Pham Thanh Cuong
Hard milling of hardened steel is commonly associated with high cutting forces, elevated cutting temperatures, rapid tool wear, and difficulty in maintaining low surface roughness. One effective approach to overcoming these limitations is to superimpose ultrasonic vibration on the cutting process; however, a prerequisite for its successful implementation is the design of a vibration transmission system capable of stable operation at resonance. This paper presents the calculation, design, fabrication, and experimental verification of an ultrasonic horn–workpiece system generating axial vibration along the Z direction at a nominal frequency of 20 kHz for application in ultrasonic vibration-assisted hard milling. By selecting 90CrSi tool steel as the material for both the horn and the workpiece, the material properties, including density (ρ) and Young’s modulus (E), were determined and used to calculate the acoustic wave velocity and wavelength, thereby establishing the half-wavelength length of the horn–workpiece assembly and the corresponding resonance condition. After fabrication, the system was characterized through impedance scanning and frequency measurement to verify its resonant behavior, while the axial vibration amplitude at the workpiece end face was also measured. The results show that the developed system achieved near-resonant operation at 20 kHz, and that the working amplitude could be adjusted through the design and calibration of the workpiece length Lp to satisfy the amplitude range required for the design of ultrasonic vibration-assisted milling experiments. The study therefore provides a practical workflow of rapid calculation, fabrication, experimental verification, and amplitude tuning that is well suited to laboratory conditions and to the localization of ultrasonic-assisted machining systems.