Overcoming 14 Common Problems When Bending Sheet Metal

Are you struggling with sheet metal bending problems? Look no further! In this article, we provide a comprehensive analysis of 14 common sheet metal bending problems and their respective solutions.

From slip material during processing to AL parts prone to cracks, we cover it all.

Our expert analysis and practical solutions will help you overcome any challenges you may face in sheet metal bending processes. Whether you are a beginner or a seasoned professional, you will find this information valuable and informative.

Say goodbye to wasted time, materials, and money due to sheet metal bending problems. With our solutions, you can improve your efficiency, productivity, and quality.

Don’t let sheet metal bending problems hold you back. Read on to discover the solutions you need to succeed.

1. Slip material during processing

Cause Analysis:

When selecting the bending die, a V-groove width of 4 to 6 times the material thickness (T) is typically chosen. However, if the size of the bend is less than half the width of the selected V-groove, slippage can occur.

Problem: The V-groove selected is too large.

Solutions:

1. Centerline deviation method (eccentric machining). When the size of the material to be bent is less than half of 4 to 6 times T, make up as much as possible.
2. Padding processing
3. Bend with a small V-groove and press with a large V-groove.
4. Select a smaller V-groove.

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

Cause Analysis:

The standard width of the lower die of the bending machine must be at least 10mm. Therefore, the material being bent must be less than 10mm in thickness. If the bend is a 90 degree angle, its length must not be less than √2 (L + V / 2) + T.

To avoid displacement of the mold and any resulting scrap or safety accidents, the mold must be securely fixed on the mold base, with the exception of any upward degree of freedom.

Solutions:

• Increase the size of the bend by negotiating with the customer and making the inner bend wider.
• Special processing of the mold.
• Use grinding tools, though this will increase processing costs.

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. If L is less than (4 to 6) times the plate thickness T divided by 2, the material will experience pull-through. This is because during the bending process, tensile force deforms the material, causing pull-through and distortion.

The minimum value of L for different plate thicknesses, based on the standard mold’s groove width, is as follows:

Solutions:

• Increase the size of the bend and trim the hem after forming.
• Expand the hole to the bend line, but only if it does not affect the appearance or function and the customer agrees.
• Use secant or crimping processing.
• Eccentrically process the mold.
• 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 is less than (4 to 6) times the plate thickness T divided by 2, the material will experience deformation during the bending process due to contact between the material and the lower mold.

Solutions:

• Use secant or crimping processing.
• Modify the material size.
• Employ special mold processing.
• Eccentrically process the mold.

5. The long flattening side rises after flattening

Cause Analysis:

The long flattening edge may not adhere tightly during the flattening process, causing it to rise at the ends. This issue is largely dependent on the flattening position, so it is important to pay close attention to the flattening position.

Solutions:

• First bend the upward angle (as shown in 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 root part.

Precautions:

The quality of the flattening process is dependent on the operator’s skills, so it is important to pay close attention to the actual situation during flattening.

6. Large-height draw bridge is easy to break

Cause Analysis:

The material is severely stretched and fractured due to the high height of the draw bridge. Other causes may include:

• Insufficient sharpening or dull special mold corners.
• Poor material toughness or a narrow draw bridge.

Solutions:

• 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. Note that this method will make the surface of the workpiece dirty and cannot be used for AL parts, etc.

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

Cause Analysis:

The workpiece is displaced forward during processing due to a forward pressing force, causing an increase in the small angle L of the front portion.

Solutions:

• Remove any shadows in the picture and try to make it up as much as possible.
• Replace worn self-positioning parts of the mold with back-initiating structures for better positioning.

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.
• Incorrect feeding size.

Solutions:

• Calculate the deviation assigned to each bend based on the total deviation and the number of bends in the deviation direction.
• If the calculated distribution tolerance is within the tolerance range, the workpiece is considered acceptable.
• If the size is too large, use a small V-groove.
• If the size is too small, use a large V-groove.

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

Cause Analysis:

• Spalling occurs due to a small R angle of the draw-hole or excessive burr on the flange.
• The riveting is loose because the draw holes are not properly aligned.
• Deformation is caused by misaligned holes or incorrect riveting method.

Solutions:

• Use a center punch with a larger R angle and pay attention to the burrs around the draw hole when flanging.
• Increase the pressure, deepen the broaching, and use a center punch with a larger R angle.
• Address the root cause of the misaligned holes and incorrect riveting method.

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

Cause Analysis:

• The workpiece is not flattened during processing.
• Uneven force or excessive pressure is applied to the lower surface of the workpiece.

Solutions:

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

11. The two sides are not parallel after offset bending

Cause Analysis:

• The mold is not calibrated correctly.
• The upper and lower die gaskets are not adjusted properly.
• The upper and lower die faces are not identical.

Solutions:

• Recalibrate the mold.
• Adjust the gaskets by increasing or decreasing them.
• Use eccentric processing for the mold.
• Ensure that the upper and lower mold have the same surface.

12. The product surface crease is too deep

Cause Analysis:

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

Solutions:

• Use a large V-groove for processing.
• Use a mold with a large R angle.
• Use padding bending (with metal or casting polyurethane).

13. The area near the bend deformed after bending

Cause Analysis:

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

Solutions:

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

14. AL parts are prone to cracks when bending

The AL material is prone to breaking along parallel lines during bending due to its special crystal structure.

Solutions:

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

Related reading: 12 Solutions for Sheet Metal Bending Problems