Rapid investment casting: direct and indirect approaches via fused deposition modelling

Investment casting (IC) offers an economical method for mass producing complex, shaped metal parts. However, high tooling cost and lead times associated with the fabrication of metal moulds for producing IC wax (sacrificial) patterns result in cost justification problems for customised single casting, small- and medium-quantity production. Rapid prototyping (RP) techniques can reduce the costs associated with single-part or small-quantity production as they can be applied to the fabrication of sacrificial IC patterns containing complex and intricate designs with significant cost and lead-time savings. In this project, a benchmark model is designed to assess the fused deposition modelling (FDM) process for creating sacrificial IC patterns. In addition, an indirect approach toward producing wax patterns via silicone rubber moulding is investigated. Cost and lead time comparisons between the two IC pattern production methods were carried out and presented. The dimensional accuracies of metal castings generated from the RP-produced patterns are also presented.     

Compact multiphoton/single photon laser scanning microscope for spectral imaging and fluorescence lifetime imaging

An inverted fluorescence microscope was upgraded into a compact three-dimensional laser scanning microscope (LSM) of 65 x 62 x 48 cm dimensions by means of a fast kHz galvoscanner unit, a piezodriven z-stage, and a picosecond (ps) 50 MHz laser diode at 405 nm. In addition, compact turn-key near infrared femtosecond lasers have been employed to perform multiphoton fluorescence and second harmonic generation (SHG) microscopy. To expand the features of the compact LSM, a time-correlated single photon counting unit as well as a Sagnac interferometer have been added to realize fluorescence lifetime imaging (FLIM) and spectral imaging. Using this unique five-dimensional microscope, TauMap, single-photon excited (SPE), and two-photon excited (TPE) cellular fluorescence as well as intratissue autofluorescence of water plant leaves have been investigated with submicron spatial resolution, <270 ps temporal resolution, and 10 nm spectral resolution.     

High-resolution wide-field surface plasmon microscopy

This paper describes the application of a Köhler illuminated high‐resolution wide‐field microscope using surface plasmons to provide the image contrast. The response of the microscope to a grating structure in both the Fourier and the image planes is presented to demonstrate image formation by surface waves. The effect of spatial filtering in the back focal (Fourier) plane to enhance image constrast is described. We also discuss how the surface wave contrast mechanism affects the imaging performance of the microscope and discuss factors that can be expected to lead to even greater improvements in lateral resolution and sensitivity.     

Characterization of crystallographic properties of SMC poly Si using electron backscattered diffraction

Crystallographic properties of silicide mediated crystallization (SMC) polycrystalline silicon (poly Si) and excimer laser annealing (ELA) poly Si were studied by electron backscattered diffraction. Large‐grain sized poly Si with a large fraction of low‐angle grain boundaries was acquired by SMC, and small‐grain sized poly Si with high‐angle grain boundaries especially around 60° was acquired by ELA. The thin film transistor (TFT) device characteristics were investigated in view of short‐range crystallinity (pattern quality) and long‐range crystallinity (misorientation distribution) of the specimens. Short‐range crystallinity did not significantly affect the TFT device characteristics, and long‐range crystallinity considering the low energy level of special boundaries could be better related to the TFT device characteristics of poly Si.     

Minimizing photobleaching during confocal microscopy of fluorescent probes bound to chromatin: role of anoxia and photon flux

Exposure to light can destroy the ability of a molecule to fluoresce. Such photobleaching limits the use of fluorescence and confocal microscopy in biological studies. Loss of fluorescence decreases the signal‐to‐noise ratio and so image resolution; it also prevents the acquisition of meaningful data late during repeated scanning (e.g. when collecting three‐dimensional images). The aim of this work was to investigate the role of oxygen in the photobleaching of fluorophores bound to DNA in fixed cells, and to explore whether anoxia could minimize such bleaching. Anoxia significantly reduced bleaching rates and changed the order of reaction of both propidium iodide (an intercalator) and chromomycin A₃ (a minor‐groove binder) bound to DNA; it afforded the greatest protection at low photon fluxes. However, it had no effect on the bleaching of the green fluorescent protein (GFP) covalently attached to a histone and so bound to DNA, probably because the protein shielded the chromophore from oxygen. Bleaching of all three fluorophores depended on photon flux. Practical ways of minimizing bleaching were examined, and examples of three‐dimensional images of DNA marked by propidium and GFP (collected under standard and optimized conditions) are presented.     

Image calibration in fluorescence microscopy

A fluorescence image calibration method is presented based on the use of standardized uniformly fluorescing reference layers. It is demonstrated to be effective for the correction of non‐uniform imaging characteristics across the image (shading correction) as well as for relating fluorescence intensities between images taken with different microscopes or imaging conditions. The variation of the illumination intensity over the image can be determined on the basis of the uniform bleaching characteristics of the layers. This permits correction for the latter and makes bleach‐rate‐related imaging practical. The significant potential of these layers for calibration in quantitative fluorescence microscopy is illustrated with a series of applications. As the illumination and imaging properties of a microscope can be evaluated separately, the methods presented are also valuable for general microscope testing and characterization.     

Numerical and experimental analysis of aerostatic thrust bearings with porous restrictors

The finite element method is used to predict the performance of aerostatic thrust bearings with a complete porous surface. Results obtained by a 1D and 3D source flow model derived from D’Arcy’s law are compared for rectangular porous bearings having an infinite width. It turns out that the 1D source flow model is adequate for practical design parameters. For a circular aerostatic porous thrust bearing results calculated with several mathematical models for the source flow and slip flow are compared with experimental results. A relatively simple model incorporating unflatness and deformation of the bearing surface correlates well with the experimentally determined bearing performance.     

A Parametric Study of Beam Steering for Ultrasonic Linear Phased Array Transducer

All the parameters of a linear phased array may affect the performance and cost of the ultrasonic inspection system. The characteristic of the acoustic field for an array transducer is the most important factor whether the echo information of the inspected area in a specimen can be obtained and utilized effectively, and it is the main basis of designing a phased array. A mathematical model was presented to simulate the characteristic of an acoustic field radiated from an ultrasonic linear phased array on the basis of Huygens' principle. Based on the model, the beam directivity function can be obtained, and the effects of inter-element spacing, number of elements, element width, and transducer center frequency on beam directivity and steerability in a linear phased array transducer are systematically discussed.     

Modelling and experimental investigation of spindle and cutter dynamics for a high-precision machining center

The geometric quality of high-precision parts is highly dependent on the dynamic performance of the entire machining system, which is determined by the interrelated dynamics of machine tool mechanical structure and cutting process. This performance is of great importance in advanced, high-precision manufacturing processes, including aerospace and biomedical applications. In this paper, the dynamics of the combined spindle/cutter system, a major component of any machine tool, is identified using impact testing techniques and is successfully approximated by a second-order linear model. Results of computer simulations of machining processes that include the identified spindle/cutter dynamics show a significant influence on the quality of the final product. From this, it is concluded that, for precision workpieces, the dynamics of the spindle and cutter system will have to be taken into account in order to improve future machining controls and processes.     

金刚石加工金属基复合材料部件

在轻质、韧性的金属基体中加入硬质、脆弱材料而制成的金属基复合材料,具有高比强度。在加工这类材料时,硬质、脆性相容易带来一系列有关表面粗糙度和快速切削磨损的问题。针对这些问题,从聚晶金刚石和金刚石研磨工具两个方面,说明了超硬工具如何有效而经济地加工多种金属基复合材料部件。