Sheet Metal Bend Allowance Unfolder
Compute flat-pattern blank lengths from material thickness, inside radius, bend angle, and K-factor β for single or multi-bend parts.
Flat-Pattern Parameters
Flat-Pattern Development Result
Total Flat Length
β
inches (blank length)
Total Bend Allowance
β
sum of all bends, inches
Sum of Leg Lengths
β
straight segments, inches
Neutral Axis Offset
β
t = K Γ T from inner face
Neutral Axis Radius
β
R + K Γ T, inches
Bends Processed
β
multi-bend breakdown below
| # | Bend Angle ΞΈ | Inside R (in) | Bend Allowance BA (in) | Running Flat Length (in) |
|---|
Formula Breakdown
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Informative Guides & Helper Articles
Best Practices for Sheet Metal Bend Allowance
Press-brake best practices for K-factor calibration, grain direction, springback compensation, and flat-pattern verification.
Read Article →Common Errors in Sheet Metal Bend Allowance
Diagnose the most common sheet metal flat-pattern errors: wrong K-factor, mixed radii, leg/angle mismatch, and springback confusion.
Read Article →Future Trends in Sheet Metal Fabrication
Press-brake automation, in-line measurement, and digital-twin simulation: where sheet metal bending and flat-pattern development are heading.
Read Article →Ultimate Guide to Sheet Metal Bend Allowance
Understand K-factor, bend allowance, and neutral-axis theory to unfold accurate sheet metal flat patterns for the press brake.
Read Article →Top Optimization Tips for Sheet Metal Bending
Optimize sheet metal fabrication: nest blanks, minimize scrap, calibrate K-factors, standardize radii, and reduce bend-shop rework.
Read Article →How to Use the Sheet Metal Unfolder
Computes flat patterns from bent sheet: bend allowance, K-factor, unfolded blank.
- Enter thickness, bend radius, angle, K-factor (~0.33-0.38 default).
- Read bend allowance and blank dimensions.
- Export the flat pattern for cutting.
Bend Allowance and the K-Factor
BA = (pi/180) x A x (r + K x t), K locating the neutral axis (0 inside, 0.5 outside; ~0.33 air-bending steel, 0.38 bottoming). Example: 90 degrees, 2 mm stock, 3 mm radius, K=0.35: BA = (pi/180) x 90 x 3.7 = 5.50 mm. Flat blank = straight legs plus allowance per bend. The K-factor is empirical - material temper, die opening, and method all move it; production shops verify with one test bend, and your CAD module runs this exact arithmetic behind the dialog.
Sheet Metal Unfolder FAQ
What is the K-factor?
Neutral-axis position as a fraction of thickness: ~0.33 air-bend steel, 0.38 bottoming. Verify with a test bend.
How is flat blank computed?
Straight legs plus bend allowance: BA = pi/180 x angle x (r + Kt). Wrong K = consistently long or short parts.
Why do first articles miss?
K varies with material lot and method. Cut one test piece, adjust - ten minutes that saves a sheet.