Types of End Mill Coatings

End Mill Coatings

A very important process that allows the carbide end mill to resist wear is the coating.  Coatings enable the cutting tool to evacuate chips from the flutes faster thereby getting the HOT chips off of the end mill's ground surface. Heat is not carbide's friend. In the last decade, the technology to provide more heat- and wear-resistant coatings has promoted longer tool life and increased productivity. 

The commercial acceptance of hard coatings for cutting tools is driven by demands on machining productivity, environmental mandates, and increased usage of new difficult-to-cut materials. Improved cutting performance is derived from synergies of machine tool system and cutting tool development. The latter strives for an optimized combination of tool material, hard coating and cutting edge geometry.

The integration of hard coatings in cutting tools has reached a mature stage after more than three decades of proven performance and productivity benefits in industrial metal cutting.

Chemical vapor deposition (CVD) was the first technology used, which advanced from single layer to current multilayer types combining TiC, TiN, TiCN and Al2O3.

​Almost 35 years later it is evident that novel physical vapor deposition (PVD) compositions have surpassed the limited set of available CVD coatings. The relative economics are debatable but it is accepted that total life cycle consideration and environmental friendliness favor PVD technology. Succeeding generations of PVD hard coatings have become commercially available, notably TiCN, TiAlN and AlCrN, with demonstrated success in expanding areas of application.

Overview: AlTiN & TiAlN

The more common coatings on the market today include TiN (titanium nitride), TiCN (titanium carbon nitride) and TiAIN (titanium aluminum nitride) or AlTiN (aluminum titanium nitride) - the latter having more aluminum content.   The coatings that have become the most popular are the TiAIN- or AlTiN-coated end mills. They are much more effective effective at dissipating heat than the TiN coatings from 20 years ago.  

The heat is dissipated so well into the chips with the AlTiN coating that dry machining is mostly recommended, except when slotting where the chips need to be expelled out of the channel. The aluminum in the coating helps form a gaseous aluminum oxide layer at the cutting edge where temperatures can reach more than 1800°F. This helps protect the carbide substrate from the damaging effects of heat. That's what makes this coating ideal for high-speed and hard milling, especially in dry cutting. 

For machining aluminum, brass, plastics and other nonferrous materials it is best to use our Stealth coated end mill with polished flutes to prevent edge buildup.

Aluminum Titanium Nitride (AlTiN) and Titanium Aluminum Nitride (TiAlN) is a thin film coating that was developed from Titanium Nitride. 

AlTiN offers higher temperature resistance than TiN, as well as slightly higher hardness and especially higher hot hardness (i.e. the hardness at high temperatures).

- Can withstand elevated temperatures up to 800°C (1450°F) in air.

- Forms a thin surface layer of Al2O3 that is hard, low in friction and oxidation resistant. As this layer wears, it is constantly rebuilt from the Al in the coating.

- Performs best in high temperature applications. Requires high temperatures to form the Al2O3 surface layer.

- Harder than TiN. But, does not outperform TiN in all applications.

- Is not a single material. No AlTiN molecule exists. Rather it is a complex structure consisting of TiN and AlN bonds in a crystalline matrix. AlTiN or TiAlN is a proprietary multilayered or graded architecture design.

- No uniform specification exists for a AlTiN or TiAlN material.

- Is harder than carbide and chrome, off the Rockwell C scale.

- Is dense and non-porous

- Tools typically last 3 to 10 times longer than uncoated tools.

- Is typically 3 micrometers or .0001” thick

- Forms an outstanding bond to the base material that will not blister, flake or chip

- Thin film coating applied by environmentally safe, Physical Vapor Deposition (PVD) vacuum system

Aluminium Titanium Nitride

This PVD coating has a gradually increasing percentage of aluminum added as it goes through the coating process. It gradually increases in the amount of Aluminum from the substrate interface until it reaches the outer surface of the coating, where there is a higher percentage (up to 65%) of aluminum in the film. As the tool heats up, the aluminum converts to aluminum oxide, staying in the film. 

This coating provides exceptional oxidation resistance and extreme hardness. AlTiN retains its hardness when the temperature is 800° to 930° C (1,470° to 1,700° F) This coating is ideal for dry machining environments. Used exclusively on our Raptor products for all: P – Steels (blue), M – Stainless Steel (yellow), K – Cast Iron (red), and S – Hi-Temp Alloys Special Alloys & Titanium (brown) materials. 

Please keep in mind that this coating CANNOT be used in Aluminum (N) machining because the Aluminum in it would have an affinity to itself and cause workpiece adhesion to the cutting tool.  

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