Join all overlapping points

CMD+A

CMD+J

Voilà

I had to deal with this on a recent vinyl cutting job.  Got the art in, it looked amazing, but there were all kinds of things that over lapped.

The easiest way that I found to deal with this was in the AI file, before exporting to DXF.
First things first, find and remove any clipping paths (use the layers panel to go through all the groups, mavoe the paths to the main group (if they are in a sub group with the clipping path) and then once the sub group has nothing but the clipping path in it you can just highlight the group and then click DELETE LAYER.  (keep an eye on the art and make sure the removal of the clipping paths doesnt change the art, if it does you may need to go in an clean up the art)

next highlight all the art.  I just use CTRL+A (command+A on mac) then press CTRL+SHIFT+F9 (Command+Shift+F9 on mac) to bring up your Pathfinder panel.

In the path finder panel (with all your art still selected) click the first icon in the top row (ADD)

BOOM! all the overlapping sections have been merged together. 

Once youve had to do this a few times it gets quick.  Depending on the art you can do it in less then 5 min.

dunaz​ I have tried that method and it can work, but it can also create "holes" where the overlap is.
I search for a few hours, and tried all the other mentioned solutions but the one I have described above worked the best for me on this job.  (converting Black and White illustrations to Vinyl decals)

Actually, you can join overlapping points. I do it all the time with dielines, as they come from the engineers as separate lines. Just select the lines that make up the shape you want to "join" and command+j. Sometimes it's tricky, depends on the direction of the lines and such, so sometimes you have to select a few pieces, join, select a few more pieces, join. Depends I guess on how the items are layered.

Check it out. Here's the info from the help files (I searched "join paths"):

Join two or more paths

Illustrator CS5 provides the option to join two or more open paths. To join one or more open paths, use the Selection tool to select the open paths and click Object > Path > Join. You can also use the keyboard shortcut Ctrl+J (Windows) or Cmd+J (Mac).

When anchor points are not overlapping, Illustrator adds a line segment to bridge the paths to join. While joining more than two paths, Illustrator first looks for and joins the paths that have end points stationed closest to each other. This process is repeated until all paths are joined. If you select only one path to join, it is converted into a closed path.