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.

合规的加工工艺，例如气缸盖抛光，适用于硬脆性陶瓷材料，能够制造出具有亚微米级形状精度和纳米级表面粗糙度的超精密自由曲面。然而，对于此类工艺中的去除机制，尚缺乏全面的理解。在本文中，基于“三区”概念——即弹性恢复、塑性去除和脆性断裂——提出了一种分析模型，以揭示材料去除行为。在微观尺度上，相应于三个过渡压力被推导出来，并通过有限元模拟进行验证。建立了三个临界压力与实际压力之间固有的关系，实际压力因弹性气缸盖工具的压缩和粗糙度效应而产生，并与之相关的不同材料去除行为进行了分析和确立。随后，在不同条件下生成了去除足迹以验证材料去除行为。最终，通过连续变化的工具角度和偏移进行的抛光试验，去除速率的一致性证明了所提出模型的准确性。