Challenge: How can you enhance tool productivity in production environments?
Solution: Use PVD-coated tools and inserts to reduce cycle times and run faster.

Physical Vapor Deposition or PVD relates to vacuum coating techniques that can deposit thin film coating on tools and inserts. In essence a solid material such as metal or a metal alloy is vaporized, often with the aid of a plasma, e.g., an electrically charged gas. The metal vapor contains both metal atoms and ions. The atoms and ions are then deposited on a substrate to form a coating. With a TiN coating, for example, a titanium source vaporized in a nitrogen atmosphere, and TiN is formed on the tools and inserts.

Production Tools and Savings

PVD coatings increase the life and productivity of production tools, saving companies billions of dollars each year. How? First, PVD-coated tools can be run faster, reducing cycle times and enabling the production of more components in less time. Second, PVD coatings reduce wear and pickup, reducing downtime due to tool replacement. FInally, PVD coatings reduce the need for cutting fluids, which can cost companies up to 15 percent of their total production costs. PVD coatings can be run dry or with a very limited amount of fluid.

The main use for PVD is in applications where sharp edges are required, such as threading, grooving, parting, end milling and drilling. For solid carbide tools such as end mills and drills, PVD is the main coating technology. PVD-coated tools are the best choice in difficult-to-cut materials such as titanium, super alloys and stainless steels, where sharper edges are needed to lower cutting forces, and high temperature stability is required to maintain cutting-edge integrity. The functionality of the coating depends ultimately on its ability to mitigate thermo-mechanical damage of the bulk material of the cutting edge under different metalcutting conditions.

Coating Materials

PVD meets the challenge of enabling coating materials to be deposited in large batches with an even coating thickness on each insert and over the whole batch. In addition, PVD meets the challenge of coating tools with sharper edges without any embrittlement effect. This is achieved by lower deposition temperatures, around 930°F, compared with the other major coatings technology, chemical vapor deposition, CVD, which requires temperatures of around 1830°F, although lower-temperature processes are becoming available. For PVD, however, there are different ways to get the right thickness, the right structure and the right composition to suit the targeted application area and the coating material.

For tooling applications, there are three main PVD processes in use today — ion plating, arc evaporation and magnetron sputtering. PVD is essentially a low-pressure, line-of-sight deposition process that uses a solid metal evaporation source. PVD uses metallic precursors that are solid, with the material to be deposited being vaporized from a solid target and deposited onto the substrate. PVD produces thin coats of a few microns that have the attributes of high hardness, fine grain size and smooth surface morphology and that are crack-free due to compressive stress. CVD coatings, by contrast, are more suitable for applications where abrasive wear is a problem, as these exhibit high wear resistance because of the thicker layer.

TiN and Drilling

The first PVD coating material to have a commercial application was TiN. Sandvik Coromant introduced its first TiN-coated tool, the delta drill, in 1982. G 1020, the first PVD insert grade, appeared in 1990.

PVD has remained at the forefront of coating developments. Materials such as TiCN, TiAlN and AlCrN and oxides such as Al₂O₃ and (AlCr)₂O₃, novel coating materials such as TiAlSiCrN and even carbon-based materials have become available as PVD coatings in expanding application areas. Innovations in the coating system process such as incorporating rf or pulsed dc power have solved the difficulty in depositing insulating coating materials. Multilayer coatings have, for example, helped enhance insert performance. Developments in PVD hardware such as new vapor sources are likely to further improve the coatings technology.

Originally published in Metalworking World 3.2011, a business magazine published by Sandvik Coromant.

Text: Elaine McClarence