Effects of Different Cavity Geometries on Machining Performance in Micro-Electrical Discharge Milling

With the increasing demand for microparts and structures in electronic, medical, aerospace, biomedical, and many other industries, developing manufacturing protocols that generate range of micro-/nano-scale patterns or components with finer dimensional tolerances and improved surface integrity becomes a great challenge. Integration of high-precision machining technologies such as milling, electrical discharge machining (EDM), electrochemical machining (ECM), and laser machining, which are controllable in terms of unit volume removal in the order of few hundred microns, ensures reproduction of microparts in batch scale. Among others, μ-EDM process utilizes short pulsed (∼80 ns) low energy (∼10⁻⁹–10⁻⁵ joules) discharge that removes material in the order of ∼0.05–500 μm³ [1] and creates micropatterns as small as 20 μm over range of conductive materials irrespective of their hardness. The process capabilities of μ-EDM are further enhanced with integration of positioning stages having submicron to nanometric travel resolution, which is widely known as micro-EDM-milling (μ-EDM-milling). This small volumetric material removal by short pulsed low energy electric discharge between unshaped electrode and the work piece with precisely controlled relative movement between electrodes provides substantial opportunities for manufacturing of microdies, microstructures like microholes, microslots, microgears, and even complex 3D structures.

In μ-EDM-milling, while the use of unshaped cylindrical tool electrode eliminates electrode shaping unlike in EDM die sinking, the secondary discharge on the side of these cylindrical electrode leads to improper flushing, tool vibration, and nonuniform wear, influencing machining performance significantly. Therefore, the practical solution for controlling the material removal, uniform tool wear, and final shape of the geometry is optimized tool path strategy and tool rotation. The shape and size of the geometry being machined dictates the tool path (electrode movement) strategy, attributes to the dimensional accuracy, surface integrity, machining time, consistency in spark gap and mode of material removal for which no systematic study has been performed yet and the process phenomenon of μ-EDM-milling is still an unsolved research problem.

In most of the μ-EDM literature, researchers have discussed various aspects including material removal rate (MRR) [2], tool wear [3], influence of machining parameters [4], machining of different work and electrode materials [5], effect of different dielectric conditions [6], use of different electrodes [7], and discharge plasma characterization [8], but very limited studies dealt with size and shape effects. However, in macroscale EDM milling, a few aspects of shape effects such as electrode wear in machining of curved surfaces, use of hollow electrodes, etc., have been investigated. For example, Kunleda et al. [9] reported that using relatively larger hollow electrode in high-speed EDM with explosive discharge results in increased MRR and tool electrode wear is reduced significantly. In the generation of 3D shapes such as curved surfaces using cylindrical tool electrode machined in multiple passes of tools, it has been found that tool path radius and pick feed rate significantly influence the MRR and tool electrode wear [10]. Like in die sinking EDM, use of dielectric media influences EDM performance. The systematic investigation performed by Tao et al. [11] both in dry and near dry EDM studied by varying air jet, gas pressure, depth, and a few other fundamental EDM process parameters has reported high MRR in dry EDM and smooth surface finish in near dry EDM process. A prismatic tool with an oblong cross section was used by Mikesic et al. [12] to machine a cavity that enhanced the debris flushing and MRR in macroscale EDM.

In μ-EDM-milling, yet the reported literature dealt with process optimization for MRR, minimum tool wear, etc., similar to the aspects studied in μ-EDM die sinking process. Bissacco et al. [13] investigated electrode wear in μ-EDM-milling, by implementing laser scan micrometer on the machine to detect the coordinates of the electrode tip before and after machining and acquired the electrode profile. Karthikeyan et al. [14] evaluated the physical behavior of μ-EDM-milling process based on channel shape, form, and surface quality. They reported that the tool rotation motion plays a significant role in determining the amount of redeposition on the microchannel surface and verified the shape of microchannels for different speed and feed directions through experiments. They found that redeposition does not take place on the surface of tool due to centrifugal force. Since tool wear affects the accuracy of the machined surface, many approaches have been taken to sense and compensate tool wear. Nguyen et al. [15] analyzed the error components of 3D μ-EDM-milling and presented geometric models to simulate its effects. Authors reported that the machining accuracy is not only influenced by the machining gap and electrode wear but also by the corner radius of the virtual electrode. Yu et al. [16] proposed a new electrode wear compensation method, which is a combination of the linear compensation method, uniform wear method (UWM) and the theoretical model, called as combined linear-uniform wear (CLU) compensation method. The authors reported that the machining performances such as MRR, electrode wear ratio, and surface roughness get improved using CLU approach as compared to that by the UWM. Yan et al. [17] demonstrated the use of a machine vision based system to constantly monitor the wear phenomenon in μ-EDM-milling in order to compensate the electrode wear.

μ-EDM-milling that combines short pulsed low energy discharge across unshaped cylindrical electrode moves precisely in lateral (X-Y) direction alters the discharge gap phenomenon, which is not studied to a great extent. While the practical approach of electrode rotation solved a few issues such as nonuniform electrode wear and inconsistency spark gap, still the combined effect of front and side discharges, tool vibration that attributes to change in spark gap and jumping of discharge, corner effects, which are driven by shape and size of cavities being machined are need to be understood. In this paper, the authors present the physical behavior of μ-EDM-milling process in machining of cavities of different shapes including circular, triangular, square, channels, and square shaped pillars generated by machining of cross channels. All these features are machined on optimized parameters and the effects of shapes are presented based on the analysis of dimensional accuracy, recast layer, microcracks, surface integrity, surface texture parameters, and effect of tool rotation.

The experiments were performed on Micro Machining Center: DT-110 of Micro Tools, installed at Micro Systems Technology Laboratory at CSIR-CMERI. The machine enables the generation of complex tool path trajectories via three-axis computer numerical control (CNC) based control. The accuracy of machine is ±1 μm per 100 mm travel and repeatability is 1 μm for all axes. A cylindrical tungsten carbide electrode of 200 μm diameter with an accuracy of ±5 μm is used as a tool electrode and alloy steel EN-24 as work piece. Like in conventional milling process, the cylindrical electrode is mounted onto the machine spindle that rotates and moves along Z-axis intermittently to impart the machining depth and the workpiece is mounted over the X-Y positioning table that moves simultaneously based on the tool path strategy (Fig. 1). Both tool and workpiece are immersed in the liquid dielectric Olio HEDMA 111 of SARIX, which is continuously circulated through a pumping system. The electrode is rotated and fed in a predefined path by a CNC controller to machine different 3D blind microcavities, i.e., circular, triangular, square, channels, and cross channels. The discharge pattern and deflection of electrodes were monitored intermittently with the help of microscopic attachment (25×) and the monochromic high-speed camera Model: Photron FastCam SA 1.1, observed at 5000 fps. The enlarged view of experimental setup on DT-110 machine and the typical image observed through high-speed camera mounted with microscopic attachment are shown in Fig. 1.

As there were no prior studies reported on shape effects in μ-EDM-milling, design of cavity shapes and dimensions, selections of electrode size, tool path strategy, and optimized machining parameters under the given constraints of machine tool (DT-110), scanning resolution of profilometer, maximum achievable aspect ratio (without considerable electrode wear and short circuiting), and machining time was a daunting task. The authors explored different possibilities: a few preliminary experiments were initially performed by machining cavities of different shapes using 100 μm electrode, which is the minimum size that can be used presently on this machine. The maximum depth of cavity that could be machined without significantly visible electrode wear and short circuiting (resulting from accumulation of debris) was a circular hole of 225 μm; square cavity of 180–250 μm; triangular cavity of ∼250 μm; channel of 160–220 μm; and square pillar (cross channels) of 160–220 μm machined in multiple passes. In order to facilitate inspection of electrode, depth of cut was fed intermittently, and once the shape of the electrode observed through microscopic attachment (25×) was found to have changed significantly, machining was stopped for that specific shape.

Further, in profilometer scanning, it was noted that 100 μm cavities (circular hole, channels, and cross channels) could not be scanned, and even for triangular and square cavities, it was found to be difficult as depth of recast layer was in the order of depth of cavity particularly at the corners. This was particularly true at low (1000 rpm) spindle speed. It was also observed that at higher spindle speed (∼3000 rpm), the debris generated was small and with the help of dielectric flushing along the spindle surface debris moved away from the cavity surface more effectively. Further increase in speed up to 5000 rpm was not found to be effective, since the dielectric flushing to the cutting edge was not effective, a very small amount of liquid gets evaporated forming fume around the discharge point. This effect was predominant in case of machining circular holes as well as channels beyond the cavity depth more than 100 μm. Machining time is another aspect that determines the productivity, μ-EDM-milling being a slow machining process; the maximum feed rate allowed without any secondary discharges and short circuiting for the linear travel of tool electrode was 4 μm/s at optimized machining parameters. Based on this preliminary experiment and also from the previous experience gained over the years by the authors, it was decided to machine all the cavities up to a depth of a 500 μm using a 200 μm electrode. After critically studying the discharge pattern, the triangular and square cavities were machined using parallel tool paths with 50% step over, and for the machining of channels and cross channels, no parallel path tool paths were used, because discharge area is almost twice that of the square and triangular cavities at any given instant (Table 1). More detailed results on discharge pattern, electrode wear, and corresponding cavity shape errors have been discussed in Sec. 3.1.

In this experiment, a tool path wherein the tool electrode follows the shape of the pocket (cavities to be machined) using parallel paths, separated by a constant step over of 50% is adopted. The dimensions of the microcavities machined and the tool paths are listed in Table 1. Based on the experience gained in preliminary experiments and authors' experience, for each selected geometry, three cavities up to 500 μm depth were machined at 3.92 × 10⁻³ J discharge energy by multiple passes using optimized machining parameters shown in Table 2. The standard resistor-capacitor (RC) circuit based EDM power generator built into the above commercial machine was used. As the discharge current could not be set in this specific EDM power generator, it was not used as a process variable in this experimental study. The depth of the cavity was controlled automatically by CNC program, and the number of passes required to produce a cavity of desired depth were found to be different. In all the experiments, straight polarity, i.e., workpiece as anode and tool as cathode, is adopted as it gives higher material removal from workpiece, lower tool wear, and lower surface finish [18]. Lower threshold value is selected as it provides sensitivity in detecting short circuiting [19].

Machined microcavities and their geometry were examined by an optical microscope. Profile projector having least count of 0.001 mm/1 min of arc was used for dimensional measurement; dimensional error and standard deviation computed are compared for different geometries. SEM micrographs were characterized critically to examine the surface integrity, formation of recast layers, microcracks, and mode of material removal. Subsequently, 3D surface texture analysis was carried out by taking scanned view of the microcavities using high resolution (0.1 Å) 3D noncontact surface profiler. Online software talysurf coherence correlation interferometry (CCI) is used to collect the surface data by CCI principle. Further, the bottom surface cavities are analyzed using the offline software talymap platinum to estimate the surface roughness.

Figure 2 shows the EN-24 steel samples machined with different geometries. These samples were measured for dimensional accuracy as well as surface quality. The effect of cavity geometry in μ-EDM-milling has been assessed on different parameters such as the shape errors, dimensional error, cavity surface integrity, microstructure, profile error, and surface finish.

In this μ-EDM-milling experiment, as mentioned in Sec. 2 constant step over tool paths strategy in which tool electrode was fed in parallel paths with respect to the outer periphery of the cavity being machined, whereas in the case of circular hole machining, the electrode was fed along the Z-axis similar to the μ-EDM die sinking. Unlike in μ-EDM die sinking operation, gap phenomenon is different in μ-EDM-milling. Depending on the geometry being machined, the discharge position and its direction is changing continuously. In addition to the front discharge across the bottom surface of electrode and cavity surface, the side discharge plays a significant role in material removal, short circuiting, instability in spark gap, jumping of discharge, and nonuniform electrode wear. This resulted in shape errors such as corner effects, distorted/perforated cavity edges, overcuts, and recast layers. Therefore, in order to understand these effects, the physical differences in gap phenomenon and the difference in discharge pattern across different cavity geometries are illustrated in Fig. 3.

In machining circular holes, as the electrode advanced in Z-axis alone, the discharge along the axis removes the material from the cavity surface; however, the secondary discharges at the side around the electrode were observed with the help of high-speed camera attached with microscopic attachment after machining 200 μm diameter holes to a depth of more than 300 μm. At the selected machining conditions, the debris removal becomes difficult, particularly at 500 μm depth even with the use of the dielectric flush. This undesired secondary discharge took place at side of the electrode attributes the overcut error. As a result, the diameter of hole formed is greater than the electrode diameter (Fig. 4(a)) by 247 μm in average. Further, it has been found that holes are circular in shape, and the computed circularity error for the holes was in the limit of ±4 μm. As the depth of hole machined is very shallow (aspect ratio = 2.5), the tapering effect was not significant.

In cases of triangular and square shaped cavities, the discharge pattern observed under microscope were similar. For the constant step over (50%), parallel path tool travel started from the outer side (near to the periphery of the desired geometry) to the center, resulting in different discharge patterns for every parallel path. However, the first path that attributes to shape error was found to have side discharge around the electrode to a segment with included angle ∼120 deg. This nonuniform discharge pattern in the triangular and square shaped cavities attributes to three types of errors. First is deflection of tiny electrode, caused by the forces induced due to combined effect of ion bombardment, dielectric breakdown, and thermomechanical waves, which are yet not understood clearly and difficult to explain with one experimental study. With the help of microscopic attachment and high-speed camera, authors observed the deflection of 200 μm electrode that altered the spark gap instantaneously. Although it was difficult to measure the amount of deflection and its effect on change in spark gap resulting jumping effects quantitatively, this effect has been confirmed by three means. First, by online monitoring of the irregular discharge intensities and the patterns are observed with the help of Tektronix Digital Phosphor Oscilloscope (Model: DPO7104C) at 20 GS/s sampling rate. Second, by offline observation of movie files recorded using high-speed camera; recording was done intermittently up to 2 min due to large file size. Third, by reviewing the perforated front cut edge of the cavity, which was a result of jumping effects of an electrode. The second error was corner effect, unlike in the shaped electrode, the cylindrical electrode used in μ-EDM-milling failed to produce the sharp corners (Figs. 4(b) and 4(c)), the rounding of edges alters the shape and it invariably requires secondary operation, in micrometer scale it becomes cumbersome to assemble the microparts. It is also noticed that the debris gets accumulating, resulting in relatively huge recast edge.

In case of channels machining, the gap phenomenon is similar to the first path movement of triangular and square cavities. The side discharge is noticed around 120 deg segment area of electrode surface in addition to the front discharge. In this case, the entrapment of debris attributes to the nonuniform layer of channel and rough bottom surface (R_a = 3.23 μm). Whereas in the triangular and square cavities, the bottom surfaces were relatively smooth. The average surface finish (Ra) values for the triangular and square cavity surfaces are 2.94 μm and 2.85 μm, respectively. This is because of the remachining of recast layers in successive discharges produced in paths with 50% step over. Moreover, the recast layer at the channel edge is significant both in channels and cross channels machined to produce the square pillar. In fact, the square pillar top edge has relatively huge recast layers compared to other shapes (Fig. 4(e)).

These microscopic images of the cavity geometries were further used in profile projector having a least count of 0.001 mm/1 min of arc for measuring the dimensions. Table 3 lists the measured dimensions and standard deviations for the selected reference dimensions. It is found that the circular holes are consistent in dimensions with the lowest standard deviation of 1.53, whereas the microchannels are relatively poor and square pillars generated by cross machining of channels are further poor in terms of dimensional control with standard deviation of 14.52. For the selected dimension range, it has been found that the nonuniform discharge pattern has a significant influence on dimensional accuracy. The circular holes have the highest dimensional stability, followed by the square, triangular cavities, and channels.

Further, the cavities were examined critically at higher magnifications under SEM to investigate the effect of electrode wear and its dependence on tool paths used for creating the desired cavity geometry. It has been observed that the vertical walls of cavities are not perpendicular particularly for the channel and square pillars (cross channels). In this study, all the cavities were machined to a depth of 500 μm controlled by CNC program. In case of square and triangular shapes, the parallel tool paths with 50% step over were used, and the discharge zone at the electrode surface at any instant was limited to the area covered by an arc with included angle ∼120 deg as illustrated in Table 1. As a result, electrode wear rate is low, and because of rotation, the electrode eroded uniformly unlike in the machining of channels. In the case of channels, at every instant, discharge area is approximately two times more than other geometries. In addition, the spark gap at the front (with respect to electrode movement) changes due to deflection of electrode. Therefore, due to the combined effect of discharge pattern and the nonuniform spark gap, the electrode wear rate is found to be relatively high and nonuniform in case of machining of channels. Further, tapering of electrode due to its wear was not found to be significant at machining depths of 500 μm; however, it might be a concern for machining cavities with higher aspect ratios, which is yet to be investigated for different geometries.

The microcavities observed under optical microscope (Fig. 4) show that the cavities have burrs at the cavity edge, which deteriorate their surface quality. These recast layers are formed after machining as the discharge process is highly stochastic due to secondary discharge. During the course of cooling down of redeposited materials, entrapped gases escape from the material leaving behind cavity, debris particles, and pockmarks on the surface of microcavities generated. The molten metal once out of the machining zone cools down forming particles of different shapes, which are either removed from the discharge zone by the combined effect of flow of liquid dielectric and tool rotation. A part of the debris stays intact and ultimately resolidifies, resulting in the formation of a recast layer. In geometries such as triangular and square, these recast layer at the bottom of its surface are being removed in successive discharges with 50% step over parallel path travel of rotating electrode. Due to this recast layer, residual stresses build-up on the surface, resulting in the increase of molten layer hardness and generation of microcracks. In Fig. 5, SEM micrographs illustrate the formation of recast layer and microcracks. At higher magnifications, SEM micrographs show that cracks are present within the recast layer, and that they originate at the machined surface and then travel perpendicularly down through the recast layer toward the parent material lattice.

In μ-EDM-milling, as the tool rotates about its axis and travels in lateral axis simultaneously, the discharge points change rapidly; although it is difficult to explain, the jumping effect of discharges was significantly visible, which were confirmed both online and offline with the help of digital oscilloscope, high-speed camera, and microscope images as explained in Sec. 3.1. The melt removed from the work piece flows away from the discharge point where its direction and ejection speed are a function of spindle speed and the liquid dielectric flow rate and flushing direction. As the melt particles are ejected out of the discharge zone, due to high surface tension and as well due to sudden quenching by the dielectric liquid, noncrystalline spherical particles called globules are being formed. This is called as spheroidization or balling effect [20]. These globules formed in this process either have hollow, or solid particles with or without dendrites at their outer surfaces depending upon the amount of gases liberating during discharge process as well as the nucleation point during cooling [21]. Figure 6(a) shows typical balling effect where the melt removed from the parent materials forms granules of varying sizes. It is very well observed that the size and number of globules increases at higher discharge energy owing to high MRR and formation of larger cavities having more surface area similar to the observation made in molecular dynamics simulations reported in Ref. [22].

The SEM micrographs shown in Figs. 6(b)–6(f) illustrate the granules formation in different cavity geometries and their dependence with the tool rotation and tool path. It has been found that when the tool rotates, the spark gap changes instantaneously at a point near junctions and corners; the spark gets either pulled or broken before the completion of discharge, resulting in the formation of shallow elongated cavities and hence increasing the probabilities of simultaneous sparking. Moreover, these dynamic changes in spark gap leads to jumping of discharges, visibly appearing to be two different discharges with little overlapping in a given spark on time. This results in an increase in heat input energy and formation of larger size globules. Contrarily, at a higher rotational speed, the stirring action of tool electrode ejects the emitted particle at higher velocity out of melt zone causing splitting of particle jet to form number of random sized finer particles. This effect was clearly visible at 3000 rpm in case of channels machining compared to lower speed. However, with a further increase in speed up to 5000 rpm, the dielectric liquid fed along the tool electrode surface failed to reach the cutting zone; the small amount entering the zone gets evaporated rapidly forming huge fume around the discharge point and results in a relatively poor ejection of debris. It is seen that at the end of the channel wherein electrode takes a return path, this effect of splitting of emitted particle was predominant and finer particles were visible under SEM (Fig. 6(e)).

Further rotation of tool electrode exerts both the viscous and centrifugal forces over globules. The viscous force imparts angular velocity to globules around the tool, and the centrifugal force separates the globule from the tool and pushes it toward the relatively cold surface of the workpiece, which is stationary. As a result, the ejected particle jets of molten metal resolidify largely on the side surface of cavities near the edge of cavity than at the cavity surface. By the combined action of both forces, the globules get smashed in a regular order resembling spherical patterns. The effects of tool rotation and tool path on molten metal flow and on globules can be easily observed in all geometries; however, formation of resolidification layer and spherical patterns was random, and no relation could be established with the experimental work carried out in this work. However, there are promising opportunities noticed in the use of μ-EDM-milling to create patterned surfaces by redeposition of molten metal removed from the cavity. The authors observed this emerging opportunity, during the experimental study. It has been noted that the size of the debris removed from the cavity at selected process conditions varies from 10 to 70 nm. Further increasing the spindle speed, formation of smaller debris in the form of finer particles would occur after being ejected out of the cavity and solidifying over the cold surfaces. This motivates the fact that if suitable techniques have been developed to eject the debris out from the cavity and spread over the nearby surface, they would form patterned surfaces over the substrate of same material, apart from the formation of textured surfaces at cavity by electric discharge machining reported in one of patents given in Ref. [23]. The authors are currently investigating such possibilities, which are beyond the scope of this paper.

To quantify the difference in profile accuracy, the cavity surfaces were examined using a 3D noncontact surface profiler (Model: CCI Lite of Taylor-Hobson). Circular (200 μm) cavity surface at 500 μm could not be scanned with this instrument; other cavities that are larger in one dimension of ∼1000 μm were scanned and analyzed for errors. For the comparison of surface texture of different microcavities, root mean square (RMS) roughness parameter (R_q) is used, because it is more sensitive to peaks and valleys than other roughness parameters. The profile has been analyzed at different locations of each cavity for obtaining average surface roughness. Based on the surface profiles shown in Fig. 7 and the RMS roughness value, it has been found that the triangular microcavities has the highest uniformity in profile and fine surface finish, while microcross channels have the lowest uniformity and poor surface finish, followed by channels, square and cross channels (Table 4). The higher average RMS value indicates lower surface finish. In order to ensure the repeatability of the measured data on profile error and surface roughness, an average of five measurements at different locations on a single cavity, repeated over three cavities of same shape is presented in Table 4.

On the other hand, R_z values are significantly high, which indicates the presence of very high peaks or deep valleys at the bottom of cavity surface. For example, the critical analysis of profilometry of the square cavity surface in Fig. 7(b) shows smooth profile, but due to the presence of two deep valleys, its R_z value becomes quite high. The micro-analysis of square cavity surfaces shows minimum or no recast layer at the center zone of the cavity. This can be attributed to the tool path pattern. In this case, the tool electrode removes the material from the outer periphery, electrode moves around the edge, and it moves toward the center in subsequent paths (Table 1), where tool electrode is stationary and discharge was only along the axis. As a result, the material removed at the last few discharges ejected out and gets deposited around the electrode surface, the deep valley might have formed between these recast droplets of debris. Whereas in the case of channel and cross channel machining, the recast layer is significant at the end, where the electrode movement stops momentarily and takes a return path, forming valleys or heights. This makes sum of heights “Z” value high, correspondingly increase of R_z values. In the case of triangular cavity, the profile scanning was performed at reference line (height of triangle), the deep valleys were present nearer to vertex point and at the edge heights were formed due to recast layers. With the help of SEM micrographs at higher magnifications, it can be concluded that secondary discharges, improper debris removal, flushing conditions, and recast layer are the possible reasons for these variations in surface finish and profile errors.

The gap phenomenon and machining performance in μ-EDM-milling of five different cavity geometries using unshaped cylindrical tool electrode is studied. The discharge pattern, shape errors, dimensional accuracy, microstructure, formation of recast layers and spheroidization, and profile errors are reported in detail. It has been found that the discharge pattern in μ-EDM-milling alters the gap phenomenon, and the side discharge covering a segment of 120 deg around the cylindrical electrode attributes to tool deflection, nonuniform spark gap, and jumping of discharges. While corner effects restrict the possibilities of creating the sharp corners, it is found that triangular and square shaped cavities are relatively accurate and have smooth surfaces. The surface of the geometries shows the presence of randomly overlapping layers of debris particles and pockmarks, leading to the formation of recast layer. The residual stresses develop microcracks, which originate at the surface and travel down perpendicularly to the parent material lattice. Rotation of tool electrode benefits significantly in terms of uniform electrode wear, and removal of debris that minimizes secondary discharges. Along with the dielectric liquid, tool rotation also contributes significantly in particle ejection, and in the formation of spheroids which are different at junctions and corners of cavity geometries. Further, combined action of both viscous and centrifugal forces control the melt flow direction and ejection speed that splits the jet of emitted particles which in turn controls the resolidification over the substrate near the edge of cavity. While profile measurements further confirm the shape effects on surface quality, this study highlights the possibility of redeposition of particles in a regular order (resembling hemispherical patterns) to produce the micro-/nano-scale patterned surfaces over metals. Having made these promising reports on cavity shape effects in μ-EDM-milling for the first time, the authors are investigating further to establish process capability mapping for different microscale geometries so as to be able to help in the design of micro-/nano-scale functional devices for which interest is rapidly growing for many advanced applications.

This investigation has been carried out at Micro Systems Technology Laboratory at CSIR-CMERI, Durgapur. Authors acknowledge the funding assistance by CSIR under 12th FYP project ESC0112.