The mechanical analysis and deformation mechanism of cap formation in orbital drilling process plays a vital role in revealing the changing law of hole-making quality at the exit machining stage. The characteristics of cap formation, generated by a dedicated cutting tool, is proposed that aimed at orbital drilling process. Especially, the cap bottom is simplified as a simply supported circular plate under a partially uniform load based on the symmetrical feature of the geometrical morphology and force condition. Its corresponding unified plastic limit analysis is developed. Then the ultimate load, stress field, and plastic deformation at the bottom of the cap are derived from the unified yield criterion. Furthermore, in terms of the Tresca yield, Huber–von Mises, and twin-shear yield criteria, the solutions are obtained by numerical calculation method and compared them with each other. Finally, conclusions were made about the cap formation mechanism in the orbital drilling of holes from the unified plastic limit analysis perspective.

轨道钻孔过程中盖帽形成的力学分析和变形机理对于揭示出口加工阶段成孔质量的变化规律具有重要作用。针对轨道钻井过程，提出了由专用切削工具产生的盖帽形成特征。特别是，基于几何形态和受力条件的对称特征，帽底被简化为在部分均匀载荷下的简支圆板。开发了其相应的统一塑性极限分析。然后根据统一屈服准则推导出瓶盖底部的极限载荷、应力场和塑性变形。此外，就 Tresca 屈服、Huber-von Mises 和双剪切屈服标准而言，解是通过数值计算方法得到的，并相互比较。最后，从统一塑性极限分析的角度对轨道钻孔中的帽盖形成机制进行了总结。