Sheet Metal Bending Process
Sheet metal bending is a fundamental process in metal fabrication and one of Safewell Fab’s core competencies. With over 20 years of experience in sheet metal processing, including bending, Safewell Fab excels in producing precise angles and shapes in metal components. This process is often the final step in shaping a part, and its quality directly impacts the final product’s dimensions and appearance. This article provides a simple overview for beginners as well as detailed technical insights to help you better understand the sheet metal bending process.
How Does Sheet Metal Forming Work?
Sheet metal bending is a metal forming process in which a metal sheet is bent to the desired angle using a bending machine, without altering the metal’s volume.
Sheet metal Bending Cases
Common Bending Methods
Air Bending
The sheet does not fully contact the die, allowing flexible angle formation. This method requires less force but offers lower precision.
Bottoming (or Coining) Bending
The sheet is pressed completely into the die to achieve precise angles. This method requires higher force but results in greater accuracy.
Roll Bending
The sheet is passed through a set of rollers to form smooth, large-radius curves, suitable for cylindrical or conical parts.
V-Bending and U-Bending
Named after their final shapes, these are the most common operations performed on press brakes.
Key Principles and Points of Attention
1.Elastic and Plastic Deformation
During bending, the metal sheet undergoes two stages: elastic deformation (temporary) and plastic deformation (permanent). Once the bending force exceeds the material’s yield strength, the shape is permanently altered.
2.Springback
After bending, the metal tends to slightly return to its original shape due to elasticity, a phenomenon known as springback. Factors influencing springback include material properties, the bending radius, part geometry, die clearance, and bending pressure. A larger ratio of inner bend radius to material thickness results in greater springback. Springback is commonly addressed by mold manufacturers through compensatory die design or by adding corrective processes after bending.
3.Pre-Processing of Holes, Grooves, and Notches
To enhance bending accuracy and prevent cumulative errors in multi-bend operations, pre-processing holes can serve as bending reference points. Additionally, local deformations during bending may affect the appearance, and process cuts can effectively prevent this issue.
4.Bending Direction
When determining the bending direction, the fracture band from blanking should ideally be on the inside of the bend to avoid crack propagation. For pipes, the weld seam should also be positioned on the inner side of the bend.
Common Bending Problems and Solutions
1. Bending Dimensions Do Not Meet Drawing Requirements
Causes: Inaccurate unfolded dimensions, inaccurate positioning, cumulative errors from multiple bends.
Solutions: Adjust bending factors and recalculate unfolded dimensions; adjust positioning; select reasonable reference points to eliminate cumulative errors.
2. Bend Angles Are Too Large or Too Small
Causes: Inappropriate die V-slot width, improper springback compensation parameters, unsuitable pressure.
Solutions: Select suitable V-slot width dies; adjust springback compensation values and pressure.
3. Inconsistent Bend Angles at Both Ends
Causes: Uneven die wear, non-parallel upper and lower dies on the press brake.
Solutions: Adjust or regrind the dies; ensure the upper and lower dies are parallel.
4. Inconsistent Bending Dimensions
Causes: Inconsistent back gauge distances from the die center; material distortion.
Solutions: Adjust back gauge positions, apply light force during bending; correct material deformation.
5. Interference During Part Processing, Bending Cannot Be Fully Completed
Causes: Improper die configuration, unreasonable bending sequence, flawed structural design.
Solutions: Reconfigure suitable dies; modify bending sequence; revise structural design.
6. Surface Indentation on Bent Parts
Causes: Small radius on the lower die.
Solutions: Regrind the die to increase the lower die radius; use non-indentation dies; place protective film between the lower die and the sheet.
7. Cracks at the Corners of Bent Sheets
Causes: Too small bending radius, grain direction parallel to the bending line, burrs facing outward, low material plasticity.
Solutions: Increase bending radius; alter material layout; place burrs on the inner corner; perform annealing or use materials with better plasticity.
