Bending laser-cut parts

In line bending, the sheet is not heated as a whole, only a narrow strip along the bend line. A heating wire brings this zone up to forming temperature; the part is then folded to the desired angle in a jig and held there until it has cooled. The rest of the sheet stays cold, flat and dimensionally accurate.

For this to work, the material has to be able to do two things: soften when heated without burning, and keep its new shape as it cools. Only thermoplastics can do that — and by no means everything that lasers well is one of them.

Radius: at least twice the material thickness

When bending, the outside is stretched and the inside compressed. The tighter the radius, the greater the difference. Below twice the material thickness, acrylic develops unacceptable stresses or compression wrinkles on the inside; with 3 mm acrylic the smallest sensible inner radius is therefore 6 mm.

With clear material, appearance comes into play as well: every bend inevitably produces a visible distortion, and it becomes more pronounced the thicker the material and the smaller the radius. If you want to look through the bend, choose the radius as large as possible.

In the modeller you can also choose a radius of 0, the sharp fold. It remains allowed because it is exactly right for some parts — but it is not low-stress: the inside is heavily compressed, and on clear material the edge is clearly visible.

Spacing between two bends

The warm zone is wider than the line itself: according to the processing guideline it should be at least three to five times as wide as the material is thick. If two bend lines lie too close together, their heating zones overlap — the second bend pulls the first one open again.

The modeller checks this: between two parallel bends, a web of at least three times the material thickness must remain alongside the two bend arcs. If it gets too tight, it tells you before you order.

The same applies to everything else in the heating zone: holes, slots and engravings right at the bend line soften along with it and distort. Plan them with some distance from the line.

How to draw a bend in the modeller

1. First choose a bendable material. For all others the “Bend” tool stays locked.
2. Use “Bend” to draw a straight line across the part. It always acts from edge to edge — partial bends do not exist.
3. On the right, set the angle, inner radius and direction: mountain (upwards) or valley (downwards).
4. Check the result in the 3D preview with “Show bent”.
5. If you later switch to a material that cannot be bent, the modeller warns you and offers to remove the bend lines.

What to bear in mind for dimensions

In the bend zone the material becomes longer on the outside and shorter on the inside. Somewhere in between lies a layer that keeps its length — the neutral axis. In acrylic it lies practically in the middle, because the thickness stays almost unchanged in the heating zone. That is why the leg lengths of a bent part are not simply the distances to the line; the 3D preview already calculates it this way.

And: bending is done by hand in the jig. The laser cut is accurate to a tenth of a millimetre; the bend angle is craftsmanship. Fits that have to sit exactly are therefore better planned on the cut edges than across a bend.

Bend lines can also be supplied in an uploaded file. Angle and radius are then encoded in the stroke colour of the line — how the colour is made up is explained on the file preparation page, together with a colour calculator.