Sheet Metal Bending: What It Is and How It Works

Table of Contents

1.0What Is Bending in Sheet Metal?
2.0How Bending Differs from Other Forming Processes
3.0How Bar Folders and Press Brakes Are Used
4.0What Are Air Bending, Bottoming, and Coining?
5.0How Roll Bending Works
6.0What Are Draw, Compression, and Press Bending?
7.0How to Bend Tubes Effectively
8.0What Is Roll Forming?
9.0How Seaming and Flanging Work
10.0How to Straighten or Flatten Metal
11.0How to Design for Better Bending
12.0How to Calculate Flat Blank Size
13.0Summary

Sheet metal bending is a fundamental plastic deformation process used in the manufacturing of countless metal components. This guide explains the principles behind bending, the types of bending operations, tooling considerations, and best practices for design and execution.

1.0What Is Bending in Sheet Metal?

Bending is a plastic deformation process where metal is deformed around a linear axis with little or no change in surface area. Key characteristics of bending include:

Tension on the outer surface of the bend
Compression on the inner surface
Thinning near the neutral axis
Springback, or the partial return of the material after deformation

2.0How Bending Differs from Other Forming Processes

Forming: Multiple bends are produced using a single die setup.
Drawing and stretching: The deformation is not limited to linear axes or may involve multiple non-independent axes.

top nature of a bend in sheet metal showing tension on the outside and compression on the inside bottom the upper portion of the bend region viewed from the side shows how the center portion — (Top) Nature of a bend in sheet metal showing tension on the outside and compression on the inside. (Bottom) The upper portion of the bendregion, viewed from the side, shows how the center portion will thin more than the edges.

3.0How Bar Folders and Press Brakes Are Used

Bar Folders

Suitable for light-gauge sheet metal
Can produce bends up to 150 degrees
Ideal for small-scale precision bending

Press Brakes

Used for thicker materials or more complex bends
Capable of forming various angles and contours with the correct tooling

press brake dies can form a variety of angles and contours — Press brake dies can form a variety of angles and contours

4.0What Are Air Bending, Bottoming, and Coining?

Air Bending

Uses a three-point bending method
The bend angle is controlled by the depth of punch penetration
Less force required, more flexible for different materials

Bottoming

The punch fully contacts the bottom die
The bend angle is fixed by the die geometry
Offers better control of springback

Coining

A high-force variant of bottoming
Material is compressed beyond its yield point
Produces precise and repeatable bends

comparison of air bend left and bottoming right press brake dies with the air bend die the amount of bend is controlled by the bottoming position of the upper die — Comparison of air-bend (left) and bottoming (right) press brake dies. With the air- bend die, the amount of bend is controlled by
the bottoming position of the upper die.

5.0How Roll Bending Works

Roll bending is a continuous form of three-point bending where plates, sheets, or beams are gradually bent between rollers. It is ideal for:

Producing large-radius bends
Forming cylindrical or curved profiles
Processing beams, tubes, and heavy-gauge materials

hydraulic three roller pipe roll benders 2 — Hydraulic Three Roller Pipe Roll Benders

6.0What Are Draw, Compression, and Press Bending?

Draw Bending: A rotating form block pulls the material into shape.
Compression Bending: A movable tool compresses the material against a fixed die.
Press Bending: A press ram drives the punch into the forming die to create the bend.

overview of common tube bending methods draw compression and press bending — (a) Draw bending, in which the form block rotates; (b) compression bending, in which a moving tool compresses the workpiece against a stationary form; (c) press bending, where the press ram moves the bending form

7.0How to Bend Tubes Effectively

Key parameters for successful tube bending include:

Outer diameter (OD)of the tube
Wall thickness
Bend radius

Proper tooling and technique prevent deformation issues such as flattening, wrinkling, or wall thinning.

a schematic representation of the cold roll forming process being used to convert sheet or plate into tube b some typical shapes produced by roll forming — (a) Schematic representation of the cold roll- forming process being used to convert sheet or plate into tube. (b) Some typical shapes
produced by roll forming

square round pipe bending machine — square &round pipe bending machine

8.0What Is Roll Forming?

Roll forming is a progressive bending process where a metal strip passes through multiple rollers, each making incremental bends. Key characteristics:

Only bending is involved, no cutting or punching
All bends are parallel
Ideal for producing long, complex profiles
Setup and changeover can be time-consuming

eight roll sequence for the roll forming of a box channel — Eight-roll sequence for the roll forming of a box channel

9.0How Seaming and Flanging Work

Seaming is used to mechanically interlock sheet edges—common in cans, containers, and drums
Flanging involves bending the sheet edge to create a rim or stiffener
Both operations rely on controlled bending along the edge of the sheet

various types of seams used on sheet metal — Various types of seams used on sheet metal

10.0How to Straighten or Flatten Metal

Straightening is often required before further forming operations to ensure flatness. Common methods include:

Roller Leveling: Material passes through alternating roller sets to gradually eliminate curvature
Stretcher Leveling: Material is clamped and stretched to achieve the desired flatness

method of straightening rod or sheet by passing it through a set of straightening rollsfor rods another set of rolls is used to provide straightening in the transverse direction — Method of straightening rod or sheet by passing it through a set of
straightening rolls. For rods, another set of rolls is used to provide straightening in the transverse direction.

11.0How to Design for Better Bending

When designing for bending, several critical factors must be considered:

What Is the Minimum Bend Radius?

The minimum bend radius depends on material ductility and thickness
Bends that are too sharp may cause cracks

How Does Springback Affect the Bend?

Large punch radii and shallow angles often result in significant springback
Tighter bends reduce springback but increase internal stress

bends should be made with the bend axis perpendicular to the rolling direction when intersecting bends are made both should be at an angle to the rolling direction — Bends should be made with the bend axis perpendicular to the rolling direction. When intersecting bends are made, both should be at an angle to the rolling direction, as shown.

Why Material Direction Matters

Bending perpendicular to the rolling direction is preferred
For intersecting bends, align both at an angle to the rolling direction to prevent cracking

12.0How to Calculate Flat Blank Size

When planning a bent part, it’s essential to determine the correct flat blank length (L). Considerations include:

Material thinning in the bend region
Bend radius (R)and thickness (t)
Use formulas or bend allowance tables to account for material behavior and dimensional changes during forming

relationship between the minimum bend radius relative to thickness and the ductility of the metal being bent as measured by the reduction in area in a uniaxial tensile test — Relationship between the minimum bend radius (relative to thickness) and the ductility of the metal being bent (as measured by the reduction in area in a uniaxial tensile test).

13.0Summary

Sheet metal bending is a versatile and essential forming technique used across industries. By understanding the principles behind the process and carefully planning the design and tooling, manufacturers can ensure high-quality, accurate parts with minimal waste. Whether using press brakes, roll forming, or advanced bending dies, the key to success lies in precision and material understanding.