New efficient CBN grades

Innovative coatings make the difference and different cutting edges and chip formers optimize chip removal

For many years, Sumitomo has earned a reputation for technical leadership and high process reliability in turning hardened materials. When it comes to machining hardened steels and the demand for good surfaces, inserts made of CBN (cubic boron nitride) from Sumitomo SUMIBORON are usually involved.

Sumitomo's modern CBN materials have long since disproved initial reservations about sensitive cutting edges. Through continuous development of the cutting materials, there is now a whole range of different CBN substrates for very different cutting conditions, which has greatly expanded the application possibilities of the superhard cutting material CBN over the years. Today, Sumitomo has a wide variety of substrates to meet all requirements. Very hard and wear-resistant substrates retain their sharp cutting edge over long contact times and offer the best surfaces in continuous cutting. For interrupted cutting, very tough CBN grades are available that promise long tool life even in heavily interrupted cutting.

At Sumitomo, however, the further development of indexable inserts goes far beyond the substrates. In the meantime, special coatings are also being offered for superhard materials, which include CBN, further pushing up tool life and technical possibilities. With innovative multi-layer coatings developed specifically to meet customer requirements, engineers at Sumitomo have succeeded in matching the new Sumiboron grades BNC2115 and BNC2125 perfectly to these application requirements. For both grades, new CBN substrates have been developed to provide good and stable cutting behavior, even with interrupted cutting.

For the BNC2115 grade, a new bonding layer was applied to the base substrate, which bonds particularly well with the sheet surface like a primer and provides the best hold for the coating even under high shear forces. A series of new, ultra-thin layers are then applied to this adhesive layer, which in turn contribute additional properties to the machining process.

First, there is a multilayer coating of high-hardness TiAlSiN, which provides low notch wear and thus ensures consistently good surface quality during machining. This layer alternates several times with a highly heat-resistant TiCN layer, which significantly reduces the dreaded scour wear and ensures long tool life. A gold-colored sliding layer was then added on top of this multilayer coating to ensure rapid chip evacuation so that there is no heat transfer from the chip into the tool. The special feature of these new layers: All this takes place in a coating thickness of only 3 µm!

This makes the CBN grade BNC2115 particularly recommended for use in high-precision machining of hardened steels at medium and high cutting speeds. With cutting speeds from 110 to 300 m/min, they cover a very wide range and, with a stated optimum cutting speed of 180 m/min at a feed rate of 0.1 mm/rev, they can be used in a variety of applications. In direct comparison to predecessor grades and competitors, BNC2115 shows a much longer tool life and the best surface finishes of the workpieces despite higher cutting speeds.

The coating combination of the Sumiboron grade BNC2125 is completely different. The optimized adhesive layer is followed here by a new multilayer coating developed for particularly high wear resistance. In addition, this multilayer coating offers significantly better protection against coating spalling, especially compared with coatings commonly used in the past. On the surface of the new CBN grade, there is a silver-colored top layer in this case to reduce adhesion between the insert and the outgoing chip and to dissipate the cutting heat quickly with the chips.

Like other CBN and PCD inserts from Sumitomo, the BNC2115 and BNC2125 innovations are available with different cutting edges and chip shaper geometries, allowing these inserts to be selected to optimally match the material being machined and to the application at hand. Thanks to continuous development and constant innovation, Sumitomo today offers an extensive standard program with a very wide selection of substrates, coatings, cutting-edge geometries, and chip formers. With the combination of all these variants, every individual task can be processed as efficiently as possible. This promises the best economic efficiency with process-reliable and optimal machining, without unplanned interruptions. This diversity of variants from Sumitomo should be one more reason to consider CBN cutting.