You know how it works. You stick down a new type of material and try the machine set-up you used last time. BANG! What happened? It is supposed to be easy to machine aluminium, right?
Aluminium requires less cutting force than harder materials like steel. But aluminium is softer and melts at a much lower temperature. This means it can be all too easy for the loose chips of material to overheat and fuse to the tool. In small quantities, this dulls the cutting edge causing greater mechanical load on the cutter and a further build-up of heat. This can then lead to premature tool failure.
So what can you do to stop this happening? Take a look at the following tips.
1. Optimise your feeds and speeds
The softer the material that you are cutting is, the faster the recommended cutting speed. At 300-600 meters per minute (using a carbide tool) aluminium has a similar cutting speed to wood. But unlike when cutting wood, the optimal feeds and speeds for your set-up will be in a much tighter range.
Machining aluminium is often characterised by a high spindle speed. Be wary of combining high spindle RPMs with feed rates that are too slow. As the tool will spend more time rubbing against the aluminium than cutting it. This will increase the working temperature and drastically reduce your tool life.
Of course, cutting any material too fast will result in the familiar sound of the broken tool flying over your shoulder and hitting the wall!
Machining aluminium at high speeds results in a large amount of waste material being rapidly produced. This can cause its own problems...
2. Keep on top of chip clearance
One of the biggest issues when machining aluminium is chip removal. Especially when cutting deep pockets into the material. The deeper the cut the more difficult it is to remove the chips from the bottom of the pocket. A build-up of chips at the bottom of a pocket is the fastest way to turn your cutter into an aluminium popsicle.
Not only will the chips stick to the cutter when heated, but they will also stick to the workpiece. This causes the work-hardening of the material surfaces. It also degrades the quality of the surface finish and can affect part tolerances.
Using a shallow depth of cut along with a blast of compressed air will help to keep the chips away from the cutter.
But, if you try to make a full diameter cut through aluminium with a 4-flute end mill the flutes will clog up and the end mill will break. Which brings us nicely on to...
3. Choose a cutter with a low flute count
The most important factor in choosing a cutting tool for aluminium is the need to maximise space for chip evacuation. The more flutes a cutter has, the less space there is to evacuate chips. Two flute cutters are ideal, with single and three flute tools also being effective.
Fewer flutes does decrease tool rigidity. So use the shortest tool possible for your application and watch out for tool deflection. Particularly when using small diameter end-mills.
4. Use the right tool material
High Speed Steel is not strong enough under the cutting conditions required for aluminium. As aluminium is relatively soft to cut, you should prioritise tool hardness over tool toughness. A harder tool material will allow the cutting edge to stay sharp for longer. Maintaining a sharp cutting edge will create a better finish. It will also reduce friction and reduce the amount of aluminium deposited on the cutting edge.
You should use tools made from carbide when machining aluminium. The higher speed, sharper-for-longer carbide cutters create a greater shearing force. This reduces the amount of that long stringy aluminium swarf that ends up fouling the cutter.
5. You don’t need a fancy tool coating
What about those nice-looking gold TiN coated end-mills? Don’t bother. The coating is designed to improve wear resistance when machining more abrasive materials. It is rougher and more chemically reactive with aluminium than the bare tool. Both of these factors will combine to increase the amount of aluminium that adheres to the tool. The same applies to TiAlN, TiCN, and AlTiN.
Use either an uncoated carbide tool or a specialised coating for cutting aluminium (such as ZrN, DLC or TiB2).
In summary, aluminium is eminently machinable but it isn’t without it’s quirks. Understanding how material behaves is the best way to learn how to machine it more effectively. Make sure your feeds & speeds are right. Use a two-flute, uncoated carbide cutter and don’t let the tool get clogged up with aluminium chips.
Still having problems? CNC Solutions has extensive experience machining a wide range of materials including aluminium. We can show you the right way to do it on a CNC training course in our cutting edge CNC Training Center.