BIZOMAT MAKEOS · Fabrication
Sheet-Metal Flat Pattern (Up to Four Bends)
What flat blank length gives this formed part with up to four bends, and are the flanges and bend radius workable on the press brake?
Flat pattern of a formed sheet-metal part with up to four bends of the same inside radius: bend allowance, outside setback and bend deduction for each bend angle from the K-factor (as the bend allowance tool), the flat length from the outside flange dimensions less the deductions, and checks that every flange is longer than its setbacks and your shortest flange for the die, and that the inside radius is at least your minimum ratio to thickness.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Thickness | mm | Sheet thickness. |
| Inside bend radius | mm | Inside radius of every bend. |
| K-factor | Position of the neutral axis as a share of thickness (about 0.33–0.45 for air bending). | |
| Flanges (outside dimensions) and bends | ||
| Flange 1 | mm | Outside length of the first flange. |
| Bend 1 angle (0 = no bend) | ° | Angle of the first bend (the change in direction; 90° for a right-angle bend; 0 if there are no bends). |
| Flange 2 | mm | Outside length of the second flange (between bends 1 and 2, outside to outside). |
| Bend 2 angle | ° | Angle of the second bend (0 to stop here). |
| Flange 3 | mm | Outside length of the third flange. |
| Bend 3 angle | ° | Angle of the third bend. |
| Flange 4 | mm | Outside length of the fourth flange. |
| Bend 4 angle | ° | Angle of the fourth bend. |
| Flange 5 | mm | Outside length of the fifth flange. |
| Your limits | ||
| Shortest flange for the die | mm | Shortest flange the press-brake die can form (see the press brake set-up tool). |
| Smallest inside radius ÷ thickness | Smallest inside radius as a multiple of thickness for the material (your value). | |
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: Thickness
- What it is
- The thickness of the sheet being bent, from the material specification or a measurement.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 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.
- Get it right
- Measure the actual sheet; gauge numbers differ between materials.
What this means: Inside bend radius
- What it is
- The inside radius of every bend in the part, as formed by the punch or set on the drawing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Inside radius, not the outside radius or the radius to the neutral axis.
What this means: K-factor
- What it is
- The K-factor: where the neutral axis lies within the sheet thickness, as a fraction measured from the inside of the bend. Take it from bend tests or your tooling records.
- Units and format
- Enter a plain number with no unit. The form accepts 0.2 to 0.55. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger K-factor increases the bend allowance and lengthens the flat pattern.
- Get it right
- Enter a fraction of thickness, not a percentage.
Flanges (outside dimensions) and bends
What this means: Flange 1
- What it is
- The outside length of the first flange, measured on the outside of the part to the outside face of the next leg.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use outside dimensions throughout; inside dimensions give the wrong flat length.
What this means: Bend 1 angle (0 = no bend)
- What it is
- The angle of the first bend, as the change in direction of the sheet. Enter 0 if the part has no bends.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 175°. 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.
- Get it right
- A right-angle bend is 90°, the change in direction, not the included angle between flanges.
What this means: Flange 2
- What it is
- The outside length of the second flange, measured outside to outside between bends 1 and 2, or to its free end if it is the last.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use outside dimensions throughout.
What this means: Bend 2 angle
- What it is
- The angle of the second bend, as the change in direction of the sheet. Enter 0 to end the part after flange 2.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 175°. 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.
- Get it right
- Bends after the first zero angle are ignored.
What this means: Flange 3
- What it is
- The outside length of the third flange, measured outside to outside between bends 2 and 3, or to its free end if it is the last.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Bend 3 angle
- What it is
- The angle of the third bend, as the change in direction of the sheet. Enter 0 to end the part after flange 3.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 175°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Bends after the first zero angle are ignored.
What this means: Flange 4
- What it is
- The outside length of the fourth flange, measured outside to outside between bends 3 and 4, or to its free end if it is the last.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Bend 4 angle
- What it is
- The angle of the fourth bend, as the change in direction of the sheet. Enter 0 to end the part after flange 4.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 175°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Flange 5
- What it is
- The outside length of the fifth flange, the free end after the fourth bend.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It is used only when bend 4 has an angle.
Your limits
What this means: Shortest flange for the die
- What it is
- The shortest end flange your press-brake die can form, set by the die opening. The first and last flanges are checked against it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take it from your die opening and tooling data.
What this means: Smallest inside radius ÷ thickness
- What it is
- The smallest inside bend radius the material can take without cracking, stated as a multiple of thickness. Take it from the material supplier or your bend trials.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 10. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- This is a ratio, radius ÷ thickness, not a radius in millimetres.
Method and formulas
- Bend allowance = θ (R + K t); outside setback = (R + t) tan(θ ÷ 2); bend deduction = 2 × setback − allowance (as the bend allowance tool).
- Flat length = Σ outside flanges − Σ bend deductions.
- Each flange must exceed the setbacks of the bends at its ends, and the end flanges your die minimum.
- Example: 2 bends of 3 mm radius in 2 mm sheet give a flat length of 101.94 mm.
Limitations
- All bends share one radius and K-factor; mixed radii need separate deductions.
- Outside dimensions to the virtual sharps; dimension to the drawing’s convention.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Cut blanks for a channel, hat or Z section
- Check a drawing’s flanges against the press brake die
- Compare K-factors for a material
Who it is for
- Sheet-metal designers
- Press brake operators
- Fabrication supervisors
What you get
- Allowance, setback and deduction for each bend
- Flat length
- Flange and radius checks
Interpreting the result
- Confirm the K-factor with a test bend: a 0.05 error changes each 90° deduction by about 0.08 t.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1346–1353. 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 · Library collection
Designing sheet metal parts for economical manufacture: bends, holes, flat patterns, fasteners and tolerances
In Manufacturing Operations and Design for Manufacture
What it covers: Sheet metal parts are cheap when designed for the cutter and press brake. How to set bend radii, place holes and flanges, get flat patterns right and tolerance folded parts.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Sheet-Metal Flat Pattern (Up to Four Bends) calculator