Micro-ultrasonic Machining Research Articles

A thermo-mechanical coupling load model for high-frequency piezoelectric ultrasonic transducer

The ultrasonic micromachining systems significantly improve machining efficiency and quality, which is increasingly being applied in the manufacturing of microstructures and micro parts. However, the mechanical and thermal loads of the high-frequency piezoelectric ultrasonic transducer (HPUT) of ultrasonic micromachining systems have serious interference with the precise control of resonance frequency tracking, which further causes uncontrollable processing quality and precision. To improve the controllability of resonance frequency tracking, a thermo-mechanical coupling load model for HPUTs is proposed to establish the relationship between the resonance frequency and thermo-mechanical coupling load by introducing the force load constants and thermal load constants into the 6-terminal network electromechanical equivalent circuit. The experimental results show that the proposed thermo-mechanical coupling load model can accurately predict the trend of the resonance frequency when the thermo-mechanical coupling load is under the axial force range of 0–10 N and temperature range of 35-60℃.

Fabrication of through alumina vias (TAV) by ultrasonic micromachining for advanced packaging applications

This article presents the fabrication of a high aspect ratio through alumina-vias (TAV) by combining ultrasonic micromachining (USM), electroless plating, and copper electrodeposition. Various horn designs, i.e., tapered, stepped, exponential, and hybrid horns, were analyzed to achieve a uniform longitudinal vibration in a 6 × 6 multi-tip tool assembly. The modal analysis determined the horn length, and harmonic analysis provided the stress distribution and vibrational amplitude. The tapered horn design was selected for its superior vibration amplification and reduced stresses. Finite element modeling predicted the geometric profiles of the microvias at various USM parameters. Experimental validation showed less than 5 % error in the depths of the microvias. Using the optimized USM parameters, a 6 × 6 array of blind and through-holes was created in a 3 mm thick alumina substrate with an average feed rate of 180 μm/min. The average tool wear was observed to be 0.5 mm when drilling through 3 mm thick alumina. Electroless deposition created a ∼100 nm seed layer on the alumina substrate and achieved good adhesion with via sidewalls. The through-holes were partially filled with a 60 μm thick copper layer by electrodeposition to create through-alumina vias (TAV) that can be used as 3D interconnects in the packaging of high-power electronics.

Analytical model for material removal rate in rotary tool micro-ultrasonic machining of hard and brittle materials

The rotary tool micro-ultrasonic machining (RT-MUSM) process is a newly developed variant of conventional micro-USM. It is preferred over conventional micro-USM due to its ability to remove material at a faster rate and with better accuracy than the machined microfeatures. Some experimental investigations have been conducted on the RT-MUSM process for the machining of hard and brittle materials. However, the theoretical model of the material removal rate (MRR) for the RT-MUSM process has not been discussed in the literature. Thus, the present research work reports on developing a predictive model of the MRR for the RT-MUSM process during glass machining. Pure brittle fracture mode was considered to be the material removal mechanism during the model's development. The developed model was verified through experiments. The estimated results were compared with the experimental results and found to be in good agreement with each other. Additionally, statistical analysis was carried out for the prediction accuracy of the developed model. The results revealed that the model is adequate, with a correlation coefficient of 0.9976 and a mean absolute percentage error of 2.45%. Hence, the developed model can be used to estimate the MRR for the RT-MUSM process of hard and brittle materials such as ceramics.

Material removal modes and processing mechanism in microultrasonic machining of ball ceramic tool

Microelectrochemical systems (MEMSs) have important applications in electronic information, aerospace, national defense and other fields. The microhemispherical concave die is the manufacturing foundation for the MEMS system. To clarify the forming mechanism of microhemispherical concave dies machined by microultrasonic machining with ceramic whole ball tools, a material removal model was presented. Furthermore, the kinetic energy model of a spherical abrasive under the action of microultrasonic and whole ball ceramic tools was also established. The model of the brittle-plastic transition removal mode is correlated with the kinetic energy of the abrasive model. The surface morphology of miniature molds exhibits significant variations attributed to the altered material removal mode, the removal mechanism was analyzed. The theoretical model is verified by experiments. Experiments were performed with lower and higher viscosity polishing fluids. The surface roughness of the plastic removal area in each group was 96.4 and 60.1 nm. Due to the high viscosity polishing fluid eliminating some of the cavitation phenomena, the overall surface quality is improved; hence, the surface roughness decreases by 37.6% under the same processing conditions. In the low-viscosity experimental group, the surface roughness was 113.61, 302.28 and 367.24 nm, respectively. The experimental verification confirmed that variations in surface morphology occur, even with the same removal mode applied at different locations on the microconcave die. The reasons for the surface roughness variation in different areas of the microconcave die are analyzed and reveal the influence of ultrasonic cavitation on the material removal mode in microultrasonic machining.

Surface topography characterization of USMM during machining of zirconia ceramic using silicon carbide abrasives: An experimental and simulation approach

Zirconia is a highly biodegradable ceramic material with excellent fracture resistance, in biomedical engineering, particularly dental implants. This research work has been focused on optimizing the quality of micro-hole generation in zirconia ceramic through ultrasonic micromachining (USMM). Three key process parameters such as abrasive slurry concentration, tool feed rate, and power rating are considered in this research work. The material removal rate, overcut, and taper angle are considered as responses. Response surface methodology has been employed for modeling during the USMM process, and a mathematical model has been developed to understand material removal mechanisms. Finite element analysis has been utilized to provide insights into the impacting process for industry requirements. A 3D model has been created to perform dynamic analysis under practical conditions. Multi-objective optimization has been applied to achieve optimum material removal rate (MRR), overcut, and taper angle. From multi-objective optimization, a slurry concentration of 49.59% g/l, tool feed rate of 1.16 mm/min, and power rating of 386.87 W has been found and in this parameter settings maximum MRR of 0.5333 mm3/min, minimum taper angle of 0.3428 degrees, and minimum overcut of 36.64 µm has been obtained during machining of ZrO2 ceramics.

Generation of array of square microcavity on quartz by ultrasonic micromachining process utilizing developed micro tool

Quartz possesses distinct characteristics such as exceptional hardness, high brittleness, non-conductivity, remarkable corrosion resistance, efficient transmission within specific wavelengths, strong electrical insulation properties, and the ability to withstand high temperatures and thermal shocks. These extraordinary attributes have led to its component in a wide range of applications, including the fabrication of microelectronic chips, biochips, biological channels, microfluidics, optical lenses, beam-splitting lenses, etc. Ultrasonic micromachining (USMM) is a highly promising technique within the realm of micromachining to create micro features on quartz surfaces. In the present research, array of square micro tools has been designed and developed by the wire-electrical discharge machining (EDM) process. By utilizing the developed array of square micro tools, microcavity arrays have been generated by the USMM process. The influences of process parameters on material removal rate (MRR), width deviation (WD), angular deviation, and taper of square microcavities have been investigated in the present research work. The higher MRR is obtained as 1.427 mm3/min at higher abrasive slurry concentration and lower WD of micro cavities is obtained as 37 µm and lower taper angle is 1.109° at 5% abrasive slurry concentration. The lower value of angular deviation is obtained as 0.836° at a lower power rating during the generation of an array of square microcavity on quartz by the USMM process. By employing array of micro tools, the accuracy of micro features can be improved, and also productivity can be increased.

Fabrication of microchannels through template-based electrophoretically assisted micro-ultrasonic machining

Fabrication of microchannels through template-based electrophoretically assisted micro-ultrasonic machining

Design of a Template-Based Electrophoretically Assisted Micro-Ultrasonic Machining Micro-Channel Machine Tool and Its Machining Experiment.

In order to achieve the high-precision and high-efficiency machining of micro-channels for hard and brittle materials, the authors innovatively proposed a new technology called template-based electrophoretically assisted micro-ultrasonic machining (TBEPAMUSM). This technology transfers the micro-channel shape punch-pin to the workpiece material through micro-ultrasonic machining to form a micro-channel. At the same time, it uses the electrophoretic properties of ultra-fine abrasive particles to ensure the existence of abrasive particles in the machining area by applying a DC electric field. According to the new technology machining principle, a machine tool of TBEPAMUSM was designed and developed. The machine tool hardware adopts a C-shaped structure, including a marble platform, an ultrasonic vibration system, a micro three-dimensional motion platform, a working fluid tank, and a pressure sensor. The machine tool intelligent control system is developed based on LabVIEW, including the initialization module, fast positioning module, constant force tool setting module, constant force control machining module, and real-time coordinate display module. Micro-channels with different structures are machined on single-crystal silicon and soda-lime glass using the designed machine tool and the developed control system. The results show that: when electrophoresis assistance is applied in machining, the edge chipping phenomenon of the micro-channel is significantly reduced, the surface roughness is reduced by about 20%, and the machining efficiency is increased by about 4%.

Processing Optimization of Shear Thickening Fluid Assisted Micro-Ultrasonic Machining Method for Hemispherical Mold Based on Integrated CatBoost-GA Model.

Micro-electro-mechanical systems (MEMS) hemispherical resonant gyroscopes are used in a wide range of applications in defense technology, electronics, aerospace, etc. The surface roughness of the silicon micro-hemisphere concave molds (CMs) inside the MEMS hemispherical resonant gyroscope is the main factor affecting the performance of the gyroscope. Therefore, a new method for reducing the surface roughness of the micro-CM needs to be developed. Micro-ultrasonic machining (MUM) has proven to be an excellent method for machining micro-CMs; shear thickening fluids (STFs) have also been used in the ultra-precision polishing field due to their perfect processing performance. Ultimately, an STF-MUM polishing method that combines STF with MUM is proposed to improve the surface roughness of the micro-CM. In order to achieve the excellent processing performance of the new technology, a Categorical Boosting (CatBoost)-genetic algorithm (GA) optimization model was developed to optimize the processing parameters. The results of optimizing the processing parameters via the CatBoost-GA model were verified by five groups of independent repeated experiments. The maximum absolute error of CatBoost-GA is 7.21%, the average absolute error is 4.69%, and the minimum surface roughness is reduced by 28.72% compared to the minimum value of the experimental results without optimization.

Predictive modeling of tool wear in rotary tool micro-ultrasonic machining

In the current research endeavor, the predictive model of tool wear in rotary tool micro-ultrasonic machining (RTMUSM) process using artificial intelligence has been reported for the first time. An adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) approaches are adopted for modeling of total volumetric wear (TVW) in RTMUSM process. The models were developed after conducting the exhaustive experimentation. Six RTMUSM input process parameters (i.e. abrasive size, rotation speed, depth of channel, slurry concentration, feed rate, and power rating) were selected as input data with TVW of tool as output data. The developed model has been validated through experimental results. Further, statistical analysis by calculating variance account for (VAF), coefficient of correlation ( R-value), mean absolute percentage error (MAPE), and root mean square error (RMSE) was carried out to estimate the potential of the models. The results obtained by statistical analysis proclaimed that the performance of ANFIS model ( R-value = 0.9966, MAPE = 1.26%, RMSE = 1.11%, and VAF = 99.94) was superior as compared to ANN model and it can be used to measure the TVW of tool in RTMUSM. Furthermore, genetic algorithm based optimization was performed and required wear compensation of tool is recommended.

Theoretical and experimental investigations on rotary ultrasonic surface micro-machining of brittle materials

Many brittle materials, such as single-crystal materials, amorphous materials, and ceramics, are widely used in many industries such as the energy industry, aerospace industry, and biomedical industry. In recent years, there is an increasing demand for high-precision micro-machining of these brittle materials to produce precision functional parts. Traditional ultra-precision micro-machining can lead to workpiece cracking, low machined surface quality, and reduced tool life. To reduce and further solve these problems, a new micro-machining process is needed. As one of the nontraditional machining processes, rotary ultrasonic machining is an effective method to reduce the issues generated by traditional machining processes of brittle materials. Therefore, rotary ultrasonic micro-machining (RUμM) is investigated to conduct the surface micro-machining of brittle materials. Due to the small diameter cutting tool (<500 μm) and high accuracy requirements, the impact of input parameters in the rotary ultrasonic surface micro-machining (RUSμM) process on tool deformation and cutting quality is extremely different from that in rotary ultrasonic surface machining (RUSM) with relatively large diameter cutting tool (∼10 mm). Up till now, there is still no investigation on the effects of ultrasonic vibration (UV) and input variables (such as tool rotation speed and depth of cut) on cutting force and machined surface quality in RUSμM of brittle materials. To fill this knowledge gap, rotary ultrasonic surface micro-machining of the silicon wafer (one of the most versatile brittle materials) was conducted in this study. The effects of ultrasonic vibration, tool rotation speed, and depth of cut on tool trajectory, material removal rate (MRR), cutting force, cutting surface quality, and residual stress were investigated. Results show that the ultrasonic vibration could reduce the cutting force, improve the cutting surface quality, and suppress the residual compressive stress, especially under conditions with high tool rotation speed.

Formation of high aspect ratio through-glass vias by the combination of Ultrasonic micromachining and copper electroplating

Fabrication of high aspect ratio (>5) multiple copper-filled through-holes in non-conductive materials like glass and single-crystal‑silicon is reported by using a faster (>8 μm/s) ultrasonic micromachining (USM). A customized stainless tool having multiple tips arranged in a 6 × 6 area-array manner was used with ~1 μm-size Silicon carbide (SiC) abrasive particles. Numerical simulations were performed to find a suitable horn to reduce the losses during the transmission of ultrasonic wave propagation. A tapered horn profile was chosen to transmit the vibrations uniformly from the ultrasonic head to the multiple tips. A novel technique was proposed to measure the vibration amplitude at different ultrasonic power ratings. >250 experiments were carried out to investigate the effect of ultrasonic power ratings and tool feed rate on the geometric characteristic of microholes. Average etch rates as high as 8 μm/s and 6 μm/s were obtained for glass and silicon, respectively. These average etch rates are higher than those obtained with plasma etching and electrochemical discharge machining. Through-holes were created in a 1.1 mm thick glass substrate in <3 min. The importance of post-USM cleaning by ultrasonic agitation was highlighted, which helped in removing the abrasive particles stuck inside the through-holes. Copper was deposited inside these through-holes using a bottom-up electroplating approach. These copper-filled through-holes can be used as 3-dimensional (3D) interconnects required in various microsystems packaging-related applications.

Effect of a protective coating on the surface integrity of a microchannel produced by microultrasonic machining

In micro-ultrasonic machining (μUSM), slight lateral vibration at the end of the tool inevitably occurs due to tool manufacturing installation errors and mechanical system vibrations. These vibrations cause overcutting and edge breakage, creating undesirable effects on heat transfer and flow deflection. Hence, this paper presented a new fabrication method that ensures high surface integrity by applying a protective coating on the substrate. To study the material removal modes during fabrication and the causes of overcutting and edge damage, a mathematical model of the microchannel surface integrity was established. The experimental parameters—feed rate, ultrasonic power, slurry viscosity, and protective coating—had a large impact on the surface integrity. The optimal parameters were a PE-Wax coating of 400 μm thickness, feed rate of 4 μm/s, 60 % ultrasonic power and 25 % slurry concentration. Under these conditions, the amount of overcutting decreased from 74.3 μm to 28 μm (62.3 % improvement) and the weighted edge damage decreased from 52.3 μm to 16 μm (69.4 % improvement), which led to a 65.85 % improvement in the surface integrity index. The experimental investigation revealed that the surface integrity of silicon microchannels and the quality of μUSM can be significantly improved by applying the protective coating.

Micro ultrasonic machining hemispherical mold for MEMS resonator gyroscope using a novel ultraprecise ceramic entire-ball tool

The manufacture of inertial-grade and tactical-grade diamond micro electro mechanical systems (MEMS) hemispherical resonator gyroscopes is limited by the manufacturing accuracy of the monocrystalline silicon hemispherical concave mold, on which the gyroscope shell is formed. To solve this problem, this paper presents a new method for micro-ultrasonic machining of microhemispherical molds for resonator gyroscopes using an ultraprecise ceramic entire-ball tool (UCET). To study the wear mechanism of the UCET and the influence of tool wear on the surface integrity and form accuracy of the microhemispherical mold, a mathematical model for the tool wear of micro-ultrasonic machining of microhemispherical molds with UCET is established and verified by experiments. The micro-ultrasonic amplitude, the abrasive material and the abrasive size is found to have significant influences on the tool wear of the UCET. The wear rates of tungsten carbide and silicon nitride ceramic tools are 2.22% and 3.64%, respectively, which are far less than the wear rate of 8.03% of bearing steel. The wear condition agrees with the theoretical model. The machining experiment shows that the radius change, ΔR, is 6.47 µm of the microhemispherical mold processed by UCET, which is much better than 32 µm of the micromold processed by micro-electro discharge machining at one time. After 10 continuous machining runs, the deviation rate of the form accuracy of the micromold is 1.71%, 3.71% and 24.21%, due to the wear of tungsten carbide, silicon nitride and bearing steel, respectively. It can be seen that micro-ultrasonic machining of microhemispherical molds using UCET has the characteristics of a high initial form accuracy, low wear rate, high integrity and form accuracy. This is a potentially effective method to obtain micromolds with high accuracy and surface integrity.

Study on manufacturing quality of micro-ultrasonic machining with force control

Micro-ultrasonic machining (MUSM) is an effective way of processing microstructures made from hard and brittle materials, although controlling the fluctuation of the machining force during processing is difficult. To control the quality of micro-holes fabricated in hard and brittle materials, MUSM with force control (MUSMFC) is used to study the edge chipping rate (ECR) and material removal rate (MRR) during micro-hole fabrication. The process is controlled using a force sensor and a processing control strategy. Various experiments are designed to assess the processing efficacy. Comparative experiments indicate that the ECR with MUSMFC is superior to that with traditional MUSM. Single-factor experiments show that the ultrasonic power and the fluctuation of the machining force exert a significant influence on the ECR. The influence of the spindle speed on the ECR is small. Orthogonal experiments show that the fluctuations of the machining force and ultrasonic power have large impacts on the MRR. The spindle speed has a significant impact on the MRR as well, whereas the mass fraction has little effect. The best combination of ECR and MRR is obtained using a spindle speed of 500 rpm, a machining-force fluctuation of 0.1 N, an ultrasonic power of 50 W, and a mass fraction of 10%.

On thermal performance of serpentine silicon microchannels

In the present study, three different serpentine microchannels (Rectangular, U and V) of rectangular cross-section with a channel span 24 mm were fabricated on a 0.525 mm thick (100) silicon substrate using micro-ultrasonic machining (micro-USM) technique. Thermal performance of the microchannels was experimentally investigated by making the working fluid (water) to flow through them at different Reynolds numbers (100–400) and at different heat fluxes (10 kW/m2, 20 kW/m2 and 30 kW/m2). Similar microchannels were modeled and analysed numerically simulating the experimental conditions. The performances of the microchannels obtained with the experimental as well as numerical results were compared in terms of pressure drop, substrate and fluid temperatures and heat transfer coefficient. The results indicate that the overall thermal performance of the microchannel heat sink mostly depends on the type of pattern as the fluid-substrate interaction area, defined by the Sink Area Factor (SAF), changes appreciably with the pattern. It was found that the U-serpentine microchannel exhibited the best thermal performance while compared to the other two serpentine microchannels. The sharp bends of the microchannel patterns and the surface roughness of the microchannel walls adversely affect the overall thermal performance of the microchannels. The study also outlines the need for a compromise in the Reynolds number, as higher Reynolds number tends to lower the overall thermal performance of the microchannels.

Influence of the Planetary Movement of Tool on the Aspect Ratio of Micro Holes Machined by Micro-Ultrasonic Machining

The micro-ultrasonic machining (USM) is suitable for machining hard and brittle materials. When a micro hole is drilled deeply using micro-USM, machining speed slows down and the breakage of micro tool may occur. To solve this problem, this paper proposes the application the planetary movement of micro tool in high-aspect ratio micro holes drilling by micro-USM. The micro holes of about 92 μm in diameter with an aspect ratio larger than ten have been machined. The processing efficiency has been improved. The influence of planetary movement parameters on processing efficiency has been investigated

On effect of tool rotation on performance of rotary tool micro-ultrasonic machining

ABSTRACTThe present research paper is based on a comparative study of stationary tool micro-ultrasonic machining (STMUSM) and rotary tool micro-ultrasonic machining (RTMUSM). Microchannels were developed on glass work material by using both processes. The effect of tool rotation on the performance of micro-USM was investigated. The performance of both processes was compared on the basis of material removal rate (MRR) and depth of channel (DOC) as response characteristics. The power rating, work feed rate, concentration of abrasive slurry, and abrasive mesh size were chosen as variable input process parameters in this investigation. The form accuracy of the fabricated microchannels was analyzed with the help of imaging technique. Also, a qualitative analysis of tool wear was carried out with the help of microscopic images. The experimental results revealed that the tool rotation significantly improved the performance of micro-USM. The RTMUSM resulted in 155% and 147% higher MRR and DOC as compared to STMUSM. The tool wear was also found to be lesser in RTMUSM as compared to STMUSM and as a result of that form accuracy of machined microchannels improved.

Micro-EDM and micro-USM combined milling of ZrB2-SiC-graphite composite for 3D micro-cavities

The ZrB2-SiC-graphite composite is one of the most promising ceramics, which show significant potential in manufacturing parts served in ultra-high temperature. Micro-electrical discharge machining (micro-EDM) is an effective method in machining this conductive hard ceramic. However, the recast layer characterized by craters and micro-cracks is formed on the machined surface, resulting in poor surface quality. In this paper, micro-EDM and micro-ultrasonic machining (micro-USM) combined milling is proposed for manufacturing 3D micro-cavities in the ZrB2-SiC-graphite composite. The micro-cavity is firstly machined by micro-EDM milling, followed by micro-USM finish milling to remove the recast layer in the same system without changing the micro-tool. The machining performances are investigated with consideration of the surface topography and finishing depth. It is found that the more recast layer is removed when a higher ultrasonic amplitude, larger abrasive grain size, and lower tool feedrate are employed. Based on the preliminary experiments, the proper machining parameters are obtained and applied to the fabrication of micro-cavities. The machining results show that the surface quality is improved with the low surface roughness and absence of defect layer. Meanwhile, the high machining accuracy in the depth direction and processing efficiency are achieved. It is verified that the micro-EDM and micro-USM combined milling process is feasible for fabricating 3D micro-cavities in the ZrB2-SiC-graphite composite.

Experiments and simulations of micro-hole manufacturing by electrophoresis-assisted micro-ultrasonic machining

Electrophoresis-assisted micro-ultrasonic machining (EPAMUSM) is an effective method for solving the problem of using traditional micro-ultrasonic machining (MUSM) to fabricate micro-holes in materials that are hard and brittle, namely the low utilization ratio of abrasive particles. EPAMUSM uses an electric field to attract the abrasive particles to the processing area during processing, which is useful for improving both the utilization ratio of abrasive particles and the processing quality. Numerical simulations of the concentration distributions of abrasive particles in MUSM and EPAMUSM show that the abrasive concentration on the tool surface is much higher in EPAMUSM. The concentration increases rapidly from 1 mol/m3 to 4.68 mol/m3 after 10 s in EPAMUSM. Comparative experiments show that EPAMUSM has advantages over MUSM under the same processing conditions: the EPAMUSM edge chipping rate (0.03) is much less than the MUSM one (0.22) and the EPAMUSM material removal rate (1.916 × 10−4 mm3/min) is marginally better than the MUSM one (1.718 × 10−4 mm3/min). Single-factor experiments are used to study how varying certain parameters (namely DC voltage, ultrasonic power, and spindle speed) affects EPAMUSM manufacturing quality and efficiency. Finally, the processing parameters are optimized by means of response-surface experiments, and the optimum EPAMUSM processing parameters are determined (namely an applied voltage of 7.5 V, an ultrasonic power of 22.5 W, a spindle speed of 300 rpm, and a mass fraction of 10%).