In the beginning, machining was less complicated, at least it seems that way from present day point of view. Material available for use was found on a much shorter list. Options for machinery and tooling were more limited. Coolants and lubricants were literally water and oil.
Today, we are presented with nearly unlimited options in the machining process. Tooling has improved, so have available coolants and lubricants. Engineers and designers are willing to stretch the limits of what is possible. Manufacturing is left to produce a part that matches the specifications of the print. A short list of available materials has expanded to include an ever increasing list of alloys, and Tooling choices now include HSS alloys, carbide, and ceramics. To add to the mix, CNC machinery allows the manufacturer to produce finished parts with incredible accuracy and speed.
Surface treatments and coatings allow us to improve tooling performance when the characteristics of the tool’s substrate (base material) have reached the limits of capability. Surface treatments like Oxide and Nitride were among the early arrivals. They addressed the need for added lubrication and surface hardness to improve part finish, reduce or tolerate heat generated by higher machining speeds, and wear-resistance.
As materials evolved, so did the available treatments to either improve tool performance, or compensate for the challenges those new materials presented to Manufacturing. Hard coatings like Titanium Nitride (TiN) offered improvements in wear-resistance for HSS tooling. Titanium Carbon-Nitride (TiCN) arrived to compensate for the limitations of TiN, especially in respect to Titanium Alloys. Titanium Aluminum Nitride (TiAlN) followed with improved tolerance to heat generated by increasing machining speeds and material resistance to the tool. Each new coating is developed to succeed where another was not well-suited to the application.
Today the list of available coatings, both hard and soft, is impressive. According to Swiss-Tek Coatings in New Berlin, Wisconsin, the three base coatings – TiN,TiCN, and TiAlN – currently make up more than 90% of the world’s coating market for cutting tools..
TiN is the general-purpose coating for cutting, forming, and injection molding. This Gold-colored coating provides a smooth surface to reduce friction, and is harder than the substrate to improve edge retention and increase tool-life.
TiCN is a conventional Titanium Carbon Nitride coating for interrupted cutting, milling and tapping, stamping, punching, and forming. This Blue-Grey colored coating has a higher hardness than TiN, and a lower friction coefficient. It has proven itself to be a good choice for tapping, both cutting and forming.
TiAlN, (Titanium Aluminum Nitride) a coating typically Violet-Bronze in color, is recognized as a universal high-performance coating for cutting. It offers capabilities similar to those of TiN and TiCN, but with higher heat resistance for high speeds and feeds, and “dry” machining.
Unfortunately, none of them are the answer to all ills. Each individual application will direct the decision of which coating might be the best choice. Usually, experience from the performance of un-coated tools will tell us what shortfalls need to be addressed. Many manufacturers, including North American Tool, will offer suggestions for application-specific tooling that include a proven coating in the design. These recommendations are based on historical application, and extensive testing.
However, science has presented all of us with a “moving target”. Materials evolve. Machine capabilities continue to advance. The demand for improvement is constant. What worked yesterday may not be the answer tomorrow. Because of these realities, it is imperative that we find trusted partners to go to for answers. Partner with Tooling Manufacturers, like North American Tool, and Coating sources that have access to information on the latest developments in tool design and treatments. They will help you make good decisions on which coating best suits your needs.