Bending in Press Working

Definition

Bending is a metal forming process in which a force is applied to a piece of sheet metal, causing it to bend at a specific angle and form a desired shape. This process occurs by plastically deforming the metal around a linear axis without changing the thickness of the material significantly.

Main Content

1. Neutral Axis and Strain

• During bending, the outer fibers of the metal are stretched (tension), while the inner fibers are compressed.
• The neutral axis is the layer within the metal that undergoes no change in length during the process; it serves as the reference point for calculating the bend allowance.

2. Springback Effect

• Springback is the elastic recovery of the metal after the bending pressure is released.
• Because the metal has elastic properties, it attempts to return to its original shape, causing the final bend angle to be slightly larger than the angle of the die.

3. Bend Allowance and Bend Radius

• Bend allowance is the length of the neutral axis between the tangent points of the bend, used to calculate the required blank length.
• The bend radius is the internal radius at the bend; a radius that is too small can cause cracking on the outer surface of the material.

       Force (Punch)
          |
        __v__
       |     |
    ___|     |___
   |   (Bend)    |
   |_____________|  <-- Sheet Metal
      /       \
     /   Die   \

(Diagram: Basic representation of a V-bending setup)

Working / Process

1. Positioning the Blank

• The flat metal sheet (blank) is placed precisely on the die surface or against a back gauge.
• Correct alignment is critical to ensure the bend line is positioned accurately for the final part dimensions.

2. Application of Force

• The press ram descends, pushing the punch into the sheet metal.
• The punch forces the material into the die cavity, overcoming the yield strength of the metal to initiate plastic deformation.

3. Completion and Stripping

• The punch reaches the bottom of its stroke, setting the bend angle.
• The press ram retracts, and a stripper mechanism removes the finished part from the punch or die to prepare for the next cycle.

Advantages / Applications

• Allows for the creation of complex structural shapes like channels, angles, and brackets from simple flat sheets.
• Highly efficient for mass production, significantly reducing the time required to manufacture automotive, aerospace, and appliance parts.
• Provides high dimensional accuracy and part repeatability when using modern CNC press brakes.

Summary

Bending is a fundamental press working operation that utilizes mechanical force to permanently deform sheet metal into specific angular geometries. The process relies on the relationship between tension and compression within the material, with careful consideration given to springback to ensure precision. Important terms to remember include neutral axis, bend allowance, springback, yield strength, and bend radius.