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Observing process recast layer
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In order to reduce the recast layer thickness of film cooling holes on turbine blade, a novel thinning process of electrical discharge machining (EDM) is investigated. To avoid the contradiction between holes drilling speed and recast layer of nickel-based superalloy, the EDM holes process consists of two steps, the drilling process for high machin...
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Citations
... The workpiece was connected to the positive terminal for higher MRR and excellent surface finish [13][14][15]. The author identified three processing parameters were identified [3,16,17] and are selected at three different levels, and were fixed, as shown in Table 3. Orthogonal experimental design method deals with multiple factors experiment [18]. The total number of experiments is an estimation of the interaction of all the input parameters and are arranged in an array. ...
... Therefore, the machined surface shows high surface roughness values. However, in the case of fine cutting (also known as trimming [14]), very fine electrical discharges are produced that melt only a tiny amount of material on the machined surface, which is easily removed by pressure waves [15][16][17]. Various researchers studied the effects of WEDM parameters on the quality of parts made of HSS. In one investigation, it was attempted to subject HSS plates of various thicknesses to EDM to determine the optimum value of current as a function of plate thickness. ...
Form-cutting tools are an economical choice for turning parts with defined profiles in mass production. The effects of the form contour of these tools—produced by the wire electrical discharge machining (WEDM) process—on tool quality were investigated in this research. This study focuses on reducing the adverse effects of the recast layer induced by WEDM on form-cutting tools. The basic component types of profile forms in form-cutting tools can be summarized by a combination of four modes, i.e., concave and convex arcs and flat and oblique surfaces. Hence, sample cutting tools with three different radii of convex and concave arcs and a flat surface were produced. During the WEDM operation, one-pass mode was used for roughing, two passes for semi-finishing, and three passes for finishing. Furthermore, the difference between the percentage of oxygen and carbon elements on the recast layer in the two areas above the workpiece or wire entry point and the bottom area of the workpiece or wire exit point was investigated. Finally, the influences of the direction, size of the curvature, and the number of passes in the wire electric discharge process on the recast layer were analyzed. It was observed that the recast layer thickness could be reduced by increasing the number of WEDM process. Additionally, the uniformity of the cutting contour was superior in the entry region of the wire going into the workpiece compared with the exit region of the wire.
... Recast is a material that melted during sparking and then rapidly solidified see Fig. 4. Due to its cracking susceptibility, high hardness, and the number of microcracks, cracks and high tensile stress [15] recast layer thickness (RLT) reduction methods have been investigated. Li described with basic process parameters such as pulse width, pulse interval, voltage, current and flushing pressure within an experiment [16]. The study enabled an RLT reduction from 10.472 µm to 2.416 µm. ...
Recently, airplane travel has become more affordable and thus more common. This has required engineers and scientists to spend thousands of hours on the development of new material and production technologies. High-pressure turbine (HPT) components are the most heavily loaded parts from the thermal, mechanical, and corrosion points of view. Therefore, both the material from which blades and vanes are cast as well as protective coatings are being constantly developed. Better material translates into longer and safer engine operation. Coatings maintain material structures within aggressive environments. However, despite the wide scope of development, there are areas that have not been investigated, one of which is electro-discharge drilling (EDD) machined cooling holes surface and its influence on environmental coating durability. In this paper, the EDD process impact on coating durability is shown. Process residuals, such as redeposited material and recast layers, result in coating inclusions. Oxidation testing also shows the relationship between the cooling hole diameter and coating durability.
... The thickness of the RCL depends on various electrical as well as non-electrical parameters. As the thickness of the RCL is not uniform throughout the surface [26], the average thickness of the RCL is considered. Initially, a machined sample is polished by using different grades of emery papers (600-2000) and polishing clothes. ...
In the present experiment, micro features were fabricated on titanium alloy by means of the micro-electrochemical spark machining (µ-ECSM) process and the micro-electro discharge machining (µ-EDM) process, using similar electrical parameters. However, in case of the µ-ECSM, the types of electrolyte (KOH, NaOH, KOH+NaOH) and their concentration (0.5 M to 2.5 M) varied from that of the µ-EDM process. In course of the study, different machining output parameters, such as, material removal rate (MRR), recast layer (RCL) thickness, heat affected zone (HAZ) and surface topography, were analysed and compared. The results indicated that the µ-ECSM process produces higher MRR (7.29 times), RCL thickness (0.436 times) and HAZ (0.595 times) as compared to the µ-EDM process. Moreover, the mixed (KOH+NaOH) electrolyte at 0.5 M concentration, 25 V machining voltage, 15% duty factor and 10 kHz of frequency showed better machining performance as compared to the parent electrolyte and produced lower RCL thickness (3.54 µm) and HAZ (26.83 µm), respectively. The surface topography of the work piece, machined by the µ-EDM process, showed rough surface whereas the NaOH electrolyte-based µ-ECSM process produced smoother and clean surface.
... Li et al. [9] studied the effects of four different dielectric fluids on the surface integrity of the recast layer formed during high-speed EDM and demonstrated that the thickness of the recast layer increased with the conductivity of the dielectric fluid. Li et al. [10] studied the recast layer thinning process of EDM drilling and trimming and reduced the recast layer thickness from 10.472 to 2.416 μm through parameter optimization. It was found that tool electrode rotation reduced the recast layer of EDM [11]. ...
This paper proposes a combined milling process of electrical discharge ablation machining (EDAM) and electrochemical machining (ECM) as an alternative to the low efficiency problem of less efficient electrical discharge machining (EDM) and to reduce the recast layer of EDAM. The working medium was a mixed aerosol of NaCl solution and oxygen, which has electrolytic and dielectric characteristics. The mechanism was analyzed: the combined milling process was a mixed process of EDAM, ECM, and EDAM-ECM combined machining. The EDAM-ECM combined machining can be divided into three stages: the electrolysis stage, discharge channel formation stage, and rapid ablative removal stage of metal substrate. Experiments were performed to compare conventional EDM milling, EDAM milling, and combined milling of EDAM and ECM. Results showed that the material removal rate (MRR) of the combined milling was 11.5 times that of EDM milling, and it increased by 18.7% compared with EDAM milling. The relative tool wear ratio (RTWR) decreased by 46.6%, and the thicknesses of the recast layer on the bottom and side were reduced by 61.2% and 49.2%, respectively, compared with EDAM milling.
... The transition to martensitic phase is reportedly improbable through processing using DW, due to the scarcity in carbon concentration/diffusion/penetration. Previously, RL was considered to be non-useful/non-advantageous and got removed by the implementation of post-processing techniques such as lapping [30] and thinning [31]. Nevertheless, the hitherto scarcely explored capabilities of the RL, has recently started gaining attention as it can get implemented as an alloying method in parallel to EDM. ...
This work investigates the potential of electrical discharge machining assisted alloying (EDA) and wire-electrical discharge machining assisted alloying (WEDA) techniques in developing tribo-adaptive layers on Ti6Al4V (Ti64) surfaces. The bare Ti64 (BTi64), electrical discharge machined and alloyed Ti64 (ETi64), and wire-electrical discharge machined and alloyed Ti64 (WETi64) specimens are subject to in-situ wear testing at high-temperature conditions (200 °C, 400 °C, and 600 °C). The SWR and CoF curves of the ETi64 follow reverse trends, with the former demonstrating a decrement with the rise in temperature. The WETi64 specimens develop phenomenal wear resistance at 200 °C and 400 °C (due to excessive formation of protective oxides) but possess similar wear response to that of BTi64 during dry sliding at 600 °C (assisted by layer spalling and delamination). The material removal mechanism of BTi64, ETi64, and WETi64 specimens shift from abrasive wear to delamination, composite wear (abrasive + oxidative) to oxidative wear, and oxidative wear to delamination, respectively, with increment in temperature during dry sliding at low load conditions (50 N). For ETi64, the recast layer (RL) over the substrate aided in achieving improved tribological characteristics by imparting stability to the developed oxides (TiO, TiO2, Ti8O15, and Fe2O3) at elevated temperatures. In the EDA process, the high carbon diffusion into the RL and low cooling rates led to the formation of hard phases in the form of carbides (TiC and Ti24C15) and microstructural transitions to ∝p and α′-phases, respectively, improving the wear-resistant characteristics of the substrate.
... The selection of dielectric medium can considerably influence the thickness of white layer on machining nickel alloy in EDM process [10]. The thickness of the recast layer thickness can be modified by changing the open circuit voltage and pulse parameters in EDM process [11]. The modification of WEDM process can enhance mechanism of the machining process which has resulted on reducing recast layer thickness of the machined specimen [12]. ...
Since the white layer thickness influences the surface quality of the machined specimens using electrical discharge machining process, the prediction of such parameter is highly important in the present scenario. Adaptive network based fuzzy inference system based white layer thickness prediction on machining processed silicon steel has been attempted in the present study. Three machining process parameters such as open circuit voltage, peak current and duty factor have been utilized for the training purpose owing their importance on determining white layer thickness. The accuracy of the prediction has been analyzed by comparing the predicted values from the architecture testing with the real time measured values. From the experimental results, it has been found that the developed adaptive network based fuzzy inference system can predict the average white layer thickness in an efficient way with accuracy of 96.8%. It has also been observed that the electrical process parameters have highly contributed on determining average white layer thickness.
... Some scholars begin with the principles of EDM to suppress the formation of recast layers. Li et al. [8,9] trimmed the recast layer by modifying the polarity during the micro-hole EDM process to effectively reduce thickness of the recast layer. In addition, they also studied the effect of different dielectric solutions on the surface integrity of the recast layer during the EDM process. ...
Micro-EDM technology is widely used in the field of micro-fabrication due to its low cost, non-contact, and other processing characteristics. The EDM method involves molding parts by implementing the principle of melting metal at a high temperature, which results in a thin recast layer on the surface of the workpiece. The recast layer can critically affect the surface topography and mechanical properties of the part, making it a potential safety hazard in fields such as aerospace and medical sciences. The purpose of this paper is to apply the electrolytic removal method of the recast layer on different microstructures, and thus solve the problem of on-line, orientation, and quantitative removal of recast layers on complex three-dimensional surfaces. In this work, the main components of the recast layer were analyzed to push the main principles and influencing factors of its participation in the electrolytic reaction. Then, the electrolysis removal experiments of the recast layer on the surface of foundation structures were carried out, and different processing strategies were proposed for different microstructures. Finally, the micro-EDM-ECM–integrated processing technology was applied, resulting in a micro-grooved structure of surface roughness Ra less than 0.3 μm.
... Electrical discharge machining (EDM) is a popular nontraditional machining method which utilizes the thermal energy generated by spark discharges for material removal [6]. However, the molten material is difficult to be completely removed by the dielectric, thereby forming a recast layer on the machined surfaces [7][8][9]. This recast layer is commonly considered to be harmful because it introduces high surface roughness [10], cracking and porosity [6,11], transition and pollution of microstructure [8,12] to deteriorate material properties. ...
The recast layer is an undesirable surface residue after the electric discharge machining of materials, which would affect the following brazing process and cause microstructure and property degradation. In this study, the effects of the recast layer composed of carbon-containing γ solid solution on the microstructure and mechanical properties of Ni-based single crystal superalloy were investigated. After brazing, the formation of carbo-borides, borides, and Kirkendall voids near the joint interface could be eliminated via the aging process to recovery the microstructure and property.
... The tapered holes especially reverse tapered holes and array holes could be generated in EDM-drilling on the new machine or new electrode designed [15][16]. To improve the quality, the two steps process was researched to thin the recast layer of work-piece in hole-drilling, while a modified 'volume removal per discharge' approach had been applied to compensate the longitudinal wear of electrode [17][18]. However, up to now most research on EDMdrilling was confined to conventional mechanical model, and the understanding of EDM-drilling did not break through the technology of machine drilling, even through change of driving energy compared with convention drilling. ...
