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Tsinghua Science and Technology

Issue S1 • Date June 2009

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  • [Front cover]

    Publication Year: 2009 , Page(s): c1
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    Freely Available from IEEE
  • Contents

    Publication Year: 2009 , Page(s): 1 - 2
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    Freely Available from IEEE
  • Rapid prototyping and manufacturing technology: Principle, representative technics, applications, and development trends

    Publication Year: 2009 , Page(s): 1 - 12
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (980 KB)  

    The rapid prototyping and manufacturing technology (RPM), is an integration of many different disciplines. It is based on an advanced dispersed-accumulated forming principle and originated from 1980s. It generates an entity by first forming a series of layers according to the dispersed section information of the digital model, and then piling the formed layers sequentially together. It is capable of forming parts with complicated structures and non-homogeneous materials. Traditional RPM techniques are mainly used as prototypes in product invention process, such as stereolithography, three-dimensional printing, laminated object manufacturing, and fused deposition modeling. Later, with the progress of material and enabling technology, many new RPM techniques emerged out and have been already applied in the fields such as rapid tooling/moulding, direct formed usable part, nano-/micro-RPM, and biomanufacturing. This high flexible digital manufacturing method has a likely ability to become an almighty forming technology. View full abstract»

    Open Access
  • Towards a medium/high load-bearing scaffold fabrication system

    Publication Year: 2009 , Page(s): 13 - 19
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2913 KB)  

    This paper describes fabrication of scaffolds for load-bearing applications, with primary consideration from the manufacturing perspective. An extrusion device, inspired by the FDM process, was used to create scaffolds from a variety of different polymeric materials and mixtures. The effectiveness of these scaffolds to host cells for bone regeneration has been investigated. This ongoing work has generated significant insight into the future direction of research and the possibilities of developing scaffolds for medium/high load-bearing applications. View full abstract»

    Open Access
  • On modeling bio-scaffolds: Structural and fluid transport characterization based on 3-D imaging data

    Publication Year: 2009 , Page(s): 20 - 23
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3232 KB)  

    Bio-scaffolds which are most commonly open celled porous structures are increasingly used for tissue engineering and regenerative medicine. A number of studies have shown that the bulk properties of such irregular structures are poorly modeled using idealized unit cell approaches. The paper therefore uses novel image based meshing techniques to explore both fluid flow and bulk structural properties of a bone scaffold, as accurate modeling of bio-scaffolds with non-uniform cellular structures is very important for the development of optimal scaffolds for tissue engineering application. In this study, a porous hydroxyapatiteltricalcium phosphate (HA/TCP) bone scaffold has been scanned in a Micro-CT scanner, and converted into a volumetric mesh using image processing software developed by the authors. The resulting mesh was then exported to commercial FEA and CFD solvers for analysis. Initial FEA and CFD studies have shown promising results and have highlighted the importance of accurate modeling to understand how microstructures influence the mechanical property of the scaffold, and to analyze flow regimes through the sample. The work highlights the potential use of image based meshing for the ad hoc characterization of scaffolds as well as for assisting in the design of scaffolds with tailored strength, stiffness, and transport properties. View full abstract»

    Open Access
  • Perusing piezoelectric head performance in a new 3-D printing design

    Publication Year: 2009 , Page(s): 24 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1084 KB)  

    Rapid prototyping (RP) is a computerized fabrication technology that additively builds highly complex three-dimensional physical objects layer by layer using data generated by computer, for example CAD or digital graphic. Three-dimensional printing (3DP) is one of such technologies that employ ink-jet printing technology for processing powder materials. During fabrication, a printer head is used to print a liquid on to thin layers of powder following the object's profile as generated by the system computer. This work looks at redesigning 3DP machine, using piezoelectric demand-mode technology head in order to improve accuracy, surface finishing and color quality of constructed models. The layers created with aforesaid system are between 25 to 150 μm(steps of 25 μm). View full abstract»

    Open Access
  • A study of melt flow analysis of an ABS-Iron composite in fused deposition modelling process

    Publication Year: 2009 , Page(s): 29 - 37
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1293 KB)  

    Fused deposition modelling (FDM) is a filament based rapid prototyping system which offers the possibility of introducing new composite material for the FDM process as long as the new material can be made in feedstock filament form. Swinburne has been undertaking extensive research in development of new composite materials involving acrylonitrile-butadiene-styrene (ABS) and other materials including metals. In order to predict the behaviour of new ABS based composite materials in the course of FDM process, it is necessary to investigate the flow of the composite material in liquefier head. No such study is available considering the geometry of the liquefier head. This paper presents 2-D and 3-D numerical analysis of melt flow behaviour of a representative ABS-iron composite through the gO-degree bent tube of the liquefier head of the fused deposition modelling process using ANSYS FLOTRAN and CFX finite element packages. Main flow parameters including temperature, velocity, and pressure drop have been investigated. Filaments of the filled ABS have been fabricated and characterized to verify the possibility of prototyping using the new material on the current FDM machine. Results provide promising information in developing the melt flow modelling of metal-plastic composites and in optimising the FDM parameters for better part quality with such composites. View full abstract»

    Open Access
  • Optimization of triangulations based on serial fault data

    Publication Year: 2009 , Page(s): 38 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (421 KB)  

    Three-dimensional reconstructions based on serial fault data can be divided into boundary contour splicing and end contour closure. In boundary contour splicing, the Delaunay triangulation algorithm can generate long, narrow triangles or radial shapes and with end contour closure, the Delaunay triangulation based on the determination of the convex-concave vertices tends to generate long, narrow triangles and triangles whose sizes differ greatly, and in some cases failure. This paper presents a Delaunay triangulation algorithm based on the shortest distance first principle for boundary contour splicing and an improved algorithm which combines Delaunay triangulation based on the determination of convex-concave vertices with interpolation for end contour closure. The results show that the algorithms retain the original advantages of the algorithms while increasing the triangulation effectiveness and enhancing the universality of the algorithms. View full abstract»

    Open Access
  • A new algorithm for feature matching in reverse engineering

    Publication Year: 2009 , Page(s): 43 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    Feature recognition and surface reconstruction from point clouds are difficulties in reverse engineering. A new surface reconstruction algorithm for slicing point cloud was presented. The contours of slice were extracted. Then, the intersection of two adjacent curve segments in the contour was obtained and curves feature was extracted. Finally, adjacent section contours were matched directly with Fourier-Mellin curve matching method for feature extraction. An example of 3-D model reconstruction shows the reliability and application of the algorithm. View full abstract»

    Open Access
  • Point-Based data analysis for extracting parameters of cutting tools

    Publication Year: 2009 , Page(s): 47 - 55
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    Various types of cutting tools are known and are in use for machining parts. The dimensional parameters associated with cutting tools need to be estimated and compared to the desired values for determining their cutting performance. In this paper, a data analysis methodology for extracting parameters from a measured point set corresponding to the surface of a cutting tool is provided. We propose that the 3-D data can be simplified into 2-D data or regular data by virtually slicing it at a predetermined section or by projecting it onto a same axial plane after a simple fixed-axis rotation. A plurality of curves can be generated and optimized based on the obtained 2-D points on a cross section for calculating the section parameters, including radial (axial) rake angle, relief angle, and land width. Other dimensional parameters can also be extracted from the contour of the presented rotary axial projection data. The experimental results have shown that the approaches elaborated in this paper are effective and robust, which can be potentially extended to other applications such as the inspection of similar parts and their parameters extraction. View full abstract»

    Open Access
  • Triangular mesh model reconstruction from scan point clouds based on template

    Publication Year: 2009 , Page(s): 56 - 61
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (822 KB)  

    For mesh reconstruction problems of point cloud models which have similar topological structure, a rapid and efficient method is presented to reconstruct triangular mesh surface. Based on projections of point cloud slicing that correspond to template sectional curves, the method constructs topological relevant information among discrete points, which makes unorganized points ordering and builds up optimal approximated B-spline curve, resamples every curve according to its curvature distribution and performes triangular mesh division on it. Finally, surface reconstruction is achieved. The experimental results demonstrate that the surface reconstruction is done as the point cloud hole is filled simultaneously. View full abstract»

    Open Access
  • A novel method for human expression rapid reconstruction

    Publication Year: 2009 , Page(s): 62 - 65
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (4177 KB)  

    Human expression rapid reconstruction has many potential applications in entertainment and social security. In this work, a rapid human expression measurement system based on a digital fringe projection and phase-shift technique is developed. The measurement system consists of a digital light processing (OLP) projector and a high-speed change-coupled device (CCD) camera. The OLP projector is used to project computer-generated fringe patterns onto the human face, and the high-speed CCO camera synchronized with the projector acquires the fringe images at a frame rate of 30 frames/so Based on a three-step phase-shifting method and an accurate phase-height mapping algorithm, each frame of the 3-D human expression can be reconstructed. The principle of the proposed method is described and some experimental results are presented to demonstrate its performance. The experiment results show that the measurement system can reconstruct accurate 3-D human expression. An obvious merit of this method is that it can reconstruct the 3-D human expression in a very short time and it is not sensitive to the movement of the face during the measurement processing. View full abstract»

    Open Access
  • 3-D shape measurement of complex objects by combining color-coded fringe and neural networks

    Publication Year: 2009 , Page(s): 66 - 70
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (5185 KB)  

    A new approach for three dimensional (3-D) shape measurement was proposed based on colorcoded fringe and neural networks. By applying the phase-shift technique to fringe projection, point clouds were generated with high spatial resolution and limited accuracy. The picture element correspondence problem was solved by using projected color-coded fringes with different orientations. Once the high accurate corresponding points were decided, high precision dense 3-D points cloud was calculated by the well trained net. High spatial resolution can be obtained by the phase-shift technique and high accuracy 3-D object point coordinates are achieved by the well trained net, which is not dependent on the camera model and will work for any type of camera. Some experiments verify the performance of this method. View full abstract»

    Open Access
  • Role assignment and cooperation of ontology and object-oriented principle in construction of digital product model

    Publication Year: 2009 , Page(s): 71 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (239 KB)  

    Powerful expressive ability of semantic information, to be easily computed and flexibility are basic features of digital product model (DPM). Using ontology and object-oriented principle (OOP) together to cope with problems in modeling is brought forward in this paper. The two are widely used and do well in modeling, but they each alone cannot cope with all issues and new challenges. Three basic requests are pointed out in DPM modeling. Status, problems, and root of current non-semantic and semantic models are introduced. Ontology, OOP, and their difference are introduced. It is found that the two are entirely complementary with each other. How to assign the roles and to cooperate for the two in coping with the three basic issues in DPM modeling are explained in detail. View full abstract»

    Open Access
  • An improved algorithm for k-nearest-neighbor finding and surface normals estimation

    Publication Year: 2009 , Page(s): 77 - 81
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1385 KB)  

    This paper is to improve the speed of k-nearest-neighbor search and put forward algorithms related to tangent plane estimation based on existing methods. Starting from the points cloud, the algorithm segments the whole data into many different small cubes in space, and the size of cube is related to the density of the points cloud. Considering the position of the point in the cube, the algorithm enlarges the area around the given point step by step until the k-nearest-neighbor is accomplished. The neighbor's least-squares tangent plane is estimated. In order to orient the planes, the k-nearest-neighbor is introduced into the problem of seeking the minimum spanning trees instead of searching the whole data. The research proved that the algorithms put forward in this paper were effective in processing data in short time and with high precision. The theory was useful for the practical application in reverse engineering and other areas related. Solution for finding k-nearest-neighbor problem, which still costs much time in present, was provided, and a propagation algorithm for orienting the planes was also discussed. The algorithm chose the orientation among the k-nearest-neighbor of the current point. View full abstract»

    Open Access
  • Personalized cranium defects restoration technique based on reverse engineering

    Publication Year: 2009 , Page(s): 82 - 88
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    The purpose of this paper is to overcome the limitations of the traditional cranial defects restoration technique and better satisfy the aesthetic and comfort demands of different patients. An arithmetic profile curve blending technique was used based on a well-proportioned points cloud data obtained by analyzing computer tomography (CT) images of the patients. This technique uses reverse engineering technique to reconstruct a model of the defective cranium, taking all the characteristics of the protruding cranium into consideration to check the form and appropriateness of the restoration and to adjust the surface in real time to obtain the ideal shape. Then, the model is transferred to a multiple-point forming (MPF) pressure machine to produce a titanium alloy restoration model. The system has greater flexibility, shorter production cycles, and lower cost through the use of digital production technology, guarantees the quality of the cranial defects restoration model, reduces the surgical risks, and alleviates the patients' pain. In addition, an improved contour curved bridge algorithm technique is used to repair any cranium defects on the contour curve to make the contour more complete and closed. View full abstract»

    Open Access
  • An approximating algorithm on reconstruction of complicated curved surface

    Publication Year: 2009 , Page(s): 89 - 93
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1165 KB)  

    An approximating algorithm on handling 3-D points cloud data was discussed for reconstruction of complicated curved surface. In this algorithm, the coordinate information of nodes both in internal and external regions of partition interpolation was used to realize minimized least squares approximation error of surface fitting. The changes between internal and external interpolation regions are continuous and smooth. Meanwhile, surface shape has properties of local controllability, variation reduction, and convex hull. The practical example shows that this algorithm possesses a higher accuracy of curved surface reconstruction and also improves the distortion of curved surface reconstruction when typical approximating algorithms and unstable operation are used. View full abstract»

    Open Access
  • Solid Freeforming and Combinatorial Research

    Publication Year: 2009 , Page(s): 94 - 99
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1764 KB)  

    A view of manufacturing processes is presented in which five distinct categories are defined as casting, deformation, machining, joining, and solid freeforming. Solid freeforming is essentially biomimetic and shares problems of morphogenesis with natural processes. Our team in University of London has been exploring three mechanisms of solid freeforming. In dry powder deposition and direct ink-jet printing, the emphasis has turned to the problem of delivering a complex shape in which the three dimensional spatial arrangement of composition is delivered from the design file. In extrusion freeforming, the aim is to control microstructure at hierarchical levels also from the design file. The quest for 3-D functional gradients is satisfied by acoustic and ultrasonic dispensing and mixing of powders so that each layer can be patterned. These methods could be extended to deliver the complex patterns demanded by left-handed microwave metamaterials. Dry powder deposition and direct ink-jet printing are turning towards combinatorial methods in which multiple sample libraries are used to accelerate discovery. In turn, this paves the way for 'autonomous research machines' which steer their own search refinements in response to our requests for new materials. In this way, solid freeforming used for sample preparation can give an 'arm' to an intelligent machine so that it can conduct its own experimentation and learning; an idea that originated with Alan Turing in the late 1940s. View full abstract»

    Open Access
  • Predictability of plastic parts behaviour made from rapid manufacturing

    Publication Year: 2009 , Page(s): 100 - 107
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (449 KB)  

    One of the most important issues to resolve in parts manufactured from rapid manufacturing (RM) technologies is to know their behavior working under real conditions. Total quality manufacturing (TOM) is only possible if mechanical properties are well known in the design stage depending on the processing parameters. This work is mainly focused on testing of several samples made with different selective laser sintering (SLS) parameters and technologies. This procedure is the starting point to establish a basis for designing for RM and the standardization of RM testing. The experiments and the analysis of variance (ANOVA) analyzed the effects of several factors on mechanical properties. The SLS technologies were 3DSystem and EOS. The results show which factor has a large effect on the variables and the interaction between them. The conclusions are very useful for developing rules for designing (designing for RM) and creating new standard rules (ISO, AISI, and DIN) for RM materials and parts testing. The ANOVA gives a better knowledge of the effects of these factors and eliminates unimportant parameters. View full abstract»

    Open Access
  • Design and manufacture of a wax injection tool for investment casting using rapid tooling

    Publication Year: 2009 , Page(s): 108 - 115
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (6800 KB)  

    A rapid wax injection tool of a gearbox shift fork was designed, simulated, and manufactured using rapid prototyping and rapid tooling technology to save time and cost of producing wax models used for the investment casting process. CAE simulation softwares, in particular, MoldFlow, are used to get wax injection moulding parameters such as filling parameters, temperature profiles, freeze time, speed, and pressure. The results of this research were compared with conventional wax model production methods. The criteria of such comparison were based upon parameters such as time, cost, and other related characteristics, which resulted in saving of 50% in time and 60% in cost. In this research, design, assembly, and wax injection operation of the wax tool took 10 days. Considering the fact that wax melting temperature is as low as 70°C and injection pressure of 0.5 MPa, the tool suffers no damage due to the thermal and pressure stresses, leading to the mass production of wax models. View full abstract»

    Open Access
  • Aerodynamically assisted tip-pen direct writing

    Publication Year: 2009 , Page(s): 116 - 119
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1566 KB)  

    Scaffolds require individual external shape and well-defined internal structure, which is of great importance for tissue engineering. Rapid prototyping (RP) uses layer-manufacturing strategies to create physical objects and has the advantage on scaffold fabrication. A new RP technology called aerodynamically assisted tip-pen direct writing was developed to construct the complex architectures. Compared with the traditional nozzle, the new nozzle has a micro-tip in the center of the micro-hole. The flow is determined by the gap between the micro-hole and micro-tip, which makes it practical for more accurate flow control. A highly accurate three-dimensional (3-D) micro-positioning system was employed with the new nozzle to deposit maltose structures. 3-D architectures had been made by this method, the width of fiber in which is about 120 urn. The results show that this method provides a possibility to construct 3-D scaffolds with tissue-scale features (i.e., 10–100 μm) without bad influence on the biological activities. View full abstract»

    Open Access
  • Scan strategy in electron beam selective melting

    Publication Year: 2009 , Page(s): 120 - 126
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1271 KB)  

    In electron beam selective melting process, powder pushed-away phenomena and uneven temperature field are two main obstacles, which are greatly associated with the electron beam scan mode. In this paper, various scan strategies, including iterative scan mode, reverse scan mode, interlaced reverse scan mode, randomized block scan mode, and constant length scan mode, are investigated. The analyses for each scan strategy are presented based on the influence to the temperature field over the formation zone and the powder pushed-away phenomena. The most promising strategy, interlaced reverse scan mode, is approved by the ANSYS simulation and a two-dimensional scan experiment. The result shows interlaced reverse scan mode can improve the uniformity of the temperature field and reduce the powder pushed-away phenomena. View full abstract»

    Open Access
  • Application of rapid prototyping technology in die making of diesel engine

    Publication Year: 2009 , Page(s): 127 - 131
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (526 KB)  

    This paper studies engineering applications of rapid prototyping (RP) technology in die making of diesel engine. On demand of product development and die making of, an integrated system of reverse engineering and rapid prototyping (RE/RP) for engineering application is constructed, and effective application of RP technology in die making is thus realized. Taking the casting die for clutch house of diesel engine as an example, this paper studied the engineering application of laminated object manufacturing (LOM) technology in rapid die making and discussed related technologies as parameter setting of temperature and pressure in heat pressing, the matching of laser power and cutting speed of laser, and layout and post treatment of the prototype in RP technology. The casting die manufactured with LOM technology has satisfactory lifetime and is successfully used in 100 rough castings of clutch house for diesel engine. The manufacturing cost for the die is decreased and the production period is shortened. View full abstract»

    Open Access
  • Deformation behaviors of laser forming of ring sheet metals

    Publication Year: 2009 , Page(s): 132 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Laser forming is a highly flexible sheet metal forming technique. In laser forming along curved irradiation paths, the heated zone is bigger and the effects of the processing parameters on the deformation are complex. The deformation behaviors of laser forming of ring sheet metals have been investigated from the thermal-mechanics analysis by the finite element (FE) simulation based on the proposed finite element method model. The effects of ring central angle and scanning path on deformation of ring sheet metal were investigated. The results are as follows: (1) in comparison with the laser bending along linear path, the marked third point has two peak temperatures during the laser forming process along curved path; (2) the forming process fluctutes continuously and the sheet edge is warped because the rigid-ends effect due to the restriction of sheet; (3) when the ring central angle increases, the displacement difference of the marked three points decreases and then increases, and the warped curvature of sheet edge decreases; (4) when the laser beam diameter increases, the displacement difference of the marked three points decreases and the warped curvature increases. View full abstract»

    Open Access
  • New Voronoi diagram algorithm of multiply-connected planar areas in the selective laser melting

    Publication Year: 2009 , Page(s): 137 - 143
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (541 KB)  

    This paper studies the practical generation of Voronoi diagrams for multiply-connected planar areas bounded by line segments. The core of the algorithm was calculating Voronoi polygon of every Voronoi object in planar areas independently. The main approach had two steps. The first step was calculating all relevant bisectors of every Voronoi object. The second was combining obtained bisectors into completed Voronoi polygons individually. All code was implemented in Visual C++ platform. The resulting code was extensively tested in real-world data and its practical running time grew only linearly. Three statistical CPU-consumption charts had been drawn with the Voronoi diagrams computation data, and compared with other published codes for computing Voronoi diagrams. The algorithm was applied to compute offsetting of slice area consisting of large-scale line segments for the selective laser melting (SLM) trajectory scanning technology which is a kind of rapid prototyping (RP). The experimental results of offsetting for slice area based on Voronoi diagrams show that the approach is effective and simple for polygon offsetting problems. The method is helpful to those offsetting work and can provide more effective offsetting solution. View full abstract»

    Open Access

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Tsinghua Science and Technology (Tsinghua Sci Technol) aims to highlight scientific achievements in computer science, electronic engineering, and other IT fields. Contributions all over the world are welcome.

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