Rapid Prototyping Journal

Cristobal Arrieta; Sergio Uribe; Jorge Ramos‐Grez; Alex Vargas; Pablo Irarrazaval; Vicente Parot; Cristian Tejos

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211271974

Purpose – In medical applications, it is crucial to evaluate the geometric accuracy of rapid prototyping (RP) models. Current research on evaluating geometric accuracy has focused on identifying two or more specific anatomical landmarks on the original structure and the RP model, and comparing their corresponding linear distances. Such kind of accuracy metrics is ambiguous and may induce misrepresentations of the actual errors. The purpose of this paper is to propose an alternative method and metrics to measure the accuracy of RP models. Design/methodology/approach – The authors propose an accuracy metric composed of two different approaches: a global accuracy evaluation using volumetric intersection indexes calculated over segmented Computed Tomography scans of the original object and the RP model. Second, a local error metric that is computed from the surfaces of the original object and the RP model. This local error is rendered in a 3D surface using a color code, that allow differentiating regions where the model is overestimated, underestimated, or correctly estimated. Global and local error measurements are performed after rigid body registration, segmentation and triangulation. Findings – The results show that the method can be applied to different objects without any modification, and provide simple, meaningful and precise quantitative indexes to measure the geometric accuracy of RP models. Originality/value – The paper presents a new approach to characterize the geometric errors in RP models using global indexes and a local surface distribution of the errors. It requires minimum human intervention and it can be applied without any modification to any kind of object.

Shwe P. Soe; Daniel R. Eyers; Toby Jones; Nigel Nayling

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211271983

Purpose – The purpose of this paper is to examine the suitability of additive manufacturing technologies in the reconstruction of archaeological discoveries as illustrative models. The processes of reverse engineering and part fabrication are discussed in detail, with particular emphasis placed on the difficulties of managing scaling and material characteristics for the manufacturing process. Design/methodology/approach – Through a case‐based approach, this paper examines the reconstruction of a fifteenth‐century ship recovered from the River Usk in South Wales, UK. Using interviews and process data, the paper identifies challenges for both archaeologists and manufacturers in the application of additive manufacturing technologies for archaeological reconstruction applications. Findings – This paper illustrates both the suitability of additive manufacturing in archaeological restoration, but also the challenges which result from this approach. It demonstrates the practical considerations of scaling process and materials, whilst also highlighting the techniques to improve accuracy and mechanical properties of the model. Originality/value – Whilst the technologies of additive manufacturing have previously been applied to model making, little scholarly research has considered the practical techniques of design elicitation and manufacturing for archaeological applications. Using an in‐depth case study, this paper highlights the principal considerations for these applications, and provides guidance in the mitigation of manufacturing issues.

Vamsi Krishna Balla; Luke B. Roberson; Gregory W. O'Connor; Steven Trigwell; Susmita Bose; Amit Bandyopadhyay

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211271992

Purpose – The purpose of this paper is to evaluate the feasibility of direct fabrication of lunar/Martian regolith simulant parts, in a freeform environment, using Laser Engineering Net Shaping (LENS™) – an additive manufacturing technology. Design/methodology/approach – Bulk lunar regolith simulant structures were fabricated using a LENS™‐750. Dense parts without any macroscopic defects were produced at a laser power of 50W, a scan speed of 20 mm/s, and a powder feed rate of 12.36 g/min. The laser processed parts were characterized using X‐ray diffraction, differential scanning calorimetry, scanning electron microscope and X‐ray photoelectron spectroscopy to evaluate the influence of laser processing on the microstructure, constituent phases and chemistry of lunar regolith simulant. Findings – A combination of laser parameters resulting in a 2.12 J/mm 2 laser energy appeared to be ideal for generating a melt pool necessary for lunar regolith powder deposition without excessive liquid pool spreading and cracking of solidified parts. The results show that LENS™ based laser processing transformed crystalline regolith into nanocrystalline and/or amorphous regolith structures as a result of complete melting followed by resolidification. Laser processing also resulted in marginal changes in the composition of the regolith. Originality/value – Establishment of a lunar/Martian outpost necessitates the development of methods to utilize in situ mineral resources for various construction and resource extraction applications. Fabrication technologies are critical for habitat structure development, as well as repair and replacement of tools and parts at the outpost. Current experimental results presented in the paper clearly demonstrate that net shape regolith simulant parts can be fabricated using LENS™ by exploiting its capabilities.

Munish Chhabra; Rupinder Singh

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211272009

Purpose – The purpose of this paper is to investigate experimentally the effect of volume of casting, pouring temperature of different materials and shell mould wall thickness on the surface roughness of the castings obtained by using ZCast direct metal casting process. Design/methodology/approach – Taguchi's design of experiment approach was used for this investigation. An L9 orthogonal array (OA) of Taguchi design which involves nine experiments for three factors with three levels was used. Analysis of variance (ANOVA) was then performed on S/N (signal‐to‐noise) ratios to determine the statistical significance and contribution of each factor on the surface roughness of the castings. The castings were obtained using the shell moulds fabricated with the ZCast process and the surface roughness of castings was measured by using the surface roughness tester. Findings – Taguchi's analysis results showed that pouring temperature of materials was the most significant factor in deciding the surface roughness of the castings and the shell mould wall thickness was the next most significant factor, whereas volume of casting was found insignificant. Confirmation test was also carried out using the optimal values of factor levels to confirm the effectiveness of this approach. The predicted optimal value of surface roughness of castings produced by ZCast process was 6.47 microns. Originality/value – The paper presents experimentally investigated data regarding the influence of various control factors on the surface roughness of castings produced by using ZCast process. The data may help to enhance the application of ZCast process in traditional foundry practice.

Cassandra Telenko; Carolyn Conner Seepersad

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211272018

Purpose – The purpose of this paper is to evaluate the energy consumed to fabricate nylon parts using selective laser sintering (SLS) and to compare it with the energy consumed for injection molding (IM) the same parts. Design/methodology/approach – Estimates of energy consumption include the energy consumed for nylon material refinement, adjusted for SLS and IM process yields. Estimates also include the energy consumed by the SLS and IM equipment for part fabrication and the energy consumed to machine the injection mold and refine the metal feedstock required to fabricate it. A representative part is used to size the injection mold and to quantify throughput for the SLS machine per build. Findings – Although SLS uses significantly more energy than IM during part fabrication, this energy consumption is partially offset by the energy consumption associated with production of the injection mold. As a result, the energy consumed per part for IM decreases with the number of parts fabricated while the energy consumed per part for SLS remains relatively constant as long as builds are packed efficiently. The crossover production volume, at which IM and SLS consume equivalent amounts of energy per part, ranges from 50 to 300 representative parts, depending on the choice of mold plate material. Research limitations/implications – The research is limited to material refinement and part fabrication and does not consider other aspects of the life cycle, such as waste disposal, distributed 2 manufacturing, transportation, recycling or use. Also, the crossover volumes are specific to the representative part and are expected to vary with part geometry. Originality/value – The results of this comparative study of SLS and IM energy consumption indicate that manufacturers can save energy using SLS for parts with small production volumes. The comparatively large amounts of nylon material waste and energy consumption during fabrication make it inefficient, from an energy perspective, to use SLS for higher production volumes. The crossover production volume depends on the geometry of the part and the choice of material for the mold.

Yongqiang Yang; Jian‐bin Lu; Zhi‐Yi Luo; Di Wang

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211272027

Purpose – The purpose of this paper is to investigate the research approach to optimize shape accuracy, dimensional accuracy and density of customized orthodontic production fabricated by selective laser melting (SLM). Design/methodology/approach – A series of process experiments were applied to fabricating customized brackets directly by SLM, using 316L stainless steel. Shape accuracy can be optimized through the study on fabricating characteristics of non‐support overhanging structure. A scanning strategy combining contour scanning with orthogonal scanning, which differ in scanning speed and spot compensations, was proposed to improve dimensional accuracy. Scanning laser surface re‐melting was added to enhance the SLM density. Findings – Optimized SLM parameters lead to high shape precision of customized brackets, and the average size error of bracket slot is less than 10 μ m. The customized brackets density is more than 99 per cent, and the surface quality and mechanical properties meet the requirements. Originality/value – The paper presents the state of the art in SLM of customized production (especially medical appliances) by optimizing part properties. It is the first time that SLM is employed in the manufacturing of customized orthodontic products. It shows the original research on overhanging structure and compound scanning strategy, approach to optimize SLM part accuracy. An improved laser surface re‐melting is employed in the density optimization.

J. Suwanprateeb; F. Thammarakcharoen; K. Wasoontararat; W. Suvannapruk

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211272036

Purpose – The purpose of this paper is to study the influence of changing printing parameters (powder layer thickness and binder saturation) in a three dimensional printing machine (3DP) on the transformation of 3DP printed plaster of paris to hydroxyapatite by low temperature phosphorization. Design/methodology/approach – Plaster of paris‐based powder mixture was used to print specimens using different powder layer thickness (0.080, 0.10 and 0.20 mm) and saturation ratio (1 and 2). Subsequently, density, microstructure, mechanical properties, transformation rate and phase composition were analyzed to compare the influence of such printing parameters on properties. Findings – It was found that printing parameters strongly affect the transformation efficiency and properties of the samples. The sample printed at layer thickness of 0.10 mm and saturation ratio of 1 yielded the highest transformation rate, density and greatest flexural modulus and strength after conversion. This was related to the sufficiently low density structure with good mechanical properties of the as‐fabricated 3DP sample which was suitable for the low temperature phosphorization process. Hydroxyapatite and monetite were found to be the main phases after conversion and the content of each phase depended on the conversion time and on also the printing parameters. Research limitations/implications – The optimal printing parameters were true for the materials used in this study. In the case of using other materials formulation, the optimal printing parameters might be different from these values. Practical implications – The results presented here can be used as a guideline for selecting printing parameters in 3DP machine for achieving properties as desired for specific applications or post‐processing techniques. Originality/value – The paper demonstrates the printing parameters that were needed to be considered for efficient phase transformation and high mechanical properties.

Dietmar Drummer; Sandra Cifuentes‐Cuéllar; Dominik Rietzel

2012 Rapid Prototyping Journal

doi: 10.1108/13552541211272045

Purpose – Fused deposition modeling (FDM) is a layer by layer technology with the potential to create complex and individual parts from thermoplastic materials such as ABS. The use of Polylactic acid (PLA) and tricalcium phosphate (TCP) as resorbable composite is state of the art in tissue engineering and maxillofacial surgery. The purpose of this paper is to evaluate the processing conditions and the performance of parts (e.g. mechanical properties) manufactured with a FDM machine. Design/methodology/approach – In this paper, the general suitability of PLA for the processing with FDM is evaluated and material specific effects (e.g. crystallization and shrinkage) are shown. Therefore, the characterization of the semi‐crystalline biodegradable material by thermal, mechanical and microscopic analysis is carried out. Findings – Facts, which affect the functional properties of the samples, are analyzed. Among them, the processing temperature and sample size significantly affect the morphology of the final components. Components from PLA/TCP with sufficient mechanical properties for their potential use as scaffolds are obtained. Originality/value – Thus, the paper shows that by thermal analysis it is possible to identify major influences on processing and part properties.