Troubleshootings in bending process

In the actual process of bending the sheet by the bending machine, there will be many various problems due to the size of the sheet or the shape of the molding. For some common problems, today we will share the corresponding reasons and reasonable treatment methods with you and hope it will be helpful to you.

1. The phenomenon of slipping during processing

Cause analysis:

(1)The die whose notch width is 4 to 6 times of the plate thickness is generally selected when bending die selection. When the size of the bend is less than half of the width of the selected V-groove, the sliding phenomenon will occur.   

(2)The selected V-groove is too large.

(3)Unqualified process treatment. 

Solution: 

(1)center line deviation method (eccentric machining): if the inner dimension of bent sheet metal is less than (4-6) t/2, it will be supplemented as much as it is smaller.   

(2)Pad processing.   

(3)Bending with small V-groove and pressurizing with large V-groove.   

(4)Choose smaller V-groove.

2. The internal bending width is narrower than the standard mold width

Cause Analysis: Since the minimum standard width of the die of the folding bed is 10mm, the bending part is less than 10mm. If it is bent at 90 degrees, its length dimension shall not be less than √2(L+V/2)+T. For this type of bending, the mold must be fixed on the mold base (that is, except that the degree of freedom in the upward direction is not limited)to avoid the displacement of the die, which may cause the workpiece to be scrapped or cause safety accidents. 

Solution: 

(1) Increase the size (to be agreed with the customer), that is, increase the width of the inner fold.

(2) Mold change processing

(3) Grinding tools (this action leads to an increase in processing costs)

3. The hole is too close to the bending line, and the bending will cause the hole to pull and turn the material

Cause Analysis: Assuming that the distance between the hole and the bending line is L, when L<(4--6)T/2, the hole will pull the material. The main reason is that during the bending process, the tensile force caused the material to deform, resulting in material pulling and turning.  

Solution:

(1) Increase the size ,trimming edges after forming.

(2) Expand the hole to the bending line (must have no effect on the appearance and function, and the customer agrees).

(3) Slicing treatment or crimping treatment

(4) Eccentric mold processing

(5) Modify the hole size

4. The distance L between the drawing edge and the bending line is small, and the drawing part is deformed after bending

Cause Analysis: when L<(4--6)T/2, the drawing is in contact with the die, and deformation occurs when the drawing is stressed during bending.  

Solution: 

(1) Secant processing or crimping processing.

(2) Modify the drawing size. 

(3) Processing with special molds

(4) Eccentric mold processing

5. The long dead edge is warped after being flattened

Cause Analysis: due to the long dead edge, it is not tightly attached when flattened, which causes the end to warp after flattening. This situation has a great relationship with the flattening position, so pay attention to the flattening position when flattening.

Solution: 

(1) Fold the warped corner before folding the dead edge, and then flatten it. 

(2) Multi-step flattening: firstly, press the end to bend the dead edge downward and flatten the root. Note: The flattening effect is related to the operator's operation skills, so please pay attention to the actual situation when flattening.

6. During changing mold processing, the processing size will run

Cause Analysis: due to the forward squeezing force of the workpiece during processing, the workpiece moves forward, which leads to the increase of the small warping angle dimension L at the front.

Solution: 

(1) Grind off the shaded part in the figure. Generally, you can make up as much as you need. 

(2) All the self-positioning parts of mold change are ground off, and the position is changed to the rear retaining material.

7. The total size of blanking (expansion) is too small or too large, which is inconsistent with the round surface

Cause Analysis: 

(1) Project deployment error.

(2) The blanking size is wrong. 

Solution: 

According to the total deviation in the deviation direction and the number of bending knives, the deviation allocated for each bend is calculated. If the calculated distribution tolerance is within the tolerance range, the workpiece is acceptable. If the size is too large, it can be processed with a small V groove. If the size is too small, it can be processed with a large V groove.

8. After the hole is riveted, it bursts or the riveting is not tight or deformed.

Cause Analysis: 

(1) Burst is caused by too small R angle of the punching punch or too large burrs on the flanging. 

(2) The riveting is not tight because the hole is not expanded properly. 

(3) Deformation is caused by hole dislocation or wrong riveting method.

Solution: 

(1) Choose a punch with a large R angle instead. Note: The burrs around the hole when the hole is flanged.

(2) Increase the pressure, increase and deepen the salad hole, switch to a punch with a big R angle.

(3) Change the riveting method and the reason for hole dislocation.

9. Stud pressure riveting is skewed or the workpiece deforms after pressure riveting

Cause Analysis: 

(1) There is no flat workpiece when processing the product.

(2) Uneven force or excessive pressure on the lower surface of the workpiece.

Solution: 

(1) When pressing the stud, the workpiece should be flattened.

(2) Make the support frame.

(3) Readjust the pressure.

(4) Increase the force range of the lower surface and reduce the force range of the punch surface.

10. The two sides are not parallel after the level difference

Cause Analysis: 

(1) The mold is not corrected.

(2) The gaskets of punch and die are not adjusted properly.

(3) The faces of punch and die have different choices.

Solution: 

(1) Re-check the mold.

(2) Increase or decrease gaskets.

(3) The mold is eccentric.

(4) Replace the surface to make the punch and die surfaces the same.

11. The crease on the product surface is too deep

Cause Analysis: 

(1) The V groove of die is small

(2) The R angle of the die V groove is small

(3) The material is too soft.

Solution: 

(1) Processing with large V groove

(2) Mold processing using large R angle

(3) Bending of cushion material (steel sheet or Uni-Glue)

12. The near bend is deformed after bending

Cause Analysis: the machine runs fast during the bending process, and the upward bending speed during the deformation of the workpiece is greater than the speed at which the operator supports the workpiece.

Solution: 

(1) Reduce the operating speed of the machine

(2) Increase the hand support speed of the operator.

13. AL parts are prone to cracks when bent

Cause Analysis: Because AL material has a special crystal structure, it is easy to break when the parallel bending.

Solution: 

(1) When cutting the material, consider cutting the AL material in the direction perpendicular to the bending direction (even if the material bending direction is perpendicular to the grain.)

(2) Increase the R angle of the punch.

14. The workpiece is deformed at the bend after bending

Cause Analysis: The deformation is mainly caused by the fast bending speed, and the hand does not keep up with the speed of the bending deformation of the workpiece.

Solution: Reduce the bending speed, hold the workpiece and the workpiece at the same time. 

15.When bending a long workpiece, the angle will be larger and smaller

Cause Analysis:             

(1) The material thickness is inconsistent, one end is thick and the other is thin.

(2) Due to the wear of the punch for a long time, the height dimension at one end is smaller than that at the other end.

(3) The middle block is not balanced and not on the same level.

Solution: 

(1) Feed back to the laser to make it pay attention to material selection. 

(2) Change the tool die.

(3) Adjust the middle block.

16.When bending Z-folding, sometimes the workpiece will be deformed

Cause Analysis: This situation occurs mainly because the first bend is the positioning of the back gauge. When the second part is bent, the workpiece bends and rises, hits the back gauge and is squeezed by the back gauge. After being bent into shape, the first place to grow out is squeezed out of shape. 

Solution: Use the back gauge and pull back function.

17. The bending size is small, it is not easy to locate, and the punch is easy to press on the backgauge

Cause Analysis: because t=0.8, press the principle of mold selection, v=5×0.8=4mm. The distance from the center of the 4V to the side is 3.5mm, and the inner dimension of 2.9mm is 2.9-0.8=2.1mm. The bending size is within the distance from the center line of the V to the side. Formal wear cannot be positioned.

Solution: You can install the die reversely, add a gasket (thin) in front of the back gauge, so that the back gauge can move back and avoid the punch.