Drilling Tests Research Articles

Cuttability and drillability studies towards predicting performance of mechanical miners excavating in hyperbaric conditions of deep seafloor mining

The research program outlined in this paper starts with the assumption that if there is a significant relationship between drilling and cutting specific energies in atmospheric conditions, there would also be a significant relationship between these variables in hyperbaric conditions. Five “model rock samples” having uniaxial compressive strength varying from 9 to 160 MPa were subjected to full-scale laboratory drilling tests with polycrystalline diamond compact (PDC) drill bits and a core drill, as well as laboratory full- and small-scale linear cutting tests with a conical and chisel cutter in atmospheric conditions. As a result, significant correlations between drilling and cutting specific energies were found for atmospheric conditions of laboratory. PDC drill bits and core drill bit used in laboratory tests were also used in the subsea drilling operations under hyperbaric conditions in Bismarck Sea. The conical cutter used in the laboratory tests are intended to be used on mechanical miners for subsea metal production. Core samples taken from Bismarck undersea mineral deposits were also subjected to physical and mechanical property tests in the deck and separately in the laboratories of Istanbul Technical University; and small-scale linear cutting tests were also applied in the university. Significant correlations were also found between the results of small- and full-scale cutting test. It is concluded that the capabilities of in-situ measurements will permit to detect some physical and mechanical properties of undersea mineral deposits. These properties interpreted with laboratory drilling and cutting tests would serve a basis to predict performance of mechanical miners to be used in hyperbaric conditions.

Investigation of ultrasonic vibration on thrust force, surface integrity, and geometrical tolerances during drilling of natural filler reinforced composites

Growing global environmental threats have attracted researchers and engineers toward design and manufacture of green materials. In this regard, natural filler reinforced composites are environmentally friendly, cost-effective materials with a lot of advantages over conventional carbon/glass fiber reinforced composites. Hence, in this study, the drilling performance of walnut shell powder reinforced composite material was experimentally investigated. For this purpose, the composite specimens were first fabricated by injection molding process, followed by further drilling tests, which were performed with and without ultrasonic vibration. The effect of drilling parameters and ultrasonic vibration was investigated on surface roughness, thrust force and geometrical tolerances (circularity and cylindricity), as the process performance parameters. The obtained results demonstrated that by increase of the spindle rotational speed and decrease of feed rate, the thrust force, surface roughness and geometrical tolerances were reduced. Also, it was seen that ultrasonic vibration could effectively enhance the performance parameters, which was attributed to the intermittent cutting process and impact action of ultrasonic vibration, leading to reduced friction, improved material removal, reduced cutting forces, and better surface quality.

EFFECTS OF DIFFERENT CRYOGENIC TREATMENTS ON DRILLING PERFORMANCE OF HSS DRILLS

Cryogenic processing is a heat treatment which has been widely used in recent years to improve the properties of tool materials. This process has been reported in the literature as it provides significant contributions to wear resistance and tool life of tool steels. This study presents the differences in tool performance between untreated and cryogenically treated M2 high speed steel (HSS) drill bits in terms of their tool wear, tool life, hardness and chip formation properties. Also, the effects of two different tempering temperatures (200 oC and 250 oC) in cryogenic treatment on tool performance are discussed. Drilling performances were studied on different workpieces of SAE 1050, lamellar cast iron and sphero cast iron, and the type of wear is characterized by a high resolution camera. Moreover, fracture tests were performed on a steel workpiece using a constant drilling speed of 1100 m/min and a feed rate of 0.5mm/rev. The microstructures of the samples were characterized using optical microscopy and SEM. The Vickers micro-hardness tests of the samples were performed using 100 g load. Microstructural studies showed that cryogenically treated samples exhibit better microstructure with finer and more homogeneous carbides which yields better tool wear and hardness properties. In paralel, cryogenically treated drills showed improved tool life than untreated drills during fracture tests. When tempering temperatures are compared, tempering at 250 °C resulted in better performance than 200 °C of tempering temperature. Also, the reduction in diameter values during drilling tests were consistent with the tool life tests.

A Study on Temperature Rise, Tool Wear, and Surface Roughness During Drilling of Al–5%SiC Composite

In the present study, passive infrared thermography and embedded K-type thermocouple were employed to investigate the tool and workpiece temperature during drilling of Al–5%SiC composite. The dry drilling experiments were performed based on the Taguchi’s L9 method with the mixed orthogonal array. The cutting factors in the range of 600–1200 rpm speeds, 0.07–0.17 mm/rev feed rates, and 90°–135° point angle tools were used for the drilling tests. The temperature line profile was used to explain the various stages of drilling mechanisms. The measured tool and workpiece temperature were correlated with the cutting parameters. A preliminary numerical model was used to simulate the workpiece temperature, and the simulation results were compared with the experimental value. The effect of cutting parameters on the tool temperature and surface roughness was studied by analysis of variance (ANOVA). The ANOVA result shows that the point angle and cutting speed were the significant factors to the tool temperature, while the feed rate was the most influential parameter for the surface roughness. The tool damage was measured and compared with the cutting tool temperature for different point angles. Additionally, the tool damage, workpiece damage, and chip formation were evaluated by using a scanning electron microscope.

Real-Time Method of Obtaining Rock Mechanics Parameters Based on the Core Drilling Test

Abstract Accurately obtaining the mechanics parameters of the surrounding rock at an engineering site in real time is a key component of the construction process that is required to determine and adjust the support scheme in a timely manner and thus ensure construction safety. Currently, studies of the real-time measurement methods of the cohesion, c, and internal friction angle, φ, of the surrounding rock at a site are relatively limited, and the digital core drilling test technique provides a new approach for obtaining accurate rock parameters (c and φ) in real time at an underground engineering site. Based on the principle of upper bound analysis, in this article, a relationship model between the core drilling parameters and rock mechanics parameters (CDP-RMP) is established, and the rock core drilling cutting strength is obtained. An inversion method is proposed to obtain the rock parameters (c and φ). Additionally, by using the multifunctional rock digital drilling test system developed, digital core drilling tests are conducted on rock specimens with different lithologies. The results show that the inversion values for the rock parameters c and φ are essentially consistent with the results of the triaxial test, which verifies the accuracy of the CDP-RMP model and that of the inversion method for the rock parameters c and φ. A real-time method for obtaining rock mechanics parameters based on the digital core drilling test is further established. This method can conveniently obtain accurate mechanical parameters for the surrounding rock onsite in real time and provides a foundation for the timely optimization of the support scheme and the informatization construction of underground engineering.

Multi-hole simultaneous drilling of aluminium alloy: A preliminary study and evaluation against one-shot drilling process

Poly-drill heads are used in mass production to increase productivity when a large number of holes are required. In this work, drilling experiments on Al5083 aluminium alloy were carried out using a poly-drill head to measure the thrust force and assess hole quality. Analysis of chip formations and post-machining tool condition were evaluated using optical microscopy. Additional drilling tests were conducted using one-shot drilling and results obtained from the two drilling techniques were evaluated against each other. The results showed that the average thrust forces obtained from poly-drill head were slightly lower than those from one-shot drilling. Improvement in hole quality in terms of surface roughness and reduction in chip length were achieved using the poly-drill head. Furthermore, visual inspection of the tools showed that adhesion and built-up edges on drills used in the poly-drill head were lower as compared to drills used in the one-shot drilling. The contribution of input parameters on the measured outputs was determined using an ANOVA statistical tool.

Simultaneous optimization of drilling responses using GRA on Al-6063/TiC composite

The aim of the current work is to optimize the drilling constraints simultaneously during drilling of an Al6063/TiC composite based on grey relational analysis. Drilling trials were performed on Al-6063 reinforced with 15 wt% titanium carbide (TiC) of size 50 μm. HSS twist drills with diameter of 10 mm under lubricated condition were utilized for performing drilling tests. Drilling parameters explicitly helix angle, spindle speed, feed rate and responses such as surface roughness, cutting force and temperature are considered in the study. Grey relational grades were calculated to find the optimum levels of parameters, and moreover major involvement of constraints was dogged by ANOVA. The drilled composite specimen surface was analyzed under scanning electron microscopy (SEM). SEM metaphors of the drilled composite face specified the charisma of grooves, micro-cracks and dents.

Study on a digital drilling test–based rock uniaxial compressive strength measurement method

Real-time and accurate measurement of the uniaxial compressive strength of rock on-site is the foundation of the design optimization and digital construction of the support structure in an underground project. Currently, effective methods to obtain the rock uniaxial compressive strength Rc in real-time on-site are scarce. Digital drilling test technology provides a new opportunity to solve this problem; however, the lack of a universal relational model for the drilling parameters versus Rc constrains further development of this technology. In this study, based on developed PDC bit for probing, the Sc parameters of rock cutting strength are proposed, and the relational equation between Sc and drilling parameters is deduced. Using an in-house-developed rock drilling test system, laboratory digital drilling tests for sandstone and mortar specimens with various strengths are performed. Based on the test results, a relational equation between Rc and Sc is developed. Subsequently, a relational model for drilling parameters versus Rc (the DP-Rc model) is developed, and its effectiveness is verified. The results show that the average difference in the uniaxial compressive strength predicted by the DP-Rc model versus the Rc measured in the uniaxial test is less than 10%, which proves the effectiveness of this model. On this basis, we propose a digital drilling test–based rock uniaxial compressive strength real-time measurement method that provides the foundation for the real-time and accurate measurement of the uniaxial compressive strength of the surrounding rock in underground projects.

Field test of a Combined Thermo-Mechanical Drilling technology. Mode I: Thermal spallation drilling

Accessing hydrocarbons, geothermal energy and mineral resources requires more and more drilling to great depths and into hard rocks, as many shallow resources in soft rocks have been mined already. Drilling into hard rock to great depths, however, requires reducing the effort (i.e., energy), time (i.e., increasing the rate of penetration) and cost associated with such operations. Thus, a Combined Thermo-Mechanical Drilling (CTMD) technology is proposed, which employs a heat source (e.g., a flame jet) and includes two main drilling modes: (I) Thermal spallation drilling, investigated here as a field test and (II) Flame-assisted rotary drilling, investigated as a field test in the companion paper. The CTMD technology is expected to reduce drilling costs, especially in hard rocks, by enhancing the rock penetration rate and increasing the bit lifetime. ModeI of the CTMD technology (thermal spallation drilling) is investigated here by implementing the concept on a full-scale drilling rig to investigate its feasibility and performance under realistic field conditions. During the test, the successful thermal spallation process is monitored, employing a novel acoustic emission system. The effects of thermal spallation in the granite rock are analyzed to provide conclusions regarding the rock removal performance and the application potential of the technology. The field test shows that thermal spallation of the granitic rock can be successfully achieved even when a liquid (water) is used as the drilling fluid, as long as the heat source is appropriately shielded by compressed-air jets. Thermal damage of the surrounding rock is investigated after the spallation test, employing micro-computer tomography imaging and modeling the stability of the cracks, generated by the spallation field test. This study shows that thermally induced damage is mainly confined within a narrow region close to the rock surface, suggesting that thermal spallation only marginally affects the overall mechanical stability of the borehole. Thus, this confirms that, as part of the Combined Thermo-Mechanical Drilling (CTMD) technology, thermal spallation drilling is a promising mode that has a high potential of facilitating the drilling of deep boreholes in hard rocks.

Fractional Fourier Transform Based Adaptive Filtering Techniques for Acoustic Emission Signal Enhancement

Acoustic emission technique (AET) is a well-known non-destructive testing method used for the detection of crack growth and monitoring structural integrity of components. The main limitation in the application of AET is the fact that acoustic emission (AE) signal is often affected by background noise. A new approach is proposed in this paper to reduce the background noise and to improve the accuracy of AE signal detection. Various noise reduction methods have been applied and studied for AE signal enhancement so far. Some of the studies proved that self-adaptive noise cancellation (SANC) and adaptive noise cancellation (ANC) are better techniques for denoising the AE signal. This paper proposes the use of ANC and SANC schemes based on Fractional Fourier Transform (FrFT) for AE signal enhancement. FrFT is the generalization of the classical Fourier Transform (FT). The use of FrFT gives an advantage of an additional degree of freedom (angle of rotation in time–frequency plane) over the traditional Fourier transform and could provide improved performance. In this method, the noisy signal is rotated in time- frequency plane to extract the signal in Fractional Fourier domain (FrFD). Two adaptive filters viz. least mean squares and normalized least mean squares are studied for FrFD based ANC approach. The performance of the proposed method is validated using real AE signals acquired from three different experiments: pencil lead break test, composite drilling test and concrete compression test. Results are compared with the time and frequency domain adaptations. Moreover, the results have also been compared with the frequency domain adaptation techniques. Results have demonstrated that FrFD based ANC approach outperforms the conventional time domain and frequency domain adaptive filtering with an improved signal to noise ratio and significantly reduces mean square error.

Estimation of Los Angeles and Micro Deval abrasion values for gneiss and granite using ANFIS approach

Gneisses and granites mechanical properties knowledge such as the Los Angeles and Micro-Deval coefficients is very important for the engineer when designing and building civil engineering works. Laboratories test often performed to obtain Los Angeles and Micro-Deval values are expensive and time consuming. For this, the depths (parallel and perpendicular to the foliation planes) obtained during a rock drilling test will be used to estimate its coefficients Los Angeles and Micro-Deval. In this study, an ANFIS approach is used to estimate gneisses and granites Los Angeles and Micro-Deval that have been compared to the Multiple Linear Regression method. For this purpose, we have used a database of a sample size of 80 to determine the parameters of the ANFIS and Multiple Linear Regression models, and a second sample of size 15 used for the validation tests. The results obtained show us that we can estimate the mechanical properties (Los Angeles and Micro-Deval) of gneisses and granites with ANFIS approach.

Investigation of the effects of drill geometry on drilling performance and hole quality

In this study, the effects of drill geometry on cutting performance and hole quality in the drilling process were investigated. Two newly developed drill geometries were compared with two commercially available drill geometries. In the drilling tests on GGG50 cast iron, 4 different drills, 4 different cutting speeds and 4 different feed rates were used for L16 experimental design. The drilling tests were performed with and without cutting fluid. The results were evaluated using the axiomatic design method, one of the multi-criteria decision making methods, in terms of thrust force, surface roughness, deviation on hole diameter and length of adhering workpiece material around the chisel edges. From the obtained results, it was seen that the best results were obtained from one of the newly developed drill geometries. In addition, wear test was carried out without cutting fluid using the drill which performed best. With this best performed drill, after 100 drilling operations in wet and dry conditions and after 1500 drilling operations in dry conditions, SEM images were taken from the used drills. After drilling 100 holes both in dry and wet drilling conditions, there was almost no wear on the drills. However, some adhered workpiece material was seen on the drills. In addition, the amount of adhered workpiece significantly increased in dry drilling condition.

The effects of stacking sequence on drilling machinability of filament wound hybrid composite pipes: Part-1 mechanical characterization and drilling tests

In the first part of this two-part comprehensive study, mechanical properties and machinability characteristic of filament wound hybrid composite pipes with various stacking sequences of glass and carbon fibers (Glass-Carbon-Glass (GCG), Carbon-Glass-Glass (CGG), and Glass-Glass-Carbon (GGC)) were investigated experimentally. In order to determine the mechanical properties of the pipes, hardness test (Shore D), ring tensile test (ASTM D2290), and burst test (ASTM D1599) were carried out. Machinability tests were performed at various feed rates (50, 150, 250 and 350 mm/min) and spindle speeds (796, 1592, 2388 and 3184 rpm) using with and without a back-up. The results showed that stacking of the carbon layer between two glass layers (GCG) presented better performance in terms of mechanical properties and machinability characteristic. The maximum ring tensile stress of GCG specimen is 27% and 19% higher than those of GGC and CGG specimens, respectively. On the other hand, the lowest thrust forces measured during the drilling of GCG specimen while the GGC represented highest values. In addition, the use of back-up led to an increase in thrust force. The highest increase was observed in GGC sample. In GGC sample, a change in a spindle speed increased thrust force by 18–35%, while a change in feed rate increased thrust force by 20–30%.

Analysis of advancing speed effect in gas safety extraction channels and pressure-relief gas extraction

Combined with the coal mining process of a high gas coal mine in Jinzhong, Shanxi Province, this paper discussed the evolution mechanism of the gas safety extraction channels induced by the mining of overburden fissures in the fully mechanized mining working face and carried out the physical similar simulation test. According to the theory of mining fracture elliptic paraboloid zone, the working face advanced speed as the key parameter, mathematical modelling of the gas safety extraction channel profile was performed. The effect of advancing speeds on the evolution of gas safety extraction channels in overburden fissures was comprehensively analysed. The results suggested that increasing advancing speed reduced the height of the caving, fractured and bending zone, enlarged average weighting intervals, and the range of development was small. What's more, with increasing advancing speed, gas safety extraction channels presented gradually reduced bed-separation volume and continuity, and the fractal dimensions (7.0 < 5.0 < 3.0 m/d) also decreased. By conducting on-site high-level drilling field tests, parameters of the high-level boreholes were optimized based on specific advancing speeds, which ensured production safety and efficiency of the mining working face. The present work contributes a theoretical guides for the identification of gas extraction area under different advancing speeds.

Compact Bone Surgery Robot With a High-Resolution and High-Rigidity Remote Center of Motion Mechanism.

Two important and difficult tasks during a bone drilling procedure are guiding the orientation of the drilling axis toward the target and maintaining the orientation against the drilling force. To accomplish these tasks, a remote center of motion (RCM) mechanism is adopted to align the orientation of the drilling axis without changing the entry point. However, existing RCM mechanisms do not provide sufficient resolution and rigidity to address hard tissue cases. We propose a new type of RCM mechanism that uses two sets of linear actuators and a gearless-arc guide to have a high resolution and rigidity. In addition, we designed a single motor-based drilling mechanism based on rolling friction. To achieve automatic control of the guiding and drilling process, we incorporated a computer-tomography-based navigation system that was equipped with an optical tracking system. The effectiveness of the integrated robotic system was demonstrated through a series of experiments and ex vivo drilling tests on swine femurs. The proposed robotic system withstood a maximum external force of 51 N to maintain the joint angle, and the average drilling error was less than 1.2mm. This study confirms the feasibility of the proposed bone drilling robotic system with a high-resolution and high-rigidity RCM mechanism. This drilling system is the first successful trial based on an RCM mechanism and a single motor-based drilling mechanism, reducing the footprint and required motors with respect to previous bone surgical robots.

Field test of a Combined Thermo-Mechanical Drilling technology. Mode II: Flame-assisted rotary drilling

To enhance the drilling performance in deep hard rocks and reduce overall drilling efforts, this work proposes a Combined Thermo-Mechanical Drilling (CTMD) technology. This technology employs a heat source (e.g., a flame jet) and includes two main drilling modes: (I) thermal spallation drilling, investigated in the companion paper and (II) flame-assisted rotary drilling, investigated here as a field test. The CTMD technology is expected to reduce drilling efforts, especially in hard rocks, enhancing the rock penetration rate and increasing the bit lifetime, all of which reduces the drilling costs. The present work investigates Mode II (flame-assisted rotary drilling) of the CTMD technology by implementing the concept in an existing drilling rig and testing the technology under relevant process conditions. This contribution studies the underlying rock removal mechanism of CTMD and demonstrates its drilling performance, compared to conventional rotary drilling methods. Acoustic emission monitoring, and analysis of the collected drill cuttings provide multiple evidences for thermal-cracking-enhanced rock removal during the flame-assisted rotary drilling. This removal mechanism appears to represent an optimal compromise to minimize rock fragmentation and cutting transport efforts during drilling, compared to a less efficient mechanical scraping of the hard granite rock, observed during the standalone-mechanical drill test. The drilling performance, in terms of removal and wear rates, are evaluated for the flame-assisted rotary drilling. This shows that the proposed drilling approach is capable of enhancing the removal process in hard granite rock, by a factor of 2.5, compared to standalone-mechanical drilling. The implementation of this drilling approach into a conventional drilling system shows that integration of thermal assistance to conventional rotary drilling requires marginal technical efforts. Additionally, this technology can profit from established knowledge in conventional mechanical drilling, facilitating its implementation to improve drilling performance in hard rocks. Hence, this study demonstrates that the Combined Thermo-Mechanical Drilling method is feasible and concludes that this technology constitutes a promising approach to improve the drilling process, thereby increasing the viability of accessing deep geo-resources in hard rocks.

3D finite element analysis of Al7075-T6 drilling with coated solid tooling

Due to the fact that simulation of drilling was added in commercial finite element analysis (FEA) software only recently, 3D finite element modelling is an invaluable asset during related researches. The present study employs 3D FEA to model the drilling process of Al7075-T6 alloy with solid carbide tooling, investigates important phenomena that occur during drilling and finally compares the simulated results with experimental data. A number of simulations were performed with DEFORM3D™ software at different cutting conditions; cutting speed of 50m/min, 100m/min, 150m/min and feed of 0.15mm/rev, 0.20mm/rev, 0.25mm/rev. The proposed model takes into consideration certain aspects like damage initiation and evolution of the material, contact interface between the drill bit and the workpiece and standard boundary conditions. Eventually, the acquired numerical data for thrust force were compared to the experimental results for the same cutting conditions and parameters. To obtain the experimental data, a series of nine drilling tests were performed. Upon validation of the numerical data, the temperature distribution on the tool tip – workpiece interface, as well as the chip morphology (shape and curling radius) were determined. Results showed a good agreement between the numerical and the experimental data. Specifically, thrust force and chip morphology exhibited an agreement of about 95% and 90% respectively, which confirms the potential of 3D FEA implementation on machining investigations.

Taguchi Grey Relational Analysis based Optimization of Micro-Drilling Parameters on Carbon Fiber Reinforced Plastics

The paper presents the optimization of micro drilling parameters in the Carbon Fiber Reinforced Plastics (CFRP), using different drill bits of measurement 0.7mm, 0.8mm, and 0.9mm by the Taguchi Grey Relational analysis (TGRA). For the Micro drilling test, the process parameters chosen are spindle speed, feed rate and drill diameter. The experiments are designed by the Taguchi's L27 orthogonal array. The trials are directed to enhance the machining condition and at the same time minimize the delamination factor, tool wear rate and boost the material removal rate. The optimum values for the minimized delamination factor, maximized material removal rate and the minimized the tool wear rate are identified by the performing the Taguchi Grey Relation Analysis. ANOVA of the S/N ratio is also performed to identify the percentage contribution of the selected parameters.

Energy analysis-based core drilling method for the prediction of rock uniaxial compressive strength

The uniaxial compressive strength (UCS) of rock is a basic parameter in underground engineering design. The disadvantages of this commonly employed laboratory testing method are untimely testing, difficulty in performing core testing of broken rock mass and long and complicated onsite testing processes. Therefore, the development of a fast and simple in situ rock UCS testing method for field use is urgent. In this study, a multi-function digital rock drilling and testing system and a digital core bit dedicated to the system are independently developed and employed in digital drilling tests on rock specimens with different strengths. The energy analysis is performed during rock cutting to estimate the energy consumed by the drill bit to remove a unit volume of rock. Two quantitative relationship models of energy analysis-based core drilling parameters (ECD) and rock UCS (ECD-UCS models) are established in this manuscript by the methods of regression analysis and support vector machine (SVM). The predictive abilities of the two models are comparatively analysed. The results show that the mean value of relative difference between the predicted rock UCS values and the UCS values measured by the laboratory uniaxial compression test in the prediction set are 3.76 MPa and 4.30 MPa, respectively, and the standard deviations are 2.08 MPa and 4.14 MPa, respectively. The regression analysis-based ECD-UCS model has a more stable predictive ability. The energy analysis-based rock drilling method for the prediction of UCS is proposed. This method realized the quick and convenient in situ test of rock UCS.

Prediction Model of Drilling Performance for Percussive Rock Drilling Tool

This study suggests a method for quantitatively estimating the drilling performance of the down‐the‐hole (DTH) hammer during percussive drilling of rock surfaces. A pneumatic dynamic model of the DTH hammer was developed that considers the mass flow rate relations representing the orifice opening areas of the air tube, the piston, and bit flushing channels. A drill bit motion model was developed to represent the dynamics of a drill bit impacted by a dropped piston and explain the impact stress propagation and rock‐crushing mechanism. The rock‐crushing effect of the drill button bit was measured through a piston drop test. The pneumatic hammer model and drill bit motion model were then combined in a prediction model to determine the impact efficiency according to different rock types (i.e., soft, medium‐hard, and very hard). The drilling efficiency was defined as the input value of the prediction model, which was used to simulate the drilling performance of DTH hammers considering the rock type and dynamic effect of the drill bit. Finally, the simulation results were compared with the results of in situ drilling tests for verification.