Abstract: To reduce the impact of machining vibration on the machining quality of the assembly interface of large aircraft in finishing, it is necessary to understand the dynamic characteristics and the modal parameters of the assembly interface. Hence, an optimized Space Time Domain (STD) method is proposed to identify the modal parameters during the dynamic finish machining. Firstly, a Toeplitz matrix is generated by the measured machining vibration data of the assembly interface and is treated as the input of the STD method. Secondly, the relative stable modal parameters are selected as the modal parameters of the assembly interface in terms of the modal confidence factor and the Modal Assurance Criterion (MAC). Finally, the correctness and effectiveness of the optimized STD method are validated through impact tests and cutting experiments. In detail, the results of the impact test are regarded as the referenced modal parameters of the assembly interface. Taking the 1st-order modal identification result as an example, the modal identification accuracy of the optimized STD method is improved by 12.7% and 3.82% compared with the traditional STD and SSI methods. The identification accuracy of the modal parameters of the rest orders can also be improved to a certain extent as well. Therefore, the modal parameters of the assembly interface can be accurately and efficiently identified via the optimized STD method, which can theoretically and technically support the reasonable selection of the finish machining parameters.

Key words: assembly interface, optimized STD method, impact test, modal confidence factor, modal assurances criterion