Vibration-assisted Drilling Research Articles

Design and Finite Element Analysis of Axial Low-frequency Vibration Tool-holder

Vibration-assisted drilling can significantly reduce the drilling force and cutting heat during deep hole machining, improve tools life and hole machining quality. As a branch of vibration drilling technology, axial low-frequency vibration-assisted drilling has a broad application prospect in the field of drilling because of its simple structure and easy implementation. A mechanical axial low-frequency vibrating tool-holder (ALVT) is designed, and the overall structure layout and working principle of the vibrating tool-holder are analyzed. The rotary motion of the machine tool spindle is used as the power input to drive the sinusoidal surface to rotate to achieve the amplitude output. The vibrating tool-holder model is simplified, and the ABAQUS finite element software is used to simulate the titanium alloy material for ordinary drilling and axial low-frequency vibration drilling (ALVD), and the axial force and cutting temperature changes are compared and analyzed. The results show that ALVD of titanium alloy can reduce the average axial force by about 47% and the cutting temperature by about 11%, which can significantly improve the drilling conditions and the quality of hole machining.

Parametric analysis of a dynamical model of the axial vibration of a vibration-assisted drilling tool, a vibro-impact system with multiple impacts

The aim of this work is to analyze the axial nonlinear dynamics of a drilling tool. The force at four impact surfaces are analyzed. Then, a parametric analysis is performed to investigate the effect that some parameters have on the dynamic behavior of the axial nonlinear dynamics of a drilling tool. Furthermore, a measure is proposed to evaluate the efficiency of the process, and used for design modifications of the current vibro-impact system. The results reveal the possibility of 85% increase in the impact force transfer and 125% increase in the mud flow operating range, when compared with the original design.

Analysis of low-frequency vibration-assisted bone drilling in reducing thermal injury

ABSTRACT Thermal injuries inflicted during bone drilling significantly affect the success rate of surgery, hence, it is important to control thermal injury through temperature reduction. Low-frequency vibration-assisted drilling (LFVAD) is proposed here to reduce thermal injury to bones. Subsequently, the effectiveness of this process is experimentally verified. Based on the trajectories of the cutting edge in LFVAD, the duty ratio and maximum uncut chip thickness are analyzed by varying the amplitude and feed per tooth. A special fixture is designed and the temperature field is measured using an infrared thermography camera. Furthermore, a verification experiment is performed on the machine tool using a low-frequency vibration tool holder. The maximum temperature rise is used to evaluate the drilling temperature, and a thermal injury factor is proposed to evaluate the size of the thermal injury area. Results show that LFVAD effectively reduced thermal injury during bone drilling. The non-cutting effect during LFVAD interrupted the continuous accumulation of cutting heat and promoted the dissipation of cutting heat. Under the experimental parameters used in this study with LFVAD, the maximum temperature rise reduced up to 29.7% and the thermal injury factor reduced up to 18.3%, as compared to those of conventional drilling.

Influence of dynamic angles and cutting strain on chip morphology and cutting forces during titanium alloy Ti-6Al-4 V vibration-assisted drilling

Vibration-assisted machining (VAM) is implemented in titanium alloy processing to solve some challenges, such as difficulty in chip breaking, large cutting forces, and high cutting temperatures. Based on the multi-region dynamic angles and the double-side wedge angle deformation mechanism, this study improves the vibration-assisted drilling (VAD) cutting forces and chip breaking model. The dynamic kinematics angles, the behavior of parameter influence, and the cutting strain effect of intermittent VAM are analyzed. VAD and conventional drilling (CD) experiments are carried out for model validation and mechanism analysis. The experiments show that the maximum deviation of the drilling forces simulation value and the experimental value is 9.13 %. Compared with the CD, the cutting force of the VAD is decreased by 10.1 %–46.2 %. The dynamic feed angle causes multiple cutting angles fluctuations, which affects cutting performance. The adjustment of the VAD cutting parameter value could reduce the chip length by 26.6 %–43.9 %. Material cutting strain presents multi-region characteristic, which influences the chip morphology. This study provides a reference for VAM parameter optimization.

Analysis of machining process and thermal conditions during vibration-assisted cortical bone drilling based on generated bone chip morphologies

When the temperature during bone drilling exceeds the safety threshold, the bone tissue surrounding the drilling site can be irreversibly damaged. To investigate the influence of vibration-assisted drilling (VAD) methods on the temperature increase during bone drilling and the causes for temperature increase, drilling experiments were performed on fresh bovine femur samples. The morphology and granularity distribution of the generated bone chips were innovatively used to directly compare the machining processes and thermal conditions of conventional drilling (CD), low-frequency vibration-assisted drilling (LFVAD), and ultrasonic vibration-assisted drilling (UVAD). The experimental results indicated that LFVAD produced the lowest temperature increase of 31.4°C, whereas UVAD produced the highest temperature increase of 44.1°C with the same drilling parameters. Additionally, the morphologies and granularity distributions of the bone chips significantly differed among these methods. We concluded that the smaller temperature increase in LFVAD was mainly attributed to the improved thermal conditions resulting from the periodic cutting/separation motion and the reliable geometric chip-breaking mechanism. In contrast, the unfavourable thermal conditions of UVAD were caused by the higher applied frequency, which created a significantly larger amount of friction heat. This was the main cause for the highest observed temperature increase, resulting in bone crushing processes that generated additional heat.

Improvement of micro-hole precision by ultrasound-assisted drilling of laser powder bed fused Ti6Al4V titanium alloy

Ti6Al4V alloy can be successfully used to fabricate complex near-net-shape industrial products and prosthetic components with enhanced biocompatibility by means of additive manufacturing (AM) technologies. Post-processing machining of such components are still necessary steps; however, the different machinability that characterizes AM products affect the manufacturing process in a great extent. To this aim, Ti6Al4V cylindrical samples were produced by laser powder bed fusion (LPBF) and micro-holes were machined on their surfaces by varying the cutting speed and feed per tooth, using both vibration-assisted drilling (VAD) and conventional drilling (CD). The drilled holes were comprehensively characterized in terms of geometrical, dimensional and outer edge quality, surface roughness, surface defects and microstructure. In general, VAD was found to improve the overall quality of the holes, regardless the cutting parameters applied thanks easier evacuation of the chips as well as enhanced material flow. To find the optimize process parameters conditions, all the characterization outcomes were combined in a global quality index (Qi). The highest cutting speed, the lowest feed per tooth and the use of VAD undoubtedly leads to the formation of the holes characterized by the best surface quality. The improvement given by VAD with the respect of the corresponding CD operation is found equal to 65%. These findings confirm the effectiveness of using VAD when approaching difficult to cut materials such as titanium alloys produced by LPBF.

Exit burr height mechanistic modeling and experimental validation for low-frequency vibration-assisted drilling of aluminum 7075-T6 alloy

The burr influences the surface quality and the performance of the part. Nowadays, vibration-assisted drilling (VAD) is used to decrease the exit burr size. However, further analysis of the VAD burr formation mechanism is required. A mathematical burr prediction model of low-frequency VAD is proposed for the aluminum 7075-T6 alloy cutting. This model includes material deformation mechanisms, multi-region thrust force, and VAD kinematic characteristics. In the material deformation process of VAD, the Johnson-Cook model and fracture model are considered. The results indicate that the experimental burr height is consistent with the model prediction values, and the deviation is less than 8%. The average burr height of VAD decreases by 49.5 %–52.6 % compared with conventional drilling (CD). The parameter analysis shows that the vibration amplitude had the highest sensitivity to the burr height. In the Multivariate regression analysis (MRA), the regression coefficient sum of vibration-related parameters’ absolute values (0.676) approximates the sum of other parameters’ absolute values (0.817).

Chip Control Analysis in Low-Frequency Vibration-Assisted Drilling of Ti–6Al–4V Titanium Alloys

In this study, control research of chip morphology and removal is conducted theoretically and experimentally on the basis of the low-frequency vibration-assisted drilling process of titanium alloy. The chip morphology prediction model is established on the basis of the modified kinematic model, in which the shear angle variation, critical cutting thickness, and stiffness of a vibration generator system are considered. In terms of chip removal monitoring, a new monitoring method based on high speed camera is proposed in this paper. And the reliability of the new method is verified by comparing the signals obtained by the power sensor and the force sensor. An empirical prediction model for chip removal is also established on the basis of the modified kinematical model, the chip morphology prediction model, and the force balance analysis of fragmental chips. Validation experiments show that the mean error of chip radian, which can reflect the difference between the predicted chip morphology and the experimental one, is 6%. The mean error of the predicted chip removal index compared with the experimental one is 10.4%. The results obtained show that chip removal can be controlled effectively by low rotation speed, small chip radian, light chip weight, high minimum quantity lubrication cooling pressure, and high oscillation frequency. On the basis of the prediction model of chip removal, the effects of drilling parameters on chip removal behavior are analyzed, and the optimal drilling parameter combination with highest processing efficiency is given.

Effect of process parameters on chip formation during vibration-assisted drilling of Ti6Al4V

Vibration-assisted drilling (VAD) of Ti6Al4V is typically used in the aerospace industry to enhance the performance of the machining process. A mix of continuous and saw-tooth chip formation is associated with VAD of Ti6Al4V. In this paper, a comprehensive experimental study is developed to examine the effect of process parameters on the dominant chip formation mechanisms and the associated effects on the thrust forces and machined surface finish. The results indicate a significant change of the chips free surface produced by VAD. The kinematics of VAD showed a direct relation between the VAD amplitude and the effective rake angle. In agreement with the theory of saw-tooth formation due to cyclic crack formation, the scanning electron microscopy (SEM) examination showed a gross crack (GC) and micro crack (MC) along the shear plane. The GC increased from 20 μm for conventional drilling to 224 μm for VAD at the highest amplitude. Moreover, increasing the VAD amplitude to 160 μm showed an obvious enhancement of the machined surface finish. In addition, the study presents the influence of VAD on the tool wear mechanisms through the composition analysis of the chips machined surface using Energy Dispersion X-ray Spectroscopy (EDS).

Information feedback self-adaptive harmony search algorithm for the bovine cortical bone vibration-assisted drilling optimization

In orthopedics and surgery, bone drilling is an important operation. Increasing demands call for bone drilling force prediction and minimization. Vibration-assisted drilling (VAD) provides an opportunity to reduce the force. In the study, the information feedback self-adaptive harmony search (IFSHS) algorithm is presented for the thrust force minimization in bovine cortical bone VAD. The IFSHS improves the drilling parameters which leads to the optimal cutting state. The dynamic searching parameters, optimization parameters evaluation, and evaluation information feedback are applied to search the optimal solution. This force model was developed and employed with IFSHS. The VAD drilling experiments and parameters analysis are carried out. Experimental results have shown that the VAD has the potential to reduce the thrust force. Compared with conventional drilling (CD), the thrust force decreased by 18.4%–33.2% under suitable VAD parameters. Compared with the results of the original VAD parameters, the optimized thrust force decreased by 20.19%.

An investigation of the mechanism and benefits of ultrasonic vibration-assisted drilling of hard brittle materials such as Hotan jade

The ultrasonic vibration-assisted drilling process and the surface micro characteristics of Hotan jade were evaluated in detail. Because of the special physical properties of Hotan jade, traditional machining methods have great limitations. In consequence, it is difficult to achieve the required precision and surface quality. In this study, the physical properties of Hotan jade were considered and its unique cutting and machinability characteristics were evaluated for comparison purposes. The design principles of UV drilling and the important components of such a system were examined. The material removal mechanism of UV drilling was evaluated in detail. Finally, comparative tests using UV drilling and traditional drilling were carried on Hotan jade. The test results were evident from the degree of tool wear, degree of reaming, the extent of damage at the entrance to the drilled hole, the outlet burr and the roughness of the hole surface. The results of the machining trials confirmed that UV drilling not only was an easier process, but the straightness of the hole could be guaranteed, and the machined quality and drilling efficiency usually were better than was the case using traditional machining.

Elimination of delamination and burr formation using high-frequency vibration-assisted drilling of hybrid CFRP/Ti6Al4V stacked material

The superior physical and mechanical characteristics of CFRP/Ti6Al4V stacked structures explain their widespread use in the aerospace industry. However, the unacceptable machining-induced tensile surface residual stresses and reduced surface integrity are the main challenges that are faced in the conventional drilling process. These types of damage are attributed to the relatively high thermal load and poor chip evacuation mechanism. Vibration-assisted drilling is a promising technique to control the uncut chip thickness, and consequently reducing the cutting energy. Moreover, the axial tool oscillation provides a mechanism for effective chip evacuation. This study presents an experimental investigation relating the high-frequency vibration-assisted drilling (HF-VAD) machining parameters to the Ti6Al4V burr formation and induced residual stresses, as well as CFRP delamination during the drilling of CFRP/Ti6Al4V staked material. Additionally, this study presents an assessment and comparison between HF-VAD and LF-VAD of CFRP/Ti6Al4V hybrid structure. The results showed up to approximately 26%, 37%, and 86% reduction in the thrust force, cutting temperature, and the exit burr height, respectively. The effect of HF-VAD on surface integrity and Ti6Al4V residual stresses are also presented. The drilling process of HF-VAD resulted in free exit delamination of CFRP with compressive residual stress on the Ti6Al4V machined surface.

Study on modal analysis and chip breaking mechanism of Inconel 718 by ultrasonic vibration-assisted drilling

In this study, both theoretical and experimental research was conducted to investigate the role played by a difficult-to-machine material, Inconel 718, in improving the surface finish quality in drilling holes. Ultrasonic vibration technology was applied to assist with the drilling process. An axial ultrasonic vibration-assisted drilling (UAD) system was designed to determine the structural relationships between different component parts, based on which an axial UAD model was established. Abaqus finite element software was applied to perform model simulation and an analysis was conducted of the structure to find its optimal natural frequency and vibration mode. The conditions for complete geometric chip breaking based on the mechanisms of UAD and chip breaking, as well as pre-set parameters, were inferred and the theoretical domain of complete geometric chip breaking was mapped. Subsequently, a range of different parameters was applied to conduct experiments on the drilling process, from which it was established that the characteristics of chipping satisfy the conditions required for complete geometric chip breaking. Finally, under the circumstances where the parameters for the drilling process are identical and chip breaking conditions are met, UAD was found to be advantageous over conventional drilling (CD) as the former produces a more apparent chip breaking effect. Additionally, UAD can reduce the Ra value and abrasion of cutting tools, thus improving the quality of the hole drilling process.

An Investigation into Tool Wear and Hole Quality during Low-Frequency Vibration-Assisted Drilling of CFRP/Ti6Al4V Stack

The use of lightweight material such as CFRP/Ti6Al4V in stacked structures in the aerospace industry is associated with improved physical and mechanical characteristics. The drilling process of nonuniform structures plays a significant role prior to the assembly operation. However, this drilling process is typically associated with unacceptable CFRP delamination, hole accuracy, and high tool wear. These machining difficulties are attributed to high thermal load and poor chip evacuation mechanism. Low-frequency vibration-assisted drilling (LF-VAD) is an advanced manufacturing technique where the dynamic change of the uncut chip thickness is used to manipulate the cutting energy. An efficient chip evacuation mechanism was achieved through axial tool oscillation. This study investigates the effect of vibration-assisted drilling machining parameters on tool wear mechanisms. The paper also presents the effect of tool wear progression on drilled hole quality. Hole quality is described by CFRP entry and exit delamination and hole accuracy. The results showed a significant reduction in the thrust force, cutting torque, cutting temperature, and flank wear-land.

Experimental investigation of the temperature elevation in bone drilling using conventional and vibration-assisted methods

Bone drilling is widely used in orthopaedics for inserting screws and fixing prostheses. Thermal necrosis is one of the major problems that may seriously affect post-operative recovery. Accordingly, this paper mainly focuses on comparing the influences of conventional drilling (CD), ultrasonic vibration-assisted drilling (UVAD) and low-frequency vibration-assisted drilling (LFVAD) methods, and drilling parameters on the temperature elevation in bone drilling process. A full factorial experiment was performed, and the temperatures were measured using an infrared camera. The lowest temperature elevation was obtained by LFVAD compared with CD and UVAD at the same drilling conditions. Setting CD as a reference, the maximum difference between LFVAD and CD was approximately −4 °C, whereas that between UVAD and CD was approximately 16 °C. The temperature elevation increases linearly with the spindle speed and follows an inverted U-shaped curve, with the feed rate having a peak at 40 min/mm in each drilling method. The results were discussed with regard to the features of LFVAD and UVAD. It was expected that the LFVAD could achieve minimal thermal damage and attain better results in the medical bone drilling process.

Experimental study: comparison of conventional and low-frequency vibration-assisted drilling (LF-VAD) of CFRP/aluminium stacks

The increasing substitution of metallic structural components by carbon fibre reinforced polymers (CFRP) in aerospace applications results in a growing need for drilling metal and CFRP in one operation, the so-called stack machining. The different material properties of the stack components in combination with high geometrical tolerance requirements result in large challenges for the drilling tool and the process strategy. Focussing on the process strategy, this paper deals with an extensive comparison of conventional and low-frequency vibration-assisted drilling (LF-VAD) of CFRP/aluminium stacks. The influence of the cutting speed, the feed rate and the amplitude of the superimposed oscillation in LF-VAD on the resulting bore quality is analysed. For the bore quality, three separate aspects are considered, namely, damages at the CFRP entrance, burr formation at the aluminium exit and deviations from the nominal diameter in both materials. Online temperature and force measurements enable interpretation of the influence on the bore quality. Based on experimental data, a clear dependency of the bore quality and the chip transport on both, the process parameters and the drilling strategy are identified. Based on high-speed recordings, the dynamic loading situation due to the superimposed oscillation in LF-VAD is found to be crucial for the formation of peel-up delaminations.

Surface and microstructure characterization of low-frequency vibration-assisted drilling of Ti6Al4V

A continuous curled chip formation with a high thermal load is a critical challenge during conventional drilling process of Ti6Al4V. In addition, adverse side effects will take place on the drilled hole quality, as well as the drill tool performance, which is not acceptable in the aerospace industry. Chip segmentation using low-frequency vibration-assisted drilling (LF-VAD) is a promising technology aimed at reducing the difficulties associated with conventional drilling. Compressive residual stresses, lower cutting zone temperature, higher hole size accuracy, and smoother surface finish are of the main advantages that could be achieved with the interrupted cutting technique. The primary objective of this paper is to investigate the effect of LF-VAD machining parameters on the Ti6Al4V residual stresses, microstructure, and surface integrity, for a wide range of modulation amplitude, feed, and cutting speed, for a new frequency range for the first time. The effect of LF-VAD on the chip morphology and subsurface examination of microstructure, surface, and depth profile of residual stress are examined. The experimental results showed that LF-VAD has a significant influence on the induced residual stress. A 35.8% reduction in the cutting temperature has been observed at the exit surface. This method has improved the residual stress to compressive which has a significant impact on the part fatigue life.

Chip Morphology and Delamination Characterization for Vibration-Assisted Drilling of Carbon Fiber-Reinforced Polymer

Carbon fiber-reinforced polymers (CFRP) are widely used in the aerospace industry. A new generation of aircraft is being built using CFRP for up to 50% of their total weight, to achieve higher performance. Exit delamination and surface integrity are significant challenges reported during conventional drilling. Exit delamination influences the mechanical properties of machined parts and, consequently, reduces fatigue life. Vibration-assisted drilling (VAD) has much potential to overcome these challenges. This study is aimed at investigating exit delamination and geometrical accuracy during VAD at both low- and high-frequency ranges. The kinematics of VAD are used to investigate the relationship between the input parameters (cutting speed, feed, vibration frequency, and amplitude) and the uncut chip thickness. Exit delamination and geometrical accuracy are then evaluated in terms of mechanical and thermal load. The results show a 31% reduction in cutting temperature, as well as a significant enhancement in exit delamination, by using the VAD technology.

Design and fabrication of a novel vibration-assisted drilling tool using a torsional magnetostrictive transducer

In this paper, a vibrational drilling tool using a magnetostrictive torsional transducer is designed and fabricated. The torsional transducer is a hollow cylinder, which is made up of “2 V permendur.” Passing an alternating current through the material creates a variable circular magnetic field and exciting a coaxial coil with a direct current generates a constant axial field in the material. According to the Wiedemann effect, the magnetic domains of the material rotate helically in the direction of the external field and cause a shear strain in the material. To utilize the maximum torque and amplitude of the transducer as well as to maintain the transducer’s resonance conditions, a wave transmitter is designed to connect the transducer to a drill bit. The dimensions of the vibrating tool are calculated theoretically and verified by the finite element software of COMSOL. Friction couplings are designed to connect the transducer, wave transmitter, and the drill bit. This torsional drilling tool is used for drilling of aluminum workpieces. The tests show that torsional vibrations reduce the required drilling torque by 60% in comparison to conventional drilling. In addition, usage of the torsional vibrations has the effect of the chip breaking, improving the accuracy of the hole size by 55.4%, and reducing the drilling surface roughness by the percent of 25.3% in comparison to conventional drilling.

Deep Hole Drilling of Large-Diameter Titanium Alloy With a Novel Rotary Low-Frequency Vibration Device

Titanium alloy (Ti) has been widely used in aerospace industry due to excellent mechanical properties and the demands of Ti parts with a high length-to-diameter ratio and a large diameter are increasing. However, deep hole drilling of large-diameter Ti holes is usually both time-consuming and cost-consuming due to a series of problems such as unfavorable chip removal, helical structure on the hole surface, poor hole precision and severe tool wear. This paper reports on the cutting mechanism and experimental results of low-frequency vibration-assisted single-lip drilling (LFVASLD) of large-diameter Ti holes (O17mm) for the first time. In this paper, a novel rotary low-frequency vibration device was developed and the vibration generation mechanism was analyzed. Thereafter, the material removal mechanism of LFVASLD was established. Then, the comparative experiments between LFVASLD and conventional single-lip drilling (CSLD) of Ti were conducted. The experimental results show that, compared with CSLD, LFVASLD can significantly prolong the drilling depth by 9 times due to reduced tool wear and alleviate helical structure on the hole surface due to the separated cutting mode. Furthermore, the influence of drilling parameters in LFVASLD on hole quality were also investigated. It is concluded that, the LFVASLD method is suitable for deep hole drilling of large-diameter titanium alloy and the developed rotary low-frequency vibration device can be used as a machine tool accessory to significantly improve the processing capacity in the industrial practice.