Bending Sheet Metal: 14 Problems and Solutions

In the process of sheet metal bending, you must encounter various problems.

Today, let’s specifically analyze 14 different sheet metal bending problems and solutions.

I believe you will benefit a lot after reading this book.

Let’s dive right into it.

Common Problems and Solutions For Bending Sheet Metal

1. Slip material during processing 

Cause Analysis: 

  • Generally, (4-6) T V groove width is selected when bending die selection. When the size of the bend is less than half the width of the selected V-groove, slippage will occur.
  • The V groove selected is too large
  • Processing according to techniques


  • Centerline deviation method (eccentric machining). If the size of the bent material is less than one-half of (4-6) T, make up as much as possible.
  • Padding processing
  • Bend with small V-groove, press with large V-groove.
  • Select a smaller V-groove.

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

Cause Analysis:

Since the standard width of the lower die of the bending machine is at least 10MM, the bending processing part should be less than 10MM. If it is a 90-degree bend, its length must not be less than √2 (L + V / 2) + T.

For this kind of bending, the mold must be fixed on the mold base (except that the degree of freedom in the upward direction is not limited) to avoid the displacement of the mold and cause the workpiece to be scrapped or cause a safety accident.


  • Increase the size (negotiate with the customer), that is, increase the width of the inner bend.
  • Special mold processing
  • Grinding tools (this will increase the processing cost)

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

Cause Analysis: 

Suppose the distance of the hole from the bend 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 material is deformed by tensile force, which causes the phenomenon of pulling and turning.

For different plate thicknesses, according to the groove width of the existing standard molds, the minimum L value is as follows:


  • Increase the size, trim the hem after forming.
  • Expand the hole to the bend line (must have no effect on the appearance and function, and the customer agrees).
  • Secant processing or crimping processing
  • Mold eccentric processing
  • Modify the hole size

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

Cause Analysis: 

When L <(4 — 6) T / 2, due to the contact between the drawing and the lower mold, the drawing will be deformed during the bending process.


  • Secant processing or crimping processing.
  • Modify the drawing size.
  • Using special mold processing
  • Mold eccentric processing

5. The long flattening side rises after flattening 

Cause Analysis: 

Due to the long flattening edge, it does not stick tightly when flattened, which causes its ends to rise after flattening.

This situation has a lot to do with the flattening position, so pay attention to the flattening position when flattening.


  • First bend the uplifting angle (see the diagram) before bending the dead edge, and then flatten it.
  • Flatten in multiple steps
  • Press the end first to bend the dead side down.
  • Flatten the roots part.


The flattening effect is related to the operator’s work skills, so please pay attention to the actual situation when flattening.

6. Large-height draw bridge is easy to break 

Cause Analysis: 

  • Because the height of the draw bridge is too high, the material is severely stretched and fractured.
  • Special mold corners are not sharpened or not sharpened enough.
  • The toughness of the material is too poor or the bridge is too narrow.


  • Lengthen the process hole on one side of the fracture.
  • Increase the width of the draw bridge.
  • Repair the special mold R angle and increase the arc transition.
  • Add lubricant to the draw bridge. (Therefore, this method will make the surface of the workpiece dirty, so it cannot be used for AL parts, etc.)

7. During special mold processing, the processing size will change

Cause Analysis: 

Because the workpiece is subjected to a forward pressing force during processing, the workpiece is displaced forward, resulting in an increase in the small angle L of the front portion.


  • Remove the shadows in the picture. It is usually made up as much as possible.
  • All the self-positioning parts of the easy mold are worn away, and position with back initiating structure.

8. The overall size of the blanking (referring to the expansion) is too small or too large, which is not consistent with the round surface.

Cause Analysis: 

  • Project deployment error.
  • The feeding size is wrong.


According to the total deviation and the number of bending times in the deviation direction, the deviation assigned to each fold is calculated.

If the calculated distribution tolerance is within the tolerance range, the workpiece is acceptable.

  • If the size is too large, you can use a small V-groove.
  • If the size is too small, you can use a large V-groove.

9. Spalling or loose of the draw-hole after riveting and cause deformation.

Cause Analysis: 

  • Spalling is due to the small R angle of the draw-hole or the burr of the flange is too large.
  • The riveting is not tight because the draw holes are not in place.
  • The deformation is caused by the hole misalignment or the wrong riveting method.


  • Choose a center punch with a large R angle instead. Pay attention to the burrs around the draw hole when flanging.
  • Increase the pressure, increase and deepen the broaching and use a large R angle center punch instead.
  • Change the cause discovery of riveting method and hole misalignment.

10. The riveting of the stud is skew or the workpiece is deformed after riveting

Cause Analysis: 

  • The workpiece is not flattened when processing the product.
  • Uneven force or excessive pressure on the lower surface of the workpiece.


  • Flatten the workpiece when pressing the stud.
  • Make a support frame.
  • Readjust the pressure.
  • Increase the stress range of the lower surface and reduce the force range of the upper surface.

11. The two sides are not parallel after offset bending 

Cause Analysis: 

  • The mold is uncorrected.
  • The upper and lower die gaskets are not adjusted.
  • The upper and lower die faces are different.


  • Re-calibrate the mold.
  • Increase or decrease the gaskets.
  • The mold uses eccentric processing.
  • Change the surface and take the same surface of the upper and lower mold.

12. The product surface crease is too deep

Cause Analysis: 

  • Small V-groove in the lower die
  • The R angle of the V-groove in the lower die is small
  • The material is too soft.


  • Using large V-groove to process
  • Use mold processing with large R angle
  • Padding bending (pad with metal or casting polyurethane)

13. The area near the bend deformed after bending

Cause Analysis: 

The machine runs fast during the bending process, and the upward bending speed during the workpiece deformation is greater than the speed at which the operator is holding the workpiece by hand.


  • Reduce machine running speed
  • Increase the operator’s hand holding speed.

14. AL parts are prone to cracks when bending 

Cause Analysis: 

Due to the special crystal structure of the AL material, it is easy to break in the direction of parallel lines when bending.


  • When blanking, rotate the AL material to the direction perpendicular to the bending, then cut (that is, make the material bending direction perpendicular to the texture ).
  • Increase the R angle of the upper die.

Related reading: 12 Solutions for Sheet Metal Bending Problems

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2 thoughts on “Bending Sheet Metal: 14 Problems and Solutions”

  1. You mentioned that you have been in metalworking for 10 years and you show 14 bending problems. Where is “Parts bent backwards” on your list? I have been in metalworking for over 31 years and I can tell you, “Parts bent backwards” is by far the most common bending problem. Looking for suggestions to fix “Parts bent backwards”.

    1. ① Case 1: the bending line of the workpiece to be bent is not parallel to the edge line of the workpiece, that is, one end has a fulcrum on the lower groove of the bending machine and the other end has no fulcrum. The physical object of the workpiece is shown in Figure 5, where L is the slit length.
      ② Case 2: the bending line of the workpiece to be bent is parallel to the edge line of the workpiece, but both ends have no fulcrum on the lower groove of the bending machine. The technological measures taken are as follows: ① increase slit treatment.

      For case 1, the process personnel added a slit along the bending line of the workpiece in the blanking drawing, the length of which is the outward offset of the bending line of the workpiece, and the offset width is half of the lower groove width of the selected bending machine. ② Increase allowance treatment.
      For case 2, the process personnel increased the size of the blanking drawing so that the edge has a fulcrum on the lower groove of the bending machine to meet the bending. After the bending process is completed, the cutting allowance shall be processed according to the product drawing, and the cutting opening shall be polished to meet the product quality requirements.

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