Research Papers

J. Micro Nano-Manuf. 2015;3(4):041001-041001-7. doi:10.1115/1.4030704.

Whirling is applied to machining of microscrews on thin wires. A micro whirling machine has been developed for this. In order to suppress the vibration of the workpiece, the wire is inserted in polyurethane tubes clamped on a metal bar. Frequency analyses have been conducted by loading impulse forces at the center of the wire. The dynamic response is improved with reducing the vibration in the clamping force by the developed clamping system. Thirty micrometers microgrooves have been machined on 0.3 mm diameter stainless steel wires with fine surface finish, with the developed machine tool.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041002-041002-8. doi:10.1115/1.4031135.

This paper is aimed at investigating the effects of graphene oxide platelet (GOP) geometry (i.e., lateral size and thickness) and oxygen functionalization on the cooling and lubrication performance of GOP colloidal suspensions. The techniques of thermal reduction and ultrasonic exfoliation were used to manufacture three different types of GOPs. For each of these three types of GOPs, colloidal solutions with GOP concentrations varying between 0.1 and 1 wt.% were evaluated for their dynamic viscosity, thermal conductivity, and micromachining performance. The ultrasonically exfoliated GOPs (with 2–3 graphene layers and lowest in-solution characteristic lateral length of 120 nm) appear to be the most favorable for micromachining applications. Even at the lowest concentration of 0.1 wt.%, they are capable of providing a 51% reduction in the cutting temperature and a 25% reduction in the surface roughness value over that of the baseline semisynthetic cutting fluid. For the thermally reduced GOPs (TR GOPs) (with 4–8 graphene layers and in-solution characteristic lateral length of 562–2780 nm), a concentration of 0.2 wt.% appears to be optimal. The findings suggest that the differences seen between the colloidal suspensions in terms of their droplet spreading, evaporation, and the subsequent GOP film-formation characteristics may be better indicators of their machining performance, as opposed to their bulk fluid properties.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041003-041003-9. doi:10.1115/1.4031136.

Part II of this paper is focused on studying the droplet spreading and the subsequent evaporation/film-formation characteristics of the graphene oxide colloidal solutions that were benchmarked in Part I. A high-speed imaging investigation was conducted to study the impingement dynamics of the colloidal solutions on a heated substrate. The spreading and evaporation characteristics of the fluids were then correlated with the corresponding temperature profiles and the subsequent formation of the residual graphene oxide film on the substrate. The findings reveal that the most important criterion dictating the machining performance of these colloidal solutions is the ability to form uniform, submicron thick films of graphene oxide upon evaporation of the carrier fluid. Colloidal suspensions of ultrasonically exfoliated graphene oxide at concentrations < 0.5 wt.% are best suited for micromachining applications since they are seen to produce such films. The use of thermally reduced (TR) graphene oxide suspensions at concentrations < 0.5 wt.% results in nonuniform films with thickness variations in the 0–5 μm range, which are responsible for the fluctuations seen in the cutting force and temperatures. At concentrations ≥ 0.5 wt.%, both the TR and ultrasonically exfoliated graphene oxide solutions result in thicker and nonuniform films that are detrimental for machining results. The findings of this study reveal that the characterization of the residual graphene oxide film left behind on a heated substrate may be an efficient technique to evaluate different graphene oxide colloidal solutions for cutting fluids applications in micromachining.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041004-041004-11. doi:10.1115/1.4031382.

Wrinkling of thin films is a strain-driven process that enables scalable and low-cost fabrication of periodic micro- and nano-scale patterns. In the past, single-period sinusoidal wrinkles have been applied for thin-film metrology and microfluidics applications. However, real-world adoption of this process beyond these specific applications is limited by the inability to predictively fabricate a variety of complex functional patterns. This is primarily due to the inability of current tools and techniques to provide the means for applying large, accurate, and nonequal biaxial strains. For example, the existing biaxial tensile stages are inappropriate because they are too large to fit within the vacuum chambers that are required for thin-film deposition/growth during wrinkling. Herein, we have designed a compact biaxial tensile stage that enables (i) applying large and accurate strains to elastomeric films and (ii) in situ visualization of wrinkle formation. This stage enables one to stretch a 37.5 mm long film by 33.5% with a strain resolution of 0.027% and maintains a registration accuracy of 7 μm over repeated registrations of the stage to a custom-assembled vision system. Herein, we also demonstrate the utility of the stage in (i) studying the wrinkling process and (ii) fabricating complex wrinkled patterns that are inaccessible via other techniques. Specifically, we demonstrate that (i) spatial nonuniformity in the patterns is limited to 6.5%, (ii) one-dimensional (1D) single-period wrinkles of nominal period 2.3 μm transition into the period-doubled mode when the compressive strain due to prestretch release of plasma-oxidized polydimethylsiloxane (PDMS) film exceeds ∼18%, and (iii) asymmetric two-dimensional (2D) wrinkles can be fabricated by tuning the strain state and/or the actuation path, i.e., the strain history. Thus, this tensile stage opens up the design space for fabricating and tuning complex wrinkled patterns and enables extracting empirical process knowledge via in situ visualization of wrinkle formation.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041005-041005-6. doi:10.1115/1.4031491.

Product miniaturization has become a trending technology in a broad range of industries and its development is being pushed by the requirements for complexity and resolution of micromanufactured products. However, there still exists a gap in the manufacturing spectrum for complex three-dimensional (3D) structure generation capabilities with micron and submicron resolution. This paper extends the near-field electrospinning (NFES) process and develops a direct-writing (DW) technology for microfiber deposition with micrometer resolution. The proposed method presented uses an auxiliary electrode to generate an electric field perpendicular to the fiber flight path. This tunable electric field grants the user real-time control of the fiber flight path, increasing the resolution of the deposited structure. The use of an auxiliary electrode ring for fiber manipulation is proposed to further improve control over the deposition process.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041006-041006-10. doi:10.1115/1.4031462.

A new three-dimensional (3D) printing process designated as shockwave-induced freeform technique (SWIFT) is explored for fabricating microparts from nanopowders. SWIFT consists of generating shockwaves using a laser beam, applying these shocks to pressure sinter nanoparticles at room temperature, and creating structures and devices by the traditional layer-by-layer formation. Shockwave cold compaction of nanoscale powders has the capability to overcome limitations, such as shrinkage, porosity, rough surface, and wide tolerance, normally encountered in hot sintering processes, such as selective laser sintering. In this study, the window of operating parameters and the underlying physics of SWIFT were investigated using a high-energy Q-switched Nd: YAG laser and nanodiamond (ND) powders. Results indicate the potential of SWIFT for fabricating high-performance diamond microtools with high aspect ratios, smooth surfaces, and sharp edges. The drawback is that the SWIFT process does not work for micro-sized powders.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041007-041007-12. doi:10.1115/1.4031492.

This paper presents a computational approach for simulating the motion of nanofibers during fiber-filled composites processing. A finite element-based Brownian dynamics simulation (BDS) is proposed to solve for the motion of nanofibers suspended within a viscous fluid. We employ a Langevin approach to account for both hydrodynamic and Brownian effects. The finite element method (FEM) is used to compute the hydrodynamic force and torque exerted from the surrounding fluid. The Brownian force and torque are regarded as the random thermal disturbing effects which are modeled as a Gaussian process. Our approach seeks solutions using an iterative Newton–Raphson method for a fiber's linear and angular velocities such that the net forces and torques, including both hydrodynamic and Brownian effects, acting on the fiber are zero. In the Newton–Raphson method, the analytical Jacobian matrix is derived from our finite element model. Fiber motion is then computed with a Runge–Kutta method to update fiber position and orientation as a function of time. Instead of remeshing the fluid domain as a fiber migrates, the essential boundary condition is transformed on the boundary of the fluid domain, so the tedious process of updating the stiffness matrix of finite element model is avoided. Since the Brownian disturbance from the surrounding fluid molecules is a stochastic process, Monte Carlo simulation is used to evaluate a large quantity of motions of a single fiber associated with different random Brownian forces and torques. The final fiber motion is obtained by averaging numerous fiber motion paths. Examples of fiber motions with various Péclet numbers are presented in this paper. The proposed computational methodology may be used to gain insight on how to control fiber orientation in micro- and nanopolymer composite suspensions in order to obtain the best engineered products.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2015;3(4):041008-041008-8. doi:10.1115/1.4031666.

A novel method of using atomized dielectric spray in micro-electric discharge machining (EDM) (spray-EDM) to reduce the consumption of dielectric is developed in this study. The atomized dielectric droplets form a moving dielectric film up on impinging the work surface that penetrates the interelectrode gap and acts as a single phase dielectric medium between the electrodes and also effectively removes the debris particles from the discharge zone. Single-discharge micro-EDM experiments are performed using three different dielectric supply methods, viz., conventional wet-EDM (electrodes submerged in dielectric medium), dry-EDM, and spray-EDM in order to compare the processes based on material removal, tool electrode wear, and flushing of debris from the interelectrode gap across a range of discharge energies. It is observed that spray-EDM produces higher material removal compared to the other two methods for all combinations of discharge parameters used in the study. The tool electrode wear using atomized dielectric is significantly better than dry-EDM and comparable to that observed in wet-EDM. The percentage of debris particles deposited within a distance of 100 μm from the center of EDM crater is also significantly reduced using the spray-EDM technique.

Commentary by Dr. Valentin Fuster

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