Hole Drilling Process Research Articles

Machining Characteristics During Short Hole Drilling of Titanium Alloy Ti10V2Fe3Al.

The single-phase titanium ß-alloy Ti10V2Fe3Al (Ti-1023) has been widely used in the aerospace industry due to its unique mechanical properties, which include high fatigue strength and fracture toughness, as well as high corrosion resistance. On the other hand, these unique properties significantly hinder the cutting processes of this material, especially those characterized by a closed machining process area, such as drilling. This paper is devoted to the study of the short hole drilling process of the above-mentioned titanium alloy using direct measurements and numerical modeling. Measurements of the cutting force components in the drilling process and determination of the resultant cutting force and total cutting power were performed. The macro- and microstructure of chips generated during drilling were analyzed, and the dependence of the chip compression ratio and the distance between neighboring segments of serrated chips on cutting speed and drill feed was determined. Experimental studies were supplemented by determining the temperature on the lateral clearance face of the drill's outer cutting insert in dependence on the cutting modes. For the modeling of the drilling process using the finite element model, the parameters of the triad of component submodels of the numerical model were determined: the machined material model, the model of contact interaction between the tool and the machined material, and the fracture model of the machined material. The determination of these parameters was performed through the DOE sensitivity analysis. The target values for performing this analysis were the total cutting power and the distance between neighboring chip segments. The maximum deviation between the simulated and experimentally determined values of the resulting cutting force is no more than 25%. At the same time, the maximum deviation between the measured values of the temperature on the lateral clearance face of the drill's outer cutting insert and the corresponding simulated values is 26.1%.

Tool wear feature extraction in BTA deep hole drilling process based on maximum probability multi-synchrosqueezing transform of spindle current signal

Multi-synchrosqueezing transform (MSST) enhances the concentration of the time–frequency representation (TFR) of time-varying signals by introducing multi-instantaneous frequency (IF) estimation operator. However, the existence of estimation bias may lead to uncertainty in the discrete values of IF during computer computations, causing issues with non-reassigned points. In this paper, a maximum probability multi-synchrosqueezing transform (MPMSST) is proposed, which incorporates distribution probability during the discretization process of the IF, taking the frequency corresponding to the maximum distribution probability as the determined value of IF. Through verification with multi-component time-varying simulation signals, MPMSST not only effectively eliminates non-reassigned points but also accurately estimates the theoretical time–frequency curve. By applying MPMSST to analyze spindle motor current signals during deep hole machining, TFRs under different tool wear states are obtained. The singular value decomposition (SVD) method is utilized to extract the principal component of the TFR, and a tool wear state feature index is constructed based on the sum of squares of the first 10 singular values. The correlation coefficient and covariance between the proposed feature index and the tool wear curve are 0.835 and 5.704 respectively, indicating a good consistency of the index with tool wear changes, and a high sensitivity to variations in tool wear state.

Interaction of Mechanical Characteristics in Workpiece Subsurface Layers with Drilling Process Energy Characteristics

The performance properties of various types of parts are predominantly determined by the subsurface layer forming methods of these parts. In this regard, cutting processes, which are the final stage in the manufacturing process of these parts and, of course, their subsurface layers, play a critical role in the formation of the performance properties of these parts. Such cutting processes undoubtedly include the drilling process, the effect of which on the mechanical characteristics of the drill holes subsurface layers is evaluated in this study. This effect was evaluated by analyzing the coincidence of the energy characteristics of the short hole drilling process with the mechanical characteristics of the drilled holes’ subsurface layers. The energy characteristics of the short-hole drilling process were the total drilling power and the cutting work in the tertiary cutting zone, which is predominantly responsible for the generation of mechanical characteristics in the subsurface layers. As mechanical characteristics of the drill holes’ subsurface layers were used, the microhardness of machined surfaces and total indenter penetration work determined by the instrumented nanoindentation method, as well as maximal indenter penetration depth, were determined by the sclerometry method. Through an analysis of the coincidence between the energy characteristics of the drilling process and the mechanical characteristics of the subsurface layers, patterns of the effect of drilling process modes, drill feed, and cutting speed, which essentially determine these energy characteristics, on the studied mechanical characteristics have been established. At the same time, the increase in the energy characteristics of the short-hole drilling process leads to a decrease in the total indenter penetration work and the maximum indenter penetration depth simultaneously with an increase in the microhardness of the drilled holes’ subsurface layers.

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.

Numerical modelling of the BTA deep hole drilling process

The BTA deep hole drilling process is applied in order to produce bores with a large length to diameter ration at comparably high diameters of the bores. During drilling, first, the bore is cut by the cutting edge and shortly after that, a guide pad slides over the newly produced bore wall, burnishing the surface. These two effects condition the bore wall and alter its surface integrity depending on the process parameters. In the past, extensive destructive and non-destructive tests were conducted to obtain information on the surface integrity of the machined parts. Furthermore, a large number of in- and off-process measurements were carried out in material and cost-intensive experiments to determine values such as residual stresses or white etching layers. The presented work shows different finite element models of the BTA deep hole drilling process using continuous remeshing and, in order to reduce the calculation times, the Coupled Eulerian-Lagrangian (CEL) method as well. The results simulated based on this models comprise temperatures, process forces and surface properties that are compared to measured values from pervious works for validation. The various approaches are evaluated to determine whether they predict the bore hole surface integrity and thus support future investigations.

Numerical Modeling of Cutting Characteristics during Short Hole Drilling: Modeling of Kinetic Characteristics

Analyzing the cutting process characteristics opens up significant opportunities to improve various material machining processes. Numerical modeling is a well-established, powerful technique for determining various characteristics of cutting processes. The developed spatial finite element model of short hole drilling is used to determine the kinetic characteristics of the machining process, in particular, the components of cutting force and cutting power. To determine the component model parameters for the numerical model of drilling, the constitutive equation parameters, and the parameters of the contact interaction between the drill and the machined material on the example of AISI 1045 steel machining, the orthogonal cutting process was used. These parameters are determined using the inverse method. The DOE (Design of Experiment) sensitivity analysis was applied as a procedure for determining the component models parameters, which is realized by multiple simulations using the developed spatial FEM model of orthogonal cutting and the subsequent determination of generalized values of the required parameters by finding the intersection of the individual value sets of these parameters. The target values for the DOE analysis were experimentally determined kinetic characteristics of the orthogonal cutting process. The constitutive equation and contact interaction parameters were used to simulate the short hole drilling process. The comparison of experimentally determined and simulated values of the kinetic characteristics of the drilling process for a significant range of cutting speed and drill feed changes has established their satisfactory coincidence. The simulated value deviation from the corresponding measured characteristics in the whole range of cutting speed and drill feed variation did not exceed 23%.

Experimental Research and Analysis of Soil Disturbance Behavior during the Hole Drilling Process of a Hanging-Cup Transplanter by DEM

This study provides a basis for designing and optimizing the key components of hanging-cup transplanters. The discrete element method, a high-speed photography test, and indoor soil bin tests were used to explore soil disturbance behavior during the hole drilling process. A comparative analysis of the discrete element method and the high-speed photography test indicated that soil particles are mainly affected by the coupled effects of the shear force and the squeezing force of the planter. The soil disturbance range in the horizontal and longitudinal sections gradually increases with the movement of the planter. The change in the soil particle velocity of the horizontal and longitudinal sections in different zones shows a trend of first increasing, then decreasing, and finally stabilizing. The velocity of soil particles in the longitudinal section varies significantly in the direction of burial. The soil in the horizontal section mainly moves to both sides when the duckbill is opened. The closer the soil particles are to the outer wall of the duckbill, the greater the change in velocity is. The soil bin tests and simulations were carried out under different conditions, but the change trend of the simulation results is consistent with the soil bin test results, proving that the simulation model is reliable. With the forward speed of the transplanter, planting depth, and soil compactness as the test factors, and the hole depth and hole longitudinal length as the response values, an orthogonal test of three factors and three levels was designed. A regression model between each element and response value was established. The optimal parameter combination was obtained when the forward speed was 1.25 km/h, the planting depth was 80 mm, and the soil firmness was 140~150 (N/cm2); these results were experimentally verified.

A Study of the Kinematics System in Drilling Inconel 718 for Improving of Hole Quality in the Aviation and Space Industries.

This article discusses experimental results concerning the quality of through holes drilled in Inconel 718. The tests involved hole cutting under 27 different conditions using different values of the feed per revolution and spindle speed, and different types of kinematic system. The drilling was performed on a CTX Alpha 500 universal turning center using tools with internal coolant supply. Three kinematic systems were considered for hole cutting. The first, based on the driven tool holder, had a stationary workpiece and a rotating and linearly fed tool. In the second, where drilling was based on the spindle rotations, the workpiece rotated while the tool moved along a straight line. In the third system, the workpiece and the tool rotated in opposite directions; the tool also performed a linear motion. The study aimed to assess the quality of holes on the basis of the following output parameters: the hole diameter, cylindricity and straightness errors, and the surface texture. A multifactorial statistical analysis was used to determine how the hole quality was dependent on the process parameters and the type of drilling kinematics. The findings confirm that the kinematic system, as well as the feed per revolution, are the key factors affecting the quality of holes drilled in Inconel 718. The analysis of the hole drilling process for Inconel 718, performed using a CNC turning center, shows that the third kinematic system was the best option as all the four parameters describing the hole quality had the lowest values. The best results were obtained in the 6th (n = 637 rpm, fn = 0.075 mm/rev, KIN III) and 8th experiments (n = 955 rpm, fn = 0.075 mm/rev, KIN II), because the parameters were then the lowest, with the scatter of results being up to 30%.

Cutting fluid behavior under consideration of chip formation during micro single-lip deep hole drilling of Inconel 718

ABSTRACT When micro-single-lip deep hole drilling the efficiency of the cutting fluid supply cannot be investigated experimentally due to the inaccessibility of the cutting zone. For this reason, this paper examines the cutting fluid behavior, taking into account the chip formation and the transient chip position, with the help of various combined simulation methods. Therefore, experimentally obtained chips are digitalized and converted into a Computer-Aided Design model for the following simulations. Furthermore, for a comparison of the simulations with the experiments, the velocity of the cutting fluid in the chip flute of the tool is measured by a similar Particle Image Velocimetry method. Then, a transient coupled particle simulation of Smoothed Particle Hydrodynamics and the Discrete Element Method is performed to obtain the transient chip positions along the chip flute under the influence of the cutting fluid. Based on these chip positions, a Computational Fluid Dynamics simulation follows to derive insights about the flow field and pressure field at certain points in time. This multi-physics simulation chain allows to deal with experimental results in a simulation context to gain further insights about the deep hole drilling process, which are experimentally inaccessible and allows further connections between experiment and simulation.

Fatigue life enhancement of additive manufactured 316l stainless steel by LSP using a DPSS laser system

ABSTRACT Present work aims to study the fatigue life behaviour of additively manufactured (AM) stainless steel 316L in a laser shock peening (LSP) process. The fatigue behaviour of as-built samples and LSPeened sample were studied on the AM samples. A new diode-pumped laser system was utilized as an instrument to perform LSP operations. LSP operation was performed under two different sacrificial layers of different materials i.e. vinyl tape and aluminium tape. The other essential LSP parameters, namely energy, pulse width, spot size, overlap, and number of layers were kept constant based on the previous experimental findings. The characterization was done for analyzing the residual stresses using a hole drilling process, and a 4-point bending machine. A considerable improvement in compressive residual stress and fatigue life was observed in the LSPeened samples. Such improvements in residual stresses and fatigue life may pave a road to establishing diode-pumped lasers for LSP applications.

Effect of cryogenic cooling in deep hole drilling process – a stride in the direction of green manufacturing

ABSTRACT In this study research efforts have been made to unveil the ability of Cryogenic machining as a sustainable manufacturing process for deep hole drilling of AISI 1045 and Ti6Al4V. Environmental protection is the most pressing concern for manufacturers today when it comes to adverse health effects caused by cutting fluid and its disposal after usage. For better machining results, choosing the right cutting fluid is important. Investigation on drilling performance is done in terms of tool wear, hole wall temperature (HWT), circularity, surface roughness (Ra) to study the effects of input parameters such as cutting speed, coolant used, feed rate and coolant pressure. The type of coolant employed, cutting speed, feed and coolant pressure have a significant impact in determining the hole quality. Furthermore It was found that the employment of cryogenic coolant (LCo2) was effective on Ti6Al4V in compared with AISI 1045 in many output parameters. HWT of Ti6Al4V was higher compared with AISI 1045 Surface finish was better in Ti6Al4V, tool wear was considerably low while performing deep drilling on Ti6Al4V.

Analysis of the cooling lubricant flow during ejector deep hole drilling by in-process volume flow and pressure measurements

Ejector deep hole drilling is required for a variety of drilling applications with length-to-diameter-ratios larger than l/D > 10 and high quality demands, e.g. on roundness, diameter accuracy and surface quality. The ejector effect is essential for the process and decisive for a stable ejector deep hole drilling process by supplying the working zone with cutting fluid. In order to realize an enhanced fundamental understanding of the ejector effect with its process-typical specialties, a demanding experimental setup for in-process fluid volume flow measurement is developed. On the basis of the resulting deeper process understanding of the cooling lubricant behavior during ejector deep drilling, new optimization strategies for increasing deep hole drilling efficiency in the industry can be achieved.

Influence of the cutting edge on the surface integrity in BTA deep hole drilling - part 1: Design of experiments, roughness and forces

The BTA deep hole drilling process is used to machine deep bores with a large diameter. The cutting process, consisting of the material removal by cutting edge and the surface burnishing by the guidepads influence the surface of the bore. To separate the impact of the cutting edge from that of the guidepads on the surface of the bore and the subsurface zone an experimental model setup in analogy to the BTA process was developed. This paper covers the differences to the conventional BTA deep hole drilling, the experimental boundary conditions and the measurement of the surface roughness. The results are compared to previous analysis of the surface integrity of BTA deep hole drilled specimens. Furthermore, conclusions about the process forces are drawn from the documented loads occurring for the machine axes. In part 2 of this study, the surface integrity of the specimens is further analyzed using destructive and non-destructive methods.

Measurement and analysis of the thermal load in the bore subsurface zone during BTA deep hole drilling

To machine bores with larger diameters (D > 40mm) and a length to diameter ratio greater than ten (lb/D > 10) the BTA deep hole drilling process is often used. The cutting action of the cutting edge and the burnishing of the guide pads influence the resulting surface and the subsurface zone of the machined bore. The guide pads support the BTA drill head against the machined bore to prevent straightness deviations. A thermo-mechanical load, which results from the cutting and burnishing, influences the surface of the bore and effects the surface integrity, i.e. micro hardness, residual stress state, microstructure or the surface roughness, of the bore. In this paper, a measurement strategy to determine the thermal load in the subsurface zone using thermocouples is presented. Furthermore, a fiber-optic ratio pyrometer was used to measure the temperature in the contact zone between the cutting edge and the wall of the bore. The experiments were carried out using different workpiece materials, tool coatings and cutting parameters. The measurements are analyzed and set in context with previous studies.

Microstructure analysis of single-lip deep hole drilled bores by electron backscatter diffraction and magnetic Barkhausen noise

The surface integrity is crucial for the capability of machined parts; therefore, a detailed characterization of the obtained microstructure is very important for the assessment of machining processes. In this paper, the microstructure of single-lip deep drilled specimen, especially the formation of white etching layers (WEL), is considered by microscopic and micromagnetic investigations. Due to its asymmetrical nature, the single-lip deep hole drilling process induces severe plastic deformations in the bores surface. These severe deformations lead to a desirable fine-grained microstructure and the induction of beneficial compressive residual stresses. When too hard drilling parameters are chosen, the formation of a WEL can occur. These layers tend to be brittle and have tensile compressive stresses. The microstructures resulting from varied process parameters are characterized by light and electron microscopy as well with electron backscatter diffraction. These findings were correlated to the non-destructive magnetic Barkhausen noise measurement with a tailored bore sensor. This correlation enables an efficient and reliable evaluation of the process-induced microstructure and associated surface integrity.

Whirling detection in deep hole drilling process based on multivariate synchrosqueezing transform of orthogonal dual-channel vibration signals

In the deep hole drilling process, whirling vibration is easily initiated due to slender drill bar having larger length to diameter with low torsional and bending stiffness, which may increase the roundness error and roughness of the hole, even damage the tool and the wall of hole. Therefore, whirling detection is an important task to improve part quality and productivity in the deep hole drilling process. Due to the background noise and other disturbances, the whirling feature signal contained in the vibration signal is very puny. The whirling detection in deep hole drilling process based on vibration signal has turn into a challenging task. In this paper, a whirling detection method is proposed based on multivariate synchrosqueezing transform (MSST) of orthogonal dual-channel vibration signals. Firstly, the empirical wavelet transform method is used to extract the high multiple frequency components of the spindle rotation frequency. And then, the MSST is introduced to enhance the whirling feature signal contained in the high multiple frequency components. Finally, singular value decomposition (SVD) method is employed to condense the time–frequency spectrum of MSST and the whirling indicator is constructed based on the singular values. The proposed method is validated with BTA deep hole drilling tests, and the results show the superiority of the proposed method and indicate the proposed method has great potential to be used for the online whirling detection.

Investigation into deep hole drilling of austenitic steel with advanced tool solutions

Deep hole drilling processes for high-alloyed materials are characterised by worn guide pads and chatter vibrations. In order to increase feed rates, process stability and bore quality in STS deep hole drilling, various investigations were carried out with adjustments to the tool. First, a new process chain for the production of tribologically optimised guide pads and their effects on the guide pad shape is described in detail. The results of these studies show that the shape change in the area of the axial run-in chamfer through a micro finishing process leads to a better bore hole quality. Furthermore, the influence of guide pad coating and cooling lubricant on the deep hole drilling process was investigated. In addition, the machining of the austenitic steel AISI 304 is analysed by using a conventional steel boring bar and an innovative carbon fibre reinforced plastic (CFRP)-boring bar. While the conventional drill tube oscillates with different eigenfrequencies, the CFRP-boring bar damps chatter vibrations of the drill head and stabilises the process. Even at higher feed rates up to f = 0.3 mm, it is possible to machine austenitic, difficult-to-cut-materials with significantly reduced vibrations.

A prediction model of drilling force in CFRP internal chip removal hole drilling based on support vector regression

Drilling force is the main factor affecting the quality of carbon fiber-reinforced polymer (CFRP) holes and tool wear. Choosing appropriate process parameters can effectively control the drilling force and improve the quality of hole making and tool life. This study aimed to accurately predict and effectively control the drilling force during the chip removal hole drilling process in CFRP. First, a CFRP internal chip removal machining drilling force prediction model was derived based on the support vector regression (SVR) theory, and a suitable kernel function and loss function were introduced into the model to improve the prediction accuracy of the model. Second, a drilling experiment of the given type of CFRP material with internal chip removal was designed, and sequential minimal optimization was applied to solve the unknown parameters in the prediction model. The drilling force and tool parameters, suction parameters, and cutting parameter prediction models were constructed for processing a given type of CFRP material. Finally, using the constructed prediction model, the relationship between cutting parameters (speed and feed), tool parameters (drill diameter, peak angle, and relief angle), and suction parameters (negative pressure) and axial force during CFRP internal chip removal hole drilling was predicted and studied. The relationship between the aforementioned parameters and the axial force was in line with the research results of existing studies, and the selection range of tool parameters, cutting parameters, and suction parameters when processing a given CFRP material using an internal chip removal process was also given.

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.

Real-time observation with metallurgical examination for laser percussion drilling in stainless steel sheets using simultaneous magnetic-ultrasonic assistance

Using simultaneous assistance of the water-based ultrasonic vibrations and a side-loaded magnetic field, the transient real-time observation and metallurgical examination were carried out for laser percussion drilling in stainless steel sheets, aiming for demonstrating the effect of the magnetic-ultrasonic assistance on the hole-drilling process and the metallurgical alteration characteristics. The effect of the camera shooting distance on the signal detection below the hole exit was discussed for laser drilling of through holes. The laser drilling efficiency was characterized based on the real-time observation. It was found that the camera shooting distance affected the signal observation below the hole exit after a workpiece was drilled through due to an optical shield effect of its border side. The influence of the magnetic-ultrasonic assistance was much more notable when the dominant or sufficient heat input for drilling through a hole could not be provided by using a smaller pulse energy, a smaller pulse duration or a bigger laser fluence. The average recast layer thickness of the through-hole middle generated using a millisecond laser could be less than around 5μm when using the water-based ultrasonic assistance accompanied with the magnetic assistance. Compared to the corresponding case without external assistance, a reduction of 40μs was achieved for drilling through a hole by using the simultaneous magnetic-ultrasonic assistance. The average grain size number became bigger for validating the grain refinement in the heat affected zone after laser drilling using the water-based ultrasonic vibrations with and without magnetic assistance.