The flat patterns had just gone out the door: thirty-eight sheet metal parts for a machine frame with guarding. Two hours later the laser cutter calls. On three files the bend lines sit on the same layer as the cutting contour, one engraving is mirrored and the quantities for the small covers are missing. Could the package be delivered again, please. There goes the head start that outsourcing was supposed to buy.
Sound familiar? Then it pays to set up the route from flat pattern to DXF for laser cutting in Inventor properly, once. In this article we walk that route step by step: checking the flat pattern before you export, delivering layers and contours the way the nesting software expects them, sending engravings and bend lines along without the laser cutting them out, and handing the whole thing over per material thickness. The export work itself is something you automate with a toolbox like Thundercad; the agreements around it you make once with your cutter and then never again.
One subject we deliberately leave aside: the general choice between DWG and DXF as an exchange format. We covered that earlier in DWG or DXF? What your shop, supplier and customer really need. Below we assume DXF, because that is what almost every cutting table runs on.
First get the flat pattern right, then export
A DXF is never better than the flat pattern underneath it. So walk through the sheet metal part first. Does every part actually have a flat pattern, and is it current? A flat pattern that was never revisited after a model change will happily produce the cutting file of the previous revision. You notice that only when the blank does not fit during bending, and by then it has already been cut.
Then the developed length. It is determined by the bend compensation: the k-factor or the bend table in your sheet metal style. Which value is the right one depends on machine, tooling and material, and only one party knows for sure: whoever does the bending later on. Ask your cutter or press brake operator for their bend table and adopt it in your style, instead of sailing on the default value for years. That is all the bending theory a good cutting file needs; what matters is that your flat pattern and their press brake calculate with the same compensation.
Finally, check that the sheet thickness in the model matches what is being ordered. A part modeled as 2 mm but cut in 3 mm needs a different flat pattern and different bend compensations. On the cutting table you cannot see that difference, at the first bend you can.
Layers and contours: the language of the nesting software
Nesting software does not read a drawing, it reads layers. Whatever sits on the cutting layer gets cut. Whatever sits on the engraving layer gets engraved. Whatever the software does not recognize gets ignored or, more annoyingly, cut anyway. The layout almost every cutter wants to see:
- the outer contour on its own layer, as a closed contour;
- inner contours and holes on their own layer, closed as well;
- engraving text and markings on an engraving layer;
- bend lines on a separate layer, clearly separated from all cutting geometry;
- helper geometry, such as centerlines and frames, not in the file at all.
The exact layer names and colors differ per company; ask your cutter for their delivery protocol. Two technical agreements always belong in it. Contours must genuinely be closed: one gap of a tenth of a millimeter and the nesting software no longer sees a part, just a collection of loose lines. And do not deliver splines. Inventor can convert splines to lines and arcs during export; switch that conversion on, because plenty of machine controls cannot handle splines.
Engravings and bend lines: sending information along without cutting it
With one cover you can see the bend direction at a glance. With two hundred nearly identical blanks from one nest you cannot. So put the part number as an engraving on every part you have cut: the shop floor then sorts flawlessly, even when three variants differ by only a few millimeters. Pick a fixed spot, for example near a corner on the non-visible side, and keep the text short.
Bend lines get their own layer, with the direction added where needed: bend up or bend down. Do check first whether your cutter wants them at all. Some companies prefer to pull the bending information from the 3D model and want bare cutting contours; others engrave the bend lines as a guide for the press brake. Both are fine, as long as it is an agreement and not a surprise.
Finally, watch out for mirroring. The cutter looks at the sheet from above, so agree on which side is up; usually the rule is that engraved text must be readable. Export the flat pattern from the wrong side and the part gets cut in mirror image. On a symmetrical part that does not matter, but on a cover with an off-center cutout there will soon be a stack of mirrored parts sitting next to the scrap container.
Exporting from Inventor: set up once, identical every time
From the flat pattern, Inventor exports straight to DXF, through a dialog full of choices: layer mapping, colors, spline conversion, file version. That is exactly where the variation creeps in. Whoever exports another eight covers at the end of the day and sets one checkbox differently delivers files that deviate just slightly from a colleague's. The cutter notices, emails about it, and the back and forth begins.
This is the point to automate. With Export DXF in Thundercad you export a flat pattern in one click according to fixed preferences: the same layers, the same conversion, the file straight into the right folder. That way the whole department delivers identical work, including the colleague who only occasionally touches sheet metal. And if you want all flat patterns of a complete assembly in one go: that is on the Thundercad roadmap as Batch Flatpattern.
Sending every flat pattern out with the same layers and the same preferences saves you discussions with your cutter and repair rounds afterwards. You set up that fixed export once, after that everyone just clicks.
Try 30 days freeDelivering per material thickness
A nest is built per combination of material and thickness. So deliver your files that way too, instead of dumping forty loose DXF files into one folder. An approach that lands well with every cutter:
- one folder per combination: steel 2 mm, steel 3 mm, stainless 1.5 mm;
- the quantity per part included, in a short list or in the file name;
- part number and revision in every file name, so an old version never quietly gets cut again;
- specifics stated explicitly: protective film, grain direction on brushed stainless, visible side.
For parts that will be bent, send a drawing or the 3D model along for reference; the cutter then sees immediately what happens to the part after cutting. How to get such a package to your supplier without endless emailing, and how to prevent three versions of the same package from circulating, is what we described in Delivering files to subcontractors without the email ping-pong.
Frequently asked questions
Should I include bend lines in the DXF?
Your cutter decides. Some companies want bare cutting contours only and pull the bending information from the 3D model, others engrave bend lines as an aid for the press brake. Ask, record the choice in your export preferences and in any case never put bend lines on the cutting layer.
Why does my developed length differ from what the press brake operator measures?
Almost always because different bend compensations are being used. The k-factor or bend table in your sheet metal style has to match the machine and tooling of whoever does the bending. Adopt their bend table in Inventor and the difference disappears.
Can I export all flat patterns of an assembly in one go?
By default Inventor exports per part, and with Export DXF you do that in one click with fixed preferences. Bulk export of complete assemblies is on the roadmap. If you want to feel in the meantime what fixed export preferences save you: try Thundercad 30 days free.