We have an application where I'm cutting .020" 6061 AL sheet. We are doing it on a Bridgeport CNC which can go up to about 3500rpm or so. We're taking a piece thats 9" x 2" and I am cutting out a bunch of channels with a 1/16" endmill. The item is a heatsink and I need the channels cut out so that it will not touch any exposed traces on a circuit board when its installed, so they need to be accurately cut and with as good and "square" a cut as possible.
I am having a couple of problems. The first is that its extremely hard to hold down the sheet. Because I am cutting it, there ends up being small peninsulas of metal which are not very rigid. Any tips on holding it down? Problem is it will be bonded with epoxy to a PCB later, and if I use tape it can leave residue which is tough to get off (since the sheet is thin you can't rub it hard without bending/deforming it a little). I thought about making a custom adapter plate for a vacuum clamp? I also thought about taking a thicker piece of material (maybe steel) and cutting out the same channels in maybe 3/64 width and clamping that down over my AL sheet before milling. We also thought about stacking the sheets maybe 3-4 thick and clamping them down with a top-plate to help with the problems. Any other ideas? Which of these ideas sounds best?
Second problem - getting a pretty bad finish on the cuts. There are tons of burrs and hanging bits of shredded AL all along the edges of the cut. Is this a vibration problem? A tool deflection problem? A feed/speed problem? Or maybe a combination? I am cutting dry with no coolant, and the last time was full depth of cut (.02"), about 3,000RPM with about 4ipm feed. That was a "WAG" )wild-assed-guess) so I could be way off. What could I do to help with this? Different feed/speed? Fixture the part better? Carbide endmill? Less depth of cut? Is my DOC OK doing the full .02 at a time with a 1/16" endmill? Or should I try to take it easier?
And last but not least, I am not necessarily tied to 6061AL nor to .02" material (but I'd like to stay somewhat close). If I went to .05 or .06" thickness AL would it be easier to machine and fixture? I am also not tied to 6061AL. I can get 7075 in the same sheet size, so thats an option too. Being more brittle I wondered if it might flake easier and not burr up so muhc?
Any tips welcome - trying to get this figured out in the next day or so