Design and numerical analysis of block-like horn with complex 3D working surface for ultrasonic plastic welding

In ultrasonic welding, the uniform displacement of the working surface profile has a significant influence on the quality of the weld. The more uniform the displacement, the higher the quality of the weld. In particular, for block-like horns with a complex curved surface profile, achieving uniform displacement is difficult. In this study, the displacement uniformity of horn has been improved by optimizing the design of the block-like horn. An optimal design method for block-like horn with a complex curved surface profile used for welding of turn signals was developed and verified. The optimal design of block-like horn is achieved by integrating three techniques including finite-element method, response surface methodology, and genetic algorithm. A multi-objective function is established for the optimization problem in which the displacement uniformity of the working surface profile is set to the largest weight factor. The results show that the optimized block-like horn has a displacement uniformity of 92.2%. This result is expected to significantly improve weld quality. In addition, the frequency separation between the longitudinal frequency and the pre and post-ones are 1271 and 1424 Hz, respectively. These values are within the safe range of the design which is with the value of 1000 Hz. This helps to avoid the phenomenon of mode coupling of the horn, which also affects the displacement uniformity of the working surface profile. Additionally, the longitudinal natural frequency of the horn is predicted at 19909 Hz, closely aligning with the frequency transducer of 20000 Hz, with an error of only 0.46%. This results in maximizing energy efficiency. The findings of this study contribute to the construction and development of a methodology for the design and optimization of block-like horns with complex working profiles, which are widely used in other industries such as children's toys, TV remote controls, print cartridges, and so on. By addressing the critical challenges of displacement uniformity and mode coupling, this research contributes significantly to advancing ultrasonic welding technology.