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Research Papers

J. Micro Nano-Manuf. 2015;4(1):011001-011001-10. doi:10.1115/1.4031461.

Kinetic Monte Carlo (KMC) is regarded as an efficient tool for rare event simulation and has been applied in simulating bottom–up self-assembly processes of nanomanufacturing. Yet it has limitations to simulate top–down processes. In this paper, a new and generalized KMC mechanism, called controlled KMC or controlled KMC (cKMC), is proposed to simulate complete physical and chemical processes. This generalization is enabled by the introduction of controlled events. In contrast to the traditional self-assembly events in KMC, controlled events occur at certain times, locations, or directions, which allows all events to be modeled. A formal model of cKMC is also presented to show the generalization. The applications of cKMC to several top–down and bottom–up processes are demonstrated.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):011002-011002-9. doi:10.1115/1.4031667.

Fracture in cutting of ductile as well as brittle materials can be characterized using parameters such as K, G, R, and J-integral; of these, R has been widely used. To accurately evaluate the contribution of fracture energy in total cutting energy, J-integral would provide a more comprehensive basis as it encompasses several fracture modes, material plasticity, and nonlinear behavior. Therefore, this work adopts J-integral to evaluate the contribution of fracture energy to the size effect during microcutting of AISI 1215 steel. The work uses explicit integration method within ansys/ls-dyna to simulate two-dimensional (2D) orthogonal microcutting. U- and V-shaped cutting edges were used to represent a sharp crack-tip and a blunt crack-tip, respectively. Considering several alternative contours around crack-tip, covering the plastic zone, J-integral was calculated. Upon benchmarking J-integral values with other simulations in the literature, the approach was adopted for microcutting simulations in this work. It is observed that J-integral increases with uncut chip thickness, whereas it decreases with cutting speed, rake angle, and tool edge radius. The term (J/t0) defines contribution of fracture to the size effect in terms of J-integral, which is in the range of 4–24% under various parametric conditions. The corresponding values of R were always found to lie above those of the J-integral indicating that J-integral is relatively more appropriate parameter to quantify the fracture energy during microcutting.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):011003-011003-8. doi:10.1115/1.4031773.

In electrodischarge machining (EDM), the thermal energy causing material removal at the electrodes is given by the electrical energy supplied to the discharge. This electrical energy, also known as the discharge energy, can be obtained from time-transient voltage and current waveforms across the electrodes during a discharge. However, in micro-EDM, the interelectrode gaps are shorter causing the plasma resistance to be significantly smaller than other impedances in the circuit. As a result, the voltage and current waveforms obtained by a direct measurement may include voltage drop across the stray impedances in the circuit and may not accurately represent the exact voltage drop across micro-EDM plasma alone. Therefore, a model-based approach is presented in this paper to predict time-transient electrical characteristics of a micro-EDM discharge, such as plasma resistance, voltage, current, and discharge energy. A global modeling approach is employed to solve equations of mass and energy conservations, dynamics of the plasma growth, and the plasma current equation for obtaining a complete temporal description of the plasma during the discharge duration. The model is validated against single-discharge micro-EDM experiments and then used to study the effect of applied open gap voltage and interelectrode gap distance on the plasma resistance, voltage, current, and discharge energy. For open gap voltage in the range of 100–300 V and gap distance in the range of 0.5–6 μm, the model predicts the use of a higher open gap voltage and a higher gap distance to achieve a higher discharge energy.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):011004-011004-9. doi:10.1115/1.4031892.

Nanosecond laser machining of titanium has gained increased interest in recent years for a number of potential applications where part functionalities depend on features or surface structures with microscale dimensions. In particular, titanium is one of the materials of choice to sustain the demand for advanced and miniaturized components in the biomedical and aerospace sectors for instance. This is due to its inherent properties of high strength-to-weight ratio, corrosion resistance, and biocompatibility. However, in the nanosecond laser processing regime, the resolidification and deposition of material expelled from the generated craters can be detrimental to the achieved machined quality at such small scale. Thus, this paper focuses on the investigation of the laser–material interaction process in this pulse length regime as a function of both the delivered laser beam energy and the pulse duration in order to optimize machining quality and throughput. To achieve this, a simple theoretical model for simulating single pulse processing was developed and validated first. The model was then used to relate (1) the temperature evolution inside commercially pure titanium targets with (2) the morphology of the obtained craters. Using a single fiber laser system with a wavelength of 1064 nm, this analysis was conducted for pulse durations comprised between 25 ns and 220 ns and a range of fluence values from 14 J cm−2 and 56 J cm−2. One of the main conclusions from the study is that the generation of relatively clean single craters could be best achieved with a pulse length in the range of 85–140 ns when the delivered fluence leads to the maximum crater temperature being above but still relatively close to the vaporization threshold of the cpTi substrate. In addition, the lowest surface roughness in the case of laser milling operations could be obtained when the delivered single pulses did not lead to the vaporization threshold being reached.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):011005-011005-9. doi:10.1115/1.4031916.

In an effort to provide insights into the thermochemical composition of a microwave plasma chemical vapor deposition (MPCVD) reactor, the mole fraction of H2 is measured at various positions in the plasma sheath, at pressures of 10 and 30 Torr, and at plasma powers ranging from 300 to 700 W. A technique is developed by comparing the Q(1)01 transition of experimental and theoretical spectra aided by the Sandia CARSFT fitting routine. Results reveal that the mole fraction of H2 does not vary significantly from its theoretical mixture at the parametric conditions examined. Furthermore, the ν=1ν=2 vibrational hot band was searched, but no transitions were found. An analytical explanation for the increase in the temperature of H2 with the introduction of N2 and CH4 is also presented. Finally, because the mole fraction of H2 does not appear to deviate from the theoretical composition, the rotational and translational modes of H2 are shown to be approximately in equilibrium, and therefore, the rotational temperatures may be used to estimate the translational temperatures of H2.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):011006-011006-7. doi:10.1115/1.4032035.

This paper reports on design, fabrication, and characterization of a microfilter to be used in biomedical applications. The microfilter, with mesh of 80 μm, is fabricated by micro-injection molding process in polymeric material (polyoxymethylene (POM)) using a steel mold manufactured by micro-electrical discharge machining process. The characteristics of the filter are investigated by numerical simulation in order to define a suitable geometry for micro-injection molding. Then, different process configurations of parameters (melt temperature, injection velocity, mold temperature, holding pressure and time, cooling time, pressure limit) are tested in order to obtain the complete part filling via micro-injection molding process preventing any defects. Finally, the component is dimensionally characterized and the process parameters optimized to obtain the maximum filtration capacity.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(1):011007-011007-5. doi:10.1115/1.4032155.

Electrical discharge machining (EDM) is widely used to manufacture complex shaped dies, molds and critical parts in conductive materials. With the help of an assisting electrode (AE), EDM process can be used to machine nonconductive ceramics. This paper evaluates the mechanical properties of three high-performance nonconductive ceramics (ZrO2, Si3N4, and SiC) that have been machined with the EDM process using AE. Mechanical properties such as Vickers hardness (HV 0.3), surface roughness (Sq), and flexural strength of the machined and the nonmachined samples are compared. The EDM process causes decrease in Vickers hardness, increase in surface roughness, and decrease in flexural strength.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Micro Nano-Manuf. 2015;4(1):014501-014501-4. doi:10.1115/1.4031740.

The microsensors are mainly made with the single crystal silicon which requires expensive equipments and complicated process. Here, the micro-electroforming technology is used to fabricate the microresonant gas sensor. The fabricating process of the microresonant gas sensor is proposed. A microcantilever beam resonator 900 μm long, 300 μm wide, and 10 μm thick is fabricated. The resonant frequency shift is measured when exposed to ethanol vapor. Results show that the shift in the resonant frequency is approximately proportional to the ethanol vapor concentration, and the detection accuracy to ethanol vapor with the sensor is about 1 ppm per Hz frequency shift.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;4(1):014502-014502-4. doi:10.1115/1.4031739.

High density oxygen plasma-etching was applied to microtexturing onto the diamondlike carbon (DLC) films coated on the die-unit substrates. This mold-die unit with microtextured DLC coating was fixed into a cassette die for computer numerical control (CNC) stamping with the use of precise control both in loading and feeding the sheet materials. In particular, the pulsewise-motion control in stamping was employed to describe the effect of loading and unloading subsequences in the incremental motion on the microtexturing with reference to the normal loading motion. The macroscopic plastic deformation as well as the microscopic metal flow were studied to prove that the pulsewise-motion should be responsible for homogeneous duplication of microcavity patterns into a pure aluminum sheet with high aspect ratio.

Commentary by Dr. Valentin Fuster

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