B. Wiedemann, K.‐H. Dusel and J. Eschl
To facilitate the selection of stereolithography resins, methods have been developed which evaluate photopolymers with respect to dynamics of polymerization and shrinkage, and…
Abstract
To facilitate the selection of stereolithography resins, methods have been developed which evaluate photopolymers with respect to dynamics of polymerization and shrinkage, and also the sensitivity of polymerization with respect to process conditions and ambient influences. To use the whole potential of a resin it is necessary to identify the material behaviour related to the build process. The process parameters have to be adapted to the individual material. Describes how numerical simulation of part distortion can help in understanding the interaction between material properties and process parameters. Concludes by stating that the build process must be optimized to reduce internal stresses and to cater for post‐curing effects.
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This article describes new approaches in rapid prototyping large sand moulds using industrial robots. In contrast to state of the art processes, the new approaches work…
Abstract
This article describes new approaches in rapid prototyping large sand moulds using industrial robots. In contrast to state of the art processes, the new approaches work three‐dimensionally taking advantage of the large working area of industrial robots.
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Rapid prototyping technologies have introduced a new generation of rapid tooling processes. Many of these rapid tools have been used for injection moulding where the thermal…
Abstract
Rapid prototyping technologies have introduced a new generation of rapid tooling processes. Many of these rapid tools have been used for injection moulding where the thermal properties of the tool material are critical to the quality of parts produced. Rapid tools are often made from materials with substantially different thermal properties than conventional metal tools. Engineers wishing to make use of these technologies to produce technical prototypes must be aware of the effect this will have on final part properties. Some previous research has been undertaken in this area. Reviews the work done in the field of rapid tooling used for injection moulding. The review shows that, whereas a range of techniques and final part materials has been studied, the results obtained are incomplete and often unexplained. The authors draw conclusions as to why this is so and go on to identify areas for further work that will be pursued.
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D. Karalekas and D. Rapti
This paper presents an experimental study undertaken to determine the polymerisation‐induced residual stresses generated in stereolithography (SL) built test specimens, by using…
Abstract
This paper presents an experimental study undertaken to determine the polymerisation‐induced residual stresses generated in stereolithography (SL) built test specimens, by using the hole‐drilling strain gage method of stress relaxation. Experimentally measured strains, using special three‐element strain gage rosettes, were input into the blind‐hole analysis to calculate the induced residual stresses. The mechanical properties of resin specimens fabricated by the solidification process using an epoxy based photopolymer and post‐cured under ultraviolet (UV) and thermal exposure were determined and incorporated into the subsequent drill‐hole analysis. The effect of the pre‐selected fabrication parameters (hatching space and curing depth) and subsequent by the post‐curing procedure (UV, thermal curing) on the magnitude of the recorded strains is also presented.
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The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a…
Abstract
Purpose
The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a photocurable resin used in 3D microfabrication.
Design/methodology/approach
The followed approach consists of embedding a 1,300 nm FBG into a cylindrical specimen, fabricated into a transparent mould, being exposed to ultraviolet laser light. The further development of the cure induced strains under thermal treatment was also studied by post‐conditioning the cylindrical specimen in an oven at 70°C.
Findings
The experimental results demonstrate the capability of the FBG sensor to provide useful information on the strain build‐up during laser solidification and their post‐cure evolution under the presence of a thermal environment.
Research limitations/implications
Future work should involve the use of smaller diameter FBG sensors in microstereolithography built parts.
Practical implications
It is shown that considerable cure strains are developed at the end of the photo‐polymerisation process that eventually can affect the structural resolution of final parts fabricated by microstereolithography.
Originality/value
The presented method can be used to investigate other photopolymers used in micro‐stereolithography.
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K. Chockalingam, N. Jawahar and U. Chandrasekhar
Mechanical properties such as tensile, yield, impact strengths, and development of residual stresses play an important role intooling applications. The objective of this paper is…
Abstract
Purpose
Mechanical properties such as tensile, yield, impact strengths, and development of residual stresses play an important role intooling applications. The objective of this paper is to investigate the effect of layer thickness – one of the influential process parameters in stereolithography (SL) process, on mechanical properties of SL components.
Design/methodology/approach
Test specimens are constructed as per the ASTM standards for different layer thicknesses in SL 5000 machine, using epoxy resin CIBA tool ® SL5530, a high temperature resistant SL material that is suitable for rapid tooling applications. Tensile, yield and impact tests are carried out with suitable equipments. Residual stress is analysed using hole drill method.
Findings
The analysis reveals that when the layer thickness is smaller, the strength of the part is higher.
Research limitations/implications
Conclusion of this research is drawn based on the analysis of the most widely used three layer thicknesses of 100, 125 and 150 μm. X‐ray diffraction or molecular resonance analysis may be useful to understand the reason for the variation in mechanical properties.
Originality/value
This experimental study provides the useful information to the SL machine users in the selection of layer thickness to manufacture rapid tools.
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Lai Jiang, Xiaobo Peng and Daniel Walczyk
This paper aims to summarize the up-to-date research performed on combinations of various biofibers and resin systems used in different three-dimensional (3D) printing…
Abstract
Purpose
This paper aims to summarize the up-to-date research performed on combinations of various biofibers and resin systems used in different three-dimensional (3D) printing technologies, including powder-based, material extrusion, solid-sheet and liquid-based systems. Detailed information about each process, including materials used and process design, are described, with the resultant products’ mechanical properties compared with those of 3D-printed parts produced from pure resin or different material combinations. In most processes introduced in this paper, biofibers are beneficial in improving the mechanical properties of 3D-printed parts and the biodegradability of the parts made using these green materials is also greatly improved. However, research on 3D printing of biofiber-reinforced composites is still far from complete, and there are still many further studies and research areas that could be explored in the future.
Design/methodology/approach
The paper starts with an overview of the current scenario of the composite manufacturing industry and then the problems of advanced composite materials are pointed out, followed by an introduction of biocomposites. The main body of the paper covers literature reviews of recently emerged 3D printing technologies that were applied to biofiber-reinforced composite materials. This part is classified into subsections based on the form of the starting materials used in the 3D printing process. A comprehensive conclusion is drawn at the end of the paper summarizing the findings by the authors.
Findings
Most of the biofiber-reinforced 3D-printed products exhibited improved mechanical properties than products printed using pure resin, indicating that biofibers are good replacements for synthetic ones. However, synthetic fibers are far from being completely replaced by biofibers due to several of their disadvantages including higher moisture absorbance, lower thermal stability and mechanical properties. Many studies are being performed to solve these problems, yet there are still some 3D printing technologies in which research concerning biofiber-reinforced composite parts is quite limited. This paper unveils potential research directions that would further develop 3D printing in a sustainable manner.
Originality/value
This paper is a summary of attempts to use biofibers as reinforcements together with different resin systems as the starting material for 3D printing processes, and most of the currently available 3D printing techniques are included herein. All of these attempts are solutions to some principal problems with current 3D printing processes such as the limit in the variety of materials and the poor mechanical performance of 3D printed parts. Various types of biofibers are involved in these studies. This paper unveils potential research directions that would further widen the use of biofibers in 3D printing in a sustainable manner.
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Kamran Kardel, Ali Khoshkhoo and Andres L. Carrano
The purpose of this paper is to investigate the effects of layer thickness, aspect ratio, part thickness and build orientation on distortion to have a better understanding of its…
Abstract
Purpose
The purpose of this paper is to investigate the effects of layer thickness, aspect ratio, part thickness and build orientation on distortion to have a better understanding of its behavior in material jetting technology.
Design/methodology/approach
Specimens with two layer thicknesses (14 and 28 µm) were printed in two aspect ratios (2:1) and (10:1), four thickness values (1, 2, 3 and 4 mm) and three build orientations (45d, XY and YX) and scanned with a wide-area 3D surface scanner to quantify distortion. The material used to build the test specimens was a commercially available resin, VeroWhitePlus RGD835.
Findings
The results of this study showed that all printed specimens by material jetting 3D printers had some level of distortion. The 1-mm thickness specimens, for both layer thicknesses of 14 µm and 28 µm, showed a wide range of anomalies including reverse coil set (RCS), reverse cross bow (RCB), cross bow (CB), wavy edge (WE) and some moderate twisting (T). Similar occurrences were observed for the 2-mm thickness specimens as there were RCS, WE, RCB and T anomalies that show the difference between the thinner specimens (1- and 2-mm) with the thicker ones (3- and 4-mm). In both 3- and 4-mm thickness specimens, there was more consistency in terms of distortion with mainly RCS and RCB anomalies. In total, six different types of flatness anomalies were found to occur with the following incidences: reverse coil set (91 specimens, 63.19%), reverse cross bow (50 specimens, 34.72%), wavy edge (23 specimens, 15.97%), twist (19 specimens, 12.50%), coil set (11 specimens, 7.64%) and cross bow (7 specimens, 4.86%).
Originality/value
This study expands the research on how the preprocess parameters such as layer thickness and build orientation and the geometrical parameters such as part thickness and aspect ratio cause dimensional distortion. Distortion is a pervasive consequence of the curing process in photopolymerization and explores one of the most common defects that come across in polymeric-based additive manufacturing. In addition to the characterization of the type and magnitude of distortion, the contributions of this work also include establishing the foundation for design guidelines aiming at minimizing distortion in material jetting.
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M. Atif Yardimci and Selçuk Güçeri
Explains the fused deposition process and examines the rationale behind the cooling process model. Outlines the complexity of the problems and characteristics of fused deposition…
Abstract
Explains the fused deposition process and examines the rationale behind the cooling process model. Outlines the complexity of the problems and characteristics of fused deposition. Presents a general formulation for road cooling followed by results and their implications. Concludes with proposed directions for future work.
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Morteza Vatani, Farshad Barazandeh, AbdolReza Rahimi and Amir Sanati Nezhad
In stereolithography (SL), the total exposure absorbed by photopolymer is variable and is a function of height. This phenomenon causes heterogeneous properties and develops…
Abstract
Purpose
In stereolithography (SL), the total exposure absorbed by photopolymer is variable and is a function of height. This phenomenon causes heterogeneous properties and develops residual stresses during process. Consequently, a pronounced deformation occurs especially when small and more intricate objects are fabricated. The purpose of this paper is to predict this deformation when miniature and complicated parts are fabricated.
Design/methodology/approach
In this paper classical lamination theory is employed to model mechanical properties of layers, layers shrinkage and residual stress growth during SL process. Distortion is predicted based on the developed model.
Findings
Results show that final distortion is proportional to part thickness and it increases exponentially as parts thickness or layers thickness decrease.
Practical implications
To verify the results, several test pieces were built with SLA 5000 machine and SOMOS 11120 resins. Their distortions were measured with video measuring machine (VMM‐3020D machine). The estimation agrees very well with the experimental results (less than 10 per cent error).
Originality/value
The paper considers the heterogeneous properties of SL parts during fabrication process; an item which was ignored in previous researches. This theoretical and experimental study provides useful information about estimation of deformation of SL parts after building. This information helps the SL machine user to select the best parameters when fabricating miniature and intricate features, especially for biomechanics parts.