Cutting aluminium on a CNC router or CNC Gantry Mill

People often ask if a CNC Router can cut aluminium.  They’re used to seeing the Router cut wood and plastics.  The answer is “Yes, any CNC Router can cut aluminium with some care and attention.” 

You will discover that machining aluminium with a CNC Router is not only hassle-free, but very productive.  Using a CNC Router for aluminium parts can be a very successful pursuit with a little care and preparation, There are some things to have in mind as regards to the difference between aluminium(and other metals) and wood or plastics. 

With aluminium, “stickiness” can be a factor.  Aluminium tries to stick to the tool.  As a matter of fact, this occurs to the point that its welded to the tool. When you have deposits of sticky aluminium on your cutting edges, the tool might not last long, especially not at 20,000 rpm or more, using a 2 or 3 flute endmill with no coating or ZRN coating can greatly increase your CNC router’s performance in alu.

8 TIPS N TRICKS FOR MACHINING ALUMINUM ON A SMALL CNC MILL OR CNC ROUTER

  1. Use Carbide endmills for Aluminium.

CNC Routers often use different specialized cutters that shouldn't be used with aluminum.  Downcut Spirals, Compression Cutters, and the rest do not have a place in aluminum work.

Cutters are you need should be specifically  made for aluminum.  Most of the CNC world makes use of 2 or 3 flute carbide endmills for this. http://customcarbide.com.au/products/end-mill-3-flute-all-sizes-tialn-coated-solid-carbide-for-cnc-slot-endmill-tool-aluminium

 

This helps to increase the recommended rpm to be sure your cutters are happy going at the high rpms CNC Router Spindles operate at.  The measurement that determines this is called surface Speed. Carbide cutters can go much faster than HSS cutters.  Forget HSS and Cobalt cutters for aluminum.

 

  1. If the machine can’t feed fast enough, Use less flutes

Normally,  3 or fewer flutes is used with aluminum – do not try a four or more flute cutter in aluminium! 

 This is because aluminium produces really large chips.  The lesser the flutes, the more space between the cutting edges, and the more room for the big chips to escape and be blown away.  With too many flutes, the chips back in too tightly,  jam up the flutes, and the cutter is soon damaged.

The answer is to try less flutes.  A 2 flute cutter needs a much slower federate than a  4 flute. 

Also, with the discussion about cutting aluminum, it’s possible that the situation can get worse with wood because you can cut the softer material so much faster. 

The other thing to be aware of is what’s called “Radial Chip Thinning“.  If your cut width is less than 1/2 the cutter diameter, it is necessary to speed up the feedrate due to the fact that the machine is producing abnormally thin chips due to Radial Chip Thinning. 

  1. Clear your chips, or else

This cannot be overemphasized. Especially if the material has a tendency to bond with the cutter (like aluminum)

Chips repeatedly being cut accounts for the breaking of cutters more than most any other thing I see happening.  Beware of clearing the chips.  There is no need to count on a nearby vacuum dust collection system unless you have personally verified it sucks the chips out of even the deepest cuts.  More reliable is an air blast fixed to the spindle and pointing right at where the cutter meets the material being cut.

 If you’re standing there, nozzle in hand (or worse a brush) thinking you can keep things tidy, you’re not paranoid enough about clearing chips.

 

  1. Work with the machine not against it

A CNC Router can cut aluminum, but it is not the best tool for hogging out big aerospace parts like wing spars. For you to succeed at this, the price is slowing things down.  Beware that I’m not suggesting that you literally slow down the feeds and speeds, but the total Material Removal Rates will be less than what can be obtained with a CNC mill built for this purpose.  The machine should be allowed to carry out it’s function.

One advantage is that a good-sized CNC Router can fit a lot more material on its table than most any CNC mill.  After loading it up, push the green button, and let the machine do the rest.

 

  1. Use smaller diameter cutters and forget HSS

Another way to turn up the rpms is to use smaller diameter cutters.  Forget about 12mm or 1/2″ endmills.  Reduce to 6mm or 1/4″ maximum and typically less. Because you’re now using smaller diameters, more rigid cutters are required lest tool deflection starts to be a problem

Carbide is much more rigid than HSS, so this is one more reason to favor carbide.

The moral of the story is to carefully match tooling to the capabilities of the machine, smaller cutters will work more effectively at the higher RPM’s of a CNC router.

 

   6. Pay attention to cut depths and slotting

The more you cut into and get closer to a slot the cutter travels in, the more difficult it is to clear the chips out of the base of the hole. Make more passes to cut down to required depth and to open up the shallower depths for better access.

     

    1. Lubricate the job

    The next problem is providing lubrication to cut down on the tendency for the chips to stick to the cutting edges.

    Many CNC Router users hate to use any coolant of any kind, but it is still important to use some kind of lubricant to cut anything but the thinnest aluminum reliably.  Since you’ve presumably already rigged up a compressed air blast, you may as well run coolant mist through the same mechanism. A mister should be bought to provide air blast and coolant mist.  It’s easy and not expensive.

    The mist can be set so that very little fluid is released to reduce the mess, this is okay as long as what is sprayed goes on the cutter.

    At times, it is impossible to make use of the mist, however, there is still a need to cut aluminum. If the aluminum to be cut is very thin, or to take shallow passes, this might work without lubrication. It is necessary to carry out tests to verify.

     

    1. Don’t slow down the feedrate too much!

    Going too slow on the feedrate might risk making the tool to rub rather than cut. The risk is bigger for CNC Router users than mill users just because the spindle is almost always going quite fast.  To maintain the recommended chip loads with rpms that high it is necessary to keep the cutter moving relatively quickly

    For example, the 3/16″ cutter at 21K rpm wants to feed quickly,  slowing down too much, say to 1/4 of that might feel like the machine and tool isn't used to full potential.  Nothing could be further from the truth.  If you wind up going slow enough that the cutter starts rubbing at 20K rpm, the work will get heated up and drastically shorten the tool life.