Finishing operations are one of the most challenging tasks during a manufacturing process, and are responsible for achieving dimensional accuracy of the manufactured parts and the desired surface topography properties. One of the most advanced finishing technologies is grinding. However, typical grinding processes have limitations in the acquired surface topography properties, especially in finishing difficult to cut materials such as Inconel 625. To overcome this limitation, a new type of grinding wheel is proposed. The tool is made up of grains of different sizes, which results in less damage to the work surface and an enhancement in the manufacturing process. In this article, the results of an experimental study of the surface grinding process of Inconel 625 with single-granular and multi-granular wheels are presented. The influence of various input parameters on the roughness parameter (Sa) and surface topography was investigated. Statistical models of the grinding process were developed based on our research. Studies showed that with an increase in the cutting speed, the surface roughness values of the machined samples decreased (Sa = 0.9 μm for a Vc of 33 m/s for a multigranular wheel). Observation of the grinding process showed an unfavorable effect of a low grinding wheel speed on the machined surface. For both conventional and multigranular wheels, the highest value for the Sa parameter was obtained for Vc = 13 m/s. Regarding the surface topography, the observed surfaces did not show defects over large areas in the cases of both wheels. However, a smaller portion of single traces of active abrasive grains was observed in the case of the multi-granular wheel, indicating that this tool performs better finishing operations.
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 industrial application of electrical discharge machining (EDM) for manufacturing injection molding, in many cases, requires forming depth cavities with high length-to-width ratios, which is quite challenging. During slot EDM with thin-walled electrodes, short-circuits and arcing discharges occur, as a result of low efficiency in removing debris and bubble gas from the gap. Furthermore, unstable discharges can cause increases in tool wear and shape deviation of the machined parts. In order to characterize the influence of the type of electrode material and EDM parameters on the deep slot machining of high-thermal-conductivity tool steel (HTCS), experimental studies were conducted. An analytical and experimental investigation is carried out on the influence of EDM parameters on discharge current and pulse-on-time on the tool wear (TW), surface roughness (Ra), slot width (S)—dimension of the cavity, and material removal rate (MRR). The analyses of the EDS spectrum of the electrode indicate the occurrence of the additional carbon layer on the electrode. Carbon deposition on the anode surface can provide an additional thermal barrier that reduces electrode wear in the case of the copper electrode but for graphite electrodes, uneven deposition of carbon on the electrode leads to unstable discharges and leads to increase tool wear. The response surface methodology (RSM) was used to build empirical models of the influence of the discharge current I and pulse-on-time ton on Ra, S, TW, and MRR. Analysis of variance (ANOVA) was used to establish the statistical significance parameters. The calculated contribution indicated that the discharge current had the most influence (over 70%) on the Ra, S, TW, and MRR, followed by the discharge time. Multicriteria optimization with Derringer’s function was then used to minimize the surface roughness, slot width, and TW, while maximizing MRR. A validation test confirms that the maximal error between the predicted and obtained values did not exceed 7%.
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