If you ask five CNC machinists the same question, you’re bound to get seven answers. But that doesn’t mean they're indecisive, just there are many different ways to perform any given CNC operation. That being said, there is no 100% right or wrong way to cut aluminum, but here are a few things to keep your eyes on when buying end mills.
Carbide
Carbide stays sharper longer. While it might be more brittle than other end mills, we’re talking aluminum here, so carbide is great. The biggest downside to this type of end mill for your CNC is that they can get pricey. Or at least more expensive than high-speed steel. As long as you have your speeds and feeds dialed in, carbide end mills will not only cut through aluminum like butter, but they will also last quite a while. Get your hands on some carbide end mills here.
Coatings
Aluminum is soft when compared to other metals. This means chips can clog up the flutes of your CNC tooling, especially with deep or plunging cuts. Coatings for end mills can help alleviate the challenges that sticky aluminum can create. Titanium carbo-nitride coatings are slippery enough to help keep chips moving, especially if you aren’t using coolant. This coating is often used on carbide tooling. If you’re using high-speed steel (HSS) tooling, look for coatings like titanium carbo-nitride (TiCN). That way you get the lubricity needed for aluminum, but you can spend a little less cash than on carbide.
Read: 4 Things We All Hate About Aluminum
Flutes
This is arguably the most important feature to consider when choosing an end mill for CNC machined aluminum. Again, aluminum is gummy and soft, which means it tends to stick in the flutes of your CNC mill. While coatings can help alleviate this issue, if you’re using a 4- or 5-flute end mill to cut aluminum, even the best coatings may not help. One of the main goals of flutes when cutting aluminum is to clear CNC machined chips. While having fewer flutes makes your tool less rigid, it also allows for more efficient movement of those chips. If you don’t get chips out of there, you risk ruining your surface finish, by re-cutting chips, or worse, destroying your end mill by friction welding the chips right to your cutter - every CNC machine owners worse nightmare! Your best bet for an end mill in aluminum is two or three flutes. While you can get away with more flutes, if you are really concerned about rigidity, your risk of destroying your end mill will go up.
Geometry
So much of CNC machining is about math, and choosing an end mill is no different. While the number of flutes is an important consideration, flute geometry should also be considered. High-helix flutes help dramatically with CNC chip evacuation, and they also help with the cutting process. High-helix geometries have more consistent contact with your workpiece… meaning, the cutter is cutting with fewer interruptions.
Interrupted cuts are hard on tool life and surface finish, so using high-helix geometries allows you to stay more consistent and move CNC machine chips out faster. Interrupted cuts wreak havoc on your parts. This video shows how interrupted cuts with a chipped end mill can affect your cutting strategies.
If you’re looking to cut aluminum, fear not… it’s a forgiving material. If you want to cut aluminum better, look for end mills with high lubricity and an efficient flute design for chip evacuation. With some fine-tuning in your feeds and speeds, you’ll use your CNC machine to make piles of aluminum chips in no time.
