sheet metal bending
It refers to the processing of changing the angle of the plate or plate. Such as bending the sheet into V shape, U shape, etc. In general, there are two methods for sheet metal bending: one method is mold bending, which is used for sheet metal structures with complex structures, small volumes, and mass processing; the other is bending machine bending, which is used It is suitable for processing sheet metal structures with relatively large structure sizes or with low output. These two bending methods have their own principles, characteristics and applicability.
Die bending:
For structural parts with an annual processing volume of more than 5,000 pieces and the part size is not too large (300X300 in general), processing manufacturers generally consider opening stamping molds for processing.
Commonly used bending dies
Commonly used bending dies, as shown in the figure below. In order to prolong the life of the mold, rounded corners should be used as much as possible when designing parts.
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If the flange height is too small, it is not conducive to forming even if the bending die is used. Generally, the flange height L≥3t (including wall thickness).
Processing method of steps
For some low-height sheet metal Z-shaped step bending, processing manufacturers often use simple molds to process on punch presses or hydraulic presses. If the batch size is not large, they can also be processed on bending machines with segmental differential molds, as shown in the figure below. 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 this mold step can be adjusted by adding shims, so the height H can be adjusted arbitrarily, but there is also a disadvantage, that is, the length L is not easy to guarantee, and the verticality of the vertical side is not easy to guarantee. If the height H dimension is very large, it is necessary to consider bending on a bending machine.
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The bending machine is divided into two types: ordinary bending machine and CNC bending machine. Due to high precision requirements and irregular bending shapes, the sheet metal bending of communication equipment is generally bent with a CNC bending machine. The basic principle is to use the bending knife (upper die) and V-shaped groove (lower die) of the bending machine Die), bending and forming sheet metal parts.
Advantages: convenient clamping, accurate positioning, fast processing speed;
Disadvantages: The pressure is small, only simple forming can be processed, and the efficiency is low.
Fundamentals of Forming
The basic principle of forming is shown in the figure below:
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Bending knife (upper die)
The form of bending knives is shown in the figure below. During processing, it is mainly selected according to the shape of the workpiece. Generally, manufacturers have more shapes of bending knives, especially for manufacturers with a high degree of specialization. In order to process various complex bending , Customize bending knives of many shapes and specifications.
The lower mold generally uses a V=6t (t is material thickness) mold.
There are many factors that affect the bending process, mainly including the arc radius of the upper die, the material, the thickness of the material, the strength of the lower die, and the size of the die opening of the lower die. In order to meet the needs of the product and ensure the safety of the bending machine, the manufacturer has serialized the bending dies. We need to have a general understanding of the existing bending dies during the structural design process. As shown in the figure below, the upper mold is on the left and the lower mold is on the right.
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Basic principles of bending processing sequence:
(1) Bending from inside to outside;
(2) Bending from small to large;
(3) Bending the special shape first, and then bending the general shape;
(4) After the previous process is formed, it will not affect or interfere with the subsequent process.
The current bending form is generally as shown in the following figure:
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2 bending radius
When bending sheet metal, there must be a bending radius at the bending point, and the bending radius should not be too large or too small, and should be selected appropriately. If the bending radius is too small, it is easy to cause cracking at the bending point, and if the bending radius is too large, the bending is easy to rebound.
The optimal bending radius (inner bending radius) of various materials and different thicknesses is shown in the table below
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The data in the above table are preferred data and are for reference only. In fact, the rounded corners of the manufacturer's bending knives are usually 0.3, and the rounded corners of a small amount of bending knives are 0.5.
For ordinary low-carbon steel plates, anti-rust aluminum plates, brass plates, copper plates, etc., there is no problem with an inner fillet of 0.2, but for some high-carbon steel, duralumin, and super-duralumin, this kind of bending fillet This can cause the bend to break, or the bullnose to crack.
3 bending rebound
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Rebound angle Δα=b-a
In the formula, b - the actual angle of the workpiece after springback;
a—the angle of the mold.
The size of the rebound angle
See the table below for the springback angle when a single angle is bent freely at 90°.
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Factors Affecting Springback and Measures to Reduce Springback
(1) The mechanical properties of the material The springback angle is proportional to the yield point of the material and inversely proportional to the elastic modulus E. For sheet metal parts with high precision requirements, in order to reduce springback, the material should be as low-carbon steel as possible, instead of 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 rebound angle Δα. This is a relatively important concept. The rounded corners of sheet metal bending should be as small as possible when the material properties allow, which is conducive to improving accuracy. In particular, it should be noted that the design of large arcs should be avoided as much as possible, as shown in the figure below, such large arcs are more difficult for production and quality control:
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4 Calculation of the minimum bending edge of a bending
The starting state of the L-shaped bending is shown in the figure below:
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The initial state of the Z-shaped bending is shown in the figure below
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The minimum bending size L corresponding to sheet metal Z-bending with different material thicknesses is shown in the table below:
