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Historic quay walls in many Dutch cities are supported by an array of vertical timber piles which run through soft soil deposits and rest on a sand layer, providing end-bearing support. As these structures experience horizontal loads, the foundation piles are loaded in bending. This is the dominant loading case of pile foundations of dams, lock heads, and sometimes bridge abutments as well. To accurately model and evaluate the timber pile foundations, a proper estimate of their bending properties is essential. Therefore the mechanical properties of existing spruce foundation piles, retrieved from a historic quay wall (1905) at Overamstel in Amsterdam, Netherlands, were studied. Six piles were subjected to a four-point bending experiment. The outer fiber stress was kept constant between the point loads, leading to a failure at the weakest cross section. Measurements of the curvature and force distribution were taken along the pile length during loading. In addition, biological decay in the outer layer of the timber piles, also referred to as the soft shell, was identified with microdrillings. Internal strains were measured successfully by gluing fiber-optic wires inside the soft shell of the timber piles. The experiments indicated significant variations in modulus of elasticity and modulus of rupture across the tested population, but indicated a strong correlation. Modulus of elasticity averaged 16.5 GPa with a variation coefficient of 0.30, whereas the modulus of rupture averaged 23.2 N/mm2 with a variation coefficient of 0.26. Bacterial deterioration was found to be independent of both the outer pile diameter and the location along the timber pile. The soft shell had an average thickness of 21 mm, but it did not contribute significantly to the structural strength of the piles. This study could present a template for assessing the remaining service life not only of historic quay walls but also of other timber pile foundations under bending loads. [ABSTRACT FROM AUTHOR]

The acoustic signals used by tool wear monitoring systems adopted in microdrilling are degraded by the noise present in manufacturing environments. To overcome this problem, the present study designed a system containing a 4 × 4 microelectromechanical system microphone array and a three-axis accelerometer to achieve accurate tool wear monitoring in noisy manufacturing environments. Features that were moderately to strongly correlated with tool wear were selected as inputs for this system's one-dimensional (1D) convolutional neural network (CNN) model for predicting tool wear. Pearson correlation analysis revealed that the frequency-domain signal features captured by a 4 × 4 microphone array with minimum variance distortion-less response (MVDR) beamforming had stronger correlations with tool wear than did those captured by a 4 × 4 or 1 × 2 microphone array with delay-and-sum beamforming or by a single microphone; this was because the signals captured by the 4 × 4 array with MVDR beamforming were less noisy. For the aforementioned microphone configurations, under the presence of noise, the 1D CNN model predicted severe wear with higher accuracy when it was trained using fused high-correlation features obtained from the signals captured by the 4 × 4 microphone array with MVDR beamforming and an accelerometer (97.6%) than when it was trained using unfused signal features captured by the accelerometer (86.7%) or the 4 × 4 microphone array with MVDR beamforming (90.3%) alone. The tool wear prediction accuracy obtained using the aforementioned fused features was close to that obtained using fused features acquired from the signals of one microphone and an accelerometer in a quiet environment (97.0%). [ABSTRACT FROM AUTHOR]

Purpose: To investigate the surgical outcomes of arthroscopic pull-out repair for medial meniscus root tear (MMRT) combined with the marrow stimulation procedures (MSP) for accompanying high-grade cartilage lesions. Methods: Patients who underwent arthroscopic pull-out repair for MMRT between 2010 and 2019 were retrospectively reviewed. Patients who had at least 3 years of follow-up were included and classified into two groups according to whether MSP (microfracture or microdrilling) were performed on cartilage lesions in the medial tibiofemoral joint (group 1, patients with International Cartilage Repair Society [ICRS] grade 0–3a lesions and did not undergo MSP; group 2, patients with ICRS grade 3b–3d lesions and underwent MSP). Comparative analyses, including non-inferiority trials, were conducted between groups for subjective and objective outcomes. In addition, group 2 was further divided into two subgroups according to cartilage lesion size and compared with group 1 (group S, ≤ 2.0 cm2; group L, > 2.0 cm2). Results: A total of 94 patients were included (group 1, 68 patients; group 2, 26 patients). There were no significant differences in clinical scores at postoperative 3 years and final follow-up between groups 1 and 2, but group 2 failed to satisfy the non-inferiority criteria compared to group 1 overall. In objective outcomes, group 2 did not meet the non-inferiority criteria for the rate of osteoarthritis progression compared to group 1, and it also showed a significantly higher proportion of high-grade osteoarthritis at final follow-up (P = 0.044) and a higher degree of osteoarthritis progression than group 1 (P = 0.03 for pre- to postoperative 3 years, and P = 0.006 for pre- to final follow-up). In additional evaluations comparing the subgroups of group 2 and group 1, group S showed relatively favourable results compared to group L in objective outcomes at final follow-up. Conclusion: Patients who underwent arthroscopic pull-out repair for MMRT combined with MSP for accompanying high-grade cartilage lesions showed suboptimal outcomes compared to those with no or low-grade lesions at mid-term follow-up. High-grade cartilage lesions ≤ 2.0 cm2 may be candidates for the surgical repair of MMRT if MSP are performed, but those with larger lesions may require alternative treatment strategies. Level of evidence: III. [ABSTRACT FROM AUTHOR]

Micro-EDM is an unconventional technology used to machine every type of electrically conductive material regardless of its mechanical properties. Material removal occurs through electrical discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling operations, the technology is able to realise microholes with excellent quality in terms of precision, quality surface, roundness, and taper to the detriment of the machining time, which is less than other technologies. Several efforts are being made to improve different features related to the process performance that are severely affected by both the operative conditions, such as the electrode material or the type of dielectric, and process parameters. The typical indexes used to characterise the performance are the machining time, the material removal rate, and the geometric indexes. These indexes are very effective and are easily measurable, but they do not give information about the evolution of the drilling process, which could be irregular due to the different phenomena occurring during machining. The aim of this paper is the development of a method able to elaborate the motion law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was manufactured in several steps, recording both the machining time and electrode wear for each step. In this way, the actual position of the electrode during the drilling can be measured without the use of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did not introduce new phenomena, in contrast to the traditional drilling operation. This method was used to study the effects of the electrode diameter, the type of electrode, the length of the electrode out of the spindle, and the entity of the run-out on the process performance. The tests were executed on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It was found that the descent of the electrode into the workpiece was not regular, but it depended on the level of debris concentration in the machining zone. The debris concentration was influenced by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM drilling process, contributing to a better understanding of the physical aspects of the process. [ABSTRACT FROM AUTHOR]

Recently, there has been a growing awareness of environmental issues, and the concept of sustainability has been introduced. This concept applies to different fields, including the manufacturing industry. This study focuses on the sustainability of the micro-electrical discharge machining (EDM) drilling process. In EDM technology, the critical aspects of sustainability are consumed energy, electrode wear, gas emissions, and generated waste. The operational conditions impact consumption and emissions. The aim of this study is to develop a CO2 efficiency index for evaluating the environmental–economic efficiency of the micro-EDM drilling process. The index was calculated as the emissions that occurred during machining and logistic activities divided by the added value, and it was expressed as the kg equivalent CO2 per unit money. For the emissions, all process activities that have an environmental impact were considered, such as transportation, absorbed energy generation, production of fumes by the dielectric during machining, and emissions attributed to the production of nonconforming pieces. The proposed index was applied to a medical case study in which titanium bone plates were produced for fractures of small body parts. It was found that the process performance significantly depended on the operation conditions of the dielectric fluid and electrode. The material removal rate (MRR) significantly influenced the index. Quality problems and scraping influenced the overall performance significantly, whereas dielectric management had a moderate effect. The optimum conditions were determined by varying the dielectric fluid, electrode material, and process parameters. Demineralized water was the best dielectric because it facilitated a high MRR, whereas hydrocarbon oil resulted in a high quality and a low scrap rate. Vegetable oil caused problems, resulting in a low MRR and poor quality. Further investigations should be conducted to improve its performance in microdrilling applications. [ABSTRACT FROM AUTHOR]

The mechanisms of deep-hole microdrilling of pure Mg material were experimentally studied in order to find a suitable setup for a novel intraocular drug delivery device prototyping. Microdrilling tests were performed with 0.20 mm and 0.35 mm microdrills, using a full factorial design in which cutting speed v c and feed f z were varied over two levels. In a preliminary phase, the chip shape was evaluated for low feeds per tooth down to 1 μm, to verify that the chosen parameters were appropriate for machining. Subsequently, microdrilling experiments were carried out, in which diameter, burr height and surface roughness of the drilled holes were examined. The results showed that the burr height is not uniform along the circumference of the holes. In particular, the maximum burr height increases with higher cutting speed, due to the thermal effect that plasticizes Mg. Hole entrance diameters are larger than the nominal tool diameters due to tool runout, and their values are higher for high v c and f z . In addition, the roughness of the inner surface of the holes increases as f z increases. [ABSTRACT FROM AUTHOR]

Micro-EDM is an unconventional technology used to machine every type of electrically conductive material regardless of its mechanical properties. Material removal occurs through electrical discharges between the workpiece and the electrode immersed in a dielectric fluid. In drilling operations, the technology is able to realise microholes with excellent quality in terms of precision, quality surface, roundness, and taper to the detriment of the machining time, which is less than other technologies. Several efforts are being made to improve different features related to the process performance that are severely affected by both the operative conditions, such as the electrode material or the type of dielectric, and process parameters. The typical indexes used to characterise the performance are the machining time, the material removal rate, and the geometric indexes. These indexes are very effective and are easily measurable, but they do not give information about the evolution of the drilling process, which could be irregular due to the different phenomena occurring during machining. The aim of this paper is the development of a method able to elaborate the motion law of the electrode during the micro-EDM drilling operation. In order to do this, a single hole was manufactured in several steps, recording both the machining time and electrode wear for each step. In this way, the actual position of the electrode during the drilling can be measured without the use of a predictive model for electrode wear. It was tested to confirm that the multistep procedure did not introduce new phenomena, in contrast to the traditional drilling operation. This method was used to study the effects of the electrode diameter, the type of electrode, the length of the electrode out of the spindle, and the entity of the run-out on the process performance. The tests were executed on titanium alloy sheets using a tungsten carbide electrode and hydrocarbon oil as the dielectric. It was found that the descent of the electrode into the workpiece was not regular, but it depended on the level of debris concentration in the machining zone. The debris concentration was influenced by the type and diameter of the electrode, its length out of the spindle, and, to a lesser extent, the run-out. This method was found to be a useful method for an in-depth analysis of the micro-EDM drilling process, contributing to a better understanding of the physical aspects of the process.

The global demand for air travel and air transport is expected to further increase in the next couple of years, and so the environmental protection will also increasingly come into focus again. In the aviation sector, this means not only saving fuel and reducing emissions but also reducing the noise pollution caused by aircrafts. For this purpose, sound-absorbing acoustic liners are used, which consist of a sandwich structure with one perforated skin layer. To reduce weight, these outer layers are often made of carbon fiber-reinforced plastic (CFRP). For manufacturing these CFRP skin layers, laser drilling offers specific benefits, but when it comes to industrial applications, further process improvements are necessary. Although laser microdrilling is a well-known process in laser materials' processing, it has not yet been sufficiently investigated for the processing of carbon fiber-reinforced plastics. This study investigates the quality and efficiency of laser microdrilling with a 1.5 kW nanosecond-pulsed high-power laser for percussion drilling and helical drilling of thin CFRP laminates. The efficiency was evaluated in terms of drilling depth, the amount of energy required to remove a specific volume of material, and the time required to remove a specific volume of the material. The quality evaluation focused on the heat-affected zone and the hole taper. The efficiency and quality results were set in relation to higher-level parameters such as energy fluence in the laser spot, pulse overlap, or total energy applied. This facilitates future transferability to similar laser processes that may use laser machines and system technology with deviating specifications. [ABSTRACT FROM AUTHOR]

In microbiochips and microfluidic devices, microholes are a basic and important feature. The microdrilling of glass materials without cracks is still challenging in the fabrication of glass-based microdevices. This paper investigates the characteristics of microdrilling fused silica using polycrystalline diamond (PCD) tools fabricated by electrical discharge machining (EDM). In particular, peak forces, which are observed at the beginning of drilling, are discussed because crack formations are related to peak forces. To reduce peak forces and to minimize cracks, the effects of drilling conditions, such as tool shape, the surface roughness of a tool, and axial feedrate, were therefore investigated. It was observed that D-shape tools with high surface roughness was useful to reduce the peak force. In through-hole drilling, a sacrificial layer was used to prevent exit cracks, and a variable feedrate was applied to increase drilling speeds. Finally, a dressing process using EDM was conducted to recondition the worn tool's surface. [ABSTRACT FROM AUTHOR]

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This study analyses the possibility of assessing standing-tree wood density by microdrilling during tending forestry work carried out on Norway spruce stands. The research material comes from 4 experimental plots and consists of 270 trees (78 trees = control variant, 85 trees = moderate variant, and 107 trees = strong variant). The research objectives were to: (1) highlight wood density particularities, (2) identify wood resistance to microdrilling particularities, and (3) assess standing-tree wood density by microdrilling. For the control variant, average density recorded values of 0.357 ± 0.021 and 0.386 ± 0.027 g·cm−3; in the moderate variant, values were between 0.359 ± 0.029 and 0.393 ± 0.027 g·cm−3; and the strong variant was characterized by the limits of 0.364 ± 0.020 and 0.397 ± 0.027 g·cm−3. Average microdrilling resistance values were between 16.6 ± 2.6 and 22.5 ± 3.0% for the control variant; the moderate variant was characterized by the limits of 18.3 ± 3.1 and 23.4 ± 3.3%; and the strong variant recorded value of 19.7 ± 2.6 and 20.5 ± 2.6 (1.5)%. The linear regression results showed that microdrilling resistance increased as wood density increased. Additionally, generalized linear models showed that, when using covariates of microdrill resistance and tree diameter at breast height, there was a significant influence on the dependent variable, wood density, for all considered work variants. These results suggest that it is possible to consistently estimate both quality and resistance in Norway spruce standing trees using microdrilling. Our findings suggest that wood density and microdrilling resistance are dependent on biometric and qualitative characteristics, as well as the amount of tending forestry work conducted on Norway spruce stands. [ABSTRACT FROM AUTHOR]

This study analyses the influence of a planting scheme on physical properties of Norway spruce wood. The research material consisted of 326 Norway spruce trees (Picea abies (L.) H. Karst) selected from an experimental plot with four planting variants (2500, 3330, 5000, and 7510 trees·ha−1). The research aspects were: (1) wood density (measured by volumetric method and using microdrilling resistance as proxy), (2) microdrilling resistance, and (3) sound speed. There was a decrease in wood density values (from 0.3376 to 0.3367 g·cm−3) and in microdrilling resistance values (from 15.136% to 14.292%) as the number of trees·ha−1 used for plantation increased from 2500 to 5000. The planting variant with 7510 trees·ha−1 had the largest value (0.3445 g·cm−3 for wood density and 15.531% for microdrilling resistance). Sound speed decreased from 1032.8 to 989.8 m·s−1 as the number of trees·ha−1 increased from 2500 to 7510. These results show a relationship between DBH values and studied physical properties. This relationship is more evident for variants with low planting density (e.g., 2500, 3330 trees·ha−1) than that of dense planting variants (e.g., 7510 trees·ha−1). The explanation may be that the growth of trees in dense plantings is slower; in less dense planting variants, the increase in wood is greater, and as a result, wood volumetric density dependence on the DBH value is greater. [ABSTRACT FROM AUTHOR]

The mechanisms of deep-hole microdrilling of pure Mg material were experimentally studied in order to find a suitable setup for a novel intraocular drug delivery device prototyping. Microdrilling tests were performed with 0.20 mm and 0.35 mm microdrills, using a full factorial design in which cutting speed vc and feed fz were varied over two levels. In a preliminary phase, the chip shape was evaluated for low feeds per tooth down to 1 μm, to verify that the chosen parameters were appropriate for machining. Subsequently, microdrilling experiments were carried out, in which diameter, burr height and surface roughness of the drilled holes were examined. The results showed that the burr height is not uniform along the circumference of the holes. In particular, the maximum burr height increases with higher cutting speed, due to the thermal effect that plasticizes Mg. Hole entrance diameters are larger than the nominal tool diameters due to tool runout, and their values are higher for high vc and fz. In addition, the roughness of the inner surface of the holes increases as fz increases.

In microbiochips and microfluidic devices, microholes are a basic and important feature. The microdrilling of glass materials without cracks is still challenging in the fabrication of glass-based microdevices. This paper investigates the characteristics of microdrilling fused silica using polycrystalline diamond (PCD) tools fabricated by electrical discharge machining (EDM). In particular, peak forces, which are observed at the beginning of drilling, are discussed because crack formations are related to peak forces. To reduce peak forces and to minimize cracks, the effects of drilling conditions, such as tool shape, the surface roughness of a tool, and axial feedrate, were therefore investigated. It was observed that D-shape tools with high surface roughness was useful to reduce the peak force. In through-hole drilling, a sacrificial layer was used to prevent exit cracks, and a variable feedrate was applied to increase drilling speeds. Finally, a dressing process using EDM was conducted to recondition the worn tool’s surface.

The ability to drill smaller size holes down to micron level is a challenging task in many industries that manufacture high-tech products. Due to restriction in the tool size existing in conventional manufacturing, nonconventional approaches are being adopted to meet the challenges related to miniaturization. Laser sources have emerged as a clean source of energy for microfabrication techniques. In this work, micron level holes in the polyethylene terephthalate (PET) substrate are fabricated with fiber laser machining arrangement. Design of experiments (DOE) was used to perform the experiments giving equal weightage to all the input variables and the results were analysed through analysis of variance (ANOVA) to develop the optimization model. Experiments have been performed while taking power, frequency, pulse on time and cycle time as process parameters and hole diameter and heat affected zone (HAZ) as output parameters. Further, a mathematical model has also been developed and simulated for the hole fabrication through laser as the energy input. The experiment conducted using the optimized parameters resulted in hole diameter of 457 µm and HAZ thickness of 284 µm. [ABSTRACT FROM AUTHOR]

Aims: The modeling of the surgical steps with creating a suitable laboratory models is critically important issue in the successful gaining of microneurosurgical practice. In this experimental study, a laboratory-training model was created for microneurosurgical drilling of delicate and thin cranial base bones using walnut shell in the repetitive repeating of experimental microsurgical training technique. Materials and Methods: All steps of this study were performed under the operating microscope. Twenty-five walnut shells were used for this experimental feasibility study. The difficulty and suitability of the model were evaluated in terms of the usability in the training of microneurosurgical microdrilling. Difficulty of the procedure was divided into three degrees (very easy, easy, and difficult). The objective criterion for the evaluation of the difficulty of the procedure was the protection of the interior organic material during the procedure. The suitability of the procedure was also evaluated within three groups, bad, good, and perfect. Results: In three (12%) walnut shells, the microdrilling was evaluated as difficult. The microdrilling procedures of the twelve (48%) walnut shells were evaluated as easy procedure. Microdrilling procedure of the remaining ten (40%) of the walnut shells was evaluated as very easy. The suitability of the model was evaluated as bad in two (8%) of the walnut shells. The suitability was found as good in 17 (68%) of the walnut shells. In microdrilling of the remaining six (24%) of the walnut shells, the suitability of the model was evaluated as perfect. Conclusion: Microsurgical drilling of the walnut shells without any interior organic injury is accepted as the indication of the successful surgical microdrilling process. Consolidation of the surgical practice in a laboratory setting, grasping, and using of microsurgical instruments can be repeated several times in this model. We believe that this model will contribute to the practical training of microneurosurgery. [Arch Clin Exp Surg 2018; 7(1.000): 24-28]

Micromachining is becoming most viable with assorted revamped technologies, due to their numerous ultra-rigor machining criterions. An advanced manufacturing practice like electrochemical micromachining (EMM) grips multitudinous applications with a notable demand in the advancement of microproducts like microfluidic systems, chemical reactors, and heat exchanger components. This paper justifies the channelling and drilling acts over one of the idiosyncratic super alloys, i.e. Hastelloy C-276, with a mask-less SS-304 tool electrode using NaNO3 electrolyte by EMM, to construe the impact of stray current and its consequences over the mask-less electrodes and most possibly endeavour to attain dimensionally altered features. The current research work highlights to discern the effects of process criterions like pulse on/off time, electrolyte concentration, applied voltage and microtool feed rate during the perusal experimentation; a reified study over the machined surface has also been scrutinized through by means of microstructural and EDS analysis. Experiments were planned and empirical models were developed for various process parameters on output responses by endorsing response surface methodology. Validations of the models were tested and optimal sets of outputs have been found by the endorsement of multi-objective desirability–based optimization using particle swarm optimization (MOPSO). [ABSTRACT FROM AUTHOR]

Over past few decades, the electronic boards density and performance are enhanced by entrenching the components in the interior surfaces of the printed circuit boards (PCBs).The worthiness of this novel innovation has to be probed to warranty the functioning of electronic boards acquiesced to callous environments. In this study, a novel advancement concentrating on the development of bio‐based materials for the PCB applications has been documented. The bio‐based composite from rice husk‐epoxy resin could impendingly substitute the conventional synthetic fiber reinforced epoxy composites in PCB applications. The essential properties of biocomposites were assessed such as tensile and bending properties, dielectric property, thermal properties, moisture absorption, microdrilling, biodegradability, and flammability. Results obtained found that, these biocomposites were promising for PCB application. [ABSTRACT FROM AUTHOR]

The development in manufacturing has insisted upon the fabrication of microdrilled holes on orthopedic implants, with finished side wall (devoid of cracks and burr), thin recast layer, low taper, and improved circularity at entry and exit of the hole. In this study, therefore, a multiobjective optimization of wire electric discharge machining microdrilling response characteristics is addressed in order to improve the hole quality characteristics and viability of implants. To improve the quality characteristics of the hole, a hybrid statistical analysis is developed based on grey relational analysis and coefficient of variation. It identifies the key process parameters that are responsible for improving the quality of the hole. The parametric study also reveals that wire feed rate and servo feed rate have a striking effect on the quality of the hole. An important implication of this study is that a thin recast layer, improved entry and exit circularity, adequate taper were observed under optimum drilling condition. [ABSTRACT FROM AUTHOR]

In laser beam micromachining process, the quality of the drilled hole is of great importance. The quality of the microdrilled hole mainly depends on appropriate selection of process parameters. Predefined diameter of hole with minimum taper is of today's demand. The composite used for microdrilling operation is alumina–aluminium (Al2O3–Al) interpenetrating phase composite (IPC), which is widely used in aircraft and space stations. Until date, no experimental study has been done to obtain microdrilled hole of desired diameter. In the present paper three hole qualities such as hole diameter at entry, at exit and hole taper have been optimized individually as well as simultaneously using a central composite design (CCD) based on response surface methodology (RSM) during pulsed Nd:YAG laser microdrilling operation on alumina–aluminium IPC sheet of 1.14 mm thickness. The analysis of variance (ANOVA) test has also been done to identify the process parameters that contributed the most to get desired hole quality.

Background and Objective: Repetitive practicing of microneurosurgical techniques in experimental laboratory using real surgical instruments on training models is extremely important before starting the real surgical interventions. The modeling of the surgical steps with creating of suitable laboratory models is also another important issue in the successfully gaining of microneurosurgical practice. Materials and Methods: In this experimental study, it was created a laboratory training model for microneurosurgical drilling of cranial bones including the close location with the neural and vascular structures. All steps of this study were performed under the operating microscope. Twenty-five fresh chicken wings obtained from supermarket were used for this study. The difficulty and suitability of the model was evaluated in terms of the usability in the training of microneruosurgical microdrilling. Difficulty of the procedure was divided as three degree (very easy, easy, and difficult). The objective criterion for the evaluation of the difficulty of the procedure was the protection of the neurovascular and muscular structures during the procedure. Results: The suitability of the procedure was also evaluated within three groups as bad, good, and perfect. In four (16%) chicken wing's bone, the difficulty of the microdirilling was evaluated as difficult. Fifteen (60%) of the chicken wing's bones were microsurgically drilled with easy procedure. The remaining six (24%) of the wing's bone microdrilling was evaluated as very easy procedure. The suitability of the model was evaluated as bad in three (12%) of the chicken wing's bone. The suitability was found as good in 16 (64%) of the bones. In the remaining three (24%) of the chicken wing's bone microdrilling, the suitability of the model was evaluated as perfect. Conclusion: Microsurgical drilling of the chicken wing's bone without any vascular and muscular injury is accepted as the indication of the successfully surgical microdrilling process. Consolidation of the surgical practice in a laboratory setting, grasping and using of microsurgical instruments, can be repeated in several times in this model. We believe that this model will contribute to the practical training of microneurosurgery. [ABSTRACT FROM AUTHOR]

Day-to-day interest is growing in the drilling of high aspect-ratio deep microholes in various hard-to-machine and newer materials. Besides cost-effectiveness in the manufacturing process, an accurate dimension with the good surface finish is essential for microhole drilling. The conventional methods encounter various problems such as residue stresses, heat generation near cutting zone, high tool-wear, etc. Electrochemical microdrilling (ECMD) is one of the cost-effective techniques, provide a better alternative in drilling microholes with reasonably accurate dimensions and good surface finish in various industrial applications especially in computer, electronic, and aerospace industries. This article reviews current researches and developments of electrochemical processes for circular microholes drilling. It highlights the effects of various key factors (such as the development of microtools, electrolyte, inter-electrode-gap monitoring and control, etc.) on the aspect-ratio and accuracy of circular microholes, produced by ECMD. For further research, it will open up various challenging opportunities, especially in the field of (i) development and handling of microtool electrodes, (ii) development and handling of electrolytes medium, (iii) development in monitoring and controlling techniques of inter-electrode-gap, and (iv) development in strategies for process control for drilling high quality, deep and high aspect-ratio circular microholes into hard-to-machine materials using ECMD. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of process parameters on the hole geometric features, experiments were conducted based on response surface methodology (RSM) as one of the most useful design of experiments (DOE) approaches. Frequency of the laser beam (80 to 240 Hz), duty cycle (20.00 to 40.00%) and laser power (100.00 to 200.00 W) were considered as independent variables, while the entrance and exit hole diameters and their circularity as well as the hole taper were raised as process outputs. The experiments were performed on samples of thin AMS 5510 stainless steel 321 sheet with thickness of 0.01 inch by a 500.00 W fibre laser. The results indicated that the entrance hole diameter and hole taper decrease when the laser pulse frequency increases and laser power decreases. Also, laser frequency has a double reaction before duty cycle and laser powers on circularity of entrance hole. Minimum hole taper, minimum entrance diameter, and maximum circularity of entrance hole were considered as optimization criteria. Verification experiments were carried out to analyse the results obtained via software. [ABSTRACT FROM AUTHOR]

Plagioclase crystals in andesites from the Cabo De Gata region show generally radiogenic Sr isotope compositions and consistent core to rim increases in 87 Sr/ 86 Sr that are indicative of open system processes in the lithosphere and crustal contamination during crystallization. High-grade metamorphic rocks of the Alpujárride and Nevado-Filábride complexes represent the most likely crustal contaminants. The plagioclases are characterized by subtly zoned and resorbed calcic cores (An 73–86 ). These cores also have radiogenic 87 Sr/ 86 Sr (0.7127–0.7129), although typically less radiogenic than plagioclase rims, groundmass plagioclase and whole rock compositions (up to 87 Sr/ 86 Sr = 0.7135). These cores are interpreted to represent early crystallization of plagioclase from hydrous melts emplaced into the lower crust. The parental melts to these andesites must therefore have already inherited their radiogenic Sr isotope compositions prior to entering the lower crust and before the onset of crystallization of plagioclase, which is inconsistent with previous models suggesting that the generally radiogenic nature of Sr in these volcanics reflects large amounts of crustal contamination. Instead, the isotope systematics are consistent with models invoked significant addition of a subducted sediment component to the mantle source. The high-An% plagioclase cores are characterized by resorption textures, which are consistent with dissolution during rapid decompression and/or devolatisation during magma migration from the lower crust into upper crustal magma chambers. [ABSTRACT FROM AUTHOR]

Laser beam micromachining of aluminium 5052 was conducted to investigate the effect of four process parameters: lamp current; pulse frequency; pulse width; and assist gas pressure on quality characteristics of drilled hole. Hole taper and hole circularity are important attributes that effect the drilled hole quality are selected as machining responses. Response surface methodology (RSM) was used to design the experiments and to develop the mathematical model. A sensitivity analysis has been conducted on the developed mathematical model to determine the relative influence of different parameters on the process outputs. [ABSTRACT FROM AUTHOR]

The combination of multiple physical, chemical and biological factors causes the weathering of limestone used in the field of cultural heritage. To overcome the limitations of traditional consolidating products and to meet the requirements of the historical building substrates, during the European collaborative project NANOMATCH, alkaline earth alkoxides were developed and studied as consolidating agents for limestone. Among these new products, calcium ethoxide, with the formula Ca(OEt)2, was chosen for this study and investigated in depth as an alternative consolidating treatment. It was first characterized through a study of the carbonation process: its kinetics, reaction pathway and the evaluation of formed mineralogical phases. Subsequently, it was applied on limestones with different total open porosity to test its performance as a consolidating agent. The compatibility and the efficiency of the treatment were investigated with a multi-technique approach and compared with results obtained with a reference product, based on nanolime. This study indicates that calcium ethoxide shows better results with respect to the reference product, both in terms of compatibility and consolidation effect. [ABSTRACT FROM AUTHOR]

Compared to the traditional strontium isotope analytical method, a micro-sample strontium isotope system study can reveal the heterogeneity of analyzed samples and is widely used in various fields of geology, such as crust-mantle interaction, genesis and evolution of magmas, open magma systems, tracing provenance of sedimentary basin and climate research. Accurate measurement of Rb-Sr isotopic ratios is the premise to apply Sr isotope in these research fields. Two detailed and widely used analysis methods for micro-sample Sr isotope measurement are microdrilling-TIMS/MC-ICPMS and LA-MC-ICPMS. These two methods have different advantages and disadvantages in sample preparation, interference correction and measurement in mass spectrometry. The greatest advantage of microdrilling-TIMS/MC-ICPMS is that this technique can acquire high quality data (external precision is better than 100×10-6, 2SD). However the tedious chemical separation is very time-consuming (about 10 days) and the chemical procedure blank must be critical to low level. The large sampling depth (100-2000 μm) and diameter (200-2000 μm) reduce the spatial resolution. However, with chemical separation this method can effectively measure samples with high Rb content. Simple sample preparation and fast analysis are the most outstanding advantages of LA-MC-ICPMS which can analyze lots of samples in a much shorter time than that of microdrilling-TIMS/MC-ICPMS. The laser spot size is mainly from 60 to 300 μm. Based on Sr contents in samples, the method of LA-MC-ICPMS improved spatial resolution, compared to microdrilling-TIMS/MC-ICPMS technique. However, without chemical separation, many kinds of interferences (e.g. Rb, Ca, Kr and REEs) hinder this technique to obtain high quality data (external precision is about 200×10-6, 2SD and accuracy is about 150×10-6). LA-MC-ICPMS is only suitable for high Sr and low Rb samples, instead of samples with high content of interferences. Further studies are required for the microdrilling-TIMS/MC-ICPMS method to improve the efficiency of chemical separation, also microdrilling technology with increasing of spatial resolution by reducing spot diameter and depth. Meanwhile, a better solution for interferences of Kr, Rb and REEs is needed for LA-MC-ICPMS in order to improve precision and accuracy of high interference samples. Instrumental sensitivity improvement is also needed to satisfy Sr isotope measurement for samples with relative low Sr content.

In-line Fabry−Perot cavities manufactured by a new technique using electric arc fusion of NIR laser microdrilled optical fiber flat tips were studied herein for refractive index sensing. Sensors were produced by creating an initial hole on the tip of a standard single-mode telecommunication optical fiber using a Q-switched Nd:YAG laser. Laser ablation and plasma formation processes created 5 to 10 micron cavities. Then, a standard splicing machine was used to fuse the microdrilled fiber with another one, thus creating cavities with lengths around 100 micrometers. This length has been proven to be necessary to obtain an interferometric signal with good fringe visibility when illuminating it in the C-band. Then, the sensing tip of the fiber, with the resulting air cavity, was submitted to several cleaves to enhance the signal and, therefore, its response as a sensor, with final lengths between tens of centimeters for the longest and hundreds of microns for the shortest. The experimental results were analyzed via two signal analysis techniques, fringe visibility and fast Fourier transform, for comparison purposes. In absolute values, the obtained sensitivities varied between 0.31 nm−1/RIU and about 8 nm−1/RIU using the latter method and between about 34 dB/RIU and 54 dB/RIU when analyzing the fringe visibility.

To investigate the influence of fibre laser percussion drilling process parameters on the hole geometric features of Inconel 718 with thickness of 1.0 mm experiments were conducted based on response surface methodology (RSM). Frequency of the laser beam (200 to 400 Hz), duty cycle (30 to 50%), laser power (375 to 425 W) and focal plane position (0.7 to 1.5 mm) were considered as independent variables, while the entrance and exit hole diameters, as well as the hole taper were raised as process outputs. The obtained results indicate that the entrance hole diameter increases as the laser pulse frequency, laser power, duty cycle and focal plane position increase; furthermore, by increasing duty cycle and focal plane position, the hole taper decreases. Minimum hole taper, maximum exit diameter, and minimum entrance diameter were considered as optimization criteria. Verification experiments were carried out in order to analyse the results via software. [ABSTRACT FROM AUTHOR]

Micro electrodischarge (micro EDM) machining, due to its wide application range, is one of the most commonly used technologies for machining in micro scale. Common application of precise micro EDM drilling among others concerns machining of holes in fuel injectors or drug delivery orifices. The paper presents results of research of the micro EDM drilling at Institute. There are derived characteristics of micro drilling in the stainless steel samples depending on the electrode tool length (distance between machined surface and tool electrode clamp). The main comparison coefficients are tool wear ratio, material removal rate / machining efficiency and machining accuracy / quality. Presented results concern micro EDM drilling experiments which were performed for tool electrode diameter of 0,1 mm and workpieces of 1 mm thick. There are also derived conclusions on process optimization and process planning for cost and time effective machining, taking into account the machining time, electrode tool re-clamping time depending on the number of micro-holes to be drilled in the single workpiece. Presented results and their discussion cover problems which we came across during investigations and commercial micro EDM drilling services. [ABSTRACT FROM AUTHOR]

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Fine polished and 4 N (99.99 %) pure gold is irradiated using Nd:YAG laser (1064 nm, 50 mJ, 10 Hz). Drilling is performed in air by increasing number of laser shots on the target surface. After each set of shots, the surface morphology and crater dimensions have been taken into account. SEM JEOL (JSM-7500F) and optical microscope (STM6-LM OLYMPUS Corporation) are used as characterization tools. It is revealed from SEM micrographs that heat conduction is non-uniform and more in the upward direction. Ripples, cones, and cone-like topography are observed. Droplets of micron size and nanoparticles have also been formed at 3000 number of laser shots where perforation occurs. Combining the investigations of SEM and optical microscope, it is observed that with the increase in laser shots, the crater width along horizontal increases and then decreases. It follows the Gaussian trend of variation. Crater width along vertical also increases and then decreases showing Gaussian trend of variation. Crater depth increases by increasing number of laser shots till perforation occur, chasing a linear growth. Heat-affected zone (HAZ) expands, exhibiting the Gaussian way of expansion with increase in laser shots. [ABSTRACT FROM AUTHOR]

Microholes for the production of high precision devices were obtained by ultrashort pulsed laser machining of martensitic stainless steels. A micro-drilling cycle based on the sequence of a drilling through phase, an enlargement and finishing phase is proposed in order to solve the trade-off between process time and quality of the ablated surfaces without making use of complex design of experiments. The three phases were studied taking into account the evolution of the microhole shape as a function of the main process parameters (number of passes per phase, incidence angle and radius of the beam trajectory respect to the hole׳s axis). Experiments testified that the drilling strategy was able to produce cylindrical holes with diameter of 180±2 μm on a 350 μm thick plate in total absence of burrs and debris within a drilling time of 3.75 s. Repeatability tests showed a process capability of nearly 99%. SEM inspection of the inner surface of the microholes showed the presence of elongated and periodic ripples whose size and inclination can be controlled adjusting the incidence angle of the beam over the tapered surface before the ultimate finishing phase. [ABSTRACT FROM AUTHOR]

Micromachining, which is a manufacturing technique to produce miniature parts, carries with it the major factor of precision in machining. The various processes of micromachining, be it contact or non contact methods, have their own merits and demerits. However, producing microstructures such as micro-holes which find widespread application in highly sensitive products such as automotive fuel injection nozzles, watches, medical electronics, and camera parts requires a high degree of accuracy in its profile parameters. Microdrilling, the most ideal micromachining process to generate micro-holes, can generate deeper holes with better straightness, better roundness, and smoother surfaces. This paper focuses on all existing microdrilling techniques that have been used in producing micro-holes along with the various strategies that have been adapted to improve the accuracy in hole dimensioning and its shape. The review of the various accuracy-related microdrilling operations will enable one to understand better the need for accuracy in micro-hole production, the various microdrilling techniques, and most essentially how the accuracy has been improved with technology advancement and better research. It also provides an overview which will help further propagation and implementation of more techniques to further enhance the accuracy of microdrilling operations, bringing about precise components of micromachining. [ABSTRACT FROM AUTHOR]

Sr-isotopic microanalysis has been performed on selected minerals from the Campi Flegrei caldera, together with Sr and Nd isotopic ratio determinations on bulk mineral and glass fractions. The aim was a better characterization of the chemically homogeneous, but isotopically distinct magmatic components which fed volcanic eruptions of the caldera over the past 5 ka, in order to enhance our knowledge about one of the most dangerous volcanoes on Earth. Information on the involved magmatic endmembers, unobtainable by analyzing the isotopic composition of whole rock samples and bulk mineral fractions, has been acquired through high-precision determination of 87 Sr/ 86 Sr on single crystals and microdrilled mineral powders. We focused our investigations on the products emplaced during the Astroni 6 eruption (4.23 cal ka BP), assumed representative of the expected event in case of renewed volcanic activity in the Campi Flegrei caldera. Data on single crystals and microdrilled mineral powders have been compared with Sr and Nd isotopic compositions of bulk mineral fractions from products emplaced during the whole Astroni activity, which included seven distinct eruptions. The 87 Sr/ 86 Sr ratios of single crystals and microdrilled mineral powders are in the 0.7060 to 0.7076 range, much wider than that of bulk mineral fractions, which range from 0.7066 to 0.7076. Moreover, the Sr isotopic ratios are inversely correlated to 143 Nd/ 144 Nd. The new data allow us to better define the magmatic endmembers involved in mingling/mixing processes that occurred prior to/during the Astroni activity. One magmatic endmember, characterized by average 87 Sr/ 86 Sr ratio of ~ 0.70750, was quite common in the past 15 ka activity of the Campi Flegrei caldera; the other, as evidenced by the isotopic composition of single feldspar and clinopyroxene crystals, is less enriched in radiogenic Sr ( 87 Sr/ 86 Sr ~ 0.70724). The latter is interpreted to represent a new magmatic component that entered the Campi Flegrei caldera feeding system in the past 5 ka, the previously recognized Astroni 6 component. However, diopside crystals in Astroni 6 are characterized by even lower 87 Sr/ 86 Sr, in the range of 0.7060–0.7068 and by the highest 143 Nd/ 144 Nd ratios measured in the products of Astroni activity. These diopsides may represent another common magmatic component, as they have been found in most of the Phlegrean Volcanic District products emplaced over the past 75 ka. These diopsides, crystallized in a mantle-derived mafic magma, were entrapped by the Astroni 6 magma during ascent, before it mingled/mixed with the more differentiated and enriched in radiogenic Sr resident magma, thus attaining an intermediate Sr-Nd isotopic fingerprint. These results have an important outcome on the understanding of the volcano behavior, as renewed activity can be triggered by the arrival of fresh magma in the feeding system that would mingle/mix with the resident magma. Such an event may be able to start an unrest phase at the volcano that could last for years or decades, perhaps culminating in a new eruption. [ABSTRACT FROM AUTHOR]

In the first part of the article the review of ceramic materials drilling possibilities was presented. Among the described methods special attention is paid to electrodischarge drilling. This process have especially been predicted for machining difficult-to-cut electrically conductive materials. The second part consist of the results analysis of electrodischarge microdrilling of siliconized silicon carbide. The experiment involves the impact of current amplitude, discharge voltage and pulse time on the hole depth, side gap, linear tool wear and mean drilling speed. The results shows that electrodischarge drilling is a good alternative when machining inhomogeneous ceramic materials and gives possibility to drill high aspect ratio holes with relatively high efficiency (the drilling speed >2 mm/min). [ABSTRACT FROM AUTHOR]

This paper details the fundamental principles of the machining method spark assisted electrochemical machining (SAEM). SAEM is a further development of the electrochemical arc machining (ECAM) which makes use of the electrochemical discharge phenomenon to machine electrically conductive materials. ECAM is not able to drill micro-holes, but now, using SAEM a postponed electrochemical finishing of the SAEM drilled micro-hole can be realized. The mass flow calibration of a throttle plate can be done immediately after SAEM microdrilling by electrochemical machining (ECM) with a still axis-symmetrically located tool electrode with the same machining equipment, working media, and power source. To enable ECAM to drill micro-holes, its material removal mechanism is improved by combination with the contact arc as an additional mechanism. This mechanism is presented and explained herein. The machining efficiency of the newly developed SAEM is optimized by adjusting the gap control in such a way that the contact arc is generated with an adequate frequency. This reduces the machining time by almost 50 %. Some examples of SAEM drilled micro-holes, for which different electrolytes are used, are presented and the surface and heat affected zone of those micro-holes are examined. [ABSTRACT FROM AUTHOR]

Microholes for gasoline direct injection (GDI) nozzles were obtained in martensitic stainless steel AISI 440C with conventional micro-EDM and two laser based processes: water-jet guided μs-laser and fs-laser. Since the analyzed drilling methods heavily differ for their thermal input on materials, the three processes were compared from the perspective of the microstructural changes induced in the bulk material after drilling. Moreover, the sharpness of the edges was taken into account as distinctive feature for a comparison among the three processes, being the spray atomization maximized by a cavitation process inside the microhole. A tailored procedure was optimized to prepare the samples for Scanning Electron Microscopy (SEM) and metallographic analyses. The cross sections of micro-EDM drilled samples revealed the presence of a recast (white) layer of 1-2 μm in thickness even using the lowest spark energy in the tested range. Samples drilled by water-jet guided μs-laser are affected by the same phenomenon, with an even more pronounced effect. Moreover, they showed the extrusion of the melt material along the hole axis under the action of the water-jet conveying the beam. The extremely fast cooling of this layer also makes the machined surfaces prone to cracking. Conversely, metallographic analysis of cross sections of ultrashort pulsed laser drilled samples, showed no modification of the base metal microstructure in the sub-surface regions, thus testifying that the fs-pulsed laser drilling was an almost pure ablation process and not affected by a remarkable liquid phase as for the other two thermal processes. Periodicity and dimensions of laser induced periodic surface structures (LIPSS) generated by ultrashort pulsed laser were characterized by means of Scanning Electron Microscopy. SEM analysis of the microhole edges revealed burrs for the water-jet guided μs-laser while radii of 3-4 μm for micro-EDM and less than 1 μm for fs-lasers were measured. [ABSTRACT FROM AUTHOR]

[Display omitted] • The parallel transient and selective laser processing using the spatial light modulators is developed. • The methods to combine the two lasers with a different wavelength controlled with each spatial modulator is reported. • Two 100-µm depth 10-µm diameter holes are drilled in 50 µs with the parallel transient and selective laser processing. • The processing condition in the parallel transient and selective laser processing is studied. To use glass as the substrate material in next-generation large-scale integrations and biochips, the high-speed fabrication of high-aspect-ratio microholes is necessary. Transient and selective laser (TSL) processing significantly reduces the processing time per hole. To further improve the processing efficiency, parallel TSL processing using a spatial light modulator is proposed in this study. Two 100-µm depth holes are successfully machined in parallel, in 50 µs. Furthermore, the process control parameters are investigated through high-speed observation and the laser irradiation conditions required for processing are clarified. Parallel processing of three or more holes and depth control of each hole is expected to be realized in future. [ABSTRACT FROM AUTHOR]

This article presents an experimental investigation on microdrilling of austenitic stainless steel which is a difficult material for machining because of its properties like high strain-hardening rate, low thermal conductivity, and high fracture toughness. Microholes are produced on X5CrNi18-10 austenitic stainless steel workpiece using 0.5 mm diameter solid carbide microdrills. Two factors (cutting speed and feed) and three levels (low–center–high) full-factorial design of experiment are performed. Response surface methodology is used to developed mathematical models (quadratic and bilinear regression models) for cutting forces in microdrilling. The experimental analysis shows that feed affects the cutting force components (radial and thrust) significantly. Additionally, it also shows that there are only minor effects from cutting speed, square of cutting speed, square of feed and product of speed, and feed on the cutting forces. Finally, the optimized cutting conditions are proposed for minimum cutting forces. [ABSTRACT FROM PUBLISHER]

Technology development has led to the need of micro and miniaturized products in the field of automobile, aerospace, electronics, medical implants, biomedicine, robotics, and so on. Micromachining is the key technology to satisfy the need of the industry in terms of functionality and miniaturization in size. In this article, state-of-the-art review on tool-based micromachining processes such as microturning, microdrilling, micromilling, electric discharge micromachining (Micro-EDM), and electrochemical micromachining (Micro-ECM) has been carried out. The review begins with an overview of micromachining, classifications, and discussions about different aspects of tool-based micromachining processes. The research works carried out for the past 10 years are analyzed in terms of materials perspective, process parameters, size effects, performance characteristics, condition monitoring, product development, micro features generation, and fabrication of micro tools. A statistical analysis has been performed with respect to the previous review articles, numbers of publications in the related area, and their research gap. Finally, the possible future research direction is presented. [ABSTRACT FROM AUTHOR]