MS, University of Cincinnati, 2018, Engineering and Applied Science: Mechanical Engineering

Engineering materials such as glass and ceramics are finding numerous applications in electronics and communication, optics, chemical, aerospace, and medical industries. Glass being a hard and brittle material poses huge machining challenges especially during micromachining. Traditional machining of glass by methods such as drilling or milling is generally difficult to achieve due to reasons ranging from excessive tool wear to abrupt breakage of glass. Chemical etching techniques can produce a smooth machined surface on glass. Yet, the chemical machining process is usually slow and often fail to produce high aspect ratio unless combined with some other additional masking techniques which are usually expensive. Laser beam machining when performed on glass produces micro-cracks along the machined edge due to uneven temperature distribution and residual stresses due to heat affected zones (HAZ). Wet laser beam machining, i.e. laser beam machining when performed under water instead of air results in considerable reduction in thermal defects. However, a portion of laser energy is wasted in wet laser machining as heat loss in water. The motivation of this study is to use to minimize this loss and explore the possibility of utilizing this laser energy being absorbed by the medium to further increase machining. To achieve this, a novel chemo-thermal machining process is proposed in this work. Chemo-thermal micromachining is a laser beam machining process in wet condition where laser beam machining is performed on glass specimen submerged in NaOH solution. Material removal mechanism in chemo-thermal micromachining process is a combination of laser ablation and chemical machining. When laser beam is incident on glass workpiece submerged under NaOH solution, a part of laser energy is absorbed by the electrolyte solution iii thus raising the electrolyte temperature locally thus increasing the rate of chemical reaction as chemical machining process is highly dependent on temp (open full item for complete abstract)

Committee: Murali Sundaram Ph.D. (Committee Chair); Woo Kyun Kim Ph.D. (Committee Member); Jing Shi Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2013, Engineering and Applied Science: Mechanical Engineering

Demand for miniaturized products is ever increasing as they accomplish the task of providing the desired functionalities with high efficiency using minimalistic raw material. In order to execute functionalities like high strength and sustainability with minimal use of space, the raw materials used should possess good mechanical, chemical and physical properties. This requirement poses several challenges including high tool wear and lack of precision in the micromachining of such superlative engineering materials. Although, electrical discharge machining (EDM) and electrochemical machining (ECM) are well established nontraditional techniques to meet these challenges, they are restricted to electrically conductive materials. Several electrically non-conductive materials like ceramics and fiber-reinforced composites are increasingly being used in miniaturized pumps, reactors, accelerometers and many other biomedical devices. Micro Electrochemical Discharge Machining (micro-ECDM) has the capability to meet these challenges. However, machining high aspect ratio features on ceramics like glass still remains a formidable task due to overcut. Since electrolyte concentration plays an important role in overcut its effects on material removal needs to be studied in order to enhance the capability of this technology in machining complex and high aspect ratio features.

Committee: Sundaram Murali Meenakshi Ph.D. (Committee Chair); Anil Mital Ph.D. P.E. (Committee Member); David Thompson Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2012, Engineering PhD

Terahertz radiation, a region in the electromagnetic spectrum which lies between the microwave and infrared, has gained considerable attention recently due to interesting properties exhibited by materials exposed to this radiation. Dielectric materials such as glass, paper, plastic, and ceramics that are usually opaque at optical frequencies are transparent to terahertz radiation. This led to interesting terahertz spectroscopy and imaging applications. Finite element method simulations of plain, tapered and periodically corrugated metal terahertz wire waveguides have been conducted at the end of the waveguides. This modeling was used to guide the choice of design parameters for the fabrication of waveguides with laser micromachining. The waveguides were characterized with a fiber-coupled terahertz time-domain spectroscopy and imaging system. The THz pulses emitted at the transmitter excite the surface plasmon polaritons in the metal waveguide and propagate as surface waves that are detected at the receiver. This work involved studying the propagation properties as well as the frequency dependent diffraction at the end of the wire waveguides. The temperature dependent propagation properties of the waveguides have also been studied. The THz waveguide properties propagating along the surface of the plain, corrugated and tapered wire waveguides have been successfully demonstrated using both simulations and experimental work.

Committee: Jason Deibel PhD (Advisor); Raghavan Srinivasan PhD (Committee Member); Sharmila Mukhopadhyay PhD (Committee Member); Douglas Petkie PhD (Committee Member); Peter Powers PhD (Committee Member) Subjects: Materials Science; Physics

PhD, University of Cincinnati, 2001, Engineering : Electrical Engineering

Ga + focused ion beam (FIB) micromachining was utilized on GaN for the fabrication of photonic devices, such as channel waveguides, laser facets, reflectors, etc. FIB micromachining can provide several advantages on device fabrication: maskless and resistless process, local modification of the process conditions, and smooth surface on desired features. GaN and related materials are of great success for visible and UV optical devices. However, some fabrication issues are still remaining to overcome on sample preparation and processing. In particular, high reflectivity mirror facets is hard to obtain by conventional processing procedures due to the large misalignment between sapphire and GaN-based materials. Therefore, it is important to develop a simple and efficient processing technique. The main objective of this work is to combine dry etching techniques to manufacture the ridge waveguides and FIB micromaching to fabricate small period Distributed Bragg Reflector (DBR) mirrors. The milling selectivity of GaN to the grown substrates such as sapphire, SiC and Si (111) is 3x better. By introducing I 2 gas, the etching rates of FIB micromachining with gas-assisted etching are enhanced 6 - 8x faster than that of FIB micromachining alone on GaN. To fabricate GaN waveguides, the optimized conditions of reactive ion etching are 20 sccm of Cl 2 , 400 Watts of RIE power as well as the chamber pressure of 5 mTorr. Rapid thermal annealing is to recover the ion damages created in the processing of dry etching and FIB micromachining. The modeling of Jone's matrix theory is to provide the information of reflectivity for the structure of Bragg gratings. The effect of gratings is obtained from loss measurement to measure the propagation of laser light sources in the SiON ridge waveguides. However, the width shifting of gratings generated by FIB micromachining causes the reflectivity shifting in the loss measurements. The AFM scanning and modeling confirm that phenomena due to the p (open full item for complete abstract)

Committee: Dr. Andrew Steckl (Advisor) Subjects:

MS, University of Cincinnati, 2001, Engineering : Electrical Engineering

The subject of this work is the fabrication and characterization of microneedles using the Coherent Porous Silicon (CPS) etching technology. This forms the bases for an integrated fluidic interchange system that can be used in drug delivery systems and in fluidic analysis systems. This work concentrates on the fabrication of microneedles and addresses issues that might influence the penetration of durable media with these microneedles. The microneedles have been fabricated using the CPS etching technology. The needles have a central silicon channel that can be used to carry fluids and a silicon dioxide sidewall that is used to penetrate biological media. When biological media are involved the issue of biocompatibility arises and a silicon dioxide sidewall eliminates that problem because of its relative inertness in bio-medical applications. Microneedle arrays with different diameters and different spacing between successive needles have been fabricated. Microneedles have been characterized with regard to sharpening of sidewalls, spacing between successive needles and microneedle sidewall thickness. These issues are key issues with regard to penetration of biological media and all of these issues have been treated extensively. Solutions have been suggested with supporting evidence to overcome the shortcomings of the CPS technology that affects the fabrication of microneedles to suit different applications. Needle testing has also been carried out and compression and shear stresses that these structures can withstand has been explored. Further tests have been carried out to determine the ability of these microneedle structures to penetrate polymer films in an attempt to replicate the real situation with skin/ artificial skin.

Committee: Dr. Thurman Henderson (Advisor) Subjects:

PhD, University of Cincinnati, 2000, Engineering : Electrical Engineering

The development of MicroElectroMechanical Systems (MEMS) switch technology and integration of this technology into Radio Frequency (RF) electronics has created numerous applications. The incorporation of RF MEMS switches into microwave systems offers unprecedented reductions in insertion loss (on-resistance) with extremely low switching power levels as compared with active devices such as Field Effect Transistors (FETs) and Positive-Intrinsic-Negative (PIN) diodes. The objective of this research was to investigate the interactions of mechanical design, material properties, and processing conditions on the electrical performance of RF MEMS switches, as measured by RF device performance. The design goal included development of low actuation voltage electrostatic actuated switches fabricated on gallium arsenide substrates. Two types of switch structures were investigated, cantilever beams and microbridges. These structures provided a controllable medium to allow for fundamental examination of the performance dependencies. The switches were designed for capacitive coupling and operated in a series configuration. The switches consisted of a suspended metal beam over a dielectric-isolated bottom metal. An applied direct current voltage was used to actuate the switch while the RF signal passed through the dielectric. The electrical and structural integrity of the switches was investigated by evaporating bilayer films of titanium and gold, while maintaining a constant total thickness of 1.5 micrometers. Results demonstrated that a thick titanium layer of 0.5 micrometers gold on 1.0-micrometers titanium produced functional cantilevers with no discernible curling due to stress gradients within the film. Cantilevers 300 micrometers long exhibited an insertion loss of -0.5 dB with an isolation of -11.7 dB at 10 GHz, with an actuation voltage of 20 V. Other bilayer combinations resulted in a stress gradient that caused the cantilevers to curl excessively, but resulted in functio (open full item for complete abstract)

Committee: H. Thurman Henderson (Advisor) Subjects:

MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

The ability to offer multiple functionalities with minimal space, material and energy utilization has led to increase in demand for micro products with sizes ranging from tens of micrometers to few millimeters. Micro system products have several applications in biotechnology, electronics, optics, medicine, avionics, automotive and aerospace industries. Superior mechanical and physical properties offered by advanced engineering materials comprising metals, ceramics and fiber-reinforced composites have led to their increased usage in micro system products such as X-ray lithography masks, micro-fluidic devices, micro-scale heat sinks, biomedical instruments, and miniaturized mechanical devices like actuators, gears and motors. Advanced engineering materials used in these microsystems are often hard, brittle, and electrically nonconductive and pose micromachinability challenges. Micromachining with sub-micron cutting depth by micro-sized abrasive tools is capable of deterministic material removal with minimal sub-surface damage in advanced composites and ceramics. To achieve this, it is essential to fabricate precise abrasive microtools to enable abrasive micromachining. In this research work, an experimental system has been designed and built in-house for fabrication of abrasive microtools using the principles of pulse-current electrodeposition. Abrasive microtools of diameter 300 ¿¿¿¿m embedded with 2-4 ¿¿¿¿m diamond grit have been produced using this system. A mathematical model has been developed and experimentally verified to predict the weight percent of micro abrasive particles incorporated in binder matrix, for a given set of pulse-plating conditions. Designed experimental studies have been conducted using Taguchi method to understand the effect of process parameters on proportion of abrasives embedded during the tool making process. These studies indicated that shorter pulse durations at higher duty factors result in nominal extent of abrasive incorporation, at (open full item for complete abstract)

Committee: Murali Sundaram (Committee Chair); Sundararaman Anand (Committee Member); Jay Kim (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2011, Engineering and Applied Science: Mechanical Engineering

High aspect ratio metallic cylindrical rods having diameters in the sub millimeter range are increasingly being used as micro tools to machine complex micro features including deep hole micro drilling in a wide variety of engineering materials including metals and ceramics. They are also being used in applications such as ultrafine micro needles for intracellular sensing probes and micro robotic manipulators. Accurate and precise micro tools are essential for the micromachining of these highly complex features. Micro tools produced by the well known wire electro-discharge grinding suffer deformation due to the thermal stresses. Therefore, electrochemical machining has been explored as an alternate micro tool manufacturing technique. In this thesis, a micro electrochemical machining system has been designed and built in-house and a mathematical model has been developed to predict the final diameter of the anode based on the velocity of the cathode movement. Experimental verification of the model reveals good correlation with theoretical predictions. Large pulse on-times have successfully been used to fabricate micro tools having diameters of 10 micrometers with aspect ratios as high as 450. Pulse on-time between 5 to 10 ms was found to be an optimum range for successful micromachining using the in-house built micro electrochemical system. Pulse on-times lower than this optimum range result in a conical shape while pulse on-times higher than the optimum range result in a reverse conical shape.

Committee: Murali Sundaram Meenakshi PhD (Committee Chair); Sundararaman Anand PhD (Committee Member); David Thompson PhD (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2003, Engineering : Electrical Engineering

The objective of this work is to develop plastic microlenses using high throughput injection molding techniques. In this work, plastic microlenses have been designed, fabricated and characterized for future applications in optical communications and biochemical chip detection systems. Microlenses, that have wide ranging applications in image processing, displays, communications and biochemical detection have been researched for the past two decades. Various fabrication techniques have been developed using a wide range of materials. Plastic as a material for fabricating microlenses has been investigated in recent years. Soft lithography and hot embossing are examples of two of the techniques that have been used to fabricate plastic microlenses. The primary reason for using plastics as the material is their potential for high volume replication at a very low cost. However, a suitable technique for high volume fabrication of plastic microlenses has not been optimized yet. This work has successfully implemented a fabrication technique that enables high volume replication of plastic microlenses using injection molding techniques. A replaceable injection mold disk was fabricated using metal electroforming. The initial microlens mold was realized using the photoresist reflow technique. The fabricated mold disk was used as the master mold for the injection molding process. The microlenses were fabricated using two new plastics, COC and Poly IR 2 that have excellent optical transparency in the visible and infrared wavelength regions respectively. The plastic microlenses were characterized in terms of their focal lengths and surface roughness. The plastic microlenses developed in this work hold lot of promise for numerous applications in optical communications and biochemical detection.

Committee: Dr. Chong H. Ahn (Advisor) Subjects:

MS, University of Cincinnati, 2003, Engineering : Electrical Engineering

In this work, new polymer MEMS technology has been developed and characterized for the development of disposable microfluidic devices and lab-on-a-chips on plastic substrates. The developed technology will allow numerous applications for disposable biochips and polymer microstructures at low cost. Microfluidics has been applied for drug discovery, genomics, proteomics, clinical diagnostics, etc. So far, silicon and glass have been the two major substrate materials for the fabrication of lab-on-a-chips and microfluidic devices. The disadvantages of these substrate materials are relatively high cost compared with plastic substrates, and difficulty of mass manufacturable approaches in low-cost for the fabrication of the microfluidic devices. But for the development of low cost disposable lab-on-a-chips, novel microfabrication methods for microfluidic devices on substrates other than silicon and glass are highly desirable. Commercialization of microfluidics technology also requires low-cost and high volume fabrication methods of these microfluidic devices. Polymers are one of the good alternative substrates at low cost and their mass fabrication methods have already been established for macro polymer structures. Nickel electroplating technique has been developed for the fabrication of the master mold structure for replication of the plastic microfluidic devices. Injection molding and hot embossing techniques have been explored and optimized for high fidelity replication of the microstructures. UV LIGA technology (UV based lithography, electroplating and replication) has been adopted for manufacturing the microfluidic devices. UV lithography was done using thick photoresist (SU 8 2000 series), and the process was optimized for production of thick structures with aspect ratios of up to 10. A new polymer, cyclic olefin copolymer (COC) was extensively characterized in this work for the development of plastic microstructures using injection molding and hot embossing. Polycar (open full item for complete abstract)

Committee: Dr. Ramachandran Trichur (Advisor) Subjects:

MS, University of Cincinnati, 2002, Engineering : Electrical Engineering

In this work, we present a simple method for bonding micromachined glass biochips. Our approach relies on medical-grade UV-cured adhesives and UV-transparent substrates. The adhesive polymerizes forming the bond between two substrates when cured by a UV-source and the UV-transparent substrates enable the passage of UV-light through them to the adhesive. Using this method, several biochips were fabricated with UV-transparent low-cost microscopic glass cover slips. Microchannels were fabricated using standard fabrication procedures such as e-beam evaporation, photolithography, and wet etching. Commercially available 150 cP UV-cured adhesive was spin coated to a bare substrate at room temperature. The bare substrate was capped with the substrate containing the channels and a UV-source of intensity 7 mW/cm2 cured the adhesive at the interface for 4 min, enabling the formation of an adhesive bond. Following fabrication, the biochips were packaged and tested with colored dye and the channels were found to be leak-proof. Several tests were performed to characterize the bonding process including adhesive thickness analysis, adhesive removal analysis, bond strength analysis, reversibility test, re-packaging test, sterilization test, and lifetime test. The bonding approach has several advantages including room-temperature processing, reversibility, rapid 4-min bonding, a high process yield nearing 100%, and biocompatibility. Further, the use of low-cost glass substrates enables a cost-effective approach, disposability, and transparency. To demonstrate this method, fluid-delivery biochips were fabricated for an application involving tissue-culture. In this biosystem, the chemical stimuli used for stimulating tissue-engineered implants are delivered through these biochips. Using a computer controlled syringe pump, we automate and control flow rates and volumes of chemical stimuli flowing through the biochips, thus monitoring tissue growth.

Committee: Dr. Ian Papautsky (Advisor) Subjects:

PhD, University of Cincinnati, 2002, Engineering : Electrical Engineering

We have investigated the capability of focused ion beam (FIB) in the microfabrication of photonic devices. Novel liquid metal ion sources (LMIS) for FIB have been developed. With these LMIS, implantation-doping of different ion species into semiconductors for local modification of their electrical and photonic properties has been studied. FIB micromachining of semiconductors has also been investigated. Methods of micromilling of microgratings, photonic band-gap (PBG) structures, micromirrors, microlenses, Bragg type grating structures have been developed. An approach to form microstructures on an arbitrary angled facet has been invented. The application of FIB milling of microgratings has been pioneered, and a prototype of a wavelength-division multiplexing (WDM) demultiplexer utilizing the micrograting and optical fiber technologies has been demonstrated.

Committee: Dr. Andrew Steckl (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2011, Industrial and Systems Engineering

Microscale materials fabrication processes are necessary for many applications. Clean room techniques can be used to fabricate micro/nano scale device for biomedical applications, but they require masking and multiple steps as well as hazardous chemical reagents. One of the non-clean room techniques that achieves microscale resolution is laser ablation, specifically femtosecond laser ablation. Laser ablation by pulses with duration on the sub-picosecond or femtosecond time scales can remove materials with lower residual thermal effect, and the accuracy and quality of the device is often superior to conventional longer-pulse lasers. Also, it provides a convenient, economical and flexible way to fabricate programmable 3-dimensional patterns by varying the beam scanning speed during ablation as well as laser pulse energy. In addition, femtosecond laser ablation technique can be combined with other fabrication techniques as a primary or a post process. In this dissertation, femtosecond laser micromachining technique was employed for microscale functional device fabrication with different materials to support biomedical researches. Femtosecond laser and material interaction properties, such as ablation threshold fluence, and incubation coefficient, were experimentally study for the bovine cortical bone and ethylene glycol dimethylacrylate (EGDMA) polymer. Ablation features were also characterized. Developed femtosecond laser micromachining was then used to fabricate microscale device for biomedical applications. Micropillar on bovine cortical bone was made for micromechanical test purpose. Inlet/outlet microchannels were made on EGDMA polymer for cell loading. Array of microwells were patterned on blended electrospun poly(ε-caprolactone)/gelatin (PCL/gelatin) nanofiber scaffolds for tissue engineering application. Microchannels were made on electrospun poly(ε-caprolactone) (PCL) nanofiber scaffolds for vascular tissue engineering application. Sub-micron size of pores we (open full item for complete abstract)

Committee: Dave Farson (Advisor); John Lannutti (Committee Member); L. James Lee (Committee Member) Subjects: Industrial Engineering; Materials Science; Nanotechnology

Master of Science, The Ohio State University, 2009, Materials Science and Engineering

Bone is an anisotropic, hierarchically structured material, and as a result, its mechanical behavior is highly statistical in nature. It has been shown for other engineering materials that mechanical testing at the microscale enables characterization of individual microstructural components in an effort to understand their role in the macroscopic mechanical behavior. The application of such microscale testing to bone will permit modeling of the aggregate material to predict effects of age, disease, or injury on the mechanical properties, thus enabling a better understanding of the disease state.In the present work, dual focused ion beam (FIB) and femtosecond (FS) laser micromachining techniques are employed to produce microscale mechanical test specimens of bovine cortical bone on the order of 10 – 30 µm. A FIB is advantageous for micromachining pillars as it is capable of producing small scale features by applying a Ga+ ion beam that penetrates and removes the surrounding material. A FS laser uses ultrashort laser pulses to ablate the material by locally heating it to its vaporization temperature, creating a plasma that is dissipated into a flowing gas. The FS laser is advantageous for micromachining of biological materials because it may be used in ambient, non-vacuum environments, making it a flexible tool for machining the bone surface while preserving its microstructure. The short pulse duration minimizes thermal diffusion and heating of the surrounding material. Prior research suggests that FS laser machining causes very little residual damage to the surrounding bone tissue. Processing parameters and feasible specimen geometries and dimensions are discussed. The fabrication of such pillars allows for micromechanical compression testing of time independent behavior using a modified nanoindenter with a flat punch tip. By achieving successful fabrication of micron scale pillars, it is possible to test the constitutive mechanical properties of mineralized tissue t (open full item for complete abstract)

Committee: Katharine Flores PhD (Advisor); Heather Powell PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2007, Welding Engineering

Femtosecond laser ablation has interesting characteristics for micromachining, notably non-thermal interaction with materials, high peak intensity, precision and flexibility. In this dissertation, the potential of femtosecond laser ablation for fabrication of biomedical and electronic devices is studied. In a preliminary background discussion, some key literature regarding the basic physics and mechanisms that govern ultrafast laser pulse interaction with conductive materials and dielectric materials are summarized. In the dissertation work, results from systematic experiments were used characterize laser ablation of ITO (Indium Tin Oxide), stainless steel (hot embossing applications), polymers (PMMA, PDMS, PET, and PCL), glass, and fused quartz. Measured parameters and results include ablation threshold, damage threshold, surface roughness, single- and multiple-pulse ablation shapes and ablation efficiency. In addition to solid material, femtosecond laser light interaction with electrospun nano-fiber fiber mesh was analyzed and studied by optical property measurements. Ablation of channels in nano-fiber mesh was studied experimentally. Internal channel fabrication in glass and PMMA polymers was also demonstrated and studied experimentally. In summary, it is concluded that femtosecond laser ablation is a useful process for micromachining of materials to produce microfluidic channels commonly needed in biomedical devices such as micro-molecular magnetic separators and DNA stretching micro arrays. The surface roughness of ablated materials was found to be the primary issue for femtosecond laser fabrication of microfluid channels. Improved surface quality of channels by surface coating with HEMA polymer was demonstrated.

Committee: Dave Farson (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, Case Western Reserve University, 2012, Chemical Engineering

There are several applications necessitating a demand for new technologies for the micro fabrication of three dimensional work pieces in several fields including the semiconductor industry and microsystem technology. While lithographic processes can be used in the fabrication of electronic devices with high precision, the produced structures have low aspect ratio making them almost two dimensional. Micro Electrochemical machining with ultra-short voltage pulses (¿¿¿¿-EChM) is a method which allows well-defined machining of 3-dimensional structures with very high precision in the nanometer range. The primary goal of this contribution is to present a first principles theoretical model to account for the essential features of a ¿¿¿¿-EChM process. More specifically, and in marked contrast with other work published in the literature, our strategy relies on solving the transient transport differential equations that govern transport of solution phase species in the presence of an electric field together with Poisson's equation to yield self-consistent transient potential and concentration profiles. A model that accounts for the effect of the changing geometry due to the resulting dissolution has also been presented. The overall result is a functional, predictive theoretical model that reproduces the essential features of the observed experimental results which is the high resolution and precision through the localization of the driving overpotential. This work also provides a quantitative basis for the development of a functional ohmic microscope capable of generating in situ spatially-resolved images of heterogeneous electrode surfaces. This was done through verification of experimentally obtained potential distribution with both analytical and numerical models. This work also proposes mechanisms to account for unique features observed in polarization curves acquired with a rotating disk electrode for the electrooxidation of hydroxylamine, NH2OH, on Au. A quantitative (open full item for complete abstract)

Committee: Daniel Scherson PhD (Advisor) Subjects: Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2013, Industrial and Systems Engineering

Conventional micromachining methods often require the use of complex facilities, templates and repeated mechanical alignments. These methods are essentially 2.5D processes. This research is to establish a cost-effective, high precision, 3D micromachining method with high flexibility. To this end, a combination of ultraprecision micromachining and high volume replication methods, such as microinjection molding and 3D photolithographic projection, was investigated. Preliminary study was conducted to investigate the 3D micromachining capability of 3D photolithographic projection method. A 3D microlens array was directly machined by the slow tool servo technique as the projection optic. Patterns on a mask were projected on the photoresist deposited on a curved substrate. After photolithography and thermal reflow process, 3D microlenses formed on the curved substrate. Numerical simulation and experiments were conducted to evaluate process parameters, and the 3D microlenses were evaluated through both geometrical measurements and optical testing, proving they are functional. The 3D photolithography projection method was then utilized to produce a functional device, which was used to control non-planar polymeric surface roughness y generating micro square arrays. Subsequent experimental results using a goniometer showed that this method could create functional microstructures for wettability control on steep curved substrates. The 3D micromachining capability of the microinjection molding method was also investigated. A 3D microlens array on a steep curved substrate was manufactured using this method. The corresponding injection molds were directly machined using a voice coil based fast tool servo technique. Injection molding process parameters were evaluated using both experimental results and numerical simulation. Additionally, both geometrical error and optical performance tests showed that the molded polymer microlens arrays could be used in wide angle imaging app (open full item for complete abstract)

Committee: Allen Yi (Advisor); Jose Castro (Committee Member); Betty Anderson (Committee Member) Subjects: Engineering

MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

Pulse electrochemical micromachining (PECMM) is an unconventional noncontact manufacturing method suitable for the production of micro sized components on a wide range of electrically conductive engineering materials such as metals, semiconductors, and metal matrix composites. Absence of tool wear is a major advantage expected of PECMM. However, tools are often chemically corroded by certain electrolytes used in PECMM. In this thesis a novel approach i.e. cryogenic treatment of in-house made microtools has been studied to reduce/eliminate tool wear in PECMM. An automated PECMM system has been designed and built in-house. A LabVIEW based process monitoring system has been developed for accurate gap control. An analytical model has been developed for the prediction of diameter of the tools produced by PECMM. Using this noncontact machining system ultra-high aspect ratio (400) tungsten microtools have been fabricated for wide range of applications from neural implants to deep micro hole drilling. Excessive wear was noticed during the application of these tools in the micromachining of difficult to machine tungsten carbide. Cryogenic treatment was performed on tungsten microtools to improve the corrosion resistance and obtain increased tool life in PECMM. Process parameters for the PECMM of tungsten carbide metal matric composite were established to ensure higher machining accuracy with lesser short circuits. By using optimum cryogenic cycle parameters, 200% increase in material removal rate, and 45% reduction in tool wear was achieved in the pulse electrochemical micromachining of tungsten carbide metal matrix composite using cryogenically treated microtools.

Committee: Sundaram Murali Meenakshi PhD (Committee Chair); Hongdao Huang PhD (Committee Member); Anil Mital PhD PE (Committee Member) Subjects: Mechanics