Improved Superalloy Grinding Performance with Novel CBN Crystals

The retention of key mechanical properties by nickel-based superalloys at high operating temperatures makes them suitable for use in aircraft engines, petrochemical industries, and premium automotive exhaust applications. However, superalloys are difficult to grind materials: prone to thermal damage with associated high tool wear. In addition, the adherence of grinding debris to the wheel necessitates frequent process interruptions to re-profile the wheels with a diamond dressing roll. Ensuring adequate thermal management during grinding by way of a sharp, thermally conductive abrasive is important. Cubic boron nitride (CBN), with its high hardness and thermal conductivity, coupled with a vitrified bond system, is ideally suited for superalloy grinding. Even so, the high specific energy in superalloy grinding can cause dulling of the CBN crystals with potential detrimental effects on workpiece microstructure and properties.

Superalloy grinding efficiencies can be improved by maintaining CBN crystal sharpness or by reducing the grinding cycle time while ensuring negligible thermal damage in the part. In this paper, in creep-feed grinding of Inconel-718, we compare the wheel wear and workpiece attributes when using currently available CBN crystals against two newly developed CBN crystals. The new CBN crystals enable a reduction in wheel dressing frequency by over 60% compared to that with standard CBN at the same material removal rates (Q’). The specific energy with the new CBN crystals is also lower by about 20%. Finally, the new CBN crystals also lend themselves to grinding at 33% higher Q’ without inducing workpiece damage; the higher Q’, though, is accompanied by a higher wheel wear than at standard Q’. We compare the physical properties and shape characteristics of the new CBN crystals with standard crystals and speculate on possible mechanisms that enable both the slower grinding wheel wear and the improved cutting efficiency.