目的 对纵扭复合超声端面铣削加工表面微结构进行预测，以优化加工参数。方法 对纵扭复合超声端面铣削进行运动学分析，并在其基础上建立三维运动轨迹方程。对刀尖轨迹仿真，且研究该运动方式下的加工特性。通过对切削刃和工件离散化建立纵扭复合超声端面铣削表面微结构理论模型，并利用MATLAB进行三维表面仿真。对TC4钛合金进行超声振动切削试验。结果 理论仿真和切削试验结果均表明超声纵扭端面铣削时，随振幅的增加，由振动引起的表面微观结构特征愈加明显。扭纵幅值比增大时，加工表面微观结构凹坑效应弱化，At/Al=0.55时，加工表面呈条形片状微观结构。振动频率和主轴转速会影响表面微观结构单元的疏密程度。结论 加工表面微结构的生成与振动频率、振幅、扭纵复制比、切削速度等加工参数相关，铣削实验得到的加工表面变化趋势与表面理论模型吻合，该表面模型能够优化超声加工参数。

The work aims to predict the microstructure of the machining surface by longitudinal-torsional compound ultrasonic end milling, to optimize the machining parameters. Kinematics analysis was conducted to the longitudinal-torsional compound ultrasonic end milling and the three-dimensional motion trajectory equation was established based on this. The tool trajectory was simulated and the machining characteristics of the tool were studied. By discretization of cutting edge and workpiece, a theoretical model of surface microstructure under longitudinal-torsional compound ultrasonic end milling was established and 3D surface simulation was carried out by MATLAB. Ultrasonic vibration cutting experiment was carried out to TC4 titanium alloy. Theoretical simulation and cutting test results showed that the surface microstructure characteristics caused by vibration became more obvious with the increase of amplitude in longitudinal-torsional ultrasonic compound end milling. The pit effect of machined surface microstructure was weakened with the increase of ratio of torsional longitudinal amplitude. When At/Al=0.55, the machined surface presented strip-shaped microstructure. Frequency and speed affected the density of surface microstructure units. The characteristics of microstructure of machined surface are related to machining parameters such as frequency, amplitude, ratio of torsional and longitudinal amplitude, and cutting speed. The variation trend of the machined surface obtained from the milling experiment is consistent with the theoretical model of the surface.