Drilled Hole Wall Research Articles

Study on the influence of cortical bone heterogeneity on the spatio-temporal distribution of drilling temperature

The degree of thermal damage during cortical bone drilling is an important factor in determining the success rate of surgery and postoperative recovery time. In this study, high and low feed rate drilling experiments are carried out on bovine femoral cortical bone by chisel edge thinning drill. Combined with the characterization of cortical bone tissue structure and the measurement results of important thermal property parameters, the potential impact mechanisms of cortical bone heterogeneity on the spatio-temporal distribution of drilling temperature and thermal damage are analyzed. The temperature rise rate and overheating duration at different distances from the hole wall in cortical bone drilling under different feed rates are also compared. The experimental results show that the specific heat gradually increases and the thermal conductivity gradually decreases from the periosteum to the endosteum. The hole wall temperature and thermal diffusion of cortical bone with different tissue structures are different under high and low feed rates. The closer to the cortical bone endosteum, the lower the drilling temperature, thermal diffusion and thermal damage area. This is not only related to the contact time between the drill bit and the hole wall of cortical bone with different tissue structures, but also closely related to the heterogeneous structure of cortical bone. In addition, it is found that in high feed rate cortical bone drilling, the temperature rise rate at different positions from the hole wall is higher and the overheating duration is shorter.

Material removal and surface damage mechanisms in micro drilling of Nd:YAG material

Neodymium-doped Yttrium Aluminum garnet (Nd:YAG) materials enable the vital applications in both industrial and military fields. In this study, the nanoscratch and micro drilling tests were conducted to investigate the material removal and surface damage mechanisms of Nd:YAG. The brittle-ductile transformation and intermittent edge breaking mechanisms were elaborated in the nanoscratch tests. After the scratch load exceeded 37 mN, the material removal mechanism transforms from elastic-plastic deformation to brittle fracture. Subsequently, the various material removal and surface damage mechanisms were observed on the hole surface and hole wall in micro drilling, which was consistent with the scratch test results. On the hole surface, the discontinuous edge-breaking defects with a petal shape are the primary surface damages, which encircle the hole surface to form a sunflower shape. However, the hole wall quality primarily depends on the proportion of flaky exfoliation and the brittle fracture zones on the hole wall, and the hole wall roughness increased with the drilling speed and feed rate. This study aims to understand the material removal mechanisms and optimise the machining parameters in micro drilling of hard and brittle materials.

Drill string’s axial force transfer law in slide directional drilling in underground coal mine

During the slide directional drilling with long directional near-horizontal drilling technology, the weight on bit (WOB) at the bottom of the hole is exerted by pushing the drill pipe with the power head of the orifice drill. With the increase of drilling depth, the friction resistance between drill string and hole wall also goes up, resulting in problems including insufficient WOB, low drilling efficiency, and surge of feeding pressure. If the orifice feeding pressure continues to rise, the drill string will buckle or fracture. In our study, the field test method is adopted to explore the drilling string’s axial pressure transfer law. By comparatively analyzing different stratigraphic characteristics of five directional boreholes with an average radius of deflection, the deep-hole drill string transmitting pressure model with nine curvature radiuses is set up for simulating the relationships between drill string friction, hole depth, and strata characteristics under different working conditions. The results show that when the hole is relatively shallow, the relationship between the friction resistance and the hole depth is basically linear, which gradually develops into an exponential one with the increase in the hole depth. For the borehole with a curvature radius less than 200 m, the friction resistance is greatly affected. The softer the formation is, the greater the linear range of friction resistance becomes with the increase in the hole depth, the latter the hole depth with an exponential growth occurs, and the longer the limit depth is. The findings reveal the axial pressure transfer law of the drill string, which will facilitate future design of the drilling hole, optimize the control of drilling trajectory, and matter a lot to engineering practices.

Methods to create slots–stress raisers in near-wellbore zone

The author reviews methods and tools for cutting slots–stress raisers in drill hole walls for directional hydraulic fracturing. Based on the review, the classification is proposed for the known tools by the method of initiating slotting: mechanical cutting; indentation of hard indenters; percussion effect by a plastic substance; blasting of jet charges. By the number of the patented engineering solutions and the level of implementation, the most popular technique is mechanical cutting. The known tools only ensure creation of slots–stress raisers in soft and medium-hard rocks. It is required to continue studies and to develop new methods and tools for cutting initiating slots for the directional hydraulic fracturing in solid ore.

Microstructural evolution of soft magnetic 49Fe-49Co-2V alloy induced by drilling

Mechanical drilling can change the microstructure of the regions near the hole wall, remarkably affecting the working performance of precision parts. The present work investigated the microstructural evolution in the regions from the drilled hole wall to the inner matrix of the soft magnetic 49Fe-49Co-2V alloy after the common drilling experiments were carried out. The microstructures and microhardness in different regions near the hole wall along the radial direction were characterized with OM, SEM, TEM, EBSD and Vickers Microhardness tester. The experimental results show that the nearest region to the hole wall is constituted of nano-sized refined grains. It exhibits a disordered BCC phase due to the rapid cooling from the high temperature during the drilling, different from the dual-phase of BCC and B2 of the matrix. The second-nearest region to the hole wall is distributed by a huge number of dislocations, leading to a maximum in microhardness. The microstructural evolution contributes to the variation of the microhardness, which increases firstly, reaches a maximum, and then decreases to the level of the matrix with the distance increasing from the hole wall. This variation tendency is discussed in light of both refined grain-boundary strengthening and dislocation strengthening mechanisms.

Rigid-flexible coupled multi-body dynamics analysis of horizontal directional drilling rig system

To reduce the failure probability of gas drainage drilling holes in coal mines, a new modeling method of gas drainage drilling machine is presented. Firstly, each drill pipe is regarded as a flexible body, and the Lagrange’s equation of second kind is used to model it. Secondly, the joint of drill bit, hole wall and drill pipe are regarded as rigid bodies, and the Newton-Euler method is used to model it. Thirdly, the rigid-flexible coupling multi-body dynamic model of drilling rig-drill pipe-hole wall system in medium and short horizontal section of soft coal seam is established by using relative node coordinate method, and the time complexity and operation complexity of modeling are reduced by using ADAMS macro program. Finally, the finite element method is used to discretize the model, and the virtual prototyping technology is used to solve the mathematical model. The simulation results show that the coupling of friction and vibration does not necessarily increase the probability of drilling failure, but sometimes reduces the amplitude of vibration. Compared with the length of each drill pipe, the influence of drilling depth on the system is greater, and the bit-bounce behaviours is more likely to occur in the deep hole. The operating frequency range of the drilling rig is 6.9E-3 to 2.1E+4Hz. When the length of the drill pipe is constant, the natural frequency of the system increases with the increase of the order, while the natural frequency of the deep hole section is almost unaffected by the order. In practical engineering, the vibration excitation of the actuator should be controlled to avoid the natural frequency. Meanwhile, the modal frequency should be avoided as far as possible to reduce the vibration and the failure probability of drilling holes. The model can simulate a series of dynamic responses of drilling rig system in drilling process, and provide theoretical support for subsequent multi-factor coupling modeling.

Estimation of mechanical energy consumption of the drill string in rotary drilling

The article is devoted to the study of dynamic phenomena in the drill string based on energy positions. Thefriction of mechanical transmissions in rotor drive, curved sections of the drill string on drill-hole walls in thedrilling mud and change in the torque on the bit are the main causes of the mechanical energy consumption in theprocess of drilling. In this case, the required engine power is used for to provide drill string rotation in the well withsome unevenness and bottom-hole deepening. 
 The power balance equation of the mechanical system “power drive–drill string–bottom hole” is analyzed. Theauthors have developed the problem for defining the kinetic energy of drill string in rotor drilling, which is spent onovercoming the friction in drive transmissions and drill string on drill-hole walls in the drilling mud as well as ondrilling the bottom hole. The use of the defined mathematical dependencies is demonstrated by the nomograph fordetermining the friction power in case of drill string free run in the well. The obtained results of theoreticalresearch can be used by engineering and manufacturing divisions of drilling enterprises for the engineeringestimate of energy consumption in rotary drilling.

Numerical and experimental investigations on temperature distribution of plain-woven aramid fiber-reinforced plastics composites with low-mild spindle velocities

Temperature distribution of plain-woven aramid fiber-reinforced plastics (AFRP) composites was investigated by numerical and experimental methods for their drilling process with low-mild spindle velocities. A three-dimensional (3-D) numerical model was proposed for predicting the temperature distribution. Drilling experiments were carried out to verify the proposed numerical model and investigate the thermal damages with low-mild spindle velocities. The accuracy of the proposed numerical model was acceptable with less than 8% relative errors compared with experimental results. Cutting heat easily accumulated even the AFRP composites were drilled with low-mild spindle velocities for their poor thermal conductivity. Temperature distributions presented a rounded diamond shape, which diagonal direction was consistent with the fiber direction. With the high heat accumulation, although the drilled hole wall was damaged by the high temperature, carbonation phenomenon was not serious for the low spindle velocity drilling. For the mild spindle velocity drilling case, a serious carbonation phenomenon had been observed, and the heat-affected layer in the hole wall was about 0.3 mm.

Enhancing Efficiency of Rock Drilling Tool in Permafrost

The development of a large-diameter (from 500 m and more) rotary drill tool (drill bit) for exploration of placers in permafrost is discussed in the article. It is shown that at the contact of drill bits and bottomhole, permafrost thaw takes place with the further adhesion and congelation of the drill tool and hole walls, which degrades coring. The dependence of heat emission at bottomhole on cutter configuration radius on drill bit is determined. The developed design of a drill bit ensures efficient destruction of bottomhole with minimized heat emission, and a prototype drilling assembly is manufactured for large-diameter rotary drilling. The in situ test data are presented.

Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling

The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock material, and the conditions of the rock drilling operation. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. In the present study, the surface degradation and wear mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling have been characterized based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam cross-sectioning (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).The results show a significant difference in surface degradation and wear between the front and peripheral buttons of the drill bits. While the front buttons display a relatively smooth worn surface with shallow surface craters the peripheral buttons display a reptile skin pattern, i.e. plateaus, 200–300µm in diameter, separated by valleys, typically 40–50µm wide and 15–30µm deep, The reptile skin pattern is obtained in regions where the peripheral buttons are in sliding contact against the drill hole walls and exposed to high surface temperatures caused by the frictional heating. The results indicate that the reptile skin pattern is related to friction induced thermal stresses rather than mechanical contact stresses, i.e. the reptile skin pattern is formed due to thermal fatigue, rather than mechanical fatigue, caused by the cyclic frictional heating generated at the cemented carbide button/iron ore interface.

Enhancement of long hole drilling efficiency with drilling units with replaceable core tubes

The article presents a procedure to calculate fluid pressure losses in hole drilling with units equipped with replaceable core tubes and using non-Newtonian mud fluids. It is found that main hydraulic loss takes place when mud fluid flows in clearing between a drill string and drill hole walls. Numerical modeling has shown that it is possible to reduce hydraulic pressure loss by 76.5–89.0% by increasing drill string diameter by 2 mm. Based on the analytical research results, diamond drill bits and underreamers with the outer diameters of 78.0 and 78.4 mm, respectively, are manufactured for drilling operations in Talnakh ore field.

Effect of modified drill point geometry on drilling quality characteristics of metal matrix composite (MMCs)

The abrasive reinforcement present in ‘Metal matrix composites’ (MMCs) is responsible for numerous machining challenges for the research fraternity. The increase in tool wear, burr formation, surface roughness, and increase in cutting forces are few of such machining challenges during the drilling of MMCs. The present research investigation explores the effect of change in drill point geometry on the drilling Quality characteristics (QCs) of the drilled hole wall. The drilling QCs under investigation are, Specific cutting pressure (SCP) and Surface roughness (SR) of the drilled hole wall. The levels of the input process parameters for optimum values of the output responses were established by Taguchi’s methodology. SEM images and contour plots of drilled hole wall have been used to qualitatively explain the drilling behavior of MMCs. The chip formation mechanism observed during drilling establishes the cutting behavior of the different cutting edges of the modified drill point geometry. It has been observed that the single conical chips were produced by primary cutting edge and single ring type chips were produced by secondary cutting edge. The step diameter is the main factor which influences the SCP followed by the feed and point angle. The surface roughness of the drilled hole wall has been governed by the cutting speed, feed and step diameter. Burnishing and honing effect were observed on the drilled hole wall surface because of entrapped free SiC particles using SEM.

ChemCam investigation of the John Klein and Cumberland drill holes and tailings, Gale crater, Mars

The ChemCam instrument on the Mars Science Laboratory rover analyzed the rock surface, drill hole walls, tailings, and unprocessed and sieved dump piles to investigate chemical variations with depth in the first two martian drill holes and possible fractionation or segregation effects of the drilling and sample processing. The drill sites are both in Sheepbed Mudstone, the lowest exposed member of the Yellowknife Bay formation. Yellowknife Bay is composed of detrital basaltic materials in addition to clay minerals and an amorphous component. The drill tailings are a mixture of basaltic sediments and diagenetic material like calcium sulfate veins, while the shots on the drill site surface and walls of the drill holes are closer to those pure end members. The sediment dumped from the sample acquisition, processing, and handling subsystem is of similar composition to the tailings; however, due to the specifics of the drilling process the tailings and dump piles come from different depths within the hole. This allows the ChemCam instrument to analyze samples representing the bulk composition from different depths. On the pre-drill surfaces, the Cumberland site has a greater amount of CaO and evidence for calcium sulfate veins, than the John Klein site. However, John Klein has a greater amount of calcium sulfate veins below the surface, as seen in mapping, drill hole wall analysis, and observations in the drill tailings and dump pile. In addition, the Cumberland site does not have any evidence of variations in bulk composition with depth down the drill hole, while the John Klein site has evidence for a greater amount of CaO (calcium sulfates) in the top portion of the hole compared to the middle section of the hole, where the drill sample was collected.

Nonlinear Dynamics Research between Drill Pipe and Coal Hole Wall during Gas Extraction Drilling

This paper analyzes the impact of gas drainage borehole drilling rod vibration phenomena stability.Taking 100m hole depth in underground coal mine as an example, the dynamic simulation analysis of the underground gas drainage drilling rod was carried out by using the ANSYS finite element dynamic analysis module LS-DYNA method.According to the collision course between the drill pipe and the coal hole wall, the Lagrange algorithm is introduced to analyze the stress change of drill pipe in the collision course of 98mm, 108mm, 118mm and 128mm. The failure mechanism of drill pipe fatigue fracture and hole wall instability caused by the collision between drill pipe and coal hole is analyzed. The results show that the stress caused by the impact of drilling speed, drilling pressure and coal hole diameter is larger than that caused by the collision between drill pipe and coal wall.

Study the drilling behaviour of aluminium 6061 metal matrix composites using Taguchi's methodology

Drilling of holes in MMCs with conventional tool lead to a novel set of challenges for researchers. The abrasive nature of the reinforcement causes high tool wear rate, increase in cutting forces and surface roughness of the drilled hole wall. The various machine tool parameters and cutting tool parameters (tool material, point angle, drill point geometry, etc.) have been investigated to obtain an optimum combination of parameters for optimised output quality characteristics.

Experimental Investigation on the Basic Law of the Fracture Spatial Morphology for Water Pressure Blasting in a Drillhole Under True Triaxial Stress

The present literature on the morphology of water pressure blasting fractures in drillholes is not sufficient and does not take triaxial confining stress into account. Because the spatial morphology of water pressure blasting fractures in drillholes is not clear, the operations lack an exact basis. Using a large true triaxial water pressure blasting experimental system and an acoustic emission 3-D positioning system, water pressure blasting experiments on cement mortar test blocks (300 mm × 300 mm × 300 mm) were conducted to study the associated basic law of the fracture spatial morphology. The experimental results show that water pressure blasting does not always generate bubble pulsation. After water pressure blasting under true triaxial stress, a crushed compressive zone and a blasting fracture zone are formed from the inside, with the blasting section of the naked drillhole as the center, to the outside. The shape of the outer edges of the two zones is ellipsoidal. The range of the blasting fracture is large in the radial direction of the drillhole, where the surrounding pressure is large, i.e., the range of the blasting fracture in the drillhole radial cross-section is approximately ellipsoidal. The rock near the drillhole wall is affected by a tensile stress wave caused by the test block boundary reflection, resulting in more flake fractures appearing in the fracturing crack surface in the drillhole axial direction and parallel to the boundary surface. The flake fracture is thin, presenting a small-range flake fracture. The spatial morphology of the water pressure blasting fracture in the drillhole along the axial direction is similar to a wide-mouth Chinese bottle: the crack extent is large near the drillhole orifice, gradually narrows inward along the drillhole axial direction, and then increases into an approximate ellipsoid in the internal naked blasting section. Based on the causes of the crack generation, the blasting cracks are divided into three zones: the blasting shock zone, the axial extension zone, and the orifice influence zone. The explosion shock zone is the range that is directly impacted by the explosive shock waves. The axial extension zone is the axial crack area with uniform width, which is formed when the blasting fracture in the edge of the explosion shock zone extends along the drillhole wall. The extension of the orifice influence zone is very large because the explosion stress waves reflect at the free face and generate tensile stress waves. In the water pressure blasting of the drillhole, the sealing section should be lengthened to allow the drillhole blasting cracks to extend sufficiently under the long-time effect of the blasting stress field of quasi-hydrostatic pressure.

Investigation of Drilling Conditions of Printed Circuit Board Based on Data Mining Method from Tool Catalog Data-Base

Data-mining methods using hierarchical and non-hierarchical clustering are proposed that will help engineers determine appropriate drilling conditions. We have constructed a system that uses clustering techniques and tool catalog data to support the determination of drilling conditions for printed wiring boards (PWBs). Variable cluster analysis and the K-means method were used together to identify tool shape parameters that have a linear relationship with the drilling conditions listed in the catalogs. The response surface method and significant tool shape parameters obtained by clustering were used to derive drilling condition decision equations, which were used to determine the indicative drilling conditions for PWBs. Comparison of the conditions recommended by toolmakers demonstrated that our proposed system can be used to determine the drilling condition for PWBs. We carried out the drilling experiments in accordance with the catalog conditions and mining conditions, and estimated the board temperature around a drilled hole, the drilling forces, and the roughness of the drilled hole wall.

Design and development of abrasive-assisted drilling process for improvement in surface finish during drilling of metal matrix composites

A novel technique called abrasive-assisted drilling has been designed and developed to improve the surface finish of the drilled hole wall during the drilling of Al6063/10%SiC metal matrix composites. The developed process eliminates the use of supplementary surface finishing process such as abrasive flow machining or deburring of drilled hole, which adds to the cost of product. With the help of this technique, fine polished drilled hole wall surface can be produced by removing small fragments of material generated by the high-energy abrasive particles. A considerable increase in surface finish of the drilled hole wall has been observed for metal matrix composites. Taguchi’s methodology has been used to explore the effect of input process parameters on the surface roughness and hole oversize of the drilled hole. The input process parameters under consideration are rotational speed, finishing time, abrasive size and abrasive concentration.

Circulation system of a pneumatic drill with central drilling mud removal

The article describes experimental testing of a pneumatic drill tool with reverse circulation of drill fluid. The authors assessed suitable clearance between downhole packer and drill hole walls and propose engineering design aimed for higher performance of the pneumatic drill circulation system.

Novel System Technology for Trepanning a Laser Beam at Arbitrary Developments of Angle of Incidence and Lateral Focus Position

In laser materials processing, trepanning optics are used to fabricate laser drilled holes of high aspect ratios (> 10) and controllable drill-hole conicity. However, trepanning optics available up to today are limited to circular trepanning geometries. Thus, only circular holes with drill-hole wall angles of rotational symmetry are feasible. Within this paper we will present a novel trepanning optic based on two piezo-actuatoric tip/tilt mirrors, being first of its kind, which allows arbitrary developments of propagation angle and lateral position of the laser beam, both being independent of each other. Consequently, the novel trepanning optic allows arbitrary drill-hole geometries such as circular, elliptical, rectangular etc. At the same time the drill-hole wall angle may be varied freely. Thus, asymmetric drill-hole wall angles are feasible such as tilt of the drill hole or wobbling of the drill-hole wall angle for instance. Demonstrative drill-holes of different shapes produced with an ultrashort pulsed laser prove the flexibility of the trepanning optic presented.