BIZOMAT MAKEOS · Fabrication
Sheet-Metal Bracket: Flat Blank, Nesting, Bending Force and Cost
What flat blank, sheet yield, bending force and cost per part does this bent sheet-metal bracket have?
Cost build-up of a one- or two-bend sheet-metal part: developed flat length from outside dimensions with the bend allowance and deduction (K-factor), parts per sheet in the better orientation with spacing, material utilisation and cost per part, press brake force per bend, and labour cost from bend and blanking times with set-up spread over the batch.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Part | ||
| First flange (outside) | mm | Outside length of the first flange. |
| Web (outside) | mm | Outside length of the web between bends. |
| Second flange (outside, 0 = one bend) | mm | Outside length of the second flange (0 for an L-bracket). |
| Part width | mm | Width of the part along the bend line. |
| Thickness | mm | Material thickness. |
| Inside bend radius | mm | Inside radius of the bends. |
| K-factor | K-factor locating the neutral axis (about 0.33–0.45 for air bending). | |
| Bend angle | ° | Bend angle of each bend. |
| Sheet and material | ||
| Sheet length | mm | Length of the stock sheet. |
| Sheet width | mm | Width of the stock sheet. |
| Spacing and edge margin | mm | Spacing between blanks and at the sheet edge. |
| Density | kg/m³ | Material density. |
| Sheet price | $/kg | Price of the sheet per kilogram. |
| Tensile strength | MPa | Tensile strength of the sheet. |
| Press brake and labour | ||
| Die opening | mm | Opening of the bending die (6–12 × thickness). |
| Air-bending factor | Air-bending force factor (1.33 is common). | |
| Shop rate | $/h | Machine and labour rate. |
| Time per bend | s | Handling and bending time per bend. |
| Blanking time per part | s | Time to cut each blank. |
| Set-up time per batch | min | Set-up time for the batch. |
| Batch quantity | Parts in the batch. | |
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.
Part
What this means: First flange (outside)
- What it is
- Outside length of the first flange, from its free edge to the outside face of the web, as dimensioned on the drawing.
- 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 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, not inside or centreline; the bend deduction here assumes outside dimensions.
What this means: Web (outside)
- What it is
- Outside length of the web, the leg between the bends, measured over the outside faces (to the free edge on an L-bracket).
- 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 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Outside dimension over both bends, as for the flanges.
What this means: Second flange (outside, 0 = one bend)
- What it is
- Outside length of the second flange of a channel or U-bracket, measured from its free edge to the outside face of the web.
- 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
- 0 = one bend: the part becomes an L-bracket and the blank has one bend deduction instead of two.
What this means: Part width
- What it is
- Width of the part measured along the bend line, which is also the length of each bend formed on the press brake.
- 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 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force rises in proportion to width; it also sets the blank width for nesting.
What this means: Thickness
- What it is
- Thickness of the sheet, from the material order or a micrometer reading of the actual stock.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 30 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
- Bending force rises with the square of thickness for the same die opening.
- Get it right
- Measure the sheet; gauge numbers mean different thicknesses for different materials and standards.
What this means: Inside bend radius
- What it is
- Radius on the inside of each bend, as dimensioned on the drawing or as produced by the punch and die.
- 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 2 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 outside: outside radius = inside radius + thickness.
What this means: K-factor
- What it is
- Where the neutral layer, which neither stretches nor shrinks, sits within the thickness, as a fraction of thickness from the inside face. It sets the bend allowance.
- Units and format
- Enter a plain number with no unit. The form accepts 0.2 to 0.5. 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.
- Get it right
- Best found from a test bend on your own press brake and material; it varies with radius, thickness and bending method.
What this means: Bend angle
- What it is
- Angle each bend turns the material through, measured from flat. Both bends of a channel use this same angle.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 10° 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
- Bend angle from flat, not the included angle between flanges: an included angle of 120° is a 60° bend.
Sheet and material
What this means: Sheet length
- What it is
- Length of the stock sheet the blanks are cut from, as bought from the supplier.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2500 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Sheet width
- What it is
- Width of the stock sheet the blanks are cut from, the shorter side of a standard sheet as bought.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Spacing and edge margin
- What it is
- Clear space left between neighbouring blanks and at the sheet edges for the cutting kerf, piercing and handling.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- The same value is used between blanks and as the margin at each sheet edge.
What this means: Density
- What it is
- Mass of one cubic metre of the sheet material, from the supplier or a materials reference. It turns the sheet size into kilograms for costing.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 20000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Sheet price
- What it is
- What you pay per kilogram of sheet, delivered, from your supplier’s current quotation.
- Units and format
- Enter a number in $/kg: money per kilogram. The form accepts $0/kg to $10000/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $1.5/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Material cost per part rises in direct proportion.
- Get it right
- The whole sheet is costed and shared over the parts, so offcuts are paid for; enter price per kilogram, not per sheet.
What this means: Tensile strength
- What it is
- Ultimate tensile strength of the sheet material, from the mill certificate or data sheet, used to estimate the press brake force.
- 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 450 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force is proportional to tensile strength.
- Get it right
- Use tensile strength, not yield strength.
Press brake and labour
What this means: Die opening
- What it is
- Width of the V opening of the bottom die, measured across its top edges. It sets the leverage in air bending.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 500 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 16 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force is inversely proportional to the die opening.
- Get it right
- Measure across the top of the V, not its depth.
What this means: Air-bending factor
- What it is
- Multiplier in the air-bending force formula that accounts for die geometry and friction, from the press brake or tooling maker.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.33 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Bending force is proportional to this factor.
What this means: Shop rate
- What it is
- Hourly charge for the machines and operator together, including overheads, applied to blanking, bending and set-up time.
- Units and format
- Enter a number in $/h: money per hour. The form accepts $0/h to $10000/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $90/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Time per bend
- What it is
- Time to pick up, position and form one bend on one part, including turning the part between bends.
- Units and format
- Enter a number in s: seconds. The form accepts 0 s to 3600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Labour cost per part rises with the number of bends times this time.
- Get it right
- Seconds per bend per part; a channel has two bends, so its time counts twice.
What this means: Blanking time per part
- What it is
- Time to cut one blank from the sheet on the laser, punch or shear, including its share of sheet loading and unloading.
- Units and format
- Enter a number in s: seconds. The form accepts 0 s to 3600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Seconds per part, not per sheet.
What this means: Set-up time per batch
- What it is
- Time to change over the cutting machine and press brake for this part, shared across every part in the batch.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 100000 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Its cost per part falls in proportion to batch size.
- Get it right
- Minutes, not seconds or hours.
What this means: Batch quantity
- What it is
- Number of parts made in one run after a single set-up.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 100000000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Larger batches spread the set-up cost over more parts.
Method and formulas
- Bend allowance BA = θ (R + k t); outside setback = (R + t) tan(θ ÷ 2); deduction = 2 × setback − BA (as the bend allowance tool).
- Flat length = sum of outside dimensions − bends × deduction.
- Parts per sheet = best of the two orientations of ⌊(L_s − gap) ÷ (blank + gap)⌋ × ⌊(W_s − gap) ÷ (width + gap)⌋.
- Bend force = k W t² UTS ÷ V; cost = sheet cost ÷ parts + rate × (bends × t_bend + t_blank) + set-up share.
- Example: the default bracket blanks at 172.8 × 100 mm, nests 161 per sheet and costs about 2.1571 each.
Limitations
- Rectangular blanks on a simple grid; true nesting software can do better.
- Holes, notches and finishing are not costed.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Quote a bent bracket or cover
- Choose sheet size for best yield
- Check press brake capacity for a part
Who it is for
- Estimators
- Fabrication supervisors
- Design engineers
What you get
- Flat blank and parts per sheet
- Bending force
- Cost per part
Interpreting the result
- Utilisation under about 75% suggests trying another sheet size or orientation.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1346–1353. Topic reference; no source tables or recommended settings are reproduced.
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Open the Sheet-Metal Bracket: Flat Blank, Nesting, Bending Force and Cost calculator