Sheet metal parts structural design specification and process rationality requirements
Sheet metal parts structural design specification and process rationality requirements
Sheet metal parts is the most important and the most common structural parts design form, it is made of sheet metal materials through stamping processing. The geometric shape, size and processing accuracy of sheet metal parts directly affect the processing technology of parts, and the processing technology also restricts the material, process, mold life, product quality and product cost.
At present, the basic processing methods of sheet metal parts are: blanking, bending, stretching, forming and so on. The following is to sort out several processing methods of sheet metal parts, which can be used as a reference and guidance for the structural design of sheet metal parts.
blanking
Blanking is divided into ordinary blanking and precision blanking. At present, common blanking is usually used in the structural parts of electronic communication products. The blanking process listed below refers to the structural process of ordinary blanking.
1
The shape and size of blanking parts should be as simple and symmetrical as possible
The shape and size of the punching parts are simple and symmetrical, which can make the waste material at least when punching and arranging, and is conducive to saving materials.
2
The shape and inner hole of blanking parts should avoid sharp angles
For the shape and inner hole of blanking parts, the connection of the straight line or curve should be an arc connection transition, usually the arc radius R≥0.5t (T is the material thickness).
3
Narrow long cantilevers or grooves should be avoided in blanking parts
The length and width of the protruding or concave part of the blanking part, in general, should be greater than 1.5T (T is the thickness of the material). At the same time, narrow long incision and too narrow groove should be avoided to increase the cutting edge strength of the corresponding incision part of the mold, improve the life of the mold, and reduce the difficulty of mold processing.
4
Punching shape and minimum size requirements
The shape of the punching hole should be round, and the minimum size of the punching hole is related to the shape of the hole, the mechanical properties of the material and the thickness of the material.
5
Hole spacing and hole margins for blanking
The minimum distance between the punching edge of a part and the material edge of the part is related to the shape of the part and the hole, as shown in the figure below. Among them, when the edge of the punching hole is uneven with the outer edge of the part, the minimum distance A should be greater than the material thickness T; When the edge of the punch is parallel to the edge of the shape of the part, the minimum distance B should be greater than 1.5T.
6
Punching in bending parts and drawing parts
When punching a hole in a bending or stretching piece, the distance between the hole wall and the straight wall of the part is related to the radius of the inner fillet and the thickness of the material, as shown in the figure below.
7
Through and countersunk head holes for screws, bolts and rivets
Screw, bolt and rivet through hole and countersunk head hole structural dimensions are usually selected according to the corresponding table. For countersunk head holes of countersunk head screws and rivets, if it is difficult to ensure both the hole size D2 and the countersunk hole size D due to the small thickness of sheet metal materials, the hole size D2 should be guaranteed first.
8
Limit of burr of blanking parts and requirements of drawing design
Sheet metal material after blanking will form burr on one side of the plane, in order to ensure the surface quality of parts, prevent unnecessary injury, injury problem, usually hedge cutting burr height will have restrictions, as shown in the following table, f (precision) is suitable for higher requirements of parts; Class M (medium grade) is suitable for parts with medium requirements; Class G (rough) is suitable for less demanding parts. In part design drawings, it is usually necessary to deburr the outer surface of parts, cable holes and edges easily touched by hands.
Ⅱ
bending
Sheet metal bending refers to the process of changing the Angle of the plate or plate, such as bending the plate into V shape, U shape and so on. In general, there are two methods: one is the mold bending, used for complex structure, small volume, mass processing of sheet metal structure, the other is the bending machine bending, used for processing structure size is relatively large or production is not too large sheet metal structure bending process notes are as follows.
The minimum bending radius of a bending piece
When sheet metal material is bent, the outer layer is stretched and the inner layer is compressed at its rounded corners. When the thickness of the material is constant, the smaller the inner R is, the more serious the tensile and compression of the material is. When the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and fractures will occur. Therefore, the structural design of bending parts should avoid too small bending fillet radius. The minimum bending radius of commonly used materials is shown in the table below
2
The straight edge height of the bending part
1) The minimum height of the straight edge under general conditions
The minimum height of the straight edge of the bending piece shall be: H > 2t, where T is the thickness of the material, as shown in the figure below
2) Special requirements of straight edge height processing method
If the design needs the straight edge height of the bending piece H ≤2t, first increase the edge height, and then process to the required size after bending; Or in the bending deformation area, the process pressure groove is first processed and then bent, as shown in the following figure
3) The straight edge height requirement with bevel Angle on the side of the bending piece
When the side of the bending piece with bevel Angle, the minimum height of the straight side of the side is required to be: H = (2 ~ 4) t > 3mm.
3
The hole margin of bending parts is generally required
When the machining process is first punching and then bending, the position of the hole should be designed outside the bending deformation zone to avoid the deformation of the hole when bending. The distance from the hole wall to the bending edge is shown in the following table.
4 Local bending process cut
1) Local bending design and processing method
When the edge of a certain section is partially bent, the bending line can be moved a certain distance to avoid the point of dimensional mutation in order to prevent the bending crack caused by stress concentration at the sharp corner (Figure A). Or use the method of opening process groove treatment (Figure B). Size requirements: S≥R; Groove width k p t; Groove depth p t L + R + k / 2.
2) The cut form when the hole is located in the bending deformation zone
When the hole is in the bending deformation zone, the incision form can be used, as shown in the figure below