Ultrasonic Hammering of Electrodischarge Hardened Steel Surface

Abstract

Electrodischarge hardening or coating process being used to elongate steel tool life has a demerit of rough surface finish compared with its thin thickness.
In order to get more smooth surface without removing its material ultrasonic hammering process is investigated.
A diamond ball fixed on an ultrasonic vibrating tool was pressed onto the electrodischarge machined surface or the electrodischarge coated surface of the work on the vibrating table.
Experiments were carried out under the following conditions: diamond ball diameter 5.6mm, ultrasonic frequency 22kHz, generator output power 100-300W (tool amplitude 13-24μm), pressing force 1-3kgf, feeding speed 60mm/min, work amplitude 4mm, work frequency 950cpm.
Die steel works after EDM or electrodischarge coating were finished by the ultrasonic hammering. EPMA analysis, microhardness and roughness measurements result in the followings:
1) Roughness of electrodis charge machined steel surface (initially R_max 26μm) is smoothened by ultrasonic hammering (finally R_max 3μm) and increases its hardness (in H_v 100-200).
2) Surface layer generated by the electrodischarge coating consists of the two electrode materials.
3) Electrodischarge coated steel surface with a cemented carbide electrode decreases its roughness from R_max 18μm to 3μm and increases its hardness up to H_v 1300.
4) In cutting-off of mild steel rod high speed steel lathe tool increases its life in 2 times after the electrodischarge coating and 2.6 times after the ultrasonic hammering of it.