Endmill
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Image:MillingCutterSlotEndMillBallnose.jpg An endmill is a type of Milling cutter, a cutting tool used in industrial milling applications. It is distinguished from its cousin, the drill bit, in its application, geometry, and manufacture. The term "endmill" is sometimes considered to be machinist's slang, but has come into standard usage in industry publications, trade magazines, and manufacturers catalogues.
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Types
A broad category of end and face milling tools exists, such as flat bottom, ball nose, radius, inverted radius, and chamfer tools. Each category may be further divided by specific application and special geometry.
It is becoming increasingly more 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 (unlike the majority of drills) in both imperial and metric shank and cutting diameters, depending on the country of origin. 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, however, metric diameters are standard.
Applications
Endmills are used in milling applications such as profile milling, tracer milling, face milling, and the like. Depending on the material being milled, different tool types and geometry may be used. For instance, when milling a material like aluminum, it may be adventageous to use a tool with a very shallow flute depth, and a pre-dulled (but polished) cutting edge.
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 cut into blanks of industry-standard sizes.
In the early 1990's, coatings to reduce wear and friction (among other things) began to come into wide use. 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 blueish-grey coating)
- TiAlN (an extremely popular dark purple coating).
Advances in endmill coatings are being made, however, with coatings such as Amorphous Diamond 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 nitrite (when grinding cobalt steel), and others material (when grinding, for instance, ceramics), set in a bond (sometimes copper).