R. Ryan Vallance

Micro machining glass with polycrystalline diamond tools shaped by micro electro discharge machining

Brittle materials are difficult to mechanically micro machine due to damage resulting from material removal by brittle fracture, cutting force-induced tool deflection or breakage and tool wear. This paper demonstrates the feasibility of micro machining glass materials with polycrystalline diamond (PCD) micro tools that are prepared in a variety of shapes using non-contact micro electro discharge machining. The PCD tools contain randomly distributed sharp protrusions of diamond with dimensions around 1 µm that serve as cutting edges for micro machining grooves in soda-lime glass and pockets in ultra-low expansion glass. Results indicate that smooth surfaces are obtained with process conditions allowing material removal by ductile regime cutting instead of brittle fractures, and the PCD tools show very little wear. With further improvements in material removal rate, micro machining with PCD tools is a promising approach for producing micro molds and micro fluidic devices in glass materials.

Characterizing field emission from individual carbon nanotubes at small distances

This article demonstrates the characterization of field emission from individual carbon nanotubes (CNTs) attached to a tungsten tip, when the separation distance s between the anode and tip of the CNT (cathode) is less than 15μm. The separation distance is adjusted with a nanopositioning stage after establishing a datum by detecting the anode surface with the CNT tip. Our separation distance s differs by the height h of the CNT from the distance d that is often measured between the planar anode and the planar substrate of an emitting cathode. Consequently, the electric field at the tip of the CNT is modeled by F=λV∕s, where λ is our field amplification factor, rather than by F=γV∕d, where γ is the more conventional field enhancement factor. Twenty-four sets of current-voltage I(V) data were measured from an individual multiwall CNT at separation distances s between 1.4 and 13.5μm. A nonlinear curve-fitting algorithm extracted Fowler-Nordheim (FN) parameters from each set of I(V) data, rather than conventi...

Nanometer-Level Comparison of Three Spindle Error Motion Separation Techniques

This work demonstrates the state of the art capabilities of three error separation techniques for nanometer-level measurement of precision spindles and rotationally-symmetric artifacts. Donaldson reversal is compared to a multi-probe and a multi-step technique using a series of measurements carried out on a precision aerostatic spindle with a lapped spherical artifact. The results indicate that subnanometer features in both spindle error motion and artifact form are reliably resolved by all three techniques. Furthermore, the numerical error values agree to better than one nanometer. The paper discusses several issues that must be considered when planning spindle or artifact measurements at the nanometer level.

Micro-machining and micro-grinding with tools fabricated by micro electro-discharge machining

This paper provides an overview of several approaches to micro-machining by mechanical and electro-discharge means of material removal. Two steps are required in machining micro features. Firstly, a custom-shaped tool is created from suitable stock. In many cases, this is carried out using a small-scale version of wire Electro-Discharge Machining (EDM) in tool materials such as sintered PolyCrystalline Diamond (PCD) or tungsten carbide. Then the micro-tool can be used as a miniature end mill, drill or abrasive wheel. Each of these mechanical machining methods can be combined with EDM to achieve a customisable surface finish and feature accuracy. Trade-offs such as tool wear, Material Removal Rate (MRR) and machining time are discussed in this paper within the context of several examples.

Nano-Scale Machining Via Electron Beam and Laser Processing

It is recently conceptualized that nano-scale machining might be achieved by coupling electron emission with radiation transfer. A laser may be used to heat a workpiece to a threshold temperature, and a nano-probe might then transfer additional energy via electron emission to remove a minute amount of material To investigate this hypothesis, a detailed numerical study is presented. The electron-beam transport is modeled using a Monte Carlo approach, and a radiation transfer model that includes Fresnel reflections is adapted to simulate laser heating. The numerical study suggests that approximately 0.5 W from a single electron-beam is sufficient to initialise local evaporation from a gold film. With the use of a laser, the required power can be halved if the film is sufficiently thin. This paper describes the details of the numerical study and establishes guidelines for such naon-scale machining processes.

Stiffness of desiccating insect wings

The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be a significant aid in planning experiments as well as interpreting data from such experiments. This communication presents a comprehensive experimental analysis of the change in mass and stiffness of gradually desiccating forewings of Painted Lady butterflies (Vanessa cardui). Mass and stiffness of the forewings of five butterflies were simultaneously measured every 10 min over a 24 h period. The averaged results show that wing mass declined exponentially by 21.1% over this time period with a time constant of 9.8 h, while wing stiffness increased linearly by 46.2% at a rate of 23.4 µN mm(-1) h(-1). For the forewings of a single butterfly, the experiment was performed over a period of 1 week, and the results show that wing mass declined exponentially by 52.2% with a time constant of 30.2 h until it reached a steady-state level of 2.00 mg, while wing stiffness increased exponentially by 90.7% until it reached a steady-state level of 1.70 mN mm(-1).

Effects of Spherical Targets on Capacitive Displacement Measurements

Capacitive displacement sensors are widely used in precision manufacturing and metrology because they measure displacements with nanometer resolution. Prior literature usually treats capacitive sensors consisting of electrodes arranged as parallel plates. In this work, the target electrode is spherical, which is common in machine tool metrology, spindle metrology, and the measurement of sphericity. The capacitance due to a gap between flat and spherical electrodes is less than that of two flat electrodes, which causes four effects. As the diameter of the target electrode is reduced, the sensitivity increases, the sensing range decreases, the sensing range shifts toward the target, and the sensor becomes nonlinear. This paper demonstrates and quantifies these effects for a representative capacitive sensor, using finite element analysis and experimental testing. For larger spheres, the effects are correctible with apparent sensitivities, but measurements with the smallest spheres become increasingly nonlinear and inaccurate.

A COMBINED EXPERIMENTAL-NUMERICAL STUDY OF THE ROLE OF WING FLEXIBILITY IN INSECT FLIGHT

An integrated program of research aimed at understanding wing flexibility and its implications for flight in insects is described. The experimental component of the research involves quantitative, high-speed videogrammetry of insects in free flight along with measurements of the mass and structural properties of the insect body and wings. The computational component of the research is centered on high-fidelity, flow and flowstructure interaction (FSI) modeling of insects in flight. The experiments provide data for the parameterization as well as the validation of the computational models.

Micro-tool characterization using scanning white light interferometry

Micro-electro-discharge machining produces tools for micro-machining processes with diameters down to 3 ?m and lengths up to fifty times their diameter. This paper describes a metrology technique for characterizing the geometry of these tools by the standardized components of roughness, waviness and form. In this technique two-dimensional (2D) profiles are extracted from three-dimensional (3D) surface measurements acquired by scanning white light interferometry with height resolution below 1 nm. The profiles are transformed into the frequency domain and separated into form (wavelengths longer than 100 ?m), waviness (wavelengths between 10 ?m and 100 ?m) and roughness (wavelengths shorter than 10 ?m). Standard height and shape parameters are computed from the roughness, waviness and form profiles for 81 tools, enabling relative comparison of tool geometry in a quantitative and reproducible manner. This approach provides a more comprehensive quantification of geometry than alternatives such as measuring the diameter at a few points along the tool or scanning probe microscopy over small areas. The utility of the technique is demonstrated by characterizing the precision of three micro-tools produced by wire electro-discharge grinding (WEDG).

Predicting surface figure in diamond turned calcium fluoride using in-process force measurement

Single crystal calcium fluoride (CaF2) shows significant variation in material properties as a function of crystallographic orientation. The surfaces generated by material removal processes such as diamond turning are influenced by this anisotropy and consequently show periodic undulations aligned with the crystal structure. This article explores the relationship between surface figure and cutting forces measured during the diamond turning of single crystal calcium fluoride. The cutting forces, when mapped to the physical geometry of CaF2 plano (flat) optics, show good correlation with surface figure measured by interferometry. A model is presented to predict the surface figure error from the experimentally measured normal component of the cutting force. The model also shows how the surface figure obtained under various machining parameters may be extrapolated from force measurements made during a single diamond turning operation.