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<p>Near-dry electrical discharge machining (NDEDM) of nitinol using compressed air-based dielectrics (air + deionized water and air + EDM oil) was compared to conventional EDM with brass and titanium electrodes. NDEDM with air + deionized water achieved the best surface topography with the largest inter-electrode gap, widest craters, and shallowest depths. Breakdown voltage delay times decreased by 30 and 15% for air + deionized water and air + EDM oil, respectively, compared with EDM using brass electrodes, whereas titanium electrodes exhibited minimal reductions (2–8%). Material removal rates (MRR) in NDEDM with air + deionized water were 11 times higher than EDM and 6 times higher than air + EDM oil, peaking at 4.03 mm<sup>3</sup>/min for brass electrodes, 34% higher than titanium. Conventional EDM had the highest tool wear rate (TWR), with brass electrodes reaching 9.93 mm<sup>3</sup>/min—50 times higher than titanium in NDEDM. Surface roughness (SR) reduced by 19% with air + deionized water, achieving 0.37&#xa0;μm for brass electrodes. Recast layer thickness (RLT) decreased by 41.5% for brass (10.04&#xa0;μm) and 46.5% for titanium (10.79&#xa0;μm) compared to wet EDM. Radial overcut (ROC) was slightly higher in NDEDM but produced harder surfaces due to localized heating, particularly with titanium electrodes. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) showed that air and deionized water with titanium electrodes resulted in a nitinol surface composition resembling its raw form. This process enhances oxidation, forming a NiTiO<sub>2</sub> protective layer that reduces nickel ion release and improves biocompatibility. NDEDM with air and EDM oil consumes only 4-5 liters of oil compared to 20 liters in wet EDM, offering economic advantages. With air and deionized water, NDEDM reduces ecological impact, eliminates harmful emissions, and enhances corrosion resistance, making it suitable for biomedical applications like stents and implants.</p>

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Investigation of an Environmentally Friendly EDM Process for Nitinol: A Comparative Study of Dielectrics and Tool Electrodes

  • 期刊论文

  • 发表日期：

    2025年9月2日

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  • M. Muniraju,
  • Gangadharudu Talla

摘要

Near-dry electrical discharge machining (NDEDM) of nitinol using compressed air-based dielectrics (air + deionized water and air + EDM oil) was compared to conventional EDM with brass and titanium electrodes. NDEDM with air + deionized water achieved the best surface topography with the largest inter-electrode gap, widest craters, and shallowest depths. Breakdown voltage delay times decreased by 30 and 15% for air + deionized water and air + EDM oil, respectively, compared with EDM using brass electrodes, whereas titanium electrodes exhibited minimal reductions (2–8%). Material removal rates (MRR) in NDEDM with air + deionized water were 11 times higher than EDM and 6 times higher than air + EDM oil, peaking at 4.03 mm3/min for brass electrodes, 34% higher than titanium. Conventional EDM had the highest tool wear rate (TWR), with brass electrodes reaching 9.93 mm3/min—50 times higher than titanium in NDEDM. Surface roughness (SR) reduced by 19% with air + deionized water, achieving 0.37 μm for brass electrodes. Recast layer thickness (RLT) decreased by 41.5% for brass (10.04 μm) and 46.5% for titanium (10.79 μm) compared to wet EDM. Radial overcut (ROC) was slightly higher in NDEDM but produced harder surfaces due to localized heating, particularly with titanium electrodes. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) showed that air and deionized water with titanium electrodes resulted in a nitinol surface composition resembling its raw form. This process enhances oxidation, forming a NiTiO2 protective layer that reduces nickel ion release and improves biocompatibility. NDEDM with air and EDM oil consumes only 4-5 liters of oil compared to 20 liters in wet EDM, offering economic advantages. With air and deionized water, NDEDM reduces ecological impact, eliminates harmful emissions, and enhances corrosion resistance, making it suitable for biomedical applications like stents and implants.