Thermal Drilling Research Articles

STUDY OF THE USE OF THERMAL DRILLING IN MECHANICAL JOINING OF MG SHEET AND GFRP/CFRP COMPOSITES WITH THERMOSOFTENING MATRIX

The paper discusses the joining of magnesium based metallic sheet and composites with thermosoftening polypropylene matrix reinforced with bi-directional continuous glass and carbon fibers by thermal drilling technology. The bushing formation has been investigated by separately drilling AZ91 Mg alloy sheet at two rotational speeds and feed rates to find out the parameters at which a bushing with optimum length and thickness, suitable for joining with the composite, is formed. Under these conditions, the joining of the metal sheet and composite was then carried out by simple thermal drilling. During simple drilling, delamination of the composite occurred in the vicinity of the hole, which was resolved by flanging the bushing with a penetration of the tool from the opposite side. When AZ91 was joined to carbon fibers reinfirced composite, there was a lack of bushing formation due to the higher resistance of the carbon fibers, which are present in the composite in greater numbers compared to the glass fibers. This problem was solved by sequential drilling, which means that a flowdrill tool was used to create a hole in the composite itself, then overlaid with Mg sheet and again drilled, forming the bushing and flanging the bushing from the opposite side. The sequential drilling resulted in joints with a load capacity of 0.8 - 1.4 kN, which exhibit the characteristics of a hybrid - mechanical and adhesive joint.

Hybrid Joining of Dissimilar Thin Metallic Sheets—Mechanical Joining and Adhesive Bonding

This paper deals with joining dissimilar materials using thermal drilling technology as well as the combination of thermal drilling and adhesive bonding. The base materials for the experimental work were deep-drawn low-carbon steel DC04, HSLA steel TL 1550-220 + Z, and structural aluminum alloy EN AW-6082 T6 (AlSi1MgMn). The geometry of the formed joints was tested metallographically as the load-bearing shear capacity under the tensile shear test of single-lapped joints and the resistance of the joints against corrosion-induced disbonding in a climate chamber. The energy dissipated by the joints up to fracture was calculated from the load–displacement curves. The hybrid joints were compared with the bonded joints with the same overlap area in terms of the load-bearing capacity and energy dissipated at joint failure. The hybrid joints formed by thermal drilling and adhesive bonding with a rubber-based adhesive confirmed the synergistic effect—the adhesive provides the high load-bearing capacity of the joint, and the bushing formed by thermal drilling increases the dissipated energy of the joint at failure. The exposure of the joints in the climatic chamber did not cause a relevant reduction in the characteristics of the joints.

Ice ridge evolution: Investigation in-situ and computer simulations

The article presents a two-dimensional three-layer non-stationary thermodynamic model allowing to calculate the annual variation (thermodynamic evolution) of the ice ridge using external meteorological and hydrological parameters as well as the information on the initial ice ridge porosity. For the test model simulation, the results of the study of morphometric characteristics of the ice ridge carried out in May-June 2011 and in April 2012 at « North Pole −38» and «North Pole −39» drifting stations were used. These studies were conducted using electric thermal drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.5 m intervals. Cross-sectional profiles of ice ridge are illustrated. Applying the proposed model, it was possible to adequately reproduce the observed evolutionary changes in the main morphometric parameters (sail height, keel depth, thickness of the consolidated layer) of the investigated ice ridge.

FLUID CHARACTERISTICS AND POLISHING EXPERIMENT OF INCLINED HOLE ARRAY USING ABRASIVE WATER FLOW

Inclined hole arrays on superalloys have important applications in aeroengines. However, defects occur during fabrication of inclined holes using thermal drilling methods, i.e. electrical discharge drilling (EDD), including a recast layer and microcracks on the hole wall. Therefore, abrasive water flow polishing (AWFP) of a superalloy inclined hole array machined via EDD was investigated in this study. Two types of specimens were designed: a hole array of identical size and a hole array with an identical inclination angle. The fluid simulation revealed that the fluid velocity and pressure on the lower edge of the inclined hole were significantly higher than those on the upper edge when the fluid flowed forward. The fluid characteristics exhibited opposite trends when backward flow was implemented. Time-division bidirectional flow can effectively compensate for flow field nonuniformity and improve material removal consistency during polishing. The experimental results show that for inclined holes with identical inclination angles, the size expansion decreases with an increase in the hole diameter owing to the lower fluid velocity and material removal volume in the relatively larger holes. Consequently, surface roughness Ra increases with hole size. For inclined holes with identical diameters, the size expansions of the entrance and exit approach the same level; whereas, Ra decreased with an increase in the inclination angle. The hole taper slightly reduced in all cases. Using garnet abrasives with 1300 mesh size, 1.5 wt.% abrasive concentration, and 3 MPa fluid pressure, the surface roughness Ra of target holes was reduced from pre-polishing [Formula: see text] 5.0 [Formula: see text]m to approximately post-polishing 1.0 [Formula: see text]m. The recast layer on the hole wall caused by EDD was completely removed.

Thermal drilling for application in gas and oil wells: Efficiency enhancement by acoustic inspection

Thermal drilling has recently attracted the attention of researchers due to its high efficiency in breaking hard rocks. However, the advent of low-efficiency processes, such as melting and evaporation, is challenging thermal drilling performance. The implementation of realistic guidelines to monitor spallation may help enhance the performance of this technology. In this article, the results of the continuous and intermittent application of butane oxygen flame on dry and wet limestone were compared with the results of diamond drilling based on the resulting rate of penetration and specific energies. A high-quality camera was operated as a device for visual inspection of the processes to determine any obvious macroscopic physical and chemical changes. In addition, acoustic monitoring of the processes involved during the thermal heating experiments was carried out using a microphone with a frequency response region below 20 kHz. The background noise in the recorded acoustic signals was eliminated by using noise reduction methods in MATLAB. The software performed Fast Fourier Transform (FFT) on the obtained clean signals to reveal the related frequency spectrograms. According to our experimental observations, the frequency response for spallation occurrence in wet and dry samples appears to be around 7 kHz and 15 kHz, respectively. However, the frequency response for fracture formation did not reveal a sensible dependence on moisture content in the limestone samples. Under continuous heating, the rate of penetration and the specific energy for wet samples were respectively 131% higher and 68% lower than those for the dry samples. In the dry samples, wetting between the two heating processes led to a considerable increase in the penetration rate and a dramatic decrease in the specific energy due to keeping the local temperature gradient high in the rock texture.

Pomiar zużycia energii w trakcie cyklu wiercenia termicznego

The work presents the issue of measuring and analyzing energy consumption during a thermal drilling cycle. A research stand based on a CNC lathe was presented, the equipment of which was an experimental energy consumption system based on an electricity meter and a force gauge. The measuring devices used allowed for recording the load on the power grid, the load on the machine tool drives, the axial force, the drill braking torque, the current rotation of the machine tool spindle, the position of the drill in relation to the workpiece and the values of auxiliary parameter registers in the strategy of adaptive feed control. Two cases of a drilling cycle were considered: making a single hole and making a series of holes in one cycle. Five feed control strategies were tested during the drilling cycle, including adaptive feed control and a recursive feed optimization method. For comparison, holes were also made with traditional HSS twist drills. Based on the obtained test results, it can be concluded that the friction drilling method can be included in the energy-saving methods of making holes in thin-walled elements.

A comparative study on drillability of Inconel 625 alloy fabricated by wire arc additive manufacturing

In recent years, the cost-effective wire arc additive manufacturing (WAAM) method is increasingly replacing traditional production methods for Ni-based superalloys. However, the effect of high heat input and elemental segregation in the WAAM method on machinability has not yet been adequately investigated. For this purpose, drilling of wrought and WAAM Inconel 625 samples with thermal (i.e., die-sinking micro-EDM and micro-EDM) and mechanical drilling techniques (i.e., orbital and conventional drilling) was investigated in this study. It was observed that thermal drilling methods formed a white layer with a thickness of 20-25 μm and 35-50 μm in the cross-section of wrought and WAAM specimens, respectively, while no white layer was formed in the mechanical methods. The average surface roughness of the inside hole, Ra, obtained in the conventional drilling process has improved by 46.15 %, 94.62 %, and 92.82 %, compared to the orbital, die-sinking, and micro-EDM methods, respectively. Because the drill cutting form and helix angle used in this method facilitated chip evacuation. The best surface roughness was obtained respectively by conventional (0.27–029), orbital (0.51–0.53), die-sinking (4.54–5.88), and micro-EDM drilling (3.54–4.25) methods. In addition, a larger kerf angle is obtained in the WAAM sample compared to the wrought one due to higher residual stress and higher dislocation density in the WAAM alloy. On the other hand, the higher hardness value of WAAM samples provided better surface quality in mechanical drilling methods than wrought material. An increase in surface hardness values up to 25 μm from the surface was detected due to the recast layer formed in thermal drilling methods and the strain hardening occurring on the surface in mechanical drilling methods.

ТОРОСЫ ПРОЛИВА ШОКАЛЬСКОГО (АРХИПЕЛАГ СЕВЕРНАЯ ЗЕМЛЯ): ИССЛЕДОВАНИЯ 2019 Г

Morphological characteristics of three first-year ice ridges were investigated in the Shokalsky Strait in April and May 2019 by hot-water thermal drilling with the recording of penetration rate. Boreholes were drilled along the ice ridge cross-section with an interval of 0.25 m. The ice ridge cross-sectional profiles are presented. The sail height for the investigated ridges varied within 1.8-2.7 m, and the keel draft varied from 7.0 to 9.1 m. The ratio of the keel draft to the sail height was equal to 2.7-5.2, the thickness of the consolidated layer was 2.4-2.7 m. The mean porosity of the unconsolidated part of the keel in the ice ridges made up 28-36%. The porosity distributions for the unconsolidated part of the keel along the drilling profile are given for the analyzed ice ridges. The main feature of one of the ridges was an almost rectilinear slope of the keel, which laterally extended for 16 m.

Device for fusion drilling with simultaneous or follow-up reaming of wells in ice

The paper deals with a new opening technology for subglacial reservoirs, which ensures environmentally friendly geological exploration. The technology is based on the results of the first openings of the subglacial Lake Vostok in Antarctica (February 2012 and January 2015). The primary goal of further studies of the subglacial Lake Vostok is to take clean samples of lake water and bottom sediments, which requires direct penetration into the lake. There is a number of conditions to be met in order to conduct further studies of the lake using a clean access well at the Vostok drilling complex. The article summarizes the main results including technological and engineering solutions protected by the patent of the Russian Federation. A detailed consideration is given to a new device for fusion drilling with simultaneous reaming of an ice hole. This device combines two technological processes: drilling due to contact melting, and an increase in the diameter of the well due to the creation of a vortex flow of a continuously heated coolant in the bottomhole zone. The thermal method of ice breaking ensures the ecological cleanliness when opening subglacial reservoirs and is a priority method that favorably differs from the existing ones. The device was named a “thermal drill reamer” (TDR). During the seasonal work of the 64th Russian Antarctic Expedition bench tests of the TDR 132/400 were carried out, the results of which confirmed that the device is capable to ensure 132 mm drilling with simultaneous reaming up to 400 mm.

Piezoelectric effect does not contribute in thermal drilling of quartz bearing rocks

This paper presents a numerical study on a possible piezoelectric effect in thermal drilling of Quartz bearing rocks. For this end, the governing piezoelectro-thermo-mechanical problem is solved with the finite element method. The granitic rock material, consisting of Quartz, Feldspar and Biotite minerals, is taken as linear elastic but heterogeneous and anisotropic. Temperature dependence of material properties is neglected. The simulation demonstrates that the secondary stresses arising from converse piezoelectric effect are three orders of magnitude smaller than the primary thermal stresses, which means that the piezoelectric effect is negligible.

Thermal jet drilling of granite rock: a numerical 3D finite-element study.

This paper presents a numerical study on thermal jet drilling of granite rock that is based on a thermal spallation phenomenon. For this end, a numerical method based on finite elements and a damage-viscoplasticity model are developed for solving the underlying coupled thermo-mechanical problem. An explicit time-stepping scheme is applied in solving the global problem, which in the present case is amenable to extreme mass scaling. Rock heterogeneity is accounted for as random clusters of finite elements representing rock constituent minerals. The numerical approach is validated based on experiments on thermal shock weakening effect of granite in a dynamic Brazilian disc test. The validated model is applied in three-dimensional simulations of thermal jet drilling with a short duration (0.2 s) and high intensity (approx. 3 MW m-2) thermal flux. The present numerical approach predicts the spalling as highly (tensile) damaged rock. Finally, it was shown that thermal drilling exploiting heating-forced cooling cycles is a viable method when drilling in hot rock mass. This article is part of the theme issue 'Fracture dynamics of solid materials: from particles to the globe'.

О ПОРИСТОСТИ НЕКОНСОЛИДИРОВАННОЙ ЧАСТИ КИЛЯ ТОРОСОВ

The paper discusses the distribution of porosity of the unconsolidated part of the keel of ten first-year ice ridges investigated in the central Arctic basin and the Shokalsky Strait (Severnaya Zemlya) in 2012–2019. These studies were performed using thermal drilling with the computer (logger) recording of penetration rate. Boreholes were drilled along the cross-section of the ridge crest, mainly at 0.25-m intervals. The porosity values for the unconsolidated part of the keel are presented on the diagram as a point cloud. The horizontal position of the points is determined by the relative distance between the borehole and the point where the keel has the maximum draft. As moving away from this point, the average porosity of the unconsolidated part of the keel tends to increase. This feature is a consequence of the Archimedes force effect and agrees with the model of porosity changes from the theory of granular media.

New Findings in the Field of Thermal Drilling of Aluminum Alloys.

This paper explores the joining of materials by a new progressive method of thermal drilling. Many types of joints are utilized in industrial production, especially in the automotive industry, which requires the joining of different types of materials with different thicknesses. For these needs, it will be appropriate to apply the joining method of thermal drilling technology. The used material, its mechanical properties, and the preparation of the joint by assembly and disassembly operations play an equally important role. By using new friction technologies, we can reduce production time, increase joint quality, offer automation in certain types of operations, save economic costs, and protect the environment. In this contribution, the authors present the results of their scientific research work focused on an investigation, comparison and testing of thermal drilling effects on the behavior of aluminum alloys (AlMgSi). The holes, collars and bushings formed by the drilling method were subjected to visual shape evaluation. Based on the evaluation of the samples, the quality of the evaluated joints was assessed. The best shape and strength properties at higher speeds of the drilling machine were obtained at 3400 rpm. The results of the methods of macroscopy and microscopy investigations, as well as the results of the methods of scanning electron microscope (SEM) and energy dispersive X-ray (EDS), are presented in this contribution.

Use of combined tools to reduce axial force during thermal drilling

In engineering, thin-walled products are widely used, providing for the threaded fastening of various parts to them. The shaping of threaded holes in thin-walled parts is a complex technological task. One of the methods for producing holes is thermal drilling - this is the process of shaping holes for threads by plastic deformation in sheet blanks with temperature effects from the friction forces of the tool on the workpiece. In the process of thermal drilling around the formed through hole on the workpiece, flanged edges are formed on both sides, thereby increasing the length of unscrewing. The main problem is deformation of the workpiece due to the action of axial force on it. This article describes the design of a combined tool and presents experimental and theoretical studies of the influence of the rotational speed and axial feed of the tool on the value of the axial force for various thicknesses of the blanks.

Study of geometrical parameters of flanged edges of holes formed by thermal drilling with a combined tool

Currently, sheet metal parts are widely used, involving fastening of various components to them using a threaded fastener. As a rule, the sheet thickness is not sufficient for shaping the minimum required number of threads, ensuring reliability of the fastener. To increase the length of unscrewing, various methods are used: sheet bending, welding of bushings or nuts, stamping in closed and open dies, etc. These methods are not technologically advanced. This problem can be solved using the method of thermal drilling of holes - the process of shaping holes by plastic deformation in sheet blanks with a temperature effect from friction forces of the tool on the workpiece. The main problem is the lack of available data on the geometric parameters of the obtained flanged edges in the available reference books. These data are needed to determine the number of threads in the hole being shaped and the strength of the threaded fastener. The article examines dependences of the geometrical parameters of flanged edges on cutting modes and sheet thickness as a result of thermal drilling.

Experimental study of thermal fracturing of Hot Dry Rock irradiated by moving laser beam: Temperature, efficiency and porosity

Abstract A new laser irradiation fracturing method is employed to crack the Hot Dry Rock (HDR) and variations of rock temperature, specific energy (SE) and modified specific energy (MSE), thermal damages and open porosity of granite samples caused by moving laser beams with various irradiating conditions including laser power, diameter and moving speed of laser beam were investigated. Results indicate that rock temperature and the corresponding temperature gradients near the laser beam spots are strongly dependent on the laser power, beam diameter and irradiation time. The high temperature generated by the laser irradiation melts and cracks the HDR samples. The removed mass, cracked mass and size of grooving kerf induced by laser irradiation are also related to various irradiation conditions. SE and MSE are found nonlinearly reduced with the increased laser power density. Laser irradiation has a greater enhancement to thermal fracturing of granite than it does to thermal drilling. The open porosity (OP) of irradiated HDR samples increases with increasing laser power, decreasing diameter and moving speed of laser beam. The results can provide some guidance to those seeking a new economical and reasonable fracturing method for the HDR geothermal exploitation.

Anchoring thermal drills for icy moon stability and mobility

Exploring the ice surface of Europa and other icy moons will be scientifically exciting, but very challenging for mobile autonomous robotics. This paper presents a new concept to address the challenge of moving across vacuum-exposed cryogenic ice terrains - a thermal pick that functions both as a thermal drill and an ice anchor.Earlier investigators demonstrated that cryogenic ice can be thermally drilled in simulated planetary conditions, but the efficiency was found to be a hindrance for power-limited systems. A rover on Europa may need to drill and anchor many times throughout the lifetime of the vehicle, so the primary focus of this work is reducing the energy cost of operation. Using the thermal drill as an anchor also adds a new requirement, maintaining the structural integrity of the ice. This work demonstrates a highly efficient (up to 50%) intermittent mode of operation for thermal drilling as well as an approach to avoiding degradation of the ice structure. This allows for anchoring strengths in excess of 130 ​N, which is the weight of 100 ​kg on Europa.

Simulation of rock failure modes in thermal spallation drilling

Thermal spallation drilling is a contact-less means of borehole excavation that works by exposing a rock surface to a high-temperature jet flame. In this study, we investigate crucial factors for the success of such thermal drilling operations using numerical simulations of the thermomechanical processes leading to rock failure at the borehole surface. To that end, we integrate a model developed for spalling failure with our thermomechanical simulations. In particular, we consider the role of material heterogeneities, maximum jet-flame temperature and maximum jet-flame temperature rise time on the onset of inelastic deformation and subsequent damage. We further investigate differences in energy consumption for the studied system configurations. The simulations highlight the importance of material composition, as thermal spallation is favored in fine-grained material with strong material heterogeneity. The model is used to test the relationship between the jet-flame temperature and the onset of thermal spallation.

Effect of Thermal Drilling Modes for Making Holes in Barely Deformable Materials Exerted on Tool Wear

This paper presents the results of experimental studies on the process of thermal drilling in workpieces made of barely deformed alloys by the example of the alloy HN62VMYuT-VD. A comparative analysis is presented, and the modes efficient from the standpoint of thermal drill wear and the process productivity are demonstrated. In addition, the revealed geometrical parameters and material of the tool required for the implementation of the thermal drilling operation are presented. The results of simulation with the use of the QForm VX software package are shown in comparison with the experimental results obtained.

Analysis of Hollow Shape Semi Rigid Joints Made by Use of Thermal Drilling Technology

The results of numerical and empirical analysis of a new type frame T- joints for rectangular hollow sections are presented. The butt T-joints are designed as connected by screws into bushes formed in the wall of rectangular hollow sections bars by use of a thermal drilling technology. Literature in this subject applies only to joints without additional stiffeners or T-joints with concrete filled hollow steel columns. In the paper deals with the 4 proposals of a new butt T-joints for hollow sections including additional stiffeners. Numerical analyses conducted for the designed new types of T-joints proved that the proposed joints stiffeners lead to higher capacity than in case of unstiffened joint. Experimental verification of the joints behaviour confirmed results of the numerical simulation.