Basic Tutorial for CNC Bending Machine in Sheet Metal Factory

ⅠPunch of Press Brake

The punch is also called bending knife, which is divided into two types: integral type and split type. Integral type length: 415mm and 835mm.

Split length: 10, 15, 20, 40, 50, 100 (left horn), 100 (right horn), 200, 300 (mm); can be combined into different lengths of bending length with split molds.

The punch is divided into four types: straight knife, bending knife, arc knife and special knife.

1. Types of straight knife and processing characteristics

Suitable for bending and symmetrical products, the front and rear direction can avoid the position, the tool thickness is 6mm, so the bending opening can be as small as 6mm.

Tool analysis: From the tool bending simulation diagram, it can be seen that the front and rear of the tool can be avoided, but the length of Z and W is less than the length of X and Y. The knife tip angle of this tool is 88 degrees, and the knife tip R angle is 0.2, In addition, the usage of tool with angle of 30 degrees and 45 degrees is common.

Tool analysis: knife tip angle 30 degrees, knife tip R angle 0.67, so you can bend angle 30 degrees to 180 degrees, using the small angle of the knife tip can dodge the bud hole or nut, etc. And can also be used as a deep insert mold. Both front and rear tools can be avoided.

2. Types of bending knife and processing characteristics

Tool analysis: The tool mainly uses the avoidance in the W direction during the bending process. When X>15MM, the avoidance effect is getting worse and worse. When Y>30, the bending condition is satisfied, otherwise it will hit the tool back. The tool is commonly known as a small bending knife.

Tool analysis: The tool mainly uses the avoidance in the W direction during the bending process. When X>25MM, the avoidance effect is getting worse and worse. When Y>75, the bending condition is satisfied, otherwise it will hit the tool back. The tool is commonly known as the big bending knife.

3. The type of arc knife and processing characteristics

Tool analysis: The arc knife is divided into fixed type and movable type. The arc knife is to meet the processing conditions of 1 different arc bending by replacing the round bar. When the X-shaped knife is X10>10MM, it avoids it. The bit effect is the same as that of the small machete. The popular selection criteria for the die V-groove is the diameter of the arc plus two plate thicknesses.

4. Types of special knife and processing characteristics

Special knife for press brake includes offset punch and die, hemming punch and die and some special shapes of punches.

● The existing of the offset punch and die is divided into two types: 415mm and 835mm. The size of the divided shape is the same as that of the tool. The bending shape of the drawing specification is formed, but when the thickness of the sheet is thick, such as T= 2.0, considering the more serious indentation and the limitations of the mold itself, it will be difficult to form.

● The punch of the hemming punch and die is a flat die, and the die can be replaced by a common bending die, but the V-groove should be avoided. It is mainly used for the processing of dead-side flattening, rivet nuts and so on.

Ⅱ Die of Bending

1. The die of press brake has a bending die, an insert deep die, a hemming die, and so on.

⑴  Die of bending

The selection of the bending die of press brake is mainly considering the thickness of the processed product. At present, the new die selection standard of Yi Xin Company is 6T, which is the standard when working in the field under non-special circumstances. When processing large V or small V groove, the bending coefficient needs to be adjusted accordingly.

Mold analysis: The picture shows one of the types of the die. The types of V-grooves mainly include 4V, 6V, 7V, 8V, 10V, 12, 16V, 25V and some special large V-groove bending knifes. The die is divided into two types according to the height: 46 high and 26 high. 

⑵ Insert deep die

Mold analysis: One of the types of V-grooves is shown in the figure. The types of V-grooves are mainly 4V, 6V, 8V, 12 and some special insert deep dies, suitable for bending at any angle between 30-180 degrees. 

⑶  Hemming die

At present, the company does not have a special hemming die, which is usually replaced by a bending die.

2. Forming method of press brake

⑴  L-bending processing

The basic shapes of the bend, the bending angle is between 30 degrees and 180 degrees.

When bending the acute angle, you need insert the deep die and the acute punch, and bend 90 degrees or obtuse angle can choose any mold processing.

① The principle of the L-bending processing

A: Based on the principle of two rear gauges (two points), and positioned by the shape of the workpiece.

B: When a rear gauge is in position, pay attention to the skew, and the required bending dimension is on the same center line.

C: When the small bend is made, the reverse position processing is optimal.

D: It is better to lower the middle of the rule according to the back rule (the rule is not easy to lift after the position is fixed).

E: It is better to rely on the side to the nearest rule.

F: It is better to rely on the long side.

G: Use the jig as an auxiliary position (the bevel and the irregular side are bent).

② L-internal bending processing precautions

A: When the mold is being assembled, the bending is performed, and the rear gauge needs to be pulled back to prevent the workpiece from being deformed during the bending process;

B: When the internal part of the large workpiece is bent, Due to the shape of the workpiece is large, and the bending area is small, the knife and the bending area are difficult to overlap, which makes the positioning of the bending workpiece is difficult or the bending of the workpiece is damaged.

③ L-shape bending processing precautions

A: When the small size is bent, whether the punch and the rear gauge interfere.

B: When the hole position is closer to the bend line or the bend edge size is less than half a V groove, pay attention to the bend pull material.

④ Special bending method for L-bending processing

A: Eccentric bending method

Process analysis:

The eccentric bending has the difference between the positive and negative loading of the die. When processing, the drawing material is placed on the inner side or the outer side of the bending line to make a difference. In addition, the eccentric bending is a special processing method, which has certain dangers, and do not use in special circumstances.

B: Line bending method

Process analysis:

Due to the shearing effect of eccentric bending, some products with high surface requirements are not used. The timing of pressing and bending is the same as that of eccentric bending. Before bending, you can use 88-degree cutter or special pressing die to fold. Press the line at the bend line and bend with the normal mold.

C: small V bend large angle large V pressure.

Process analysis: first use a small V-slot to bend into a large angle, and then use the normal mold to bend, this processing method can avoid the small expansion size caused by the direct bending of the small V-slot.

D: plus gasket strip bending

Process analysis: This processing method is more suitable for products with stricter requirements on the shape of the workpiece. In addition, it is limited to sample processing in most cases.

The above four processing methods can also be combined, and the molding effect will be more ideal.

⑵ Z-bending processing

Definition: Any bend formed into a reverse is a Z-bending.

Processing range of standard bending: height of Z-bending > edge distance of V-groove plus T.

The minimum size of the machining is limited by the machining mold, and the maximum machining size is determined by the shape of the processing machine.

① Z-processing Z steps

A: First, the L-bending is processed according to the L-bending processing method;

B: Processing Z-bending by L-bending;

(Or process Z-bending on the other side of the L-bending.)

② Z processing Z-bending principle

A: It is convenient to rely on position and good stability;

B: Generally, the position is the same as the L-bending;

C: When the second position is processed, the workpiece and the die are required to be flat.

③ Z-processing precautions

A: The processing angle of the L-bending must be in place, generally requiring 89.5 degrees to 90 degrees;

B: After the rule is set, pull back to prevent the workpiece from deforming.

④ Z-general processing methods

A: should consider the processing sequence in the following figure, first bend 1 and then bend 2.

B: First bending type of L-bending and then processing Z-bending, and confirm whether the Z bending process interferes with the machine platform.

a: If interference, first bend 1 to a large angle, then bend 2, then pressurize 1;

b: If there is no interference, according to the general Z-bending processing method, first bend 1 and then bend 2.

C: Two acute angles Z-bending, first bend into 90 degrees, then insert depth 2, insert depth 1.

⑤ Z-bending special processing methods:

A: Eccentric machining of the lower die;

B: Processing with a small V-groove;

C: first bend the large angle and then pressurize;

D: Select the grinding die.

⑥ Other Z-bending processing methods:

A: Processing with offset mold;

B: Formed by easy mold.

⑶ N-bending processing

Definition: Continuous processing twice in the same processing surface for N-bending processing.

① N-bending general processing considerations:

A: The first folding processing angle should be less than or equal to 90 degrees;

B: After the second fold is processed, the gauge should be based on the machined surface.

② N-special processing methods:

A. When the N-bending Y-size interference upper mold is slight ==>Flexing N-bending and then using hemming punch and die shaping

B. When the N-bending Y-size interference is very large

==>A bend the line and bend it to the interference. After the B is bent, the B is folded and then used (hemming punch and die + padding) shaping.

C: Processed with a grinding knife.

⑷ Arc processing

The circular arc machining is divided into two types: rounding with a bending die and machining with a circular arc. The arc knife is divided into two types: fixed and round.

① Processing precautions:

A: When machining with 90-degree die, there will be cases where the processing is not in place, so it is necessary to push by hand or if the condition allows 88-degree die;

B: The detection fixture is mostly used to ensure the appearance size of the workpiece;

C: Processing 90-degree arc, the selection of the die is 2 (R+T).

3. Bending process layout

⑴ The basic principles of bending process layout

A. Bending from inside to outside

B. Small to large bending

C. First bend the general shape, then bend the complex shape

D. The pre-process bending does not affect the post-process principle

⑵ Process layout example

No matter how complicated the workpiece is, it is composed of several kinds of processing methods separately. Therefore, it is necessary to master the operation method of each bending method, and learn to use it in combination to be able to arrange the bending for different workpiece shapes in the operation. 

3. The choices of positioning benchmark

A. Positioning on the nearest side;

B. Positioning with wide sides;

C. Try to reduce the cumulative error by folding the edges without folding or bending.

D. The number of punched workpieces, positioning without burrs and joints;

E. Positioning with a small amount of deformation of the workpiece;

F. Try to choose two subsequent fixed positions;

G. Can add auxiliary positioning at both ends of the mold, such as magnets;

H. For irregular workpieces, use laser to cut the positioning fixture;

I. Large angle or U-shaped bend does not choose positioning.

5. Principles for selection of on-site work machines

A. select the machine according to the bending width;

B. Select a machine according to the length of the bend;

C. Select the machine according to the pressure required for bending;

D. Select the machine according to the number of processing stations;

E. According to the type of the on-site machine, the number of the machine is selected.

F. Select the machine according to the special requirements of the mold;

G. Select the machine according to the avoidance requirement;

H. Select the machine according to the moving range of the post-rule;

I. Select the machine according to the shape of the post-rule.

6. The control methods of bending size

A. Avoid cumulative error, and measure the unfolded size for each processing.

B. Avoid leaning against the bending edge to avoid a large angle.

C. It must be a product that has been bent against the edge, and the angle of the first fold should be slightly less than 90 degrees;

D. Determine the accuracy of the gage before processing;

E. Do the first inspection before the formal processing, and do a good inspection during the processing;

F. According to the precision requirements of the processed products, select the appropriate machine;

G. Avoid selecting tools with different hearts. Confirm that the punch points are on the same line before machining.

H. Choose a good processing method and a good process layout method to simplify the processing difficulty;

I. Accurate position, there is an abnormal position to be detected immediately.