Sheet Metal Bending Technology
Sheet Metal Bending Technology
Bending of sheet metal
It refers to the process of changing the angle of sheet metal or sheet metal. Such as bending the plate into V-shaped, U-shaped, etc. Generally, there are two methods for sheet metal bending: one is die bending, which is used for sheet metal structure with complex structure, small volume and mass processing; the other is bending machine, which is used for processing sheet metal structure with larger size or less output. These two bending methods have their own principles, characteristics and applicability.
1, Common Sheet Metal Bending Tools
Commonly used bending die, as shown below. In order to prolong the life of the die, fillets should be used as far as possible in part design. Normally included V profile bending, U profile bending and Z profile bending.
If the bending height is too small, even using the bending die is not conducive to forming. Generally, the bending height L is more than 3T (including wall thickness).
Processing method of step
Some low-height sheet metal Z-step bending, processing manufacturers often use simple die in punch or hydraulic press processing, small batch can also be used in bending machine segment differential die processing, as shown in the following figure. However, its height H can not be too high, generally should be in (0-1.0) t, if the height is (1.0-4.0) t, according to the actual situation to consider the use of loading and unloading structure of the die form.
The height of the step can be adjusted by adding gaskets, so the height H can be adjusted arbitrarily. However, there is also a disadvantage, that is, the length L dimension is not easy to guarantee, and the verticality of the vertical edge is not easy to guarantee. If the height H is large, bending on the bending machine should be considered.
Bending machine is included Torsion Bar NC metal bending machine and CNC Synchro Bending machine. Because of high precision and irregular bending shape, sheet metal bending of communication equipment is usually done by numerical control bending machine. Its basic principle is to bend and form sheet metal parts by using the bending tool (upper die) and V-groove (lower die) of the bending machine.
Advantages: convenient clamping, accurate positioning, fast processing speed;
Disadvantage: Low pressure, can only process simple forming, low efficiency.
Basic Principle of Forming
The basic principle of forming is shown in the figure below.
Bending tooling (top punch)
The form of bending punch is shown in the following figure. It is mainly selected according to the shape of workpiece. Generally, the shape of bending knife of processing factories is more, especially those with high degree of specialization. In order to process various complicated bending knives, many shapes and specifications of bending knives are customized.
The lower die is usually V = 6-10t (t is material thickness) die.
There are many factors affecting the bending process, such as the arc radius of the upper die, material, material thickness, strength of the lower die, size of the lower die and so on. In order to meet the needs of products, in order to ensure the safety of the use of bending machine, the manufacturer has serialized the bending die, we need to have a general understanding of the existing bending die in the process of structural design. See figure below for upper die on the left and lower die on the right.
Basic Principles of Bending Processing Sequence:
(1) Bending from inside to outside;
(2) Bending from small to large;
(3) First bend the special shape, then bend the general shape;
(4) There is no influence or interference on the subsequent process after the former process is formed.
When sheet metal is bent, the bending radius should be at the bending point. The bending radius should not be too large or too small, and should be selected appropriately. Too small bending radius is easy to cause cracking at the bending point, and too large bending radius makes bending easy to rebound.
For ordinary low-carbon steel plate, rust-proof aluminium plate, brass plate, copper plate and so on, inner corner 0.2 is not a problem, but for some high-carbon steel, hard aluminium, superhard aluminium, such bending round corner will lead to bending fracture, or cracking of outer corner.
Material Bending Spring back
Factors Affecting Spring back and Measures to Reduce Spring Back
(1) The resilience angle of the material is 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, materials should choose low carbon steel as far as possible, not high carbon steel and stainless steel.
(2) The larger the relative bending radius r/t, the smaller the degree of deformation and the larger the springback angle alpha. This is a relatively important concept. The rounded corner of sheet metal bending should be selected as small as possible to improve the accuracy when the material properties permit. In particular, it should be noted that the design of large arcs should be avoided as far as possible. As shown in the figure below, such large arcs are more difficult for production and quality control.