Microfluidic Channel Fabrication With Tailored Wall Roughness

Realistic random roughness of channel surfaces is known to affect the fluid flow behavior in microscale fluidic devices. This has relevance particularly for applications involving non-Newtonian fluids, such as biomedical lab-on-chip devices. In this study, a surface texturing process was developed and integrated into microfluidic channel fabrication. The process combines colloidal masking and Reactive Ion Etching (RIE) for generating random surfaces with desired roughness parameters on the micro/nanoscale. The surface texturing process was shown to be able to tailor the random surface roughness on quartz. A Large range of particle coverage (around 6% to 67%) was achieved using dip coating and drop casting methods using a polystyrene colloidal solution. A relation between the amplitude roughness, autocorrelation length, etch depth and particle coverage of the processed surface was built. Experimental results agreed reasonably well with model predictions. The processed substrate was further incorporated into microchannel fabrication. Final device with designed wall roughness was tested and proved a satisfying sealing performance.

Application of OLI Electrolyte Simulation to the Resolution of Corrosion Concerns Within a Reciprocating Compressor

A 38 MMSCF/D Cooper Bessemer Model LM-9 reciprocating compressor in hydrogen service at the Praxair Westlake LA facility has experienced notable particulate contamination within the feed gas. The particulates were believed to be caused by upstream piping corrosion; however, to definitely state the cause, the properties of the fluid existing in the five-stage compressor needed to be more fully understood. An OLI electrochemical simulation software was used for dew point prediction, determination of the condensed phase ionic equilibria, and corrosion rate prediction. These tasks were beyond capabilities of the site-licensed UniSim software, as presently configured. Specifically, the model was used to identify the dew point conditions (temperature, pressure) and properties of the condensed water (pH, corrosivity, dissolved O2, and chlorine speciation). Model results were compared with site inspection findings. Subsequently, recommended limits for chlorine and oxygen in the feed gas were established to improve long term compressor reliability.

Thin-Film PVDF Sensor Based Monitoring of Cutting Forces in Peripheral End Milling

A sensor module that integrates a thin film Polyvinylidene Fluoride (PVDF) piezoelectric strain sensor and an in situ data logging platform has been designed and implemented for monitoring of feed and transverse forces in the peripheral end milling process. The module, which is mounted on the tool shank, measures the dynamic strain(s) produced in the tool and logs the data into an on-board card for later retrieval. The close proximity between the signal source and the PVDF sensor(s) minimizes the attenuation and distortion of the signal along the transmitting path and provides high-fidelity signals. It also facilitates the employment of a first principles model based on Euler-Bernoulli beam theory and the constitutive equations of the piezoelectric sensor material to relate the in situ measured PVDF sensor signals to the feed and transverse forces acting on the tool. The PVDF sensor signals are found to compare well with the force signals measured by a platform type piezoelectric force dynamometer in peripheral end milling experiments.

Initial Investigation Into Helical Milling of Laminated Stacks of Electrical Steel

This paper serves to report the findings of an initial study on the holing of laminated stacks of electrical steels. Three different holing methods were considered: plunge milling, helical milling (orbit milling), and drilling. Stack delamination, axial thrust force, and burr formation were measured at various feed rates for each process and utilized as comparison metrics. Results from the initial experimental investigation indicate that drilling produces significant burr and plunge milling, whilst reducing burr formation compared to drilling, led to delamination of the stack. Helical milling minimized thrust forces, avoided delamination and minimized burr formation. An interesting spring back effect was also observed during the cutting of the laminated stacks. It is concluded that helical milling is a viable and effective processing method for making holes in laminated stack of hard electrical steels.

An Analysis of Polishing Forces in Magnetic Field Assisted Finishing

Magnetic field assisted finishing (MAF) is used to polish free-form surfaces. The material removal mechanism can be described as a flexible “magnetic brush” that consists of ferromagnetic particles and abrasives that arrange themselves in the working gap between the magnet and the work piece. Relative motion between the brush and the work piece causes micro-cutting and improves surface finish. In this study, the contributions of the magnetic and polishing force components to the total force were evaluated. The effect of varying the polishing conditions, such as the working gap and the size of the ferromagnetic iron particles, on polishing forces and surface roughness was also analyzed. It was observed that the polishing forces varied considerably with working gap. Also, the iron particle size was found to have a strong relation to the rate at which the surface roughness decreased. Surface area roughness of 2–3 nm was achieved.

AFM-Based Nanoindentation Process: A Comparative Study

Atomic force microscopy (AFM) has been widely used for nanomachining and fabrication of micro/nanodevices. This paper describes the development and validation of computational models for AFM-based nanomachining. Molecular Dynamics (MD) technique is used to model and simulate mechanical indentation at the nanoscale for different types of materials, including gold, copper, aluminum, and silicon. The simulation allows for the prediction of indentation forces at the interface between an indenter and a substrate. The effects of tip materials on machined surface are investigated. The material deformation and indentation geometry are extracted based on the final locations of the atoms, which have been displaced by the rigid tool. In addition to the modeling, an AFM was used to conduct actual indentation at the nanoscale, and provide measurements to which the MD simulation predictions can be compared. The MD simulation results show that surface and subsurface deformation found in the case of gold, copper and aluminum have the same pattern. However, aluminum has more surface deformation than other materials. Two different types of indenter tips including diamond and silicon tips were used in the model. More surface and subsurface deformation can be observed for the case of nanoindentation with diamond tip. The indentation forces at various depths of indentation were obtained. It can be concluded that indentation force increases as depth of indentation increases. Due to limitations on computational time, the quantitative values of the indentation force obtained from MD simulation are not comparable to the experimental results. However, the increasing trends of indentation force are the same for both simulation and experimental results.

Mixed Lubrication Model for Cold Rolling Considering the Inlet and Deformation Zones

A mixed lubrication model for cold rolling was developed by separating, according to common concepts, the domain of calculation into two zones: the inlet zone and the zone of plastic strip bulk deformation. The analysis of the inlet zone mainly focuses on film formation from different lubricants based on the evolution of layers consisting of neat oil on the metallic surfaces. In the zone of plastic strip bulk deformation, contributions of boundary and hydrodynamic friction are modeled incorporating longitudinal and transversal roughness components. Lubricant pressure, which is influenced by the geometry of these roughness structures, is governed by hydrodynamic mechanisms. Additionally, lubricant temperature in the roll bite is predicted by an integrated thermodynamics sub-model. While coupling between the inlet and plastic deformation zones is performed iteratively, the highly non-linear and coupled equations for the latter zone are solved simultaneously by applying a variant of the well-known damped Newton-Raphson method.

Remote Tool Health Monitoring Using Wireless Sensors on Rotational Machinery

A key concern in modern day manufacturing is developing a reliable method for monitoring tool health. This involves not only establishing a mathematical method for deriving tool failure, but also developing a reliable method for collecting and transmitting this information. This paper presents a reliable wireless network for collecting, analyzing, and predicting tool failure. The wireless network consists of three remote nodes and one coordinator node. Each remote node is mounted on a 1″ R8 mill tool holder and consists of three major components: an accelerometer, microcontroller, and wireless transceiver. These wireless nodes transmit the Z-axis acceleration (the machines vertical Z-axis) as seen by the tool holder back to a central computer. This computer utilizes LabVIEW in order to collect and analyze the acceleration data. The LabVIEW program also acts as a simple user interface for indicating states of tool failure, along with providing a means for publishing the information to the internet for process monitoring by remote users. The wireless network discussed in this paper is robust, inexpensive, and was found to reliably monitor and predict tool health conditions. The innovative aspect of this work is the ability to use commercial-off-the-shelf wireless sensors to remotely monitor multiple rotational machines from a single location on site and over the internet to off-site locations.

Finite Element Modeling of Pad Deformation due to Diamond Disc Conditioning in Chemical Mechanical Polishing (CMP)

Chemical mechanical planarization (CMP) is widely used to planarize and smooth the surface of semiconductor wafers. In CMP, diamond disc conditioning is traditionally employed to restore pad planarity and surface asperity. Pad deformation which occurs during conditioning affects the material removal mechanism of CMP since pad shape, stress and strain are related to cut rate during conditioning, pad wear rate and wafer material removal rate (MRR) during polishing. Available reports concerning the effect of diamond disc conditioning on pad deformation are based on simplified models of the pad and do not consider its microstructure. In this study, a two-dimensional (2-D) finite element analysis (FEA) model is proposed to analyze the interaction between the diamond disc conditioner and the polishing pad. To enhance modeling fidelity, image processing is utilized to characterize the morphological and mechanical properties of the pad. An FEA model of the characterized pad is developed and utilized to study the effects of process parameters (conditioning pressure and pad stiffness) on pad deformation. The study reveals that understanding the morphological and mechanical properties of CMP pads is important to the design of high performance pads.

Studying the Temperature Effect During the High-Pressure Phase Transformation of Silicon via Indentations

Micro-laser assisted machining (μ-LAM) is a novel micro/nano machining technique developed for ductile mode machining of ceramics and semiconductors. Ductile mode material removal is possible in a nominally brittle material due to the high-pressure phase transformation (HPPT) phenomenon during the machining process. This study isolates the pressure and temperature effect in the μ-LAM process. The μ-LAM process is unique whereby the pressure and temperature effect occur concurrently leading to the material removal process. The effect of temperature and thermal softening is studied via indentation tests using a cutting tool. In the precisely controlled indentation tests, laser heating is applied at various stages to determine the phase (i.e. atmospheric Si-I phase or high pressure phases that benefits most from the thermal softening effect. The indentation depths are measured and compared for each condition to identify the enhanced ductility of the nominally brittle material caused by the laser irradiation.