Studying ultrasonic oscillations impact on the surface roughness at the electrical discharge machining

DOI: 10.34759/vst-2021-1-187-199

Аuthors

Bogdanov K. A.

NPO “Technomash”, 40, 3rd proezd Mar’inoi Roshchi, Moscow, 127018, Russia

e-mail: kab1002@bk.ru

Abstract

The studies on estimation of the external ultrasonic field impact on the surface quality of the obtained small diameter orifices in corrosion-resistant steels and electric discharge machining productivity were performed within the framework of the presented work.

The purpose of the performed studies consists in determining quantitative characteristic of the roughness indicator when small-diameter orifices processing by electrical discharge machining with ultrasonic oscillation superposition the part under treatment or EDM tool.

The combined machining method is based on superposition of thermal action of the electric current impulses, fed continuously to the section of the workpiece being machined, with forced impact of ultrasonic oscillations for erosion products evacuation from the inter-electrode gap.

The 12Х18Н10Т-grade austenitic stainless steel was selected as the material to be machined for experimental studies for accuracy increasing,while the small-diameter orifices through-piercing, the presented work employs the guide alignment bushing, made of wearproof dielectric material, trough which the electrode-tool is delivered and fixed.

Based on preliminary studies on the process fluid selection, preference was given to the IonoPlus IME-MH synthetic dielectric fluid for axial drilling machines, which is applied for finishing and semifinishing. Process fluid is forcefully fed through the guide sleeve.

Prior to the experiments commence, a study was performed to select the ultrasonic field sources. Piezoceramic and magnetostrictive ultrasonic field sources were being considered. Based on the previous experiments, a magnetostrictive transducer was selected, which has a wider range of oscillations amplitude adjustment.

The machining time was recorded with a calibrated stopwatch; and the tool wear was recorded by touching the surface of the part before and after machining.

The article considers methods and technological solutions on the effective small-size orifices machining aimed at quality enhancement of the machined surface and electrical discharge technology productivity.

In the process of experimental studies, various options for the ultrasonic head installing and the electrolyte supply direction to the treatment zone were applied

The modes and schemes for the parts samples treatment were obtained based on the materials selection for the electrode-tool and operation modes of electrical discharge and ultrasonic equipment.

Experimental results allow comparing electrical discharge machining methods by technological indicators of machining time and the obtained surface quality. Thereby, they give notion on ultrasonic oscillations impact on the productivity, accuracy and quality of electro-erosion piercing of the small-size diameter orifices.

The experimental studies revealed that the high-frequency oscillations transmitting to the electrodetool lead to productivity increasing due to h short-circuit prevention between the EDM-tool and part being processes.

Graphical interpretations of the obtained numerical values allow quantifying the relationship between the processing time and the EDM tool wear, with account for various schemes of the ultrasonic application while piercing orifices in the samples of plates and nozzles.

The studies of the orifices’ treated surfaces roughness, obtained by the electrical discharge machining with the ultrasonic oscillations superposition and working fluid flowing into the processed zone were performed.

The superposition of ultrasonic oscillations to the EDM tool facilitates obtaining a low roughness in comparison with the roughness obtained by traditional EDM machining by 15-25% due to a decrease in the number of burns and short-circuits.

Keywords:

external ultrasonic field, machined surface quality assessment of the small-diameter orifices, graphical interpretation of the numerical values

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