Fabrication Of Micro-holes Research Articles

A Study on the Influence of Central Edge Absence in Helical Grinding for Micro-Hole Fabrication

The fabrication of micro-holes in hard-to-machine materials presents considerable challenges in precision machining. This study proposes a novel approach that employs high-strength micro-grinding tools with a central abrasive grain absence to create micro-holes through helical grinding. Due to the random distribution of abrasive grains, the absence of grains at the tool’s center becomes an inevitable technical challenge. This research examines the correlation between the diameter of the absence zone and the bottom morphology of the machined hole, highlighting the potential formation of disc-shaped or cylindrical residues. A model for predicting the height of the disc-shaped residues is developed, and the mechanisms governing their removal during grinding are further explored. The findings indicate that when a central grain absence exists, the first abrasive grain surrounding the absence zone, referred to as the inner-edge grain, is responsible for removing the disc-shaped residues. Based on these results, a novel 0.8 mm diameter micro-PCD milling–grinding tool with a central edge absence is designed, and experimental validation is performed using 65% SiCp/Al composite materials. The experimental results confirm that the central grain absence leads to the formation of disc-shaped residues at the bottom of the machined hole during helical grinding, and the morphology of the experimentally obtained residues aligns with the theoretical predictions and simulations. This study significantly advances micro-grinding wheel technology and provides a solid foundation for the precision machining of micro-holes in hard-to-machine materials.

Comparative Analysis of Simultaneous Electrochemical and Electrodischarge Machining Process

Abstract Recent advances have established electrochemical discharge machining (ECDM) as an effective alternative to electrical discharge machining (EDM) for producing microholes in conductive materials. However, ECDM leaves nonuniform layers, including recast layers and heat-affected zones, rendering it unsuitable for materials vital to aerospace, defence, and biomedical applications. To address this issue, the present work investigates a novel electrochemical machining (ECM)-based frugal engineering process known as simultaneous electrochemical and electrodischarge machining (SECEDM) for microhole fabrication. To evaluate the process effectiveness, the machining results of the SECEDM process were compared with ECDM, EDM, and ECM. The obtained results present the fundamental distinction between the process mechanism of SECEDM and ECDM. SECEDM has been reported to produce microholes with improved machined surfaces characterized by their freedom from recast layer and ECDM-induced defects. Moreover, SECEDM facilitated meticulously controlled high-speed anodic dissolution of work material, surpassing the material removal rate (MRR) achieved through ultrasonic-assisted ECDM (U-ECDM), ECM, and EDM processes by 2.67, 4.2, and 6.2 times, respectively. Furthermore, the substantial 67.72% and 68.82% reduction in the average machined hole diameter than ECM and U-ECDM, respectively, with a noteworthy 13.69% enhancement in average roundness error achieved while maintaining the repeatability accuracy with an accuracy range within ±0.009 mm through SECEDM process underscore SECEDM's accuracy and repeatability. In addition, lower surface roughness by 31.6% and 68% compared to ECM and EDM, along with reduced carbon and oxygen content as examined through energy dispersive X-ray (EDX) analysis, signifies the SECEDM process efficiency in microfabrication.

Communication—Fabrication of Micro-Holes in PMMA Using Micro-ECDM Process: Geometric Characteristics and EC Discharge Behaviour

High-quality micro-features with low production cost are in high demand for the development of cost-effective microfluidic devices. In this work, we present a scalable and cost-effective fabrication process for fabricating blind micro-holes in PMMA substrates via micro-electrochemical discharge machining (Micro-ECDM) for the first time. By providing the suitable applied voltage (Va), uniformity of the electrochemical (EC) discharges and subsequent geometric characteristics of the micro-holes can be controlled. The stable and unstable EC discharge zones and micro-hole machining quality for different Va and tool conditions have been identified. For unstable and non-uniform EC discharge zone at Va of 26 V, the variation in the micro-hole output parameters is higher compared to stable and uniform EC discharge zones at Va of 28 V and 30 V. Based on the results, micro-holes with appropriate quality have been fabricated and characterized.

Fabrication of micro holes using low power fiber laser: surface morphology, modeling and soft-computing based optimization

Fabrication of micro holes using low power fiber laser: surface morphology, modeling and soft-computing based optimization

Laser-induced bubble dynamics optimization for high-aspect-ratio 3D micro-fluidic channels fabrication

In this study, we demonstrate a high-aspect-ratio microhole fabrication method that uses a femtosecond laser to drill from the rear side of transparent borosilicate glass in a specific solution environment with an assisted ultrasonic field. The experimental results show that an ablation enhancement effect could be achieved by mixing ethanol with distilled water with a volume fraction of approximately 20 %. The craters produced in the mixed solution were wider than those produced in water. An assisted ultrasonic field was introduced to further improve the drilling depth and avoid the termination of the drilling process caused by bubble aggregation and debris blockage. The bubble dynamics induced by the femtosecond-laser-induced breakdown effect were observed using shadowgraphs. The shadowgraphs of the high-speed camera revealed that the cavitation bubbles in the mixed solution had more than twice the maximum diameter and a significantly higher number of bubble expansions than those in water, which may cause a stronger impact pressure. The coupling effect of laser ablation enhancement and bubble bursting impact helped achieve a high material removal rate and significantly improve drilling depth. This indicates that an ultrahigh-aspect-ratio straight (∼273) microhole with a ∼2 µm diameter can be fabricated. By designing machining paths, we can machine 3D complex curved microchannels such as spirals. This method shows considerable potential in biomedical and microelectronics applications, for example to fabricate calibrated microholes for container closure integrity testing (CCIT).

Fabrication of Micro-Hole in 3D Printed CFRP Composite by Electrical Discharge Machining Process

Carbon fiber-reinforced polymer (CFRP) composite has extensive application in several industries, including the automotive and aerospace industries. Fabrication of micro-features in CFRP composite is an important process that is frequently performed for various applications including for micro-products and micro-components. The fabrication of precise micro-features in CFRP composite is difficult to achieve by conventional means, even by additive manufacturing (AM). Thus, in this study, the machinability characteristics of the CFRP composite were experimentally investigated. CFRP composite was fabricated by using the AM technique. The different process parameters of 3D printing (infill density and layer sequence) and micro-EDM (voltage, capacitance, and tool rotation) were considered to investigate their effect on the hole quality and productivity. The optimization of the different parameters chosen for the purpose of the investigation was also carried out. The important process parameters that have an impact on the process were identified and analyzed. The better machining performance of CFRP composite was noticed at higher infill density and alternative fiber arrangement. The capacitance was the most significant parameter among all the EDM parameters to produce good quality micro-holes in CFRP composite.

Experimental investigation and optimization of modification during backside-water-assisted laser drilling using flowing water

Backside-water-assisted laser drilling (BWALD) is a laser drilling process in which the workpiece is partially submerged in water. The backside of the workpiece is surrounded by water, and its upside directly contacts the air. In this study, flowing water was used to solve the problem where the generated air bubbles and debris prevent water from penetrating the through-hole and achieve the fabrication of micro-holes with high aspect ratios via BWALD. Moreover, a two-step micro-hole processing strategy was proposed to divide the BWALD into punching-through and modification steps. The modification process is the key to improve the machining performance, but involves numerous processing parameters. So, the effects of modification parameters (pulse energy, modification speed, frequency and number of modifications) on the responses of the micro-hole diameters and roundness were investigated during BWALD using flowing water on the basis of the response surface methodology (RSM). To achieve the optimal combination of parameters for a given situation, the regression models for the inlet diameter, outlet diameter, inlet roundness and outlet roundness of the modified micro-holes were developed. The adequacies of the developed models were subsequently verified by the analysis of variance (ANOVA) method. Finally, the well-rounded micro-hole with an inlet diameter of 105.62 μm and an outlet diameter of 96.65 μm which taper was only 0.21° was obtained with the optimum modification parameters: pulse energy of 15.9 μJ, frequency of 52.9 kHz, modification speed of 4.7 mm/s and number of modifications of 313.

Multi-objective optimization in electrochemical micro-drilling of Ti6Al4V using nature-inspired techniques

ABSTRACT Current study investigates the efficacy of electrochemical micro-drilling (ECMD) process during micro-hole fabrication on a Ti6Al4V alloy sheet of 1.2 mm thickness using a cylindrical-shaped micro-tool. Ethylene glycol-based electrolyte was selected to overcome excessive passivation. Experiments were conducted by altering voltage, feed rate (FR), and electrolyte concentration (EC) using a central-composite-design to observe their effects on the output parameters. The desired response parameters, such as radial overcut (ROC), and taper were examined while fabricating dimensionally accurate micro-holes including the volume removal rate (VRR) that occurred during the process. ANOVA results established voltage as the major significant input parameter that affects all the responses, followed by FR. In addition, different nature-inspired optimization techniques, namely Multi-Objective Grey-Wolf Optimizer (MOGWO), Multi-Objective Bonobo Optimizer (MOBO), and Multi-Objective Particle Swarm Optimization (MOPSO), were employed. MOBO reported the best Pareto-surface in terms of uniformity and spread measures and suggested a FR of 0.3 μm/s for optimal micro-drilling operations.

Micro drilling of PMMA with double-pulse femtosecond laser

Micro holes drilling in polymers have a variety of applications in industry and research. Especially, the fabrication of micro hole with high aspect ratio is a key technology for advanced applications. In this work, we report an improvement in drilling on poly-methyl methacrylate (PMMA) by using double-pulse femtosecond laser. Compared to single pulse, the achievable depth by double pulses can be increased by 50% when the pulse delay is 100 fs and gradually decreases with delay increasing. The depth evolution with the increasing of pulse number is investigated. When the micro hole depth reaches a certain value, the processing speed of double pulse is less restricted than single pulse. Furthermore, the relationship between the depth improvement and electrons decay together with absorption increase is studied.

Fabrication of high aspect ratio micro-holes on 304 stainless steel via backside-water-assisted laser drilling

Backside-water-assisted laser drilling (BWALD) is a viable and effective alternative of laser direct drilling (LDD) to fabricate micro-holes. However, it still has its own limitations, primarily due to the generated air bubbles and debris during the drilling process and the involvement of various processing parameters, especially when fabricating micro-holes with high aspect ratios on the non-transparent materials. In this study, a two-step processing strategy based on the sequence of punching through and modification was developed to fabricate the micro-holes on 304 stainless steel. Based on this strategy, two modification methods, namely single circle modification (SCM) and concentric circle modification (CCM), were proposed to amplify the advantages of BWALD during the modification process. Experiments testified that the two-step processing strategy was capable of reducing the taper and improving the roundness during BWALD process. Furthermore, a new strategy of using flowing water (backside-flowing-water-assisted laser drilling, BFWALD) was proposed to solve the problem that the generated air bubbles and debris prevent the water from penetrating the through-hole. It was found that the BFWALD could effectively improve the stability during the modification process and achieved the fabrication of micro-holes with an aspect ratio of 10:1 and a taper of only 0.38° successfully.

Fabrication of micro-hole using novel Maglev EDM

In the current scenario, micro-manufacturing through the electro-discharge machining (EDM) process is a prominent technique for achieving desired complex micro/nano-features of any product. The precision and accuracy of producing features are the prerequisites of micro-machining. The current work aims to check the feasibility of the novel Maglev EDM for fabricating micro-holes on a thin nickel sheet (thickness = 500 μm). The study presents the viability of the newly developed system by comparing it with the conventional EDM process. A pure direct current power supply is assembled with a magnetic levitation-based gap monitoring mechanism to overcome the setbacks of conventional EDM. The novel setup utilizes the combined effect of the permanent electromagnet to diminish arcing and short-circuiting. The control parameters for the operation were 12 V open-circuit voltage and 2 A peak current while maintaining a duty factor of 95.564 percent. The measured discharge voltage and discharge current were 6.64 V and 900 mA, respectively. Tungsten rod (ø 650 μm) and deionized water were used as a tool and a dielectric medium, respectively, for the experiment. Further, the machined micro-hole and micro-tool analysis have been carried out using high-resolution microscopy, scanning electron microscopy and energy dispersive spectroscopy reports. The newly developed Maglev EDM’s feasibility to produce micro-holes on conductive materials has been confirmed in the present work with an average material removal rate of 40 μg/min.

One Step Fabrication of Micro-hole on SiCp/Al Cambered Surface by Micro-EDM and Mechanical-reaming Combined Machining

One Step Fabrication of Micro-hole on SiCp/Al Cambered Surface by Micro-EDM and Mechanical-reaming Combined Machining

Investigation of machining characteristics during micro-hole fabrication in CFRP composite by ECDM process

Carbon fiber reinforced polymer (CFRP) composites have gained significant popularity in the field of aerospace, automotive, electronic, and sports due to its versatile properties. Although, fabrication of micro-holes in CFRP composite is troublesome by the conventional processes because of its anisotropic and abrasive behaviour. To overcome this difficulty, recently, an unconventional hybrid process such as electrochemical discharge machining (ECDM) is extensively used to machine such types of materials. This paper highlights the experimental and statistical analysis of machined micro-holes which was fabricated in CFRP composite using ECDM process. The experimentation was performed according to Taguchi’s L9 orthogonal array. The input parameters were (a) voltage, (b) tool rotation, (c) tool travel rate, and (d) duty cycle, each at three levels. Hole overcut and taper was measured as output responses. TOPSIS-Entropy based multi-response optimization technique was applied to optimize the chosen parameters. The hole overcut and taper was measured and analysed using SEM images. The parametric combination of 50 V, 360 RPM, 0.5 mm min−1, and 60% resulted minimum overcut and taper of 227 μm and 72 μm, respectively. The morphology of the machined hole exhibited better surface characteristics at a high tool travel rate and low duty cycle. Tool wear in terms of lateral wear and flank wear was observed during machining at high voltage and high duty cycle. From the TOPSIS Entropy analysis, the optimal condition for both overcut and taper was found as 50 V, 360 RPM, 0.5 mm min−1, and 60%.

Energy Channelization Analysis of Rough Tools Developed by RM-MT-EDM Process during ECSM of Glass Substrates.

In the present work, the effect of tool surface roughness on energy channelization behavior was analyzed during the fabrication of micro holes by an electrochemical spark machining (ECSM) process. In this study, rough tools were fabricated by a rotary mode multi tip electric discharge machining (RM-MT-EDM) process. The electrical characterization was also carried out to investigate the electric field intensity over the surface of tool electrode, and it was found that the use of rough tools improves the electric field intensity by 265.54% in comparison to the smooth tool electrodes. The use of rough tools in the ECSM process forms thin and stable gas film over the tool electrode, and as a result the rough tools produced high frequency spark discharges. Energy channelization index and specific energy were considered as response characteristics. The use of rough tools improves energy channelization index by 248.40%, and the specific energy is reduced by 143.263%. The material removal mechanisms for both of the processes (RM-MT-EDM and ECSM process) have also been presented through illustrations.

PRELIMINARY INVESTIGATION OF POWDER-MIXED MICROELECTRICAL DISCHARGE DRILLING OF CFRP COMPOSITE

This work investigates the fabrication of microholes in carbon-fiber-reinforced polymer (CFRP) composite by powder-mixed microelectrical discharge drilling (PM[Formula: see text]EDD) method. Initially, pilot experiments were carried out to understand the effect of powder concentration on the machining time and material removal mechanism. Then the full-factorial experimental analysis was performed to investigate the micromachining performance of CFRP composite. The input factors considered for the full-factorial analysis were powder concentration (2, 4, and 6 g/L), capacitance (100, 1000, and 10,000 [Formula: see text]F), and tool rotation (300, 400, and 500 rpm). The regression analysis was carried out to assess the significance of the chosen input factors. The surface morphology of the fabricated microhole was extensively studied to establish the material removal mechanism and failure mechanisms of the composite constituents.

Study on reducing burrs of super alloy through structures in water jet guided laser ablation

With the increase of thrust-weight ratio of aero-engine, the working temperature of core parts is becoming higher and higher. In order to improve the service life of core parts, many high-precision micro holes are machined on those core parts. To realize the fabrication of micro hole with less burrs on super alloy substrates, a novel water jet guided laser processing method is proposed in this paper. A material removal principle based on plasma detonation assistant machining is proposed and proved to be valid through experiments. Then a laser-induced plasma assisted ablation method using sacrificial layer in the machining of through holes and grooves on super alloy is approved. This method can get higher machining efficiency and avoid longtime trimming in subsequent experiments. The size of burrs in through hole decreases 57.89%, while the area of burrs decreases 42.32% after using 304 stainless steel as sacrificial layer in the machining of through hole. Grooves with fewer burrs are also achieved on super alloy with this method. That method can also be used to fabricate a variety of functional structures.

A performance study of electrochemical micro-machining on SS 316L using suspended copper metal powder along with stirring effect

ABSTRACT Electrochemical micro-machining (ECMM) is widely used for machining small-sized components, intricate shapes, and hard materials. Fabrication of micro-holes in stainless steel 316L (SS 316L) can be effortlessly achieved by the ECMM process rather than other machining methods, owing to its favorable machining characteristics and advantages. This paper tries to elucidate the performance of ECMM on the machining of SS 316L using an eco-friendly citric acid as an electrolyte medium, and the results are compared with copper metal powder suspended in a citric acid electrolyte (suspended electrolyte) and copper metal powder suspended in a citric acid electrolyte with the assistance of a mechanical overhead stirrer (suspended electrolyte with stirrer effect). The output performance parameters such as MRR and overcut are calculated by varying the input response parameters such as machining voltage, duty cycle, and electrolyte concentration. From the experimental results at higher parameter levels, the highest MRR and moderate overcut are obtained for suspended electrolyte with stirrer effect. For suspended electrolyte, moderate MRR and the highest overcut are detected. The least MRR and reduced overcut are found for citric acid electrolyte. SEM and EDAX analysis have been carried out to see the machined micro-hole and the composition present in the specimen.

Modeling and simulation of micro-hole fabrication on brittle material using abrasive air jet machining

The investigation of overlapping impacts and resultant erosion is of great significance for improving the AAJ micromachining performance of brittle and difficult-to-machine materials. In this work, a computational model coupling the Monte Carlo (MC) method and discrete element method (DEM) is developed to study the erosion process of micro-hole fabrication on glass using abrasive air jet (AAJ) at a 90° impact angle. We employ the MC method combined with probability distribution functions to model the impinging particle flow. Brittle erosive behaviors of the overlapping impacts between the impacting particles and the target specimen are simulated by the DEM model. The modeling framework is firstly validated by experimental results using patterns and sizes of micro-holes on the specimen. We then conduct mechanism investigations on the particle and crack behaviors in the erosion process and the overlapping condition effect in the multiple impacts. The relationship between the jet characteristics with the machining efficiency and surface quality of micro-holes is further discussed. The results indicate that the presented DEM model can capture the particle interference effects, which play an essential role in controlling the material removal and microstructure geometry in AAJ machining. The model and findings can help understand the microscopic erosion mechanism and optimize the processing performances of microstructures on brittle materials in AAJ.

Performance improvement of high-speed EDM and ECM combined process by using a helical tube electrode with matched internal and external flushing

Micro-hole fabrication at a high speed and accuracy of machining while maintaining high surface quality is challenging. A core difficulty is the removal of the products of machining from extremely narrow gaps. To solve this problem, this study proposes an approach that combines high-speed electrical discharge machining (EDM) with electrochemical machining (ECM) by using a helical tube electrode with matched internal and external flushing. During high-speed electrical discharge drilling, matching the internal flushing with the clockwise rotation of the helical electrode can help remove debris from the bottom of the blind hole. During ECM, matching the external flushing with the anticlockwise rotation of the helical electrode can improve the flow of electrolyte in the gap. First, the flow field was simulated to show that matching the internal and external flushing of the helical electrode can enhance the flow of the medium and reduce particle concentration in extremely narrow gaps. Second, a series of experiments were conducted to verify that the taper of the hole and the surface quality of its wall can be improved by using the helical tube electrode. Finally, an experiment was carried out to optimize the machining parameters and yielded a minimum taper of 0.008 at a speed of rotation of 460 rpm, and pressures of internal and external flushing of 9 MPa and 4 MPa, respectively.

Fabrication of micro holes in Yttria-stabilized zirconia (Y-SZ) by hybrid process of electrochemical discharge machining (ECDM)

In the present work, the electrochemical discharge machining (ECDM) process with an integrated approach of electrolyte flow and pressurized feeding is demonstrated to produce micro-holes in Yttria-stabilized zirconia (Y-SZ). The mechanism of material removal reveals that the material is primarily removed due to the thermal spalling phenomenon over the melting and evaporation. Unlike the other glass based ceramic materials, the contribution of chemical etching phenomenon is found to be almost negligible in removing the material from Yttria-stabilized zirconia work substrate. The incorporation of electrolyte flow in the ECDM process increases the machining efficiency by improving hole depth by 42% and reducing diameter by 33% for the same processing durations. The improved frequency of electrochemical discharges (ECD’s) due to the supply of electrolyte is responsible for removing the material in controlled manner without causing any fracture at the hole edges. Moreover, the supply of electrolyte reduces the tool wear, which results in consistent machining conditions for longer machining durations. The maximum penetration speed obtained in this investigation was 126 μm/min.