12 Problems of Sheet Metal Bending Forming Technology

The bending and forming of metal sheets are carried out on the press brake machine.

The workpiece to be formed is placed on the bending machine, the brake shoe is lifted by the lifting lever, the workpiece slides to an appropriate position, and then the brake shoe is lowered onto the workpiece to be formed.

The bending and forming of metal are realized by applying force to the bending lever on the bending machine.

12 Problems of Sheet Metal Bending Forming Technology 1

The minimum bending radius is a function of the ductility and thickness of the formed metal.

For aluminum plate, the bending radius of the metal should be greater than the thickness of the plate.

During bending, due to certain springback, the angle of metal bending should be slightly larger than the required angle.

The bending of metal plates is carried out in the metal processing workshop.

Sheet metal processing is only a series of processing processes such as bending, riveting and welding of metal materials.

The following are the problems and solutions encountered in the bending process of sheet metal processing.

Problem 1: the bending edge is not straight and the size is unstable

Causes of uneven bending edge and unstable dimension:

⑴ The design process does not arrange pressing or pre-bending;

⑵ Insufficient bending force;

⑶ Asymmetric wear or uneven bending stress of round corners of male and female dies;

⑷ The height dimension is too small.

There are four solutions:

⑴ Design crimping or pre-bending process;

⑵ Increase the pressing force;

⑶ The gap between the male and female dies shall be even and the rounded corners shall be polished;

⑷ The height dimension shall not be less than the minimum limit dimension.

Problem 2: external surface scratch after workpiece bending

Causes of external surface scratch after workpiece bending:

⑴ The surface of raw materials is not smooth;

⑵ The bending radius of the punch is too small;

⑶ Bending clearance is too small.

Solutions mainly include:

⑴ Improve the finish of the male and female dies;

⑵ Increase the bending radius of the punch;

⑶ Adjust the bending clearance.

Problem 3: crack at bending angle

Reasons for cracks in bending angle:

⑴ The inner radius of bending is too small;

⑵ The material grain direction is parallel to the bending curve;

⑶ The burr side of the blank is outward;

⑷ Poor metal plasticity.

Solutions mainly include:

⑴ Increase the bending radius of the punch;

⑵ Change blanking layout;

(3) The burr shall be changed to the fillet of the part;

(4) Anneal or use soft materials.

Problem 4: hole deformation caused by bending

Causes of hole deformation caused by bending:

When using elastic bending and positioning with holes, the outer side of the bending arm will be pulled by friction between the surface of the female die and the outer surface of the workpiece, which will deform the positioning holes.

Solutions mainly include:

⑴ Adopt shape bending;

⑵ Increase the pressure of the ejector plate;

(3) Add pitting grid on the ejector plate to increase friction and prevent the parts from sliding during bending.

Problem 5: the extruded material on the curved surface becomes thinner

Reasons for thinning of extruded material on the curved surface:

⑴ The female die fillet is too small;

⑵ The clearance between male and female dies is too small.

Solutions mainly include:

⑴ Increase the fillet radius of the female die;

(2) Correct the clearance between male and female dies.

Problem 6: bulging or uneven end surface

The reasons for the bulge or unevenness of the end face of the part are:

When bending, the outer surface of the material is subject to tension in the circumferential direction to produce shrinkage deformation, and the inner surface is subject to pressure in the circumferential direction to produce elongation deformation, so that the flexural end face along the bending direction will bulge.

Solutions mainly include:

⑴ In the final stage of stamping, the male and female dies should have sufficient pressure;

⑵ Make the fillet radius of the female die correspond to the fillet of the workpiece;

⑶ Improve the added process.

Problem 7: the bottom of the concave part is uneven

The reasons for the uneven bottom of the concave part are:

⑴ The material itself is uneven;

⑵ The contact area between the top plate and materials is small or the jacking force is insufficient;

⑶ There is no jacking device in the female mold.

Solutions mainly include:

(1) Leveling materials;

⑵ Adjust the jacking device to increase the jacking force;

⑶ Add jacking device or correct;

⑷ Add shaping process.

Problem 8: after bending, the axis of the two holes on opposite sides is displaced

After bending, the reasons for the axial misalignment of the two opposite holes on both sides are as follows:

The springback of the material changes the bending angle and makes the center line shift.

Solutions mainly include:

Increase the correction process and improve the bending die structure to reduce material springback.

Problem 9: hole position and dimension accuracy cannot be guaranteed after bending

Reasons why the dimensional accuracy of hole position cannot be guaranteed after bending:

⑴ The developed dimension of the parts is wrong;

⑵ Caused by material rebound;

(3) Unstable positioning.

Solutions mainly include:

⑴ Accurately calculate the blank size;

⑵ Add correction process or improve the forming structure of bending die;

⑶ Change the process processing method or increase the process positioning.

Problem 10: the bending curve is not parallel to the center line of the two holes

The reason why the bending curve is not parallel to the center line of the two holes is:

When the bending height is less than the minimum bending limit height, the bending part will expand.

The solution is:

Increase the height and size of the bending parts and improve the process methods of the bending parts.

Problem 11: bow deflection occurs in the width direction of the bent part

The deformation in the width direction after bending, and the bow deflection in the width direction of the bent part are due to the inconsistent drawing and contraction in the width direction of the workpiece, resulting in torsion and deflection.

Solutions mainly include:

⑴ Increase bending pressure;

⑵ Add correction process;

⑶ Ensure that there is a certain angle between the material grain direction and the bending direction.

Problem 12: products with notches deflect downward

The reasons for the downward deflection of the products with notches are as follows:

The notch makes the two straight edges open to the left and right, and the bottom of the workpiece deflects.

Solutions mainly include:

⑴ Improve the structure of parts;

⑵ Increase the process allowance at the cut to connect the cuts and then cut off the process allowance after bending.

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