Refers to the process of changing the angle of plates or plates. For example, bending the plate into a V-shape, a U-shape, etc. There are generally two methods for sheet metal bending: one is die bending, which is used for sheet metal structures with complex structure, small volume and batch processing; The other is bending with a bending machine, which is used to process sheet metal structures with large structural dimensions or low output. These two bending methods have their own principles, characteristics and applicability.
1. common bending die
Commonly used bending die, as shown in the figure below. In order to prolong the life of the die, rounded corners should be used as much as possible when designing parts.
If the bending height is too small, even if the bending die is used, it is not conducive to forming. General bending height L≥3t (including wall thickness).
Processing and processing method of steps
For some low-height sheet metal Z-step bending, manufacturers often use simple dies to process it on a punch or hydraulic press, and small batches can also be processed on a bending machine with differential dies, as shown in the following figure. However, its height h should not be too high, generally it should be (0 ~1.0) t. If the height is (1.0 ~ 4.0) t, the mold form with loading and unloading structure should be considered according to the actual situation.
The height of the die step can be adjusted by adding gaskets, so the height h can be adjusted at will. But there is also a disadvantage, that is, it is difficult to ensure the length L and the verticality of the vertical side. If the height h is large, it is necessary to consider bending on the bending machine.
Bending machine is divided into ordinary bending machine and numerical control bending machine. Because of its high precision and irregular bending shape, the sheet metal bending of communication equipment is generally bent by numerical control bending machine. The basic principle is to use the bending knife (upper die) and V-groove (lower die) of the bending machine to bend the sheet metal parts.
Advantages: convenient clamping, accurate positioning and fast processing speed;
Disadvantages: low pressure, simple processing and low efficiency.
Basic principle of molding
The basic principle of molding is as follows:
Bending knife (upper die)
As shown in the following figure, the form of bending tool is mainly selected according to the shape of the workpiece. There are many bending tools in general processing plants, especially those with high degree of specialization. In order to process all kinds of complicated bends, many shapes and specifications are customized.
Generally, the lower die is V=6t(t is the material thickness).
There are many factors that affect the bending process, including the arc radius of the upper die, the material, the thickness of the material, the strength of the lower die, and the die opening size of the lower die. In order to meet the demand of products and ensure the safety of bending machines, manufacturers have serialized bending dies. In the process of structural design, we need to have a general understanding of the existing bending dies. See the figure below: the upper die on the left and the lower die on the right.
Basic principles of bending processing sequence:
(1) bends from the inside out;
(2) Bending from small to large;
(3) bending the special shape first, and then bending the general shape;
(4) After the former process is formed, it will not affect or interfere with the latter process.
The current bending form is roughly as shown in the following figure:
2 bending radius
When bending sheet metal, there should be a bending radius at the bending place, and the bending radius should not be too large or too small, so it should be selected appropriately. If the bending radius is too small, it is easy to crack at the bend, and if the bending radius is too large, it is easy to rebound.
The preferred bending radius (bending inner radius) of various materials with different thicknesses is shown in the table below.
The data in the above table is the first choice and is for reference only. In fact, the manufacturer's machete fillet is generally 0.3, and a few machetes fillet is 0.5.
Used for ordinary low-carbon steel plate, antirust aluminum plate, brass plate, copper plate, etc. 0.2 fillet is no problem, but for some high carbon steel, hard aluminum and super hard aluminum, this kind of curved fillet will lead to bending fracture or external fillet cracking.
3. Bending resilience
Rebound angle δ α = b-a
In the formula? B—— the actual angle of the parts after springback;
A- the angle of the mold.
Size of rebound angle
Single angle 90? O See the table below for the rebound angle during free bending.
Factors affecting springback and measures to reduce springback
Mechanical properties of (1) materials? The springback angle is directly proportional to the yield point of the material and inversely proportional to the elastic modulus E. For sheet metal parts with high precision, in order to reduce springback, low carbon steel should be selected as far as possible, rather than high carbon steel and stainless steel.
(2) The greater the relative bending radius r/t, the smaller the deformation degree and the greater the rebound angle δ α. This is an important concept. When the material properties allow, the bending fillet of sheet metal should be as small as possible, which is beneficial to improve the accuracy. In particular, try to avoid designing large circular arcs. As shown in the following figure, such a large arc is very difficult for production and quality control: