Boring And Trepanning Association Research Articles

Subsurface conditioning in BTA deep hole drilling for improved component performance

When bores with high length-to-diameter ratios (l/D > 10) and large diameters (D > 40 mm) are required, usually, the Boring and Trepanning Association (BTA) deep hole drilling process is used. Common industrial applications of this process are aerospace engineering and petrol exploration, where drilled components range from landing gears and engine shafts to drill collars. Since such parts tend to be particularly costly and highly safety–critical, ensuring favorable surface integrity during drilling is crucial to guarantee their reliability and performance. This study aims to identify correlations between the BTA deep hole drilling process and the resulting surface integrity using experimental and simulative approaches. The impact of feed and cutting speed on the thermomechanical loads and the resulting surface integrity are analyzed, also taking into account the occurrence of dynamic process disturbances. Particularly, the formation of white etching layers (WEL) is investigated using well-established, conventional techniques such as optical microscopy and microhardness testing. Additionally, innovative micromagnetic methods are employed. Magnetic Barkhausen noise (MBN) analysis is qualified as a well-applicable approach for rapid, non-destructive detection of WEL. To enhance understanding of MBN analysis and increase its robustness, the underlying mechanisms, governing the magnetic behavior of the subsurface are elucidated in detail by X-ray diffraction (XRD), electron backscatter diffraction (EBSD), magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) microscopy. The methodology will serve as a basis for controlled subsurface conditioning in BTA deep hole drilling.

Automatic diagnosis and thickness determination for white etching layers in deep drilled steels based on thresholding and machine learning algorithms

The reliable detection and precise assessment of white etching layers (WEL) are key challenges in the investigation of a component’s surface integrity. This paper proposes an innovative methodology for evaluating the extent of WEL in quenched and tempered steels, machined by Boring and Trepanning Association (BTA) deep hole drilling. Micrographs obtained by light microscopy were partitioned into classes by three methods, separating the WEL from the base material and the embedding resin. Traditional manual segmentation was performed as a benchmark for automatic segmentation methods. A gray level thresholding-based method served for the segmentation of micrographs partitioned into subsets. In addition to conventional manual and thresholding-based segmentation, a machine learning-based approach for image segmentation was applied. The segmented images were further analyzed by a newly developed set of algorithms, implemented to obtain detailed information on the WEL, e.g. their average thickness as well as the area covered by WEL in the micrographs. Results indicate that both, gray level thresholding, as well as machine learning-based image segmentation, show potential for the automated diagnosis and assessment of WEL. They both yield quantitatively similar, but less biased results compared to manual segmentation.

An analytical and numerical modeling method for predicting drilling force and hole expansion of a BTA drill processing Inconel 625 and FeCr alloy laminated materials

This paper aims to predict the drilling force and hole expansion of Boring and Trepanning Association (BTA) drill processing Inconel 625 and FeCr alloy laminated tube sheets, essential in petrochemical and nuclear industries. The paper proposes a combined analytical and numerical modeling approach that integrates discrete forces on multiple cutting edges and guide pads of the BTA drill, experimentally determines the mathematical relationship between the discrete forces, and predicts the drilling force using a calibrated finite element simulation of the cutting edge. Then, a comprehensive evaluation of the drilling forces revealed the torque and feed force distribution for cutting, guide pad burnishing, and friction. Furthermore, a precise finite element simulation model for guide pad burnishing hole wall is developed and combined with the burnishing force identified by the analytical model, enabling hole expansion prediction. The proposed model is validated by drilling experiments on Inconel 625 and FeCr alloy-laminated materials with average prediction errors of 8.4 %, 4.7 %, and 20.5 % for torque, feed force, and hole expansion, respectively, demonstrating the accuracy and industrial applicability of the modeling method.

Experimental Investigation of Tool Wear and Machining Quality of BTA Deep-Hole Drilling in Low-Carbon Alloy Steel SA-5083.

Nuclear power tube plates are made from the high-strength, low-carbon alloy steel SA-5083, which has high values of toughness and plasticity, though it is forged with poor consistency and entails serious work hardening. It requires a large number of deep holes with a high machining accuracy and high surface quality to be processed. However, the quality of the processed holes is often not up to the standard of the Boring and Trepanning Association (BTA) for the deep-hole drilling of tube plates; this has led to deep-hole processing becoming a bottleneck in the manufacture of steam generators for the main equipment of nuclear power islands. The variation laws of the diameter, roundness, perpendicularity, roughness, microhardness, and residual stress in relation to the feed, speed, and drilling depth are explored in the macro- and micro-dimensions; also explored is the wear morphology of BTA drills. The internal influence mechanisms between them are revealed in order to provide a scientific basis for the control of surface quality and machining accuracy as well as the optimization of process parameters. Our research results indicate that the guide block wear is mainly concentrated at the top 1-2 mm and that the drilling depth and feed have a great influence on the machining diameter. The hole wall roughness is between 0.3 and 0.6 μm, the maximum microhardness is about 2.15 times the hardness of the matrix material, and the residual stress is compressive stress. With increases in the feed and drilling depth, the hole diameter and the roughness increase. With an increase in the speed, the roughness decreases and the compressive stress of the BTA deep-hole drilling wall increases.

Tool design for the integration of piezoelectric and micro magnetic sensors to realize in-process measurements in BTA deep hole drilling

In-process measurements are often used to gain information and increase the understanding of the machining process. Furthermore, these measurements can be used to control the process during machining. In processes such as milling or turning the sensors and measuring devices can often be placed inside the working area of the machine or attached to the tool and observe the contact area between tool and workpiece. The contact area of processes such as drilling, boring or BTA (Boring and Trepanning Association) deep hole drilling is inaccessible from the outside. The BTA process is a deep hole drilling method used mainly for machining relatively large diameters in complex and cost-intensive parts often at the end of the value chain. The resulting bore surfaces of these parts are often highly stressed and are commonly subjected to post-processing. With sufcient information about the process and the produced surface integrity of the bore, this post-processing could be reduced or even omitted. In order to get information about the contact area or the resulting surface of the bore, without destroying the workpiece, sensors need to be implemented into the tool in order to measure from inside the bore. The challenges in the design process of the drill head modifcations and the implementation of two diferent sensor systems are discussed in this paper. Furthermore, the manufacturing and application of the modified BTA drill heads are described. Finally, the results from cutting tests on one of the modified drill heads are presented.

Analytical Model of Hole Diameter and Self-Guiding Machining Mechanism of BTA Deep Hole Drilling

The goal of this study was to explore the self-guided machining mechanism of boring and trepanning association (BTA) deep hole drilling and realize precise control of the machining quality. The motion analysis method was used to analyze the center motion trajectory of the drill during the entrance, and the self-guiding mechanism and hole-forming mechanism of BTA deep hole drilling were revealed. Considering the bending deformation of the drilling tube and the tool structure parameters, according to the elastic-plastic deformation theory and Hertzian contact theory, a novel analytical model of the extrusion contact between the guide pads and the hole wall of the BTA deep hole drilling was established for the theoretical prediction of the extrusion deformation and the machining hole diameter. Combined with the finite element method (FEM) simulation model, the variation law of the contact inclination angle, contact stress, and extrusion deformation of the guide pads and the hole wall with the drilling conditions were studied. The total extrusion deformation between the guide pad and the hole wall was between 10 and 50 μm. The maximum error between the FEM simulation results and the test results was 18.1%, and the maximum error between the analytical model results and the test results was 23.6%. The simulation and experimental results showed that the established extrusion contact model could accurately predict the extrusion deformation of the hole wall and the machining hole diameter.

Multiobjective Optimization of Cutting Parameters for TA10 Alloy Deep-Hole Drilling.

In order to obtain better quality TA10 pipes, the Boring and Trepanning Association (BTA) deep-hole drilling process is used. However, this type of machining leads to difficult chip removal, tool wear, and poor hole-surface quality. In this study, a deep-hole drilling experiment was conducted on TA10 workpieces using the designed tool with different process parameters, and the process parameters were optimized by machining results with multiple objectives such as chip morphologies, tool wear, hole-axis deflection, and hole surface roughness. The results show that different process parameters have a great impact on the cutting process, with a higher feed resulting in smoother chip removal and a lower spindle speed resulting in lighter tool wear and less hole axis deflection. When the spindle speed is 145 r/min and the feed is 0.12 mm/r, the machined TA10 pipe meets both the accuracy requirement of roughness and the machining efficiency.

Centering deep hole drilling system with three oil films like centering rotating journal with oil films in bearing

Purpose This study and its centering device with Archimedes spirals designed on hydrodynamic lubrication aims to reduce the deviation of deep holes because the drill tube is long and easy to deviate in deep hole machining. Design/methodology/approach The centering device with Archimedes spirals was designed and fixed between the drilling tool and the drill tube. The wall of the deep hole and the novel centering device formed three wedge-shaped oil films. When the workpiece rotated relative to the centering device, pressure was generated in the oil films; therefore, three oil films supported drilling system as oil films support rotating journal in the full-film hydrodynamic bearing. Findings When the Boring and Trepanning Association (BTA) drilling system was equipped with the centering device, the cutting oil flowed smoothly and carried all the iron chips; the motors run normally; no additional vibration or sound was detected during processing; the surface of the centering device was smooth; and the deviation of the drilled deep hole decreased with a high probability. Originality/value To the best of the authors’ knowledge, no one has designed and made the centering device with Archimedes spirals to reduce the deviation of deep holes in deep hole machining. Three oil films formed by the centering device with Archimedes spirals support drilling system and prevent it from deviating, which has never appeared before and is creative.

RECENT RESEARCH PROGRESS IN DEEP HOLE DRILLING PROCESS: A REVIEW

The requirement of deep hole drilling has tremendously increased in recent years and it extensively found applications in automobile fuel injectors, biomedical implants, aerospace landing gears, etc. These deep holes are fabricated by conventional and unconventional methods with a high aspect ratio ([Formula: see text]/[Formula: see text]) and tight tolerance. This paper is an attempt to review the research work carried out by researchers in recent years about deep hole drilling on various materials using conventional methods like Gun Drilling (GD), Boring and Trepanning Association (BTA) drilling, and Single Lip Drilling (SLD) and unconventional methods such as Laser Beam Machining (LBM), Electro-Chemical Machining (ECM), Electro Discharge Machining (EDM), and Abrasive Water Jet Machining (AWJM). The review includes the impact analysis of process parameters namely water jet pressure, stand-off distance, and abrasive mass flow rate on the responses of AWJM. The current gaps and the upcoming research directions in the deep hole drilling process are detailed.

Simulation and modeling of the residual stress state in the sub-surface zone of BTA deep-hole drilled specimens with eigenstrain theory

The BTA (Boring and Trepanning Association) deep-hole drilling process is used to machine bores with large diameters (D > 40 mm) and a bore-length (l) to diameter ratio lager than ten (l/D >10). The resulting bore surface and its sub-surface zone are influenced by the cutting action and the self-guiding effect of the tool. The Guide pads support the asymmetric tool on the bore surface while burnishing the surface. The mechanical/thermal loads induced by the process lead to hardening, microstructure alteration and substantial residual stresses in the sub-surface. Particularly the residual stress state influences the fatigue strength and reliability of the machined part. To predict the residual stress in BTA deep-hole drilling, for the first time a novel analytical modeling approach is developed based on eigenstrain theory, integrating the machining process of cutting insert and the burnishing process of guide pad. A semi-analytical 3D contact model is built for the cycling incremental plasticity due to the equivalent mechanical/thermal loading of cutting process. Furthermore, an approximate estimation is provided for the contact condition between the inclined guide pad and bore hole, which facilitates the incremental contact analysis in the burnishing process. With the induced inelastic deformation known, residual stress distribution in the machined surface is constructed based on the eigenstrain theory. The results of the model are compared to X-Ray-Diffraction (XRD) measurements of BTA deep-hole drilled specimens.

A Mathematical Model to Describe the Inner Contour of Moineau Stators

Abstract Bore holes with a large length to diameter ratio of up to l/d = 100 are typically produced using the single-tube deep hole drilling method also named BTA (Boring and Trepanning Association) deep hole drilling method. However, there are various technical applications requiring deep, complex, epitrochoid-similar and helical inner contours, such as stators used in Moineau motors and pumps. According to the current state of the art, epitrochoid-similar contours for small diameters with large drilling depths can only be produced using a special machining process which is referred to a chamber-boring process. In this paper, a developed mathematical model will be presented that describes the epitrochoid-similar contour exactly. This allows the determination of the position-dependent speed and acceleration of the tool, which are necessary for designing the joints and components of the tool system. In addition, this mathematical model can be used for a subsequent Laplace-transformation, so that could be used for a further optimization of the process dynamic in the future.

Modeling and experimental investigation of drilling force for low-frequency axial vibration-assisted BTA deep hole drilling

The ability to form regular chips and evacuate them smoothly is crucial for deep hole drilling. In this work, an eccentric cam mechanism is used to apply low-frequency axial vibration at the end of the drill tube for boring and trepanning association (BTA) deep hole machining, and the instantaneous cutting thickness equation of low-frequency axial vibration assisted drilling is derived, which can actively control the length of the chip and achieve a good chip removal effect. Considering the variable geometric parameters and the scale effect of teeth cutting, a new analytical model is established to obtain the instantaneous drilling force of staggered teeth BTA deep hole drill assisted by low-frequency axial vibration. The relevant parameters in drilling force model are identified, and the distribution laws of the normal friction angle, normal shear angle, and shear stress with instantaneous cutting layer thickness and drilling radius values are achieved. The influence of the vibration drilling process parameters, including feed, speed, amplitude, and frequency ratio, on the drilling force is investigated experimentally, and the validity of the drilling force model is verified. These results show that the drilling force model is reliable, and the thrust and torque of the low-frequency axial vibration assisted drilling relative to ordinary drilling are reduced by 21.63% and 13.74%, respectively.

Investigation of Chip Deformation and Breaking with a Staggered Teeth BTA Tool in Deep Hole Drilling

The problem of chip breaking and evacuation is the key point of staggered teeth boring and trepanning association (BTA) drilling. The factors that influence chip breaking with staggered teeth BTA deep hole drilling are analyzed by using the chip bending deformation mechanism for chip formation and flow through the rake face and chip breaker. This study investigated the distribution and variation of chip deformation and breaking along drilling conditions, with respect to drilling radius, drilling process parameters, tool wear, and chip breaker geometric parameters. The results show that the tool-chip contact length is about 1.65 times the chip thickness in staggered teeth BTA drilling. The cutting radius of the teeth has a considerable influence on the chip thickness. Compared with the drilling speed, the feed has a greater impact on chip deformation and breaking, and the chip thickness and strain increase with increased feed. Increased drilling depth and tooth wear aggravates the friction state between the chip and the rake face, augments chip thickness and tool-chip contact length, and increases the chip’s strain increment. As the width of chip breaker decreases and the height increases, the chip strain increases and the breaking conditions are improved.

IN-PROCESS MONITORING AND ANALYSIS OF DYNAMIC DISTURBANCES IN BORING AND TREPANNING ASSOCIATION (BTA) DEEP DRILLING

This paper presents an approach to monitor the dynamic disturbances of a BTA (boring and trepanning association) deep drilling system. High length to diameter ratios are the key characteristic of deep drilling processes compared to conventional drilling applications. Since length to diameter ratios of up to 150 for slender tool-boring-bar assemblies are common, the deep drilling process is sensitive to dynamic disturbances such as chatter and whirling vibrations. Whirling vibrations usually effect the shape of the hole and cause holes with several lobes. To gain a deeper understanding of the dynamic state of the process, a sensor application has been developed and was tested in practice. Experimental investigations on BTA deep drilling with continuous multi-sensory monitoring were conducted. The used setup allowed the determination of the frequencies of chatter and whirling vibrations during the cutting process by analysing the logged data using a continuous short-time Fourier transformation (STFT).

Modeling and Distribution Laws of Drilling Force for Staggered Teeth BTA Deep Hole Drill

The boring and trepanning association (BTA) deep hole drilling is a typical self-guiding machining method. The drilling force and its distribution laws along the cutting radius directly affect the stability of drilling and the quality of machined hole. Based on the oblique cutting theory, a novel drilling force model is developed to predict the thrust and torque for staggered teeth BTA deep hole drill with variable geometries. Using the constraint relationships between the cutting force components and cutting angles, combined with the measured drilling force during the drill entrance, the parameters of the model including normal shear angle, normal friction angle and shear stress involved in the cutting force coefficients along the cutting radius, and the axial and circumferential friction coefficients between the guide pads and the hole wall are obtained. The model-predicted drilling force is validated by experimental results.

The guide block structure design of boring and trepanning association (BTA) deep hole drilling

In the process of boring and trepanning association (BTA) deep hole drilling, the guide block plays the role of guiding, balancing the cutting force and extruding and polishing the machined surface ...

A novel method of experimental evaluation on BTA tool geometries

Towards the problem of closed space of Boring and Trepanning Association (BTA) drill, this paper presents a novel experimental method to evaluate BTA tool geometries, and a turning-based test is conducted to simulate drilling. The three inserts of BTA drill are replaced by the three turning inserts, the rotation of BTA drill is transformed by workpiece rotation in turning, the feed of BTA drill changes into the feed of turning inserts, and the cutting area per BTA insert is simulated by the cutting depth in turning. To implement the approach, three angles, consisting of edge inclination, flank angle and edge declination, are organised by a three-factor and three-level Taguchi experiment for each BTA insert, e.g. outside insert, centre insert and middle insert. Cutting force, chip patterns and chip curl radius are observed and measured to evaluate the insert geometries.

Rapid Modeling of BTA Deep-Hole Drill Based on Customized Development of NX

Low Pressure Heater is one of important equipment in nuclear power industry; within the manufacturing of plate of heater, the deep-hole drill technology is a key point, and BTA (Boring and Trepanning Association) is applied. It is difficult to keep the high-quality hole of BTA due to the poor cutting condition, chip breaking, heat dissipation, and low rigid of the machining system. Therefore, this proposes a high precision to drilling tools, especially the design of the blade is of great importance. Based on the analysis of drill structure, this dissertation uses the method of parametric design which is suitable for NX. Combining the Visual Studio and Microsoft Access platform develops the fast digital modeling software design. The parameterization design can not only realize the rapid modeling of BTA deep-hole drill, but also shorten the design cycle and improve the efficiency of the drill which benefited from the convenient design of the blade, which has a significantly practical application value.

Theoretical and experimental study on rifling mark generating phenomena in BTA deep hole drilling process (generating mechanism and countermeasure)

Boring and Trepanning Association (BTA) deep hole drilling is used for producing holes with high aspect ratios. In this process, chatter vibration sometimes occurs, and a rifling mark is formed on the bore surface. The rifling mark generating phenomenon is considered to be a result of self-excited vibration caused by time delay. An analytical model is proposed considering the supporting condition of the boring bar in detail. In a real machine for BTA drilling, the boring bar is supported at the oil pressure head and the supporting pad, as well as at the base. The stability of the self-excited vibration is analyzed numerically, and the result is compared with the experiment. The theoretical and experimental results agree well with each other. Furthermore, the effect of an additional guide pad proposed by the authors as a countermeasure is evaluated theoretically and experimentally.

Modified DLC-Coated Guide Pads for BTA Deep Hole Drilling Tools

The BTA (Boring and Trepanning Association) deep hole drilling process is commonly used to machine boreholes with a large drilling depth-to-diameter ratio (l/D) and outstanding workpiece quality. The asymmetric tool design leads to a nonzero radial component of the cutting force and the passive force, which are conducted to the borehole wall by so-called guide pads. These guide pads smooth the borehole wall by a forming process and improve the surface quality. Processes, that machine materials with a high adhesion tendency, such as high alloy stainless steel, suffer from poor surface quality in the borehole and the adhesion from the workpiece material on the guide pads. In this paper modified Diamond-Like-Carbon (DLC) coated guide pads for BTA deep hole drilling tools are investigated. The scope of the experiments was the reduction of the adhesion by reducing the friction coefficient of the guide pads, as well as the improvement of the quality of the borehole wall.