Cbn Insert
A CBN insert is a cutting tool made from cubic boron nitride (PCBN) used in CNC machining for hard ferrous materials like hardened steels and cast iron above 45 HRC. It offers extreme hardness and thermal stability, second only to diamond, but is chemically suitable for iron-based workpieces where diamond fails, enabling hard turning with fine finishes.
On the shop floor, CBN inserts are deployed in CNC lathes or hard-turning cells for parts exceeding 45 HRC, often post-heat treat. Typical setups use a brazed or tipped CBN layer on a carbide substrate, balancing hardness with shock absorption. CBN delivers low surface roughness (Ra 0.28–0.8 µm) and tight tolerances (±0.01 mm) on hardened steels. Applications favor dry cutting to avoid thermal shock, though coolant may be used depending on grade. Process stability demands rigid machine setups, minimal tool overhang, and consistent chip loads. CBN is primarily for finishing but some grades handle light roughing. It outperforms carbide in high-temperature conditions where carbide wears rapidly, making it essential for precision hard turning in automotive, die, and bearing industries.
When is CBN chosen over carbide?
CBN is selected for hardened ferrous parts typically above 45 HRC, especially when carbide cannot maintain size or surface finish due to rapid wear. It excels in hard turning operations where elevated cutting temperatures degrade carbide.
Why does CBN outperform carbide in hard turning?
CBN retains its hardness at high cutting temperatures, resisting thermal and mechanical wear far better than carbide. Its chemical stability with ferrous materials prevents diffusion wear, allowing sustained cutting edge integrity.
What insert constructions are available?
Common forms include solid CBN, tipped PCBN (a CBN layer brazed onto a carbide substrate), and full-face brazed designs. Solid offers maximum cutting edges but is brittle; tipped balances cost and toughness; full-face provides durability for heavy cuts.