Thick as a brick: Turning Performance

The thicker the PVD coating is on an insert, the longer users expect it to last. But a coating that is too thick tends to flake, reducing the coating’s effective life, according to Mike Raper, national sales manager for Techniks Inc. That is why most manufacturers’ PVD coatings are only 4µm thick, he noted. However, the toolmaker’s Nexus line of milling, turning and boring inserts have a PVD TiAlN LT10 coating up to 8µm thick for milling and a LT1000 coating up to 14µm thick for turning.

Courtesy of Techniks

The thickness of the Nexus Magia PVD coating compared to a conventional PVD coating and a conventional CVD coating.

Raper explained that the unique PVD formula for the Magia coating, developed by partner Lamina Technologies SA, Yverdon-les-Bains, Switzerland, prevents flaking while enabling the highest possible adhesion of the PVD to the submicron grain carbide insert, which has a special edge preparation. Prior to coating, the inserts are subjected to a micro-sandblast technique to hone the cutting edge radius to within a ±5µm tolerance. This process takes the place of brush honing, which creates an uneven edge, according to Raper.

“Our coating ends up being smoother and more uniform,” he said, adding that a post-coating polishing treatment also reduces friction.

With traditional coatings, increasing the hardness usually means reducing toughness and vice versa. Nexus’ nanocomposite coating structure, LT1000, has a high hardness and toughness at the same time, according to Chris Deis, director of marketing for Techniks. He claimed that LT1000 is the thickest supernitride PVD coating on the market and provides greater thermal insulation and more resistance to plastic deformation and shock than CVD or traditional PVD coatings.