Milling Aluminium

What is the best way to mill slots in aluminium ? Are there special cutters ?

I have a sheet of 1/2" thick aluminium (aircraft grade. not sure of spec) and used my mill to cut various shapes with new,  5mm, 2 flute slot drill and a 4 flute roughing cutter. The aluminium is sticking to the cutter. Have tried cutting dry and using an aluminium cutting fluid and tried different cutting speeds and feeds. Using a vacuum cleaner to keep swarf away from the cutter. Setting up a new mill and flood coolant not installed yet.

Paul.

Edited By Paul Lousick on 06/02/2017 01:55:00

Flood coolant is what you want, if you watch a cnc milling aluminium at high speed the coolant blasts the swarf away so as not to interfere with the cutter. Make sure your end mills are very sharp to, or they tend to smear the surface.

Thanks Ronan, I suspected that I needed flood coolant.

I recently sold my X3 mill for an RF-45 clone, (a bit bigger), and am in the process of fitting all of the accessories including a flood coolant system which was on my old mill. Making brackets to mount the DRO at the moment. Looks like I should have fitted the coolant first.

Paul.

Hi Paul,

As Ronan says; sharp cutters and coolant, and yes, there are special milling cutters for aluminium, see here, or here. I havent tried them myself, I just use new slot drills.

Thor

Use uncoated cutters and a small amount of parafin. In smaller sizes I use FC-3 Type cutters but the HSS aluminium specific ones work well too though the length of the ARC ones can cause chatter in the smaller diameters.

Couple of 6mm slots cut recently FC-3

And an aluminim cutter in action

Edited By JasonB on 06/02/2017 08:02:35

Paul,

You don't have to use flood coolant but as you found out cutting Aluminium dry is also not a good idea, try brushing on Paraffin, soluble oil or cutting oil, all will help to prevent 'sticking'

Tony

I use soluble oil in a squirt bottle. It does not take a lot prevent chips sticking. When slotting the occasional air blast will help remove swarf. I am going to try a mist coolant unit. Haven't got it set up yet.

WD 40 is also very good for milling aluminium.

George.

The grade of aluminium alloy has a huge influence. I've only once had a problem and just accepted it was a poor grade of alloy for machining and discarded it. I do all my milling dry except sometimes for a finishing cut.

Hello Paul

It looks to me as though the alloy grade might be what is marked in big black letters on the metal you have. Any clue about what it said before you attacked it?

Regards, Tim

Tim, that's my photo and the plate is 6082 T6, HE 30 in old money and I had no problem cutting it.

Edited By JasonB on 06/02/2017 17:53:55

Another vote for milling dry for machinable alloys, but sometimes using a mix of cutting oil and paraffin on "sticky" stuff.

Now for a theory which seems to work for me. Metal cutting is really a thermal process anyway where the shearing action of the tool causes the metal to soften 'cos it gets very hot near the tool tip - I read this in a long and erudite tome on machining methods some years back. I think a problem one gets sometimes is that the metal doesn't get hot enough to properly melt and detach itself from the tool. I have found that actually increasing cutting speed can make everything work better with aluminium, and since I started using my CNC mill I find that I'm usually turning the speed to max (~5000 rpm) on the biggest cutters I have a collet to hold, 10mm, on ali and having no problems. It will be even better I hope when I have my chip blower set up.

The hollow in this 6082 bar is about 275mm long and 7mm deep, I chewed it out with an ARC uncoated cutter to full depth at each pass. Not the very best finish as I was just hogging out waste to reduce weight.

I do find wd40 good on aluminium, but its expensive, and i cannot stand the pong. One reason i like a lot of coolant is it washes away the swarf, if you let it build up around and on the cutter, swarf can and does smear between the cutter and workpiece.

Screwfix do wd40 for £6 per litre if you buy 5l. More expensive than a neat cutting oil, but not rediculous.

Paraffin about £5 for 4lts from the local petrol station, garden ctr, etc and I quite like the smell

Me too, we had a paraffin heater at home when i was a kid, very distinctive smell.

if cooling is not needed then Denatured alcohol, and rubbing alcohol can be used it will stop the build up on the cutter and will evaporate and does not leave residue behind a bit of searching and £4-£6 for 5ltrs also great for cleaning

I mix paraffin and ATF [ automatic transmission fluid] at 75% to 25% ratio and find you get the best of both worlds.but any light grade hydraulic oil will work, it's just that I have gallons of the stuff.

Don't use a 4 flute cutter, there isn't enough space between the flutes to get the chips away given alloy being softer is cut faster.

Routers that cut aluminium often use 1 flute cutters, no it's not April the 1st. These have maximum chip clearance than any cutter.

Problem with flood cooling on small hobby machines with no full guarding is you can't get enough flood. You need to wash the chips out of the cut and once you are say 10m or 12 mm deep that's a fair bit of pressure to make things messy fast.

In my new proposed hobby workshop at the new house [Tm] I plan to fit curtains to the bench mill, whatever model that is. Two / three brackets screwed to the ceiling both sides to support a length of plastic conduit with a slit in it. Into this slit will be some lengths of that black plastic DPC membrane you put on brickwork as a damp course [ because it's cheap ] This can be would up when bot in use and wound down when messy milling and it will catch the chips which will fall into a designated area to be cleaned up instead of all over the shop, in me boots and down me neck as it does at the moment.

Don't know if I can apply for a patent or whether it's someones else's idea I have subconsciously remembered [ my excuse ]