KENNAMETAL has introduced a new chemical vapour deposition (CVD) coated polycrystalline cubic boron nitride (PCBN) grade, KB9610. The grade provides substantial improvements in productivity for finish-turning applications on hardened steels such as 8620, D2 tool steel, and 52100.
The grade is made of a low content PCBN tool material that is CVD coated with alumina and titanium nitride layers. It outperforms conventional PCBN grades in finish-hard turning of steels, especially in the 600 to 800 surface feet per minute range. The CVD alumina coating provides a strong barrier to crater/diffusion wear, the primary failure mechanism.
Kennametal claim a 250% increase in tool life compared to the best existing PCBN materials when using equivalent speeds and feeds. Their recommendation, however, is to obtain greater productivity by operating at higher cutting speeds.
Advancements in coating bonding technology make it possible to apply adherent CVD alumina and titanium nitride coatings to tipped PCBN tools. Although both coatings are "softer" than the PCBN substrate, the alumina coating provides thermal barrier protection to the PCBN. The outer TiN layer helps to reduce frictional forces at the chip/tool interface as well as providing a convenient means for identifying used edges on the cutting tool.
The CVD coating system provides a substantial performance improvement over uncoated PCBN grades. PCBN is a very hard material, but it normally fails through crater wear due to a chemical reaction of the work piece material with the boron or nitrogen in the tool. The inert CVD coating serves as a barrier to chemical reactions.
The new grade is more economical than solid PCBN grades because its PCBN tips are brazed onto a carbide supporting substrate. This reduces the amount of the more expensive PCBN material required for each insert. The low-content PCBN material coupled with the CVD coating provides unmatched crater wear resistance when machining hardened steels. The new grade is available in various negative Kenloc, positive screw-on, positive Kendex, and profiling insert styles. Round, square, triangle and 80°, 55° and 35° diamond insert shapes with 1/4 inch to 1/2 inch inscribed circle sizes are available. They are offered in two specially designed wiper geometries that smooth out feed marks on the work piece surface. They provide superior surface finish when compared to conventional geometries.