Tapered end mills have flutes that narrow from the shank to the tip. They are suitable for producing the draft or clearance angles in die and mold walls to facilitate ejection of the part after molding. Larger degrees of taper create larger angles, making ejection easier.
Cutter material is an important consideration when selecting an end mill. Carbide can run at higher speeds than high-speed or cobalt steel, resisting wear and high cutting temperatures. High-speed steel is compatible with a variety of materials. Cobalt steel resists abrasion and high cutting temperatures, and has higher feed rates than high-speed steel.
Some end mills are uncoated, while others are coated with finishes to enhance performance. Most finishes extend the life of the end mill and allow higher cutting speeds and feed rates. For example, a titanium nitride (TiN) finish offers high-temperature resistance and increased hardness compared to uncoated end mills, while a titanium carbon nitride (TiCN) finish lubricates the end mill for high-temperature stability and offers better abrasion resistance than TiN coating.
An end mill’s end cut type is either center cutting or non-center cutting. Center-cutting end mills can create three-dimensional shapes and profiles, and make plunge cuts similar to a drill bit. Non-center-cutting end mills are suitable for peripheral milling and finishing, but cannot make plunge cuts.
The cutting diameter references the outside diameter of an end mill’s flutes. For tapered end mills, the cutting diameter is measured at the tip of the tool, not the shank.
There are three cut types for end mills. Finishing end mills provide a smoother surface finish than general purpose or roughing end mills. General purpose end mills can be used for a range of applications, and provide a smoother finish than roughers. Roughing end mills remove more material in less time than general purpose end mills, with minimal vibration (chatter). They create a rough finish that can be smoothed by a second finishing cut.