Micro-ultrasonic Machining Research Articles

On form accuracy and surface roughness in micro-ultrasonic machining of silicon microchannels

Accuracy in manufacturing microchannels is important in order to achieve their intended function. Smooth and high aspect ratio microchannels on silicon wafer substrate are needed in the heat removal application in various microelectronic components. Generally, etching techniques are used to fabricate silicon microchannels; however, the maximum achievable limit for the channel depth is a major concern. Micro-ultrasonic machining (micro-USM) is capable of machining high aspect ratio microchannels on hard and brittle material such as silicon, glass, ceramics, etc. However, achieving reasonable form accuracy and surface roughness of the microchannels is challenging. Overcut and edge damage (stray cut) are undesirable for precision machining while surface roughness of the microchannels can be set at an optimized value to attain maximum heat transfer. In the present study, silicon microchannels were fabricated using the micro-USM technique. In order to improve the precision and quality of the fabricated silicon microchannels in terms of surface roughness, overcut and stray cut; viscous fluids with different viscosities were considered for investigation in combination with other machining conditions. The experimental investigation revealed that using low viscous fluids yields better surface roughness compared to high viscous fluid; however, overcut and stray cut were minimized while using high viscous fluids. Machining at higher feed rates could minimize the surface roughness, over cut and stray cut irrespective of the abrasive concentration percentage. Possible interactions between the tool, abrasive and workpiece in the machining zone were analyzed vis-à-vis the experimental results.

Fabrication of microchannels using rotary tool micro-USM: An experimental investigation on tool wear reduction and form accuracy improvement

Tool wear is an inevitable phenomenon and hence a prime challenge in micro-ultrasonic machining (micro-USM) process. Therefore, quantification and reduction of tool wear is essential to enhance the quality characteristics of machined microchannels. The present investigation establishes the quantitative relationships among the tool wear, form accuracy and material removal rate (MRR). This relationship is reported for the first time for rotary tool micro-USM (RTMUSM) process. An attempt has been made to understand the different types of tool wear in RTMUSM process. Later, a 2D geometrical model for the quantification of tool wear in RTMUSM process was developed. Further, the contribution of the different types of tool wear on the dimensional as well as form accuracies were evaluated. The experimental results revealed that the RTMUSM process is affected mainly by two types of tool wear (i.e. longitudinal wear and edge rounding wear). The lateral wear was revealed as negligible. It is suggested that the desired depth of channel (DOC) with best possible form accuracy of microchannels can be achieved by providing longitudinal wear compensation to the tool. The effect of process parameters such as tool rotation speed, work feed rate, power rating, slurry concentration and abrasive particle mesh size on total volumetric wear (TVW) of tool, MRR, dimensional and form accuracy of microchannels were also investigated. Additionally, the desirability approach was applied for optimization the RTMUSM process parameters for maximum MRR, DOC, form accuracy and minimum TVW and width of channel.

Surface Texturing of Polyimide Composite by Micro-Ultrasonic Machining

In this study, micro-dimples were prepared on a polyimide composite surface to obtain the dual benefits of polymer materials and surface texture. Micro-ultrasonic machining is employed for the first time for micro-dimple fabrication on polyimide composite surfaces. Surface textures of simple patterns were fabricated successfully with dimple depths of 150 μm, side lengths of 225-425 μm, and area ratios of 10-30%. The friction coefficient of the micro-dimple surfaces with side lengths of 325 or 425 μm could be increased by up to 100% of that of non-textured surfaces, alongside a significant enhancement of wear resistance. The results show that surface texturing of polyimide composite can be applied successfully to increase the friction coefficient and reduce wear, thereby contributing to a large output torque.

Reducing Edge Chipping of Micro-holes with Electrophoresis-assisted Micro-ultrasonic Machining

This paper proposes the method of electrophoresis-assisted micro-ultrasonic machining (EPAMUSM) to reduce edge chipping when machining holes in hard and brittle materials. By utilizing the electrophoresis effect of ultra-micro abrasive particles in work solution and the effect of electrophoresis-assisted electrical field, the abrasive particles in the solution can be gathered around the micro-tool, thereby reducing the edge chipping caused by direct hammering between the tool and the workpiece. EPAMUSM helps to improve the utilization of the abrasive particles and significantly improves the material removal rate compared with micro-ultrasonic machining (MUSM). Both single-factor and orthogonal experiments were performed to verify the method. The results show that abrasive particles gathered around the tool with the assistance of the electrophoretic effect and electrical field, and that the utilization of abrasive particles was enhanced during MUSM, which weakened the direct hammering between the tool and the workpiece. With the best parameter values (a machining force of 0.1 N, an abrasive-particle diameter of 0.1 μm, an electrical field voltage of 5 V, and an ultrasonic power of 21 W), micro-holes of 100 μm in diameter could be generated well in monocrystalline silicon. Compared with conventional MUSM, there was less chipping around the hole edge and the quality and material removal rate were improved greatly.

Micro hole fabrication on Quartz using Ultrasonic Micromachining Process

Ultrasonic micromachining (USMM) has immense potential for micro-machining on quartz which is used in different field of applications such as optics, metrology and micro electro mechanical system (MEMS) etc. In this paper the influences of process parameters such as power rating, abrasive slurry concentration and tool feed rate on material removal rate (MRR), overcut and taper angle of the micro hole on quartz by USMM have been investigated. Stainless steel of grade 304 has been selected as the micro-tool material for ultrasonic micro drilling on quartz. The higher value of MRR of 0.4235 mm/min has been obtained at power rating of 400 W, abrasive slurry concentration of 40% and tool feed rate of 1.2 mm/min. The lower value of overcut of 55 µm and taper angle of 0.600 of micro hole have been obtained at abrasive slurry concentration of 20%, power rating of 300 W and tool feed rate of 1 mm/min.

Experimental investigation on drilling of borosilicate glass using micro-USM with and without tool rotation: a comparative study

The application of microproducts is increasing rapidly in various fields such as automobiles, electronics, microfluidics, bio-MEMS, etc. These microproducts are generally made of hard and brittle materials, e.g., glass, quartz, ceramics and silicon, etc. The machining of these materials in micro-domain is a difficult task. Micro-ultrasonic machining (micro-USM) is a preferred process for machining of hard and brittle materials. But high tool wear and low aspect ratios limits its industrial use. This investigation compares the effect of tool rotation on material removal rate and hole overcut. Additionally, aspect ratio was measured. The variable process parameters for the investigation were power rating, static load, slurry concentration and abrasive size. Imaging was used for qualitative analysis of tool wear. The experimental results reveal that micro-USM with tool rotation resulted in higher material removal rate, lesser hole overcut, high aspect ratios and lesser tool wear in compared with micro-USM without tool rotation.

Machinability study of Zr-Cu-Ti metallic glass by micro hole drilling using micro-USM

Metallic glasses are the new class of materials researched and developed extensively for their applications in fabrication of micro components because of their exceptional mechanical properties. Micro machining of metallic glass to the required tolerance without any structural damage is a challenging task. Micro-ultrasonic machining (micro-USM) is a nontraditional machining process which can machine micro features in hard and brittle materials without heat generation. In present research work the machinability of Zr60Cu30Ti10 metallic glass is investigated by micro hole drilling using micro-USM. Machinability study is carried out by analyzing the performance measures like overcut, edge deviation, taper angle, material removal rate (MRR) and tool wear rate (TWR) with respect to the input machining parameters such as feed, abrasive grit size and concentration of abrasive slurry. The edges of the drilled holes are analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) to study the micro structural changes which are taken place in metallic glass due to micro machining. SEM and EDS analysis revealed that the amorphous structure of metallic glass is not affected during machining by micro-USM. A range of feed rate, abrasive grit size and slurry concentration are recognized for micro-USM drilling in metallic glass using multi-objective optimization on the basis of ratio analysis (MOORA) method. The micro-USM drilling in metallic glass provides a new horizon for the precision machining of glassy alloys otherwise which are very difficult to machine conventionally without any change in its amorphous structure.

Tool wear and form accuracy in ultrasonically machined microchannels

Quantifying wear on the basis of weight at micro levels may be erroneous. Moreover, information about wear distribution cannot be obtained on the basis of weight monitoring. Thus, quantification on the basis of linear measurements is an effective solution at micro levels. This paper presents a mathematical model for quantifying wear measured in two dimensions and subsequently converting it to a three dimensional wear model. The efficacy of the model was verified through machining data from ultrasonic micromachining of glass with tungsten carbide tools. The tool wear values obtained for the model was then correlated with the form accuracy of the machined microchannel which were found reasonable. Further, the effects of different process parameters like abrasive concentration, power rating, abrasive size and workpiece feed were studied on the tool wear behaviour and presented vis-a-vis microchannel form accuracy. High power rating and high abrasive concentration resulted in more tool wear and increased form inaccuracy; coarse abrasives resulted in higher form inaccuracy. Longitudinal wear resulted in decreased microchannel depth while lateral wear led to tapered microchannel walls and edge rounding wear yielded rounded corners in the fabricated microchannels.

Experimental study of electrophoretically assisted micro-ultrasonic machining

In micro-ultrasonic machining (MUSM), a major part of the material is removed by the impact of abrasive particles. In the early stage of machining, abrasive particles are distributed uniformly in the machining area. However, as the process goes on, abrasive particles will be driven out of the machining area owing to the ultrasonic vibration of the micro-tool or work-piece and the rotation of the micro-tool in the fluid. As a result, the machining precision and machining efficiency will be reduced. In this paper, we propose a new method called electrophoretically assisted micro-ultrasonic machining (EPAMUSM) in which an electric field is used to prevent the abrasive particles from being driven out of the machining area. Experiments on EPAMUSM are conducted using a self-developed micro-USM system with micro-tool vibration, in which the control system of the micro-USM machine tool controls the machining force in a constant range. First, experiments comparing micro-ultrasonic machining with and without electrophoretic assistance are conducted. It is found that, with the appropriate processing parameters, EPAMUSM can improve machining accuracy and machining efficiency. Then, experiments with an orthogonal design are performed to reveal the main effects of the process parameters (abrasive particle size, spindle speed, DC voltage, force, ultrasonic power, mass fraction, and feed rate) on the material removal rate, and the optimal processing parameters are derived from the results.

Tool wear studies in fabrication of microchannels in ultrasonic micromachining

Form accuracy of a machined component is one of the performance indicators of a machining process. Ultrasonic micromachining is one such process in which the form accuracy of the micromachined component significantly depends upon the form stability of tool. Unlike macromachining, a very small amount of tool wear in micromachining could lead to considerable changes in the form accuracy of the machined component. Appropriate selection of tool material is essential to overcome this problem. The present study discusses the effect of tool material, abrasive size and step feed in fabrication of microchannels by ultrasonic machining on borosilicate glass. Development of microchannels using ultrasonic micromachining were rarely reported. It was observed that tungsten carbide tool provided a better form accuracy in comparison to the microchannel machined by stainless steel tool. The tool wear mechanism in both materials is proposed by considering scanning electron micrographs of the tool as evidence. A one factor at a time approach was used to study the effect of various process parameters.

Influence of Process Parameters during Fabrication of Si Microchannels Using Microultrasonic Machining

Influence of Process Parameters during Fabrication of Si Microchannels Using Microultrasonic Machining

Study and Application on Ultrasonical Combined Electrical Micro-Machining the Special Shape Micro-Structures

For manufacturing the special shape micro-structures with hard and brittle materials , the ultrosonical combined electrical micro-machining method is proposed and improved. The ultrasonical combined synchronous electrochemical micro-machining system is built and optimized, which machining parameters can be adjusted in a big ranges, and the synchronous target between the ultrasonical vibration and the voltage of micro-PECM(Micro-pulse electrochemical machining) can be realized. The micro-machining electrodes are manufactured in round sections by combined micro electrical-discharged machining (EDM).The mechanism tests of ultrasonic vibration combined electrical pulse micro-machining tests are carried. It is adopted that the low amplitude of electrical voltage (no more than 6V) and the static electrolyte with lower electrical conduction rate, the good machining accuracy and surface quality are acquired. The regular morphology array micro-round holes are manufactured successfully on friction units' working surface, which can save oil , improve the friction performances and prolonging working life of important friction units. In additional, the fixed holes satisfying the precision needs are machined on the hard and brittle piezo-ceramics pieces, which are often used in many important micro-precise piezo-ceramics sensor. It is proved that ultrasonic combined electrical micro-machining is an effect method for to machine the special shape micro-structures.

A Reuse Evaluation for Solar-Cell Silicon Wafers via Shift Revolution and Tool Rotation Using Magnetic Assistance in Ultrasonic Electrochemical Micromachining

A new reuse fabrication using a tool module with rotation and revolution through a process of magnetic assistance in ultrasonic electrochemical micromachining (UEMM) for removal of the surface layers from silicon wafers of solar cells is demonstrated. The target of the proposed reuse fabrication method is to replace the current approach, which uses strong acid and grinding and may damage the physical structure of silicon wafers and pollute to the environment. A precisely engineered clean production approach to removal of surface microstructure layers from silicon wafers is to develop a mass production system for recycling defective or discarded silicon wafers of solar cells that can reduce pollution and cost. The high revolution speed of the shift with the high rotation speed of the designed tool increases the discharge mobility and improves the removal effect associated with the high feed rate of the workpiece. High frequency and high power of ultrasonic with large electrolyte flow rate and high magnetic strengths with a small distance between the two magnets provide a large discharge effect and good removal; only a short period of time is required to remove the epoxy film and Si3N4layer easily and cleanly.

Investigations on Tool Wear in Micro Ultrasonic Machining

Tool wear is a major issue in ultrasonic machining and it is more significant in case of micro-ultrasonic machining. Because of the size of the tool in micro domain; the strength is relatively poor and hence more tool wear results. Generally, in the off-line methods, tool wear is measured after machining and by the removal of the tool from the machine tool. However, it is difficult and untidy process to remove the tool for each measurement and reinstall it on the machine. In this paper a simple technique ‘Reference Point’ method has been proposed to assess the linear tool wear on the machine itself. A comparative study of tool wear in case of solid and hollow tool was made while drilling silicon wafer. Static load was considered as a process parameter. Surface topography and fracture mechanism are discussed with the help of scanning electron microscope (SEM) micrographs.

Microdrilling of difficult to cut materials for MEMS applications using ultrasonic micromachining

Microdrilling of difficult to cut materials for MEMS applications using ultrasonic micromachining

Recent Developments and Research Issues in Microultrasonic Machining

Demand for micromachining has been on the rise in recent years owing to increasing miniaturization. Production of parts in microscale, especially with brittle materials, is challenging. Ultrasonic micromachining has been gaining popularity as a new alternative in fabrication of such parts. The process gives a machining option for geometrically challenging and/or brittle material parts that are difficult to machine by conventional processes. In the recent years, possibilities have been explored to improve the “Unit Removal” in microultrasonic machining (micro-USM). However, the research in the area is yet to attain momentum. The present paper is an attempt to present the state of the art in the area of micro-USM based on the literature. Developments in the critical areas of the process like machine tool technology, machining tool head, transducers, and precision attainable in the process with challenges have been discussed. Potential research issues have been explored for future work. Possible application areas have been identified.

Applications of Ultrasonic Radiation Forces

This keynote paper aims at introducing applications of ultrasonic radiation force in industry. The chosen focus is to understand how to use it. Since the phenomenon of acoustic levitation can reflect the exciting of ultrasonic radiation force directly. The paper starts with an analysis on the tungsten ball floating on a sound field and ultrasonic micro-manipulation study in micro Electronic Mechanical System (MEMS). And ultrasound has been successfully used to degrade wastewater as its cavitation. At the same time, different kinds of micro-ultrasonic machining were used to show how exciting machining and ultrasonic radiation combined. A view from the authors and the final Conclusions show future applications of ultrasonic radiation force.

Situations and Development Trends of Ultrasonic Machining Tool and Ultrasonic Machining Technology

Based on the up to date development of the ultrasonic machining (USM) technology, applications and development trends of the ultrasonic machining tool are described. Automatic control including intelligent control and adaptive control, also tools in processing as an attachment and load matching system are trends in ultrasonic machining tool. The latest applications of ultrasonic machining technology in deep hole machining, ultrasonic elliptical vibration cutting, ultrasonic grinding, ultrasonic milling and ultrasonic combined machining are summarized, processing accuracy and processing efficiency have got a lot of progress. The development trends and future prospect of the ultrasonic machining technology are expounded. Studying the ultrasonic cutting mechanism, ultrasonic combined machining technology and micro-ultrasonic machining technology are the trends of ultrasonic machining.

A new approach for force measurement and workpiece clamping in micro-ultrasonic machining

Micro-ultrasonic machining (micro-USM) is a promising micromachining technique to meet the increasing demands of high accuracy in processing the micro-components of hard and brittle materials. Unlike the well-established conventional USM, micro-USM still lacks in its commercial viability. The major concerns in micro-USM process are the accuracy of the setup and dynamic behavior of the system associated with precise force monitoring and robust workpiece clamping. In this study, a new micro-USM system with regards to measurement and monitoring of static force as well as tooling and workpiece clamping is developed. A force measurement and control system is proposed which is well suited for machining conditions in micro-USM. Furthermore, a reliable and quick setup for the vacuum chuck is introduced, which is capable of consistently transmitting the ultrasonic vibration from horn to the workpiece. Measurement of acoustic characteristics as well as experimental investigations is carried out to validate the functionality of the proposed system.

Electrophoretic deposition characteristics of an electrical discharge machined micro-tool for micro-hole polishing in quartz

This paper examines micro-hole polishing in quartz by a micro-tool coated with SiC particles by electrophoretic deposition (EPD). Quartz is a hard and brittle material, difficult to polish and fractures occur easily. Moreover, micro-hole machining by micro ultrasonic machining (MUSM) often fills the micro-hole wall with micro-chips and micro-cracks, which necessitate further polishing for better surface quality. In this paper, a micro-tool was developed for polishing micro-holes in quartz. The micro-tool was fabricated by wire electrical discharge grinding (WEDG) and had a diameter of 100 µm. A layer of SiC particles was coated onto the micro-tool by EPD. To achieve better polishing results, optimal parameters for obtaining a uniform and stable layer by EPD were first explored. After EPD, the micro-tool was employed to polish micro-holes in quartz with the help of ultrasonic vibration machining (USM). Experimental results show that polishing for a duration of 30 min at a rotational speed of 2500 rpm using 0.25 µm SiC particles at an ultrasonic amplitude of 6.3 µm can improve the surface roughness of a micro-hole wall with Rmax being reduced from 0.48 µm to 0.08 µm.