<Emphasis Type="Bold">A Rapid Manufacturing Method for Water-Saving Emitters for Crop Irrigation Based on Rapid Prototyping and Manufacturing</Emphasis>

In order to build the complex built-in labyrinth design of an emitter which is a key element in water-saving devices, rapid prototyping and manufacturing (RP&M) is used to design the emitters and to manufacture corresponding rapid tooling (RT). Detailed CAD design of the emitter, CAD process design, and the generation of RT process modelling of the emitter have been carried out using parameterised design. Prototypes have been built using RP techniques to perform the rapid verification and modification of the emitter design; rapid tooling (RT) for the emitter has been fabricated using a metal spraying process to carry out trial-production. Finally, with the fabrication ofa precision mould as the basis, emitter mould design and manufacturing have been completed. As a result, the integration of design/verification/manufacturing of a mould and its products is realised.     

<Emphasis Type="Italic">Rapid Moulding Using Epoxy Tooling Resin</Emphasis>

Rapid prototyping (RP) is fast becoming a standard tool in today’s product design and manufacturing environment. Significant benefits in terms of lead time and cost savings have been reported with the use of RP technology. However, these benefits can be derived only during the design and planning stages of a new product where RP parts are produced in small quantities for design evaluation, form fitting, and marketing analysis. The high cost of raw material stock used in current RP systems makes them economically unsuitable even for small-batch production during the product evaluation and manufacturing stages. Further to this, the difference between the mechanical and physical properties of RP and traditional manufacturing materials limits the functionality of RP end products. Rapid tooling (RT) technology has opened up new cost-effective solutions for small-batch production. In this paper, a technique using a rapid soft-tooling approach, namely, aluminium filled epoxy resin tooling for injection mould preparation is successfully explored. An aluminium filled epoxy resin mould is evaluated and the characteristics of the injection-moulded end products are presented.     

<Emphasis Type="Italic">Development of a Tissue Engineering Scaffold Structure Library for Rapid Prototyping. Part 1: Investigation and Classification</Emphasis>

In tissue engineering (TE), a porous scaffold structure may be required as a template to guide the proliferation, growth and development of cells appropriately in three dimensions. Although TE scaffolds can be created using one of many conventional techniques available, most will suffer from a lack of mechanical strength and/or uniformity in pore distribution and sizes. This study is focused on creating scaffolds using rapid prototyping (RP) techniques. Utilising these novel techniques, a computer-aided design (CAD) of the scaffold structure must first be modelled. The scaffold structure is then fabricated directly from CAD data using a RP system. The objective of this research is to (1) investigate and select various polyhedral shapes suitable for scaffold modelling, (2) classify the selected unit cells, (3) create a parametric library of scaffold structures and (4) verify by building the CAD models using the selective laser sintering process. The first two objectives are covered in Part 1 of this two-part paper. The remaining objectives will be described and discussed in Part 2. ID="A1"Correspondance and offprint requests to: Dr C. K. Chua, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mckchua@ntu.edu.sg     

<Emphasis Type="Italic">Development of a Tissue Engineering Scaffold Structure Library for Rapid Prototyping. Part 2: Parametric Library and Assembly Program</Emphasis>

Rapid prototyping (RP) techniques have been found to be advantageous for tissue engineering (TE) scaffold fabrication due to their ability to address and overcome the problems of uncontrollable microstructure and the feasibility issues of complex three-dimensional structures found in conventional processing techniques. This research proposes a novel approach for TE scaffold manufacture using RP techniques. The approach involves the integration of medical imaging devices (CT/MRI) for the acquisition of anatomic structural data, three-dimensional CAD modelling for designing and creating the digital scaffold models and RP for fabricating the physical scaffolds. To aid the user in CAD modelling, a standard parametric library of scaffold structures is designed and developed. With the library, a user can select the geometry of the scaffold unit cell and size it to suit the end application of the TE scaffold. A developed application program will then assemble the scaffold structure from the selected unit cell, following the surface profile of the anatomic structure to be replicated. A physical scaffold will then be built using an RP system. ID="A1"Correspondance and offprint requests to: Dr C. K. Chua, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mckchua@ntu.edu.sg     

<Emphasis Type="Bold">Numerical Analysis of a Mask Type Stereolithography Process Using a Dynamic Finite-Element Method</Emphasis>

In many investigations, a liquid crystal display (LCD) has been used as the photo mask in a stereolithography system. The LCD mask has the potential to increase the speed of rapid prototyping (RP) fabrication as well as to reduce the system cost. Compared to the conventional laser-scanning technique used in 3D systems stereolithography apparatus (SLA), the reaction heat of layer curing is released as the area is exposed, and it is higher than that of the laser scanning in which the reaction heat only releases point-by-point. On the other hand, mask type stereolithography has a more serious shrinkage effect than the other methods and requires further analysis. This paper analyses the shrinkage deformation of the mask type stereolithography process. A simulation code based on the dynamic finite-element method has been developed to predict the 3D shrinkage and to monitor the RP fabrication, which consists of three stages of simulation which include the pre-processor, the analytic processor and the post-processor. In order to fabricate experimental parts, a mask type stereolithography system has been assembled. The principle of the experimental apparatus is also briefly described. For evaluation of the experimental and simulation results, a thin shell wall rectangular part was fabricated and measured. The simulation program developed has been proved to be in good agreement with the experimental results.     

<Emphasis Type="Bold">Effective Form Design of Electrode in Electrochemical Smoothing of Holes</Emphasis>

This study discusses electropolishing of holes using feeding electrodes as well as inserted electrodes for several common die materials. Traditionally, the hole polishing of a die requires a sequence of complicated premachining operations or scarce manual skill. In the current experiment, eight types of electrode are used and supplied with both continuous and pulsed direct current and another eight types of electrode are fed into holes using continuous direct current. The design features of the electrodes are of major interest for the effective electrochemical of holes. The controlled factors include the diameter of the electrode as well as the chemical composition and the concentration of the electrolyte. The experimental parameters are current density, current rating, electrode design, die material, rotational speed and feedrate of the electrode. For inserted electrodes, an electrode with a helical discharge flute performs better than one without a flute or with a straight flute. Pulsed direct current can improve the polishing effect at the expense of increased machining time and cost. For feeding electrodes, an electrode of a borer type performs better than one with a cycle lap on the leading edge. It was also found that electrobrightening after reaming needs only a short time to make the hole bright, and electropolishing saves the need for reaming, making the total process shorter than for electrob-rightening.     

<Emphasis Type="Italic">A Novel Approach to Extract Knowledge from Simulation Results</Emphasis>

The extraction of knowledge from simulation results is becoming increasingly important, as numerical simulation is being widely used in the engineering design process. Knowledge extraction systems face challenging problems as the databases of simulation results tend to be dynamic, incomplete, redundant, sparse, and very large. This paper describes a novel approach for handling them. A consistent object-oriented data model for finite-element analysis results has been created using EXPRESS-G, which has facilitated the construction of a database for the knowledge mining procedure. After briefly introducing Rough Sets Theory (RST) and principal component analysis (PCA), this paper investigates the capabilities and implementation of both methods for extracting knowledge from simulation results. The methodology developed has been applied to a real application in sheet metal forming simulation and the results are presented.     

<Emphasis Type="Bold">Cumulative Heat Effect in Excimer Laser Ablation of Polymer PC and ABS</Emphasis>

Analysis of the thermal effect and machining properties of PC (polycarbonate) and ABS (polyacrylonitrilebutadienestyrene) polymers when ablated using a KrF excimer laser is described. PC has less thermal effect on the geometric distortion than ABS in laser ablation. The cumulative heat during laser ablation results in geometric deformation in ABS micromachining. The number of laser pulses generates a greater geometric deformation in ABS than in PC according to experimental laser ablation observations. The PC ablation rate is proportional to the laser fluence, whereas ABS shows an exponential profile. The pulse repetition rate has no significant influence on PC during laser ablation, but affects the ablated patterns in ABS. During laser ablation, PC does not produce debris on the machining patterns, but debris is produced on the machining patterns with ABS.     

Effect of deposition pressure on microstructure and tribological behavior of MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Mo nanoscale multi-layer films

MoS _x /MoS _x -Mo multi-layer films consisted of several bilayers and a surface layer on steel substrate were deposited by d.c. magnetron sputtering at different deposition pressures. Each bilayer contained a MoS _x layer with 80 nm in thickness and a MoS _x -Mo composite layer with 20 nm in thickness. With the increase of deposition pressure, the perpendicular orientation of the basal plane prevailed while the parallel orientation decreased. The tribological properties of the multi-layer films were investigated by using a ball-on-disk tribometer both in vacuum and in humid air. The multi-layer film deposited at 0.24 Pa had a compact, consistent layered structure with high intensity of (002) plane and low S content compared to the others deposited at 0.32 and 0.40 Pa, and showed the lowest friction coefficient and wear rate in humid air.     

Study of <Emphasis Type="Italic">in vitro</Emphasis> wear of human tooth enamel

Wear behavior of human tooth enamel against titanium alloy has been investigated under the lubrication of artificial saliva, using a reciprocating sliding wear test machine with a normal load of 20 N, a reciprocating amplitude of 500 μm, and a frequency of 2 Hz. Tests lasting up to 10, 100, 1000, 2000, and 5000 cycles were conducted, respectively. The worn surface of enamel after different cycles was analyzed by means of various microscopic examinations. The results showed that, a delamination mechanism occurred on the surface of enamel at the early stage of wear. The wear rapidly increased in depth with the number of cycles. As the wear proceeded, the surface of enamel was gradually covered with a wear particle layer, and the wear rate decreased. Finally the wear of enamel stayed stable. Microscopic examinations indicated that the wear of enamel was controlled by the mechanical removal of materials without obvious changes in the compositions and crystal structures of the enamel. The enamel rods were worn away after the inter-rod enamel.     

A Differentiating <Emphasis Type="Italic">RC</Emphasis> Circuit in the Amplifying Section of a Photon Counting System

It was shown in experiments that the application of a differentiating RC circuit with a time constant comparable to the rise time of the single-electron pulse in the amplifying section of a photon counting system increases the linearity range of the light characteristic. In this case, the maximum recorded intensity of the light flux increases approximately by a factor of 10, as compared with the maximum intensity measured without the RC circuit.__________Translated from Pribory i Tekhnika Eksperimenta, No. 3, 2005, pp. 42–45.Original Russian Text Copyright © 2005 by Kazakov, Mikheev, Motygullin.     

Investigation of autoignition of propane and<Emphasis Type="Italic">n</Emphasis>-butane blends using a rapid compression machine

The effects of pressure and temperature on the autoignition of propane andn-butane blends were investigated using a rapid compression machine (RCM), which is widely used to examine the autoignition characteristics. The RCM was designed to be capable of varying the compression ratio between 5 and 20 and minimize the vortex formation on the cylinder wall using a wedge-shaped crevice. The initial temperature and pressure of the compressed gas were varied in range of 720-900 K and 1.6-1.8 MPa, respectively, by adjusting the ratio of the specific heat of the mixture by altering the ratio of the non-reactive components (N₂, Ar) under a constant effective equivalence ratio (ø_f=l.0). The gas temperature after the compression stroke could be obtained from the measured time-pressure record. The results showed a two-stage ignition delay and a Negative Temperature Coefficient (NTC) behavior which were the unique characteristic of the alkane series fuels. As the propane concentration in the blend were increased from 20% and 40% propane, the autoignition delay time increased by approximately 41% and 55% at 750 K. Numerical reduced kinetic modeling was performed using the Shell model, which introduced some important chemical ideas, represented by the generic species. Several rate coefficients were calibrated based on the experimental results to establish an autoignition model of the propane andn-butane blends. These coefficients can be used to predict the autoignition characteristics in LPG fueled SI engines.     

Tribological Properties of Nanocomposite CrC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/a-C:H Thin Films

Recently we showed that coatings, prepared by unbalanced magnetron sputtering from a metallic Cr target in an Ar/CH₄ discharge are composed of nanocrystalline CrC _x embedded in an a-C:H matrix. This work investigates the structural correlation of such nanocomposite CrC _x /a-C:H coatings to their tribological properties. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the phase composition and the chemical bonding in the films deposited at different experimental conditions. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy. For CrC _x -dominated coatings deposited at CH₄ partial to total pressure ratios (p_CH4/p_t) < 0.42, only minor changes regarding the friction coefficients and the abrasive wear rates were observed although microstructural changes towards a higher degree of crystallinity were proven by transmission electron microscopy and substantiated with XPS results. For a-C:H dominated coatings deposited at p_CH4/p_t > 0.42, the friction coefficients and abrasive wear rates were shown to decrease with increasing a-C:H phase content and its more sp²-like bonding configuration. It can be concluded that the microstructural changes in terms of CrC _x crystallite coarsening and bonding configuration of the a-C:H matrix phase are responsible for the observed changes of the friction coefficients and wear rates.     

Electron stimulated decomposition of fluorocarbons on amorphous hydrogenated carbon (<Emphasis Type="Italic">a</Emphasis>-CH<Subscript>x</Subscript>) overcoats used in data storage media

The electron-induced surface chemistry of perfluoropolyalkylether (PFPE) lubricants on a-CH_x films has been probed by studying the impact of free electrons on perfluorodiethylether, (CF₃CF₂)₂O, and 2,2,2-trifluoroethanol, CF₃CH₂OH, as models of the chemical functionality of PFPE lubricants such as Fomblin Zdol. Electron-stimulated decomposition of (CF₃CF₂)₂O and CF₃CH₂OH on fresh and oxidized a-CH_x is observed when the sample is unbiased and in the presence of 70 eV free electrons. Electron-induced decomposition is indicated by the deposition of fluorine onto the surface of the a-CH_x film following desorption of molecular (CF₃CF₂)₂O and CF₃CH₂OH by heating in front of a mass spectrometer. Biasing the sample to −80 V successfully eliminates the decomposition by preventing the impingement of electrons onto the surface. The electron-stimulated decomposition of PFPE lubricants may contribute to lubricant decomposition during normal drive operation.     

<Emphasis Type="Italic">Joint Design of Continuous Sampling Plans and Specification Limits</Emphasis>

This paper explores the problem of integrating a Type I continuous sampling plan (CSP-1 plan) and the design of specification limits based on Taguchi’s quality loss function. By adopting the minimax-regret principle, we can obtain the economic specification limits and the optimal inspection policy. This study is an extension of Kapur and Wang’s work. ID="A1"Correspondance and offprint requests to: C.-H. Chen, Department of Industrial Management, Southern Taiwan University of Technology, 1 Nan-Tai Street, Yung-Kang City, Tainan 710, Taiwan, Republic of China. E-mail: chench@mail.stut.edu.tw     

Relation Between Inter-Particle Distance (<Emphasis Type="Italic">L</Emphasis><Subscript>IPD</Subscript>) and Abrasion in Multiphase Matrix–Carbide Materials

Five different carbide–matrix coatings (laser claddings) have been investigated about correlation of their specific structural parameters—especially volumetric carbide distribution—with ASTM G65 abrasion wear rates. For this study, the hardphase networks of laser claddings have been characterized by specific structural parameters, such as mean inter-particle distance, mean carbide diameter, carbide area fraction, and matrix hardness. To generate quantitative values for the inter-particle distances a particular method was developed. From regression analyses, it has become evident that wear effects arising from carbide inter-particle distance surpass the influence of carbide diameter and that of carbide fraction. Only minor contribution to abrasive wear rates is related with matrix hardness.     

<Emphasis Type="Italic">In situ</Emphasis> investigation of the contact area in elastic–plastic spherical contact during loading–unloading

The real contact area between a sphere and a flat during loading, unloading, and cyclic loading–unloading in the elastic–plastic regime of deformations was investigated experimentally. A direct optical technique was used to observe in situ the evolution of the contact area. The experimental results obtained with copper and stainless steel spheres of different diameters that were pressed against a sapphire flat were compared with existing theoretical models, and whenever possible, with previous experimental works. These models are based on the assumption of either perfect slip (i.e., frictionless) or full stick contact condition. Good agreement was found between the experimental and theoretical results for the contact area and mean contact pressure. The existing models for the unloading process fail to accurately predict the residual radius of curvature of fully unloaded spheres, and the irreversibility of multiple loading unloading cycles at least for the several initial cycles. Some recommendations to improve the models are provided.     

The Role of Configuration Entropy in Boundary Lubricants Based on the <Emphasis Type="Italic">n</Emphasis>-Perfluoropropylene Oxide Main Chain Structure

We have investigated the resistance of a novel end-functionalized perfluoropolyether (PFPE) lubricant film to slider–disk interactions caused by low-flying sliders. The PFPE lubricant is based on the CF₂CF₂CF₂O main chain monomer unit. Both slider–disk interactions and the formation of lubricant moguls are significantly reduced compared to the Fomblin Z backbone, (CF₂O) _p –(CF₂CF₂O) _q . These results are interpreted on the basis of ab initio quantum chemical computations that show that the barrier to internal rotation about the C–O bond in the CF₂CF₂CF₂O monomer unit is significantly larger than in the CF₂O monomer unit that is bordered by another CF₂O monomer unit, ~8 kcal/mol compared to <2 kcal/mol, respectively. It is proposed that main chains containing CF₂O monomer units will be very flexible and hence their physical properties will be more sensitive to adhesive and cohesive interactions, while main chains containing CF₂CF₂O and CF₂CF₂CF₂O monomer units will be comparatively stiffer and hence their physical properties will be less sensitive to adhesive and cohesive interactions.     

<Emphasis Type="Bold">Determination of the Optimal Parameters for Freeform Surface Measurement and Data Processing in Reverse Engineering</Emphasis>

One objective of this work is to determine the optimal combination of the probe diameter and grid distance for freeform surface measurement, and another is to determine the optimal parameters for the local Shepard interpolation. The optimal combination of the probe diameter and grid distance for freeform surface measurement was determined through a Taguchi matrix experiment. The smaller the probe diameter and grid distance, the better the accuracy of the surface normal based on the configured matrix experimental result. The optimal parameters, namely the exponent and the radius R, for the local Shepard interpolation were determined by using the minimisation method of the root-mean-square normalised error (RMSNE) between the measured data points and the theoretical data points on a standard steel ball surface. The optimal parameters determined were actually applied to the measurement of a freeform surface (mouse surface) on a coordinate measuring machine (CMM). The local Shepard interpolation method was used to interpolate 16 control points from 1054 measured data points. Bi-cubic Bezier- and B-spline surface CAD models were constructed through these interpolated control points.     

<Emphasis Type="Bold">Two-Phase Parameter Design for the Optimisation of the Electrical-Discharge Machining Process Using a Taguchi Dynamic Experiment</Emphasis>

The paper presents the application of a Taguchi dynamic experiment in developing a robust high-speed and high-quality electrical-discharge machining (EDM) process. In this study, a two-phase parameter design strategy coupled with a double-signal ideal function methodology is proposed. In the first phase, the ideal function of the EDM process is designed as a linear relationship between the main input signal (machining time) and the first output (material removal weight). This model seeks to develop a robust machining process that leads to a high material removal rate. In the second phase, the ideal function is particularly designed as a linear relationship between the adjustment signal (electrode dimension) and the second output (product dimension). The purpose is to adjust machined product dimension of the EDM through optimised process parameters obtained in the first phase, to the desired dimension to provide an allowance for subsequent fine-polishing. Experimental results showed that using a Taguchi dynamic experiment coupled with the proposed two-phase design strategy is simple, effective, and efficient for developing a robust high-speed and high-quality EDM machining process. Optimisation of multiple quality characteristics in the EDM process has been achieved to meet the customers requirements.