the bending sheet metal, that is, H≥2t+R. As shown in the following figure, the bending height of the sheet metal is too low, and the sheet metal is easily deformed and twisted during bending, not easy get the ideal part shape and ideal dimensional accuracy.
When the bend is a hypotenuse, it is most likely that the bend is distorted due to too small a bend height. As shown in the figure below, in the original design, because the leftmost bending height is too small, twisting and deformation are likely to occur during bending, resulting in low bending quality. In the improved design, the height of the left bend can be increased or the smallest part of the bending height removed. In this way, no distortion occurs when the sheet metal is bent, and the bending quality is high.
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 of various commonly used sheet metal materials is shown in the following table:
Of course, the bending radius of the sheet metal is not as large as possible. The larger the bending radius, the greater the bending rebound and the less easy to control the bending angle and bending height. Therefore, the sheet metal radius needs to be reasonable. In addition, sheet metal mold manufacturers tend to have a bending radius of zero, so that it is not easy to rebound after bending, and the size of the bending height and bending angle is relatively easy to control. However, a bend with a bending radius of zero is likely to cause external fracture of the sheet metal bend. The bending strength of sheet metal is relatively low. After a period of production, the right angle on the mold will gradually become smooth 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 sheet metal mold manufacturers is to add a crimping process before the bending process. As shown in the figure below, this design also causes defects such as relatively low bending strength of the sheet metal and easy fracture.
The crimping process is a stamping process that forcibly displaces the material locally and extrudes a groove on the sheet metal to facilitate bending and ensure bending accuracy.
When bending the sheet metal, it should be as perpendicular to the metal fiber direction as possible. When the bending of the sheet metal is parallel to the fiber direction of the metal material, cracks are easily generated at the bending of the sheet metal, the bending strength is low, and it is easy to break, as shown in the following figure:
When the sheet metal is bent, it is often because the other features are too close to the root of the sheet metal bending, which can not be pressed and cannot be bent or the bending is seriously deformed. Generally speaking, there must be at least 2 times the thickness of the sheet metal plus the bending radius above the root of the sheet metal bending. There are no other features that block the pressing of the sheet metal during bending. As shown in the figure below, in the original design, the reverse bending flattening position was too close to the root of the sheet metal bending, which caused the sheet metal to be unable to press the material during the bending and the bending failed. As another example, the sheet metal extraction bud is too close to the bending root and the bending cannot be performed. At this time, the tooth extraction can be moved to the position of the sheet metal root. As the first design in the improved design below, if the position of extraction and bending cannot be moved due to the design requirements, a process cut can be added to the bending root corresponding to the extraction of teeth early to ensure that the bending proceeds smoothly, such as the second design of the improved design.
Due to the existence of sheet metal bending tolerances, a certain bending gap needs to be ensured in the direction of movement of the sheet metal bending to avoid bending failure caused by interference during bending. The following figure shows a complex bending sheet Simplified drawing of the gold piece, the bending sequence is that the upper side is bent first, and the right side is bent later. In the original design, there is no gap between the two bending edges. When the upper side is bent, and then the right side is bent, because of the tolerance of the sheet metal bending, the right side may be bent. Interference with the upper side during the process. In the improved design, the right side and the upper side should have a gap of at least 0.2mm, which can effectively avoid bending interference.
The bending strength needs to be ensured when the sheet metal is bent. The long and narrow bending strength is low, and the short and wide bending strength is high, so the sheet metal bending is attached to the longer side as much as possible. As shown in the following figure, for a bend with the same function, the original design has a low bending strength because the bend is attached to a relatively short edge. In the improved design, the bending is attached to a relatively long edge and the bending strength is high.
The more sheet metal bending processes, the higher the mold cost and the lower the bending accuracy. Therefore, the design of sheet metal should minimize the bending process. As shown in the figure below, in the original design, sheet metal requires two bending operations. In the improved design, sheet metal only needs one bending process to complete the bending of two sides at the same time.
Similarly, the more complicated the sheet metal bending process may result in wasted materials for parts. Therefore, when the sheet metal has a complex bend, you can consider splitting the complex bend into two parts. Although this violates the principle of reducing the number of parts, it is more likely to result in lower product costs and improved product quality. Of course, such design needs to be verified through rigorous calculations. As shown in the following figure, a sheet metal part with complex bends is split into two parts, and the two parts are assembled together by means of pull studs, self riveting, or spot welding.
Many engineers must have such a painful experience, why the holes of the screws or pegs on the sheet metal bending are always misaligned so that the screws and pegs cannot be fixed.
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