大功率纵扭复合超磁致伸缩旋转超声加工系统设计理论与加工机理

Rotary ultrasonic machining (RUM), explored in many experimental and theoretical investigations, has been regarded as an effective processing method for hard-brittle materials. Previous studies showed that the increase of ultrasonic power or additional torsional vibration in rotary ultrasonic machining could have a positive impact on the machining performance. In this study, we introduce the giant magnetostrictive transducer into the traditional rotary ultrasonic machining system, and discuss the generation mode of giant magnetostrictive longitudinal torsional vibration. An accurate coordination design method and a performence evaluation method is presented to get the best structure of ultrasonic generator, transducer, horn and abrasive tool. Influence mechanisms of the design parameters on the obtained maximum ultrasonic power and the transducer efficiency are investigated. Then, a giant magnetostrictive high-power rotary ultrasonic longitudinal torsional machining system is developed. SiC matrix composites are selected to explore the interaction behavior of tool-workpiece interface, tool wear and its material removal mechanism in the developed giant magnetostrictive high-power rotary ultrasonic longitudinal torsional machining system. Effects of structural design parameters and process variable (magnetic circuit parameters, longitudinal torsional mode, ultrasonic power, cutting parameters, etc.) on the machining performance, such as cracks generation and expansion, material removal efficiency, machined surface integrity, sub-surface damage, are discussed. A theoretical guidance is proposed for high efficiency and low damage precision processing technology of hard and brittle materials using the developed high-power rotary ultrasonic longitudinal-torsional machining system, which is the research objective of this project.

旋转超声加工已被大量的理论和试验证实是硬脆材料高效精密加工的一种有效方法。前期研究表明，提高超声加工实际输出功率和附加扭转振动均对旋转超声加工性能有积极影响。超磁致伸缩换能器可以产生远高于传统压电陶瓷换能器的机械振动动率。本课题将超磁致伸缩换能设计首次引入旋转超声加工系统，研究超磁致伸缩纵扭复合振动发生模式、超声波发生器-换能器-变幅杆-磨粒工具整体结构精确协调设计方法及性能评价方法，及其相关参数对超声功率和换能效率的影响机制，开发一种超磁致伸缩大功率纵扭复合旋转超声加工系统。选取航空航天典型SiC基/增强相复合材料研究超磁致伸缩纵扭复合超声加工过程中刀具-工件界面相互作用行为、工具磨损和材料去除机理，获取加工外场量（磁路参数、纵扭复合形式、超声功率、切削参数等）对加工效率、加工表面完整性、亚表面损伤等加工特征的影响规律，为硬脆材料大功率纵扭复合超声振动高效低损伤精密加工技术提供理论指导。

本课题将超磁致伸缩换能材料引入旋转超声加工系统，针对超磁致伸缩超声振子和纵扭复合变幅杆的设计、电学补偿、输出振幅建模、热-机载荷对系统振动性能的影响等内容，开展理论和实验研究，研制出大振幅纵扭复合超磁致伸缩旋转超声加工系统。. 以提高超声振幅为目标，提出超磁致伸缩超声振子的总体设计方案，并结合理论建模、有限元仿真和振动实验等对Terfenol-D材料的预应力、激励磁场、偏置磁场、振动部件结构尺寸、导磁材料、等效电路等关键内容开展研究并进行优化设计。提出螺旋槽超声变幅杆的设计方法，探究斜槽结构参数对扭纵振幅比率的影响规律，阐明纵扭复合变幅杆的频率耦合特性，实现具有一定扭纵振幅比率的纵扭复合振动。本课题进一步将非接触电能传输结构、刀柄壳体和超声振子集成设计为超声刀柄，并研制出配套使用的超声加工机床。建立超声加工系统的等效电路，以一定激励电压作用下的输出振幅最大化为目标，提出两种补偿方法下的最佳补偿参数模型。结果表明，电学补偿有助于大幅度降低超声加工系统的电阻抗，提高超声振幅。本课题所研制的超磁致伸缩超声加工系统的输出振幅可达27μm，较同等尺度的压电超声加工系统有明显提升。. 为实现超声振幅的准确预测和调节，建立超声加工系统输出振幅与激励电信号的关系模型，并考虑激励电流变化引起的Terfenol-D材料 效应，提高了模型的准确性。基于此，进一步提出提高振幅稳定性的两种方法：① 采用恒压激励模式；② 实现谐振频率跟踪。. 为提高超声加工系统的稳定性，研究了热-机载荷对系统谐振频率、机械品质因数、换能效率、输出振幅等关键参数的影响规律，验证了所提出的谐振频率跟踪方法的有效性，并建立考虑热-机载荷影响的超声振幅模型。. 在上述研究的基础上，采用不同的超声振幅和扭纵振幅比率在单质硬脆材料和SiC基/增强相复合材料上开展超声振动辅助加工实验，从切削力、极限切削能力、加工损伤、刀具寿命等角度，验证了大振幅纵扭复合超声加工的加工优势。