Sheet metal unfold: a flat pattern of a cone, elbow or branch in DXF
Pick one of eight shapes, set the dimensions and the sheet thickness, and get a flat pattern at 1:1 in mm. The unfold is measured on the neutral line, and the pattern downloads as DXF R12 or SVG for laser cutting.
Part of Pro, 15 EUR a month.
- 8 shapesfrom a cylinder to a T-branch
- Neutral lineD − t on an outer diameter
- DXF R12 and SVGin mm, with layers
- 5 sheet sizeshow many parts fit and how many sheets
What unfolding a cone, cylinder and other shapes means
The sheet metal unfold tool from EduFacturing, part of Pro, turns a cylinder, cone, elbow, box, transition or branch into a flat pattern. There are eight shapes, and the unfold is measured on the neutral line, not on the surface you measure with calipers.
The rectangle-to-circle transition is not developable and is approximated with triangles: the tool shows the unfold error and warns when the outline lies over itself. The box uses a bend allowance under DIN 6935.
Sheet metal unfold: eight shapes, DXF and SVG
Unfolds eight shapes
Cylinder, cone, frustum (funnel), elbow of 2 to 8 segments, box with flanges, rectangle-to-circle transition, a pipe with an angled cut, and a T-branch with the hole in the main pipe.
Measures on the neutral line
The diameter is outer, inner or mean, and the sheet thickness is up to 20 mm. Outer counts as D − t and inner as D + t.
A drawing and a rolling view in 3D
The Flat pattern tab is the drawing, and 3D and rolling rolls the pattern into a body for the cylinder, cone, frustum and angled cut. For the other four shapes the tool says why there is none.
DXF, SVG, springback and nesting
Download DXF R12 or SVG. Springback gives the angle to bend to, and nesting shows how many parts fit on a sheet and how many sheets are needed.
When you need an unfold: sheet metal, laser, boxes
A mistake in the unfold shows only once the sheet is already cut.
Sheet metal workshop
A fabricator unfolds a cone, funnel or elbow, and a branch comes out with the pipe and the hole in the main pipe.
Laser cutting
The operator cuts only the outlines of the DXF R12, while the bend axes sit on a separate layer for marking.
Boxes and enclosures
A designer sets the inner dimensions, the radius and the k factor and gets a pattern of a box with flanges.
A lesson
A teacher shows why a cone is a sector and the transition is not developable.
How the unfold is calculated on the neutral line
Each shape comes down to numbers on the neutral line, and the drawing and the figures come from the same values.
Mean diameter
The neutral line is at the middle of the thickness. An outer diameter D becomes D − t, an inner one D + t.
Shape
A cylinder is a rectangle of length π · D_m, a cone is a sector with the slant as its radius, a frustum is an annular sector, an elbow and a cut are sine curves, and the transition is a mesh of triangles.
Bending and springback
The flange of the box is shorter than the wall by (r + t) − BA / 2. Springback divides the wanted angle by a material factor.
| Applies to | Formula | Meaning |
|---|---|---|
| Cylinder | L = π · D_m | D_m = D − t on an outer diameter; at D = 100 mm and t = 2 mm: π · 98 = 307.9 mm |
| Cone | θ = 360° · r / L, L = √(r² + h²) | r is the base radius, h the height |
| Edge bend | BA = (π / 180) · φ · (r + k · t) | BA is the arc on the neutral line; φ is the angle, r the inner radius, t the thickness and k the neutral-layer factor |
| Springback | bend to = wanted angle / factor | at 90° and a factor of 0.95 (stainless 304) it is 94.7° |
Reference
Flat pattern formulas with K-factor
| Parameter | Value | Unit |
|---|---|---|
| bend allowance formula | (A * pi / 180) * (R + K * T) | mm |
| bend deduction formula | 2 * (R + T) * tan(A * pi / 360) - BA | mm |
| k_factor_by_material steel-mild mm | 0.33 | dimensionless |
| k_factor_by_material stainless-steel mm | 0.38 | dimensionless |
| k_factor_by_material aluminium mm | 0.4 | dimensionless |
| din6935_k_factor_table 0.65<r/s<=1 mm | 0.6 | dimensionless |
| din6935_k_factor_table 1<r/s<=1.5 mm | 0.7 | dimensionless |
| din6935_k_factor_table 1.5<r/s<=2.4 mm | 0.8 | dimensionless |
| din6935_k_factor_table 2.4<r/s<=3.8 mm | 0.9 | dimensionless |
| din6935_k_factor_table r/s>3.8 mm | 1.0 | dimensionless |
Bend Allowance = (A*pi/180)*(R+K*T). K-factor comes from k_factor_by_material or din6935_k_factor_table by r/t.
What is different: neutral line, layers, nesting
It says when there is no formula
The transition is unfolded with triangles, the error is a number, and an outline that lies over itself comes with a warning not to cut it.
Layers for the machine
DXF R12 puts the cut outline, the bend axes, the seam, the branch hole and the elbow segments on separate layers, so you cut only what you should.
The tool does not account for the thinning of the material in a bend. The springback factors are indicative values from practice, and the k factor (0.25 to 0.5) is your choice, checked with a trial bend in the same material.
Nesting on a sheet is by bounding box and gives a lower bound. The T-branch is only at 90° with intersecting axes. The box and the elbow do not roll in 3D.
Questions about unfolding a cone and a branch
How to unfold a cone?
Choose cone or frustum, set the dimensions and the sheet thickness, and download the pattern as DXF R12 or SVG. A cone is a sector with the angle θ = 360° · r / L, where L = √(r² + h²) is the slant, not the height.
How to calculate flat pattern for sheet metal cylinder?
A cylinder is a rectangle of length L = π · D_m, where D_m = D − t on an outer diameter. At D = 100 mm and t = 2 mm: π · 98 = 307.9 mm.
Should I enter the outer or the inner diameter?
Whichever the drawing gives, but tell the tool: the unfold is measured at the middle of the wall. An outer diameter is reduced by t and an inner one increased by t.
How to unfold a rectangle-to-circle transition?
A transition is not developable: it cannot be flattened without stretching or creasing. The tool approximates it with triangles and shows the error. An outline that lies over itself is made in two or four parts, not cut along the outline.
What is the hole for a Ø100 branch in a Ø200 pipe?
The hole is 100 mm along the axis and about 105 mm around the main pipe. That is for diameters at the middle of the wall of 200 and 100 mm: 2 · R · α, where sin α = r / R, gives 104.7 mm. The saddle depth is 13.4 mm.
How many parts fit on a sheet?
The bounding box of the pattern is placed on a 2000×1000, 2500×1250, 3000×1500, 1000×500 or 600×400 mm sheet in two orientations, and the better one is taken. It is a lower bound.
How much does the sheet metal unfold tool cost?
It is part of Pro at 15 EUR a month. Pro also opens the other Pro tools in the catalog.
The sheet metal unfold tool is part of Pro
Pro costs 15 EUR a month and opens all 45 Pro tools.
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