BIZOMAT MAKEOS · Fabrication
Sheet Metal Bending Springback
How much will this bend spring back, and how far must it be overbent?
Final bend radius and angle after springback for sheet metal from the tool radius, thickness, yield strength and modulus, with the springback factor and overbend angle.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bend radius before release (tool radius) | mm | Inside radius while the sheet is held in the tool. |
| Thickness | mm | Sheet thickness. |
| Yield strength | MPa | Yield strength of the sheet (higher strength springs back more). |
| Elastic modulus | GPa | Elastic modulus (steel 200, aluminium about 70 GPa). |
| Required final bend angle | ° | Bend angle required after release. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Bend radius before release (tool radius)
- What it is
- The inside bend radius while the sheet is still held in the tool, normally the punch or die radius.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger tool radius relative to thickness gives more springback.
- Get it right
- This is the radius under load, not the final radius after springback.
What this means: Thickness
- What it is
- The thickness of the sheet or plate being bent, measured square to its surface on the actual stock.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Thicker sheet springs back less for the same radius and material.
- Get it right
- Use the measured thickness; sheet can vary from its nominal gauge.
What this means: Yield strength
- What it is
- The yield strength of the sheet material, from the material certificate or test.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 3000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher yield strength gives more springback.
- Get it right
- Use the batch certificate value where possible; yield varies between batches.
What this means: Elastic modulus
- What it is
- The elastic (Young’s) modulus of the sheet material, which sets how much it recovers when the load is released.
- Units and format
- Enter a number in GPa: gigapascals (1 GPa = 1000 MPa). The form accepts 0.000001 GPa to 1000 GPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 GPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower modulus gives more springback.
- Get it right
- Enter gigapascals, not megapascals.
What this means: Required final bend angle
- What it is
- The bend angle the part must have after it is released from the tool, as shown on the drawing.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 1° to 179°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The angle to bend to is this angle divided by the springback factor.
- Get it right
- Use the same angle convention as your press brake: the angle bent through, not the included angle.
Method and formulas
- x = Ri × YS ÷ (E t). Ri ÷ Rf = 4x³ − 3x + 1.
- Neutral length is unchanged: (Ri + t/2) θi = (Rf + t/2) θf; springback factor K = θf ÷ θi.
- Bend angle in the tool = required angle ÷ K.
- Example: 2 mm mild steel on a 6 mm radius: K = 0.99034, so bend to 90.878° for 90°.
Limitations
- Approximate formula for free bending; bottoming and coining reduce springback.
- Material property scatter makes trial bends essential.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set overbend on a press brake
- Choose a punch radius for a final radius
- Compare materials for springback
Who it is for
- Fabrication supervisors
- Manufacturing engineers
- Estimators
What you get
- Final radius after springback
- Springback factor
- Angle to bend to (overbend)
Interpreting the result
- Large radius-to-thickness ratios and high-strength materials spring back most.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1351–1352. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Springback and overbending
In Sheet Metal Parts by the Numbers
What it covers: Estimate springback from material strength, modulus, radius and thickness, see why it grows with radius, calculate the overbend a folder needs, and what a small angle error does to a flange.
Method explained here · BIZOMAT original book
Bending plate past yield
In Yield and Plastic Flow by the Numbers
What it covers: What happens through the thickness of a bend, the tightest radius a plate takes without cracking, how much it springs back, and why a punch change and a nesting change cracked a batch of brackets.
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