Investigation of the Machinability of the Inconel 718 Superalloy during the Electrical Discharge Drilling Process

Abstract

The properties of the Inconel 718 superalloy are used in the manufacturing of aircraft components; its properties, including high hardness and toughness, cause machining difficulties when using the conventional method. To circumvent this, non-conventional techniques are used, among which electrical discharge machining (EDM) is a good alternative. However, the nature of removing material using the EDM process causes the thermophysical properties of Inconel 718 to hinder its machinability; thus, a more extensive analysis of the influence of these properties on the EDM process, and a machinability analysis of this material in a wider range, using more process parameters, are required. In this study, we investigated the drilling of micro-holes into the Inconel 718 superalloy using the EDM process. An experiment was conducted to evaluate the impact of five process parameters with a wide range of values (open voltage, time of the impulse, current amplitude, the inlet dielectric fluid pressure, and tube electrode rotation) on the process’s performance (drilling speed, linear tool wear, the side gap thickness, and the aspect ratio of holes). The analysis shows that the thermal conductivity of this superalloy significantly influences the effective drilling of holes. The combination of a higher current amplitude (I ≥ 3.99 A) with an extended pulse time (ton ≥ 550 µs) can provide a satisfactory hole accuracy (side gap thickness ≤ 100 µm), homogeneity of the hole entrance edge without re-solidified material, and a depth-to-diameter ratio of about 19. Obtaining a high dimensional shape accuracy of holes has an enormous effect on their usability in the structure of the components in the aviation industry.

Investigation and Optimization of the SLM and WEDM Processes’ Parameters for the AlSi10Mg-Sintered Part

“…However, the presence of high temperature in the machining zone, coming from the plasma channel (10,000 to 20,000 °K), caused the thermophysical properties of the processed material (such as thermal conductivity, density, melting point, evaporation temperature, and a coefficient of thermal expansion) to have a significant impact on the process and its efficiency. Among these properties, thermal conductivity is the one that had the most significant influence on the effectiveness of material removal [ 21 ]. In the case of AlSi10Mg alloy, with an increase in temperature from 250 to 750 °K, the thermal conductivity decreased from 2.4 × 10 7 to 2.0 × 10 7 erg/(cm·g·°K).…”

“…Naturally, parameters of these following processes should be matched to the specific material being machined. This is due to the specific mechanical and thermophysical properties of a given material and their influence on the machining process [ 16 , 21 ]. In SLM technology, more and more frequent use is made of metallic powders of difficult-to-cut materials (such as nickel-based superalloys and titanium alloys, hardened and high-strength steels, and composite and ceramic materials).…”

“…EDM belongs to the group of alternative technologies due to the electrothermal nature of the material removal process, in which the forces between the tool and the workpiece are negligibly small. Mechanical properties of machined material, such as hardness or ductility, do not affect this type of machining [ 21 , 25 ].…”

An Experimental Study on Processing TC4 with Nano Particle Surfactant Mixed Micro EDM

“…Micro electrical discharge machining (micro EDM) is able to remove conductive material by non-contact instantaneous high temperature, regardless of the mechanical properties of the machined materials. Therefore, micro EDM is suitable for machining difficult-to-machine material, including titanium and its alloys [4][5][6].…”

Elemental and Thermochemical Analyses of Materials after Electrical Discharge Machining in Water: Focus on Ni and Zn

“…For many years, researchers have declared that the erosion process has thermal nature [21,22] or even mixed thermal and mechanical nature [23] when the physical contact between electrodes is absent, in contrast to the mechanical nature of destruction during milling, turning, and punching operations (physical wear of the tool [24][25][26][27]).…”