Ultrasonic treatment by an intermediate striker: Tool dynamics and material improvement

A dynamic model of the ultrasonic impact tool with an intermediate striker is considered as a two-mass system with two impact joints. Direct measurements of the period of the sequence of impact pulses and duration of a single impact of striker upon the treated surface are assumed as a basis for theoretical description. Amplitude-frequency and phase-frequency characteristics of the impact oscillations of ultrasonic converter and striker are calculated with the use of methods of the theory of vibration-impact systems. An oscillatory stability of ultrasonic vibrations of striker with the rebounding from the converter tip and the surface being treated (impact mode) as well as in-phase ultrasonic vibrations without detachment of striker from the both surfaces is investigated. It is shown, that the amplitude of the impact oscillation of striker weakly depends on the pressing force in the sufficiently wide limits of variation of the pressing force value. Hardening of treated material and redistribution of residual weld stresses is investigated with the use of the metallography methods. The beneficial compressive stresses are generated (induced) inside the narrow surface layer in the result of fine crushing of crystalline grains of metal.