Investigation of critical material removal transitions in compliant machining of brittle ceramics

Compliant machining processes, such as bonnet polishing, can be used on hard and brittle ceramic materials to produce ultra-precise freeform surfaces with sub-micron form accuracy and nanometric surface roughness. However, a comprehensive understanding of the removal mechanism in such process is lacking. In this paper, an analytical model is proposed to reveal the material removal behavior on the basis of a “three zone” concept, namely elastic recovery, plastic removal and brittle fracture. The corresponding three transition pressures are derived at the microscopic scale and validated by finite element simulation. The inherent relationships of the three critical pressures with actual pressure, due to compression of the elastic bonnet tool and asperity effect, are established and analyzed in association with different material removal behaviors. Removal footprints are then generated under different conditions to validate the material removal behavior. Finally, polishing tests with continuously varying tool angle and offset were implemented, and the consistency in material removal rate demonstrates the accuracy of the proposed model.