Ply and flat part nesting

Composite parts are laid up from plies cut out of rolls of prepreg or dry fabric, and the material is expensive. Nesting arranges the plies on the roll so that the length they use, and with it the offcut, is as short as possible. For composites the fiber direction adds a rule: a ply's fibers must run at the angle the ply book gives it, so a ply can only turn on the roll in the steps the material allows. The same layout problem comes up for flat parts cut from any roll, such as textiles or foils. The tool takes the plies from DXF, SVG, STEP or BREP files, nests them and shows the used length and the material utilization, with the layout saved as DXF or PDF.

Parts and plies

Each closed outline of a file becomes a part, with the outlines inside it as its holes. A part's list of angles gives its plies, one ply per angle, and its number how many of that set are cut.

Fiber angles

The roll's fibers run along its length. A ply cut at 45° is turned so that its fibers lie along the roll; woven fabric also allows turns in 90° steps, unidirectional material a turn by 180°. The search never mirrors a ply. Flip mirrors a part upside down before it is placed, for a ply drawn from its other side, and its fiber angles turn with it.

Spacing

With a spacing of 0, parts may touch, as for a cutter that cuts a shared edge once. A spacing keeps every pair of parts at least that far apart and half of it from the roll's edges.

The layout

The used length is the length of roll from its start to the end of the last ply, and the utilization the plies' area over the roll area up to that length. The DXF file holds every ply's outline in millimeters on a layer per fiber angle, with the roll as a rectangle; the PDF shows the layout on an A3 sheet at the largest standard scale that fits, the plies filled by fiber angle.

1. Load

   The page loads Python and planex2d into this tab. Your browser keeps both in its cache, so later visits start faster.

2. Read

   The browser reads the files you add from your disk into memory and unpacks a zip in the tab. No request carries a file to a server.

3. Nest

   planex2d places the plies on the roll and searches for a shorter layout until the search time is up or you stop it, drawing the best layout as it goes.

4. Save

   The layout is saved as DXF in millimeters or as a PDF sheet.

No-fit polygons

For every pair of shapes and rotations, planex2d computes where one part may not go next to the other: the Minkowski sum of the first part and the mirrored second, built from convex pieces and united with planex2d's Boolean operations. Straight edges are exact, and arcs and splines are enclosed by polygons that lie at most 0.5 mm outside them, so a layout that fits the polygons fits the parts.

Placement

The parts go onto the roll one after the other, the largest first. For each allowed rotation, the free region is the roll minus the no-fit polygons of the parts already placed, and the part takes the free region's vertex that keeps the layout shortest.

Search

A simulated annealing search then changes the order and the rotations within the search time and keeps the shortest layout it finds. After it, small parts move into the holes of larger ones where they fit. An exact check on the real shapes confirms that no two parts overlap and that every part lies on the roll.

Supported files

Built on planex2d

The nesting is this tool's own code, not a call of the library, written with planex2d's public calls only: the readers for the parts, polygons around the curves, Boolean operations for the no-fit polygons and the free region, and offsets for the spacing. Install the library with pip install planex2d to work with the same geometry in Python.

Privacy

Limits

• In the browser, planex2d runs in one thread. Each layout takes a fraction of a second, so a longer search time lets the search try more layouts.
• The search is random: another run can give a different, sometimes shorter layout.
• A part that is wider than the roll in every allowed rotation cannot be placed.
• A layout that fails? Open an issue on GitHub and attach the parts if you can.