Electrical Discharge Machining of Al2O3 Using Copper Tape and TiO2 Powder-Mixed Water Medium

Abstract

Aluminum-based ceramics are used in industry to produce cutting tools that resist extreme mechanical and thermal load conditions during the machining of Ni-based and high-entropy alloys. There is wide field of application also in the aerospace industry. Microtexturing of cutting ceramics reduces contact loads and wear of cutting tools. However, most of the published works are related to the electrical discharge machining of alumina in hydrocarbons, which creates risks for the personnel and equipment due to the formation of chemically unstable dielectric carbides (methanide Al3C4 and acetylenide Al2(C2)3). An alternative approach for wire electrical discharge machining Al2O3 in the water-based dielectric medium using copper tape of 40 µm thickness and TiO2 powder suspension was proposed for the first time. The performance was evaluated by calculating the material removal rate for various combinations of pulse frequency and TiO2 powder concentration. The obtained kerf of 54.16 ± 0.05 µm in depth demonstrated an increasing efficiency of more than 1.5 times with the closest analogs for the workpiece thickness up to 5 mm in height. The comparison of the performance (0.0083–0.0084 mm3/s) with the closest analogs shows that the results may correlate with the electrical properties of the assisting materials.

Simulation of Mechanical and Thermal Loads and Microtexturing of Ceramic Cutting Inserts in Turning a Nickel-Based Alloy

“…The scheme of microtexturing is presented in Figure 2. A cutting insert was immersed in the TiO 2 powder suspension [38]. The dielectric fluid level was 1-2 mm above the cutting zone, and the cutting insert was held for 5-7 min in a medium before processing to avoid thermal fluctuations.…”

“…The machine uses deionized water as a dielectric medium. During the experiments, the water supply was turned off, and electrical discharge machining was conducted with the full immersion of the workpiece in a TiO2 powder and deionized water medium [38]. The microtexturing of the microwells was conducted using a tungsten wire ø0.1 mm in diameter.…”

“…The smaller the band gap is, the higher electrical conductivity the semiconductive material demonstrates [65,66]. The choice of suspension powder was grounded in [38]. The main advantages are that it is relatively safe in micro size (exposure may only cause irritation with minimal residual damage, according to NFPA 704), it exhibits chemical inertness to water, and it increases electrical conductivity in the presence of high heat (>1000 • C).…”

“…The powder subjected to granulometric analysis and optical microscopy is shown in [38]. An EL104 (Mettler Toledo, Columbus, OH, USA) laboratory balance with a measurement range of 0.0001-120 g ± 0.0001 g was used to weigh the powder portion.…”

“…The only obstacle to using high-performance electrical discharge machining methods in microtexturing the cutting inserts may be the absence of the electrical conductive properties of oxide and nitride ceramics (such as SiAlON, Si 3 N 4 , and Al 2 O 3 ) that are used in producing the most wear-resistant cutting inserts for cutting heat-resistant materials mainly used in the aviation industry (as gas turbine engines and other key parts of airplanes are subjected to the extreme operating conditions): nickel-based superalloys. However, the problem of machinability can be solved using innovative methods of electrical discharge machining of the insulating materials, which allow us to produce kerfs in the Al 2 O 3 insulating ceramics with a depth of up to 54.16 ± 0.05 µm and a blank thickness of up to 5.00 mm, using a combination of the assisting electrode technique and powder-mixed electrical discharge machining [38,39]. This approach has also shown promising results in the electrical discharge machining of Si 3 N 4 ceramics.…”