Bend Allowance (Flat Length)
Calculate the material length consumed in a bend (bend allowance), BA = (π/180)·θ·(R + K·t), from the bend angle θ (degrees), inner bend radius R (mm), thickness t (mm) and K factor (neutral-line factor, typically 0.33-0.5). This is one of the most important — and subtlest — calculations in sheet metal work: to make a bent part to correct dimensions, you must know the FLAT sheet (blank) size before bending. The catch is that, on bending, the outer face STRETCHES and the inner face COMPRESSES, and there is an intermediate line — the neutral line — that does not change length. The K factor locates that neutral line within the thickness (not exactly in the middle, but shifted inward, so K < 0.5). The total developed length is the sum of the straight flanges plus each bend's allowance. Getting this wrong makes out-of-size parts — a costly production error. So blank development (with K factors calibrated by material and process) is a critical step in sheet-part design, now automated in sheet-metal CAD. Enter the angle, inner radius, thickness and K factor.
Resultado
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Comprimento planificado da dobra
O comprimento de material consumido em uma dobra (bend allowance) é BA = (π/180)·θ·(R + K·t), a partir do ângulo de dobra θ, do raio interno R, da espessura t e do fator K (fator da linha neutra, tipicamente 0,33 a 0,5). Este é um dos cálculos mais importantes — e mais sutis — da estamparia e da funilaria: para fabricar uma peça dobrada com as dimensões corretas, é preciso saber o tamanho da chapa plana (o blank) antes de dobrar. O problema é que, ao dobrar, o material da face externa estica e o da face interna comprime, e existe uma linha intermediária — a linha neutra — que não muda de comprimento. O fator K localiza essa linha neutra dentro da espessura (ela não fica exatamente no meio, mas deslocada para dentro, por isso K < 0,5). O comprimento desenvolvido total da peça é a soma dos trechos retos (flanges) mais os bend allowances de cada dobra. Errar esse cálculo produz peças fora de medida — um erro caríssimo em produção em série, descoberto só depois de cortar e dobrar centenas de peças. Por isso o desenvolvimento de blanks (com fatores K calibrados por material e processo) é uma etapa crítica do projeto de peças de chapa dobrada, hoje automatizada nos softwares CAD de chapa metálica (sheet metal). Informe o ângulo, o raio interno, o fator K e a espessura.
Related Tools
V-Bending Force
Calculate the force to bend a sheet in a V-die, F = (C·σ_r·L·t²) ÷ V, from the process constant C (~1.33 for free V-bending), the material tensile strength σ_r (N/mm²), the bend length L (mm), the sheet thickness t (mm) and the V-die opening V (mm). V-bending is the most common forming operation on press brakes: the sheet rests on a V-shaped die and a punch forces it in, bending it to the desired angle. Force grows with the SQUARE of thickness (thicker sheets need much higher forces) and with material strength, and decreases with die opening (larger V → lower force, but larger bend radius). The rule of thumb uses V ≈ 6-8 times the thickness. Computing the force is essential to select the press brake (tonnage) and not overload the tooling. The bend-tonnage tables ubiquitous in sheet shops are exactly this formula applied to combinations of thickness, material and die opening. Enter the constant, tensile strength, length, thickness and die opening.
Half-Wave Dipole Length
Calculate the physical length of a half-wave dipole, L = (150 ÷ f)·VF, from the frequency f (MHz) and the velocity factor VF (typically ~0.95 for wires, correcting the end effect). The result, in metres, is the total length of the dipole antenna resonant at the desired frequency — each arm is half this value. The half-wave dipole is the most used reference antenna, with 2.15 dBi gain. The velocity factor makes the antenna slightly shorter than a half wavelength in vacuum. Enter the frequency and the velocity factor.
Minimum Bend Radius
Estimate a sheet's minimum bend radius, R_min = t·(50/r − 1), from the thickness t (mm) and the material's percent reduction of area r in the tensile test (%, a ductility measure). The minimum radius is the smallest inner radius you can bend a sheet to WITHOUT cracking the outer face (which is in tension). Bending below the minimum causes cracks or rupture in the outer fiber, where tensile strain exceeds the material's capacity. The minimum radius depends strongly on the material's DUCTILITY (here via reduction of area r): very ductile materials (annealed aluminum, low-carbon steels) can be bent to nearly zero radius (sharp bend), while brittle or work-hardened materials need large radii. It also depends on the bend ORIENTATION relative to the sheet's rolling direction (bending across the rolling direction allows smaller radii than along it, due to anisotropy). Knowing the minimum radius is essential in bent-part design: specifying a smaller radius than possible leads to crack scrap. It is common to express the minimum radius as multiples of thickness (e.g. '2t'). Enter the thickness and the material's reduction of area.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.