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The use of a liquid medium in near-dry electrical discharge machining (EDM) with a two-phase gas‒liquid medium endows it with desirable characteristics such as a stable discharge process and high material removal rate. However, the effect mechanism of the liquid medium in near-dry EDM is not well understood, which limits its development. In this present, a variant of the near-dry EDM technology, namely, mixed-gas atomization discharge ablation processing (MA-DAP) of titanium alloy, is used to reveal the effect mechanism of a liquid medium in the process of near-dry EDM. This technology uses a mixed gas containing oxygen and a liquid medium to form the dielectric medium, so as to obtain a higher effective material erosion ability than near-dry EDM. Through the combination of experimental and theoretical modeling and analysis, it can be concluded that liquid dielectric water has the functions of endothermic cooling, inducing an intermittent gas supply environment between electrodes, efficient etching product removal, improving oxygen utilization efficiency, controlling oxygen diffusion speed, and increasing the discharge gap between electrodes, which can significantly improve the inter-electrode discharge state and material removal rate. Compared with conventional EDM, the material removal rate associated with MA-DAP technology increases by 16 times, and the relative wear rate of the electrode is reduced by more than 93%. [ABSTRACT FROM AUTHOR]

Electrical discharge machining ablation (EDMA) technology is an EDM processing method that uses oxygen as the discharge medium. Compared with traditional EDM, EDMA can greatly improve the machining efficiency but is prone to combustion and explosion phenomena when machining titanium alloy and cannot obtain stable continuous processing. Therefore, this present first analyzes the oxidation characteristics of titanium alloy from the oxidation thermodynamics and kinetics of the material. Then, the structural characteristics of the oxide layer formed on the surface of the titanium alloy where combustion and explosion phenomena occur are analyzed, and the effects of the metal elements that constitute the titanium alloy on the oxide layer structure are studied to reveal the reasons for the explosions. Finally, a method of mixed-gas electrical discharge ablation processing for titanium alloy to avoid explosions is proposed. The material removal rate in the proposed approach is 10 times and 3.5 times greater than that of conventional nitrogen- and argon-assisted submersed gas-flushing EDM, respectively. This provides a new electric machining technology for the high-efficiency and sustainable processing of titanium alloy. [ABSTRACT FROM AUTHOR]

As a variant of highly efficient electrical discharge machining (EDM), the die-sinking mixed-gas atomization discharge ablation process (DMA-DAP) uses an atomized dielectric formed by a mixed gas, which mainly composed of oxygen and supplemented by nitrogen, and water medium as the discharge medium. In this technology, the oxygen in the medium is used for exothermic oxidation, and the vaporization and explosion of the water generates a chip removal force for highly efficient erosion. The present work uses single-factor tests to compare the characteristics of processing the difficult-to-machine material titanium-alloy special-shaped cavities using either DMA-DAP or EDM. The current, pulse width, pulse interval, and dielectric pressure are selected as the single-factor processing parameters, and how they influence the material removal rate (MRR), electrode relative wear rate (ERWR) and the surface morphology of the processed square cavities is analyzed. The results show that with DMA-DAP, the MRR is more than 12 times that of EDM, the ERWR is reduced by more than 98%, and the surface morphology is relatively good. Finally, taking an aero-engine radial diffuser as the profiling object, DMA-DAP realizes a profiling sample in the form of a variable-cross-section cavity that EDM cannot process, and the efficient die-sinking processing ability of DMA-DAP is verified. [ABSTRACT FROM AUTHOR]

The surface modification of Ti–6Al–4V alloy was achieved by using an electrical discharge machining (EDM) surface modification technology under the action of pulsed discharge to induce an in-situ synthesis reaction between the molten metallic material and the ionized elements in the atomized medium. In this study, nitrogen and urea solutions are used as the gas-liquid phases of the atomization medium. ANSYS simulation software was used to simulate and analyze the interpolar pressure and flow field of the different electrodes. The effect of different electrode forms on the EDM surface modification layer was investigated by designing comparative trials. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and other detection methods were used to characterize the process indicators, such as surface morphology, roughness, hardness, and wear resistance of the reinforced layer. It was found that a thick and uniform continuous layer can be obtained on the Ti–6Al–4V alloy substrate using multi-channel electrode machining, and the thickness is about 65 μm. XRD analysis indicates that the reinforced layer mainly contains TiN, Ti 2 N, Ti 2 AlN, Ti 2 O, and CuO phases. The samples with reinforced layers were shown to have higher hardness (1578 HV) and better wear resistance than the titanium substrates. The main wear mechanism is spalling wear and light oxidation wear. • Near-dry EDM surface modification using different channel electrodes. • Evaluating the effect of electrode forms on the state of the interpolar flow field distribution. • The multi-hole electrode contributes to the formation of modified layers. • The modified layer of multi-hole electrode has better surface morphology and performance. [ABSTRACT FROM AUTHOR]