LATROBE, PA – Advanced hard turning, or the use of superhard polycrystalline cubic boron nitride (PCBN) cutting tools for machining hardened ferrous materials like cast irons, is eagerly sought across a number of key manufacturing industries. Hundreds of millions of brakes discs, brake drums, flywheels, and wheel hubs are required annually in motor vehicle, heavy equipment, and other industries, and although superhard tools show promise for turning such tough-to-machine parts, that promise has been stalled due to the tendency of these expensive tools to shatter and break under the extreme forces required.
With decades of experience in advanced materials science and tool design, Kennametal is announcing Beyond Shield™ as the solution (responding to modern challenges in machining cast iron machining) to this situation.
“For customers machining gray cast iron brake disks and brake drums, Kennametal´s Beyond Shield™ PcBN inserts and clamping system provide up to 20% reduced tooling cost and up to 30% longer tool life compared to conventional systems,” says Dr.-Ing. Raouf Ben Amor, senior global product manager. “Beyond Shield™ provides a robust clamping system that allows smaller IC PcBN inserts to perform well in the same applications as the larger IC insert, and by excellent matchup of wear and toughness in our grade properties proven in field tests.”
Meeting the Clamping Challenge
High-performance cast-iron machining leads to extremely high mechanical and thermal loads. Conventional dimple-style clamps attempt to hold the cutting insert in place with direct point contact, which can break both clamp and insert under high pressure.
Beyond Shield has met the clamping challenge with a three-point clamp design that applies clamping force toward the front of the insert, closer to the cutting edge and significantly reducing vibrations that can lead to cracking and failure.
In addition, cast iron machining is a very aggressive environment where constant chip bombardment also cuts down clamp life. Beyond Shield provides a carbide-clad clamp through a unique Kennametal technology that improves clamp wear resistance from chip flow. Beyond Shield is also adaptable on standard toolholders, which can help control costs.
New PCBN Grades
In addition to being tough by nature, cast irons present a number of machining challenges for cutting tools. Casting quality can be unpredictable. Low sulfur content can lead to tool life decreases by up to 60 percent, and increased ferrite content can lead to high chemical wear, also substantially decreasing tool life.
With a unique “multi-modal” PCBN structure, Kennametal´s KBK35™ grade has increased cubic boron nitride content that ensures increased wear resistance and longer insert life in both roughing and finishing operations. A chemical vapor deposition (CVD) coating protects against chemical wear resistance, and post-coat treatments improve cutting-edge toughness. “Field tests have shown double the tool life for KBK35™ in aged and unaged cast iron, and in specific cases such as brake drums, up to ten times (compared to ceramic-based solutions) the number of parts completed per insert.”
For parts involving aged cast iron, Kennametal is also introducing grade KB1340™ to the Beyond Shield family. In brake disk field tests versus standard PCBN inserts, KB1340™ increased performance to 1700 pieces versus 1500 for the PCBN insert. In the same test versus ceramic inserts, tool life increases from 120 pieces to 4200.
“For customers facing the need to increase cutting parameters and yet improve process reliability and control costs, Beyond Shield™ is the way to high-performance cast iron machining,” Ben Amor says.