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Cutting with Coatings: Knowing What is Best for the Application

Coatings may seem simple on the surface, but when deciding what is best for an application, things become more complex. When looking at a cutting tool, there are three main components: the material of which the cutting tool is made; the geometry; and the coating.

With all the innovations within the industry, there have been more developments in coating technology than in material or geometry technologies. Therefore, deciding which coating would be beneficial for a particular application requires learning more about the various options available, the newest innovations and what will best support or improve a specific application.

Over the last 50 years, coatings have revolutionized cutting tools. The benefits of running tools coated instead of uncoated are numerous. Coatings provide better tool life and also provide thermal barriers, which allows them to be run at higher speeds. Coatings increase the surface hardness of a tool while adding a level of lubricity. Ultimately, there is much less friction in the cut, and the lubricity gained from the coating also helps to eliminate built-up edge, among other benefits.

Various coatings have different properties in terms of wear resistance and hardness, but the benefits depend highly on the application. There are coatings with varying lubricity, hardness and heat thresholds, as well as coatings for specific material groups. Exemplifying this are P, K and N grade inserts where different material grades are put together with different coatings in order to excel within their materials groups. Steels might require more aluminum chromium-based coatings, whereas cast iron might require silica nitride or aluminum titanium due to the abrasive nature of cast iron. The stainless steels and high-temp alloys, M and S material type grades, are designed to run in the high heat environment that is associated with machining nickel-based alloys. Lastly, aluminums and other nonferrous materials require coatings that have higher lubricity because aluminum is a material that wants to build up on an edge more than other materials; it is soft and has a lower melting point than other materials.

Whether looking at TiN, TiCN, TiAlN or a material-specific coating for an application, an operator may need to refer to the tooling manufacturer. However, many basic concepts for coatings remain consistent throughout the industry.

TiN, the first physical vapor deposition or PVD coating developed, remains the most often used, although it is not the most wear resistant. The second PVD coating to be created was TiCN, which was the first multilayer coating to be developed with layers of TiN and TiCN interlayered. Next came TiAlN. Ultimately, these three coatings are somewhat universal, so they can be used in a wide variety of applications. However, coatings have recently become more material specific. Because a new universal type coating has not been developed, these material-specific coatings focus on getting to the next level of heat resistance, hardness and wearability through different combinations and configurations of chemical elements.

Even knowing the different types of coatings does not guarantee a clear answer on what will work best in a specific application; one must examine the many different factors involved. First and foremost, know the material that is to be cut and what geometry is needed for the application. Then consult with the tooling manufacturer's recommendations in terms of what coating to use in that material. Additionally, coating choice is dependent upon the type of cutting being performed. There are many variations between thread mills, drills and end mills, for example.

If knowing this information does not lead to a clear answer on which coating to use, there are other application and environmental details to consider:

  • How hard is the material?
  • What is the machine tool and horsepower?
  • What type of coolant is available?
  • Is high pressure coolant an option?
  • What kind of penetration rate is expected?

Ultimately, one must look at the application in its entirety in order to make a sound decision as far as what tool and coating should be used.

Simply stated, coatings are extremely beneficial for cutting tools for heat and wear resistance alone. Combining different elements like aluminum, titanium, chromium or silica nitride in a coating system with different layering techniques created the coatings that exist today, and it is the same concept being used to further enhance these combinations and create new coating innovations. While choosing the right coating involves a complex chemical understanding, having ISO-specific geometries within the industry has removed much of the guesswork.

Authored by Allied Machine & Engineering Corp.

For more information contact:

Allied Machine & Engineering Corp.

120 Deeds Drive

Dover, OH 44622


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