Optimization of the longitudinal-torsional ultrasonic step-like horn design for milling tool applications via the tool load account

Ultrasonic horns are used in the ultrasonic-assisted milling and cutting tools. However, the interaction with tool end vibrations deteriorates the horn performance. In this study, the amplification coefficients and vibration node locations of an ultrasonic horn were determined via the 1D wave theory and optimized by the tool load effect account. By arranging spiral grooves at the straight part of the ultrasonic horn, a longitudinal-torsional modal converter was introduced. This made it possible to convert longitudinal vibrations into longitudinal-torsional coupled ones by the superposition of incident and reflected longitudinal waves with reflected transverse ones at grooves. Orthogonal L9 (33) tests with parameters of spiral grooves as variables were designed and conducted, and longitudinal-torsional ratios (LTR) of the milling tool end under different conditions were assessed using the commercial ANSYS software package. The in-depth analysis of simulation results implies that the LTR values are controlled by the following influence factors in the decreasing order: helical angle, number of grooves, and groove width. Single-factor tests indicate that LTR exhibits an initial drop and a further rise with the helical angle, attaining its minimal value at 30°; it drops with the number of grooves n, and remains practically unchanged with the groove width variation. Finally, the vibration tests of the proposed horn with the optimized parameters corroborated its feasibility and demonstrated its excellent performance in the ultrasonic-assisted milling tool application.