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.
Highlights
The Inconel 718 superalloy is one of the most important alloys belonging to the nickel-based superalloy family
We present the analysis of the results of the experiments on electrical discharge drilling of the Inconel 718 superalloy
An analysis of the results shows that the applied lower value of voltage (U = 60 V) and a lower current amplitude (I = 2.00 A) contribute to obtaining a too high value of the side gap thickness (SG = 217 μm and SG = 167 μm, respectively) and a decrease in drilling speed (v = 2.69 μm/s and v = 3.27 μm/s, respectively)
Summary
The Inconel 718 superalloy is one of the most important alloys belonging to the nickel-based superalloy family. This superalloy is mainly used in the aerospace industry to manufacture aerospace parts and gas engine components. Components of modern gas turbine engines, such as turbine blades, work in high-temperature conditions (in the range of 823.15–1373.15 ◦ K). This causes the production of elements from advanced engineering materials including nickel-based superalloys. Among these superalloys, Inconel 718 is one of the most widely used. To increase the durability of this superalloy, a considerable number of holes are made in the structure of turbine blades (20,000–40,000) with a diameter of 0.3–5 mm and Materials 2020, 13, 3392; doi:10.3390/ma13153392 www.mdpi.com/journal/materials
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