Fabrication and wear characteristics of open-porous cBN abrasive wheels in grinding of Ti–6Al–4V alloys

Abstract Cubic boron nitride (cBN) superabrasive wheels have been a preferential choice for grinding difficult-to-cut materials (i.e. Ti–6Al–4V alloys) in aerospace and aviation industries. However, the grinding performance and tool-life of conventional cBN abrasive wheels are severely affected by the probable macro-fracture and pull-out of cBN grains owing to their anisotropic crystalline structure. In this case, open-porous sintered cBN abrasive wheels, which are associated with excellent grinding performance and long tool-life, were developed. Pore structures were fabricated using spherical carbamide particles as space holders via the vacuum sintering process. The effects of pore structures, such as pore size and porosity, on the mechanical properties of metallic porous composites were discussed. Characterisation of pore structure and tool wear morphologies was also performed during the grinding process of Ti–6Al–4V alloys. The grinding performances, including grinding force and force ratio, tool wear evolution and machined surface quality, were discussed in detail. Results show that open-porous cBN abrasive wheels featured a desired flexural strength and excellent chip storage space after optimising the pore size of 0.6–0.8 mm and designed porosity of 40 vol.%. The strong bonding strength of porous cBN abrasive wheels was produced due to the chemical reaction in the zone of bonding interface among cBN abrasive grains, Cu–Sn–Ti alloys and MoS2 particles during liquid-phase sintering. The porous cBN abrasive wheels showed a stable grinding force ratio from 1.5 to 2.6 once the grinding speed exceeded 30 m/s. In addition, the sharpness of porous cBN wheels can remain stable in a long duration due to the dynamic changes in the chip storage space provided by the porous parameters and self-sharpening of porous cBN abrasive wheels. Moreover, the ground surface roughness rapidly declined and stabilised due to the stabilisation of the dynamic effective grains number.