Deep Hole Drilling Process Research Articles

Temperature monitoring in the subsurface during single lip deep hole drilling

Abstract The surface quality and the subsurface properties such as hardness, residual stresses and grain size of a drill hole are dependent on the cutting parameters of the single lip deep hole drilling process and therefore on the thermomechanical as-is state in the cutting zone and in the contact zone between the guide pads and the drill hole surface. In this contribution, the main objectives are the in-process measurement of the thermal as-is state in the subsurface of a drilling hole by means of thermocouples as well as the feed force and drilling torque evaluation. FE simulation results to verify the investigations and to predict the thermomechanical conditions in the cutting zone are presented as well. The work is part of an interdisciplinary research project in the framework of the priority program “Surface Conditioning in Machining Processes” (SPP 2086) of the German Research Foundation (DFG). This contribution provides an overview of the effects of cutting parameters, cooling lubrication and including wear on the thermal conditions in the subsurface and mechanical loads during this machining process. At first, a test set up for the in-process temperature measurement will be presented with the execution as well as the analysis of the resulting temperature, feed force and drilling torque during drilling a 42CrMo4 steel. Furthermore, the results of process simulations and the validation of this applied FE approach with measured quantities are presented.

High throughput deep-hole drilling of Inconel 718 using PCBN gun drill

Overcoming the myriad challenges in the high-speed machining of Inconel 718, especially for deep-hole drilling (DHD), has been a long-standing area of research for several manufacturers and researchers. Owning to the difficult-to-machine characteristics of Inconel 718, the traditional carbide-tipped gun drills often get worn at an accelerated pace and require repetitive re-sharpening or replacement. This lowers productivity and increases costs. Furthermore, it is also a challenging task to meet the stringent hole-straightness requirement of 1/1000 mm for DHD of such difficult-to-machine materials, especially using those carbide gun drills. Hence, this study presents a development of polycrystalline cubic boron nitride (PCBN)-tipped gun drill to address the rapid tool degradation and poor hole-straightness issues. The developed PCBN-tipped gun drill has a layer of PCBN on its cutting tip and bearing pads. Several gun drilling tests on Inconel 718 have been performed at high drilling speed conditions to assess the performance of developed gun drill. In contrast to traditional carbide-tipped gun drills, the developed PCBN-tipped gun drill has the capability of not only performing in the higher cutting speeds but also reducing drilling forces, drilling torques, and tool wear. Furthermore, the surface quality of drilled holes is also much better than those drilled by traditional carbide gun drills. With these results, it further validates the credibility of the developed PCBN gun drill in enhancing the deep-hole drilling process with high throughput productivity and superior quality of drilled holes, especially for difficult-to-machine materials.

Retraction Note to: Effects of multi-support misalignments on hole straightness predict model in deep hole drilling

Straightness is one of the key technical indicators for deep hole gun drilling. This work studies the effect of drill shaft support misalignment on hole straightness in relation to various control factors. Misalignments occur in machine spindles, intermediate supports and pilot bushings. A predictive hole straightness deviation model for multi-support deep hole drilling process is introduced using the Euler column theory. The model considers the effect of the misalignment of whip guides in addition to the effects of the varying distance among the supports. The model also takes into account the effects of the thrust force and the drill lengths. Through simulation, this work analyzes the effect of each control factor on the results and optimizes the setting for each control factor. Further experiments on Ti6Al4V alloy then verify these estimates. Through research, fixed support at chip box has a greater influence on straightness deviation as compared to the misalignment at other supports; the distance between supports nearer to the chip box has more control on straightness deviation as compared to the other support distances.

Vibrating-lens-assisted laser drilling

Laser ablation is a viable technology for the manufacture of deep holes in a variety of industrial applications. Therefore, approaches need to be sought that increase the efficiency of these processes. In the current work, a hybrid processing method that utilizes superimposed vibrations to increase the depth of the produced holes will be addressed. The rationale for using vibrations is to change the energy distribution of the laser beam during the process. To this end, the traditional and the vibrating-lens methods were studied from the energy distribution standpoint at locations along the sensitive direction of the laser beam in drilling processes. Comparing the fluence with the ablation threshold of the laser beam to remove the material, the reasons why the vibrating-lens method is more effective in drilling deep holes were explained through theoretical analysis. Then, a new structure for the generation of lens vibrations along the sensitive direction using a PZT actuator for vibrating-lens assisted picosecond laser processing based on simulations was designed. Finally, different parameters were used to drill holes in stainless steel by the traditional and the vibrating-lens assisted methods, considering the frequency of the vibrations, dwell time and defocusing distance. The results have shown that the vibrating-lens method can improve the depth of the holes up to 60 % compared to the traditional method at the same dwell time. Therefore, it improves the efficiency of the deep hole drilling process.

Multi-objective parameter optimization to support energy-efficient peck deep-hole drilling processes with twist drills

Reducing energy consumption (EC) is an essential strategy for improving the sustainability of manufacturing industry. Machining processes have been widely applied in manufacturing industry, and current research has demonstrated that the machining parameter optimization is an effective energy-saving measure under the given processing conditions. Drilling is a typical machining process, and it is convenient to make deep holes through peck drilling with twist drills in practice. However, owing to the inefficiency of peck drilling with twist drills, many efforts have been devoted to improving the performance of peck deep-hole drilling process (PDDP). Correspondingly, the parameter optimization considering traditional performance indicators, such as processing time, tool wear, and drilling force, has been fully investigated. Nevertheless, the existing research rarely touches on the EC optimization or the improvement of EC-related environmental impacts. To bridge this gap, an approach based on the operating parameter optimization is proposed to fulfill the energy saving of PDDP, and the corresponding mathematical model considering EC and processing time simultaneously is established. To evaluate the EC of PDDP reliably, the Therblig-based energy supply models of machines are utilized. Further, a particle swarm optimization algorithm-based solution method is adopted, which can make a trade-off between two optimization objectives objectively and acquire the most suitable operating parameters. Moreover, experiments have been made to evaluate the energy-saving potential and the performance of the algorithm. Experimental results show that there could be significant potential for improving optimization objectives simultaneously through the operating parameter optimization, and the solution method is feasible.

Vibration suppression of drilling tool system during deep-hole drilling process using independence mode space control

Deep-hole drilling technology is commonly used in the aerospace and automobile industries, for new-energy equipment manufacturing, and in the high-tech industries. While this technology produces high-quality holes, higher quality is pursued. A method to improve the processing quality is to suppress the vibration modes associated with long shafts. This problem was addressed with an aim of real-time application. In addition, a higher goal was set by way of providing a solution (in full) to the associated problem, to shed light on processes that bear similar features in manufacturing and for other industries. An operable control scheme was constructed by transforming the system dynamics to modal space for modal decoupling and truncation. The modal displacement and velocity information estimated by the modal filtering were introduced into the feedback gain matrix. All obstacles in traditional physical space were shunned. A damper/sensor position optimisation algorithm was suggested to minimise the modal spillover and acquire modal orthogonality, which led to a new method that has an edge on all preceding methods because of its stronger ability. A system capable of real-time suppression of modal vibration in a deep-hole drilling tool was built and implemented. Using hole roundness error as the criterium, it was found that further improvement of hole quality was achieved. The idea presented in this work may pave the way for elevating the quality of other manufacturing processes with similar weak stiffness features, such as those seen in long-shaft tools or thin-wall workpieces. The method may also provide a reference for other industries with relevant or comparable problems.

Enhancing Single Channel MQL through Bypass Controlled Design for Deep Hole Drilling with Small Diameter Tool

Because of significant energy savings, enablement of higher machining speed as well as environmentally friendly features, Minimum Quantity Lubrication (MQL) has been efficiently used for many machining processes. However, in deep hole drilling with small tools (tool diameter D< 5 mm and length L>25 D) there is a bottleneck for the single-channel MQL system. The single-channel MQL, based on the Venturi principle, has difficulty generating the required oil quantity due to dropped air pressure difference during the deep hole drilling process. In this paper, a system concept based on a bypass design is proposed and investigated in static and dynamic laboratory tests. In the static test, the oil volume with and without bypass control was measured. Through the spray pattern test, the aerosol distribution and the reaction time are analyzed. A dynamic machining trial with a drill tool (D=4.5 mm, L= 40 D) was carried out with the proposed system. The tool wear was tracked and analyzed up to 100 meters in drilling distance. The result shows that the single-channel MQL with a bypass control is able to overcome this limitation and enables a uniform and continuous aerosol flow to tooltips.

Analysis of the functional properties in the bore sub-surface zone during BTA deep-hole drilling

The BTA deep hole drilling process is analysed to determine the relationships between process-structure and residual stress as a function of surface conditioning during the machining process. The residual stresses, the hardness and structural changes in the microstructure are used as indicators for a following process control in order to generate an improved component service life or reliability. In the first tests, the deep-drilled samples are examined with regard to residual stresses, bore tolerances, microstructure and hardness in the sub-surface zone. Furthermore, the specimens will be subjected to a heat treatment to establish a stress-free microstructure as a reference state for the magnetic residual stress measurement.

Optimization of Surface Roughness in Deep Hole Drilling using Moth-Flame Optimization

This study emphasizes on optimizing the value of machining parameters that will affect the value of surface roughness for the deep hole drilling process using moth-flame optimization algorithm. All experiments run on the basis of the design of experiment (DoE) which is two level factorial with four center point. Machining parameters involved are spindle speed, feed rate, depth of hole and minimum quantity lubricants (MQL) to obtain the minimum value for surface roughness. Results experiments are needed to go through the next process which is modeling to get objective function which will be inserted into the moth-flame optimization algorithm. The optimization results show that the moth-flame algorithm produced a minimum surface roughness value of 2.41µ compared to the experimental data. The value of machining parameters that lead to minimum value of surface roughness are 900 rpm of spindle speed, 50 mm/min of feed rate, 65 mm of depth of hole and 40 l/hr of MQL. The ANOVA has analysed that spindle speed, feed rate and MQL are significant parameters for surface roughness value with P-value &lt;0.0001, 0.0219 and 0.0008 while depth of hole has P-value of 0.3522 which indicates that the parameter is not significant for surface roughness value. The analysis also shown that the machining parameter that has largest contribution to the surface roughness value is spindle speed with 65.54% while the smallest contribution is from depth of hole with 0.8%. As the conclusion, the application of artificial intelligence is very helpful in the industry for gaining good quality of products.

FEA of BTA Deep Hole Drilling Based on ANSYS

This paper takes BTA deep hole drilling as the research object. ANSYS software is used in the static and dynamic analysis of the force of BTA deep hole drilling process from theory and in modeling and simulation. Firstly, According to the finite element analysis, the most concentrated stress and the largest deformation of the cutting tool are the cutting edge and the cutting surface of the tool block. The main vibration of drill stem is in the form of twist and bending. Sceondly, it is concluded that the main vibration of drill stem is in the form of twist and bending through the modal analysis. Finally, the natural frequency of this type of BTA drill stem is obtained by analyzing the amplitude response curve, and it is suggested to avoid the rotational speed near the dangerous speed during machining to avoid resonance of the drill stem.

Modeling and Optimization of Machining Parameters Using Regression and Cuckoo Search in Deep Hole Drilling Process

This study presents the modeling and optimization of the machining parameters in deep hole drilling process using statistical and soft computing technique. Regression analysis is used for modeling and Cuckoo Search, CS algorithm is used for the optimization process. Design of Experiment (DoE), have been carried using a Full Factorial design with added centre point that comprises of machining parameters (feed rate (f), spindle speed (s), depth of hole (d) and minimum quantity lubrication, MQL (m)) and machining performance which is surface roughness, Ra. Next, the mathematical models (Multiple Linear Regression, MLR and 2-factor interaction, 2FI) are developed for the experimental results of Ra and Analysis of variance, ANOVA are used to check the significance of the models developed. The results showed that both of mathematical models (MLR and 2FI) have outperformed the minimum Ra value compared to the experimental result.

Experimental Investigation of Bubble-Mixed Cutting Fluid Delivery for Micro Deep-Hole Drilling

In drilling, chip-clogging results in increased drilling temperature, excessive tool wear, and poor hole quality. Especially, in microdrilling, low rigidity of the tool and inability of cutting fluid to penetrate narrower tool–workpiece interface significantly reduce the drilling performance. A novel bubble-mixed cutting fluid delivery method proposed in this research aims toward achieving a high-performance micro deep-hole drilling process with a significant reduction in the consumption of cutting fluid. Experimental results show that the bubble-mixed cutting fluid delivery method achieves lower thrust force during drilling, higher drilled depth before tool breakage, and lower dimensional and circularity errors when machining deep holes in comparison with dry cutting or conventional flood delivery method. It is also found that the smaller-sized bubbles effectively penetrate the tool–workpiece interface during the drilling producing deeper holes by better chip evacuation and cooling.

Iterative Learning Method for Drilling Depth Optimization in Peck Deep-Hole Drilling

Due to the enclosed chip evacuation space in deep hole drilling process, chips are accumulated in drill flutes as drilling depth increases, resulting in the increase of drilling torque and lead to drill breakage. Peck drilling is a widely used method to periodically alleviate the drilling torque caused by chip evacuation; the drilling depth in each step directly determines both drill life and machining efficiency. The existing drilling depth optimization methods face problems including low accuracy of the prediction model, the hysteresis of signal diagnosis, and onerous experiments. To overcome these problems, a novel drilling depth optimization method for peck drilling based on the iterative learning optimization is proposed. First, the chip evacuation torque coefficients (CETCs) are introduced into the chip evacuation torque model to simplify the model for learning. Then, the effect of chip removal process in peck drilling on drilling depth is analyzed. The extended depth coefficient by chip removal (EDCbCR) is introduced to develop the relationship between the extended depth in each drilling step and drilling depth. On the foundation of the modeling above, an iterative learning method for drilling depth optimization in peck drilling is developed, in which a modified Newton's method is proposed to maximize machining efficiency and avoid drill breakage. In experiments with different cutting parameters, the effectiveness of the proposed method is validated by comparing the optimized and measured results. The results show that the presented learning method is able to obtain the maximum drilling depth accurately with the error less than 10%.

Experimental and simulative investigation of the oil distribution during a deep-hole drilling process and comparing of the RANS kω-SST and RANS hybrid SAS-SST turbulence model

Helical deep hole drilling is a process frequently used in industrial applications to produce bores with a large length to diameter ratio. For better cooling and lubrication, the deep drilling oil is fed directly into the bore hole via two internal cooling channels. Due to the inaccessibility of the cutting area, experimental investigations that provide information on the actual machining and cooling behavior are difficult to carry out. In this paper, the distribution of the deep drilling oil is investigated both experimentally and simulatively and the results are evaluated. For the Computational Fluid Dynamics (CFD) simulation, two different turbulence models, i.e. the RANS k-ω-SST and hybrid SAS-SST model, are used and compared. Thereby, the actual used deep drilling oil is modelled instead of using fluid dynamic parameters of water, as is often the case. With the hybrid SAS-SST model, the flow could be analyzed much better than with the RANS k-ω-SST model and thus the processes that take place during helical deep drilling could be simulated with realistic details. Both the experimental and the simulative results show that the deep drilling oil movement is almost exclusively generated by the tool rotation. At the tool’s cutting edges and in the flute, the flow velocity drops to zero for the most part, so that no efficient cooling and lubrication could take place there. In addition, cavitation bubbles form and implode, concluding in the assumption that the process heat is not adequately dissipated and the removal of chips is adversely affected, which in turn can affect the service life of the tool and the bore quality. The carried out investigations show that the application of CFD simulation is an important research instrument in machining technology and that there is still great potential in the area of tool and process optimization.

Chip evacuation force modelling for deep hole drilling with twist drills

Chip evacuation is the main difficulty of deep hole drilling process. For deep hole drilling with large depth-to-diameter ratio over 10, drilling force increases significantly with the drilling depth due to the friction and pressure reaction between the continuing generated chips and the drill flutes as well as the hole wall. In practical deep hole drilling process, overlarge drilling depth will cause drill breakage due to the low rigidity of the deep-hole twist drill, while using too small drilling depth is inefficient. The existing methods for drilling depth optimization are still faced with troubles, including lack of prior knowledge input of the monitoring method and difficult to measure or calibrate model parameters of the prediction model. To overcome these problems, a novel and practical chip evacuation force model for deep hole drilling is developed in this paper. Firstly, the chip evacuation forces in deep hole drilling are derived based on the elemental chip flow method, with the expression including three chip evacuation force coefficients for the practicability of the model. Then, the chip evacuation force coefficients are calibrated in a set of drilling tests under different cutting parameters, and the relations between chip evacuation force coefficients and cutting parameters are investigated with range analysis and analysis of variance. Finally, validation experiment results show that the proposed chip evacuation force model is able to predict the drilling force with increasing drilling depth in deep hole drilling, and the maximum drilling depth can be obtained accurately with the error less than 3%.

Influence of the deep hole drilling process and sulphur content on the fatigue strength of AISI 4140 steel components

When using quenched and tempered steels in the automotive industry or other industrial applications the fatigue behavior is of elementary importance. The surface and subsurface integrity of machined parts is known as one key factor related to the fatigue strength of components and is strongly influenced by the machining process. Especially for the deep hole single lip drilling, a large part of the cutting force is transferred to the bore wall and the surface and subsurface zone are influenced by the interaction between the tool and the workpiece material.In this study, the approach of inserting residual stresses into the bore wall and influencing the microstructure of the bores subsurface in a way, that the components can withstand a higher mechanical and dynamic load, is investigated in detail. In a close cooperation between the authors the parameters of the single-lip drilling process and the workpiece material are correlated with the produced surface quality and subsurface microstructure as well as the resulting fatigue strength of the components. For the comparative characterization of the fatigue behavior, established test procedures of destructive material testing in combination with new non-destructive test methods, such as the Barkhausen noise analysis, are applied and developed further. The results of the fatigue tests in correlation with the results of the Barkhausen noise analysis are used to design a model for predicting the fatigue strength of drilled components.

Study on detection method of rifling mark in BTA deep hole drilling process

Study on detection method of rifling mark in BTA deep hole drilling process

Process-parallel center deviation measurement of a BTA deep-hole drilling tool

The BTA deep-hole drilling process is used to manufacture holes with a high length-to-diameter ratio of up to 100. A major quality criteria is the difference between the drilled hole axis and the desired, ideal straight hole axis, called center deviation. A novel measuring system is being investigated in order to measure the center deviation simultaneously to the drilling process. The deviation is determined by calculating the bending line of the boring bar using a newly developed algorithm. The measuring system consists of four subsystems: Optical fiber Bragg grating (FBG) sensors, four eddy current sensors, a rotary encoder and a displacement encoder. These subsystems enable a spatial measurement visualization of the bending line and the center deviation at the head of the boring bar. A major challenge is the separation of the bending strain from other undesired strain fractions. This is done by using an arrangement of two FBG sensors and a digital band pass filter. Experimental investigations show sufficiently good agreement between the calculated and the actual center deviation. Furthermore, drilling experiments reveal that the measurement setup can be used for additional process monitoring by using frequency analysis. Therefore, the investigated system is able to visualize and observe the center deviation. The visualization can be used to derive adequate countermeasures in order to ensure a better process control for the machine operator. The objective of the investigation is to increase the process reliability and productivity by preventing scrap parts. Within this paper, the investigated measuring system, the calculation of the center deviation and first experimental results are described.

Numerical investigation on nonlinear dynamic responses to fluid-structure interaction in BTA deep-hole drilling shaft system

Numerical investigation is conducted into the nonlinear dynamic responses to fluid-structure interaction in deep-hole drilling shaft system. Based on the theories of pipes and tubes conveying fluid, the governing equation of the drilling shaft system is obtained taking into account of the fluid-structure interaction and the effect of the motion constraints. The nonlinear partial differential governing equation of motion is discretized in modal space using the Galerkin method and then transformed into a set of ordinary different equations. Numerical solutions of these equations are then obtained using the fourth order Runge-Kutta method. The influence of the forcing frequency and the support constraints on the dynamic behaviors of the drilling shaft is examined. The nonlinear dynamic behaviors of the drilling shaft system are presented by the bifurcation diagram and phase diagram. It has been found that the magnitude of support stiffness and the number and position of support constraints have a significant influence on dynamic behaviors of the drilling shaft system. The study in the paper provides an effective guidance to maintain the stability of the BTA deep-hole drilling shaft system through selecting the favorable operation parameters in deep hole drilling process.

The thermal modeling of deep-hole drilling process under MQL condition

This study investigates the temperature distribution of a compacted graphite iron (CGI) workpiece in minimum quantity lubrication (MQL) deep-hole drilling. The temperature distribution in the workpiece is predicted using the finite element method, in which the heat flux loads on the chisel and the cutting lip applied to the finite element model are determined using analytical equations. Additionally, heat flux loads on the margin and the heat convection coefficient of the air–oil mixture are considered and calculated using the inverse heat transfer method. The inverse method is validated experimentally, and the results demonstrate good agreement with the experimental temperature measurements. The importance of drilling time was demonstrated on the temperature distribution. The maximum temperature was observed on the chisel edge near the center of the hole instead of the outer surface of the hole.