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Run out is one of the major problems in microdrilling processes, causing unexpectedly short tool life, sudden breakage, and dimensional inaccuracy. In this study, a two-step monitoring system for run out detection is proposed. The first step uses the fast Fourier transform for extracting features from the online measured force signals. In the second step, a neural network-based model predicts the process condition from the previously obtained features. The model was trained and tested by using force signals obtained from tungsten and titanium alloys, which are widely applied in electronic and aerospace industries. A 0.1-mm-diameter microdrill was used in the experimental study, and three different feed rates were applied for each material. The trained model was validated with data that was not used in the training process. In this validation, the system was able to detect more than 70 % of the run out conditions with less than 10 % of false detections. For microdrills, detecting and reducing run out can yield considerable gains in tool life and productivity. [ABSTRACT FROM AUTHOR]

Radiographic evaluation of chondral repair is an important component of postoperative care. Imaging can confirm normal postoperative appearance, objectively evaluate progression of healing, and provide early identification of postoperative complications. This article briefly discusses the techniques of chondral repair as they relate to postoperative imaging, imaging techniques to evaluate chondral repair, and the normal and abnormal appearances of tibiotalar chondral repair. We concentrate on high-resolution magnetic resonance imaging, the mainstay of chondral imaging. [ABSTRACT FROM AUTHOR]

Holes quality errors are an undesired but unavoidable consequence in drilling operations. Due to the small dimensions involved in the microdrilling processes, quality measurement and control must be carried out offline, by using microscopy or other high precision measurement devices. This paper presents a study about the correlation between the holes quality and the force signals in the microdilling process of 0.1 mm and 0.5 mm-diameter holes in a sintered tungsten-copper alloy. The surface of the obtained holes was scanned by means of an interferometry microscope and the error of the holes was computed from the scanned data. The three components of the forces were measured during all the drilling process. The behavior of these signals, in three different intervals (tool entrance, forward motion and backward motion) was described by wavelet package analysis. The features having higher correlation with the holes quality error were the average power of the axial component of the forces in the frequency bands of 0~391 Hz and 3906~4297 Hz, during the backward motion. With these features, a statistical regression model was fitted. The main outcomes of this study are the basement for obtaining reliable models for monitoring systems in microdrilling operations. [ABSTRACT FROM AUTHOR]

Highlights: [•] A sensoring system for microdrilling process of tungsten–copper alloy was studied. [•] Forces and vibration signals were measured for different tool diameters. [•] The correlation between measured signals and the number of elaborated holes was carried out. [•] Two stages (features extraction and modeling) were used in the correlations. [•] The combination of wavelet transform and adaptive-network-based fuzzy inference system (ANFIS) yielded the best results. [Copyright &y& Elsevier]

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In drilling, the primary and secondary cutting lips of the drill shear the material while the central portion of the chisel edge indents the workpiece, making the cutting process complex to understand. As we go for microdrilling, it exhibits an added complexity to the cutting mechanism as the edge radius gets comparable to chip thickness at low feeds. The presented work models the forces by the primary cutting lip of a microdrill analytically using slip-line field that includes the changes in the effective rake angle and dead metal cap during cutting for cases of shearing as well as ploughing. To study the variation of forces experimentally, the primary cutting lip and chisel edge forces ate separated out by drilling through pilot holes of diameter slightly above the drill- web thickness. Finally, the analytical and experimental results are compared and the model is calibrated. [ABSTRACT FROM AUTHOR]

Abstract: This article demonstrates the importance of treatment application procedures on the consolidation effectiveness obtained by comparison of the results obtained using three different consolidants on four carbonate stone types, and proposes a general methodology for assessing the potential effectiveness of consolidants in laboratory conditions. It stresses the relevance of taking into account the treatment methodology, given the influence application protocols can have on the overall behaviour of the consolidated material. Several mechanical properties were assessed to demonstrate this influence on the performance of the consolidant. The results demonstrate that the strengthening action achieved with a specific product can only be defined in a strict relation to the treatment protocol used to produce it. The results also contribute towards the definition of standard testing protocols on stone consolidation. The application of a consolidant by direct contact capillary absorption is a reliable procedure and the results are easier to interpret than others obtained by brushing or by full immersion, thus making this procedure a good candidate for an eventual standard laboratory assessment method of the consolidation action of any specific stone/consolidant combination. This study also showed that the best test method to assess the strengthening action of stone consolidants in soft stones is DRMS (Drilling Resistance Measuring System). Moreover, the collection of longitudinal ultrasound velocity profiles determined in stones specimens treated by contact capillary absorption was shown to be a useful non-destructive method to assess the depth of the strengthening action achieved. [Copyright &y& Elsevier]

In laser microdrilling, the formation of taper and the dimension of the heat-affected zone (HAZ) are important attributes that greatly influence the quality of a drilled hole. In this article, an experimental investigation into Nd:YAG laser microdrilling of alumina is carried out to produce desired high-quality microdrill. Four independently controllable process variables viz. lamp current, pulse frequency, air pressure, and pulse width are considered as input parameters, while hole taper and HAZ width are considered the output parameters. The Taguchi method combined with the grey relational analysis is used as a statistical design of experiment technique to set the optimal process parameters. The objective is set to minimize both quality characteristics, simultaneously. Grey relational analysis is applied to convert the multiple quality characteristics to a single performance characteristic, called grey relational grade. Optimal process parameters are then determined by the Taguchi method using grey relational grade as the quality index. Both of the quality characteristics of drilled holes are improved markedly at the optimal process condition, as verified by an additional confirmation test. This indicates the application feasibility of the grey-based Taguchi technique for continuous improvement of laser microdrilling quality in the manufacturing industry. [ABSTRACT FROM AUTHOR]

Abstract: We have developed cemented tungsten carbide (CTC) micro-cutting tools of 3μm diameter by electrical discharge machining (EDM). Microdrilling and micromilling were carried out using the developed tools, and their cutting performance was investigated. Cutting was performed in free-cutting brass plates. Ultrasonic oscillation was employed to lower the cutting resistance. As a result, holes and a slot of 3μm depth were successfully fabricated using tools made of CTC with 0.6μm grain size, indicating that successful cutting with 3μm-diameter tools was accomplished for the first time. Furthermore, CTC with 90nm grain size was used as a tool material to improve the tool breakage resistance and tool form accuracy. The drilling performance of tools made of this ultrafine-grain-sized CTC was also investigated and found to exhibit a considerably improved average tool life. [Copyright &y& Elsevier]

Laser microdrilling is the process of material removal by ablation using focused laser pulses. With brief preamble on laser system, how a micro-orifice is created successfully on 50 µm thick copper foil using modified Nd:YAG ophthalmic laser is elucidated. The micro-orifice is required to control the flow of lubricant from the centrifugal lubricator used in spacecraft moving mechanisms. The orifices are characterized using scanning electron microscope (SEM), and the process parameters are optimized. Orifices from 1.5 µm to 2.7 µm diameter are produced. The work is further extended to drill microholes in 60 µm copper wire. It is observed that the bead formed at melt zone near the hole can be conveniently used for microjoining. [ABSTRACT FROM AUTHOR]

Abstract: We present a straightforward method for fast prototyping of microelectrode arrays in the highly conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT). Microelectrode arrays were produced by electrical resistance-controlled microdrilling through an insulating polymer layer (TOPAS® 5013) covering a PEDOT layer. The sudden drop in electrical resistance between the metal drill and the PEDOT layer upon physical contact was employed as stop criterion for the drilling process. Arrays of 3×3 microelectrodes of diameter 30μm or 100μm, respectively, and having center-to-center electrode spacings of 130μm and 300μm, respectively, were fabricated. Their functionality was verified by chronoamperometry on potassium ferro-/ferricyanide. Comparison of the experimentally obtained results to finite element modeling of the respective electrode configurations shows that the conducting polymer electrodes approach the steady state currents predicted from modeling, but at a much slower rate than expected. This is shown to be caused by the use of electroactive PEDOT electrodes. Subtraction of the latter contribution gives approach to steady state currents within a few seconds, which is in very good agreement with the modeled response time. [Copyright &y& Elsevier]

Pulsed fiber lasers are innovative laser sources which promise to be suitable tools for micromachining operations due to their high beam quality, strong focusability, and high productivity. In this work, percussion laser microdrilling on 0.5-mm-thick commercially pure titanium sheets making use of a nanosecond pulsed fiber laser is investigated. The work is aimed at studying the effects of the main process parameters (pulse energy and pulse frequency) on the quality features of the machined through holes, i.e., diameters, taper, circularity, and area of top spatter. Adequate regressive models are developed to define the functional relationship between the hole quality and the main process parameters. The effects of laser microdrilling on material microstructure of the regions in close proximity to the machined holes are also investigated by means of nanohardness measurements and microstructural analyses. [ABSTRACT FROM AUTHOR]