Rapid Prototyping Journal

Published by Emerald
Online ISSN: 1355-2546
Publications
OPTOFORM process diagram 
Test closing mould 
Final part 
New product development costs 
Cost corresponding to sample parts 
Article
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 4mm and retained reliable manufacturing process.
 
Article
Rapid Prototyping (RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys Fused Deposition Modeling (FDM) is a typical RP process that can fabricate prototypes out of ABS plastic. To predict the mechanical behavior of FDM parts, it is critical to understand the material properties of the raw FDM process material, and the effect that FDM build parameters have on anisotropic material properties. This paper characterizes the properties of ABS parts fabricated by the FDM 1650. Using a Design of Experiment (DOE) approach, the process parameters of FDM, such as raster orientation, air gap, bead width, color, and model temperature were examined. Tensile strengths and compressive strengths of directionally fabricated specimens were measured and compared with injection molded FDM ABS P400 material. For the FDM parts made with a 0.003 inch overlap between roads, the typical tensile strength ranged between 65 and 72 percent of the strength of injection molded ABS P400. The compressive strength ranged from 80 to 90 percent of the injection molded FDM ABS. Several build rules for designing FDM parts were formulated based on experimental results. Electronic access The research register for this journal is available at http://www.emeraldinsight.com/researchregisters The current issue and full text archive of this journal is available at http://www.emeraldinsight.com/1355-2546.htm 1.
 
Diagram of maximum hoop stress, belonging to selected models, results by ANSYS FE analysis
Deformation of hexagonal and octagonal structures, (a,c) total deformation; (b,d) deformation of unit cells
Article
Purpose - The purpose of this paper is to present the study of octagonal lattice structure for investment casting stereolithography (SL) patterns, and compare it with the former hexagonal structure (of the QuickCast 2.0 build style). This research aims to introduce a new internal lattice structure for investment casting SL patterns. Design/methodology/approach - Applying 3D-coupled thermal-mechanical finite element analysis; magnitudes of exerted hoop stresses on ceramic shell (during burnout stage) have been computed. As an experimental observation of stress evaluation for cylindrical hexagonal and octagonal models, magnitudes of hoop and axial strains have been evaluated by installing self-temperature compensation strain gauges. In addition, practical results have been obtained by the real-time strain gauging of the cylindrical models during the heating process up to 100°C. Findings - The performance of SL pattern depends on several factors including the void ratio, drainage ability, dimensional accuracy, and burnout ability (ability of burning out the model without ceramic shell cracking). Numerical results for new octagonal structure indicate that, there is a 62 percent reduction in maximum hoop stresses exerted on the ceramic shell. Moreover, a significant reduction of strain has been observed in both hoop and axial strains applying strain-gauging analysis (near 50 percent reduction). Besides, the obtained void ratio of the QuickCast 2.0 hexagonal and the new offset octagon structures are 90 and 95 percent, respectively. Deductive investigation has been carried out for explaining the role of the other influencing factors. The 49 percent reduction of internal mass expresses the probability of dimensional accuracy improvement for the octagonal structure. Research limitations/implications - Several deductive investigations indicate the probability of better performance for the influencing factors including void ratio, dimensional accuracy and drainage ability of the new octagonal structure. However, the main scope of the paper is to compare the performance of models during burnout stage (the magnitudes of exerted stresses and strains on ceramic shell). Therefore, a more analytical and practical approach will be a good future research for other mentioned factors. Practical implications - This research aims to address the main problem, which is the shell cracking; it is essential to have more practical investigations in other concepts that are not mentioned here though. Despite of that, the new octagonal structure will be a good replacement for former hexagonal structure, ensuring the casting foundries for using the SL patterns. Originality/value - A new generation of internal structure (or a new build style) for investment casting SL patterns is presented here. The significant reduction of critical loadings on ceramic shell will ensure investment casting foundries for using SL patterns, which are by an octagonal internal structure.
 
Article
A novel rapid prototyping technology incorporating a curved layer building style was developed. The new process, based on laminated object manufacturing (LOM), was designed for efficient fabrication of curved layer structures made from ceramics and fiber reinforced composites. A new LOM machine was created, referred to as curved layer LOM. This new machine uses ceramic tapes and fiber prepregs as feedstocks and fabricates curved structures on a curved-layer by curved-layer basis. The output of the process is a three-dimensional "green" ceramic that is capable of being processed to a seamless, fully dense ceramic using traditional techniques. A detailed description is made of the necessary software and hardware for this new process. Also reviewed is the development of ceramic preforms and accompanying process technology for net shape ceramic fabrication. Monolithic ceramic (SiC) and ceramic matrix composite (SiC/SiC) articles were fabricated using both the flat layer and curved layer LOM processes. For making curved layer objects, the curved process afforded the advantages of eliminated stair step effect, increased build speed, reduced waste, reduced need for decubing, and maintenance of continuous fibers in the direction of curvature.
 
Article
Purpose - The purpose of this paper is to illustrate the classification and coding system developed for the rapid prototyping (RP) industry. Design/methodology/approach - The similarities among RP part geometries and processes are identified and related for the development of rapid prototyping coding system (RPCS). Findings - RPCS forms a base for developing "prototyping philosophy" to take advantage of parts similarities in determination of optimal build orientation and optimization of part building cost. Research limitations/implications - Most of the examples are limited to parts built by fused deposition modelling process. But, the concept is applicable to any existing RP process. Practical implications - RPCS implementation is suitable in industries where variety of RP parts are in use. Originality/value - This is the first attempt towards development of a formal coding system for the RP industry.
 
Article
Purpose ? The purpose of this paper is to present a study of the stereolithography apparatus SLA 250-50 motivated by the introduction of the new epoxy resin AccuGen?. Design/methodology/approach ? Several process variables are examined using a Box-Behnken design and optimization techniques are employed to determine their optimal settings. Findings ? The results indicate operating conditions at which high levels of performance can be achieved. Research limitations/implications ? The results reported in this research are process specific, however, the methodology employed can be readily applied to different rapid prototyping processes. Practical implications ? Effective utilization of the SL process. Originality/value ? Quantitative understanding of the process capability in relation to key process variables.
 
Article
Purpose – The purpose of this study is to characterize sintered hydroxyapatite (HA) samples produced by three-dimensional printing (3DP). This study is part of a project concerned with the fabrication of calcium phosphates implants by 3DP. However, before considering a more complex structure, like scaffolds or implants, a thorough knowledge of the role played by the sintering temperature on physical and mechanical the properties of porous HA is necessary. Design/methodology/approach – The characteristics of sintered HA samples have been analyzed by means of x-ray diffraction, scanning electron microscope (SEM) and uniaxial compression tests. The 3DP parameters used to produce the HA samples were those who led to higher accuracy and mechanical stability. Findings – Sintering temperature and powder morphology are critical factors influencing densification behavior, porosity, phase stability, mechanical strength and tangent modulus of the HA samples produced by 3DP. This study allowed us to conclude about the 3DP parameters to be used to produce porous HA specimens with the required integrity and dimensional accuracy, and the optimal post-processing sintering temperature which led to the best results in terms of porosity, microstructure, phase stability of HA and mechanical properties. Originality/value – This paper provides a method to evaluate the manufacturability of calcium phosphate models produced by 3DP.
 
Article
Purpose – This paper aims to convert surface data directly to a three-dimensional (3D) stereolithography (STL) part. The Geographic Information Systems (GIS) data available for a terrain are the data of its surface. It doesn’t have information for a solid model. The data need to be converted into a three-dimensional (3D) solid model for making physical models by additive manufacturing (AM). Design/methodology/approach – A methodology has been developed to make the wall and base of the part and tessellates the part with triangles. A program has been written which gives output of the part in STL file format. The elevation data are interpolated and any singularity present is removed. Extensive search techniques are used. Findings – AM technologies are increasingly being used for terrain modeling. However, there is not enough work done to convert the surface data into 3D solid model. The present work aids in this area. Practical implications – The methodology removes data loss associated with intermediate file formats. Terrain models can be created in less time and less cost. Intricate geometries of terrain can be created with ease and great accuracy. Social implications – The terrain models can be used for GIS education, educating the community for catchment management, conservation management, etc. Originality/value – The work allows direct and automated conversion of GIS surface data into a 3D STL part. It removes intermediate steps and any data loss associated with intermediate file formats.
 
Article
Purpose – This study aims to investigate the options for additive rapid prototyping methods in microelectromechanical systems (MEMS) technology. Additive rapid prototyping technologies, such as stereolithography (SLA), fused deposition modeling (FDM) and selective laser sintering (SLS), all commonly known as three-dimensional (3D) printing methods, are reviewed and compared with the resolution requirements of the traditional MEMS fabrication methods. Design/methodology/approach – In the 3D print approach, the entire assembly, parts and prototypes are built using various plastic and metal materials directly from the software file input, completely bypassing any additional processing steps. The review highlights their potential place in the overall process flow to reduce the complexity of traditional microfabrication and long processing cycles needed to test multiple prototypes before the final design is set. Findings – Additive manufacturing (AM) is a promising manufacturing technique in micro-device technology. Practical implications – In the current state of 3D printing, microfluidic and lab-on-a-chip devices for fluid handling and manipulation appear to be the most compatible with the 3D print methods, given their fairly coarse minimum feature size of 50-500 μm. Future directions in the 3D materials and method development are identified, such as adhesion and material compatibility studies of the 3D print materials, wafer-level printing and conductive materials development. One of the most important goals should be the drive toward finer resolution and layer thickness (1-10 μm) to stimulate the use of the 3D printing in a wider array of MEMS devices. Originality/value – The review combines two discrete disciplines, microfabrication and AM, and shows how microfabrication and micro-device commercialization may benefit from employing methods developed by the AM community.
 
Article
Purpose – The purpose of the present study is to investigate statistically controlled investment casting (IC) solution of fused deposition modeling (FDM)-based ABS replicas. Design/methodology/approach – The work started with the identification of the benchmark/component. Prototypes (to be used as pattern) were built on FDM with ABS plastic material, followed by IC. The measurements on final casting prepared were made on the co-ordinate measuring machine (CMM) from which international tolerance (IT) grades were calculated to establish the dimensional accuracy of the components. Findings – This study further highlighted the cast component properties (like hardness and surface finish) for suitability of this process. Final castings produced are acceptable as per international standard organization (ISO) standard UNI EN 20286-I (1995). Originality/value – This process ensures development of statistically controlled IC solution as technological prototypes and proof of concept at less production cost and time.
 
Article
Purpose – The aim of this work is to study the influence of the quality (surface profile) of the support base on dimensional accuracy in the Z-axis in fused deposition modeling (FDM). Design/methodology/approach – The surface profile of a support base produced using a standard (default) FDM configuration is analyzed experimentally, and two new deposition configurations are proposed. Some parts are built using these approaches, and the influence of the profile on Z accuracy is investigated. The parts are examined using a contact method and measured using a caliper. Findings – The surface profile of the support base has a direct influence on FDM part accuracy in Z. The results show that the accuracy in the Z dimension of an FDM prototype can be increased by improving the surface quality of the support base. In cases where accuracy is paramount, this can be achieved by better planning (tuning) of the support strategy. Originality/value – A significant component of the Z error in FDM has been identified and studied.
 
Comparison of powder usage between full build and compact adaptation device.
Comparison of preparation time between full build and compact adaptation device.
SLS parameters setting for PCL and PVA powder
Comparison between compact adaptation device and AAS in terms of powder efficiency.
Schematic diagram of the ASM: (a) The ASM just before activated by the triggering mechanism, (b) the activated ASM with open powder depository plate.
Article
Purpose – In recent years, selective laser sintering (SLS) has been used in the biomedical field, including building small‐scaled biomedical devices such as tissue engineering scaffolds and drug delivery devices. A compact adaptation system for the SLS is needed to obtain a more effective and efficient way of sintering small‐scale prototypes so as to reduce powder wastage. Limitations of available smaller‐scale adaptation devices include the need of additional electrical supplies for the device. The purpose of this paper is to report the development of such a system to be mounted at the SLS part bed without any additional energy supply. Design/methodology/approach – The compact adaptation device works on the concept of transferring the motion of the SLS part bed onto the part bed of the compact adaptation device. The device is an integrated attachment that is fixed onto the building platform of the SLS. The gear system of the device lifts the powder supply bed at both sides of the device simultaneously when the part bed at the center of the device is lowered. To further increase powder saving, an improved powder delivery system named alternative supply mechanism (ASM) is mounted on top of the roller to be coupled together with the compact adaptation device. Findings – Powder saving up to 6.5 times compared to using full build version of the Sinterstation 2500 has been achieved by using the compact adaptation device. Furthermore, powder wastage has been reduced by 84 percent when using the ASM compared to the compact adaptation device alone. Originality/value – The paper demonstrates the development and viability of adaptation devices for SLS to significantly reduce powder consumption by using solely mechanical means to build small parts without using external power supply.
 
Article
Purpose – The purpose of this paper is to study cyber-enabled manufacturing systems (CeMS) for additive manufacturing (AM). The technology of AM or solid free-form fabrication has received considerable attention in recent years. Several public and private interests are exploring AM to find solutions to manufacturing problems and to create new opportunities. For AM to be commercially accepted, it must make products reliably and predictably. AM processes must achieve consistency and be reproducible. Design/methodology/approach – An approach we have taken is to foster a basic research program in CeMS for AM. The long-range goal of the program is to achieve the level of control over AM processes for industrial acceptance and wide-use of the technology. This program will develop measurement, sensing, manipulation and process control models and algorithms for AM by harnessing principles underpinning cyber-physical systems (CPS) and fundamentals of physical processes. Findings – This paper describes the challenges facing AM and the goals of the CeMS program to meet them. It also presents preliminary results of studies in thermal modeling and process models. Originality/value – The development of CeMS concepts for AM should address issues such as part quality and process dependability, which are key for successful application of this disruptive rapid manufacturing technology.
 
Article
Purpose – The purpose of this paper is to propose an integrated decision-making model for multi-attributes decision-making (MADM) problems in additive manufacturing (AM) process planning and for related MADM problems in other research areas. Design/methodology/approach – This research analyzed the drawbacks of former methods and then proposed two sub-decision-making models, “deviation model” and “similarity model”. The former sub-model aimed to measure the deviation extent of each alternative to the aspired goal based on analyzing Euclidean distance between them, whereas the latter sub-model applying grey incidence analysis was used to measure the similarity between alternatives and the expected goal by investigating the curve shape of each alternative. Afterwards, an integrated model based on the aggregation of the two sub-models was proposed and verified by a numerical example and simple case studies. Findings – The calculating results of the cited numerical example and the comparison to former related research showed that this proposed model is more practical and reasonable than former methods applied in MADM problems of AM. In addition, the proposed model can be applied in other fields where MADM problems exist. Originality/value – This proposed integrated model not only considered the deviation extent of alternatives to the aspired goal but also investigated the similarity between alternatives and the expected goal. The similarity analysis compensates the drawbacks of traditional “distance-based” models or methods that cannot distinguish alternatives which have the same distance-based index value.
 
Article
Purpose – The purpose of this paper is to propose a methodology to estimate manufacturing complexity for both machining and layered manufacturing. The goal is to take into account manufacturing constraints at design stage in order to realize tools (dies and molds) by a combination of a subtractive process (high‐speed machining) and an additive process (selective laser sintering). Design/methodology/approach – Manufacturability indexes are defined and calculated from the tool computer‐aided design (CAD) model, according to geometric, material and specification information. The indexes are divided into two categories: global and local. For local indexes, a decomposition of the tool CAD model is used, based on an octree decomposition algorithm and a map of manufacturing complexity is obtained. Findings – The manufacturability indexes values provide a well‐detailed view of which areas of the tool may advantageously be machined or manufactured by an additive process. Originality/value – Nowadays, layered manufacturing processes are coming to maturity, but there is still no way to compare these new processes with traditional ones (like machining) at the early design stage. In this paper, a new methodology is proposed to combine additive and subtractive processes, for tooling design and manufacturing. A manufacturability analysis is based on an octree decomposition, with calculation of manufacturing complexity indexes from the tool CAD model.
 
Article
Purpose – The purpose of this paper is to systematically and critically review the literature related to process design and modeling of fused deposition modeling (FDM) and similar extrusion-based additive manufacturing (AM) or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature focusing on process design and mathematical process modeling was carried out. Findings – FDM and similar processes are among the most widely used rapid prototyping processes with growing application in finished part manufacturing. Key elements of the typical processes, including the material feed mechanism, liquefier and print nozzle; the build surface and environment; and approaches to part finishing are described. Approaches to estimating the motor torque and power required to achieve a desired filament feed rate are presented. Models of required heat flux, shear on the melt and pressure drop in the liquefier are reviewed. On leaving the print nozzle, die swelling and bead cooling are considered. Approaches to modeling the spread of a deposited road of material and the bonding of polymer roads to one another are also reviewed. Originality/value – To date, no other systematic review of process design and modeling research related to melt extrusion AM has been published. Understanding and improving process models will be key to improving system process controls, as well as enabling the development of advanced engineering material feedstocks for FDM processes.
 
Article
This is a journal article. It was published in the Rapid prototyping journal [© Emerald Group Publishing Limited] and the definitive version is available at www.emeraldinsight.com/1355-2546.htm (DOI: 10.1108/13552540810862073) Purpose - This paper investigates the accuracy and repeatability of the indirect selective laser sintering of aluminium process. Design/Methodology/Approach – In this paper we characterised the shrinkage of indirect SLS aluminium parts during the various stages of production. Standard scale parts were measured using a Giddings and Lewis co-ordinate measuring machine in both the green and infiltrated condition. Findings – The conducted experiments show that the most accuracy is lost during furnace cycle and that the greatest loss of accuracy occurred in the Z dimensions. Additionally the position of parts within the part bed in both X, Y and Z is shown to influence accuracy, with smaller parts being built closer to the edge of the bed later in the build. These results have been interpreted as being a result of the phenomenon of “Z-growth”. Finally the research shows that the overall accuracy of the indirect selective laser sintering of aluminium process is comparable with many existing processes such as investment casting. Originality/Value – Before any new material can be accepted, there is a need to not only fully characterise the dimensional accuracy attainable, but gain a though understanding of the processes that contribute to the inaccuracies. This paper addresses this need.
 
Article
This is a journal article. It was published in the journal, Rapid prototyping journal [© Emerald Group Publishing Limited (MCB University Press)]and the definitive version is available at: http://www.emeraldinsight.com/1355-2546.htm 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, this is explained by the fact that the tool’s surface acts in a rubber like manner during part ejection. 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.
 
Article
Attempts to answer the frequently asked questions “where is rapid prototyping now?” and “where is it going?”. Begins by assessing the state of the worldwide market for rapid prototyping (RP) systems, and goes on to detail the factors that will determine the level of future growth. Some of these are technical issues, others are human factors. Provides an overview of how RP technology is developing, and concludes with an upbeat view of the potential for growth in the industry.
 
Article
Purpose – Maxillofacial prosthetics is faced with increasing patient numbers and cost constraints leading to the need to explore whether computer‐aided techniques can increase efficiency. This need is addressed through a four‐year research project that identified quality, economic, technological and clinical implications of the application of digital technologies in maxillofacial prosthetics. The purpose of this paper is to address the aspects of this research that related to the application of rapid prototyping (RP). Design/methodology/approach – An action research approach is taken, utilising multiple case studies to evaluate the current capabilities of digital technologies in the preparation, design and manufacture of maxillofacial prostheses. Findings – The research indicates where RP has demonstrated potential clinical application and where further technical developments are required. The paper provides a technical specification towards which RP manufacturers can direct developments that would meet the needs of maxillofacial prosthetists. Originality/value – Whilst research studies have explored digital technologies in maxillofacial prosthetics, they have relied on individual studies applying a single RP technology to one particular aspect of a prosthesis. Consequently, conclusions on the wider implications have not been possible. This research explored the application of digital technologies to every aspect of the design and manufacture of a series of maxillofacial prostheses. Unlike previous research, the cases described here addressed the application of RP to the direct manufacture of substructures, retention components and texture. This research analyses prosthetic requirements to ascertain target technical specifications towards which RP processes should be developed.
 
Article
Purpose – Different metals have been processed using laser‐based solid freeform fabrication (SFF) processes but very little work has been published on the selective laser melting (SLM) of gold (Au). The purpose of this paper is to check the properties of gold powder and identify suitable processing parameters for SLM of 24 carat gold powder. Design/methodology/approach – A full factorial approach was used to vary the processing parameters and identify suitable processing region for gold powder. The effects of laser processing parameters on the internal porosity of the multi‐layer parts were examined. Findings – The gold powder was found to be cohesive in nature with apparent and tap densities of 9.3 and 10.36 g/cm³, respectively. The reflectance of gold powder was found to be 85 per cent in the infrared range. A very narrow good melting region was identified for gold powder. The balling phenomenon was observed at both low and high scan speeds. The size of droplets in the balling region tended to increase with increasing laser power and decreasing scan speeds. The porosity in gold multi‐layer parts was found to be the minimum for a laser power of 50 W and scan speed of 65 mm/s where most of the porosity was found to be inter‐layer porosity. Originality/value – This research is the first of its kind directly processing 24 carat gold using SLM, identifying the suitable processing parameters and its effect on the internal porosity and structure of multi‐layer parts.
 
Article
Purpose – This study aims to provide an overview of rapid prototyping (RP) and shows the potential of this technology in the field of medicine as reported in various journals and proceedings. This review article also reports three case studies from open literature where RP and associated technology have been successfully implemented in the medical field. Design/methodology/approach – Key publications from the past two decades have been reviewed. Findings – This study concludes that use of RP-built medical model facilitates the three-dimensional visualization of anatomical part, improves the quality of preoperative planning and assists in the selection of optimal surgical approach and prosthetic implants. Additionally, this technology makes the previously manual operations much faster, accurate and cheaper. The outcome based on literature review and three case studies strongly suggests that RP technology might become part of a standard protocol in the medical sector in the near future. Originality/value – The article is beneficial to study the influence of RP and associated technology in the field of medicine.
 
Article
Purpose To investigate the effects of the infra‐red power level on sintering behaviour in the high speed sintering (HSS) process. Design/methodology/approach Single‐layer parts were produced using the HSS process, in order to determine the effect of the infra‐red power level on the maximum achievable layer thickness, and the degree of sintering. The parts were examined using both optical microscopy and contact methods. Findings It was initially expected that an increase in the infra‐red lamp powder might allow an increase in the depth of sintering that could be achieved, as a result of increased thermal transfer through the powder. However, results in fact indicated that there is a maximum layer thickness that can be achieved, as a result of part shrinkage in the z direction. Optical microscopy images have shown that a greater degree of sintering occurs at higher power levels, which would be expected to correspond to an improvement in the mechanical properties of the parts produced. These images also indicate that the radiation absorbing material forms in small “islands” on the powder bed surface. As sintering progresses, these islands begin to merge; this occurs to a greater extent at higher infra‐red lamp powers. Research limitations/implications These results are based only on single layer parts. Further work will examine the sintering characteristics of multiple layer parts. Practical implications Results have shown that, whilst it is not possible to increase the achievable layer thickness of the parts produced by modifying the infra‐red lamp power, the degree of sintering can be improved greatly by increasing the power. Originality/value HSS is an entirely new process which is currently still under development; the results presented here will directly impact the direction of further development and research into this process.
 
Article
Purpose – The purpose of this paper is to investigate a build process variation for fused deposition modeling (FDM) in which contours and rasters (also referred to as internal fill patterns) are built using different layer thicknesses and road widths. In particular, the paper examines the effect of the build process variation on surface roughness, production times and mechanical properties. Additionally, a unique FDM process was developed that enabled the deposition of discrete multiple materials at different layers and regions within layers. Design/methodology/approach – A multi-material, multi-technology FDM system was developed and constructed to enable the production of parts using either discrete multi-materials or the build process variation (variable layer thickness and road width). Two legacy FDM machines were modified and installed onto a single manufacturing system to allow the strategic, spatially controlled thermoplastic deposition with multiple extrusion nozzles of multiple materials during the same build. This automated process was enabled by the use of a build platform attached to a pneumatic slide that moved the platform between the two FDM systems, an overall control system, a central PC and a custom-made program (FDMotion) and graphic user interface. The term multi-technology FDM system used here implies the two FDM systems and the integration of these systems into a single manufacturing environment using the movable platform and associated hardware and software. Future work will integrate additional technologies within this system. Parts produced using the build process variation utilized internal roads with 1,524 μm road width and 508 μm layer height, while the contours used 254 μm road width and 127 μm layer height. Measurements were performed and compared to standard FDM parts that included surface roughness of planes at different inclinations, tensile testing and fabrication times. Findings – Results showed that when compared to the standard FDM process, the parts produced using the build process variation exhibited the same tensile properties as determined by a student's t-test (p-values > 0.05, μ1-μ2 = 0, n = 5). Surface roughness measurements revealed that the process variation resulted in surface roughness (Ra) improvements of 55, 43, 44 and 38 per cent for respective planes inclined at 10, 15, 30 and 45° from vertical. In addition, for a 50.8 × 50.8 mm square section (25.4 mm tall), the build process variation required a minimum of 2.8 hours to build, while the standard FDM process required 6.0 hours constituting a 53 per cent reduction in build time. Finally, several manufacturing demonstrations were performed including the fabrication of a discrete PC-ABS sandwich structure containing tetragonal truss core elements. Originality/value – This paper demonstrates a build strategy that varies contour and raster widths and layer thicknesses for FDM that can be used to improve surface roughness – a characteristic that has historically been in need of improvement – and reduce fabrication time while retaining mechanical properties.
 
Article
Purpose – The purpose of this paper is to present a qualitative and quantitative comparison and evaluation of an open-source fused deposition modeling (FDM) additive manufacturing (AM) system with a proprietary FDM AM system based on the fabrication of a custom benchmarking model. Design/methodology/approach – A custom benchmarking model was fabricated using the two AM systems and evaluated qualitatively and quantitatively. The fabricated models were visually inspected and scanned using a 3D laser scanning system to examine their dimensional accuracy and geometric dimensioning and tolerancing (GD&T) performance with respect to the computer-aided design (CAD) model geometry. Findings – The open-source FDM AM system (CupCake CNC) successfully fabricated most of the features on the benchmark, but the model did suffer from greater thermal warping and surface roughness, and limitations in the fabrication of overhang structures compared to the model fabricated by the proprietary AM system. Overall, the CupCake CNC provides a relatively accurate, low-cost alternative to more expensive proprietary FDM AM systems. Research limitations/implications – This work is limited in the sample size used for the evaluation. Practical implications – This work will provide the public and research AM communities with an improved understanding of the performance and capabilities of an open-source AM system. It may also lead to increased use of open-source systems as research testbeds for the continued improvement of current AM processes, and the development of new AM system designs and processes. Originality/value – This study is one of the first comparative evaluations of an open-source AM with a proprietary AM system.
 
Article
Purpose – The purpose of this paper is to detail the development of a multimedia courseware that enhances the learning of rapid prototyping (RP) among professionals, senior year and graduate students. Design/methodology/approach – The design and development of the multimedia courseware is based on a “visit a science museum” concept where each topic can be accessed depending on the interests or the needs of users. Factors that influence learning curve such as structure of information, application of visual and auditory components and human‐computer interface are addressed and discussed. Findings – Instructions using multimedia significantly enhances the education process of RP technology. Methods to produce a good multimedia courseware have been introduced. Originality/value – This paper describes the latest version of the multimedia courseware which is an accompaniment to the third edition of the book entitled Rapid Prototyping: Principles & Applications published in 2009.
 
Article
Purpose – The purpose of this study is to explore the dependence of material properties and failure criteria for fused deposition modeling (FDM) polycarbonate on raster orientation. Design/methodology/approach – Tension, hardness and density measurements were conducted on a range of specimens at raster angles between 0 and 90° at 15° intervals. Specimens were manufactured so the raster angle was constant throughout each specimen (no rotation between adjacent layers). The yield strength, tensile strength, per cent elongation, elastic modulus, hardness and density of the material were measured as a function of raster angle. The orientation dependence of the properties was then analyzed and used to motivate a failure mechanism map for the material. Findings – The properties of the material were found to be highly orientation-dependent. The variations in mechanical properties were explained to first order using a failure mechanism map similar to those generated for fiber-reinforced composites. Originality/value – In addition to providing valuable experimental data for FDM polycarbonate, the study proposes micro-mechanisms of failure that appear to explain and capture the angular variation of strength with raster orientation. The fact that analysis methods which have been used for composites appear to apply to FDM materials suggests rich areas for future exploration.
 
Example of embossed features 
Example of minimised supports 
Surgical planning screen capture showing placement of distraction device 
Areas for design improvement 
Article
This article was accepted for publication in the Rapid Prototyping Journal [© Emerald] and the definitive version is available at: www.emeraldinsight.com/1355-2546/ Purpose – The computer-aided design (CAD) and manufacture of custom-fitting surgical guides have been shown to provide an accurate means of transferring computer-aided planning to surgery. To date guides have been produced using fragile materials via rapid prototyping techniques such as stereolithography (SLA), which typically require metal reinforcement to prevent damage from drill bits. The purpose of this paper is to report case studies which explore the application of selective laser melting (SLM) to the direct manufacture of stainless steel surgical guides. The aim is to ascertain whether the potential benefits of enhanced rigidity, increased wear resistance (negating reinforcement) and easier sterilisation by autoclave can be realised in practice. Design/methodology/approach – A series of clinical case studies are undertaken utilising medical scan data, CAD and SLM. The material used is 316L stainless steel, an alloy typically used in medical and devices and surgical instruments. All treatments are planned in parallel with existing techniques and all guides are test fitted and assessed on SLA models of the patients' anatomy prior to surgery. Findings – This paper describes the successful application of SLM to the production of stainless steel surgical guides in four different maxillofacial surgery case studies. The cases reported address two types of procedure, the placement of osseointegrated implants for prosthetic retention and Le Fort 1 osteotomies using internal distraction osteogenesis. The cases reported here have demonstrated that SLM is a viable process for the manufacture of custom-fitting surgical guides. Practical implications – The cases have identified that the effective design of osteotomy guides requires further development and refinement. Originality/value – This paper represents the first reported applications of SLM technology to the direct manufacture of stainless steel custom-fitting surgical guides. Four successful exemplar cases are described including guides for osteotomy as well as drilling. Practical considerations are presented along with suggestions for further development. Accepted for publication
 
Article
Looks at “fabbing” – digital fabricating of physical products and its future in the business world via the Internet. Concludes that this is a process that is here to stay and therefore technology needs to become more sophisticated to accommodate it. The research register for this journal is available at http://www.mcbup.com/research_registers. The current issue and full text archive of this journal is available at http://www.emerald-library.com/ft.
 
Article
Purpose – This paper aims to investigate the changes in tensile properties of novel functionally graded materials (FGMs) and wafer structures created by direct metal deposition (DMD) additive manufacturing (AM) technology. Design/methodology/approach – Laser-assisted DMD was used to create two innovative sets of metallic structures – the functionally graded and wafer-layered structures – using pairs of six different engineering alloys in different combinations. These alloys were selected due to their high popularity within a diverse range of industries and engineering applications. The laser-assisted DMD was selected as a suitable technique to create these complex structures because of its capability to deposit more than one alloy powder at a time. After creation of these structures, their tensile strength was tested in a series of tensile tests and the results were compared with those of single alloy samples. Findings – It was observed that the mechanical properties of FGMs and wafer structure samples were clearly different from those of the single alloy samples, a fact which creates a whole pool of opportunities for development of new materials or structures with desired mechanical properties that cannot be achieved in single alloy parts. Originality/value – The study demonstrates the application of the DMD process to produce unique structures and materials, which would be high in demand in engineering applications, where metallic parts are exposed to high loads and where excessive tensile stresses may adversely affect the performance of such parts.
 
Article
Purpose - This research was undertaken to develop a process chain for design and manufacture of endplates of intervertebral disc implants, with specific emphasis on designing footprint profiles and matching endplate geometry.Design/methodology/approach - Existing techniques for acquiring patient-specific information from CT scan data was and a user-friendly software solution was developed to facilitate pre-surgical planning and semi-automated design. The steps in the process chain were validated experimentally by manufacturing Ti6Al4V endplates by means of Direct Metal Laser Sintering to match vertebrae of a cadaver and were tested for accuracy of the implant-to-bone fitment.Findings - Intervertebral disc endplates were successfully designed and Rapid Manufactured using a biocompatible material. Accuracy within 0.37mm was achieved. User-friendly, semi-automated design software offers an opportunity for surgeons to become more easily involved in the design process and speeds up the process to more accurately develop a custom-made implant.Research limitations/implications - This research is limited to the design and manufacture of the bone-implant contacting interface. Other design features, such as keels which are commonly used for implant fixation as well as the functionality of the implant joint mechanics were not considered as there may be several feasible design alternatives.Practical implications - This research may change the way that current intervertebral disc implants are designed and manufactured.Originality/value - Apart from other areas of application (cranial, maxillofacial, hip, knee, foot) and recent research on customized disc nucleus replacement, very little work has been done to develop patient-specific implants for the spine. This research was conducted to contribute and provide much needed progress in this area of application.
 
Article
A processing algorithm for freeform fabrication of heterogeneous structures is presented. The algorithm was developed based on the heterogeneous fabrication structural model, which was constructed from the STL based multi-material volume regions and with material identifications. The reasoning Boolean operation based modelling approach was used to construct the heterogeneous CAD assembly and to output the needed STL format. Procedures for generating the database hierarchy and the storage of the heterogeneous structural model, and derivation for developing the processing algorithm for layered fabrication of heterogeneous structure are presented. The developed algorithm was applied to a heterogeneous structure consisting of two discrete material volumes, and the detailed processing path is described.
 
Flexural strength result of the three-point bending related to the specimen 
Comparisons of the (a) tensile test and (b) flexural test results with the production time and amount of support material 
Article
Purpose – The mechanical properties and surface finish of functional parts are important consideration in rapid prototyping, and the selection of proper parameters is essential to improve manufacturing solutions. The purpose of this paper is to describe how parts manufactured by fused deposition modelling (FDM), with different part orientations and raster angles, were examined experimentally and evaluated to achieve the desired properties of the parts while shortening the manufacturing times due to maintenance costs. Design/methodology/approach – For this purpose, five different raster angles (0°, 30°, 45°, 60° and 90°) for three part orientations (horizontal, vertical and perpendicular) have been manufactured by the FDM method and tested for surface roughness, tensile strength and flexural strength. Also, behaviour of the mechanical properties was clarified with scanning electron microscopy images of fracture surfaces. Findings – The research results suggest that the orientation has a more significant influence than the raster angle on the surface roughness and mechanical behaviour of the resulting fused deposition part. The results indicate that there is close relationship between the surface roughness and the mechanical properties. Originality/value – The results of this paper are useful in defining the most appropriate raster angle and part orientation in minimum production cost for FDM components on the basis of their expected in-service loading.
 
Article
This paper discusses how the estimation of the temperature field in the powder bed in selective laser sintering is a key issue for understanding sintering/binding mechanisms and for process optimisation. Carried out within a European research project, funded by INTAS (No. 99-1559, 2000-02), a model of independent small thermal contacts to calculate the effective contact conductivity in Ti powder bed was developed. This paper won the Emerald Literati Awards' Outstanding Paper 2004 (http://www.emeraldinsight.com/literaticlub/winners). 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 a-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. (Emerald Publishing Group Limited)
 
Article
The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones. Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are "stacked" inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone. The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing. This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate.
 
Article
Purpose – The purpose of this paper is to present a method of rapid prototyping (RP) used in the development of a regenerative pump impeller. RP technology was used to create complex impeller blade profiles for testing as part of a regenerative pump optimisation process. Regenerative pumps are the subject of increased interest in industry. Design/methodology/approach – Ten modified impeller blade profiles, relative to the standard radial configuration, were evaluated with the use of computational fluid dynamics (CFD) and experimental testing. Prototype impellers were needed for experimental validation of the CFD results. The manufacture of the complex blade profiles using conventional milling techniques is a considerable challenge for skilled machinists. Findings – The complexity of the modified blade profiles would normally necessitate the use of expensive computer numerically controlled machining with five-axis capability. With an impeller less than 75 mm in diameter with a maximum blade thickness of 1.3 mm, a rapid manufacturing technique enabled production of complex blade profiles that are dimensionally accurate and structurally robust enough for testing. Research limitations/implications – As more advanced RP machines become available in the study in the coming months, e.g. selective laser sintering, the strength of the parts particularly for higher speed testing will improve and the amount of post processing operations will reduce. Practical implications – This technique offers the possibility to produce components of increased complexity whilst ensuring quality, strength, performance and speed of manufacture. Originality/value – The ability to manufacture complex blade profiles that are robust enough for testing, in a rapid and cost effective manner is proving essential in the overall design optimisation process for the regenerative pump.
 
Article
Purpose – The paper aims to fabricate an α-tricalcium phosphate (TCP) scaffold with an interconnected porous structure via selective laser sintering (SLS). To inhibit the phase transformation from β- to α-TCP in fabrication process of porous scaffolds, a small amount (1 weight per cent) of poly (L-lactic acid) (PLLA) is added into β-TCP powder to introduce the transient liquid phase. Design/methodology/approach – The paper opted for the transient liquid phase of melting PLLA to decrease the sintering temperature in SLS. Meanwhile, the densification of β-TCP is enhanced with a combined effect of the capillary force caused by melting PLLA and the surface energy of β-TCP particles. Moreover, the PLLA will gradually decompose and completely disappear with laser irradiation. Findings – The testing results show the addition of PLLA enables the scaffolds to achieve a higher β-TCP content of 77 ± 1.49 weight per cent compared with the scaffold sintered from β-TCP powder (60 ± 1.65 weight per cent), when the laser energy density is 0.4 J/mm2. The paper provides the mechanism of PLLA inhibition on the phase transformation from β- to α-TCP. And the optimum sintering parameters are obtained based on experimental results, which are used to prepare a TCP scaffold with an interconnected porous structure via SLS. Research limitations/implications – This paper shows that the laser energy density is an important sintering parameter that can provide the means to control the micro-porous structure of the scaffold. If the laser energy density is too low, the densification is not enough. On the other hand, if the laser energy density is too high, the microcracks are observed which are attributed to the volume expansion during the phase transformation from β- to α-TCP. Therefore, the laser energy density must be optimized. Originality/value – The paper provides a feasible method for fabricating TCP artificial bone scaffold with good biological and mechanical properties.
 
Article
This is a journal article. It was published in the journal, Rapid prototyping journal [© Emerald] and the definitive version is available at: http://www.emeraldinsight.com/1355-2546.htm In this work the changes to stereolithography (SL) resin mechanical properties during the injection moulding process were evaluated. A multi-impression SL mould was built and used to inject a series of small flat mouldings. The fixed half SL tool insert included recesses to accommodate tensile test specimens. Tensile test specimens made from SL resin were positioned in these recesses and plastic parts were injected. After injecting a predetermined number of mouldings, tensile tests were performed using the tensile test specimens. The results from the tensile tests showed that the thermal cycling encountered during the injection moulding process did not significantly affect the mechanical properties of the resin. Observations indicated that reducing the temperatures encountered in the tool may lead to longer tool life.
 
Article
Purpose - Laser sintering kinetics and part reliability are critically dependent on the melt viscosity of materials, including polyamide 12 (PA-12). The purpose of this paper is to characterise the viscosity of PA-12 powders using alternative scientific methods: constrained boundary flows (capillary rheometry) and rotational rheometry.Design/methodology/approach - Various PA-12 powders were selected and characterised by both techniques. Measurement of molecular weight was also carried out to interpret the viscosity data.Findings - Results demonstrate conventional pseudoplastic flow in all PA-12 materials. Zero-shear viscosity has been quantified by rotational rheometry; a notable observation is the striking difference between virgin / used PA-12. This is interpreted in terms of molecular weight and chain structure modifications, arising from polycondensation of PA-12 held at the bed temperature during laser sintering.Research limitations/implications - Accurate zero-shear viscosity data provide scope for use in predictive computational models for laser sintering processes. Careful sample preparation and equipment operation are critical prerequisites for accurate rheological characterisation of PA-12 powders.Practical implications - Differences in flow behaviour and molecular structure allow prediction and deeper understanding of process-property relationships in laser sintering, giving potential for further optimisation of material specification and in-process machine parameter control.Originality/value - This is believed to be the first time that techniques other than MFR have been reported to measure the viscosity of PA-12 in a laser sintering context, noting the effects of pre-drying and molecular weight, then predicting differences between virgin / used powders in practical sintering behaviour.
 
Article
This is a journal article. It was published in the journal, Rapid prototyping journal [© Emerald Group Publishing Limited (MCB University Press)]and the definitive version is available at: http://www.emeraldinsight.com/1355-2546.htm 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, this is explained by the fact that the tool’s surface acts in a rubber like manner during part ejection. 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.
 
Article
Presents algorithms for determining the paths employed by the Proteus rapid prototyping system when building three-dimensional parts. Proteus is a fused deposition modeling system that extrudes a thermoplastic in beads through a nozzle. Determines within each layer of the layered manufacturing process, the material deposition paths as well as the regions where local structures are required to support these paths. Computes the paths with the goal of reducing the amount of supports needed to build the physical prototype of the part by taking advantage of the two novel manufacturing techniques of shelving and bridging that had been developed previously. The path planning algorithms presented are designed to utilize the above techniques and address the variety of conditions that appear in practice allowing the Proteus system to “build in air”.
 
Article
Analyses the market for rapid prototyping equipment and reports on the rapid growth that this market has experienced over the last ten years. Highlights the companies that are winning business and the technologies that are influencing growth. Describes applications of rapid prototyping for automotive parts, pharmaceutical pill bottles and jewellery design. Reports on new technology used by recently introduced low-cost 3D printing machines for concept modelling and outlines new materials that have been developed to improve the performance and functionality of prototypes.
 
Current prototype classes as manufactured by some RP/RT techniques 
Some indirect and direct rapid tooling routes (SLS-PM: selective laser sintering of polymer-coated metal powder) 
Comparison of the number of steps necessary to complete a part via different RT methods 
Article
Rapid prototyping technologies are now evolving toward rapid tooling. The reasons for this extension are found in the need to further reduce the time-to-market by shortening not only the development phase, but also the industrialization phase of the manufacturing process. The present state of rapid tooling is reviewed and the direct rapid tooling concept, aimed at developing direct and rapid tool manufacturing processes, is presented, along with three promising methods. Their intrinsic properties are outlined and compared. Necessary research and development are described in terms of direct rapid tooling requirements.
 
Article
Purpose ‐ Additive manufacturing raw material cost has been recently confirmed as a significant obstacle to widespread deployment of these technologies in industry. Aiming at reducing the cost of the selective laser melting (SLM) process, the purpose of this paper is to evaluate the different properties of products fabricated by SLM using low-cost ($10/Kg) feedstock 304L stainless steel powders. The entire process cost was also evaluated. Design/methodology/approach ‐ Using an experimental approach, 24 samples with different shapes and sizes were fabricated with layer thickness of 30, 50 and 70?µm and laser scanning speed set at 70 and 90?mm/s. Part geometry, dimensional tolerance, surface quality, density, mechanical properties and microstructure were evaluated. Findings ‐ Results confirmed that the SLM of low-cost 304L powder was successful and could produce functional parts with fine details and small wall thickness. Using small layer thickness and low scanning speed improved the properties by more than 20 per cent. At a layer thickness of 30?µm and speed of 70?mm/s, density was 92 per cent and hardness was 190?HV. At layer thickness of 70?µm porosity increases and cracks started to form which decreased strength and ductility. The steel remained austenitic with no carbide films at grain boundaries due to the high melting and cooling cycles. Research limitations/implications ‐ This research was limited to 304L powders. Future work should be done on different materials and should include the effect of post processing heat treatment on improving the mechanical properties and microstructure. Practical implications ‐ The cost of the SLM process using feedstock powders was less than 10per cent of the cost of using the special powders from a machine manufacturer with almost no effect on product quality. Originality/value ‐ The paper describes how cost reduction in the SLM process was achieved by using 304L powder.
 
Article
Purpose ‐ The paper aims to predict the surface roughness of fused deposition modelling prototypes. Since average roughness is not comprehensive, this study aims to extend the characterization to all the roughness parameters obtainable by a profilometric analysis. Design/methodology/approach ‐ A theoretical model of the 3D profile is supplied as a function of process parameters and part shape. A suitable geometry was designed and prototyped for validation. Data were measured by a profilometer and complemented by microscopic analysis. A methodology based on the proposed model was applied to optimise prototype fabrication in two practical cases. Findings ‐ The proposed profile is effective in describing the micro-geometrical surface of fused deposition modelling prototypes. The third dimension enables the calculation of amplitude, spatial and hybrid roughness parameters. Research limitations/implications ‐ Because of mathematical assumptions and technological aspects, the validity of the model presents limitations related to the deposition angle. Practical implications ‐ The method is an effective tool in the process planning stage: it enables knowing in advance how to assure part specifications delivering a set of technical choices. Two practical applications point out the usability in the product development and process parameters optimisation. Originality/value ‐ This work fulfils an identified need to predict a complete surface characterization of fused deposition modelling technology.
 
Article
Purpose ‐ The purpose of this paper is to relate additive manufacturing (AM) and machining (CNC) synergistically in a modular approach in the design and manufacturing domains, to generate value for end-users and manufacturers (a teleological system). Design/methodology/approach ‐ The research methodology decomposes a part into modules, by employing a teleological systems theory approach paired with principles of modular design. Modules are manufactured with either additive manufacturing (fused deposition modeling, FDM) or machining (CNC). Process selection is determined by a decision-making framework that quantifies strength and weakness comparisons of FDM and CNC machining processes, accomplished using the analytic hierarchy process (AHP). Findings ‐ The developed methodology and decision-making framework is successfully applied to the design and manufacturing of a large, complex V6 engine section sand casting pattern. This case study highlights the merits of the research. Research limitations/implications ‐ The research assumes that the processes being considered are capable of meeting the product functional requirements. The proposed methodology can be extended to evaluate additional processes. Practical implications ‐ Value is assessed in this research relative to: time and cost opportunities, managing knowledge limitations of a process by leveraging hybrid options, and aligning design and manufacturing to create a product that accomplishes the goals of the end-user (teleological effectiveness). Originality/value ‐ Utilizing the AHP process and a teleological perspective are new, and proven effective, approaches in relating additive and subtractive processes in a hybrid approach with end-user perspectives. The research demonstrates a systematic methodology to quantify additive and subtractive process selection.
 
Article
Purpose ‐ Additive manufacturing technologies such as, for example, selective laser melting (SLM) offer new design possibilities for a wide range of applications and industrial sectors. Whereas many results have been published regarding material options and their static mechanical properties, the knowledge about their dynamic mechanical behaviour is still low. The purpose of this paper is to deal with the measurement of the dynamic mechanical properties of two types of stainless steels. Design/methodology/approach ‐ Specimens for dynamic testing were produced in a vertical orientation using SLM. The specimens were turned to the required end geometry and some of them were polished in order to minimise surface effects. Additionally, some samples were produced in the end geometry ("near net shape") to investigate the effect of the comparably rough surface quality on the lifetime. The samples were tension-tested and the results were compared to similar conventional materials. Findings ‐ The SLM-fabricated stainless steels show tensile and fatigue behaviour comparable to conventionally processed materials. For SS316L the fatigue life is 25 per cent lower than conventional material, but lifetimes at higher stress amplitudes are similar. For 15-5PH the endurance limit is 20 per cent lower than conventional material. Lifetimes at higher stress also are significantly lower for this material although the surface conditions were different for the two tests. The influence of surface quality was investigated for 316L. Polishing produced an improvement in fatigue life but lifetime behaviour at higher stress amplitudes was not significantly different compared to the behaviour of the as-fabricated material. Originality/value ‐ In order to widen the field of applications for additive manufacturing technologies, the knowledge about the materials properties is essential, especially about the dynamic mechanical behaviour. The current study is the only published report of fatigue properties of SLM-fabricated stainless steels.
 
Article
Purpose – The purpose of this paper is to provide a personalised view by the Editors of the Rapid Prototyping Journal. Design/methodology/approach – It collects their years of experience in a series of observations and experiences that can be considered as a snapshot of where this technology is today. Findings – Development of these technologies has progressed according to application, materials and how the designers have applied their creativity to such a unique manufacturing tool. Originality/value – The paper predicts how the future of additive manufacturing will look from the perspective of three key elements: applications, materials and design.
 
Article
Purpose ‐ Additive Manufacturing (AM) technologies have conventionally focused on producing prototypes. However, recent trends show that AM is being increasingly used for production parts. With this shift from prototypes to production parts, there is a need to determine whether established engineering design techniques can be applied to AM processes, particularly techniques characteristic of the final implementation phase such as virtual (mathematical) modeling, or whether AM process-specific adjustments must be made. Design/methodology/approach ‐ The effectiveness of applying virtual models to design problems utilizing AM processes was addressed using two approaches in this research. Literature was first reviewed to determine the current focus of the AM industry on virtual modeling, both analytical and numerical, and its implementation. Second, experiments were conducted to validate virtual models applied to fastener mechanism designs manufactured using laser sintering (LS). Findings ‐ Limited research has been published that demonstrates the effectiveness of applying established design techniques, particularly virtual modeling techniques, to parts manufactured with AM processes. The experimental case study has demonstrated that, for the limited cases considered, design techniques capable of accommodating the complex material properties of LS materials, such as finite element analysis, are effective methods for predicting part performance in accordance with desired outcomes. Practical implications ‐ The research indicates that designers can focus on designing quality LS parts with existing technology and methods rather than revamping their design methods due to the introduction of a new manufacturing technology. Originality/value ‐ This research provides support for the application of established design methods to LS AM processes; validating what has previously been an assumed part of AM.
 
Article
Purpose ‐ The purpose this paper is to develop an additive manufacturing (AM) technique for high-strength oxide ceramics. The process development aims at directly manufacturing fully dense ceramic freeform-components with good mechanical properties. Design/methodology/approach ‐ The selective laser melting of the ceramic materials zirconia and alumina has been investigated experimentally. The approach followed up is to completely melt ZrO2/Al2O3 powder mixtures by a focused laser beam. In order to reduce thermally induced stresses, the ceramic is preheated to a temperature of at least 1,600°C during the build up process. Findings ‐ It is possible to manufacture ceramic objects with almost 100 percent density, without any sintering processes or any post-processing. Crack-free specimens have been manufactured that have a flexural strength of more than 500?MPa. Manufactured objects have a fine-grained two-phase microstructure consisting of tetragonal zirconia and alpha-alumina. Research limitations/implications ‐ Future research may focus on improving the surface quality of manufactured components, solving issues related to the cold powder deposition on the preheated ceramic, further increasing the mechanical strength and transferring the technology from laboratory scale to industrial application. Practical implications ‐ Potential applications of this technique include manufacturing individual all-ceramic dental restorations, ceramic prototypes and complex-shaped ceramic components that cannot be made by any other manufacturing technique. Originality/value ‐ This new manufacturing technique based on melting and solidification of high-performance ceramic material has some significant advantages compared to laser sintering techniques or other manufacturing techniques relying on solid-state sintering processes.
 
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