Drilling Experiments Research Articles

Experimental investigation of mechanical properties of structural interlayers for rock masses during drilling process

With the continuous development of underground engineering construction in China, it is particularly important to study the identification of structural plane characteristics of rock masses. In this study, three types of pseudo-rock specimens with structural plane interlayers were fabricated to analyze the patterns of drilling parameter changes in rock bodies with structural planes during the drilling process and to explore the characterization and identification methods of rock body structural planes. Gneiss, granite, and sandstone were used as rock materials, with gypsum mortar as the interlayer material for the structural planes in these three types of specimens. The indoor digital drilling equipment was utilized for conducting indoor digital drilling experiments. The variation patterns of drilling parameters in rock bodies with structural surfaces under different interlayer inclinations and thicknesses were analyzed. The relationship between the ratio of the change in rotational speed and drilling speed during the stable phase of the upper rock mass and the peak torque and peak drilling pressure has been established. The relationship between the structural plane inclination angle and the ratio of change in rotational speed and drilling speed has been determined. By utilizing the variation in these ratios, the impacts of the structural plane inclination angle and the thickness of the structural plane on the peak torque and peak drilling pressure have been elucidated. The research results provide a theoretical basis for the stability evaluation of rock masses with structural planes under drilling action.

Determination of elastic modulus and anisotropy for rocks using digital drilling method

The main purpose of this study is to provide a digital drilling-based method for determining rock elastic modulus and evaluating the anisotropy. By considering a concept of crushed zone, the drilling response was characterized as the function of specific energy and drilling strength. On this basis, an equivalent elastic modulus was proposed to evaluate the rock elastic modulus. Moreover, an anisotropy index was proposed according to the difference in specific energy under different borehole directions. Digital drilling experiments were conducted for three lithologies at drilling directions namely 0, 60, and 120° (Based on vertical orientation), revealing the anisotropic effect exhibited in the rock. To validate the measurement of rock elastic modulus and its anisotropy, the compressive tests under same conditions were carried out. The results suggested that the proposed indicator provided an accurate evaluation for the rock's elastic modulus, with an error margin of less than 10%. Drilling-based anisotropy is identified in the drilling response, especially the critical state between cutting and friction. The statical indicator CoV (coefficient of variation) was utilized to characterize the anisotropy along the borehole. This research's innovation lies in providing an approach to evaluating rock anisotropy and determining its elastic modulus by considering the drilling response.

Fatigue behavior of multi-row film cooling holes manufactured by lasers with different pulses under complex-temperature fields

This research investigates the fatigue behavior of multi-row film cooling holes produced by lasers with diverse pulse widths amid intricate thermal environments. Through laser drilling experiments, conjugate heat transfer simulations, and crystal plasticity finite element analyses, it explores the interplay of temperature and stress fields among multiple holes in these structures, and factors influencing fatigue damage and its severity. Additionally, it anticipates the fatigue fracture paths of multi-row film cooling hole structures. Findings reveal that while the drilling process and aerodynamic parameters significantly impact cooling effectiveness, their influence on cooling distribution is negligible. Fatigue damage distribution is shaped by structural imperfections from different processes, stress field interference among multiple holes, and material property alterations due to temperature changes. The extent of damage is primarily dictated by roundness errors resulting from the drilling process, with taper playing a minor role. Nonetheless, stress interference among multiple holes notably exacerbates stress concentration at the interference zone, leading to increased damage levels in film cooling holes crafted by picosecond lasers with minimal roundness errors. Moreover, in complex thermal environments, fatigue fracture paths of multi-row film cooling holes migrate and evolve contingent on temperature-induced shifts in material properties.

Optimizing the drilling process parameters of AZ91 based hybrid composites using TOPSIS and grey relational analysis

AZ91 is a popular magnesium alloy that contains aluminum (Al), zinc (Zn), and small amounts of other elements that offers a good balance of mechanical properties and corrosion resistance, making it suitable for various applications such as automotive, aerospace, sports, and biomedical. The current research works focused on optimizing drilling process parameters such as cutting speed, feed rate, a set of standard tools, and biofriendly coolants against the surface roughness and axial thrust force for AZ91/ nano hBN/ micron TiB2 hybrid composites. Taguchi L18 orthogonal array was used to design the drilling experiments. The axial thrust force and surface roughness of the drilled hole were observed as response of the experiments. Based on the results from TOPSIS and GRA, the optimal conditions were determined to be a spindle speed of 65 m/min, feed rate of 1 mm/rev, using a High-Speed Steel (HSS) tool, and Liquid Nitrogen (LN) coolant for 1 wt% of nano hBN in the hybrid composite. These parameters resulted in the lowest axial thrust force and surface roughness, highlighting their effectiveness in optimizing the drilling performance of AZ91/TiB2/hBN composites.

Modeling and verification of cortical bone drilling forces based on tissue structure heterogeneity

Bone drilling mechanism study is the basis for the optimization of cortical bone drilling process and drill geometry. In this paper, a drilling force model for modified drills with thinned chisel edge is established considering the heterogeneous structure of cortical bone. The bone mineral density is embedded into the established model, the model can predict the axial thrust force change along the drilling depth direction, and the model is verified through cortical bone drilling experiments. The thrust force and torque predicted by the model are in good agreement with the drilling experimental results of cortical bone drilling. Then, the drilling performance of the modified drill and the common drill is compared through cortical bone drilling experiments. Compared with common drill bits, the maximum reduction in average thrust force of the modified drill bit during stable drilling is 21.21 % (n = 2500 rpm, Vf=60 mm/min). The maximum reduction in average roughness of the hole wall is 21.87 % (n = 500 rpm, Vf=10 mm/min). The drill chisel edge thinning design reduces the negative impact of the negative normal rake angle on the cutting lip of common drill on drilling force and stability. Therefore, the drill bit chisel edge thinning design can effectively improve the drilling performance.

Experimental investigation on high voltage electric pulse rock breaking under drilling mud conditions

High voltage electric pulse rock breaking technology is a novel and promising rock breaking technique that is environmentally friendly, efficient, and nearing industrial application. However, the drilling performance of electrode bits under varied drilling muds and the mechanism of high voltage electric pulse rock breaking remain unclear. This study entails real drilling experiments conducted on red sandstone using electrical pulse drilling (EPD) under different initial voltage peaks, electrode bits, and drilling muds to investigate the impact and mechanism of EPD. A laboratory experimental system for high voltage pulse rock breaking is established based on a 0–80 kV EPD pulse generator. Three types of electrode bits are devised, namely, petal-structural, four-point-structural, and circular-ring-structural electrode bits. The EPD experiments on red sandstone are executed under seven different drilling muds at initial peak voltages ranging from 13 to 17 kV. And the efficiency of EPD rock breaking is assessed using five quantitative indexes: rate of penetration, breaking volume, specific energy of rock breaking, and the proportion of electrical fragmentation and hydraulic-electric rock fragmentation. Furthermore, the physical parameters, i.e., density, conductivity, Zeta potential, PH, and apparent viscosity, of the seven drilling muds are measured, shedding light on the rock breaking mechanism of EPD under specific drilling mud conditions. Subsequently, the designed electrode bit is evaluated, and based on experimental phenomenon, structural optimizations of the electrode bit and EPD drilling recommendations under various drilling mud conditions in real drilling scenarios are proposed. This research is poised to offer valuable insights into the design of EPD electrode bits and the selection of drilling mud for enhancing drilling efficiency.

Design and performance analysis of low damage anti-skid crescent drills for bone drilling

BackgroundWith orthopedic surgery increasing year on year, the main challenges in bone drilling are thermal damage, mechanical damage, and drill skid. The need for new orthopedic drills that improve the quality of surgery is becoming more and more urgent.MethodsHere, we report the skidding mechanism of drills at a wide range of inclination angle and propose two crescent drills (CDTI and CDTII). The anti-skid performance and drilling damage of the crescent drills were analyzed for the first time. Inclined bone drilling experiments were carried out with crescent drills and twist drills and real-time drilling forces and temperatures were collected.ResultsThe crescent drills are significantly better than the twist drill in terms of anti-skid, reducing skidding forces, thrust forces and temperature. The highest temperature is generated close to the upper surface of the workpiece rather than at the hole exit. Finally, the longer crescent edge with a small and negative polar angle increases the rake angle of the cutting edge and reduces thrust forces but increases skidding force and temperature. This study can promote the development of high-quality orthopedic surgery and the development of new bone drilling tools.ConclusionThe crescent drills did not skid and caused little drilling damage. In comparison, the CDTI performs better in reducing the skidding force, while the CDTII performs better in reducing the thrust force.

Temperature-Stress Coupling Fatigue Behavior of Film-Cooling Holes in Complex Temperature Fields.

This research investigates the complex temperature distribution and fatigue behavior of single film-cooling holes manufactured by lasers with different pulse widths in a real flow field. The aerodynamic and heat transfer characteristics of film-cooling holes manufactured using lasers with different pulse widths were analyzed through laser drilling experiments, conjugate heat transfer simulations, and crystal plasticity finite element methods. The study investigated the relationship between changes in the geometric accuracy of the film-cooling holes and the corresponding flow and temperature fields during the film-cooling process. Additionally, the effects of temperature and structural variations on the stress around the holes in a flat plate composed of the second-generation nickel-based single-crystal superalloy DD6 in real flow and temperature fields were studied. The coupling effect of the temperature and stress fields around the holes on the fatigue behavior of the film-cooling holes was examined, and the fatigue damage mechanism of film-cooling holes in complex temperature fields was analyzed. It was found that changes in the blowing ratio do not affect the temperature and stress distributions around the holes but only alter the temperature peak. An increase in the temperature peak results in a decrease in the stress peak. Additionally, the fatigue damage of single film-cooling holes is determined by both the structural defects of the holes and the changes in material behavior due to the temperature around the holes, with the structural influence being more significant.

Deep Learning–Assisted Parameter Monitoring and Optimization in Rotary-Percussive Drilling

Summary As an efficient method for hard rock fracturing, rotary-percussive drilling has been widely used in various scenarios, especially deep drilling. Drilling parameter monitoring and control are necessary to ensure stable and efficient underground drilling processes. However, this may be more difficult in deep, harsh conditions. In this paper, our goal is to establish models based on deep learning for drilling parameter monitoring and optimization. Combining impregnated diamond bits and granite rock samples, we conducted rotary-percussive rock drilling experiments using a rock drilling test rig. Real-time acoustic signals during rotary-percussive drilling were recorded, segmented, and transformed as spectra, which made up a drilling acoustic signal data set. Drilling parameters, including rotational speed (revolutions per minute, RPM), pump flow rate, pump pressure, weight on bit (WOB), torque, and rate of penetration (ROP), were logged in the meantime. Given the acoustic signal as input, we built 1D convolutional neural network (1D-CNN) models for drilling parameter prediction. The prediction results revealed the high efficiency and accuracy of 1D-CNN regression models based on deep learning in drilling condition monitoring. Batch normalization played an essential role in the regression model training processes. Given that these parameters have different units and dimensions, we compared models with different output modes to evaluate the multiparameter prediction performance of the 1D-CNN. Taking RPM, flow rate, pressure, and WOB as independent variables and torque and ROP as dependent variables, we developed a conditional variational autoencoder to realize optimization on drilling parameters based on expected drilling performance.

Dynamic Numerical Simulation and Transfer Learning-Based Rapid Rock Identification during Measurement While Drilling (MWD)

In constructing rapid rock identification models for measurement while drilling (MWD) via neural network methods, collecting actual drilling data to train the model is extremely time-consuming and labor-intensive. This requires extensive drilling experiments in various rock types, resulting in limited neural network training data for rock identification that covers a limited range of rock types. To suitably address this issue, a dynamic numerical simulation model for rock drilling is established that generates extensive drilling data. The input parameters for the simulations include torque, drill bit rotation speed, and drilling speed. A neural network model is then developed for rock classification using large datasets from dynamic numerical simulations, specifically those of granite, limestone, and sandstone. Building upon this model, transfer learning is appropriately applied to store the knowledge obtained in the rock identification based on the neural network model. Further training through transfer learning is conducted with smaller datasets obtained during actual drilling, making the model suitable for practical rock identification and prediction in the drilling processes. The neural network rock classification model, incorporating dynamic numerical simulation and transfer learning, achieves a prediction accuracy of 99.36% for granite, 99.53% for sandstone, and 99.82% for limestone. This reveals an enhancement in prediction accuracy of up to 22.94% compared to the models without transfer learning.

Identification of dynamic coefficient matrix for drilling process simulations from measured tool geometry, axial force and torque

This paper aims to quantitatively analyze the relationship between forces acting on the tool tip and tool movement during drilling operations. The study encompasses axial and lateral vibrations superimposed on the nominal tool movement, arising from rigid body motion (rotational and axial velocities). Specifically, only forces attributed to the cutting process are considered, excluding considerations of indentation forces around the chisel edge. The research adopts a generalized approach, spanning from tool measurements to establishing the force model. The investigation involves measuring cutting forces and correlating them with the varying rake and inclination angles of the drill’s cutting edges. An analytical model is proposed to describe the distribution of all local force components along drill edges, considering the evolution of forces and geometry. The dynamic coefficient matrix is evaluated by using the identified cutting coefficient and tool geometry. Validation of the proposed methodology is demonstrated through drilling experiments on Ti6Al4V alloy, utilizing three solid carbide drills with distinct geometries. The proposed procedure allows complete identification of the dynamic characteristics from the measurements taken at the entrance stage of hole drilling operation. Moreover, the influence of tool geometry on cutting coefficients and dynamic coefficient matrices are discussed.

Application of the drilling mechanical properties of rock to determine confining pressure in shallow geological formations

Confining pressure is an essential factor to consider in geological disasters in geothermal reservoirs and deep geological formations. Assessing the confining pressure holds practical importance, particularly in mitigating high-risk disasters associated with resource production. This study focuses on the development of a theoretical model for the mechanical properties of drilled rocks, specifically considering the impact of elevated confining pressure during the drilling process. Digital drilling experiments with different confining pressures are carried out to investigate the effect of confining pressure on the drilling mechanical properties of rock. A new method for identifying confining pressure and strength parameters using digital drilling is proposed. A comparison between the predicted confining pressure and the measured confining pressure is conducted to verify the accuracy of the model. The results show that the cutting force and the normal thrust at the cutting point increase with an increase in confining pressure. The drilling parameters (the bit rake angle a, the contact friction angle θ, the friction angle of rock φ, the cohesion of rock c, the effective stress generated by the drill torque St, the effective stress generated by the thrust along the normal axis Sn.) also increase gradually as confining pressure increases. Digital drilling technology offers shorter testing cycles and lower costs in comparison to traditional confining pressure testing techniques such as stress relief and hydraulic fracturing. The predicted confining pressure is consistent with the actual value. In summary, the method of determining confining pressure based on digital drilling has practical engineering significance.

Temperature prediction model of bone drilling considering the effect of tool wear

Biomass bone is biologically active and sensitive to heat; excessive temperatures would destroy the biological activity of the bone tissue or even cause bone necrosis. Therefore, it is vital to control the drilling temperature in clinical surgery for internal fixation of fractures. This paper focused on the influence of tool wear on the drilling temperature during the bone drilling process. The effect of three drilling parameters, the tool diameter, machine spindle speed and tool feed speed, on three dynamic characteristics, the drilling force, drilling temperature and tool wear, was investigated through bone drilling experiments. A prediction model of the bone drilling temperature considering the effect of the amount of wear was established based on Archard wear theory and the heat source method, and was in good agreement with the experimental results. The predicted results showed that worn bits produced drilling temperatures up to 3.4°C higher than those of new bits, and the maximum error in the prediction of the drilling temperature was 11.04%. The temperature model better extended the applicability of the existing temperature models.

An End-to-End Inclination State Monitoring Method for Collaborative Robotic Drilling Based on Resnet Neural Network.

The collaborative robot can complete various drilling tasks in complex processing environments thanks to the high flexibility, small size and high load ratio. However, the inherent weaknesses of low rigidity and variable rigidity in robots bring detrimental effects to surface quality and drilling efficiency. Effective online monitoring of the drilling quality is critical to achieve high performance robotic drilling. To this end, an end-to-end drilling-state monitoring framework is developed in this paper, where the drilling quality can be monitored through online-measured vibration signals. To evaluate the drilling effect, a Canny operator-based edge detection method is used to quantify the inclination state of robotic drilling, which provides the data labeling information. Then, a robotic drilling inclination state monitoring model is constructed based on the Resnet network to classify the drilling inclination states. With the aid of the training dataset labeled by different inclination states and the end-to-end training process, the relationship between the inclination states and vibration signals can be established. Finally, the proposed method is verified by collaborative robotic drilling experiments with different workpiece materials. The results show that the proposed method can effectively recognize the drilling inclination state with high accuracy for different workpiece materials, which demonstrates the effectiveness and applicability of this method.

Effect of anisotropy on drilling mechanical properties for rock in process of drilling

The anisotropic characteristics of rock have important value for construction safety and evaluation of rock properties. The purpose of this article is to study the variation law of drilling parameters in different rocks and their anisotropy characteristics. This article investigates drilling characteristics by conducting digital drilling experiments on six different types of rocks in three different directions. The variation law of drilling parameters (drilling speed, torque, rotational speed, thrust force) and the special energy with drilling depth are analyzed as well as the anisotropy variation of six types of rocks. The influence of anisotropy on the specific energy of six types of rocks is investigated. A special energy index f is proposed to characterize the anisotropy for evaluating different rocks. The test results show that the anisotropy of granite, slate, gneiss, red sandstone, argillaceous sandstone, and sandstone is weakened accordingly by using the special energy index f. The specific energy index after data normalization can better judge the anisotropy difference for different rocks, such as granite, slate, gneiss, and red sandstone.

Ultrasonic tool shank with multiple vibration mode for micro-nano drilling: Design, optimization and experiment

The machining effects of hole drilling is limited by merely changing the amplitude. Adjusting ultrasonic vibration frequency to expand the matching range of machining parameters optimization is necessary to improve hole drilling effects. Therefore, the design, optimization, and experiment evaluation for a novel integrated, fined, low-cost dual-frequency ultrasonic tool shank is proposed, which can work in three vibration modes for micro-nano precision drilling. The principle of the dual-frequency ultrasonic transducer is introduced. The electro-mechanical equivalent circuit model with step horn is applied to study the dual-frequency characteristics. The transducer displacement equation model based on the wave equation theory is deduced to find the shared vibration node of the first and third frequency. Sensitivity analysis by equivalent circuit model and Finite element method (FEM) simulation of the key parameter is both conducted to optimize ultrasonic transducer geometry dimension. The vibration node of mounting flange is specified in an identical position for the dual vibration modes. A prototype of ultrasonic tool shank is fabricated and evaluated in experiments. It demonstrates that the dual working frequency of the ultrasonic transducer is 34.9 kHz and 104.5 kHz in the first and third mode resonant vibration, which is benefit to the low and high frequency drilling. Three working modes of the low, high, and coupling frequency vibration is measured by a self-developed ultrasonic generator. When 40 V voltage is excited, the vibration amplitudes of the low and high frequency are 17.8 µm, and 9.3 µm, respectively, which can meet with the drilling requirement. Moreover, the coupling vibration with the low and high mode are excited simultaneously, and the motion trajectory of the coupling vibration is observed in a “M” shape, which is a novel trajectory for the precision micro-nano drilling. Micro drilling experiments show that the 35 kHz ultrasonic vibration drilling can achieve better machining effect than conventional drilling (CD). The 105 kHz ultrasonic drilling outperforms the CD, 35 kHz and coupling ultrasonic drilling at cutting force reduction. The coupling ultrasonic vibration drilling achieves the lowest chipping diameter. It is to be noted that the 105 kHz-8 µm produce the fined smoothly surface. The 35 kHz, 105 kHz and coupling ultrasonic drilling can produce better surface micro morphology with less quantity and size of craters than that of CD.

Study on the friction drilling behaviors and tribological properties of aluminum matrix composites

This study investigates Al 6063 matrix composites reinforced with different weight percentages of B4C (5%, 10%, 15%, and 20%) produced through powder metallurgy and hot extrusion. The resulting specimens were subjected to a comprehensive investigation to elucidate the effect of B4C reinforcement on the density, tensile strength, transverse rupture strength (TRS), hardness, tribological characteristics, and friction drilling behavior. The pin-on-disk wear tests were conducted in a dry environment, while the friction drilling experiments were performed under constant spindle speed and feed rate conditions, both in dry and minimum quantity lubrication (MQL) environments. The findings revealed a uniform B4C particle dispersion and strong interface bonding in the matrix and that the hardness, tensile strength, TRS, and wear resistance of the specimens increased as the weight fraction of the reinforcement increased. The 15 wt% and 20 wt% B4C composites showed the highest wear resistance, improving by 62.78% compared to Al6063. Higher B4C content reduced specific wear rates and reduced friction coefficients. Among the specimens under investigation, the Al6063 composite reinforced with 15 wt% B4C indicated the highest tensile, transverse rupture, whereas the Al6063 composite with 10 wt% B4C exhibited the best thread-pull-out strength (TPS). The friction-drilled 10 wt% B4C composites showed the highest thread-pull-out strength reaching 373.44 N/mm² in MQL and 329.74 N/mm² in dry conditions.

A novel experimental setup for axial-torsional coupled vibration impact-assisted PDC drill bit drilling.

The geological conditions of hot dry rock (HDR) reservoirs are complex. The geothermal mining of HDR faces major challenges in the drilling and construction of wells, fracturing to create storage, and flowing to extract heat. Vibration impacts help improve the rock-breaking efficiency, where the axial-torsional coupled vibration impact technology can increase the bit penetration depth and reduce the stick-slip effect. To study the feasibility and efficiency of the axial-torsional-coupled vibration impact-assisted Polycrystalline Diamond Compact (PDC) bit to break high-temperature and high-pressure rocks, a new experimental setup was designed. The system includes a drilling fluid circulation system, an axial-torsional coupled impact drilling system, a formation simulation system, and a data acquisition and control system. This setup can produce a rock-breaking torque of 2000 N·m, a drilling speed of 200rpm, a weight on bit of 100kN, an axial vibration frequency of 100Hz, and a torsional vibration frequency of 50Hz. It can simulate the formation pressure of 70 MPa and the rock temperature of 400 °C. A series of rock-breaking drilling experiments were successfully conducted using this setup. The results show that the axial-torsional coupled vibration-impact assisted PDC bit has a good performance in breaking high-temperature and hard rocks, which can accelerate the application of this new technology in deep formation drilling.

Pedicle drilling force control of a robotic surgical system via spine-soft tissue coupling model and parameters optimization

Bone drilling is a crucial operation in spinal fusion surgery that requires precise control of the applied force to ensure surgical safety. This manuscript aims to enhance the force servo performance of the orthopedic robot during automatic bone drilling operations. Firstly, an analytical model is introduced to describe the spinal mobility of the spine-soft tissue coupling structure. Then, the model is calibrated using force data obtained from stress relaxation tests. Next, optimal force controller parameters are determined through drilling force control simulations based on the identified model. The dynamic performance and robustness of the closed-loop control system are analyzed to ensure safe drilling procedures. Finally, bone drilling experiments are conducted in a force control mode to verify the effectiveness of the proposed method. The step drilling force response's steady-state error is less than 0.15 N, the relative control error is less than 3 %, and there is no noticeable force overshoot. The amplitude of the sinusoidal force response decays to −3 dB when the target force frequency is up to 3.49 rad/s, indicating a wide control bandwidth. These results demonstrate that the proposed method can rapidly and safely provide an adequate force servo to carry out automatic bone drilling.

Research on sealing mechanism and structural improvement of metal sealing structures for high speed drill bits

The main causes of metal seal failure are studied and the main judgment criteria for metal seal failure are provided based on the structural characteristics in this paper. Mechanical analysis is conducted on the assembly and compression process of single metal seals, and the theoretical relationship between the contact pressures of the dynamic sealing surface of single metal seals is obtained. The finite element software was adopted to simulate the assembly process of a single metal seal. The results show that the sealing washer limited the downward deformation of the energy supply ring. The stress is concentrated at the chamfer at the lower end of the original sealing washer and metal ring, which is leading to the failure of the sealing washer. The new sealing structure can not only enhance the function of the energy supply ring on the metal sealing force, but also reduce the normal force of the sealing washer. It is concluded that the new sealing structure can improve the bearing sealing performance of small-sized cone drills through on-site drilling experiments. The conclusion has a certain guiding effect on the design and application of high speed bit.