Vibration-assisted Drilling Research Articles

Hole-exit defect formation during traditional and ultrasonic vibration-assisted drilling of C/SiC composites

Hole-exit defect formation during traditional and ultrasonic vibration-assisted drilling of C/SiC composites

A prediction model for drilling temperature of CFRP/Ti stacks and green cooling strategy considering chip ejection process

Drilling temperature has always been a hot issue in the drilling process of CFRP/Ti stacks. Accurately predicting drilling temperature is necessary for reliable optimization of drilling parameters. However, since the drilling process involves two materials and may affect each other, the prediction of temperature during drilling is still a challenge. In this paper, a novel drilling temperature model is established to predict the temperature distribution in CFRP workpiece during the drilling process of CFRP/Ti stacks, considering the minor cutting edge and titanium alloy chip ejection process. Specifically, according to different drilling phases, in addition to considering the heat source of the cutting zone of different materials, the heat source generated by the interaction of minor cutting edge and rebound hole wall of CFRP and the heat source formed by the thermal-mechanical effect of Ti chip ejection process are also considered. The results show that the prediction errors of peak temperature in CFRP entrance and stack interface region during drilling are within 15.8 % and 10.9 %, respectively, which indicates the validity of the model. Finally, the green cooling strategy (High and low frequency compound vibration-assisted drilling) is adopted to significantly reduce the peak temperature in the drilling process by controlling the chip morphology and ejection process, which further proves that the thermo-mechanical action of Ti chips on CFRP cannot be ignored, and provides reference for temperature modeling and low-damage processing of CFRP/metal stacks.

Machinability of submillimeter holes in ceramic matrix composites by high-frequency ultrasonic vibration-assisted drilling

Ceramic matrix composites (CMCs) are highly promising for the hot components of the high thrust-to-weight ratio aeroengines because of their excellent high-temperature resistance and lightweight. Submillimeter cooling holes are necessary cooling structures for the extremely high working temperature of a CMCs hot component. However, CMCs are hard, brittle, and poorly conductive. Current machining is trapped in severe tool wear, poor hole quality, and low efficiency in machining such small size holes. This paper proposes high-frequency ultrasonic vibration-assisted drilling (UAD) to machine submillimeter holes of CMCs. It reveals that increasing vibration frequency during machining can enlarge the cutting edge's effective rake angle and reduce drilling forces. Correspondingly, the tool life and hole quality are improved. The machinability of high-frequency UAD is rationalized by both theoretical analysis and experiments. Results show that compared with low-frequency UAD and Conventional drilling (CD), the drilling force in high-frequency UAD is reduced by 47 % and 81 %, the tool life is more than three times, and the hole quality is improved by 12 % and 35 %, respectively. Therefore, the study paved the way for the machining of submillimeter cooling holes in CMCs, which is important to the industrial application of CMCs.

Understanding the mechanism of ultrasonic vibration-assisted drilling (UVAD) for micro-hole formation on silicon wafers using numerical and analytical techniques

Understanding the mechanism of ultrasonic vibration-assisted drilling (UVAD) for micro-hole formation on silicon wafers using numerical and analytical techniques

Introducing transversal vibration in twist drilling: Material removal mechanisms and surface integrity

In twist drilling, severe extrusion is unavoidable at the chisel edge zone and results in high thrust force and poor surface integrity. Traditional axial vibration-assisted twist drilling only modifies the material removed from the continuous extrusion to the interrupted extrusion for the chisel edge centre, and must satisfy the chip-breaking conditions to ensure that the cutting edge is periodically separated from the workpiece. Hence, transversal vibration, has been introduced in twist drilling to overcome the severe extrusion behaviour of the chisel edges of the twist drills, referred to as ultrasonic transversal vibration-assisted drilling (UTVD). Theoretical models revealed that the material removal behaviour of the chisel edge centre changed from extrusion in CD to cutting in UTVD. Experiments were performed on UTVD of Ti-6Al-4V to confirm the feasibility with this novel method. The results indicated that transverse vibration significantly affected the thrust force and torque, and the maximum decline was 29.4% and 31.5%, respectively, compared with CD. Generated chips verified the material removal behaviour of the chisel edge centre zone changed from extrusion in CD to cutting in UTVD. Therefore, the hole quality and surface integrity were improved significantly by UTVD. Deeper plastic deformation (∼2.5 times), higher surface microhardness and compressive residual stress were realised using UTVD. This study enhanced the understanding of material removal and formation mechanisms of the surface and subsurface in UTVD, thereby providing a novel method and theoretical basis for the high-performance twist drilling of difficult-to-cut alloys.

Finite element simulation of the mechanical loads during low frequency vibration-assisted drilling utilizing the CEL-method

Poor chip evacuation during drilling leads to increased heat generation in the contact zone and a decreased in borehole quality. This disadvantage can be overcome by low frequency vibration assisted drilling (LFVAD), which produces small, uniform shaped chips that allow better chip evacuation. The study presents the results of simulations of chip formation in conventional drilling (CD) and LFVAD based on the Coupled Eulerian-Lagrangian (CEL) method. The method does not require time consuming remeshing despite the high strains and strain rates that occur. In this work, a mesh refinement analysis in different spatial directions is performed in order to reduce the computational effort and preserve the accuracy of the numerical results.. A comparison with experimental data is performed for validation.

Enhancing engagement behavior in small-diameter deep drilling through ultrasonic vibration-assisted drilling and quantitative evaluation of hole dimensions

Enhancing engagement behavior in small-diameter deep drilling through ultrasonic vibration-assisted drilling and quantitative evaluation of hole dimensions

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.

Mechanical drilling force model for longitudinal ultrasonic vibration-assisted drilling of unidirectional CFRP

Mechanical drilling force model for longitudinal ultrasonic vibration-assisted drilling of unidirectional CFRP

Experimental Research of High-Quality Drilling Based on Ultrasonic Vibration-Assisted Machining.

Micro-hole is widely used in various fields, and common machining methods of micro-hole in factories are drilling and electrical discharge machining (EDM), but because of low machining efficiency, these methods cannot meet requirements. Therefore, it is urgent to investigate a high efficient micro-hole machining technology to meet the demands of micro-hole machining in factory. Over past few decades, ultrasonic machining technology has developed rapidly and achieved good results in solving many critical machining problems in field of difficult-to-cut materials. Therefore, this paper builds an ultrasonic vibration-assisted drilling (UAD) experiments platform to combine micro-fine small hole drilling with ultrasonic machining technology for micro-hole multi-factor experimental research. Results show that UAD machining of micro-hole below diameter 0.5 mm is comparable to conventional drilling machining because of its high-frequency pulse intermittent cutting process, stable change in machining diameter, good stability of parameters such as shape tolerance roundness and cylindricity, small cutting force during cutting, small tool wear, and small surface roughness of inner wall of micro-hole. Compared with EDM, UAD has high efficiency and good stability of parameters such as diameter and roundness of shape tolerance. Comprehensive analysis of UAD can be used as an alternative technology solution for machining small holes in non-special requirements of metal materials in factory and has technical feasibility of stable batch production.

Towards understanding the cutting temperature in ultrasonic vibration-assisted drilling based on the dynamic contact characteristics between the cutting edge and workpiece

Compared with conventional drilling (CD), ultrasonic vibration-assisted drilling(UVAD) is experimentally proven a promising method to reduce the cutting temperature. But sometimes cutting temperature also becomes higher in UVAD than in CD. To further make clear the cutting temperature mechanisms in UVAD, this study aims to study the effect of tool’s ultrasonic vibration on the cutting heat generation and heat dissipation at a relatively micro level. Firstly, drilling experiments are designed to explore the variations of cutting heat under different ultrasonic vibrations. Then, to analyze the influence of ultrasonic vibration on the cutting heat theoretically, a kinematic model is developed to describe the dynamic contact between the cutting edge and workpiece in UVAD. Besides, a cutting heat analysis model based on the contact characteristics in UVAD is proposed to study and compare the variations of cutting heat generation. The effect of ultrasonic vibration on the cutting heat generation, heat dispassion, and the resultant cutting temperature under different machining in UVAD conditions are discussed. It is indicated from the theoretical analysis that more cutting heat tends to be produced due to the significantly increased sliding velocity on the cutting edge-workpiece interface when the ultrasonic vibration is applied. The analysis agrees with the experimental results that the cutting temperature in dry UVAD is higher than in dry CD. But on the other hand, ultrasonic vibration can also improve the lubrication and cooling effect under appropriate machining conditions, which is beneficial to the reduction in cutting temperature. The investigation shows the multifaceted influences of ultrasonic vibration on the cutting temperature in the drilling process in detail, which provides a reference for UVAD parameter optimization.

Investigation of force modeling in ultrasonic vibration-assisted drilling SiCf/SiC ceramic matrix composites

Due to their exceptional high-temperature and rust resilience, SiCf/SiC ceramic matrix composites have been regarded as potential high-temperature components. For application, to overcome issues resulting from the high hardness and brittleness, the ultrasonic vibration-assisted machining technique is primarily adopted in the machining of SiCf/SiC ceramic matrix composites. It is essential to develop a force model for a better understanding of the material removal and cutting processes by applying ultrasonic vibration. As a result, studies on force modeling during ultrasonic vibration-assisted drilling of SiCf/SiC ceramic matrix composites have been conducted in this study, taking into account the trajectory of the drilling tool, the tool-workpiece contact state, and the material removal mode. Based on the coefficient calibration experiment and least square method, the irregular coefficient of abrasive grains, the crack growth parameters of materials, and the mechanical parameters that are difficult to be measured were determined. After that, the drilling parameters and vibration parameters were merged to build the analytical force model, and the parameter influence rules on the force was also studied. The suggested drilling force model concurred well with tests under the highest relative error of 17.34 %, according to the findings of the confirmation experiments.

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.

A novel model of vibration plowing effect for longitudinal ultrasonic vibration-assisted drilling

A novel model of the vibration plowing effect (VPE) is proposed for the first time to reveal hitherto not well-understood ultrasonic cutting mechanics and provide a theoretical basis for controlling the tool wear and machining quality of longitudinal ultrasonic vibration-assisted drilling (LUAD). The new model includes a condition model to judge the occurrence of the VPE on the whole flank of the drill and a volume model to calculate the vibration plowing force caused by the VPE of LUAD. For one thing, a condition model is proposed to distinguish the plowing effect of conventional machining and the VPE of LUAD by comprehensively analyzing the relationship between the clearance angle of the main cutting edge and the drill's path. For another, an analytical model of the vibration plowing volume (VPV) of LUAD is derived by integrating the plowing volume of the main cutting-edge element to improve the tool wear and machining quality. Finally, a series of comparative experiments between conventional drilling (CD) and LUAD is carried out. The validity of the proposed VPE's condition model and the VPV's analytical model is verified by the chip's micromorphology and the specific plowing force of the workpiece, respectively. The experimental results show that the fine and regular textures caused by the VPE can be observed on the chip surface and side micromorphology of LUAD. However, the coarse and irregular textures are displayed in CD, which shows that the proposed conditional model is adequate. Moreover, it is calculated by the deduced VPV's analytical model that when the ultrasonic amplitude is 3.8 and 8.3 μm, the average value of the specific plowing force of Al 6061-T6 determined in this paper is 1.399 × 105 N/mm3 and 1.274 × 105 N/mm3, respectively. These results agree with the value reported in other literature, that is 1.31 × 105 N/mm3, which proves the validity of the proposed model of the VPV. The validated analysis model is then used to conduct predictive analysis on the VPE and vibration plowing force of LUAD under a series of process parameters. The above research results clarify the mechanism of vibration plowing under ultrasonic action and provide a theoretical basis for controlling the tool wear and machining quality of LUAD.

Minimum Quantity Lubrication (MQL) multiphase dynamics of a vibration-assisted drilling process

Metalworking fluid (MWF) consumption in machining processes can be minimised using minimum quantity lubrication (MQL). In the vibration-assisted drilling process, the MWF is transported as aerosol (dispersed droplets in gas) to the cutting zone through microchannels inside the drilling tool. Numerical simulations have been applied to elucidate the multiphase flow dynamics of the MWF inside a helical microchannel of a twist drilling tool. Numerical results indicate a transition from the inserted MQL aerosol flow and a wall film already after the first helical bend of the microchannel. The wall film contains > 90 % of the lubricant and is strongly localised on only 10 % of the microchannel circumference at the tool tip. This MQL-flow behaviour has to be considered in future investigations of the processes at the borehole ground, where even more complex phenomena occur.

Experimental research on new hole-making method assisted with asynchronous mixed frequency vibration in TiBw/TC4 composites

With the gradual promotion and the application of difficult-to-machine materials such as titanium matrix composites in the aerospace field, high-quality hole-making technology has become a major demand in aviation manufacturing. In order to improve the hole-making quality of TiBw/TC4 composites, asynchronous mixed frequency vibration-assisted hole-making (AMFVAHM) method is proposed. The process consists of two steps: ultrasonic vibration-assisted drilling (UVAD) base hole and low-frequency torsional vibration-assisted helical milling (LFTVAHM) target hole. Based on this process, the cutting trajectory modeling is established, and the hole-making experiment on TiBw/TC4 composites is conducted. The experimental data show that during the hole expansion stage, the maximum XY-plane average milling force decreases by 30.96% and the maximum axial average milling force decreases by 24.49% compared with conventional helical milling (HM) when the torsional vibration frequency and the milling frequency are the same in LFTVAHM. The hole-making experiment shows that AMFVAHM can reduce the chip size, tool wear, and some other defects such as entrance/exit burrs, scratches, and fractures of the hole wall. Comparing with HM and UVAD, the verticality of hole wall increases by 71.43% and 86.21%, the inlet damage decreases by 27.98% and 31.60%, the outlet damage decreases by 2.80% and 14.47%, the hole wall roughness (Ra) decreases by 36.29% and 63.43%, and the maximum white layer thickness decreases by 19.99% and 67.66%. Meanwhile, AMFVAHM process not only reduces the cutting force and cutting temperature but also improves the hole-making quality due to the fretting friction effect of LFTVAHM in secondary hole expansion, which meets the need for high-quality hole-making of difficult-to-machine materials in practical engineering applications.

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

Defect suppression mechanism of ultrasonic vibration-assisted drilling carbon fiber/bismaleimide composite

Ultrasonic vibration-assisted drilling (UVAD) has recently been successfully applied in the drilling of carbon fiber reinforced polymer/plastic (CFRP) due to its high reliability. Multiple defects have been observed in the CFRP drilling process which negatively affects the quality of the hole. The carbon fiber/bismaleimide (BMI) composites is an advanced kind of CFRPs with greater strength and heat resistance, having been rapidly applied in lightweight and high temperature resistant structures in the aerospace field. To suppress the defect during the drilling of carbon fiber/BMI composites, it is necessary to comprehensively understand the defect formation and suppression mechanism at different positions. In this study, the defects formation in both conventional drilling (CD) and UVAD were observed and analyzed. The variation trend in the defect factor and thrust force with the spindle speed and feed rate were acquired. The results revealed that the UVAD could significantly enhance the hole’s quality with no delamination and burr. Meanwhile, the defect suppression mechanism and thrust force in UVAD were analyzed and verified, where the method of rod chip removal affected the exit defect formation. In summary, UVAD can be considered a promising and competitive technique for drilling carbon fiber/BMI composites.