[m_g]

Hello all,
I have recently started using a Chinese CNC router (2.5kw water cooled spindle) to cut small aluminium parts from 1.6 and 3mm sheet, but having trouble increasing cut depths to speed up the process. The machine has a vacuum table, but I also use the masking tape method to hold small parts in place.

I am having good success (very clean cuts, no deburring necessary) with the following:
-3mm aluminium sheet (unsure of grade)
-1 fluke up cut 3.175mm carbide bit
-0.25mm cut depth
-400mm/min feed
-20,000 rpm
-air/IPA mister



However, with the same settings, if I increase to a 0.5mm depth, I get a lot of burring and very poor finish on the cuts. I have tried decreasing feed rate, but this does not seem to help



I assume that 0.5mm is within the capacity of the machine? Any ideas on how I can achieve 0.5mm depths and still get clean parts? Or is cleanup all part of the process?

Any help much appreciated
Thanks

[joeavaerage]

Hi,
the worst thing about cutting aluminum is re-cutting the chips. At the second (or third) time the chip is cut it builds up that much heat that it will try to weld itself back to the
material or the tool. If you can, try flood cooling.

The surface speed is 0.003125 x PI x 20000= 196m/min, which is about right. The chip load is (400/60)/(20000/60)=0.02mm/tooth per rev or 20um per tooth. or 0.7% of the tool
diameter. Smaller tools tend to be weaker and a low chip load is required otherwise they'll break. With very small endmills, 0.5mm I allow 1%, with 3mm endmills you could probably push a little
harder, say 1.5%, or up to 800mm/min feed rate. I think your cutting parameters are conservative but should give you a good result at a fair speed.

It will all depend on how well you can flush the chips out, if you can do that well then you'll be able to increase the cutting load significantly.

Craig

[Jim Dawson]

Looks like a combination of not enough coolant and a dull tool.

[ToolHIT]

You should have no problem taking 0.5mm Depth of Cut. The issue looks to be you are using an Upcut Router Bit and you should be using a DownCut Router Bit (although it could also be a Dull Tool like Jim mentioned). The Upcut will pull the chips up better and leave a good finish at the bottom but it will leave a burr at the top of the workpiece, the Downcut will leave a better finish at the top of the workpiece so you won't get the heavy burr. You could also use a 2 Flute Carbide End Mill, that would also leave a nice finish.

If you need a tooling recommendation let me know. Hopefully this helps!

[m_g]

thanks all, I will try a downcut bit, and increase coolant amount