Electrical Discharge Machining of Alumina Using Cu-Ag and Cu Mono- and Multi-Layer Coatings and ZnO Powder-Mixed Water Medium

Abstract

The paper aims to extend the current knowledge on electrical discharge machining of insulating materials, such as cutting ceramics used to produce cutting inserts to machine nickel-based alloys in the aviation and aerospace industries. Aluminum-based ceramics such as Al2O3, AlN, and SiAlON are in the most demand in the industry but present a scientific and technical problem in obtaining sophisticated shapes. One of the existing solutions is electrical discharge machining using assisting techniques. Using assisting Cu-Ag and Cu mono- and multi-layer coatings of 40–120 µm and ZnO powder-mixed deionized water-based medium was proposed for the first time. The developed coatings were subjected to tempering and testing. It was noticed that Ag-adhesive reduced the performance when tempering had a slight effect. The unveiled relationship between the material removal rate, powder concentration, and pulse frequency showed that performance was significantly improved by adding assisting powder up to 0.0032–0.0053 mm3/s for a concentration of 14 g/L and pulse frequency of 2–7 kHz. Further increase in concentration leads to the opposite trend. The most remarkable results corresponded to the pulse duration of 1 µs. The obtained data enlarged the knowledge of texturing insulating cutting ceramics using various powder-mixed deionized water-based mediums.

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

“…It should be noted that any conductive coating can be used to provide conductivity to the outer layer on the surface of the insulating sample. Our research group has devoted a few studies to this; we proposed using a Ni-Cr coating (plasma vapour deposition), which has an effect on the electrical discharge machining ability of aluminum oxide [53], and a Cu-Ag multilayer sandwich coating also showed remarkable results in the electrical discharge machining of Al 2 O 3 [38,39]. All possible options for the wide range of insulating ceramics are provided in [41].…”

“…The specific electrical resistance ρ of the deposited TiN coating was controlled with a Fischer Sigmascope SMP10 instrument (Helmut Fischer GmbH, Sindelfingen, Germany). The method is described in [39]. The coating thickness was measured with a Calowear instrument (CSM Instruments, Needham, MA, USA), using the spherical notch method (diameter of a ball of 20 mm) [87,88].…”

“…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.…”

Advances in Electrical Discharge Machining of Insulating Ceramics

“…After processing, the film can be chemically removed from the ceramic surface with acetone, K 2 CrO 4 -H 2 SO 4 mixture, or other solvents [60,61]. There are several types of coating to accomplish the process, such as copper assisting electrode [56,[62][63][64][65], silver varnish [45,64], carbon conductive layer [66], multimaterial sandwich coatings [64,67], and Ni-Cr coating by plasma vapor deposition [68]. The assisting electrode made of copper tape can be removed easily from the AlN [64], Al 2 O 3 [65], and ZrO 2 [69] ceramic surface after the machining.…”

“…In [66], it was experimentally shown that machin-ability strongly depends on electrical resistivity for TiO 2 , SiC, and ZrO 2 ceramics during electrical discharge drilling when there is probably other nature (obviously, thermochemical combining with electrophysical) in Al 2 O 3 and SiO 2 ceramics machining, but the trends are similar. There are several types of coating to accomplish the process, such as copper assisting electrode [56,[62][63][64][65], silver varnish [45,64], carbon conductive layer [66], multimaterial sandwich coatings [64,67], and Ni-Cr coating by plasma vapor deposition [68]. The assisting electrode made of copper tape can be removed easily from the AlN [64], Al₂O₃ [65], and ZrO₂ [69] ceramic surface after the machining.…”