Low-frequency Vibration-assisted Drilling Research Articles

Machinability of CFRP/Ti6Al4V stacks with low-frequency-vibration assisted drilling under different cooling strategies

Carbon fiber reinforced plastic (CFRP)/Ti6Al4V stacks are widely used in the aircraft industry, and drilling these stacks is essential during the assembly process. To solve the problem of high drilling temperatures in CFRP/Ti6Al4V stacks, which lead to poor tool life and hole quality, the effects of three cooling strategies compose minimum quantity lubrication (MQL), water-based coolant, and internal air cooling, were investigated in this study. Tensile/compressive strength and fatigue-life tests were conducted to evaluate the applicability of the cooling medium before drilling. Then, low-frequency vibration-assisted drilling of CFRP/Ti6Al4V stacks was performed to investigate and analyze their machinability under the three cooling strategies by analyzing the drilling temperature, thrust force, tool wear, chip removal capacity, and hole quality. The results show that the selected cooling media, including Rhenus XT46 and Accu-Lube LB2000, are applicable in CFRP drilling, whereas the adopted media, compared with water, have little influence on the tensile/compressive strength and fatigue life of the CFRP. Compared with internal air cooling and MQL, water-based coolant can more effectively improve the machinability of CFRP/Ti6Al4V stacks, decreasing the CFRP drilling temperature by 41.6 % and 40.1 %, respectively, while the reductions in the Ti6Al4V drilling temperature are 76.7 % and 57.4 %, respectively. Meanwhile, under water-based coolants, the thrust force reductions in the drilling of CFRP are 13.1 % and 11.7 %, whereas those in the drilling of Ti6Al4V are 11.0 % and 7.8 %, respectively, compared with the internal air and MQL. In addition, under the water-based coolant condition, the tool wear rate is the slowest and the hole quality is the best among the three cooling strategies, whereas a high injection pressure further decreases the VBmax value. Furthermore, under the water-based coolant conditions, the Ti6Al4V exit burr height and CFRP exit delamination are the lowest. These findings provide useful insights into improving the machinability of CFRP/Ti6Al4V stacks in the aerospace industry, particularly for drilling that requires high-quality holes and a long tool life.

Surface Characteristics and Residual Stress Variation in Semi-Deep Hole Machining of Ti6Al4V ELI with Low-Frequency Vibration-Assisted Drilling

This study examined the impact of vibration-assisted drilling (VAD) on hole quality and residual stress in Ti-6Al-4V ELI (Extra Low Interstitials) material. Ti-6Al-4V ELI possesses excellent mechanical properties but presents challenges in machining, including chip evacuation, burr formation, and elevated cutting temperatures. VAD, particularly low-frequency vibration-assisted drilling (LF-VAD), has been explored as a potential solution to address these issues. The research compares LF-VAD with conventional drilling (CD) under various cutting and cooling conditions. LF-VAD exhibits higher maximum thrust forces under specific conditions, which result in accelerated tool wear. However, it also demonstrates lower RMS (root mean square) forces compared to CD, offering better control over chip formation, reduced burr formation, and improved surface roughness within the hole. Furthermore, LF-VAD generates greater compressive residual stresses on the hole’s inner surface compared to CD, suggesting enhanced fatigue performance. These findings indicate that LF-VAD holds promise for improving the hole’s surface characteristics, fatigue life, and overall component durability in Ti-6Al-4V machining applications.

Investigation of transient machining in the cortical bone drilling process by conventional and axial vibration-assisted drilling methods.

A temperature exceeding the safety threshold and excessive drilling force occurring during bone drilling may lead to irreversible damage to bone tissue and postoperative complications. Previous studies have shown that vibration-assisted drilling methods could have lower temperatures and drilling forces than those of the conventional drilling method; we hypothesized that the main reason for these reductions stems from the differences in the transient machining processes between conventional and vibration-assisted drilling methods. To investigate these differences, comparative experiments and two-dimensional finite element models were performed and developed. The differences in the transient machining processes were verified by experimentation and clearly exhibited by the finite element models. Compared with the steady cutting process that produced continuous-spiral chips in the conventional drilling method, transient machining in the low-frequency vibration-assisted drilling method was a periodically dynamic cutting-separation process that produced uniform petal chips with specific settings of drilling and vibration parameters. Moreover, the transient machining process in the ultrasonic vibration-assisted drilling method was transformed into a combined action with high-speed impact and negative rake angle cutting processes; this action produced a large proportion of powdery chips. Therefore, it could be concluded that the superposed axial vibration significantly changed the transient machining process and radically changed the mechanical state and thermal environment; these changes were the main reason for the apparent differences in the drilling performance levels.

Deep-hole axis deviation mechanism of weak stiffness small-diameter single-lip tool in low-frequency vibration-assisted drilling

Deep-hole axis deviation mechanism of weak stiffness small-diameter single-lip tool in low-frequency vibration-assisted drilling

Experimental investigation and optimization of low-frequency vibration-assisted drilling

Experimental investigation and optimization of low-frequency vibration-assisted drilling

Theoretical and experimental analyses of dynamic deformation in low-frequency vibration-assisted drilling of CFRP/Ti stacks

Hole-making of stacks composed of carbon-fiber-reinforced plastic (CFRP) and titanium alloy under Low-frequency vibration-assisted drilling (LFVAD) is beneficial to both machining quality and tool wear. However, complicated deformation of the bottom Ti layer and even severe interfacial damage appears under the thrust forces with periodic fluctuations. Owing to lack of theoretical guidance in suppressing the deformation, this study established an analytical model to explain the influence of the fluctuating thrust force on the deformation of the workpiece. Data from validation trials performed on the CFRP/Ti stacks show that the deformation and thrust forces exhibit the same fluctuation behavior. The prediction errors of the average value and vibration amplitude of the Ti deformation were within 0.9 % and 10.7 %, respectively. Finally, a case study was conducted to optimize the drilling parameters in LFVAD of CFRP/Ti stacks based on the proposed model. As a result, the CFRP delamination damage was reduced by 17.0 %, and the stack drilling efficiency increased by 40.8 %.

Influence of parameters on temperature rise and chips morphology in low-frequency vibration-assisted bone drilling

In orthopedics and surgery, bone drilling is an important operation for inserting screws and fixing prostheses. A nonnegligible problem which can affect post-operative recovery is the thermal necrosis. For this problem, the method of low-frequency vibration-assisted drilling (LFVAD) was applied in the process of bone drilling in this paper. The influences of parameters (feed rate, rotational speed, vibration frequency and amplitude) on the cutting performances (cutting temperature and chip morphology) were investigated. The results indicate that LFVAD can produce lower temperature compared with conventional drilling (CD). In LFVAD, rotational speed and vibration amplitude are more important parameters on the drilling temperature and chip morphology compared to feed rate and vibration frequency. In addition, according to the trajectories of the cutting edge of drill bit, a mathematical model of heat generation and dissipation was developed in LFVAD.

Mechanism and feasibility study of low frequency vibration assisted drilling of a newly developed CFRP/Al co-cured material

CFRP/metal co-cured structure has been increasingly applied in the aerospace industry due to its outstanding mechanical properties of high specific strength and high stiffness. Compared with the stack structure, the co-cured material of which the metal was heavily wrapped by the CFRP prepregs has better interface performance due to the absence of interface gap, being helpful to improve the bonding strength with other parts. Hole making is an inevitable manufacturing process for the assembly of co-cured material while there still exists several challenges during the drilling operation. To be specific, the hole size with low accuracy and hole morphology with severe defects are the main concerns for the manufacturers, which can be mainly attributed to the tangled chips and high cutting temperatures. To solve the aforementioned problems, the low frequency vibration assisted drilling (LFVAD) operation was performed for the newly developed CFRP/Al co-cured material in the present work. The mechanism and feasibility of controlling the machining defects via LFVAD were theoretically and experimentally explored and the influence of vibration amplitude (VA) on the cutting responses was specially studied. The results show that LFVAD can reduce the average thrust forces and drilling temperatures compared to conventional drilling while the maximum thrust force shows larger magnitude with the elevation of VA, in which the VA of ∼30 μm presents the best one. Meanwhile, LFVAD can on the one hand reduce the scratch traces on the hole wall surface owing to its superior chip breakage effect and thereby improve the drilled hole accuracy, and on the other hand shrink the lower interface damage area due to the reduction of cutting temperatures. The obtained findings of the present work indicate that the proposed LFVAD method presents great superiority for the CFRP/Al co-cured material concerning the machining responses of higher hole accuracy and lower interface damage.

Development of a low-frequency vibration-assisted drilling device for difficult-to-cut materials

In the drilling process of difficult-to-cut materials, conventional drilling has resulted in various problems such as high drilling temperature and poor machining quality. Low-frequency vibration-assisted drilling has great potential in overcoming these problems since broken chips are generated. In this paper, a low-frequency vibration-assisted drilling device is developed by using a novel ring flexure hinge as the elastic recovery mechanism. Firstly, based on the theory of elastic mechanics and mechanical vibration, the deflection of ring flexure hinge is designed theoretically, and the influence of its structural parameters on its deflection is analyzed. Then, the correctness of theoretical design is further verified by static and dynamic simulation and stiffness test. Finally, the vibration performance of the device is tested under no-load condition, and actual drilling test is conducted to verify the drilling performance. The results show that the device could realize the axial low-frequency vibration with constant frequency-to-rotation ratio and amplitude stepless adjustment and present good working stability under no-load and load conditions. In the actual drilling test of titanium alloy and carbon fiber–reinforced plastic (CFRP)/titanium alloy laminated structure, the device under appropriate processing parameters breaks titanium alloy chip into small pieces and reduces drilling temperature by 44% and inhibits secondary damage of CFRP. It provides the reference and guidance for the development of LFVAD device in presented work.

Machining performance of PCD drill in low-frequency vibration-assisted drilling of CFRP/Ti6Al4V stack: with special emphasis on the plowing behavior

Machining performance of PCD drill in low-frequency vibration-assisted drilling of CFRP/Ti6Al4V stack: with special emphasis on the plowing behavior

The Effect of MQL on Tool Wear Progression in Low-Frequency Vibration-Assisted Drilling of CFRP/Ti6Al4V Stack Material

In this paper, the tool wear mechanisms for low-frequency vibration-assisted drilling (LF-VAD) of carbon fiber-reinforced polymer (CFRP)/Ti6Al4V stacks are investigated at various machining parameters. Based on the kinematics analysis, the effect of vibration amplitude on the chip formation, uncut chip thickness, chip radian, and axial velocity are examined. Subsequently, the effect of LF-VAD on the cutting temperature, tool wear, delamination, and geometrical accuracy was evaluated for different vibration amplitudes. The LF-VAD with the utilization of minimum quantity lubricant (MQL) resulted in a successful drilling process of 50 holes, with a 63% reduction in the cutting temperature. For the rake face, LF-VAD reduced the adhered height of Ti6Al4V by 80% at the low cutting speed and reduced the crater depth by 33% at the high cutting speed. On the other hand, LF-VAD reduced the flank wear land by 53%. Furthermore, LF-VAD showed a significant enhancement on the CFRP delamination, geometrical accuracy, and burr formation.

Finite element simulation of low frequency vibration-assisted drilling with modification of oscillation modes

Low frequency vibration assisted drilling (LFVAD) is an important cutting process, especially for hard-to-machine materials and materials that tend to produce long chips. In LFVAD the continuous axial tool movement in feed direction is superimposed with a sinusoidal oscillation of the tool. Due to the vibratory movement in axial direction an interrupted cut is enforced leading to the generation of comparatively small chips. In the present study, a chip formation simulation utilizing DEFORM for predicting thrust force and drilling torque was set up aiming at an optimization of LFVAD of the titanium alloy Ti6Al4V by means of modifications of the vibratory tool movement. In order to reduce computation times an initial borehole topography was generated utilizing a kinematic model of the process prior to the chip formation simulation. The simulation results regarding the time-dependent thrust force and drilling torque are compared with measurements. The results show that the modification of the oscillation mode can significantly decrease the maximum thrust force and the torque. Thus the finite element simulation of the process enables a predictive optimization of oscillation modes in LFVAD.

Influence of the workpiece material on the cutting performance in low frequency vibration assisted drilling

Fundamental problems in drilling processes are associated with the unfavorable machining conditions in the tool center and the difficult chip removal. Low frequency vibration assisted drilling (LFVAD), in which the linear tool feed is superimposed with a vibratory motion in feed direction, is a promising process to overcome these problems. Aiming at a systematic analysis of the influence of workpiece material properties, results from LFVAD experiments with Ti6Al4V, AlMgSi0.5 and 42CrMo4 in different heat treatment states are presented. Specifically the dependence of optimal oscillation amplitudes on the workpiece material behavior is analyzed.

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.

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.

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.

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.

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.

Tool wear mechanism in low-frequency vibration–assisted drilling of CFRP/Ti stacks and its individual layer

In this paper, a novel tool wear mechanism in low-frequency vibration–assisted drilling (LFVAD) of carbon fiber–reinforced plastic (CFRP)/Ti stacks and its individual layer has been proposed. Firstly, the difference of the effective rake angle, effective clearance angle, undeformed chip thickness, and tool-workpiece contact length between low-frequency vibration–assisted drilling and conventional drilling (CD) was analyzed based on the kinematic model. Then, the strength at different positions of the cutting edge was evaluated. Furthermore, the drilling experiments of CFRP/Ti stacks, CFRP plate, and Ti plate individually were taken under LFVAD and CD processes. Finally, the tool wear mechanism and the benefit of CFRP/Ti stacks and CFRP plate processed by LFVAD were expounded by kinematic analysis results, the analysis of drilling force, SEM images, and the profile of the cutting edge. The results show that the inner edge close to the chisel edge could be the weakest position of the drill in LFVAD. As the mean drilling force of LFVAD is lower than CD, the total wear volume of LFVAD is smaller than CD. Due to the change in the resultant cutting speed angle and the undeformed chip thickness, LFVAD produces the longer tool-workpiece contact length on the rake face and the flank face, which directly leads to a more uniform tool wear and a self-sharpening effect on the cutting edge. Thus, the reduction in the effective rake of the drill used in LFVAD is obviously smaller than the reduction in conventional drilling. The reduction in the effective clearance angle of the drill used in the LFVAD is also less than the reduction in conventional drilling, while this difference is attenuated as the cutting radius increases. The edge radius of the cutting edge is found to be much smaller than CD. In summary, the difference in the cutting edge geometry between LFVAD and CD is the root cause of the tool used in LFVAD to avoid severe edge chipping.