Views: 90 Author: Site Editor Publish Time: 2021-09-14 Origin: Site
Sheet metal refers to a steel plate whose thickness is much smaller than its length and width. Its lateral bending resistance is poor, so it is not suitable for occasions subjected to lateral bending loads. The thin plate is metal in terms of its material, but because of its special geometric shape and small thickness, the processing technology of sheet metal components has its particularity. According to the basic processing methods of sheet metal parts, it can be roughly divided into the following types: blanking, bending, stretching, forming, and welding. The structural design of sheet metal structural parts should mainly consider the requirements and characteristics of the processing technology. In addition, pay attention to the batch size of the components.
Sheet metal structural parts are widely used because sheet metal has the following advantages:
● Easy to deform, so that a simple processing technology can be used to manufacture various forms of components.
● The thin plate member is light in weight.
● The amount of processing is small, because the surface quality of the thin plate is high, and the dimensional tolerance in the thickness direction is small, the surface of the plate does not need to be processed.
● Easy to cut and weld, and can manufacture large and complex components.
● The shape is standardized, which is convenient for automatic processing.
According to the different processing methods, blanking can be divided into general punching, number punching, shear cutting, laser cutting, and wind-cutting. Due to the different processing methods, the processing technology of the blanking is also different. Sheet metal blanking methods are mainly digital punching and laser cutting.
● Numerical punching is processed by a CNC punching machine. The thickness of the plate is processed by cold-rolled plate and hot-rolled plate less than or equal to 3.0mm, aluminum plate less than or equal to 4.0mm, and stainless steel less than or equal to 2.0mm.
● There is a minimum size requirement for punching.
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.
● The number of punched holes and hole margins.
The minimum distance between the punching edge of the part and the shape is limited depending on the shape of the part and the hole. When the edge of the punching hole is not parallel to the edge of the part shape, the minimum distance should not be less than the material thickness t; when it is parallel, it should not be less than 1.5t.
● When punching the bent and stretched parts, a certain distance should be maintained between the hole wall and the straight wall.
When punching a bent or stretched part, a certain distance should be maintained between the hole wall and the straight wall of the workpiece.
● Through holes and countersunk heads for screws and bolts.
The structural dimensions of screws, bolt through holes and countersunk head seats are selected according to the following table. For countersunk head sockets of countersunk head screws, if the plate is too thin to ensure both via d2 and counterbore D, the via d2 should be guaranteed first.
● Laser cutting is a flight cutting process with a laser machine. The thickness of the plate is processed by the cold-rolled board and hot-rolled board, which is less than or equal to 20.0mm, and stainless steel is less than 10.0mm. The advantage is that the thickness of the processed plate is large, the shape of the cutting workpiece is fast, and the processing is flexible. The disadvantage is that it cannot be processed into shape, and the mesh parts are not suitable for processing in this way, and the processing cost is high.
The minimum bending radius of the bent part.
When the material is bent, the outer layer is stretched while the inner layer is compressed on rounded corners. When the thickness of the material is constant, the smaller the inner r, the more severe the stretching and compression of the material; when the tensile stress of the outer fillet exceeds the ultimate strength of the material, cracks and breaks will occur. Therefore, the structure of the bent part The design should avoid too small a bend radius.
● The height of the straight side of the bent part.
The minimum straight edge height requirement under normal circumstances.
The height of the straight side of the bent part should not be too small, and the minimum height should be as required: h>2t.
Straight edge height for special requirements.
If the design requires the straight edge height of the bent part h≤2t, then the flange height must be increased first, and then processed to the required size after bending; or the shallow groove is processed in the bending deformation zone before bending.
The height of the straight edge with a bevel on the side of the flange.
When the bent side has a beveled part, the minimum height of the side is: h=(2～4)t＞3mm.
● The margin of the hole on the bent piece.
Hole margin: punch holes first and then bend. The hole position should be outside the bending deformation zone to avoid deformation of the hole during bending.
● Partially curved craft incision.
The bending line of the bent part should avoid the position of sudden size change.
When a certain segment of the edge is partially bent, in order to prevent the stress concentration at the sharp corners from bending and cracking, the bending line can be moved a certain distance away from the sudden size change, or a process groove or a process hole can be punched. Note the size requirements in the figure: S≥R; slot width k≥t; slot depth L≥t+R+k/2.
When the hole is located in the bending deformation zone, the cut form is taken.
When the hole is in the bending deformation zone, an example of the cut form is used.
● Bending edges with beveled edges should avoid the deformation zone.
● Design requirements for the dead side.
The length of the dead edge is related to the thickness of the material. Generally, the minimum length of the dead edge is L≥3.5t+R.
Where t is the wall thickness of the material, and R is the minimum inner bending radius of the previous process of the dead edge.
● Process positioning holes added during design.
To ensure the accurate positioning of the blank in the mold and prevent the blank from shifting during bending and generating waste products, process positioning holes should be added to the design in advance. Especially for parts that are bent and formed multiple times, the process hole must be used as the positioning reference to reduce the cumulative error and ensure the quality of the product.
● When marking the relevant dimensions of the bent part, the manufacturability should be considered.
Punching first and then bending, the accuracy of L dimension is easy to guarantee, and the processing is convenient. If dimension L requires high precision, it is necessary to first bend and then process the hole, which is troublesome.
● Springback of bent parts.
There are many factors that affect springback, including the mechanical properties of the material, wall thickness, bending radius, and the positive pressure during bending.
The larger the ratio of the inner corner radius of the bending piece to the plate thickness, the greater the springback.
Examples of methods to suppress springback in design.
The springback of bent parts is currently mainly circumvented by manufacturers taking certain measures during mold design. At the same time, improving certain structures from the design to promote the rebound angle: pressing the stiffener in the bending zone can not only increase the rigidity of the workpiece but also help suppress the rebound.
English
Pусский
