Study on taper reduction of high aspect ratio micro-shafts fabricated by twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG)

Abstract

• New method, named TMTF-WEDG, was proposed for manufacturing micro-shaft. • The main reasons for the taper of micro-shaft are the deformation of the micro-shaft and the wear of wire electrodes. • According to the experimental results, the parameters were selected to control the discharge energy to minimize the taper. • The feed strategy was improved to avoid the effect of wire electrode wear on taper. • High-precision micro-shaft with small diameter and large aspect ratio was successfully prepared. Efficiently fabricating large-aspect-ratio micro-shaft with small diameter and high accuracy is a significant technology in micro-manufacturing. In this paper, based on the newly proposed method, named twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG), we developed the micro-shaft fabrication system to improve the efficiency by twin-mirroring-wire and accuracy by tangential feed. Besides, the narrow slit formed by twin-mirroring-wire constrains the diameter of micro-shaft, which allows improving the repeatability of micro-shaft diameter by controlling the tangential feed distance and narrow slit width. But during the TMTF-WEDG, we found that the micro-shafts with small diameter and large-aspect-ratio tend to have processing taper. The reasons for the tapered micro-shaft are the wire electrode wear due to non-running during finishing and the deformation of micro-shaft with low stiffness due to the small diameter and large aspect ratio. The heat generated by the discharge causes the deformation and its conduction inside the micro-shaft. Discharge energy needs to be controlled during the finishing of TMTF-WEDG, which was achieved by controlling processing parameters. By studying the effects of parameters on the processing taper, optimized parameters minimized the taper of the micro-shaft. The feed strategy was improved so that the micro-shaft always discharges with new wire electrodes. In this way, we successfully fabricated a tungsten micro-shaft with a diameter of 8.5 μm and a length of 400 μm, and the diameter variation is less than 2 μm. The aspect ratio of another micro-shaft with a diameter of 39.38 μm is larger than 50, with the diameter variation within ± 2 μm. By using such micro-shaft, we performed micro-holes processing by micro-EDM on a 304 stainless steel sheet, and the accuracy of 49 micro holes was controlled within 1 μm.