Endmill

An endmill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit, in its application, geometry, and manufacture. Whereas a drill bit can only cut in the axial direction, a milling bit can generally cut in all directions, though some cannot cut axially.

Types

Several broad categories of end- and face-milling tools exist, such as center-cutting versus non-center-cutting (whether the mill can take plunging cuts); and categorization by number of flutes; by helix angle; by material; and by coating material. Each category may be further divided by specific application and special geometry.

It is becoming increasingly common for traditional solid endmills to be replaced by more cost-effective inserted cutting tools (which, though more expensive initially, reduce tool-change times and allow for the easy replacement of worn or broken cutting edges rather than the entire tool).

Endmills are sold in both imperial and metric shank and cutting diameters. In the USA, metric is readily available, but not commonly used by machine shops; in Canada, due to the country's proximity to the US, much the same is true. In Asia and Europe, while imperial is readily available, metric diameters are standard.

Applications

Endmills are used in milling applications such as profile milling, tracer milling, face milling, plunging, etc. Depending on the material being milled, and what task should be performed, different tool types and geometry may be used. For instance, when milling a material like aluminum, it may be advantageous to use a tool with very deep, polished flutes and a very sharp cutting edge. When machining a tough material such as stainless steel, however, shallow flutes and a squared-off cutting edge will optimize material removal and tool life.

Raw Materials

Endmills have traditionally been made from high speed steel, but are now mostly made of tungsten carbide, a rigid and wear-resistant material, usually pressed from carbide powder into rods, which are then ground into blanks of industry-standard sizes.

In the early 1990s, use of coatings to reduce wear and friction (among other things) became more common. Most of these coatings are referred to by their chemical composition, such as:
* TiN (a basic yellowish coating that has fallen out of wide use)
* TiCN (a popular bluish-grey coating)
* TiAlN (an extremely popular dark purple coating)
* TiAlCrN (PVD coating).
* PCD veins. Though not a coating some endmills are manufactured with a 'vein' of polycrystaline diamond. The vein is formed in a High Temperature-High Pressure environment. The vein is formed in a blank and then the material is ground out along the vein to form the cutting edge. The tools can be very costly, however can last many times longer than other tooling.

Advances in endmill coatings are being made, however, with coatings such as Amorphous Diamond and nanocomposite PVD coatings beginning to be seen at high-end shops (as of 2004).

Manufacture

Endmills are typically made on CNC (Computer Numeric Control) machines under high-pressure lubricants such as water, water-soluble oil, and high-flashpoint oil. Grinding inside the machine is accomplished with abrasive wheels mounted on a spindle (and in some cases, multiple spindles). Depending on what material is being ground, these wheels are made with industrial diamond (when grinding tungsten carbide), cubic boron nitride (when grinding cobalt steel), and other materials (when grinding, for instance, ceramics), set in a bond (sometimes copper).

References