Metal sheet bending refers to the process of changing the angle of a sheet or plate. Such as bending the plate into a V shape, U shape and so on. In general, there are two methods for sheet metal bending: one method is die bending, which is used for sheet metal structures with complex structures, small volumes, and large-volume processing; the other is a mechanical press brake machine bending. It is used to process sheet metal structures with large structure size or not too large output. These two bending methods have their own principles, characteristics, and applicability.
As a press brake machine operator in the sheet metal industry, some basic knowledge must be known. Of course, the bending operator must see the workpiece drawing. This is the first condition. At the same time, working experience in this position is also important. There are many types of bending machinery and equipment, but the basic structure and working principle of CNC hydraulic press brake must also be understood.
For the learning of the bending process at work, you should first understand the basic knowledge first.
Bending molds are divided into standard molds and special bending molds according to the bending process. Under standard bending conditions (right-angle and non-right-angle bending), standard molds are usually used for bending, and special molds are used for bending some special structural parts (such as step bending, pressing dead edges, etc.). In addition, when bending different thickness sheets, the opening dimension "V" of the die under bending is selected differently. Generally, the size of the "V" -shaped slot opening is 6-10 times the thickness of the plate (0.5 ~ 2.6mm is 6t, 3 ~ 8mm is 8t, 9 ~ 10mm is 10t, and 12mm is 12t). When the plate is thin, the orientation is chosen to be a small number, and when the plate is thick, the orientation is chosen to be a large number. For example: when bending a 2mm plate, a 12mmV slot can be used. The standard bending angle is generally not less than 90 degrees, and the sharp angle of the upper and lower dies of the standard bending machine is usually 88 degrees. In the case of non-standard bending, different upper mold shapes can be selected to bend the sheet at different angles and shapes. For special shaped sheet metal parts, special bending molds can be selected for forming and 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.
A. Common Bending Mould
Common bending dies, as shown below. In order to extend the life of the mold, rounded corners are used whenever possible when designing the part.
If the height of the flange is too small, even the use of a bending mold is not conducive to forming. Generally, the height of the flange L≥3t (including wall thickness).
B. The Processing method of step
Some low-profile sheet metal Z-shaped steps bending, processing manufacturers often use simple molds to process on punches or hydraulic presses. If the batch size is not large, they can also be processed on the press with segmented dies, 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, consider using a mold with a loading and unloading structure according to the actual situation.
The height of this molding step can be adjusted by adding shims. Therefore, the height H can be adjusted arbitrarily. However, there is also a disadvantage that the length L cannot be easily guaranteed and the verticality of the vertical edges cannot be easily guaranteed. If the height H size is large, it is necessary to consider bending on a press brake bending machine.
The press brake bending machine is divided into two types: NC press brake machine and CNC press brake machine. Due to high accuracy requirements and irregular bending shapes, sheet metal bending of communication equipment is generally bent by CNC press brake machines. The basic principle is to use the bending knife (upper die) and V-groove (lower die) of the CNC hydraulic press brake machine to bend and form sheet metal parts.
Advantages: convenient clamping, accurate positioning, fast processing speed.
Disadvantages: low pressure, only simple forming can be processed, and the efficiency is low.
C. Basic principles of forming
Bending knives are mainly selected according to the shape of the workpiece. Generally, there are many bending knives in processing manufacturers, especially those with a high degree of specialization. In order to process various complex bendings, many shapes and specifications of bending knife are customized.
The lower mold is generally V = 6t (t is the material thickness).
There are many factors that affect the bending process, mainly including the radius of the upper mold arc, material, material thickness, strength of the lower mold, and die size of the lower mold. In order to meet the needs of the product, the press brake manufacturer has serialized the bending knife mold under the condition that the hydraulic press brake machine is safe to use. We need to have a general understanding of the existing bending knife mold in the structure design process. See the figure below left for the punch and the right for the die.
Generally, the standard length of the CNC press machine mold is 835mm. In principle, it can only bend large-size work.
The mold is divided into small sections of different lengths. By freely combining different mold lengths, it is convenient to bend box-shaped workpieces or boxes of different lengths. In the industry, the segmentation of the bending mold has a standard segmentation size, such as: standard segmentation 835 segmentation: 100 (left ear), 10, 15, 20, 40, 50, 200, 300, 100 (right ear) = 835mm. Of course, it can also be divided according to user requirements.
If we want to bend a relatively large and thick plate, we must first understand the required bending tonnage force. Then we can calculate the tonnage required for bending (recommended that the pressure required for the bending of the workpiece is within 80% of the rated tonnage of the equipment). Through calculation, we can also determine the tonnage equipment required for bending. The mold V groove is reasonable. The choice also affects the bending force. The calculation method is as follows:
Calculation formula: P = 1.42 x L x T x S² / (1000 x V)
P = bending force (KN)
L = sheet length (M)
T = material tensile strength (soft steel: 45Kg / mm2)
S = sheet thickness (mm)
V = die width (mm)
Example: Take the bending of 2 meters long and 3 mm thick soft steel as an example to calculate its bending force:
T = material tensile strength (soft steel: 45KN / mm2)
P = 1.42xLxTxS² / 1000xV
= 1.42x2000x450x9 / 1000x24
= 48 tons
BLMA Machinery is a professional press brake manufacturer and has 32 years of experience in the production of press brake machines. It provides high-quality NC press brake machines and CNC hydraulic press brake machines. If you have any needs, please contact us.