articles+ search results

SUMMARY A study was undertaken to determine the dimensional accuracy of anatomical replicas derived from X-ray 3D computed tomography (CT) images and produced using the rapid prototyping technique of stereolithography (SLA). A dry bone skull and geometric phantom were scanned, and replicas were produced. Distance measurements were obtained to compare the original objects and the resulting replicas. Repeated measurements between anatomical landmarks were used for comparison of the original skull and replica. Results for the geometric phantom demonstrate a mean difference of + 0.47 mm, representing an accuracy of 97.7-99.12%. Measurements of the skull produced a range of absolute differences (maximum +4.62 mm, minimum +0.1 mm, mean +0.85 mm). These results support the use of SLA models of human anatomical structures in such areas as pre-operative planning of complex surgical procedures. For applications where higher accuracy is required, improvements can be expected by utilizing smaller pixel resolution in the CT images. Stereolithographic models can now be confidently employed as accurate, three-dimensional replicas of complex, anatomical structures. [ABSTRACT FROM AUTHOR]

Presents the background to and efforts being made to find a direct production route using rapid prototype (RP) parts as the electrodes for electrical discharge machining (EDM). It would have the double effect of unlocking the potential of the EDM die sinking process and expanding the role of RP in the production environment. Thin coated stereolithography (SL) models have been used to erode hardened tool steel to a depth of 4mm. Machining efficiency of these copper coated RP models is not comparable to that of conventional machined solid copper electrodes. Parametric optimization has been applied, achieving substantial improvements in machining efficiency. At present these electrodes are suitable for semi-roughing or finishing cuts in EDM die sinking. Electroforming copper into SL cavities shows potential for manufacture of electrodes with comparable performance to that of solid copper. [ABSTRACT FROM AUTHOR]

We investigate the accuracy of complex anatomical replicas derived from X-ray computed tomography data linked to the rapid prototyping technique of stereolithography. Data processing by specific softwares (segmentation, three-dimensional interpolation) allows direct interfacing with the stereolithography apparatus to build a resin replica with reproduction of internal cavities. Our preliminary results about surface and dimensional accuracies suggest that the reproduction of complex anatomical structures by stereolithography is reliable enough to be used for surgical planning, for custom-made implants and for surgical anatomy teaching. [ABSTRACT FROM AUTHOR]

Ceramic three-dimensional parts can be produced by a stereolithography (SL) process using a ceramic suspension containing alumina powder, UV curable monomer, diluent, photoinitiator and dispersant. The monomer reacts to UV radiation (argon ionized laser) and is transformed into a solid polymer which is then removed by thermal treatment (debinding). Subsequent sintering of green parts leads to dense ceramic parts. The effect of each component on the rheology of the alumina suspensions has been studied first. Both the addition of dispersant and diluent and the increase in temperature allow a significant decrease of the viscosity of the suspensions. The highly loaded (more than 55 vol. per cent), homogeneous and stable suspensions have a shear thinning behaviour which is favourable for casting the layers. Adequate cured depth (above 200μm) and satisfactory transversal resolution have been obtained and these allow the production of ceramic parts, which demonstrates the feasibility of the process. Sintering at 1,580°C leads to dense ceramic parts with homogeneous microstructure. The process still needs to be optimized to improve even more the mechanical properties. [ABSTRACT FROM AUTHOR]

At The Institute of Physical and Chemical Research (RIKEN) a new process named multiple LED photographic curing (MPC) has been developed. As a matter of priority, MPC is thought to be applied to concept modelling. The building data are available in bitmap or voxel representation respectively. In MPC, light is generated by light-emitting diodes (LEDs). Exposing of a photopolymer happens through raster scanning. An array of multiple beams of light is projected onto the resin surface while the scan head moves across the vat. The fabrication of test parts has proven the system's practical ability to create geometric objects. Surface finish is quite good, certainly adequate for most concept verification. Some obstacles such as low exposure energy have yet to be overcome. Scaling up the build envelope enables fabricating much larger parts. [ABSTRACT FROM AUTHOR]

Rapid prototypes formed using stereolithography (SL) method have to undergo post-curing to increase their strength and rigidity. This study attempts to reduce, if not eliminate, post-cure distortion by characterising curing behaviours. Curing (both heat and UV initiated) characteristics of an acrylic-based photopolymer under actual fabrication conditions were studied using Raman spectroscopy as well as differential scanning calorimetry (DSC) and differential scanning photo-calorimetry (DSP). Specimens of single photopolymer lines were created using a SL machine. Raman spectroscopy was used to quantify the curing percentage at different areas on the cross-section of these lines. Curing percentages before and after post-curing were also obtained from the experiments. Difference in percentage of post-curing gave an indication of the distortions faced. It was found that uncured and partially cured resins trapped within the photopolymer resulted in inhomogeneity of curing in the specimens causing shrinkage and distortion. [ABSTRACT FROM AUTHOR]

The ability to evaluate and determine the best part building orientation for different rapid prototyping (RP) processes is important for building a satisfactory part/prototype within the limits of manufacturing time and building cost. It is also an essential step towards the identification of the most suitable RP process with a given RP application. This paper discusses the selection of building direction for four RP processes, namely stereolithography (SL), selective laser sintering (SLS), fusion deposition modelling (FDM) and laminated object manufacturing (LOM). Main differences in the four processes are first examined with emphasis on the effects of these differences with regard to the building inaccuracy, the surface finish, the manufacturing time and cost. An optimal orientation algorithm is demonstrated on a part considered for processing with one of the four RP processes. The influence of the process characteristics on the selection of appropriate orientation with different RP processes is illustrated in the example. [ABSTRACT FROM AUTHOR]

A common procedure for processing stereolithography epoxy injection molds includes a one hour post-cure in a UV chamber. This research investigates the degree of cure achieved in the UV chamber and the degree of cure achieved by heating in a thermal oven. It is hypothesized that a more fully cured mold is harder and hence will produce more parts before failure. This research investigates various post-cure processes and suggests a post-cure strategy to achieve this end. [ABSTRACT FROM AUTHOR]

A method to control raster-based exposure in multiple-LED photographic curing (MPC) is introduced. During the build process, beams of multiple sources, each exposing a separate area, are projected vertically onto the resin surface while the projector moves continuously across the resin vat. In the projector, 1,024 beams of light are arranged in an array of eight staggered rows. Part-building data are written in numerical control (NC) geometric details (G)-codes to produce a physical replica of the digital part design. The sliced 3D data are converted into bitmap data, an image consisting of tiny dots called pixels. The individual layers of a part are built up through pixels arranged in a bitmap. The formation of objects happens through curing in an orthogonal raster with a mesh of 62.5mm. To obtain even intensity in the surface, five beams are used to cure a single string. In part-building experiments, microscopic photographs taken of parts clarified the characteristic pattern of the exposure technique. [ABSTRACT FROM AUTHOR]

The effects of the addition of short glass fibers into an acrylic-based photo-polymer (De Solite SCR310) used in the laser solidification process have been studied. Comparisons of the mechanical properties between pure-polymer specimens and their fiber-filled counterparts were made by subjecting the parts to tensile tests. It was observed that the fiber-reinforced specimens yielded higher measured values of elastic modulus and ultimate tensile strength. The amount of shrinkage encountered by the reinforced prototypes during post-curing was also found to be less than their non-reinforced counterparts. It was also found that the mechanical properties of the post-cured fiber-reinforced specimens were functions of the layer pitch and laser exposure density used during fabrication. By increasing the laser exposure density and decreasing the layer pitch, the mechanical properties of the post-cured fiber-reinforced prototype can be improved, leading to the realization of end products with higher mechanical strengths and better dimensional accuracy. [ABSTRACT FROM AUTHOR]

In the industrial use of stereolithography, precision is always a problem. The basic phenomenon of solidification shrinkage has not been sufficiently investigated. This study aims at clarifying the initial linear shrinkage of cured resin in a minute volume. Experimental equipment has been developed which measures the time history of the single strand in situ in a stereolithography machine. An analysis model of the time history of a minute volume linear shrinkage was shown using the measured shrinkage of a cured line segment. The relation between the time history of the linear shrinkage and temperature was measured and the shrinkage in the minute volume after irradiation was found to result due to temperature variation. Deformation and linear shrinkage were measured with two scanning orders to control the thermal distribution in layer forming. The effects of thermal distribution were also observed in one layer forming. [ABSTRACT FROM AUTHOR]

The build characteristics of two liquid crystal (LC) reactive monomers were studied using a table-top stereolithography apparatus (TTSLA). LC materials contain stiff, rod-like mesogenic segments in their molecules, which can be aligned causing an anisotropy in properties. When cured in the aligned state the anisotropic structure is "locked in" resulting in materials with anisotropic physical and mechanical properties. By varying the alignment of layers, properties such as thermal expansion coefficient can be optimized. High heat distortion (or glass transition) temperatures are possible depending on the monomer chemical structure. Working curves for the LC resins were developed under various conditions. A permanent magnet placed outside the TTSLA vat was used to uniformly align the monomer in the nematic state. Photo-initiator type and content; alignment of the nematic phase; and operating conditions affected the working curve parameters. Glass transition temperatures of post-cured parts ranged from 75 to 1488C depending on the resin and processing conditions. Mechanical analysis data revealed a factor of two difference between glassy moduli measured in the molecular alignment versus the transverse alignment directions. Based on these initial studies, more advanced resins with higher glass transitions are being developed at the University of Dayton. [ABSTRACT FROM AUTHOR]

Determining whether a set of tolerances on a part can be met by a rapid prototyping (RP) machine is often difficult. To achieve a set of tolerances as closely as possible, relationships between part geometry, tolerances, and process variables must be understood quantitatively. This paper presents an empirical model for stereolithography apparatus (SLA) accuracy, as specified by geometric tolerances, and a process planning method based on response surface methodology and multiobjective optimization. Response surfaces are used to capture the relationships among part surfaces, tolerances, and process variables. These response surfaces were generated by extensive design-of-experiment studies for a variety of geometries. An annotated STL data format is also presented that enables the inclusion of tolerance and surface information in faceted representations. Application of the accuracy models and process planning method is illustrated on one part. [ABSTRACT FROM AUTHOR]

Presents a method of Max-Fit biarc curve fitting technique to improve the accuracy of STL files and to reduce the file size for rapid prototyping. STL file has been widely accepted as a de facto standard file format for the rapid prototyping industry. However, STL format is an approximated representation of a true solid/surface model, and a huge amount of STL data is needed to provide sufficient accuracy for rapid prototyping. Presents a Max-Fit biarc curve fitting technique to reconstruct STL slicing data for rapid prototyping. The Max-Fit algorithm progresses through the STL slicing intersection points to find the most efficient biarc curve fitting, while improving the accuracy. Our results show that the proposed biarc curve-fitting technique can significantly improve the accuracy of poorly generated STL files by smoothing the intersection points for rapid prototyping. Therefore, less strict requirements (i.e. loose triangle tolerances) can be used while generating the STL files. [ABSTRACT FROM AUTHOR]

Stereolithographic (SL) biomodelling is a relatively new technology that allows three-dimensional (3D) computed tomography (CT) data to be used to generate accurate solid plastic replicas of biological structures (biomodels). A prospective trial to investigate the utility of biomodelling in palaeontology was performed. Seven fossil specimens were selected. Volumetric 3D reconstructions were generated on each specimen. The data of interest were edited and converted into a form acceptable for SL. SL uses a laser to selectively polymerize photosensitive resin to manufacture each biomodel. The biomodels were assessed for fidelity, internal morphology and for use in display and demonstration. Biomodelling was found to faithfully replicate the fossilized specimens. The most important variable affecting biomodel accuracy was the initial acquisition of 3D CT data. Biomodelling is intuitive, user-friendly technology that facilitates morphological assessment and specimen reconstruction. Biomodelling allowed both internal and external features of fragile specimens to be safely replicated without risk. [ABSTRACT FROM AUTHOR]

Advances in rapid prototyping and machining have resulted in reduced lead times for injection moulding tooling. Comparisons between aluminium and stereolithography (SL) tools are made with regard to the ejection forces required to push mouldings from the tools, heat transfer through the tools and the surface roughness of the tools. The results show that ejection forces for both types of tools are increased when a longer cooling time prior to ejection is used. The ejection forces required from a rough aluminium tool are considerably higher than those from a smooth aluminium tool. SL tools do not appear to be subjected to any smoothing as a result of moulding polypropylene parts. The rubber like nature of the tool's surface is as a direct consequence of the low glass transition temperature and low thermal conductivity of the tool material. Further potential benefits of the low thermal properties of the tool are discussed. [ABSTRACT FROM AUTHOR]

The commercialization of new products integrating many functions in a small volume requires more and more often the rapid prototyping of small high-resolution objects, having intricate details, small openings and smooth surfaces. To give an answer to this demand, the stereolithography process has started to evolve towards a better resolution: the "small spot" stereolithography technology allows to reach a sufficient resolution for the manufacturing of a large range of small and precise prototype parts. Microstereolithography, a technique with resolution about an order of magnitude better than conventional stereolithography, is studied by different academic research groups. The integral microstereolithography machine developed at the Swiss Federal Institute of Technology in Lausanne is described in this paper, and potential applications are presented. The resolutions of conventional, small spot and microstereolithography technologies are compared and the potential of the microstereolithography technique is shown for the manufacturing of small and complex objects. [ABSTRACT FROM AUTHOR]

Identifies trends in the rapid prototyping market worldwide, reports on new rapid prototyping techniques, reviews the latest developments in 3D printers, highlights new metal spraying and direct metal deposition processes. [ABSTRACT FROM AUTHOR]

Injection molding is a very mature technology, but the growth of layer-build, additive, manufacturing technologies (rapid prototypying) has the potential of expanding injection molding into areas not commercially feasible with traditional molds and molding techniques. This integration of injection molding with rapid prototyping has undergone many demonstrations of potential. What is missing is the fundamental understanding of how the modifications to the mold material and mold manufacturing process impact both the mold design and the injection molding process. This work expanded on an approach to utilize current numerical simulation programs and created a tool for optimizing the creation and use of non-metal molds for injection molding. Verification and validation work is presented. The model was exercised by studying the effect of varying the thermal conductivity on final-part distortions. This work clearly showed that one could not obtain reasonable results by simply changing a few input parameters in the current simulations. Although the approach did produce more realistic results, more work will be required for a tool capable of accurate, quantitative predictions. [ABSTRACT FROM AUTHOR]

Describes how a set of criteria for the design of build structures that allow the successful autoclaving and subsequent investment casting of stereolithography models have been developed. Details of the background research are presented along with a new design of internal build structure that allows stereolithography models to be used as sacrificial patterns in the investment casting process. Further work into the characteristics of draining uncured resin from parts built in the new structure is also presented. [ABSTRACT FROM AUTHOR]

In recent days, rapid machining through digital prototyping has been popular for its applicability in a wide range of complex and useful parts. Rapid construction of prototypes from point cloud data based on section plane method is available, which is an approximate method. Discusses some suitable methodology for conversion of point cloud data to a physical prototype where data acquisition is through a mechanical touch trigger probing process using CNC milling machine. The process is quite useful for reverse engineering of complex sculptured parts. A concept called tangent plane method is adopted for the generation of 3D geometry on point cloud data of sculptured parts with due emphasis on probe radius compensation after data capture and tool radius compensation during tool-path generation. Computer simulated results are presented, based on real-world point cloud data. [ABSTRACT FROM AUTHOR]

Adhesion has been measured between a powder injection molded (PIM) part and the stereolithography epoxy mold surrounding it after cooling. Analysis of release behavior suggests a link to the thermal properties of the mold material. Subsequent measurements of cooling in the part and at the part/mold interface are consistent with a one-dimensional heat transfer model. Adhesion development at the part/mold interface shows a complex dependence on the thermal characteristics of both the mold and the PIM feedstock. [ABSTRACT FROM AUTHOR]

Stereolithography apparatus (SLA) is capable of in situ fabrication of complex parts, as well as mechanisms and complex devices with embedded components. In this paper, a series of example devices are presented to illustrate the power of building around embedded components (inserts). The problem formulation, solution approach, and specific rules and procedures are presented using these examples and experimental results. A case study approach is used for presentation. These procedures and results lend insight into promising new applications of SLA technology, as well as novel methods of implementing additional functionality into SLA and other rapid prototyping technologies. [ABSTRACT FROM AUTHOR]

Stereolithography (SL) is a kind of rapid prototyping technology which uses the laminate manufacturing to fabricate parts. With the development of RP, some new RP processes have boomed rapidly. Compact prototyping system (CPS) is a kind of novel stereolithography method which utilizes conventional UV light as the light source. After transmitting by optic fiber and focusing through lens set, the light is intensified and can be used to cure the photopolymer. Compared with the laser SL prototyping apparatus, this apparatus has unique characteristics on its driving system and light path system. Discusses the characteristics and corresponding consequences of the driving system and light path system, and analyzes the light energy distribution and the corresponding line shapes. Since each layer is constructed from a serial of lines, the scanning parameters, especially scanning speed and hatch gap, will influence the overall light intensity which determines the layer thickness, section shape and ultimately the prototyping accuracy. The driving system, due to the non-uniform moving speeds, could cause the shape error of the lines. A light shutter, keeping the light only illuminating on resin surface within given curing areas, is employed to solve this deficiency. [ABSTRACT FROM AUTHOR]

The development of a physical model of cancellous bone whose structure could be controlled would provide significant advantages over the study of in vitro samples, making repetitive or comparative testing possible. This would enable the relationship between the mechanical integrity (and hence fracture risk) of cancellous bone and its structural properties to be more exactly defined. Whilst the use of RP to generate these porous objects was a considerable challenge such objects would have been impossible to manufacture using any other approach. This short technical note describes how stereolithography was used to create over 25 accurate models, which were required to perform physical experiments to validate the results of the FEA. The note highlights how problems associated with STL and SLC file formats, support generation and software limitations were overcome to produce stereolithography models of highly complex, naturally occurring three-dimensional structures. [ABSTRACT FROM AUTHOR]

Conventional shaping processes for ceramics are mostly based on a powder-technological molding process using a negative mold and subsequent thermal compaction. Especially for prototypes and small lot series of microcomponents the outlay for molds are the major costing factor. Consequently the use of rapid prototyping (RP) processes can decisively reduce the costs and time in product development of ceramic microcomponents. In spite of the fact, that a large number of freeform fabrication techniques for different materials were developed in recent years, most generative techniques of ceramics still have different drawbacks for the fabrication of prototypes and often exhibit limited resolution compared to those of polymers. The combination of RP techniques such as micro stereolithography and ceramic injection molding in a RP process chain can fill in the gap between the limited applicability of solid freeform fabrication of ceramics and the restricted material properties of polymers. [ABSTRACT FROM AUTHOR]

The characteristics of PZT suspensions have been studied and fit to stereolithography restraints. On one hand, researches concern the influence of fillers contents, dispersant concentration, temperature and resins nature and amount on suspensions rheological behaviour. On the other hand, the influence of photoinitiator and PZT concentrations, density of energy and nature of the resin on suspension reactivity was investigated. These experiments have led to the choice of two photosensitive suspensions suitable for stereolithography purpose; which use depend on the fillers content. Furthermore, the stereolithography process has been modified owing to the balance between suspensions rheological and photochemical properties in order to shape piezoelectric ceramics. Thanks to these improvements, PZT ceramics/polymer composites dedicated to transducers and medical imaging applications have been fabricated. [ABSTRACT FROM AUTHOR]

This paper presents the design of a 3 degrees of freedom build platform for a Stereo-lithography Apparatus machine (older model without Zephyr coating). The Pahl and Beitz methodology is used to systematically design such a component. The various steps are illustrated and the final design described. The impetus for the research is the need to reduce layering errors in layer-based machines. The final solution allows the platform to rotate along two axes and be elevated along the Z-axis with minimal disruption to the present set-up. [ABSTRACT FROM AUTHOR]

This paper proposes a tolerant slicing algorithm for processing slice contours for Layered Manufacturing (LM). The algorithm aims to overcome the constraints of computer memory and the computation instability commonly inherent in conventional slicing methodologies. It minimizes memory usage by adopting a pick-and-drop approach, which extracts one facet for slicing from the Stereolithography (STL) file at a time. The facets that intersect with the cutting plane are read in, sliced and then disposed of from the memory one by one for subsequent construction of slice contours. Only the slice data and the associated topological information of the current layer are temporarily stored in the memory. This approach greatly reduces the amount of computer memory required and it involves much less computationally intensive searching operations. Thus, STL models of virtually unlimited file size can be sliced to facilitate the LM processes. The algorithm is also relatively fault-tolerant in that common defects of STL models may be tolerated and the resultant inconsistent contours are effectively repaired. [ABSTRACT FROM AUTHOR]

In this paper, methods and algorithms are presented for an efficient slicing process specifically designed for microstereolithography, a high-resolution rapid prototyping technology. Modifications are given for different implementation environments (FPU, Parallel Computing, directly wired processes). They use the common STL-format as the description of the 3D objects and compute bitmapped layers for the layered manufacturing step. Specific attention was paid to the requirements for flexibility, accuracy, supporting standards and performance. A layer-resolution of up to 32767x32767 pixels is supported. The described system is a flexible solution easy to be coupled with almost any system controller for a micro-stereolithography machine using the integral irradiation process. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the applicability and effectiveness of Stereolithography rapid prototyping to the field of scale modelling for architectural design evaluation and demonstration purposes. Two scale models concerning a modern renovated track and field sports facility and a reconstructed ancient stadium are examined. Both models were constructed by assembling together resin parts fabricated with Stereolithography instead of milling. Critical issues encountered during the building phase of the two models are addressed and presented in detail. Comments are made on the CAD requirements of the parts geometry, on the part building and the post-processing phases as well as on the end achieved accuracy. Problems associated with the computational time, related to the 3-D solid modelling, and with the physical properties of the parts, are also discussed. The present Stereolithography methodology is compared to conventional model building techniques by investigating efficiency and productivity factors, quality matters and time requirements. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study undertaken to determine the polymerisation-induced residual stresses generated in stereolithography (SL) built test specimens, by using the hole-drilling strain gage method of stress relaxation. Experimentally measured strains, using special three-element strain gage rosettes, were input into the blind-hole analysis to calculate the induced residual stresses. The mechanical properties of resin specimens fabricated by the solidification process using an epoxy based photopolymer and post-cured under ultraviolet (UV) and thermal exposure were determined and incorporated into the subsequent drill-hole analysis. The effect of the pre-selected fabrication parameters (hatching space and curing depth) and subsequent by the post-curing procedure (UV, thermal curing) on the magnitude of the recorded strains is also presented. [ABSTRACT FROM AUTHOR]

RAPID prototyping, NEW product development, PROTOTYPES, RAW materials, SHEAR waves, PHOTOPOLYMERIZATION, MANUFACTURING processes, and FINITE element method

Stereolithography is one of the rapid prototyping processes which uses a photopolymer as the raw material to build prototypes. The photopolymer absorbs energy by selective laser exposure. The curing effect starts when the absorbing energy exceeds a critical value, and the process is called photopolymerisation. The photopolymerisation changes the phase from liquid to solid. The cured volume can expand and then shrink on cooling. The process parameters such as the scanning speed, scanning path, scanning pitch, and the slicing thickness, lead to different shrinkage and curl distortion, so, the photopolymerisation process is a dynamic material behaviour. In this study, a dynamic finite element simulation code has been developed to simulate the photopolymerisation process. The simulated result for a suspended beam which corresponds to the process parameters shows that a short raster causes less curl distortion than a long raster. The experimental result agrees very well with the simulated result. [ABSTRACT FROM AUTHOR]

LIQUID crystal displays, LIQUID crystal devices, NEW product development, MANUFACTURING processes, LITHOGRAPHY, RAPID prototyping, FINITE element method, and COMPUTER simulation

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. [ABSTRACT FROM AUTHOR]

RAPID prototyping, PROTOTYPES, CONCURRENT engineering, MANUFACTURING processes, and TOMOGRAPHY

A limestone cube from Tunisia with embedded thalli of the Permian, coenocytic, cyathiform green alga, Ivanovia tebagaensis, was CT (computed tomography) scanned as a nondestructive method to study some of its morphological features. Two sets of scans were used to make three physical three-dimensional models of Ivanovia structures by rapid prototyping stereolithography or layer manufacturing: (1) an asexual reproductive bud using the initial medical CT scans; (2) a cyathiform thallus with an attached bud and a second cup fused to the bottom of the first; and (3) about ten per cent of the total rock volume. A set of high resolution scans was used to construct (2) and (3). Study of the models suggested new information on developmental stages of budding and the great extent of membrane connections. [ABSTRACT FROM AUTHOR]

RAPID prototyping, LITHOGRAPHY, MOLDING (Founding), MORPHOLOGY, PLASTICS, and METALS

The direct use of moulds produced by stereolithography (SL) provides a rapid tooling technique which allows low volume production by plastic injection moulding. The greatest advantage of the process is that it provides parts that are the same as those that would be produced by metal tooling in a fraction of the time and cost. However, work by the authors demonstrates that the parts possess different characteristics to those produced by metal tooling. This knowledge defies the greatest advantages of the SL injection moulding tooling process – the moulded parts do not replicate parts that would be produced by metal tooling. This work specifically demonstrates that a different rate of part shrinkage is experienced and subsequently investigates the mechanisms in SL tooling that induce these different part properties. The work culminates in different approaches to modifying the moulding process which allow the production of parts whose key morphological characteristics are closer to those that have been produced from metal moulds. [ABSTRACT FROM AUTHOR]