The German tooling company Horn, which has a UK subsidiary, Horn Cutting Tools Ltd in Ringwood, has announced an expansion of its product portfolio to include tools tipped with cubic boron nitride (CBN) for machining difficult materials such as superalloys and hardened steels.

The ultra-hard material is capable of smooth machining, even during interrupted cutting when hard turning and grooving. By extending its existing standard ranges of Supermini 105, Mini 11P, 229 and 315 systems, Horn can deliver the CBN tools quickly from stock.

The Supermini system is available in left- and right-hand versions with different corner radii. The CBN-tipped variants are for internal machining from a diameter of 2mm. Different lengths of solid carbide body are available. Tools in the Mini family can be used from an internal diameter of 6.8mm and are also available in left- and right-hand versions.

The single-edged tool type 315 is for external grooving from a width of 0.5mm. In the cutting insert system 229, the previous CBN substrate CB 50 is replaced by the higher performance substrate CB 35. Inserts are available with two different corner radii and cutting widths from 3 to 6 mm.

Horn says CBN is the second-hardest material after diamond, adding that tools made from CBN wear much more slowly than other cutting materials when used appropriately, making it possible to achieve higher dimensional and profile accuracy — even when machining hard materials such as steel up to 70 HRC.

“There are no different grades of CBN. Differentiation between tools is down to the CBN volume fraction, the fillers, grain size and the ceramic/metallic binder phase (cobalt/nickel). This results in different CBN substrates.

“Hard machining is usually carried out without coolant, as these cutting materials have high-heat resistance and the elevated temperature within the chip formation zone has a positive effect; and whereas carbide suffers a significant loss of hardness at around 800°C, the hardness of CBN remains almost unchanged at temperatures up to 1,200°C. Another significant advantage is good chemical resistance — even at these high temperatures.”