Thursday, August 4, 2011

Laser Cutting Designs from Inventor

This is a guide showing the work flow I've been using to get parts out of Autodesk Inventor 2011 and into the vector format needed to send to a laser cutter.  I've been using this quite a bit this summer for my internship, since the company happens to have a laser cutter in their shop.

First thing first, you need to design all of your parts in Inventor, or whatever 3D CAD program you happen to be using.  Designing for laser cutting is relatively easy; A single sketch, extrude for the material thickness, assemble.  You do want to consider the implications of having sharp corners being cut out of acrylic, or whatever material you're using.  Sharp corners will make it more vulnerable to cracking.
Here is the completed assembly for what I'm working on, to make sure everything fits together virtually, since bits are cheaper than acrylic.
Once the 3D design is done, drop each part into its own 2D drawing.  I opted to actually dimension and tolerance everything, but all you really need is the base view.
 Autodesk developed the drawing exchange format back in the 80's, which allows us to be able to export these .idw drawings to something Inkscape can open, namely the .dxf format.  Inventor is a little screwy, because it has several different types of saving, with subtle differences.  You can't "save as" a .dxf file, but can only "save copy as" a .dxf file, so make sure you select the correct menu option.
When saving as a .dxf file, make sure to go into the options menu and select "model geometry only," since otherwise the laser cutter will start cutting out all of our dimension and reference lines, which isn't really what we want.



Now you should have .dxf files for each part.  Next is to open them with a vector image editor (the de facto free one being Inkscape), and convert your parts into the .svg and/or .pdf files your laser cutter or laser cutting service expect.
When you try to open the .dxf files in Inkscape, it will ask you what scaling factor to use.  This is because Inkscape by default expects the .dxf files to be in millimeters, but of course, Inventor saves it into whatever units you happened to be using, so since I'm a mechanical engineer working in the US, I need to convert it from inches, so enter a manual scale factor of 25.4 (mm/inch), otherwise your parts will end up the WRONG size.
You should end up with something like this, with all of the views from your drawing now sitting somewhere in Inkscape.  Obviously, you only need the top-down one, so click-drag-delete the side view, and select the main view and move it back to the origin.
At this point, you also want to set up the document properties correctly for your laser cutter or service.  (Many services will provide vector templates for you to work from.) My Laser cutter happens to have a 16"x12" bed, so in the document properties (File > Document Properties...) (Shift-Ctrl-D) change the default units to inches, and the document size units to inches, and type in the appropriate geometry. Also consider that you can add some grids in the grids tab, which is kind of handy some times, but can get a little annoying when parts start trying to snap to it instead of go where you want it.
Now with the outline selected, open the Fill and Stroke dialog (Object > Fill and Stroke...) (Shift-Ctrl-F), and set the stroke width to 0.001".  This is because some laser cutters will decide between vector cutting the line and rasterizing it (shading) based on how thick the line is, so the default thickness will end you with all of your parts merely shaded on the sheet, not actually cut out of it.

Now all that's left is changing the stroke color to the correct one for cutting.  This is because laser cutters will have several different power settings, for say cutting, engraving, deep engraving, raster, etc, and will distinguish between which modes you want to use by the color of the lines.  My cutter uses red (#FF0000) for cutting, but others will use black (#000000) or blue (#0000FF), so make sure to read the documentation and check your settings.  Select all of your lines, and right click the correct color at the bottom of the Inkscape window and select "Set stroke"  This should now have you with vector files you can send off to be cut out.

Now, in addition to the basic outline from your 3D CAD program, you can also quite easily add notes on the material using the text tools, or pretty much everything, in Inkscape.  Just make sure you remember to set the stroke of the text to 0.001" so it doesn't end up just rasterized, and turn off the fill if you don't want to pay for several minutes worth of laser time to shade in your letters (not that I totally made that mistake and turned a 45 second cut into 6 minutes).

And as always, print everything out on paper or cardstock beforehand, to save you the expense of noticing something obvious in $5/sq ft material.

Finally, consider the implications of that the laser will burn off about 10 thou of material where it cuts.  For most applications, this isn't a big deal, but if you're trying to get some tight-tolerance fits, you'll need to move the cut vectors out about ~5 thou to actually get what you drew.
 All being said and done, three hours later and $15 in material, and that which I imagined, becomes reality.  I hope you find this all useful.

1 comment: