Micro-hole Drilling Research Articles

Experimental Study on the Wellbore-Cleaning Efficiency of Microhole-Horizontal-Well Drilling

SummaryMicrohole-drilling technology is a high-efficiency and low-cost technology that has developed rapidly in recent years. However, during microhole-horizontal-well drilling, cuttings are easy to deposit at the bottom of the wellbore because of gravity and nonrotation of drillpipe. Inadequate drill-cuttings removal can cause costly problems such as excessive drag, and even mechanical pipe sticking. Therefore, many laboratory studies as well as field observations have been directed toward addressing the cuttings-transport problem. In the present study, a full-scale horizontal-cuttings-transport flow loop was set up and a total of 136 experiments were conducted. By analyzing the cuttings volumetric concentration and the dimensionless height of the cuttings bed, the effects of flow rate (0.00058–0.00078 m3/s), cuttings diameter (0.0003–0.005 m), rate of penetration (ROP) (0.00211–0.00636 m/s), eccentricity (0–0.8), and wellbore diameter (0.04–0.08 m) on wellbore-cleaning efficiency were obtained. It was found that cuttings-transport efficiency increased first and then decreased as cuttings diameter increased. Flow rate was the main parameter. Higher flow rate, lower ROP, lower eccentricity, and smaller drillpipe/wellbore-diameter ratio all led to higher wellbore-cleaning efficiency in microhole horizontal wells. In addition, a model for estimating the cuttings volumetric concentration and the cuttings-bed height was proposed by dimensional analysis dependent on the thorough understanding of the effects of various variables. The predictions were good when they were compared with the experimental data obtained. Major factors influencing cuttings transport in the field during microhole drilling and conventional rotary drilling were compared, and the reasons for their differences were discussed. The limitations of the proposed model in this study were also discussed. These results could provide a factual basis for improving microhole-drilling hydraulics.

Enhancement of electrochemical discharge machining accuracy and surface integrity using side-insulated tool electrode with diamond coating

Electrochemical discharge machining (ECDM) is an emerging non-traditional processing technology used to machine electrical non-conductive material like glass and ceramics, by using the electrochemical discharge phenomena around the tool electrode. In the general ECDM drilling process, the gas film forms and electrical discharge appears at both the tool end and the tool sidewall that were exposed to the electrolyte. The undesirable sidewall discharge enlarges the hole entrance diameter and destroys the hole surface integrity. In order to prevent the sidewall discharge, a side-insulated tool electrode with a 4 μm-thick diamond coating layer was used in ECDM micro-hole drilling. The gas film formation and electrical discharge mostly happened on the tool end due to the insulation layer on the tool sidewall. Experiments showed that, compared with the traditional tool electrode, the side-insulated tool electrode achieves a smaller hole diameter and better surface integrity without an obvious heat affected zone at the hole entrance. Furthermore, the hole diameter nearly remains the same as the machining depth increases from 50 μm to 500 μm. The side-insulated electrode has an advantage in enhancing shape accuracy by reducing the taper angle of the micro hole. When the machining depth is 600 μm, the side-insulated electrode achieves a much smaller hole taper angle () than the traditional tool electrode does ().

Micro-Hole Drilling on Glass Substrates—A Review

Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (μTAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Advancements are constantly being made in this field, yet machining smooth through-glass vias (TGVs) with high aspect ratio remains challenging due to poor glass machinability. As TGVs are required for several micro-devices, intensive research is being carried out on numerous glass micromachining technologies. This paper reviews established and emerging technologies for glass micro-hole drilling, describing their principles of operation and characteristics, and their advantages and disadvantages. These technologies are sorted into four machining categories: mechanical, thermal, chemical, and hybrid machining (which combines several machining methods). Achieved features by these methods are summarized in a table and presented in two graphs. We believe that this paper will be a valuable resource for researchers working in the field of glass micromachining as it provides a comprehensive review of the different glass micromachining technologies. It will be a useful guide for advancing these techniques and establishing new hybrid ones, especially since this is the first broad review in this field.

Drilling of Microholes by Electrochemical Machining Using Ultrashort Voltage Pulses

Drilling of Microholes by Electrochemical Machining Using Ultrashort Voltage Pulses

Simulation of Spinneret Micro-hole Spade Drill Drilling Based on DEFORM-3D

An emulation study of the drilling by the spade drill on the spinneret micro-hole is conducted by using FEM analysis software Deform-3D. According to application of finite element software Deform-3D, some characteristic parameter of the work piece and the cutting tool material are set. The distributed situation of cutting force, cutting temperature and tool wear in different cutting parameters are simulated analysis. By discussing the location of the spade drill drilling wear, further optimization of parameters cutting and tool for the spinneret micro-hole drilling provide the better basis.

Effect of tool wear on microrods fabrication using reverse μEDM

ABSTRACTArrayed microrods are used to drill array of microholes in workpieces by Micro electrical discharge machining (μEDM). In comparison to a single microrod, the use of an array of microrods enables drilling of multiple microholes in lesser time, and hence it offers a higher productivity. The present work focuses on the effect of tool wear on the dimensions of the machined array of microrods through reverse micro electrical discharge machining (R-μEDM). The effects of the input parameters such as voltage, capacitance and feed rate on the obtained length and diameter of the microrods have been investigated. This study introduces a simple analytical model to evaluate the amount of tool wear and material removal from a bulk rod. As the levels of voltage and capacitance increase from lower to higher, the tool wear increases by 574%. At lower levels of voltage and capacitance, a straight array of microrods with a longer length of about 1.961 mm is obtained. On the other hand, at higher levels of voltage and capacitance, the obtained microrods are found to have a shorter length of 1.725 mm but with taper. Scanning electron microscope (SEM) and optical microscope images are also analyzed for describing the effects of tool wear on the shape and size of the fabricated microrods.

A highly efficient, stable, durable, and recyclable filter fabricated by femtosecond laser drilling of a titanium foil for oil-water separation

It has been a long standing challenge to efficiently separate oil and water since prehistoric times, and now it has become even more desirable in oily wastewater purification and oil spill cleanup. Here we introduce a super oil–water separation filter with superhydrophilicity and underwater superoleophobicity, fabricated using femtosecond laser micro-hole drilling of a titanium foil. Such a simply-made filter, without any modification, can achieve a separation efficiency exceeding 99% in eight typical oil–water mixtures. It remains highly efficient after 40 cycles of recycling and after suffering erosion by corrosive media. Furthermore, the used filter, polluted with oil, could be recovered by ultraviolet illumination. The flux of filtered water is tunable by simply selecting the aperture of the microhole or the spacing between adjacent microholes. Such advanced functionality is due to roughness and the TiO2 layers on the ablated surface during fabrication. With superhydrophilic and superoleophobic surfaces, this oil-water filer is also suitable for applications in anti-fouling, anti-smudge, anti-fog, and self-cleaning.

Preiskava profilov luknje pri globokem vrtanju mikroluknje v AISI 420 nerjavnem jeklu s pomočjo dielektrične tekočine s primešanim prahom

Preiskava profilov luknje pri globokem vrtanju mikroluknje v AISI 420 nerjavnem jeklu s pomočjo dielektrične tekočine s primešanim prahom

Drilling of Rod End Faces Using Micro-Cutting Tools

There have been few reports on the drilling of microholes on rod end faces by cutting, which can be employed for fabricating micronozzles or microneedles. Such drilling was therefore attempted in the present study using a micro turn-milling machine with the tool and workpiece axes being parallel. The drilling was performed on the end faces of brass rods with cemented tungsten carbide micro-cutting tools processed by electrical discharge machining (EDM). As a result, a microhole 12‍ μm in diameter was successfully drilled using a 10-μm-diameter tool at a feed speed of 0.5‍ μm/s. The feed speed could be increased to 25 μm/s for a tool with a diameter of 20 μm and body length of 50 μm.

Laser micro-hole drilling in thermal barrier coated nickel based superalloy

This investigation deals with laser drilling of micro holes in yttria stabilised zirconia coated nickel based superalloy using a power modulated fiber laser. The parameters taken into account are assist gas pressure, modulation frequency, pulse on time and hole inclination angle. These parameters affect the important geometrical characteristics of holes, e.g., hole diameter, hole wall smoothness, taper angle and recast layer thickness. It has been found that the assist gas pressure has a significant effect on hole entry and exit diameter, taper angle and hole wall smoothness. It has also been observed less number of pulses of higher energy produces a hole with smaller entry and exit diameter, smaller taper angle, smoother hole wall and a thin stretched recast layer (∼ 15μm). The minimum achieved hole entrance diameter, exit diameter and taper was 342 μm, 200 μm and 3.54° respectively. Off normal drilling produces a hole with elliptical entrance. The eccentricity of such holes increases with inclination angle. Thick recast layers are produced at high inclination angles.

Movement characteristics of micro drill bit during entry period in PCB high speed drilling

Purpose The purpose of this paper is to study the movement characteristics of micro drill bit during entry period in printed circuit board (PCB) high-speed drilling and to present an effective method to conduct quantitative analysis of the wandering of drill bit based on high-speed video capturing. Design/methodology/approach Based on the high-speed camera technology, experiments are conducted to get a series of time sequence images and the wandering of micro drill tip and the radial run-out of drill body, and the max-deformation of drill bit are calculated by using a quantitative analysis method. Finally, the movement characteristics of micro drill bit during entry drilling period PCB high-speed drilling are evaluated. Findings With the increasing spindle speed, the radial run-out of drill body decreases gradually, whereas the wandering amplitude of the drill point gradually increases; micro drill bit itself has an ability of positioning deviation correction after contacting the entry sheet; the feed rate within a certain range could slightly worsen the deformation of drill tip at the instant of impingement. Research limitations/implications With the improvement of spindle speed, the camera’s shooting speed needed will increase accordingly, thus, the resolution of the pictures will decline, which always affects the analysis precision. Originality/value A series of effective methods to conduct quantitative analysis of the wandering micro drill bit by using high-speed camera technology is presented; a reference for the optimization of micro-hole drilling is provided.

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

The moderately high lateral RS gradients (on the order of tens of MPa/μm) near shot peened notches in conjunction with the shallow treatment depth (some hundreds of microns) limit the application of far-field and/or high resolution synchrotron diffraction residual stress measurement techniques. Recently proposed Focused Ion Beam – Scanning Elecron Microscope – Digital Image Correlation (FIB-SEM-DIC) based micro mechanical stress relaxation methods for the measurement of residual stress at the micron scale became suitable techniques for local evaluation of residual stresses and stress gradients in shot peened specimens. In this paper ultra-high resolution (~0.5–0.8 μm depth and 5–10 μm lateral resolution) mechanical relaxation stress measurements were used to evaluate the stress variation local to individual peening dimples in ceramic (60–120 μm diameter beads) shot peened Al-7075-T651 double notched samples having 0.15, 0.5 and 2.0 mm radii using Micro-Hole Drilling (μHD), Micro-Slot Cutting (μSC) and micro X-ray Diffraction (μXRD) methods. The micron-sized sampling volumes enabled the stress to be evaluated in individual impact craters (dimples) showing significant point-to-point variation (~ +/−150 MPa) (with certain dimples even recording tensile stresses). After around 30 μm of layer removal the heavily deformed region had largely been removed and the stress profile became much more homogeneous. At this depth the μHD and μSC results were in good accord with those from μXRD measurements which sample over a much larger volume (~40 μm depth × 50 μm laterally) showing an in-plane compressive stress of around 150 MPa far from the notches with the residual stress rising to about 200 MPa at a blunt (2 mm) notch and 500 MPa for a sharp (0.15 mm) one. Further, these recorded variations of residual stresses were correlated with microstructural features, e.g. grains, networks of sub-surface cracks, intermetallics and highly deformed sub-surface regions, revealed by large volume Serial Sectioning Tomography using Plasma Xe+ Focus Ion Beam – Scanning Electron Microscope (PFIB-SEM), EDS and EBSD maps. This allowed for the first time characterize large volume (100 × 66 × 30 μm3) of shot peened regions with resolution of dozens of nanometers and correlate residual stress depth profiles with 3D microstructural features. Finally, in (Benedetti et al. 2016, Int. J. Fatigue) these RS measurements are used to reconstruct the RS field through finite element (FE) analyses.

The effect of residual stress on the Preferential Intergranular Oxidation of Alloy 600

Alloy 600 was exposed to H2-steam to simulate the oxidation that occurs in high temperature water where this alloy is known to be susceptible to SCC. Analytical electron microscopy was employed to characterize the early stages of oxidation to aid in developing an understanding of the stress corrosion cracking behaviour of this alloy. The oxide consisted of sub-surface Cr2O3 particles, preferential intergranular oxidation and formation of surface Ni nodules. The measurements of residual stresses at the microscopic level using a recently-developed FIB micro-hole drilling technique revealed a correlation between local stress variations at the grain boundaries and the oxide morphology.

Fabrication of disk microelectrode arrays and their application to micro-hole drilling using electrochemical micromachining

Minimal-taper microholes are widely used in modern industries. Electrochemical micromachining (EMM) has been demonstrated to be a feasible method to fabricate these microholes. In this study, based on its unique processing properties and productivity, a disk microelectrode array was fabricated via electrolysis for producing micro-holes. The dimensions of the cathode for hydrolysis were optimized by applying the finite element method to the constructed physical model. A 3×3 disk microelectrode array and a 5×5 cylindrical microelectrode array with uniform dimensions were then fabricated using the optimized cathode. Micro-holes were drilled on stainless-steel plates using both disk and cylindrical microelectrode arrays. The taper of the resulting micro holes obtained using the new disk microelectrode array was lower than that of the holes formed using the cylindrical microelectrode array. The effects of EMM parameters, including the applied voltage, feeding speed, and pulse-on time, on the hole diameter and taper were also investigated. The results suggest that appropriate machining parameters should be selected in consideration of the effects of these parameters on hole diameter, taper, localization, and material removal rate.

Laser drilling of micro-holes with small diameter beyond the limits of focused spot by using a sieve plate or a cover plate

To break through the limits of the focused spot diameter to achieve holes with smaller diameter, a method is proposed by using a sieve plate or a cover plate. The experiments were conducted on 2-mm-thick stainless steel workpieces by using a millisecond pulsed laser. Four variables including pulse frequency, focal plane position, sieve diameter, and distance were chosen as the parameter variables. The entrance and exit diameters were measured with a confocal microscope. And, the taper was calculated. The results show that the focal plane position and distance were significant influencing factors. Negative focal plane position and a short distance could get smaller-diameter holes with lower taper. However, the pulse frequency had no significant influence on the entrance diameter and taper. A small sieve diameter was useful to get smaller-diameter holes with lower taper; however, it needed to apply a thicker cover plate to obtain a small diameter hole. The smallest holes obtained by using a sieve plate or a cover plate were at least 10 % less than the focused spot diameter and 20 % less than the diameter by laser directly drilling.

Modeling and Multiresponse Optimization of Quality Characteristics for the Micro-EDM Drilling Process

Micro parts of various kinds are now in demand for fabricating high-tech products such as micro-electronic parts and MEMS applications. In order to supply these micro parts, the development of micromachining technology becomes increasingly important. Among the various stages of micromachining, the fabrication of holes and pins of precise nature are essential for many miniature components. Micro-hole drilling, is used in various precision industries, such as the production of automotive fuel injection nozzles, watch and camera parts to generate deeper holes with better straightness, better roundness and smoother surfaces. Electrical discharge machining (EDM) is a non-contact machining process for electrically conductive materials which can produce high aspect ratio holes, particularly useful in the tool making industry. The objective of the study on micro-EDM drilling process parameters is to analyse the effect of drilling parameters such as the feed rate (A), capacitance (B) and voltage (V) on machining stainless steel shim using a tungsten electrode of 300 µm diameter. The performance measures are surface roughness (Ra), metal removal rate and tool wear ratio. Response surface methodology has been used and experiments have been conducted using central composite design. Statistical models of the output responses have been developed using three level full factorial design of experiment. The developed models have been used for multi response optimization by desirability function approach to determine the optimum machining parameters. These optimal machining parameters are then validated experimentally, and it is observed that the response values are very close to the predicted values with less error.

Residual stresses reconstruction in shot peened specimens containing sharp and blunt notches by experimental measurements and finite element analysis

The knowledge of the residual stress (RS) field in the vicinity of a notch is of paramount importance to understand the fatigue resistance of shot peened components containing such stress raisers. In the first part of this work (Winiarski et al. 2016, Exp. Mech.), RS were measured along the notch bisector using non-destructive and destructive techniques, namely micro-XRD and FIB-SEM DIC micro-slot cutting (μSC) and micro-hole drilling (μHD). These indicate an increasing concentration of the longitudinal residual stress component with increasing sharpness of the notch. In this paper, these linescan measurements are used to reconstruct the complete RS field through finite element (FE) analyses. Specifically, RSs are introduced into the FE model using thermal misfit strains (eigenstrains), whose intensity and spatial distribution are deduced by fitting the experimental data. Since the eigenstrains depend on the actual notch geometry, their distribution cannot be estimated from residual stress distributions measured on plain or notched specimens of different geometry. The proposed approach can be very useful to estimate the notch fatigue resistance of shot peened components on the basis of local stress and fracture mechanics approaches.

A study to explore the properties of electrochemical discharge effect based on pulse power supply

Spark assisted chemical engraving (SACE) is an effective non-traditional processing technique that can be used to process non-conductive and hard brittle materials, like glass and engineering ceramics. In this study, the properties of electrochemical discharge effect based on pulse voltage were explored. To research the critical voltage of the electrochemical discharge, the effect of the electrolyte and its concentration, the diameter and the rotational speed of the tool electrode, the pulse frequency, and the duty cycle of the pulse voltage were discussed. The results indicate that changes of the parameters, except changing the rotational speed, have great influence on the critical voltage. The film formation time and the mean electric current were also discussed in this study by measuring electric current signal. In addition, the micro-hole drilling was carried out. The results show that the machining accuracy is better at the initial voltage.

Study of Vibration Assisted Inclined feed Micro-EDM Drilling

Transport of the fresh dielectric fluid into the discharge gap as well as debris removal from the hole becomes more difficult and essential in micro-EDM deep hole drilling. To solve this problem horizontal-feeding of electrode in EDM drilling of micro hole had been investigated, but the depth of hole which can be drilled is still very limited. An approach of micro-EDM drilling by inclined feeding of the electrode incorporated with vibration of the electrode in the longitudinal direction is proposed and implemented. It is found that either inclined feeding or axial vibration of the electrode leads to an increase of the depth of the hole being drilled as compared with horizontal-feeding method. A significant improvement is obtained when both are applied simultaneously. The depth of hole is increased by 75% when the aluminum alloy 6061 is drilled by a 200μm in diameter electrode using a 10-degrees downward electrode feeding together with the axial vibration having the frequency and amplitude of 250Hz, and 5μm, respectively. The maximum aspect ratio achievable is 24 in this case. It is 26 for the stainless steel drilled by a 100μm in diameter electrode, and 18 when the size of electrode is reduced to 50μm in diameter.

超短電圧パルスを用いた電解加工による微細穴あけ加工

超短電圧パルスを用いた電解加工による微細穴あけ加工