Showing papers in "Rapid Prototyping Journal in 2003"

Mechanical characterization of parts fabricated using fused deposition modeling

Abstract: Layered manufacturing is an evolution of rapid prototyping (RP) techniques where the part is built in layers. While most of the previous applications focused on building “prototypes”, recent developments in this field enabled some of the prototyping methods to achieve an agile fabrication technology to produce the final product directly. A shift from prototyping to manufacturing of the final product necessitates broadening of the material choice, improvement of the surface quality, dimensional stability, and achieving the necessary mechanical properties to meet the performance criteria. The current study is part of an ongoing project to adapt fused deposition modeling to fabrication of ceramic and multi‐functional components. This paper presents a methodology of the mechanical characterization of products fabricated using fused deposition modeling.

Slicing procedures in layered manufacturing: a review

Abstract: Layered manufacturing (LM) or rapid prototyping is a process in which a part is produced using layer‐by‐layer addition of the material. In LM, slicing of the CAD model of a part to be produced is one of the important steps. Slicing of CAD model with a very small slice thickness leads to large build time. At the same time if large slice thickness is chosen, the surface finish is very bad due to staircasing. These two contradicting issues namely reduction in build time and better surface quality have been a major concern in laminated manufacturing. This contradiction has led to the development of number of slicing procedures. The present paper reviews various slicing approaches developed for tessellated as well as actual CAD models.

Mechanical behavior of acrylonitrile butadiene styrene fused deposition materials modeling

Abstract: Analytical/Computational models for the fused deposition (FD) material stiffness and strength as a function of mesostructural parameters are developed. Effective elastic moduli are obtained using the strength of materials approach and an elasticity approach based on the asymptotic theory of homogenization. Theoretical predictions for unidirectional FD‐acrylonitrile butadiene styrene materials are validated with experimentally determined values of moduli and strength. For moduli predictions, the results were found to be satisfactory with difference between experimental and theoretical values of less than 10 percent in most cases.

Mechanisms of selective laser sintering and heat transfer in Ti powder

Abstract: Coupled metallographic examination and heat transfer numerical simulation are applied to reveal the laser sintering mechanisms of Ti powder of 63‐315 μm particle diameter. A Nd:YAG laser beam with a diameter of 2.7‐5.3 mm and a power of 10‐100 W is focused on a bed of loose Ti powder for 10 s in vacuum. The numerical simulation indicates that a nearly hemispherical temperature front propagates from the laser spot. In the region of α‐Ti just behind the front, heat transfer is governed by thermal radiation. The balling effect, formation of melt droplets, is not observed because the temperature increases gradually and the melt appears inside initially sintered powder which resists the surface tension of the melt.

Improved surface finish in 3D printing using bimodal powder distribution

Abstract: The use of bimodal powders has been shown to offer the possibility of dramatically improved surface finish in 3D printing. This work focused on individual lines, the primitive building block of 3D printed parts. It was observed that the fine component of bimodal ceramic powders, while uniformly distributed in the original powderbed, was preferentially found at the surface of the printed line, while the interior of the line was denuded of fines. Microscopic examination and approximate quantitative analysis supports the assertion that essentially all the fines have moved to the surface of the line. The mechanism for this rearrangement is not known, but is speculated to be related to the relative difficulty of wetting fine powders. The parameter space in which this phenomenon can be observed was examined in a preliminary manner.

Freeform fabrication of Nylon‐6 tissue engineering scaffolds

Abstract: The aim of this research is to develop, demonstrate and characterize techniques for fabricating such scaffolds by combining solid freeform fabrication and computational design methods. When fully developed, such techniques are expected to enable the fabrication of tissue engineering scaffolds endowed with functionally graded material composition and porosity exhibiting sharp or smooth gradients. Results of bio‐compatibility and in vivo implantation are presented.

A 3D surface offset method for STL‐format models

Abstract: This paper presents a new 3D offset method for modifying CAD model data in the STL format. In this method, vertices, instead of facets, are offset. The magnitude and direction of each vertex offset is calculated using the weighted sum of the normals of the facets that are connected to each vertex. To facilitate the vertex offset calculation, topological information is generated from the collection of unordered triangular facets making up the STL file. A straightforward algorithm is used to calculate the vertex offset using the adjoining facet normals, as identified from the topological information. This newly developed technique can successfully generate inward or outward offsets for STL models. As with any offset methodology, this technique has benefits and drawbacks, which will be discussed in this paper. Finally, conclusions will be made regarding the applicability of the developed methodology.

Design for medical rapid prototyping of cranioplasty implants

Abstract: Design methods for medical rapid prototyping (RP) of personalized cranioplasty implants are presented in this paper. These methods are applicable to model cranioplasty implants for all types of the skull defects including beyond‐midline and multiple defects. The methods are based on two types of anatomical data, solid bone models (STereoLithography files – STL) and bone slice contours (Initial Graphics Exchange Specification – IGES and StrataSys Layer files – SSL). The bone solids and contours are constructed based on computed tomography scanning data, and these data are generated in medical image processing and STL slicing packages.

The production of copper parts using DMLR

Abstract: The relationship between the major process variables (laser power, laser scan speed, scan length, beam overlap and Q‐switch pulse frequency) of direct metal laser re‐melting and their effect on the structure of single‐ and multi‐layer copper coupons has been investigated. The work successfully produced selectively fused copper powder layers and simple three‐dimensional copper structures with suitable laser parameters being identified for the production of parts, including thin‐walled cubic structures. It was shown that the specific energy density needed to melt thick powder beds was less than that to melt multi‐layer builds and that the type of substrate material used significantly affected the process parameters. Thus, the substrate and its thermal properties have a significant effect on the melt pool size and freezing rate.

Parametric error modeling and software error compensation for rapid prototyping

Abstract: This paper is motivated by the need for a generic approach to evaluate the volumetric accuracy of rapid prototyping (RP) machines The approach presented in this paper is inspired in large part by the techniques developed over the years for the parametric evaluation of coordinate measuring machine (CMM) errors In CMM metrology, the parametric error functions for the machine are determined by actual measurement of a master reference artifact with known characteristics In our approach, the RP machine is used to produce a generic artifact, which is then measured by a master CMM, and measurement results are used to infer the RP machine's parametric error functions The results presented demonstrate the feasibility of such an approach on a two‐dimensional model

Stereo‐thermal‐lithography: a new principle for rapid prototyping

Abstract: A new fabrication process for rapid prototyping is proposed in this paper. Optical and thermal effects are simultaneously used in this process to locally induce a phase change in a liquid resin. This phase change phenomena is used to “write” three‐dimensional shapes or patterns. Such objects or patterns can involve macroscopic engineering prototypes through to nanostructures for exploitation in waveguiding and photonic crystals. Several advantages can be achieved through this new process, in terms of accuracy, cost and time.

Process speeding up via deposition planning in fused deposition‐based layered manufacturing processes

Abstract: Compared to conventional manufacturing processes, fused deposition (FD)‐based layered manufacturing processes have dramatically reduced the part design and manufacturing time. However, it is necessary to further enhance their process productivity. To this end, improvement of FD process efficiency is studied in this paper. A build time analysis is conducted and the deposition parameters that can be used to speed up fabrication processes are identified. The tool path‐based deposition planning approach is extended for ensuring layer quality when the build process is expedited under adjusted deposition parameters. A test part was built to demonstrate the proposed approach.

Selective laser sintering of single‐ and two‐component metal powders

Abstract: A comparative characterisation of selective laser sintering (SLS) mechanisms of single‐ and two‐component powders is presented The effects of the volume fraction of liquid phase and the powder absorptance were discussed Single‐component Ni‐alloy, Fe and Cu powders as well as two‐component powder systems based on Ni‐alloy, Fe and Cu were investigated In particular, the following types of two‐component powder systems were studied: Ni‐alloy‐Cu and Fe‐Cu powder mixtures as well as Cu‐coated Ni‐alloy powder and Cu‐coated Fe powders SLS experiments were performed with a CW‐ Nd:YAG laser (λ=106 μm) The acting mechanism in all cases was liquid phase sintering

SIS-A New SFF Method Based on Powder Sintering

Abstract: Selective inhibition of sintering (SIS) is a layered fabrication process which is capable of rapidly producing accurate functional parts out of polymers and metals using a relatively inexpensive machine. This article presents a brief overview of the research and development aimed at establishing the feasibility and the potential of the process.

Integration of CAD and rapid manufacturing for sand casting optimisation

Abstract: In order to reduce the time and costs of the products development in the sand casting process, the SMC Colombier Fontaine company has carried out a study based on tooling manufacturing with a new rapid prototyping process. This evolution allowed the adequacy of the geometry used for the simulation to the tooling employed physically in the production. This allowed a reduction of the wall thickness to 4 mm and retained reliable manufacturing process.

Rapid prototyping for treatment of canine limb deformities

Abstract: This report describes Rapid Prototyping (RP) ‐aided assessment and preoperative planning for treatment of bilateral multifocal pelvic limb deformities in a 1 year old German Shepherd dog. Computed tomography (CT) scans were acquired on a General Electric CT scanner and converted to solid models using Mimics software from Materialise. Stereolithography patterns were prototyped using QuickCast build style on a SLA ‐190. Room temperature vulcanized silicone molds were constructed and three sets of polyurethane patterns were cast for pre‐surgical planning and rehearsal. The paper compares traditional osteotomy planning procedures using only radiographs and 2D CT images to planning with full‐scale physical biomodels. The biomodels had a clearly beneficial impact on the accuracy of surgery and positively influenced the clinical outcome.

A comparative evaluation of industrial design models produced using rapid prototyping and workshop‐based fabrication techniques

Abstract: This paper discusses a research programme in which the 3D computer aided industrial design geometry for a consumer product was translated into appearance models using the contrasting techniques of workshop‐based fabrication techniques and rapid prototyping using stereolithography. The research also examined the capacity to extend the use of the rapid prototype components for the production of a fully working prototype. The ability to combine an appearance model and a working prototype into a single “appearance prototype” was a significant advance in the application of RP within industrial design.

A Study on Effects of Process Parameters in Rapid Freeze Prototyping

Abstract: Rapid freeze prototyping is a relatively new solid freeform fabrication process, which builds a three‐dimensional part according to a CAD model by depositing and freezing water droplets layer by layer. A study on the effects of RFP process parameters including the nozzle scanning speed, droplet size, and droplet frequency in building ice parts with a single‐nozzle work head is made. Presented in this paper are the results of this study which indicate that these process parameters determine the ice layer thickness and ice line width, which in turn determine the surface roughness and the waiting time required after depositing each layer of water (i.e. between successive layers) during the ice part building process.

Biomaterial forming research using RP technology

Abstract: This paper introduces a new subject called bio‐manufacturing. Bio‐manufacturing combines life science with manufacturing science, and uses manufacturing method to form materials with bio‐activity and bio‐degradability into scaffolds. In this paper, we discuss the hierarchy of bio‐manufacturing: the lower grade uses undegradable bio‐material to form permanent organ replacement such as auricular cartilage and the higher grade uses biodegradable bio‐materials to repair organ damage or organ replacement which degrades after embedded in the human body. They all adopt jetting/extrusion deposition process (fused deposition modelling or 3D printer), the distinct different point being the temperature of the forming chamber. The samples of bones and auricular cartilage produced by those processes had been practiced on dogs and rabbits, repaired their damage.

Recent developments in metal laminated tooling by multiple laser processing

Abstract: Time reduction and quick geometrical changes of complex components and tools are currently the most important demands in product development. The manufacturing process presented in this paper is based on multiple additive and subtractive technologies such as laser cutting, laser welding, direct laser metal deposition and CNC milling. The process chain is similar to layer‐based Rapid Prototyping Techniques. In the first step, the 3D CAD geometry is sliced into layers by a specially developed software. These slices are cut by high speed laser cutting and then joined together. In this way laminated tools or parts are built. To improve surface quality and to increase wear resistance a CNC machining center is used. The system consists of a CNC milling machine, in which a 3 kW Nd:YAG laser, a coaxial powder nozzle and a digitizing system are integrated.

Investigation of an electrophotography based rapid prototyping technology

Abstract: A method for rapid prototyping based on electrophotographic powder deposition was investigated to study its potentials and to identify design and implementation challenges. This technique is referred to here as the electrophotographic rapid prototyping (ERP). In this technique, powder is printed layer‐by‐layer in the shape of the cross‐sections of the part using electrophotography a very widely used non‐impact printing method. Each layer of powder is consolidated by fusing before the next layer of powder is printed. A fully automated test bed was constructed that consists of a printing system, fusing/heating plate, build platform that has two‐degrees of freedom as well as software that drives the system.

Selective laser sintering: qualifying analysis of metal based powder systems for automotive applications

Abstract: Metal‐based powder systems for selective laser sintering applications provide flexibility in the part geometry and promise a high quality profile regarding their material technologies characteristic. In this field of application, materials have to fulfil high demands on their properties already in the conceptual phase of development. For the integration of selective laser sintered parts into the development process, determining their properties using material engineering methods is absolutely essential. This paper concerns with the methods of material analysis, the particular material properties of sintered metals and finally with the description of the properties of the powder systems EOS DirectSteel 20 and 3D Laser Form ST100 in comparison to conventional materials used in automotive engines and power trains.

A finish machining strategy for rapid manufactured parts and tools

Abstract: Rapid prototyping (RP) techniques are being increasingly used to manufacture injection molding and die casting core and cavity sets, known as tools, and for other tooling‐related parts, such as EDM electrodes. This paper presents a STL‐based finish machining technique for tools and parts made using RP techniques in order to achieve the tight tolerance and surface finish requirements necessary for tooling applications. Rotate, scale, translate and offset algorithms are used to pre‐process the 3D model prior to its manufacture. A machining strategy of adaptive raster milling of the surface, plus hole drilling and sharp edge contour machining, is developed to finish the parts and tools after fabrication using RP. Finally, a benchmark part was designed and fabricated using the above‐mentioned strategies and the results show the effectiveness of the developed software.

Vacuum casting with room temperature vulcanising rubber and aluminium moulds for rapid manufacturing of quality parts: a comparative study

Abstract: The purpose of this study was to compare costs and dimensional control parameters between same geometry parts obtained by same prototyping techniques using different material moulds. Vacuum casting was used to obtain prototypes of a three‐blade helix of a motor boat propeller. Aluminium and room temperature vulcanising (RTV) rubber moulds were manufactured and tested within the study. Manufacturing costs and dimensional control parameters were used within the comparison study. For the dimensional deviation performance factor used, no significant differences were observed relatively to the dimensional control parameters measured. However, the average deviations were smaller for the RTV rubber mould prototype.

Thermal modeling of selective area laser deposition (SALD) and SALD vapor infiltration of silicon carbide

Abstract: A 3D finite element model was developed that simulates selective area laser deposition vapor infiltration (SALDVI) of silicon carbide. The model predicts the laser input power history needed to maintain constant surface temperature and the distribution of vapor deposited SiC within the powder bed as well as on the surface of the powder bed. The model considers a moving Gaussian distribution laser beam, temperature‐ and pore‐dependent thermal conductivity, specific heat and temperature‐dependent deposition rate. Furthermore, the model also includes closed‐loop control of the laser power to achieve a desired target processing temperature on the surface of the power bed. Effects of laser scanning rates have been investigated. The simulated solid fraction and SALD distributions are also consistent in the trend with the experimental data.

The rapid tooling testbed: a distributed design‐for‐manufacturing system

Abstract: A new design‐for‐manufacturing method, called the geometric tailoring (GT), and the associated digital interface concept have been developed that enable the design activities to be separated from the manufacturing activities. Conditions for the successful application of this method are investigated. The GT method is demonstrated for rapid prototyping and rapid tooling technologies, where prototype parts are required to match the production properties as closely as possible. This method is embodied in a system called the rapid tooling testbed (RTTB). Research work is presented on GT and the distributed computing environment underlying the RTTB. Examples are summarized from the usage of this method and testbed.

An original approach for the memorisation and the generation of rapid product development processes

Abstract: This paper introduces a knowledge‐based environment dedicated to the choice of rapid product development processes. Rapid product development processes are not limited to layer‐manufacturing machines, but they also integrate CAD, reverse engineering, indirect methods for metallic and plastic part manufacturing, etc. The aim of the proposed knowledge‐based environment is to propose, from a detailed functional specification, different alternatives of rapid product development processes, which can be ordered and optimised when considering a combination of different specification criteria (cost, quality, delay, aspect, material, etc.).

The customized mandible substitute based on rapid prototyping

Abstract: Traditional standard bone substitutes cannot realize the individualized matching for the bones of different patients. In order to make a bone substitute match the shape of a patient's bone easily, a technology based on reverse engineering (RE) and rapid prototyping (RP) is put forward to design and fabricate a customized bone substitute. By RE, the customized bone substitute is designed according to the CT sectional pictures, and the customized localizer is designed to locate the customized bone substitute in the patient's body at the right position. A customized mandible substitute designed and fabricated by RE and RP has been put into clinical use and is discussed in detail. The results confirm that the advantage of RP in the field of bone restoration is that it can fabricate the customized bone substitute rapidly and accurately.

Application of similitude techniques to functional testing of rapid prototypes

Abstract: Functional testing of rapid prototypes (RP) represents an exciting area of research in solid freeform fabrication. One approach to functional testing is to use similitude techniques to correlate the behavior of an RP model and a product. Previous research at UT, Austin has resulted in the development of an empirical similitude technique for correlating the behavior of parts with different material properties. Advances in the empirical similitude technique are presented in this paper. Sources of coupling between material properties and geometric shape that produce distortions in the current empirical similitude technique are outlined. A modified approach that corrects such distortions is presented. Numerical examples are used to illustrate both the current and the advanced empirical similitude methods.

Environmental effects on the dimensions of SL5195 resin

Abstract: The effect of humidity, temperature and temperature ramping rate on the dimensional changes of the photo‐cured stereolithography (SL) resin SL5195 was investigated. It was found that moisture absorption by the SL resin is a very slow process at ambient temperatures. Varying relative humidity (RH) between 20 and 90 per cent in the environment only produced slight changes in the sample dimensions during the time period investigated. Increasing the environment temperature caused a significant increase in the sample dimensions through thermal expansion along with accelerated moisture absorption at 50 per cent or higher RH. Increasing the temperature ramping rate reduces the moisture absorption during the thermal cycles.