SEAM-ECM jet milling TC4 titanium alloy using gas–liquid mixed medium

Shengsheng Zhang,Lizhong Wang,Xiangyu Dai,Weixing Qiu,Guoyu Hu,Shuaishuai Wang,Jianping Zhou,Yan Xu

doi:10.1007/s00170-021-08544-8

Abstract

This paper proposes a novel combined machining approach. The approach is focused on combining short electric arc machining and electrochemical machining (SEAM-ECM). It aims to improve the surface integrity of TC4 titanium alloy by adding compressed air and electrolyte into the SEAM. This approach can change the material removal mechanism of the conventional SEAM and improve the gap flow field distribution and discharge state using the dual fluid properties of electrolyte and air mixed medium. Flow field simulation demonstrates the effects of gas addition on the state of the gap flow field and the electrical conductivity of the mixed medium. The experiments compare the effects of the presence or absence of air and the electrical conductivity of the solution on the machining performance. The results show that SEAM-ECM with electrolyte and air reduces the relative electrode wear rate (REWR) while maintaining a good material removal rate (MRR). In addition, SEAM-ECM utilizes the electrolytic effect to weaken the recast layer compared to SEAM with deionized water and air. The addition of high-speed air reduces defects such as melt drops, particles, and holes. It performs with higher precision and finish than ECM alone, and the overall surface integrity is significantly improved.

Highlights

TC4 titanium alloy is widely used in aerospace, marine chemical industry, and medical application because of its high specific strength, corrosion resistance, and anti high temperature performance[1]
Deionization is accomplished after Pulse switch out, which generates some spark waveforms during machining[23], and at the same time, the DI water has weak electrical conductivity, leakage current is generated during the spark breakdown delay phase, which can lead to microelectrolysis[24], and machining in DI water can be classified as short electric arc machining (SEAM), EDM-electrolytic machining (ECM) combined machining
When the medium is electrolyte and air, the waveforms are distributed at intervals of arcs and electrolysis, which shows that SEAM and ECM are alternated during the machining process, but the electrolysis current and arc current are reduced compared with both pure arc machining and pure electrolysis machining, the energy acting on the workpiece surface is reduced, which is beneficial to reduce the thickness of the recast layer on the workpiece surface

Summary

Introduction

TC4 titanium alloy is widely used in aerospace, marine chemical industry, and medical application because of its high specific strength, corrosion resistance, and anti high temperature performance[1]. Due to the inherent properties of this material such as poor thermal conductivity and low modulus of elasticity, conventional machining cannot meet the machining requirements of titanium alloys[2], which can lead to tool wear and incipient fault during the production process[3]. When the medium flows through the gap causing the molten material to sharply cool and crumple to form particles, the remaining molten material is deposited on the workpiece surface to form recast layer[7,8,9]. The rapid heating and cooling lead to the brittle structure of the recast layer[10], and the uneven temperature gradient causes residual tensile stresses in the material during deposition, which seriously affects the fatigue life of the workpiece[11]. ECM is prone to stray corrosion, and machining localization is difficult to guarantee[15], while subsequent ECM is hard to conduct due to the extreme oxidation of the surface of titanium alloys during corrosion[16]

Methods

Results

Conclusion