Ultrasonic micro-forging by two coaxial longitudinal waveguides with a fixed gap: model and application

Abstract

Ultrasonic metal forming technology has a great potential for highly productive manufacture of miniature parts. Extremely high plasticity can be achieved under the condition of ultrasonic impact loading of the small-height and thin samples (the so-called “ultrasonic dynamic impact effect”). Despite this, the wide use of ultrasonic micro-forming processes is restricted with some technical challenges including, in particular, a short tool-life due to the strong impact forces and severe tribological conditions. In this paper the tool-saving scheme of ultrasonic wibro-impact metal forming is proposed. The workpiece is drawn through the gap between the working ends of two rigidly mounted longitudinal waveguides. The gap width exceeds the amplitude of idle vibrations. This processing scheme prevents direct contact of working surfaces and provides the long service life of ultrasonic tools. The objectives of this work are to study the applicability of the proposed technological scheme for the mass production of precision miniature parts, to determine the conditions for the occurrence of the impact modes in an ultrasonic vibratory system, and to examine the shape accuracy and the microstructure of processed samples. For this purpose a dynamic model of the forced oscillations of two coupled resonant waveguides is developed. The workpiece is considered as a connecting link and also as a technological load. It is shown that the anti-resonant mode of operation of the vibratory system is the most effective. The necessary condition for plastic flow during vibro-impact processing is derived. Recommendations on the design parameters and resonance tuning of the ultrasonic system are given. Applications of the ultrasonic micro-forging technique for sharpening and rounding the edges of flat samples are exemplified. Metallographic research and microhardness tests show extremely high degree of deformation and significant strain hardening of processed metal. The enhanced metal formability with a long service life of ultrasonic tools gives reason to consider the proposed processing technology as a promising method for the mass production of miniature metal parts.