1. Minimum bending radius of plate
When the material is bent, the outer layer is stretched and the inner layer is compressed in the fillet area. When the thickness of the material is constant, the smaller the inner radius r is, the more serious the tensile and compression of the material will be; When the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and breaks will occur. Therefore, the structural design of bending parts should avoid too small bending fillet radius. Specify the minimum bending radius for this purpose.
L The bending radius refers to the inner radius of the bending piece, and t is the wall thickness of the material.
L t is the material wall thickness, M is the annealed state, Y is the hard state, and Y2 is the 1/2 hard state.
For the closed bending parts as shown in the figure below, the maximum bending height h shall not exceed 40mm. If it is required to exceed 40mm, it must be checked before use.
2. Minimum straight edge height for bending
The straight edge height of bending should not be too small, otherwise it is not easy to form enough bending moment, and it is difficult to obtain the parts with accurate shape. The value h ≥ R+2t is acceptable.
① Minimum straight edge height requirements in general
The straight edge height of bending parts shall not be too small, and the minimum height shall be h ＞ 2t according to the drawing requirements.
Minimum straight edge height of bent parts
② Height of straight edge with special requirements
If the straight edge height h ≤ 2t of the bending part is required in the design, the bending height shall be increased first, and then the bending shall be processed to the required size; Or bend after machining shallow grooves in the bending deformation area.
Requirements for straight edge height in special cases
③ Height of straight edge with bevel on the side of curved edge
When the bending part with bevel angle is on the side of the bending edge, the minimum height of the side is: h=(2 ～ 4) t ＞ 3mm
Height of straight edge with bevel on the side of curved edge
3. Deformation treatment of bent straight edges
① When a ＜ R, after bending, there is still a residual arc near a on surface b. In order to avoid the residual arc, a ≥ R must be made.
② On U-shaped bending pieces, the two bending edges should be equal in length to avoid displacement to one side during bending. If not allowed, a process positioning hole can be set.
③ Prevent cracks or deformities when the side (trapezoid) is bent. The reserved groove shall be designed, or the root shall be changed to a stepped shape. Groove width K ≥ 2t, groove depth L ≥ t+R+K/2.
④ The reserved notch shall be designed to prevent the fillet from wrinkling after extrusion due to compression during bending. Such as the cut form at the fillet of the side plate (upper end, lower end) of the outdoor unit.
B is equal to the cover plate thickness (t)
⑤ To prevent wrinkles on both sides of the right angle after bending, the reserved cut shall be designed.
⑥ Cut form to prevent springback after bending.
A ≥ 1.5t (t - material thickness)
⑦ . Cut form to prevent cracks caused by bending after punching.
⑧ Prevent one side from contracting inward when bending. The process locating hole can be designed, or both sides can be bent at the same time, or the shrinkage problem can be solved by increasing the width.
⑨ The lapping form is bent into a right angle.
4. Bending of convex part
If the bending curve is consistent with the step line as shown in figure a, sometimes it will crack and deform at the root. Therefore, make the bending curve keep away from the step line as shown in Fig. b, or design the notch as shown in c and d.
5. Hole edge distance on the bending piece
Hole edge distance: punch the hole first and then bend it. The position of the hole should be outside the bending deformation area to avoid deformation of the hole when bending. The distance from the hole wall to the bending edge is shown in the table.
Table Hole edge distance on bending piece
① When bending, the hole on the bending surface will be deformed after being stressed, and the value A of the hole edge distance (to the bottom root) is ≥ 4.
② When punching the bending edge, the distance L from the hole edge to the center of the bending radius R shall not be too small to avoid the hole deformation after bending and forming. Its value L ≥ 2t.
6. Process cut with local bending
① The bending line of the bending part shall avoid the location of sudden change in size
When bending the edge of a section locally, in order to prevent bending cracks caused by stress concentration at sharp corners, the bending curve can be moved a certain distance to leave the sudden change of size (Figure a), or the process groove (Figure b) can be opened, or the process hole (Figure c) can be punched. Note the dimension requirements in the drawing: S ≥ R; Groove width k ≥ t; Groove depth L ≥ t+R+k/2.
② When the hole is located in the bending deformation zone, the cut form adopted
Example of the cut form used when the hole is in the bend deformation zone
7. Design requirements for dead edge
The length of the dead edge is related to the thickness of the material. As shown in the figure below, generally the minimum length of dead edge L ≥ 3.5t+R.
Where, t is the material wall thickness, and R is the minimum internal bending radius of the previous process.
8. Process locating hole added during design
In order to ensure the accurate positioning of the blank in the mold and prevent the offset of the blank during bending from generating waste products, the process positioning holes should be added in advance during the design, as shown in the following figure. Especially for the parts formed by multiple bending, the process hole must be used as the positioning benchmark to reduce the cumulative error and ensure the product quality.
9. When marking the relevant dimensions of bending parts, consider the manufacturability
10. Springback of bending parts
There are many factors affecting springback, including mechanical properties, wall thickness, bending radius and positive pressure when bending.
(1) The greater the ratio of the inner radius of the bending part to the plate thickness, the greater the springback.
⑵ Examples of methods for restraining rebound in design.
At present, the springback of bending parts is mainly avoided by the manufacturer when designing the mold. At the same time, some structures are improved in design to reduce the springback angle, as shown in the figure below: pressing stiffeners in the bending area can not only improve the rigidity of the workpiece, but also help to restrain springback.
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