Surface texture of S 718 after electrical discharge machining assisted with ultrasonic vibration of a tool electrode

Abstract

IntroductionCurrently, successive development of materials engineering is observed, which offers new materials with unique properties. Their rational implementation in industrial applications depends on the development of efficient methods of their machining. The aerospace industry, where these materials are used, constantly sets new, rigorous requirements on machining accuracy and quality of surface finish. Elements manufactured for these industries are made of special, difficult to machine alloy and composite materials, which are characterized by very good mechanical and chemical properties at increased temperatures. Effective machining of difficult to machine materials with satisfactory performance and surface finish is difficult, and in some cases almost impossible to achieve by traditional methods of machining. Due to the above reasons, unconventional methods of machining are becoming increasingly popular in manufacturing processes, i.e. electrical discharge machining, which allows machining of materials regardless of their mechanical and physicochemical properties [1÷6].In the electrical discharge machining material ,is removed from the workpiece as a result of electrical discharges between the tool electrode and the workpiece immersed in the liquid dielectric, which lead to melting of the material and its evaporation. As a result of the impact of thermal effects that lead to the loss of material, the shape of the working electrode gradually replicates on the workpiece [2,4]. The physics of removing material from the workpiece is completely different from other traditional machining methods, and its effects determine the functional properties of the surface layer. Electrical discharge machining is mainly used to manufacture difficult to machine objects with complex geometrical shapes, e.g. injection molds, forging dies, as well as parts used in the aerospace and nuclear industries [7÷9].In order to improve the technological indicators of manufacturing processes, new varieties of hybrid electrical discharge machining are developing, which rely on the simultaneous interaction of various mechanisms or sources of energy. One of their variations is the electrical discharge machining AbstractInconel 718 is one of the modern materials widely used in the aviation and space industry, due to their excellent mechanical and chemical properties at elevated temperatures. These parts work in difficult conditions and they are required to be characterized by good accuracy and high quality surface finish to ensure greater durability and fatigue strength. Conventional machining of these materials is difficult and ineffective due to low thermal conductivity of the alloy. Electrical discharge machining (EDM) is often used to machine materials regardless of their mechanical and physical properties. In this process material is removed from the workpiece through series of electric discharges occurring in the sparking gap between a tool electrode and the workpiece. The physics of removing material from the workpiece is completely d...

The Accuracy of Finishing WEDM of Inconel 718 Turbine Disc Fir Tree Slots

“…Aspinwall et al [ 33 ] investigated the surface quality of Inconel 718 alloy after WEDM using the minimum damage generator technology. Due to the constant increase in aircraft engines performance, which is achieved while simultaneously reducing exhaust emission and noise (The Advisory Council for Aeronautics Research in Europe predicts a reduction in COx and NOx emission by 75% and noise reduction by 65% by 2050), newer materials are used, which are more and more difficult to machine [ 34 , 35 ]. The latest solutions in the design and control of WEDM machines allow achieving a surface roughness of 0.2 μm and a heat-affected zone (HAZ) thickness close to 0 μm [ 27 ].…”

“…The research conducted so far has focused mainly on the roughing machining of Inconel 718 [ 8 , 39 , 40 ]. The studies of the finishing machining of Inconel 718 pertained to discharge energy, machining efficiency, and the effect of a single parameter [ 33 , 35 , 41 ]. The following article presents the results of the research on the influence of many parameters, such as electrode infeed, mean gap voltage, peak current, pulse off-time, and discharge energy on the surface quality and shape accuracy of Inconel 718 fir tree slots in turbine discs.…”

Experimental Investigation on the Impact of Graphite Electrodes Grain Size on Technological Parameters and Surface Texture of Hastelloy C-22 after Electrical Discharge Machining with Negative Polarity

“…In the opposite configuration, the polarity is positive [6,7]. The choice of polarity is mainly determined by the higher efficiency of material removal from the workpiece [8][9][10][11][12][13][14]. The phenomenon of material removal in the EDM process is complex, and it relies on the concept of thermoelectric erosion caused by electrical sparks between two conductive materials.…”