纵-扭复合超声钻削TC4钛合金振动系统设计与试验

螺旋沟槽变幅杆能够实现超声振动模式的转换，对单激励纵-扭复合振动的实现具有结构简单和操作可行的优点。基于弹性波场论对超声波在复合变幅杆中发生模式转换的原因及振动特性进行分析，并从超声波的入射角入手，分析入射角对振动模态的影响。在圆锥复合变幅杆的圆锥段开设螺旋沟槽，建立三维模型，并进行有限元仿真和试验验证，结果表明超声波入射角的改变对纵-扭复合变幅杆的扭-纵比影响显著。当入射角为46.5°和67.2°时，在变幅杆的输出端纵振模态和扭振模态发生明显的变化，实测的扭-纵比前者较后者提高约5.1倍。通过普通钻削与超声钻削实验对比，在不同的入射角条件下，超声钻削的平均钻削力均低于普通钻削力。与入射角为67.2°时对比，当入射角为46.5°时，平均钻削力降低约46%，并提高了制孔的质量，从而为模态转换的纵-扭复合变幅杆设计提供一定的理论依据。

Design and experimental investigation on vibration system of longitudinal-torsional ultrasonic drilling TC4 titanium alloy

The composite horn with helical slots can make the ultrasonic vibration convert and it has the advantages of simple structure and feasible operation for single excitement in longitudinal-torsional composite vibration. Based on the elastic wave-field theory, the reason of mode-conversion and the characteristics of vibration in composite horn were analyzed. The effects of incident angle on vibration mode are also analyzed. The helical slots are made in conical section of the composite horn and the finite element analysis of 3D model was erected. An experiment was carried out to verify the analysis. The results show that the ultrasonic incident angle had significant influence on the amplitude ratio of torsional vibration to the longitudinal vibration. The torsional vibration and longitudinal vibration changes obviously at the output of the horn when the incident angle was 46.5° and 67.2°, and the measured amplitude ratio of torsional vibration to the longitudinal vibration in the former is improved by 5.1 times than that in the latter. Compared with conventional drilling, the average drilling force in ultrasonic vibration drilling is lower at different incidence angles. Simultaneously, the average drilling force at the incident angle of 46.5° is reduced by 46% than that under the angle of 67.2°, and the machined effect of hole is better. The results provide theoretical and experimental basis for the design of the longitudinal-torsional horn.