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Knowledge of structural design of sheet metal parts (4) [structural design criteria (3)]
2.8 avoidance of small round coiling criteria
There are many advantages for the edge - edge structure of a thin plate member. (1) strengthen the stiffness; (2) avoid sharp edges; (3) beauty. But we should pay attention to two points for curling, one is the thickness of the plate that should be greater than 1.5 times, and the two is not completely circular, so it is difficult to process. The curl shown in Figure 18B is easier to process than the curling edges shown by a.
2.9 groove edge non bending criterion
The edge of the curved edge and the edge of the slot must be a certain distance, and the recommended value is the wall thickness of 2 times the radius of the bending. The bending zone has a complex stress state and a low strength. Notched holes should also be excluded from this area. It is possible to keep the whole slot away from the curved edge or to allow the slot to cross the whole curved edge (see Figure 19).
2.10 complex structure combination manufacturing criteria
The structure of space structure is too complex, and it is difficult to be formed completely by bending. Therefore, we should try to simply design the structure. In the case of non complex and impossibility, we can use composite components to combine multiple simple sheet members with welding and bolting. The structure of figure 20b is easier to be machined than the structure of its figure 20A.
2.11 principle of avoiding straight line penetration
The thin plate structure has the disadvantage of poor lateral bending stiffness. The large plate structure is prone to buckling and instability. Further bending fracture. Pressure grooves are usually used to improve their stiffness. The arrangement of the pressure grooves has a great influence on the effect of improving the stiffness. The basic principle of the groove arrangement is to avoid the straight line penetration in the pressure free groove area. The narrow narrow band through which is through is easy to become the inertia axis of the buckling of the whole plate. The instability always revolves around an inertial axis, so the groove is arranged to cut off the inertia shaft so that the shorter the better. In the structure shown in Figure 21a, a number of narrow strips are formed in the area without pressure grooves. Around these axes, the bending stiffness of the whole plate is not improved. The structure shown in Fig. 21b has no potential connection instability inertia axis. Figure 22 lists the common groove shape and arrangement way, from left to right stiffness enhancement effect gradually increases, irregular arrangement is an effective way to avoid straight line penetration.
2.12 the connecting rule of pressure grooves
The low end fatigue strength of the groove is the weak link. If the pressure groove is connected, the partial end point will be eliminated. Figure 23 is a truck's battery box, which is loaded with dynamic load, and the structure of figure 23a produces fatigue damage at the end of the pressure groove. The structure of graph 23B does not exist. The end face of a steep pressure groove should be avoided, and when possible, the groove is extended to the boundary (see Figure 24). The penetration of the trough eliminates the weak end. However, there should be enough space at the intersection of the pressure grooves to reduce the interaction between the pressure grooves (see Figure 25).
2.13 space pressure groove criterion
The instability of the spatial structure is not limited to only one aspect. Therefore, the pressure groove only on one plane can not achieve the effect of improving the stability of the whole structure. For example, the U and Z structures shown in Figure 26, their instability will occur near the edges. The way to solve this problem is to design the pressure slot into space (see the structure of the 26b. )
2.14 local relaxation criterion
Thin local deformation wrinkles can be severely hampered when. The solution is arranged in the pressure tank several small wrinkles near, so reduce the local stiffness, reduce the deformation of blocks (see Figure 28).
2.15,The configuration criterion of blanking parts
1. Minimum length minimum diameter or square hole punching
When punching, the strength of the punch should be limited. The size of the punching hole should not be too small, otherwise the punch can be damaged easily. The minimum piercing diameter and minimum side length see the table.
* t is the thickness of the material, and the minimum size of the punching hole is generally not less than 0.3mm.
The punching gap principle.
The punching gap should be avoided as shown in a figure sharp. Sharp form easy to shorten the service life of the die, and the corner crack. It should be changed to as shown in the B diagram.
R = 0.5T (t thickness)
To B map
The shape of the blanking parts and the inner holes should be avoided. In the connection line or curve to arc connecting radius R = 0.5T. (t is material wall thickness)
2.16, structural criteria for bending parts
The minimum bending radius of plate
When the material is bent, the outer layer is stretched on the corner area and the inner layer is compressed. When the material thickness, the inner radius of R is smaller, the tensile and compressive ultimate tensile strength is more serious; when the outer fillet stress exceeds the material, will crack and break, so the structure design of bending parts of the bending radius should avoid too small. The minimum bending radius is stipulated for this purpose.