There are many ways for CNC press brake to bend plates, and there are many classification methods for different principles. This article specifically introduces several common bending methods from the different relative positions of the upper and lower molds and the different folded shapes during bending, and details the bending process and precautions.
The Relative Bending Position of Press Brake Tooling
First of all, according to the difference in the relative positions of the upper and lower molds during the bending process, the bending process is divided into two forms: gap bending and bottom pressing. The characteristics and differences between the two are as follows:
- Gap Bending
The CNC press brake is not pressed between the upper die and the lower die during the bending process. The required bending angle is obtained by adjusting the depth of the upper die entering the opening of the lower die. This bending method is called gap bending.
The deeper the upper die enters the lower die, the smaller the bending angle; otherwise, the larger it is. Due to the elasticity of the material, it is also necessary to consider excessive bending to control the amount of spring-back when bending.
The advantage of gap bending is that a smaller number of molds can be used to realize forming processing of various angles, and the required processing pressure is small. Usually, in order to obtain the best bending effect, the ratio of the thickness B of the material to the width V of the V-shaped opening of the lower die can be selected as follows:
- When the material thickness is below 12.7mm, B: V is 1:8;
- When the material thickness is 12.7~22.2mm, B: V is 1:10;
- When the material thickness is more than 22.2mm, B: V is 1:12.
The above three ratios are standard mold ratios, the material is low carbon steel, and the material strength is 43.4kg/mm2. When compiling a bending processing program, the above parameters can be set in the numerical control system, and the processing program will be generated by the system after automatic processing.
- Bottom Bending
When the CNC press brake adopts the bottom bending, the plate is pressed between the upper and lower dies, so as to obtain the required bending angle and elbow radius. CNC bending machine press bottom bending is suitable for processing metal sheets with a thickness of less than 2mm in batch and large-scale production in enterprises.
Its bending radius is small, the bending precision is high, and the precision is good. It should be noted that the working pressure of bottom pressing is greater than that of clearance bending, generally more than three times.
The angle of the bottom pressing die should be adapted to the plate angle and material. Usually, when bending low carbon steel at the bottom, the angle of the upper and lower molds should be consistent with the required angle of the plate. When the bottom pressing method is used for processing, the die ratio, that is, the ratio of the sheet thickness B to the opening distance V of the lower die, is B: V=1:6.
During the bending process to determine the working tonnage, the force between the upper and lower dies is applied to the material, causing the material to plastically deform. Working tonnage refers to the bending pressure during bending. The influencing factors for determining the working tonnage are bending radius, bending method, mold ratio, elbow length, thickness and strength of bending material, etc.
According to the different shapes formed after bending, the bending process is divided into L-fold, N-fold, Z-fold, reverse folding and flattening, pressing hardware, and other forms.
Different Bending Type
- L Fold
According to the angle, it is divided into 90° fold and non-90° fold. The processing is divided into general processing (L>V/2).
The mold is selected according to the material, plate thickness, and forming angle.
Relying on the principle:
- Based on the principle of two post-fixed positions, and positioning according to the shape of the workpiece.
- When the CNC press brake machine back gauge is in position, pay attention to the deflection, and it is required to be in the same center as the workpiece bending size.
- When small bends are made, it is better to process them in the reverse position.
- It is better to be at the back and lower in the middle. (The rear gauge is not easy to lift when it is in position).
- It is better to be close to the rear set.
- It is better to lean on the long side.
- Use a jig to assist the positioning (irregular positioning of the hypotenuse).
Matters needing attention: Pay attention to the positioning method during processing and the movement mode specified in the various positioning processing methods. The mold is bent when it is installed, and then it is required to be pulled back to prevent the workpiece from being deformed during bending.
When a large workpiece is internally bent, because the workpiece has a large shape and a small bending area, it is difficult for the tool and the bending area to overlap, resulting in difficult positioning of the workpiece or damage to the bending workpiece. In order to avoid the above situation, a positioning point can be added in the longitudinal direction of the processing, so that the positioning and processing are carried out in two directions, which makes the processing and positioning convenient, and improves the processing safety, avoids the damage of the workpiece, and improves the production efficiency.
- N Fold
N folds require different processing methods according to different shapes. When bending, the inner side of the material should be greater than 4mm and the size of the X dimension is limited by the shape of the mold. If the inner side of the material is less than 4mm, special methods are used for processing.
Die selection is based on material thickness, size, material, and bending angle.
Relying principle: ensure that the workpiece does not interfere with the tool
- Make sure that the reclining angle is slightly less than 90 degrees.
- It is best to use two post-fixed positions, except in special cases.
After bending the L-fold, the angle should be guaranteed to be 90 degrees or slightly less than 90 degrees to facilitate processing and positioning.
When the second fold is processed, it is required that the locating position is centered on the processing surface.
- Z Fold
Z-fold of CNC press brake machine is also called step difference, that is, one positive and one negative bending. According to the angle, it can be divided into hypotenuse and straight edge. The minimum size of the bending process is limited by the processing die, and the maximum processing size is determined by the shape of the processing machine. Under normal circumstances, when the inner side of the Z-folded material is less than 3.5T, differential die processing is used. When it is larger than 3.5T, the normal processing method is adopted.
Relying on the principle:
- It is convenient to rely on and has good stability.
- Generally, the position is the same as the L-fold.
The secondary position is to require the workpiece to be flat with the lower die.
- The processing angle of the L-fold must be in place, generally 89.5~90 degrees.
- When the latter is required to be pulled back, pay attention to the deformation of the workpiece.
- The order of processing must be correct.
- For special processing, the following methods can be used: center-line separation method (eccentric processing), small V processing (need to increase the bending coefficient), easy mold forming, and grinding lower mold.
- Reflex Flattening
Reverse folding and flattening are also called dead edge pressing. The processing steps of the dead edge are: the first bend and insert to a depth of about 35 degrees, and then use a flattening die to flatten it until it is flat and tight.
- Die selection method: according to 5–6 times the material thickness, select the V-groove width of the lower die with a depth of 30 degrees, and select the upper die according to the specific conditions of processing dead edges.
- Matters needing attention: Pay attention to the parallelism of the two sides of the dead edge. When the processing size of the dead edge is long, the flattened edge can be folded first and then flattened. For shorter dead edges, dunnage can be used.
- Press hardware
The use of a folding machine to press and hold hardware parts generally requires the use of auxiliary molds such as concave molds and jigs. In general, there are pressure nuts, pressure studs, pressure screws, and some other hardware.
- When the shape of the workpiece needs to be avoided for processing, it should be avoided.
- After processing, it is necessary to check the torque, whether the thrust reaches the standard and whether the hardware and the workpiece are flat and tight.
- When pressing after bending, when pressing besides the machine tool, pay attention to the machining avoidance and the parallelism of the mold.
- If it is an expansion, it should also be noted that there should be no cracks on the edge of the expansion, and the edge of the expansion should not be higher than the surface of the workpiece.
Estimated reading time: 9 minutes