硬脆材料孔加工出口破损形成机理

Formation mechanism of exit chipping in drilling hard-brittle material

为研究BK7玻璃孔加工过程中出口破损的形成机理,本文在对破损形貌进行显微观测的基础上,基于断裂力学理论,分析了工件加工面所受载荷随裂纹扩展过程的演变规律及其对出口破损形成过程的影响;采用光滑质点流体动力学法对出口破损的形成过程进行了数值模拟,研究了出口破损的形成机理。结果表明:出口破损可分为初始裂纹区及扩展裂纹区,挤压载荷和弯矩的耦合作用驱使初始裂纹沿圆周方向扩展,显著增加了裂纹的倾斜角度和破损宽度,导致破损表面产生大量散射状条纹;借助光滑质点流体动力学法实现了对出口破损形成及脱落过程的数值模拟,发现初始裂纹贯穿整个未穿透厚度,刀具的瞬时切削力减小了78%;并且随着裂纹间歇性地沿圆周方向扩展,刀具切削力呈现出剧烈的周期性波动特征。

This study aims to investigate the formation mechanisms of hole exit chipping in diamond drilling of BK7 glass.Based on the microscopic observations of the chipping morphology and fracture mechan⁃ics theory,the evolution of extrusion load exerted on the machining surface with crack propagation was explored and its effects on the chipping formation was analyzed.The smooth particle hydrodynamic method(SPH)was applied to numerically simulate the formation process of exit chipping to investigate its forma⁃tion mechanisms.Results suggest that the exitchipping morphology could be divided into the incipient crack area and extended crack area.The coupling effects of the extrusion load and bending moment pro⁃moted the incipient crack extended in the circumferential direction,which significantly increased the inclination angle of the crack and width of exit chipping,thereby resulting in the occurrence of scattered stripes on the chipping surface.With the SPH method,the simulation of the chipping formation and shedding pro⁃cesses was realized,revealing that the penetration of incipient crack through the entire unpenetrated thickness could reduce the instantaneous cutting force of the tool by 78%.In addition,the cutting force of tool presented periodic fluctuation characteristics with the circumferential progradation of the in⁃cipient crack.