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Fir tree slots in engine disks pose a great challenge to the production process, especially due to the use of increasingly filigree geometries. Broaching with high-speed steel (HSS) as cutting tool material has been established as the state of the art process. However, this manufacturing process obtains the disadvantages of high tool costs and long waiting times in case of geometry adaptations. Alternative manufacturing technologies, namely electrochemical machining (ECM) and wire electrical discharge machining (WEDM) offer the potential to replace broaching. Because of their removal mechanism being independent of the mechanical properties of the material, these processes are not hindered by increasingly higher thermomechanical material properties. Furthermore, the tool in WEDM is not specific to geometry, allowing fast adaptations. Nevertheless, the technology specific white layer may reduce the mechanical integrity of the engine disk. ECM in contrast has no negative impact on the rim zone of the workpiece but the tool is still specific to the slot geometry. Consequently, this paper experimentally investigates the three different manufacturing technologies in order to evaluate their capability to manufacture fir tree slots with respect to geometric accuracy and surface integrity. Subsequently, the technology specific manufacturing costs are considered to outline the economic potential of each process while taking into account the influence of the batch size.

Electric Discharge Machining (EDM) is one of the leading non-conventional machining processes used to machine hard-to-cut materials in wide range of industrial, biomedical, automotive, defense and aerospace applications. EDM is a controlled spark generation process, which is usually used for machining of difficult to cut materials. In this study, experiments were performed on Titanium Alloy (Ti6Al4V) using thin-film multi-wall Carbon Nanotubes (MWCNT) coated electrode and uncoated aluminum electrodes. Morphological and structural investigations of MWCNT coating were performed using Scanning transmission electron microscope (TEM) and Raman spectroscopy. All experiments were designed with Taguchi’s L16 orthogonal array. Each experiment performed under different condition of current, gap voltage and pulse on time. MRR, TWR, SR and OC are studied for each experiment. It was observed that MWCNT coated electrode gives better surface roughness, higher material removal rate, and lower tool wear rate. The experimental result showed that MRR increased by 14.15%, tool wear rate decreased by 23.40%, surface roughness reduced by 22.14 % and overcut reduced by 23.43 % respectively as compared to uncoated aluminum electrodes. All performance responses improved with thin-film MWCNT coated electrode due to magnificent electrical conductivity and chemical stability of CNT. Analysis of Variance (ANOVA) carried out to understand significant process parameters and its contribution in mentioned response variables. Multi-Wall CNT shows better results at high temperature and prevents the tool wear rate. The surface roughness of Ti6Al4V improved with MWCNT coated electrode and it was evident with scanning electron microscope (SEM) images of workpiece. Comparative study of coated and non-coated gives new development of novel electrode tool for electric discharge machining processes.

Ceramic materials are known for their high hardness and strength-to-weight ratio, resistance to wear, and chemical inertness. These materials can be deployed at elevated temperature even to the limit where super alloys cannot be used. The distinctive properties of ceramics make them difficult to machine by conventional processes because of their brittleness. Electrical discharge machining (EDM) is a non-contact machining process that can machine any workpiece irrespective of its hardness, as long as the material is electrically conductive. Therefore, the challenge that comes with the EDM of ceramics is the electrical non-conductivity. In this study, an innovative method (modified assisted-electrode method) has been proposed, which can be used to successfully machine through holes in pure and non-conductive ceramic materials using the EDM process. The effect of machining parameters and conductive coating has been studied. In addition, the possible material removal method has been investigated using the scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis. It is found that multi-layer coating with conductive copper tape sandwiched with graphene and carbon nanotubes in between the tape worked as a successful assistive electrode method. The SEM and EDS analysis indicates melting and thermal spalling as possible material removal mechanisms during EDM of electrically non-conductive Aluminum nitride (AlN) ceramics. The deposition of carbon at the edge of the holes indicate generation of conductive carbon layer favoring continuous sparking during the machining process, and this makes the EDM of non-conductive AlN possible. The walls of the drilled holes become conductive and allow the machining to go through even beyond the conductive layer range. The performance characteristics depends on both the electrical parameters and assistive electrode method.

Ultra–Agile Advanced Manufacturing System (U–AMS) has been proposed for an agile prototyping system of research and development, and Super Processing Center (SPC) has been developing as a core machine tool of U–AMS. SPC has high accuracy and rigidity by double column structure based on a vertical precision machining center, hydrostatic oil guides and hydro static/dynamic hybrid oil bearing. In addition, SPC can perform various processing functions by mounting various processing units. Micro grooving by grinding has been researching for one of the SPC unit. PCD blade was developed for micro grooving using SPC. PCD blade was made from PCD disc using wire electrical discharge machining. This paper describes the fabrication method of PCD blade, and the machining characteristics of cemented carbide using PCD blade. In the fabrication method of PCD blade, it was clarified that the cross-sectional shape of PCD blade depended on the feed speed of wire electrode. Micro grooving on cemented carbide surface was performed using developed PCD blade and SPC. As a result, it was confirmed that the micro grooves can be machined using PCD blade, and the width of groove was almost same value as the width of PCD blade. The wear of PCD blade after grooving with 200 grooves was estimated by the depth of grooves. As a result, it was clarified that the wear of PCD blade is approximately 5 μm.

Tube electrode high-speed electrochemical discharge machining (TSECDM) has been effectively used in the manufactures of micro holes with difficult-to-cut conductive materials in the field of aerospace industry. The design and parameters of circuit are critical for the machining performances of TSECDM. In this paper, the influences of circuit on the TSECDM performances are studied. Firstly, a relaxation type RLC generator is designed and analyzed by MATLAB simulation. Secondly, the effects of RLC circuit parameters such a resistor (R), capacitor (C) and inductor (L) on machining performances are investigated by experiments on the bulk of SS304 alloys by limiting factors changing. Finally, the analysis achievement indicated that the circuit selection parameters value R (15Ω); C (220nF); L (0.13mH) can be used to obtain a better machining performance.

Ceramic materials possess excellent properties like high hardness, superior corrosion resistance and great resistance to wear. These materials are low in density and demonstrate high strength to wear ratio. There is an increasing need to machine these hard and brittle materials as they have various engineering applications. The distinguishing properties of ceramics do not allow them to be machined by conventional processes. Electrical discharge machining (EDM) is a non-conventional process and a viable option to machine and generate complex shapes in hard materials. EDM can be used on materials irrespective of its hardness and wear resistance as it is a non-contact machining process and no active force is applied between the workpiece and electrode during machining. As EDM requires the workpiece to be electrically conductive, machining ceramics by this process is a challenge. Alterations need to be carried out in order for insulating ceramics to be machined by this process. This paper discusses the basics of EDM process and its control parameters. A classification of ceramic materials based on their electrical conductivity is established and their relevance to the respective material removal mechanisms have been identified. Different approaches to successfully machine ceramics by EDM have been reviewed. The challenges and modifications of each method have been discussed. An outline and expectations for machining a particular ceramic material and its composites have been generated. Finally, the prospects of future research in this area have been identified.

Bulk Metallic Glass (BMG) is a solid metallic material with disordered atomic structure, that has the characteristics of high elasticity, hardness, fracture toughness, and superior corrosion resistance. High aspect ratio micro-through holes on BMG has prospective applications in space, nuclear reactor, thermodynamics engineering, biomedical, and electronics industries. In this study, the micro-EDM machinability of BMG (Vit 1b: Zr67Cu10.6Ni9.8Ti8.8Be3.8 (wt%)) is evaluated. The micro-EDM machinability of BMG has been assessed based on the volume of material removal rate (MRR), tool wear rate (TWR), micro-hole surface quality, and dimensional accuracy. The effect of various electrical and non-electrical parameters is studied. It is found that micro-EDM is capable producing high aspect ratio micro-holes on difficult-to-machine BMG. The deposition of resolidified debris around the edge of the micro-holes, both at the entrance and exit side, are found to be a common phenomenon in micro-EDM of BMG. The reduction of capacitance was found to be the effective way for reducing the resolidified debris around the edges. Capacitance was found to be have more pronounced effect, with gap voltage having little effect on the quality of micro-holes. The electrode rotational speed had insignificant effect on the quality of micro-holes. In terms of dimensional accuracy, which was measured by overcut and taper angle, both the gap voltage and electrode rotational speed had little effect. The lower electrode rpm was found to reduce the taperness of the micro-holes, although the material removal rate decreases and tool wear rate increases. Finally, analysis of the composition of tool electrode before and after machining indicates the migration of materials from the dielectric and workpiece to the tool electrode and vice versa.

Titanium alloy Ti-6Al-4V is used extensively in aerospace engines because of its high strength-to-weight ratio and corrosion resistance. Machining of cooling holes in turbine blades for aerospace engines is one of the major challenges faced in aerospace industries. Ti-6Al-4V is known as a difficult to be machined material by conventional machining processes, and machining of micro-through-holes with diameter less than 100 microns is even more challenging. Therefore, the objective of this study is to investigate the feasibility of machining high aspect ratio micro-through holes in Ti-6Al-4V using micro electrical discharge machining (micro-EDM) with the silver (Ag) nanopowder mixed dielectric. The machining time, overcut, recast layer, crater size, aspect ratio and surface finish of the micro-holes were evaluated. In order to minimize the positional inaccuracy and spindle runout, the microelectrodes were fabricated in-situ using block micro-EDM process. In this study, as received electrode of 300 microns diameter tungsten wire was reduced to about 50 microns diameter rod by micro block EDM using a tungsten carbide block. The effect of powder concentration, gap voltage, capacitance and electrode rotational speed was studied. It is found that high quality micro-holes of about 50 microns diameter can be achieved successfully and repeatedly using powder mixed micro-EDM (PM-μEDM). The micro-holes generated by PM-μEDM provides comparatively smoother surface finish and minimal recast layer around the rim of the micro-holes. In addition, PM-μEDM process improves machining stability, thus allowing to minimize the hole size and quality, thus enhancing the aspect ratio of micro-holes.

Construction industry is about to embrace 3D printing as a viable technology for fabricating structures that are not physically or commercially impractical. These include curved components that could be embedded in buildings. On the other hand, whole house building by 3D printing has been attempted around the world using giant concrete printers. The main question is how to integrate steel rebars in concrete by 3D welding and still maintain the structural integrity and reliability of the conventional rebars. To accomplish the incorporation of rebars in concrete, steel must be welded within concrete. Heat dissipation rates may be different in different directions when the 3D molten weld pool solidifies, especially when the substrate is concrete. This may affect the strength of the material along and across the weld bead. To investigate this effect, it is important to study the mechanical properties of 3D welded steel in the directions of length, thickness and width. Experiments conducted in this study include the 3D welding of steel on concrete tiles by attaching the torch of a MIG welder to a meter-scale 3D printer carriage. The weld beads were then cross sections in directions along the weld bead, across the bead and perpendicular to the ceramic substrate. Dog-bone shaped micro-scale samples were extracted along those direction by CNC machining and EDM milling. The specimens were then mounted on the grippers of a hybrid micro-tester and tensile tests were carried out. The results of the tests are reported, and the implications of the findings in terms of the feasibility of 3D printing of steel reinforced concrete are discussed.

The demand for higher efficiency in aircraft propulsion engines leads to materials with increasing thermo-mechanical strengths and new designs inducing filigree geometries of blisks and disks. Because of new designs which induce tighter tolerances, the high mechanical process forces in conventional cutting processes like broaching cause inacceptable geometrical deviations and high tooling costs. Due to the electro-thermal material removal mechanism, electrical discharge machining (EDM) ensures a force free and thus precise machining. The manufacture of fir tree slots in nickel-based alloys by wire EDM has been investigated in the last few years and the process was verified as an alternative technology for broaching. To get a better competitive position, the productivity can be prospectively increased by using an additional indexing rotary axis which ensures a precise and automated production of rotationally symmetric components and reduce production times e.g. for the manufacture of fir tree slots on a disk. Nevertheless, the application of these axes cause changed flushing conditions and can also affect the electrical contacting as well. Both influence the process performance and demand a technology development or adjustment of standard machining technologies. The influence of these changed machining conditions has not been investigated scientifically to date. In this paper, the surface integrity and process performance of fir tree slots machined by wire EDM on the machine table are compared with the manufacture by using an additional indexing rotary axis. The results of the investigations are supposed to create a basis for technology adaptions when using additional axes in wire EDM.

The standardization of any mechanical material characterization is aiming to get homogenization on the testing physical execution by independent laboratories and to drive for accurate material evaluation between different entities. However, from time to time, standard tests may be reconsidered in order to improve their efficacy, execution time and incorporate new testing techniques or technologies without compromising the testing results and consistency. In the present work, fracture toughness crack tip opening displacement (CTOD) testing is addressed and particularly the need to perform fatigue pre-cracking prior monotonic testing. Without the fatigue pre-cracking, CTOD testing time can be significantly reduced during the preparation of specimens, meaning that specimens can be tested as soon as they are machined. Wire electro-discharge machining (EDM) technique allows generating sharp tip notches, and presents a good alternative to the standards specified fatigue pre-cracking [1–2]. In addition, this machining technology reduces the risk of rejecting the specimen testing, particularly when targeting weld heat affected zone/fusion line (HAZ/FL) microstructure on specimens with surface notch DNV-ST-F101 Figure B-9 [3], where it is specified that the crack tip shall be within a narrow distance (0.5 mm) from the fusion line (FL) or assess grain coarsened heat affected zone (GCHAZ) microstructure as indicated in DNV-ST-F101 section B.2.8.7 [3]. Herein, it is presented an assessment carried out in order to identify the notch type effect over the fracture toughness (CTOD) considering notches conditions as standard fatigue pre-crack and wire electro-discharge machining (EDM). Fifteen (15) CTOD specimens were manufactured from plain pipe material (same pipe), 251.3 mm OD × 20.9 mm WT, SMLS 450PD and tested according to ISO 12135 recommendations [1], they were distributed as follow; five (5) specimens according to standard recommendations with fatigue pre-cracking length ≥ 1.3 mm or 2.5%W (whichever is bigger), five (5) specimens with a fatigue pre-cracking length < 1.3 mm (between 0.5 mm to 1 mm), and five (5) specimens without fatigue pre-cracking (EDM notch), additionally, results from five (5) specimens previously tested in a round robin (RR) testing performed internally by Tenaris using the same LP material and standard fatigue pre-crack length. The crack length target (a/W) was kept 0.5 for all cases. Even if the sampling population is relatively small considering the three notch conditions, it seems that EDM might be an alternative to the standard specified fatigue pre-cracking. Thus, this experimental assessment aims to open the discussion on the use of EDM notch as alternative.

Wire electric discharge machining (EDM) is a non-traditional machining method that has the ability to machine hard, conductive materials, with no force and high precision. This technology is used in industries, like the aerospace industry, to create precision parts used in high stress applications. Wire EDM is also commonly used in additive manufacturing (AM) applications to remove printed parts from the base-plates onto which they are printed. Numerous studies show the effects of EDM parameters, like pulse-on time, pulse-off time, and cutting voltage, on the processing of traditionally fabricated metal parts. However, very few studies identify how the parameters of wire EDM affect the processing of AM parts. This paper studies the effect of wire EDM pulse-on time, pulse-off time, and cutting voltage on the machining time, surface roughness, and hardness of additively manufactured 316L stainless steel cylinders. The effects of these wire EDM parameters are then tested on the machining time, surface roughness, and hardness of wrought 316L stainless steel cylinders. It was found that machining time of AM samples was statistically significantly lower than wrought samples and also had better surface finish and lower surface hardness.

Titanium and its alloys are a class of metallic materials having high strength to weight ratio with excellent properties of resistance to temperature, corrosion and oxidation. These properties increase their use in aerospace, chemical and biomedical industries. Electrical discharge machining (EDM), a non-conventional machining process, is the most suitable process for the machining of titanium and its alloys. Generally, tool electrode for EDM application is prepared through various conventional and non-conventional machining processes. The cost of production of EDM electrodes accounts for more than 50% of the cost of the final product. Therefore, additive manufacturing (AM) technology can be suitably applied for direct manufacturing of the complex EDM electrodes. Selective laser sintering (SLS) is one of the appropriate AM processes for preparation of EDM tool electrode. In the present work, machining performance of the AlSi10Mg tool electrode produced through AM process along with copper and brass tool electrodes have been studied considering titanium alloy (Ti6Al4V) as work piece material and commercial grade EDM 30 oil as dielectric fluid. In addition to the tool electrodes, two more EDM parameters such as pulse-on-time (Ton) and discharge current (Ip) have been considered. Four performance measures like material removal rate (MRR), tool wear rate (TWR), average surface roughness (Ra) and surface crack density (SCD) are used to assess the machining performance. In order to reduce the number of experiments, design of experiment (DOE) approach like Taguchi’s L9 orthogonal array is used. Since the performance measures are conflicting in nature, grey relational analysis (GRA) is used to convert four performance measures into an equivalent single performance measure. The best parametric condition is reported for optimal grey relational grade.

Shape Memory Alloys are smart materials that tend to remember and return to its original shape when subjected to deformation. These materials find numerous applications in robotics, automotive and biomedical industries. Micromachining of SMAs is often a considerable challenge using conventional machining processes. Micro-Electrical Discharge Machining is a combination of thermal and electrical processes, which can machine any electrically conductive material at micron scale independent of its hardness. It employs dielectric medium such as hydrocarbon oils, deionized water, and kerosene. Using liquid dielectrics has adverse effects on the machined surface causing cracking, white layer deposition, and irregular surface finish. These limitations can be minimized by using a dry dielectric medium such as air or nitrogen gas. This research involves the experimental study of micromachining of Shape Memory Alloys using dry Micro-Electrical Discharge Machining process. The study considers the effect of critical process parameters including discharge voltage and discharge current on the material removal rate and the tool wear rate. A comparison study is performed between the Micro-Electrical Discharge Machining process with using the liquid as well as air as the dielectric medium. In this study, microcavities are successfully machined on shape memory alloys using dry Micro-Electrical Discharge Machining process. The study found that the dry Micro-Electrical Discharge Machining produces a comparatively better surface finish, has lower tool wear and lesser material removal rate compared to the process using the liquid as the dielectric medium. The results of this research could extend the industrial applications of Micro Electrical Discharge Machining processes.

Ti-6Al-4V (grade 5 titanium alloy) is one of the most widely used materials in aerospace applications including turbine blades for aerospace engines. Due to the difficulty of machining titanium alloys using conventional machining processes, wire-electro-discharge machining (wire-EDM) is used extensively for cutting titanium parts with complex geometries and profiles. The objective of this study is to investigate the effect of two important non-electrical parameters in wire-EDM, i.e. wire feed rate and wire tension, on the geometric corner and profile accuracies of the Ti-6Al-4V parts machined by wire EDM. A complex profile was designed for machining in two different thicknesses of titanium alloy using each set of experimental parameters. The complex part includes corners with 45°, 90° and 112.5°, as well as thin wall section for measuring the kerf accuracy. It was found that with the increase of wire tension, the corner accuracies at almost all the angles improved. however, too high wire tension caused inaccuracies by providing larger angles than the target values. The effect of wire tension was dependent on the thickness of the machined part. For thinner workpiece the results of the angles generated barely followed a trend, whereas for thicker part, the measured angles followed an excellent trend. The kerf accuracies were found to improve with the increase of wire tension for thin part, whereas for thick part the results of kerf width accuracies were inconsistent. In case of wire feed rate, it was found that comparatively lower settings of wire feed rates were favorable for machining thinner parts with enhanced corner accuracies. On the other hand, slightly higher wire feed rates provided better corner accuracies for thick part. Besides corner inaccuracy, profile undercuts and deviations from the machining paths were observed for lower wire tensions. Finally, it can be concluded that comparatively lower wire feed rate and higher wire tension provides improved corner and profile accuracies. however, for machining thinner sections using wire-EDM, the trends are not obvious.

Components with best surface integrities — without any white layer or mechanically damaged rim zones — and regardless of mechanical properties of the material can be produced with electrochemical machining (ECM). Wire ECM combines the outstanding advantages of the ECM working principle with the kinematic of wire electrical discharge machining (wire EDM). A task-specific tool design — such as for classical sinking ECM — is not required for cutting 2.5-dimensional geometries like fir tree slots in turbine discs. Established manufacturing technologies for fir trees are broaching and recently wire EDM. However, high requirements on surface integrity of these turbine parts afford cost intensive finishing processes. Thus, wire ECM could be an attractive cost efficient alternative manufacturing process. Due to an insufficient flushing concept, a process development of wire ECM for fir tree slots with relevant disc heights failed in the past. A combination of an axial flushing with rotating structured electrode provides a promising approach to meet these challenges. Therefore, this paper presents investigations of cutting Inconel 718 direct-aged using the new flushing principle. Workpieces with heights up to 40 mm are machined, which is comparable to a low pressure turbine disc height. Reachable feed rates respectively cutting rates are presented. Due to the process specific edge rounding, the formation of the leading edges is examined. Finally, the evolving surface integrities with the help of surface roughness, cross sections and residual stresses are investigated and discussed.

The geometric error is an important indicator for the product performance in the Wire Electric Discharge Machining (WEDM) process, however, few studies have focused on the geometric error caused by thermal deformation, which can reach as high as 6.5% when machining thin-wall components. In this paper, some complex thermal deformation phenomena were found and analyzed in wire electric discharge machining different materials under different conditions (such as different thickness, various process parameters). Based on a large number of experiment, the reasons for these thermal deformation were figured out by studying the effect of various process parameters on thermal deformation and mechanical properties of thin-wall components, and the results revealed that the water pressure and pulse duration are two most significant factor influencing the thermal deformation. It’s concluded that a long pulse duration for rough cut and a short pulse duration for trim cut under low water pressure is recommended to decrease the geometric error caused by thermal deformation.

Wire Electrical Discharge Machining (WEDM) is a versatile process to generate intricate and complex shapes on conductive work material with high dimensional accuracy and surface finish. Since the process is stochastic, its input parameters play critical role for achieving desired accuracy and precision of the component. Inconel 718, High-Strength-Temperature-Resistant (HSTR) material, has wide applications in the field of aerospace, automobile, mould making and medical industries. Hence, machining of Inconel 718 using WEDM is a challenging task. Also experimentation on Inconel 718 with WEDM is costly as well as time consuming process. Therefore to study the behavior of WEDM process with different process parameters for effective and efficient operation, process modeling and simulation using appropriate software is highly essential. In the present investigation, a 3-D single spark finite element thermal model for WEDM process has been developed using ANSYS software. This model has some more realistic assumptions like heat flux following Gaussian distribution and spark radius as a function of time and energy. Plasma incident region is meshed by keeping elemental size equal to one tenth of entire plasma radius, so that exact ten elements can be fitted. Identified elements were thermally loaded by applying element wise different temperatures for getting more accurate temperature distribution profile. This profile was found to be having crater shape matching with earlier Finite Element Models (FEM) available in the literature. Along with the shape, it also helps to decide the elements having temperatures greater or equal to melting point leading to estimate Material Removal Rate (MRR). Later on single spark MRR can be used to estimate multi-discharge-MRR by calculating pulse rate. Model MRR is validated with the experimental MRR which show a very good agreement, but little variation. This variation in the modeling could possibly due to assumptions like no delay in ignition, non-deposition of recast layer (100% flushing efficiency), etc. The factors like incomplete flushing of debris and inter-electrode gap arcing cause the variation in machining conditions thus reducing the actual MRR. In the present investigation, the use of dielectric is considered only for convection, but in reality, it acts as an insulator, coolant and also as debris remover. Melting and vaporization of material is the main phenomena for material removal. Dielectric fluid partially removes the molten metal because at the same time, the molten metal is under very high pressure due to plasma channel. Its adhesive property resists the material removal. It is very difficult to incorporate all real effects in the model, however the obtained results in the present study show good agreement between model MRR and experimental MRR within 10% variation.Copyright © 2016 by ASME

In this experimental work, the cryogenic cooling of the Micro-EDM (μEDM) drilling process for improving the performance and quality of micro holes. The controllable parameters such as the current (Ip), pulse on time (Ton), Pulse off time (Toff) and gap voltage (Vg) were chosen for further investigation. The Taguchi L27 orthogonal array is preferred to achieve the best experimental runs. Case hardened AISI 304 stainless steel is selected to perform the experiments. The overall machining performances of geometrical characterization such as taper angle, Overcut, Circularity at the entry and exit and the performance evaluation such as the material removal rate and electrode wear rate are analyzed. It is found that the taper angle improved by 91%, overcut improved by 17 to 66%, Circularity improved up to 70% and 68% respectively, material removal rate increased from 9 to 70% and electrode wear rate reduced up to 76%. It is found that pulse off time plays a vital role in the quality of micro holes drilled in both conventional and cryogenic micro-EDM (CμEDM) processes.Copyright © 2016 by ASME

Glass is a hard-to-machine material with vast industrial application. Electrochemical discharge machining (ECDM) is a non-traditional machining technology that has shown potential for effective glass machining. However, ECDM has not been widely used in industry despite being studied for over a decade. Major challenges of ECDM include limited machinable depth and low material removal rate. In this paper, an innovative hybrid machining process combining ECDM and traditional cutting is presented, namely electrochemical discharge assisted cutting. The material removal rate of the hybrid ECDM process is significantly higher than conventional processes. Experimental results are presented to prove the feasibility and capability of the process. Discussion concentrates on the improvement of geometric accuracy and surface integrity through experimentation.Copyright © 2016 by ASME

Wire Electrical Discharge Machining (WEDM) is a specialized thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. Selection of cutting parameters for obtaining higher cutting efficiency or accuracy in WEDM is still not fully solved, even with most up-to-date CNC WEDM machine. It is widely recognised that Acoustic Emission (AE) is gaining ground as a monitoring method for health diagnosis on rotating machinery. The advantage of AE monitoring over vibration monitoring is that the AE monitoring can detect the growth of subsurface cracks whereas the vibration monitoring can detect defects only when they appear on the surface. This study outlines the estimation of AE parameters viz., signal strength, absolute energy, RMS in the WEDM. Stavax (modified AISI 420) steel material was machined using different process parameters based on Taguchi’s L’16 standard orthogonal array. Among different process parameters voltage and flush rate were kept constant. Parameters such as pulse-on time, pulse-off time, current and bed speed was varied. Molybdenum wire having diameter of 0.18 mm was used as an electrode. Simple functional relationships between the parameters were plotted to arrive at possible information on surface roughness and AE signals. But these simpler methods of analysis did not provide any information about the status of the work material. Thus, there is a requirement for more sophisticated methods that are capable of integrating information from the multiple sensors. Hence, methods like Multiple Regression Analysis (MRA) and Group Method of Data Handling (GMDH) have been applied for the estimation of surface roughness, AE signal strength, AE absolute energy and AE RMS. The GMDH algorithm is designed to learn the process by training the algorithm with the experimental data. The experimental observations are divided into two sets: the training set and testing set. The training set is used to make the GMDH learn the process and the testing set will check the performance of GMDH. Different models can be obtained by varying the percentage of data in the training set and the best model can be selected from these, viz., 50%, 62.5% and 75%. The best model is selected from the said percentages of data. Number of variables selected at each layer is usually taken as a fixed number or a constantly increasing number. It is usually given as fractional increase in number of independent variables present in the previous level. Three different criterion functions, viz., Root Mean Square (Regularity) criterion, Unbiased criterion and Combined criterion were considered for the estimation. The choice of criterion for node selection is another important parameter for proper modeling. From the results it was observed that, AE parameters and estimated surface roughness values were correlates well with GMDH when compare to MRA.Copyright © 2015 by ASME

In this research work, experiments were conducted using Electrical Discharge Machining (EDM) in dry and conventional mode, and the results were compared and analyzed. LM13 Aluminium alloy is used as the workpiece and pure cylindrical copper rod is used as the tool electrode. Since the machining was difficult in dry EDM, some modifications were made in the existing tool design to conduct the experiments in dry EDM. The experiments were designed using Taguchi’s L27 orthogonal array. Discharge current (I), gap voltage (V), pulse on time (TON), pressure (P) and speed (N) were chosen as the various input parameters. Three levels of values were chosen for each input parameter, whereas speed was chosen as the fixed parameter. The variation in the material removal rate (MRR), surface roughness (SR), surface morphology and elemental composition of the machined surface due to variation in the input parameters were analyzed in both dry and conventional mode. Better MRR, and surface roughness were observed in the work piece machined under conventional EDM process. The MRR is observed to be 84% more in the conventional mode when compared with dry EDM. Also, when compared to the dry EDM, about 15.33% better SR values is observed in the conventional EDM process.Copyright © 2015 by ASME

Wire Electrical Discharge Machining (WEDM) is a specialized thermo electrical machining process capable of accurately machining parts with varying hardness or complex shapes. Present study outlines the comparison of machining performances in the wire electric discharge machining using group method data handling technique and artificial neural network. HCHCr material was selected as a work material. This work material was machined using different process parameters based on Taguchi’s L27 standard orthogonal array. Parameters such as pulse-on time, pulse-off time, current and bed speed were varied. The response variables measured for the analysis are surface roughness, volumetric material removal rate and dimensional error. Machining performances were compared using sophisticated mathematical models viz., Group Method of Data Handling (GMDH) technique and Artificial Neural Network (ANN). GMDH is ideal for complex, unstructured systems where the investigator is only interested in obtaining a high-order input-output relationship. Also, the method is heuristic in nature and is not based on a solid foundation as regression analysis. The GMDH algorithm is designed to learn the process by training the algorithm with the experimental data. The experimental observations are divided into two sets viz., the training set and testing set. The training set is used to make the GMDH learn the process and the testing set will check the performance of GMDH. Different models were obtained by varying the percentage of data in the training set and the best model were selected from these, viz., 50%, 62.5% & 75%. The best model was selected from the said percentages of data. Number of variables selected at each layer is usually taken as a fixed number or a constantly increasing number. It is usually given as fractional increase in number of independent variables present in the previous level. Three different criterion functions, viz., Root Mean Square (Regularity) criterion, Unbiased criterion and Combined criterion were considered for estimation. The choice of the criterion for node selection is another important parameter for proper modeling. The Artificial Neural Network is used to study and predict the machining responses. Input data are fed into the neural network and corresponding weights and bias are extracted. Then weights and bias are integrated in the program which is used to calculate and predict the machining responses. Estimation of machining performances was obtained by using ANN for various cutting conditions. ANN estimates were obtained for various percentages of total data in the training set viz., 50%, 60% & 70%. The best model was selected from the said percentages of data. Estimation and comparison of machining performances were carried out using GMDH and ANN. Estimates from GMDH and ANN were compared and it was observed that ANN with 70% of data in training set gives better results than GMDH.

The fabrication of personalized implants, tailored on patient needs, is a key issue for the future of several surgical fields. The presence of a prototyping service inside the hospital would be an added value for improving clinical activity. In this context, micro-Electro Discharge Machining is exploited to customize fixation devices in orthopedic surgery. An overview of the main devices is carried out in order to identify the main characteristics and to define the common fixation system specifications. The experimentation includes a technological evaluation of the proper micro-EDM technology, chosen according to the final design of the components. Two materials are investigated for the device fabrication: titanium and Si3N4-TiN ceramic composite. An optimization of the main technological parameters is performed in order to maximize the material removal rate ensuring the accuracy of the micro-features required. Finally, a test case is selected in order to evaluate the entire fabrication process chain.Copyright © 2015 by ASME

Electro discharge machining (EDM) technique is widely used in the die and mold industries for its distinct advantages in machining hard metals. Nevertheless, the properties of EDM treated steel, especially its corrosion resistance, have not been well understood or clearly identified. In this paper, electrochemical corrosion behavior of EDM treated AISI H13 steel in NaOH solution was investigated, with the diamond polished being reference specimen. The corrosion resistance of the specimens was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The morphology and microstructure of the machined surface layer were also observed. Electrochemical experimental results revealed that EDM treated specimen has a weaker resistance to corrosion compared with diamond polished one. This weakening is considered to be correlated to differences in surface morphology and subsurface microstructure.Copyright © 2015 by ASME

Electrical Discharge Machining (EDM) is a non conventional machining process capable of accurately machining parts with high hardness and of complex shapes. The sparks produced during the EDM process cause localized melting on the work surface. The formation of recast layer is very common on EDMed surfaces. The recast layer reduces the service life of the die or mould surfaces, especially under fatigue loads. In the present work, Magnetic Abrasive Finishing (MAF) process has been explored as a method to remove the recast layer formed on a EN 31 steel cylindrical specimen machined by EDM. MAF process is one of promising methods capable of removing the material at micro/nano level under gentle mechanical forces. The diamond based sintered magnetic abrasives have been used to machine the EDMed surface. The experimental results indicate that the EDMed surface of EN-31 steel can be successfully finished with diamond sintered magnetic abrasives. On the finished surfaces, no evidence of micro cracks, voids and recast layer has been seen. Moreover, an average improvement in the surface finish up to 80% over the initial surface finish has been obtained. The micro hardness measurement on MAFed surface shows that brittle and hard layer has been removed. SEM photographs indicate the success of MAF for removal of EDMed surface.Copyright © 2015 by ASME

Micro-electrical discharge machining (μ-EDM) is a non-traditional manufacturing technique that has been widely used in the production of precision engineering components throughout the world in recent years. The most important performance measure in μ-EDM is the surface roughness. The Silicon Carbide is a reaction bonded advanced ceramic that is the fourth hardest material after Diamond, boron nitride and boron carbide. Due to low fracture toughness, machining of Silicon Carbide is accomplished with EDM. In this study, the experimental studies were conducted under varying gap voltage, capacitance and threshold. The numbers of experiments were reduced by L9 array of Taguchi’s theory of DOE. Signal-to-noise (S/N) ratio was employed to determine the most influencing levels of parameters that affect the surface roughness in the μ-EDM of conductive silicon carbide. To validate the study, confirmation experiment has been carried out at optimum set of parameters and predicted results have been found to be in good agreement with experimental findings. A fuzzy logic model for predicting surface roughness during μEDM was also developed on MATLAB software and the goodness of fit of predicted values with experimental values was tested using chi-square test.Copyright © 2014 by ASME