Ultrasonic Milling Research Articles

Investigating the Surface Quality of Aramid Honeycomb Materials Through Longitudinal–Torsional Ultrasonic Milling

During the milling process of aramid honeycomb, residual stresses arise, which will affect the surface quality of the honeycomb. Studies have shown that reasonable processing techniques can reduce residual stresses, indicating a close relationship between residual processing stresses and the processing parameters, such as technique. By investigating the changes in residual stresses after the processing of aramid honeycomb materials, the influence of processing techniques on these changes is analyzed. Leveraging the correlation between residual stresses and surface quality, this study proposes the use of residual stress as an indicator for evaluating processing techniques. The longitudinal–torsional ultrasonic vibration milling method is applied to the processing of aramid honeycombs. A single-factor experimental approach is adopted, utilizing ABAQUS 2020 software to mimic the longitudinal–torsional ultrasonic milling process. This study explores the influence patterns of various process parameters on the residual stresses generated during the milling of honeycombs. The simulation results indicate that within the selected range, the residual stress decreases as the tool rotation speed increases, while it increases with the increase in feed rate. The influence of milling depth on residual stress can be negligible. Furthermore, experiments were conducted based on the proposed correlation between residual stress and surface quality. The experimental results show good agreement with the simulation results, indicating that under reasonable process parameters, the residual stress values decrease, thereby improving the milling surface quality of aramid honeycomb materials. Therefore, measuring residual stress can serve as an effective method for evaluating the processing technique.

Multidimensional ultrasonic vibration machining modeling of SiCp/Al cutting forces with different volume fractions: Experiments and numerical simulations

The cutting properties of the particles of aluminum-based silicon carbide (SiCp/Al) and the base material are so disparate that it is challenging to ensure the surface quality of machining. The cutting force significantly influences the quality of the machined surface. Therefore, real-time cutting force prediction is paramount for ensuring the workpiece's desired surface quality. This paper presents a 3D ultrasonic milling force model, established from four aspects: cutting formation force, extrusion friction force, SiC particle crushing force, and ultrasonic impact force. The model is based on the ultrasonic action of the cutting process and the unique removal characteristics of the material. A 3D ultrasonic milling system was constructed to experimentally verify the milling force model. The effects of each parameter on the milling force were analyzed through orthogonal experiments, which resulted in the effects of depth of cut, rotational speed, volume fraction, ultrasonic amplitude, and feed rate. The ultrasonic amplitude, feed rate, and other factors were found to influence the milling force to varying degrees. The milling force was observed to be 42.47 %, 22.37 %, 10.85 %, 12.67 %, and 11.64 % affected by the factors mentioned above, respectively. The single-factor experiment was conducted to analyze the cutting force at different machining parameters. The experimental results and the MATLAB numerical simulation results exhibited a similar trend of change. The maximum absolute error between the two was 12.71 %, with an average absolute error of 3.735 %.

Investigation on fiber fracture mechanism and milling force model of CF/PEEK by ultrasonic milling

Ultrasonic milling can achieve high machining efficiency and surface quality on CF/PEEK composites due to its advantages of low cutting force, high material removal rate, improved surface quality, long tool life, and eco-friendly machining technology. This method is widely used in many scenarios such as aerospace, navigation, and new types of weapons. However, the changes in fiber fracture mode and the effects of fiber friction caused by high-frequency ultrasonic vibration cannot be ignored. To study this, first, a fiber fracture model is constructed based on experiments to describe the fiber fracture mechanism. Then, the machined surface and subsurface are analyzed to establish the relationship between feed speed and fiber deformation depth. Increasing the feed can increase the fiber deformation depth by 3.17 times. Finally, an analysis of the single fiber fracture mechanics is carried out and a force model is created that considers the friction between the tool tip and the fiber during ultrasonic milling. The predictive force model, integrated with the fiber distribution, was validated against experimental results, showing a maximum force error of 5.722 %. This model effectively explains the fracture mechanism of CF/PEEK fibers during ultrasonic milling at the microscopic level.

Cutting Performance of a Longitudinal and Torsional Ultrasonic Vibration Tool in Milling of Inconel 718

Inconel 718 has excellent thermal and chemical properties and is widely used in the manufacture of aerospace parts; however, there are some problems in the machining of Inconel 718, such as a large milling force, serious tool wear, and poor surface quality. In this research, a type of longitudinal–torsional ultrasonic milling (LTUM) tool is designed based on theoretical computations and FEM simulation analysis. To verify the design rationality of the developed LTUM tool, milling experiments are performed. It is verified that the LTUM tool can realize an elliptical vibration path at the tool tip. The resonance frequency of the tool is 21.32 kHz, the longitudinal amplitude is 6.8 µm, and the torsional amplitude is 1.4 µm. In the milling of Inconel 718, the experimental data of LTUM are compared with those of conventional milling (CM). The comparative experiments show that the LTUM tool can effectively lessen the milling force and tool wear in the milling of Inconel 718, improve the surface quality, inhibit the generation of burrs, and improve the chip breaking ability. The application potential of the LTUM tool in high-performance milling of Inconel 718 parts is proven.

Micro/nano-surface modification of titanium implant enhancing wear resistance and biocompatibility

Micro/nano structured surface has been shown to effectively enhance the biological performance of titanium alloy implants, exhibiting faster postoperative recovery. However, a common drawback of bio-functionalized surfaces featuring structured characteristics is their susceptibility to wear. This study proposed a novel micro/nano surface modification method using ultrasonic milling and anodization to enhance both biocompatibility and wear resistance of the implant surface. First, hierarchical structures are fabricated on the titanium surface by utilizing ultrasonic milling and anodization to generate micro-scale and nano-scale structures, respectively. Linear reciprocating tests, contact angle tests, and surface morphology observation were conducted to investigate the surface properties. Then, cell proliferative and adhesive abilities were tested on different modified surfaces by using mouse osteoblasts. Finally, nonosilver coatings were created on the structured surface by vapor deposition and the antibacterial performance was tested using staphylococcus aureus. The experiment results reveal a significant improvement in wear resistance, biological properties, and antibacterial capabilities of the processed surface, demonstrating the great application potential of the proposed method for implant surface modification.

Surface fractures in pre-crystallized and crystallized zirconia-containing lithium silicate glass-ceramics generated in ultrasonic vibration-assisted machining

Machining-induced surface fractures in ceramic restorations is a long-standing problem in dentistry, affecting the restorations’ functionality and reliability. This study approached a novel ultrasonic vibration-assisted machining technique to zirconia-containing lithium silicate glass-ceramics (ZLS) and characterized its induced surface fracture topographies and morphologies to understand the microstructure-property-processing relations. The materials were processed using a digitally controlled ultrasonic milling machine at a harmonic vibration frequency with different amplitudes. Machining-induced surface fracture topographies were measured with a 3D white light optical profilometer using the arithmetic mean, peak and valley, and maximum heights, as well as the kurtosis and skewness height distributions, and the texture aspect ratios. Fracture morphologies were analysed using scanning electron microscopy (SEM). The surface fracture topographies were significantly dependent on the material microstructure, the mechanical properties, and the ultrasonic machining vibration amplitudes. Larger scale fractures with higher arithmetic mean, peak and valley heights, and kurtosis and skewness height distributions were induced in higher brittleness indexed pre-crystallized ZLS than lower indexed crystallized ZLS by conventional machining. Conchoidal fractures occurred in pre-crystallized ZLS while microcracks were found in crystallized state although brittle fractures mixed with localized ductile flow deformations dominated all machined ZLS surfaces. Ultrasonic machining at an ideal vibration amplitude resulted in more ductile removal, reducing fractured-induced peaks and valleys for both materials than conventional processing. This research demonstrates the microstructure-property-processing interdependence for ZLS materials and the novel machining technique to be superior to current processing, reducing fractures in the materials and potentially advancing dental CAD/CAM techniques.

Analysis and modeling of cutting force considering the tool runout effect in longitudinal-torsional ultrasonic vibration-assisted 5 axis ball end milling

The longitudinal-torsional ultrasonic vibration-assisted milling (LTUVAM) can improve the machining quality compared with conventional milling (CM), and the machining quality is closely related to cutting force which is affected by the tool runout effect. In this study, a mechanistic force model for longitudinal-torsional ultrasonic vibration-assisted 5 axis ball end milling considering the tool runout effect is proposed. First, the cutting edge motion model considering the effects of tool runout and ultrasonic vibration is established. Then, based on the analysis of the cutting edge motion relative to the workpiece, the uncut chip thickness (UCT) is computed by means of the geometrical calculation method, and the engaged cutting edge elements are determined according to the Z-map method, the ultrasonic milling force model is established after determining the cutting force coefficients and tool runout parameters through calibration tests. Moreover, the impact of different parameters on dynamic separating characteristics of LTUVAM is studied by the tool-workpiece contact rate. Finally, the verification tests are carried out, and the experimental results show the effectiveness of the ultrasonic milling force model.

Investigation on fiber fracture mechanisms in rotary ultrasonic milling of carbon fiber composites

Investigation on fiber fracture mechanisms in rotary ultrasonic milling of carbon fiber composites

Simulation and experimental study of ultrasonic vibration-assisted milling of GH4169 high-temperature alloy

GH4169 high-temperature alloy is widely used in aerospace and other fields because of its excellent fatigue, radiation, oxidation, and corrosion resistance. However, milling forces, high temperatures, and machining hardening can occur during milling processing. To explore the machining characteristics of GH4169 high-temperature alloy, an ultrasonic vibration-assisted milling model was established to study the effect of ultrasonic milling parameters on the milling process. The simulation results show that: the increase of ultrasonic amplitude can effectively reduce the machining stress, improve the chip-breaking effect and reduce the milling force; with the rise of milling speed, the separation characteristic is weakened, which is not conducive to chip breaking; the increase of radial cutting width will increase the machining stress and improve the milling force. Finally, by comparing the actual machining and simulation results, the error is within 10%, which verifies the feasibility of the simulation study and provides guidance for ultrasonic milling of GH4169 high-temperature alloy.

Effect of crack propagation on surface formation mechanism and surface morphology evaluation of longitudinal–torsional composite ultrasonic mill grinding of Si3N4

Crack propagation is critical in determining the surface forming process and machined surface quality of hard brittle materials. However, there is still a lack of research on this subject. In this work, the effect of crack propagation on the surface formation mechanism and surface morphology of silicon nitride ceramics was investigated via longitudinal–torsional composite ultrasonic-assisted mill grinding, and a reconstruction model of the machined surface morphology considering crack propagation was proposed. This model was quantitatively characterized and evaluated by the average roughness Sa and the kurtosis Sku. It was found that the simulation results considering crack expansion are in good agreement with the experimental results. The average relative errors in the average roughness and kurtosis were found to be 7.95% and 9.46%, respectively. A primary effect analysis was performed to understand the influence of the process parameters on the machined surface morphology. It was found that ultrasonic vibrations lead to changes in the shear angle and shear velocity of abrasive grains, thereby changing the machined surface morphology. The results presented here provide a practical method for predicting and controlling the machined surface quality during precision machining of ceramic materials.

Controllable fabrication of microstructures on the metallic surface using oblique rotary ultrasonic milling

Rotary ultrasonic milling emerges as a new and efficient fabrication method for surface microstructures. However, a phenomenon of secondary back-cutting interference exists in conventional rotary ultrasonic milling. It destroys the fabricated microstructure and leads to poor controllability of the surface geometries. In this study, oblique rotary ultrasonic milling (ORUM) is proposed to improve the process controllability by eliminating secondary back-cut interference. In the ORUM, the tool rotation axis is slightly inclined with an oblique angle of around 0.15°. In this way, surface texturing can be established by face milling without secondary back-cutting interference. A kinematic model was developed to predict the surface geometries of fabricated microstructures. Finite element analysis was performed to explore the material removal behavior for different vibration trajectories. Moreover, surface texturing tests were conducted on aluminum and titanium alloy to verify the efficacy of the proposed texturing process. The experimental results showed that the ORUM could texture microstructures on the metallic surface with much better geometric regularity than conventional ultrasonic milling. The model-predicted surface morphology of microstructure agrees well with the experimental results, verifying the high process controllability of ORUM. The effects of process parameters, including the depth-of-cut, spindle speed, and feedrate were presented to further demonstrate the process flexibility of ORUM in terms of the geometry adjustment of microstructures. Finally, fish-scale microstructures were fabricated on freeform surfaces like aircraft wings and implant hip joints, which implies the potential of ORUM for industrial applications.

Fabrication of hierarchical micro/nanostructures on titanium alloy by combining rotary ultrasonic milling and anodizing

Hierarchical micro/nanostructures provide an efficient method for the surface wettability modulation of titanium alloy in biomedical applications. In this study, a new approach for the controllable fabrication of hierarchical micro/nanostructures is proposed by combining rotary ultrasonic milling and anodizing. Microstructures with a diameter of 90–120 μm were fabricated by rotary ultrasonic milling, then TiO2 nanotubes with a diameter of 60–80 nm were produced on the microstructured surface by anodizing. Wettability tests demonstrate that the titanium surface with hierarchical micro/nanostructures has the lowest contact angle than that with single-level microstructures or nanostructures, verifying the efficacy of the proposed approach.

(Invited) Preparation and Characterization of WS2–TiO2–Au Nanohybrid System Using Hydrothermal Synthesis for Photocatalysis Under Visible Light

We have developed a new visible light responsive photocatalytic material by combining tungsten disulfide (WS2), a nanosheet semiconductor material that has attracted much attention in recent years, gold nanoparticles that strongly absorb visible light, and titanium dioxide (TiO2), a highly active photocatalyst1. Ultrasonic milling and hydrothermal synthesis methods were utilized to successfully synthesize the ternary nanohybrid materials and improve their visible light photocatalytic performance. The mechanism was elucidated based on the detailed characterization of structural properties, spectroscopic properties, photocatalytic reaction properties, and electron transfer reaction dynamics using femtosecond transient absorption spectroscopy.Reference Kejun Wu, Pankaj Koinkar, and Akihiro Furube, International Journal of Modern Physics B, 35, 2140046 (2021)

Investigation of deviation and surface topography in ultrasonic vibration-assisted milling

Thin-walled structures have many applications in the aerospace industry. An important feature of them is their high strength to weight. When milling the thin-walled part, the thickness decreases step by step by cutting, which causes the process to be complex and dependent on process parameters. In the present study, thin-walled aluminum structures are investigated using conventional and ultrasonic milling processes, and distortion, surface roughness, surface texture, and average thin-wall forces are also investigated. Therefore, 18 tests are performed on parts made of 7075T6 aluminum alloy using various feeds, spindle speeds, and machining modes. The results showed that the machining type and spindle speed had 47% and 33% effect on distortion, respectively. In addition, the results showed that by applying vibrations to the milling, the amount of distortion can be reduced by up to 30% and effectively optimized. This technique is suitable for manufacturing industries that require high dimensional accuracy. Also, the surface texture and burr formation are investigated. In particular, the surface roughness in ultrasonic milling decreased compared to conventional milling.

Machining Strategy and Experimental Study of Ultrasonic-Assisted Bidirectional Progressive Spiral Milling of Carbon Fiber Holes

Carbon fiber-reinforced composites (CFRP) are widely used in aerospace structural holes due to their superior mechanical properties. However, fiber pulling, delamination, burr and other defects often occur in the parts, which seriously affect the accuracy and service life of the products. The traditional cylindrical milling cutter is easy to lead to the exit delamination defects due to the large axial force at the bottom edge, concentrated wear at the periphery edge, and weak rigid constraint at the exit machining position. Therefore, this paper proposed a new hole machining strategy, analyzed the kinematic law of the tapered progressive spiral milling hole, studied the cutting mechanism of the four stages of the tapered spiral bidirectional milling hole, explored the material removal force state of the ultrasonic augment-assisted progressive milling hole, and established the prediction of the layered axial force of the ultrasonic progressive milling hole. Finally, combined with the material removal mechanism of ultrasonic vibration, the self-designed bidirectional progressive spiral milling cutter was used to verify the mechanism of material removal by progressive milling, in which the axial force could be effectively reduced. After 60 and 90 holes were processed, the axial force was about 18.5 and 23.3 N, respectively, the critical force of delamination could be improved, and the hole quality could be guaranteed without obvious burr and delamination phenomena.

Research on stability of robotic longitudinal-torsional ultrasonic milling with variable cutting force coefficient

With their successful applications in handling, spraying, arc welding and other processing fields, industrial robots are gradually replacing traditional CNC machine tools to complete machining tasks due to the wider working envelope and the higher flexibility. Aiming at the chatter problem, a robotic longitudinal-torsional ultrasonic milling method with variable force coefficient is proposed in this paper. Taking carbon fiber-reinforced plastics (CFRP) as the processing object, the influence of the fiber layup angle on the milling force is analyzed first; then, the robot milling force parameters are determined, and the robot milling kinematics model is established. Furthermore, the ultrasonic function angle is defined, and the cutting layer thickness model, the dynamic milling force model, and the dynamic differential equation under ultrasonic vibration are established to analyze the stability of robotic longitudinal-torsional ultrasonic milling of CFRP. Finally, the full discrete method is used to obtain stability lobe diagrams.

Development of a high-precision piezoelectric ultrasonic milling tool using longitudinal-bending hybrid transducer

A novel piezoelectric ultrasonic milling tool based on a longitudinal-bending hybrid piezoelectric transducer (LBHT) is proposed. The major novelty of the proposed tool is that through longitudinal vibration and bending vibration of the tool the impact ironing effect (IIE) and intermittent cutting effect (ICE) simultaneously, thus achieving high-precision milling. Above all, the structure and operation principle of the longitudinal-bending hybrid vibration-assisted milling (LBHVAM) system is amply depicted. Then, simulations and analyses are carried out to design and analyze the structure size and critical ICE conditions. Ultimately, a prototype is manufactured and the vibration tests and machining experiments have been carried out. The results indicate that the cutting force of LBHVAM of titanium alloy is 39.3% and 27.2% lower than the conventional milling (CM) and longitudinal vibration-assisted milling (LVAM), and the propensity of burr formation is significantly reduced. Furthermore, the surface roughness under LBHVAM reaches Sa 0.102 μm, which is 85.2% and 54.5% lower than CM and LVAM. Above results demonstrate that the proposed LBHVAM tool not only has unique advantages in reducing cutting force and burr formation but also possesses great potential in improving machining accuracy, which is highly desired in ultra-precision machining of difficult to cut materials.

Study on formation mechanism of edge defects of high-volume fraction SiCp/Al composites by longitudinal-torsional ultrasonic vibration-assisted milling

SiCp/Al composites are a kind of particle-reinforced composite material, which has been widely used in various fields due to its excellent performance. However, during the machining, the damage and failure of the SiC particles, the aluminum matrix, and the interface phase will cause many surface and edge defects. These defects will seriously affect the application of SiCp/Al composites. In this paper, a finite element model of randomly distributed multi-cell SiCp/Al composites with longitudinal-torsional ultrasonic vibration-assisted milling was established to analyze the formation mechanism of edge defects of the material. The simulation results showed that the main reason for the formation of edge defects was that the interface, SiC particles, and the Al matrix will produce cracks during machining, and these cracks will propagate and cause particle breakage, matrix tearing, and edge gaps. According to different machined parameters, the ultrasonic vibration-assisted milling experiment was carried out. The test results showed that the actual processed workpiece does have defects such as edge gaps. The depth of cut and the feed per tooth had a serious influence on the edge defect value, while the cutting speed had a small effect. Moreover, under the condition of applying appropriate ultrasonic amplitude, the phenomenon of edge defects and the surface quality were significantly improved. Therefore, the application of ultrasonic vibration-assisted milling can improve the surface and edge quality of SiCp/Al composites.

Modeling of cutting forces in 1-D and 2-D ultrasonic vibration-assisted milling of Ti-6Al-4V

To meet the modern demands for lightweight construction and energy efficiency, hard-to-machine materials such as ceramics, superalloys, and fiber-reinforced plastics are being used progressively. These materials can only be machined with great effort using conventional machining processes due to the high cutting forces, poor surface qualities, and the associated tool wear. Vibration-assisted machining has already proven to be an adequate solution in order to achieve extended tool lives, better surface qualities, and reduced cutting forces. This paper presents an analytical force model for longitudinal-torsional vibration-assisted milling (LT-VAM), which can predict cutting forces under intermittent and non-intermittent cutting conditions. Under intermittent cutting conditions, the relative contact ratio between the rake face and the sliding chip is utilized for modelling the shearing forces. Ploughing forces and shearing forces under non-intermittent cutting conditions are calculated by using an extended macroscopic friction reduction model, which can predict the reduced frictional forces under parallel and perpendicular vibration superimposition. The force model was implemented in MATLAB and can predict cutting forces without using any experimental vibration-assisted milling (VAM) data input.

On the material removal mechanism in rotary ultrasonic milling of ultralow-density silica aerogel composites

Silica aerogel composite with ultralow density is a kind of highly porous solid with excellent property of thermal conductivity. It is widely used for thermal insulation in aerospace, national defense and military industries. However, silica aerogel composites are difficult to process, due to the poor mechanical properties, low strength and high brittleness. Therefore, it is necessary to investigate the processing characteristics and material removal mechanism of silica aerogel composites. In this article, a cutting model of silica aerogel composites is established firstly and the fracture mechanism of fiber was analyzed. Then the ultrasonic milling and conventional milling experiments were performed respectively to obtain the features of machined surface. Macro morphology and surface roughness of machined surfaces in different process conditions are compared to investigate the influence of different process conditions on the processing quality. Scanning electron microscope (SEM) was used to obtain the micro morphology of processed surfaces. By comparing and analyzing the micro morphology of processed surfaces, the influence of process conditions on removal mechanism was investigated. The theoretical cutting force and experiment cutting force is compared to verify the cutting model. The results show that the burrs and pits decrease with the ultrasonic vibration amplitude, and increase with the tool diameter. Processing quality of up-milling is better than down-milling. It is indicated that shearing and pulling off are the main removal mechanism of silica aerogel composites. When the silica aerogel composites are processed by rotary ultrasonic milling and up milling, the fibers will be mainly removed by shearing mechanism and the proportion of fibers removed by shearing facture mechanism will be improved with the increase of ultrasonic amplitude.