Analysis of thermal errors in a high-speed micro-milling spindle

Thermally induced errors account for the majority of fabrication accuracy loss in an uncompensated machine tool. This issue is particularly relevant in the micro-machining arena due to the comparable size of thermal errors and the characteristic dimensions of the parts under fabrication. A spindle of a micro-milling machine tool is one of the main sources of thermal errors. Other sources of thermal errors include drive elements like linear motors and bearings, the machining process itself and external thermal influences such as variation in ambient temperature. The basic strategy for alleviating the magnitude of these thermal errors can be achieved by thermal desensitization, control and compensation within the machine tool.This paper describes a spindle growth compensation scheme that aims towards reducing its thermally-induced machining errors. The implementation of this scheme is simple in nature and it can be easily and quickly executed in an industrial environment with minimal investment of manpower and component modifications.Initially a finite element analysis (FEA) is conducted on the spindle assembly. This FEA correlates the temperature rise, due to heating from the spindle bearings and the motor, to the resulting structural deformation. Additionally, the structural deformation of the spindle along with temperature change at its various critical points is experimentally obtained by a system of thermocouples and capacitance gages.The experimental values of the temperature changes and the structural deformation of the spindle qualitatively agree well with the results obtained by FEA. Consequently, a thermal displacement model of the high-speed micro-milling spindle is formulated from the previously obtained experimental results that effectively predict the spindle displacement under varying spindle speeds. The implementation of this model in the machine tool under investigation is expected to reduce its thermally induced spindle displacement by 80%, from 6 microns to less than 1 micron in a randomly generated test with varying spindle speeds.     

Regulation of Reproduction in the Primitively Eusocial Wasp <Emphasis Type=Italic>Ropalidia marginata</Emphasis>: on the Trail of the Queen Pheromone

Queens and workers are not morphologically differentiated in the primitively eusocial wasp, Ropalidia marginata. Upon removal of the queen, one of the workers becomes extremely aggressive, but immediately drops her aggression if the queen is returned. If the queen is not returned, this hyper-aggressive individual, the potential queen (PQ), will develop her ovaries, lose her hyper-aggression, and become the next colony queen. Because of the non-aggressive nature of the queen, and because the PQ loses her aggression by the time she starts laying eggs, we hypothesized that regulation of worker reproduction in R. marginata is mediated by pheromones rather than by physical aggression. Based on the immediate loss of aggression by the PQ upon return of the queen, we developed a bioassay to test whether the queen’s Dufour’s gland is, at least, one of the sources of the queen pheromone. Macerates of the queen’s Dufour’s gland, but not that of the worker’s Dufour’s gland, mimic the queen in making the PQ decrease her aggression. We also correctly distinguished queens and workers of R. marginata nests by a discriminant function analysis based on the chemical composition of their respective Dufour’s glands.     

Sulfur Nanoparticles Synthesis and Characterization from H2S Gas, Using Novel Biodegradable Iron Chelates in W/O Microemulsion

Sulfur nanoparticles were synthesized from hazardous H₂S gas using novel biodegradable iron chelates in w/o microemulsion system. Fe³⁺–malic acid chelate (0.05 M aqueous solution) was studied in w/o microemulsion containing cyclohexane, Triton X-100 and n-hexanol as oil phase, surfactant, co-surfactant, respectively, for catalytic oxidation of H₂S gas at ambient conditions of temperature, pressure, and neutral pH. The structural features of sulfur nanoparticles have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), diffused reflectance infra-red Fourier transform technique, and BET surface area measurements. XRD analysis indicates the presence of α-sulfur. TEM analysis shows that the morphology of sulfur nanoparticles synthesized in w/o microemulsion system is nearly uniform in size (average particle size 10 nm) and narrow particle size distribution (in range of 5–15 nm) as compared to that in aqueous surfactant systems. The EDS analysis indicated high purity of sulfur (>99%). Moreover, sulfur nanoparticles synthesized in w/o microemulsion system exhibit higher antimicrobial activity (against bacteria, yeast, and fungi) than that of colloidal sulfur.     

Microstructure and mechanical properties of Al2O3 matrix nanocomposites produced by solid state precipitation

A novel and economical processing route for the production of Al₂O₃-based ceramic nanocomposites via solid solution–precipitation is reported. Dense (>98% ρ_th) and homogeneous solid solutions of 10 wt.% Fe₂O₃ in Al₂O₃ were produced by pressureless sintering at 1450 °C in air. Aging of the solid solutions in a reducing atmosphere at temperatures in the range 1250–1550 °C for different durations (up to 50 h) resulted in the precipitation of FeAl₂O₄ as second phase particles throughout the bulk of the samples. The optimum aging schedule resulted in a final microstructure comprising nano-sized (～100 nm) intragranular FeAl₂O₄ particles, along with coarser micro-sized particles on the matrix grain boundaries and triple point corners. Additionally, surface layers containing metallic Fe and with thicknesses up to ～100 μm were formed due to the further reduction of FeAl₂O₄. After removal of this surface layer, the hybrid nano/microcomposites possessed improved fracture toughness (by ～40%) and flexural strength (by ～50%) with respect to monolithic Al₂O₃.     

Mechanically driven phase transformation in single phase Al62.5Cu25Fe12.5 quasi-crystals: Effect of milling intensity

In this work the effect of mechanical milling on the structure, thermal stability and hardness of single phase Al_62.5Cu₂₅Fe_12.5 icosahedral quasi-crystals has been investigated for different milling intensities. The results indicate that, irrespective of the milling intensity used, the quasi-crystals transform to a body-centered cubic (bcc) phase during milling. This transformation starts when the grain size of the QC phase is about 10 nm, which represents the critical grain size initiating the phase transformation. Upon heating the milled powder displays grain growth of the bcc phase at low temperatures, followed by transformation to the original icosahedral QC phase at higher temperatures. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the indentation hardness, which can be tuned within a wide range (7–10 GPa) as a function of the volume fractions of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by appropriate thermo-mechanical treatments.     

Synergistic Effects of Polybenzimidazole and Aramide on Enhancing Flame-Retardancy and Solubility

Aromatic and functional polymers with processibility derived from biobased starting materials are prerequisite considering sustainable society. Poly(2,5-benzimidazole)s are rigid-rod polymers to show ultrahigh thermal stability such as flame retardance, while usually suffer from poor solubility. Here, poly(benzimidazole-co-amide)s are synthesized from two biobased monomers, 3,4-diaminobenzoic acid and a semirigid comonomer, 4-aminohydrocinnamic acid. The copolymers with an amide composition of 80 mol% and higher are soluble in widely used polar solvents to fabricate the films keeping high flame retardance, which is comparable with popular high-performance polymers such as aromatic polyimides, polyetheretherketone, polyphenylene sulfide, etc.     

THERMOELASTIC INTERACTIONS WITHOUT ENERGY DISSIPATION IN AN UNBOUNDED MEDIUM WITH A SPHERICAL CAVITY DUE TO A THERMAL SHOCK AT THE BOUNDARY

Thermoelastic interactions without energy dissipation in an unbounded elastic medium with a spherical cavity have been investigated. The cavity surface is assumed to be stress free and is subjected to a thermal shock. The solutions for displacement, temperature, and stresses are obtained using the Laplace transform procedure. The discontinuities of the distributions of the physical quantities are determined and compared with earlier findings. The inversions are also carried out with a numerical method based on Fourier series expansions of functions. The results are compared with the corresponding results obtained in cases of conventional thermoelasticity theory and the generalized theories of thermoelasticity with thermal relaxation time parameters.     

On the Fundamental Solutions of Generalized Thermoelasticity with Three Phase-Lags

The aim of the present work is to derive the fundamental solutions in the linear theory of generalized thermoelasticity with three phase-lags, recently introduced by Roychoudhuri (2007). We consider the case of homogeneous and isotropic bodies and present a solution of the Galerkin-type of field equations. The solution is then used to determine the effects of concentrated loads and heat sources in an unbounded medium. The fundamental solutions of the field equations in case of steady vibrations are also derived.     

Steady boundary layer slip flow and heat transfer over a flat porous plate embedded in a porous media

A mathematical model is presented for analyzing the boundary layer forced convective flow and heat transfer of an incompressible fluid past a porous plate embedded in a Darcy porous medium. Velocity and thermal slips are considered instead of no-slip conditions at the boundary. The similarity solutions for the problem are obtained and the reduced nonlinear ordinary differential equations are solved numerically. In case of porous plate, fluid velocity increases whereas non-dimensional temperature decreases for increasing values of suction parameter but it increases with increasing blowing parameter. Our analysis reveals that the increase of velocity slip parameter reduces the momentum boundary layer thickness and also enhances the heat transfer from the plate. On the other hand, heat transfer decreases with thermal slip parameter.     

Optimization of extraction process for phenolic acids from black cohosh (Cimicifuga racemosa) by pressurized liquid extraction

An investigation to optimize the extraction of phenolic acids from black cohosh using a pressurized liquid extractor system was studied with the aim of developing a generalized approach for sample preparation of phenolic compounds from plant matrices. Operating parameters such as solvent composition, solid‐to‐solvent ratio, temperature, particle size distribution, and number of extraction cycles were identified as main variables that influence extraction efficiency. A mixture of methanol and water (60:40 v/v) was found to be the best solvent for total phenolics (TP) and individual phenolic acids. The four phenolic acids extracted from black cohosh were identified by HPLC and LC‐MS as caffeic acid, ferulic acid, sinapic acid and isoferulic acid. Over 96% of the measured phenolics were extracted in first two cycles. The extraction efficiency for black cohosh with MeOH:H₂O (60:40 v/v) was found to be maximum at a solid‐to‐solvent ratio of 80 mg ml^?1. TP content of the extract was found to increase with temperature up to 90 °C. Particle size was found to have a large impact on extraction efficiency of TP. Samples with particle size between 0.25 mm and 0.425 mm provided optimum extraction of phenolics from black cohosh. Published in 2005 for SCI by John Wiley & Sons, Ltd.