If you’re having trouble cutting aluminum with general purpose mills, there’s a reason. Aluminum is a soft metal that requires end mills with specific geometries and characteristics. Here’s the details.
Because of the soft nature of aluminum, a sharp edge and high rake angle are required to separate chips from the workpiece. Positive rake angles up to 25 degrees radial and 20 degrees axial are commonly used.
When cutting aluminum, a high helix angle, around 45 degrees is also optimal. The helix helps move chips out of the cutting zone and provides an excellent surface finish. The high angle also softens the impact at the entrance of the cut, resulting in a smoother cut.
A two or three-flute mill with open flute design is needed for easy chip movement away from the cutting zone. Surface finish on the flute is also important. Long-chipping, low silicon aluminum alloys will typically stick to end mills. As a heated chip flows over the flute, it will try to adhere to the tool surface. One solution to this is an extremely slick commercial tool coating that reduces the friction coefficient on the flute surface. A good example of this is a ZRN coating that has a friction coefficient of less than 0.1.
When chip management becomes an issue, consider using a coolant-through end mill. Coolant ducts exit in the flute area and help move chips out of the cutting zone.
All of these end mill and coating features help reduce the probability of built up edge, a problem that occurs when a general-purpose end mill is used in aluminum machining. Built up edge is the accumulation of material on the cutting edge. Once this happens, the cutting action becomes more of a tearing action. Surface finish is reduced immediately and spindle load increases dramatically. If your application requires cutting a full width slot, tool breakage is likely before you can adjust the feed hold control.
Midwest Cutting Tools manufactures a broad range of outstanding aluminum end mills, both standards and specials and offers ZRN coatings. To learn what end mill is right for your aluminum machining job, contact us today.