Micro-hole Machining 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.

Ultrasonic vibration-assisted grinding of quartz glass micro-hole

Quartz glass is extensively utilized in the aviation and biomedical fields. However, achieving high-quality ultrafine micro-holes on quartz glass is difficult because edge chipping and internal surface defects are prone to occur during processing. Therefore, the ultrasonic vibration-assisted grinding (UVAG) was proposed to realize efficient and low-damage precision machining of quartz glass micro-holes. First, the brittle-to-plastic transition depth and theoretical motion trajectory of a single grit of quartz glass in UVAG were analyzed. Subsequently, comparative experiments were conducted between UVAG and conventional grinding (CG) to machine quartz glass micro-holes. Finally, the influences of different parameters on grinding force, edge chipping, entrance and exit diameters, and internal surface quality were investigated. The experiments demonstrated that the grinding force, edge chipping at the entrance and exit, and internal surface roughness can be effectively reduced by UVAG compared to CG. After UVAG, the axial grinding force, size of the edge chips at the entrance and exit, and internal surface roughness decreased by 40.97 %, 36.28 %, 42.09 %, and 12.59 %, respectively. After optimizing the process parameters of UVAG, the size of edge chipping at the entrance and exit were 6.5 μm and 7 μm, respectively, and the internal surface roughness reached 0.146 μm. In this case, the diameter of the micro-hole was 112 μm, and had a depth-to-diameter ratio greater than 10.

A Study on the Characteristics of Micro-hole Machining for Difficult-to-cut Al 30%/SiC 70% Metal Matrix Composite Materials

A Study on the Characteristics of Micro-hole Machining for Difficult-to-cut Al 30%/SiC 70% Metal Matrix Composite Materials

Research on the key techniques of composite processing of EDM and vibration ultrasonic drilling

PurposeUtilizing electrical discharge machining (EDM) to process micro-holes in superalloys may lead to the formation of remelting layers and micro-cracks on the machined surface. This work proposes a method of composite processing of EDM and ultrasonic vibration drilling for machining precision micro-holes in complex positions of superalloys.Design/methodology/approachA six-axis computer numerical control (CNC) machine tool was developed, whose software control system adopted a real-time control architecture that integrates electrical discharge and ultrasonic vibration drilling. Among them, the CNC system software was developed based on Windows + RTX architecture, which could process the real-time processing state received by the hardware terminal and adjust the processing state. Based on the SoC (System on Chip) technology, an architecture for a pulse generator was developed. The circuit of the pulse generator was designed and implemented. Additionally, a composite mechanical system was engineered for both drilling and EDM. Two sets of control boards were designed for the hardware terminal. One set was the EDM discharge control board, which detected the discharge state and provided the pulse waveform for turning on the transistor. The other was a relay control card based on STM32, which could meet the switch between EDM and ultrasonic vibration, and used the Modbus protocol to communicate with the machining control software. FindingsThe mechanical structure of the designed composite machine tool can effectively avoid interference between the EDM spindle and the drilling spindle. The removal rate of the remelting layer on 1.5 mm single crystal superalloys after composite processing can reach over 90%. The average processing time per millimeter was 55 s, and the measured inner surface roughness of the hole was less than 1.6 µm, which realized the micro-hole machining without remelting layer, heat affected zone and micro-cracks in the single crystal superalloy.Originality/valueThe test results proved that the key techniques developed in this paper were suite for micro-hole machining of special materials.

Investigation of continuous wave/coaxial waterjet-assisted laser combined machining of micro holes in GH3536

A two-step combined processing technique, combining a continuous-wave laser with a waterjet-assisted nanosecond laser, has been introduced to enhance the quality and efficiency of laser micro-hole processing for nickel-based superalloys. Initially, a through-hole was created using a continuous-wave laser, followed by hole refinement with a coaxial waterjet-assisted nanosecond laser. In the first step, orthogonal testing methods were employed to investigate the impact of various parameters, including power, duty ratio, frequency, defocusing amount, and processing time, on the entrance and exit apertures, as well as the hole taper. Through the analysis of variance (ANOVA) method, the optimal parameter combination A2B1C4D3E1 was identified, achieving the minimal hole taper. This combination comprised a power level of 80 %, a duty ratio of 15 %, a frequency of 400 Hz, a defocusing amount of 2 mm, and a processing time of 10 ms. In the second step, a comparison was made between scanning and trepan drilling machining methods. The results unequivocally demonstrated that scanning drilling achieves superior entrance and exit morphologies. Furthermore, the effect of water jet velocity on the morphology of micropores was thoroughly analyzed. The voltage range of the water pump was adjusted from 10 V to 24 V, revealing that a voltage of 20 V produced the smallest hole taper. The scanning filling diameter was accurately preset according to the preformed hole aperture as well as the thickness of the recast layer. Finally, after coaxial waterjet-assisted laser precision machining, the inner wall of the hole is free of cracks, and the recast layer and oxide layer are effectively minimized. The initial hole prefabrication with the continuous-wave laser took merely 0.01 s, and the subsequent fine-tuning with the coaxial waterjet-assisted laser took 2 min and 25 s.

Investigating mechanisms of debris removal in ultrasonic vibration-assisted EDM drilling

In traditional electrical discharge machining (EDM) of micro-holes, the debris removal becomes increasingly challenging as hole depth increases, significantly affecting the machining of difficult-to-machine materials. To address this issue,we first developed a micro-hole gap flow field model for a novel longitudinal–torsional ultrasonic vibration (LTV) electrode EDM drilling method. We analyzed the effects of three types of electrodes — rotation electrodes, longitudinal ultrasonic vibration (LUV) electrodes, and LTV electrodes — on the flow velocity in the micro-hole interstitial flow field. Next, we simulated the motion of fluid and debris in the interstitial flow field of micro-holes, theoretically verifying the advantage of electrode ultrasonic vibration in enhancing debris removal efficiency. Additionally, we observed the electrode tip morphology, the elemental composition on the electrode surface, and the morphology of the micro-hole inlet/outlet and inner wall to further elucidate the debris removal mechanism and confirm the superior drilling performance of the ultrasonic vibration electrodes. At an optimal ultrasonic amplitude (AL=4μm), the LUV electrode demonstrated improved consistency in the micro-hole inlet/outlet and achieved a micro-hole taper of 0.014°. The material removal rate (MRR) using the LTV electrode reached 5.14 × 105μm3/s, nearly 1.5 times higher rotation electrode. This method successfully produced a positively tapered hole suitable for injector nozzles.

A novel path planning approach to minimize machining time in laser machining of irregular micro-holes using adaptive discrete grey wolf optimizer

As an essential technique in fabricating substrates for flexible printed circuit boards, laser drilling of polyimide films facilitates the production of smaller holes of superior quality, which is crucial for preserving the structural integrity and functional reliability of materials. This advanced technology is increasingly critical in sectors demanding high performance, such as high-speed communications and biomedical devices. However, challenges such as the diverse sizes of micro-holes, their irregular placement, and the inherent limitations of scanning components on speed and operational range make efficient and rapid laser drilling a complex endeavor. In this paper, we develop a processing time evaluation model and present a new adaptive discrete grey wolf optimizer (A-D-GWO). The A-D-GWO utilizes exchange, shift, and 2-opt operations to enhance search efficiency and includes an adaptive parameter mechanism, improving its adaptability to various problem sizes and ensuring faster convergence. Experimental results confirmed the algorithm’s effectiveness, reducing processing times by 38.9%, 53.6%, and 55.5% for files containing 90, 286, and 649 holes, respectively. When compared to traditional algorithms, A-D-GWO showed better stability and accuracy, suggesting its suitability for inclusion in laser processing technologies.

Multi-energy field simulation and experimental research on laser composite machining of micro-holes

Thin-walled micro-holes are frequently used in aerospace components to achieve specific functions, such as heat dissipation and filtration. However, traditional manufacturing technologies face difficulties in achieving precision machining of these holes due to deformation caused by cutting force or heat. Laser machining is a highly flexible and efficient advanced processing technology that aims to achieve precise machining of thin-walled holes. However, it is important to note that the thermal energy generated by the laser can cause deformation of the thin walls. To address these issues, this paper proposes a process that combines laser and backside electrochemical composite machining. The model for laser electrochemical composite processing after through-hole formation suggests that the laser's temperature rise effect on the electrolyte can significantly enhance the efficiency of electrochemical processing. Furthermore, the laser exerts a micro-zone stirring effect on the electrolyte in the processed micro-zone, which promotes the liquid-phase mass transfer process during the electrochemical reaction. Furthermore, a one-way experiment was conducted to investigate the effects of the main laser parameters on the processing results. The results indicated that higher laser power, as well as lower laser frequency and scanning speed, significantly reduced the edge damage and pore taper of the processed micro-holes. The language used is clear, concise, and objective, adhering to a formal register and avoiding biased or ornamental language. Technical terms are consistently used and explained when first introduced. The text is grammatically correct and free from spelling and punctuation errors. Furthermore, this process has significantly reduced the oxygen content and surface roughness of the sidewalls of the micro-holes.

Processing parameter effect, formation mechanism and inhibition method of micro-hole exit defects in rotary ultrasonic pecking drilling of SiCf/SiC composites

High brittleness and anisotropy of ceramic matrix composites lead to great challenges for micro-hole machining. Micro-holes with large depth-to-diameter ratio (10:1) of SiCf/SiC composites were machined by rotary ultrasonic pecking drilling process. Based on the mechanical theory and structural characteristics of SiCf/SiC, a critical thrust force model was established. The effects of processing parameters on machining accuracy and machining quality of micro-hole exits were analyzed and parameters were optimized. The formation mechanism of exit defects includes interfacial debonding, fiber bending and matrix fracture. A method based on the surface morphology to inhibit exit defects by increasing the support stiffness of the material was proposed, under which the exit roundness all reached IT8 level and chipping factors decreased by 53 %–67 %, and only a small amount of chipping and micro-cracks was at the exit. The proactive control of micro-hole exit defects was realized, and a better machining quality was obtained.

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.

Machining of micro-hole on nitinol alloy by UV-MFEDM process

ABSTRACT Nitinol alloy is widely utilized across various industries due to its special properties. In this paper, the compound effects of two kinds of energy fields on material removal rate (MRR), hole wall quality, machining accuracy, and recast layer in ultrasonic combined magnetic field assisted EDM (UV-MFEDM were studied and analyzed. In addition, the influence of magnetic field intensity on the efficiency and accuracy of micro-hole machining is analyzed systematically. The results show that the surface quality of the micropore is significantly improved, the MRR is increased by 31.6%, the taper of the micropore is reduced by nearly 30%, the overcut diameter is reduced by nearly 23%, the recast layer is more uniform and the thickness of the recast layer is reduced by nearly half. Appropriate magnetic field intensity proves beneficial for improving micro-hole machining efficiency while reducing both taper angle and diameter overcut of micro-holes.

Computational modelling and experimental investigation of micro-electrochemical discharge machining by controlling the electrolyte temperature

Glass vias are emerging as a favourable option for radiofrequency-based micro-electromechanical system packaging. For the micromachining of glass, electrochemical discharge machining (ECDM) could be the most suitable technique if issues pertaining to the process stability are addressed thoroughly. The electrolyte temperature has immense influence on the viscosity and conductivity of the electrolyte, which percolate the stability of the ECDM process. Therefore, this article investigates the effects of the electrolyte temperature and applied voltage on the performance characteristics of ECDM for the micromachining of borosilicate glass. The machining rate (MR) and hole overcut (HOC) of the machined microholes are considered as performance characteristics. A 3D thermal-based finite element model (FEM) was developed for the thermal analysis in the machining zone. In the thermal analysis, the heat flux by thermal discharge was assumed to have Gaussian distribution, and accordingly, temperature profiles in the thermal zone were analyzed by controlling the electrolyte temperature and voltage at various levels. Further processing of temperature profiles in the thermal zone was utilized in the estimation of MR and HOC. Electrostatic-based FEM was utilized to assess the intensity of the electric field in the proximity of the tool electrode to analyze the probable locations of thermal discharge and its impact on the geometrical characteristics of the machined microholes. The simulation outcomes were validated experimentally, and show good agreement. A field emission electron microscope with energy dispersive spectroscopy was used for the characterization of the machined surface to observe the effect of the electrolyte temperature.

Thermal simulation of microelectrode machining process during block electrical discharge grinding

Electrical discharge machining is widely used in aerospace industries, semiconductor applications, micro-electromechanical systems, and other fields of the machining of micro-holes, micro-shafts, and micro-structures due to non-contact stress during the electrical discharge machining process. In the electrical discharge machining process, the machining precision of electrical discharge machining depends on the dimensional precision of the tool electrode, therefore, the machining process of microelectrode has attracted growing concern. In this study, a thermal model of the microelectrode machining process was proposed to simulate the formation process of microelectrode based on the temperature distribution during block electrical discharge grinding of the microelectrode process. According to the microelectrode machining process, the thermal model considers the main influential factors such as random distribution of discharge points, time-dependent discharge channel radius, Gauss heat source, phase transformation latent heat, etc. Through the thermal simulation analysis, the temperature distribution and the dynamic spark-erosion process of the microelectrode based on random repetitive spark discharges were obtained during block electrical discharge grinding of the microelectrode. Besides, it is found that the maximum temperature value and discharge crater volume of the electrode surface fluctuate and gradually decrease with the increase of discharge times. In addition, the effect of pulse width on the machining process of microelectrode was investigated by numerical simulation and block electrical discharge grinding of microelectrode experiment. The results indicated that the crater volume and the maximum temperature value on the surface of the microelectrode increased with the increase of pulse width. The formation process of microelectrode was considered a significant indicator to determine the machining precision and machining efficiency of the electrical discharge machining process.

Tribological Synergism of Anodic Aluminum Oxide Surface Containing Micro-Holes and Nanopores under Lubricated Reciprocation

Micro-drilled aluminum surfaces containing micro-holes were anodized to produce nanopores over the machined and lapped surfaces. The anodized nanopores had an approximate diameter of 30–40 nm and a depth distribution of 20–30 μm from the surface. The diameter and depth of the machined micro-holes were 125 μm and 300 μm, respectively. Anodization itself did not change the surface roughness because the nanopores were very small. Ball-on-disk reciprocating tests were performed under lubricated conditions for 2 h using a frequency of 2 Hz, a load of 2 N, and a travel distance of 5 mm. The results showed that both the micro-drilled and anodized surfaces greatly reduced the coefficient of friction compared with the lapped bare surface; however, the coefficient of friction of the hole-textured specimen was not maintained till the end. Contrary to expectations, the lubricant retention capability of the textured structure declined because of hole failure that occurred during oscillation. This gradually increased friction until the end of the reciprocating test. When the micro-drilled surface was anodized, the coefficient of friction decreased again, implying that non-anodized micro-holes alone were ineffective for reducing friction. The surface hardness of Al increased owing to anodization, and thus the micro-holes remained intact. Therefore, it is concluded in this study that a prerequisite for friction reduction in Al is to increase the hardness to minimize the failure of micro-holes, which can be achieved by anodization. The synergistic lubricant retention capability can be maintained by the presence of both nanopores and micro-holes.

Ultrasonic Vibration-assisted Electrochemical Discharge Machining of Quartz Wafer Micro-Hole Arrays

The micro-hole machining of quartz wafers depends on photolithography techniques akin to those used in semiconductor fabrication. These methods present challenges due to high equipment setup costs, large space requirements, and environmental pollution risks. This research applies ultrasonic vibration assistance in electrochemical discharge machining to create an array of micro-holes on quartz wafers. In the experiments, a self-prepared tungsten carbide micro-electrode array served as the tool electrode. This electrode was a 2 × 2 square array, with needles measuring 30 × 30 μm. A series of experiments was conducted to investigate the effects of various machining parameters, including working voltage, feed rate, duration time, duty factor, and ultrasonic power level, on the characteristics of the micro-hole array. The characteristics included average hole diameter and through-hole surface morphology. The experimental objective was to achieve a through-hole diameter of 80 μm with an accuracy of ±8 μm. During the electrochemical discharge machining, suitable ultrasonic vibrations can thin the insulating gas film coating on the electrode surface, resulting in a more uniform gas film. As the insulating gas film’s thickness decreased, so did the critical voltage needed for the electrochemical discharge machining, reducing the hole’s diameter expansion. The ultrasonic vibration assistance can enable the satisfaction of the dimensional accuracy requirement. The experimental results indicate that ultrasonic vibration assistance can effectively improve the processing capacity and reduce sample fragmentation. A working voltage of 44 V, feed rate of 1 μm/6 s, duration time of 30 μs, duty factor of 30%, and ultrasonic power level of 1 resulted in better inlet and outlet surface morphology without outlet fragmentation. Moreover, the average diameters of the inlet and outlet were roughly 80 μm while meeting the through-hole diameter of 80 μm with accuracy of ±8 μm.

Femtosecond laser processing of controlled tapered micro-holes based on dynamic control of relative attitude

Femtosecond laser drilling of metal necessitates precise control over taper to ensure dimensional accuracy. However, conventional vertical incidence laser processing methods result in micro-holes with inherent taper and a beam waist at the midportion. To address this issue, this paper proposes a micro-hole machining method that involves adjusting the relative attitude between the laser beam and the workpiece, enabling controlled machining of micro-holes with varying tapers. The feasibility of the method is validated by simulating theoretical hole profile using an isophote model, which exhibit good agreement with experimental results. Experimental findings on nickel-based alloys demonstrate a linear correlation between the attitude angle and hole taper. By manipulating the attitude angle, it is possible to achieve controllable machining, ranging from positive taper to negative taper. This approach eliminates the waist within the micro-hole and enhances chip removal space, resulting in improved hole wall quality. Moreover, employing multi-attitude angle and dynamic attitude angle processing, in addition to single attitude angle control, effectively eliminates the core generated during drilling. This method prevents the exacerbation of multiple reflections caused by the core and the reduction of chip removal space, leading to enhanced energy coupling between the laser and the material in the ablation area. As a result, the maximum depth of the hole is increased, allowing for the realization of no tapered micro-holes on 5 mm thick nickel-based alloys. Furthermore, laser processing introduces a significant amount of dislocation structures in the microstructure near the hole wall. This study introduces a novel approach to achieve controllable taper in femtosecond laser drilling. It offers both theoretical and experimental support for understanding the hole shape evolution process in femtosecond laser drilling.

Experimental Investigation of the Machining Characteristics in Graphite-Powder-Mixed Electrochemical Discharge Machining of Microholes in Glass.

The effect of graphite powder on the machining characteristics in graphite-powder-mixed electrochemical discharge machining of microholes was still not clear. How the discharge mechanism changed with the addition of graphite powder into the electrolyte, which further led to changes in the morphology of the machined holes, remained to be revealed. In this study, a series of microhole machining experiments were conducted in glass. Comparisons of the discharge energy, microhole entrance diameter, hole taper, and tool electrode morphology after machining were made when machining in the electrolytes with and without graphite powder. Experimental results revealed that there were a lot of small pulse currents distributed on the current waveform when machining with the graphite-powder-mixed electrolyte. The average discharge energy of the small pulse current was 2.8 times as much as that of the general electrochemical discharge. After introducing graphite powder into the electrolyte, the entrance diameter of the hole became larger when the hole depth was deeper than 200 μm. The HAZ width increased with increasing hole depth at the voltage of 37-41 V, while it decreased at the voltage of 43 V. A reduction in hole taper angle with a range of 0.5° to 2.3° was achieved. In addition, after machining in electrolytes with and without graphite powder, the tool electrode surfaces showed different morphologies due to different discharges.

Process applicability and hole wall microstructure evolution mechanism of femtosecond laser spiral drilling

In this work, a 1.5 mm thick GH3044 nickel-based superalloy is processed by femtosecond laser to obtain a micro-hole for the fuel nozzle of an aerospace engine with a large thrust-to-weight ratio. To address the issue of sidewall adhesion during micro-hole machining, a spiral drilling method implemented with a rotating wedge scanning module is used. Combined with a two-step drilling strategy, it achieves flexible removal of adhesion while ensuring machining efficiency and further improving the quality of drilling. The effect of different drilling strategies on the sidewall roughness of micro-holes is investigated. After process optimization, the roughness of the the micro-hole sidewalls is reduced to below Rq 0.4 μm, which is approximately 8% compared to the traditional one-step drilling strategy. Based on the EBSD analysis results, it is observed that the microstructure of the micro-hole sidewalls remains largely unchanged regardless of the drilling strategy employed. The analysis of the micro-hole sidewalls shows the presence of periodic microstructures. When aiming for low roughness, the geometric characteristics of these periodic microstructures can be adjusted by manipulating the laser's single pulse energy. These experimental findings present a new perspective for optimizing the femtosecond laser drilling process and provide theoretical support for future enhancements in the actual fuel injection effect.

Experimental Research of High-Quality Drilling Based on Ultrasonic Vibration-Assisted Machining.

Micro-hole is widely used in various fields, and common machining methods of micro-hole in factories are drilling and electrical discharge machining (EDM), but because of low machining efficiency, these methods cannot meet requirements. Therefore, it is urgent to investigate a high efficient micro-hole machining technology to meet the demands of micro-hole machining in factory. Over past few decades, ultrasonic machining technology has developed rapidly and achieved good results in solving many critical machining problems in field of difficult-to-cut materials. Therefore, this paper builds an ultrasonic vibration-assisted drilling (UAD) experiments platform to combine micro-fine small hole drilling with ultrasonic machining technology for micro-hole multi-factor experimental research. Results show that UAD machining of micro-hole below diameter 0.5 mm is comparable to conventional drilling machining because of its high-frequency pulse intermittent cutting process, stable change in machining diameter, good stability of parameters such as shape tolerance roundness and cylindricity, small cutting force during cutting, small tool wear, and small surface roughness of inner wall of micro-hole. Compared with EDM, UAD has high efficiency and good stability of parameters such as diameter and roundness of shape tolerance. Comprehensive analysis of UAD can be used as an alternative technology solution for machining small holes in non-special requirements of metal materials in factory and has technical feasibility of stable batch production.

A novel EDM method using longitudinal-torsional ultrasonic vibration (LTV) electrodes to improve machining performance for micro-holes

This study proposes a new EDM method using longitudinal-torsional ultrasonic vibration (LTV) electrodes for micro-hole machining to address the problems of debris removal and difficult working fluid exchange in micro-hole processing, which can enhance the micro-hole machining performance. A 38.9 kHz ultrasonic vibration transducer is developed for LTV electrodes, and the fluid distribution in the micro-holes gap is simulated when LTV electrodes were used to process micro-hole. The effect of ultrasonic amplitude on flow rate and debris removal efficiency is discussed. A study is conducted to analyze the morphogenesis of the electrode extremity and the micro-hole inlet/outlet at different amplitudes. This study finds that applying appropriate ultrasonic amplitude (2–4μm longitudinal amplitude, 0.2–0.35μm torsional amplitude) to the electrode effectively reduces the electrode tip and corner wear and the flanging burr of the micro-hole inlet/outlet. Compared EDM micro-hole machining with the rotating electrode only, the material removal rate (MRR) is increased by nearly two times with the simultaneous application of 4 μm longitudinal ultrasonic amplitude and 0.35μm torsional ultrasonic amplitude to the electrode, and reduction of electrode wear and micro-hole taper by approximately 60% and 80% respectively.