James Robert Wingham, Robert Turner, Joanna Shepherd and Candice Majewski
X-Ray-computed micro-tomography (micro-CT) is relatively well established in additive manufacturing as a method to determine the porosity and geometry of printed parts and, in…
Abstract
Purpose
X-Ray-computed micro-tomography (micro-CT) is relatively well established in additive manufacturing as a method to determine the porosity and geometry of printed parts and, in some cases, the presence of inclusions or contamination. This paper aims to demonstrate that micro-CT can also be used to quantitatively analyse the homogeneity of micro-composite parts, in this case created using laser sintering (LS).
Design/methodology/approach
LS specimens were manufactured in polyamide 12 with and without incorporation of a silver phosphate glass additive in different sizes. The specimens were scanned using micro-CT to characterise both their porosity and the homogeneity of dispersion of the additive throughout the volume.
Findings
This work showed that it was possible to use micro-CT to determine information related to both porosity and additive dispersion from the same scan. Analysis of the pores revealed the overall porosity of the printed parts, with linear elastic fracture mechanics used to identify any pores likely to lead to premature failure of the parts. Analysis of the additive was found to be possible above a certain size of particle, with the size distribution used to identify any agglomeration of the silver phosphate glass. The particle positions were also used to determine the complete spatial randomness of the additive as a quantitative measure of the dispersion.
Practical implications
This shows that micro-CT is an effective method of identifying both porosity and additive agglomeration within printed parts, meaning it can be used for quality control of micro-composites and to validate the homogeneity of the polymer/additive mixture prior to printing.
Originality/value
This is believed to be the first instance of micro-CT being used to identify and analyse the distribution of an additive within a laser sintered part.
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Barry Haworth, John R. Tyrer and Zhou Zhou
There is a requirement to match selective laser melting (SLM) technologies to a wider range of polymeric materials, as the existing market for SLM powders is dominated by…
Abstract
Purpose
There is a requirement to match selective laser melting (SLM) technologies to a wider range of polymeric materials, as the existing market for SLM powders is dominated by polyamide PA12. Drivers include the tailoring of physical properties to individual applications or cost reduction. Polypropylene (PP) currently has limited use in SLM; so, this paper aims to explore the potential use of PP materials of varying molecular weight (Mw).
Design/methodology/approach
PP polymers of differing Mw were characterised using a range of analytical techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rotational rheometry and real-time hot-stage (optical) microscopy.
Findings
The techniques are sufficiently sensitive to distinguish Mw effects, notably in terms of material viscosity. The stable sintering region for SLM has been defined clearly. Some success was achieved in melting parts using all grades of PP, including higher Mw grades, which potentially offer improved mechanical performance.
Research limitations/implications
The range of techniques (DSC, oxidative induction time and TGA) form an effective analytical package with which to consider new polymeric materials for SLM.
Practical implications
High-Mw PP polymers, in tape or powder form, have potential use in SLM processes, providing scope to enhance part properties in future.
Originality/value
This is believed to be the first in-depth study noting the influence of PP Mw on important physical performance in a proprietary SLM process, using holographic beam manipulation.
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Grazielle de Oliveira Setti, Jorge Vicente Lopes da Silva, Marcelo Fernandes de Oliveira, Izaque Alves Maia, Dosil Pereira de Jesus, Raluca Savu, Thebano Emilio de Almeida Santos, Rita de Cássia Zacardi de Souza and Ednan Joanni
The purpose of this paper is to characterize polyamide parts prepared by the SLS process using techniques that are dependent on surface properties and compare the results to…
Abstract
Purpose
The purpose of this paper is to characterize polyamide parts prepared by the SLS process using techniques that are dependent on surface properties and compare the results to density measurements in order to assess which technique better reflects the degree of densification achieved using different laser power levels.
Design/methodology/approach
Fabrication of Nylon 12 (Duraform PA) samples and their characterization by apparent density measurements, perfilometry, Raman spectroscopy, scanning electron microscopy, specific surface area and contact angle measurements.
Findings
Methods dependent on surface analysis are not suitable indicators of the degree of sample densification. Among the surface methods, the results from Raman spectroscopy are the ones with the best performance. Incipient sintering of the superficial layers and raw material powder on the surface, inherent to the parts made by the SLS process, strongly interfere with the characterization.
Originality/value
Quantitative comparison of a number of surface probing methods for monitoring densification of SLS parts. Characterization of sample surfaces with and without raw material powder.
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Jan Patrick Deckers, Khuram Shahzad, Ludwig Cardon, Marleen Rombouts, Jozef Vleugels and Jean-Pierre Kruth
The purpose of this paper is to compare different powder metallurgy (PM) processes to produce ceramic parts through additive manufacturing (AM). This creates the potential to…
Abstract
Purpose
The purpose of this paper is to compare different powder metallurgy (PM) processes to produce ceramic parts through additive manufacturing (AM). This creates the potential to rapidly shape ceramic parts with an almost unlimited shape freedom. In this paper, alumina (Al2O3) parts are produced, as Al2O3 is currently the most commonly used ceramic material for technical applications.
Design/methodology/approach
Variants of the following PM route, with indirect selective laser sintering (indirect SLS) as the AM shaping step, are explored to produce ceramic parts: powder synthesis, indirect SLS, binder removal and furnace sintering and alternative densification steps.
Findings
Freeform-shaped Al2O3 parts with densities up to approximately 90 per cent are obtained.
Research limitations/implications
The resulting Al2O3 parts contain inter-agglomerate pores. To produce higher-quality ceramic parts through indirect SLS, these pores should be avoided or eliminated.
Originality/value
The research is innovative in many ways. First, composite powders are produced using different powder production methods, such as temperature-induced phase separation and dispersion polymerization. Second, four different binder materials are investigated: polyamide (nylon-12), polystyrene, polypropylene and a carnauba wax – low-density polyethylene combination. Further, to produce ceramic parts with increased density, the following densification techniques are investigated as additional steps of the PM process: laser remelting, isostatic pressing and infiltration.
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K.W. Dalgarno and R.D. Goodridge
This paper reports the results of a compression test benchmarking study carried out to investigate the mechanical properties of layer manufactured metal components in order to…
Abstract
This paper reports the results of a compression test benchmarking study carried out to investigate the mechanical properties of layer manufactured metal components in order to assess their suitability in load bearing applications. Compression tests were carried out on the DTM LaserForm ST‐100 material, ARCAM processed H13 tool steel, EOS DirectSteel (50 μm), and the ProMetal material. It is concluded that the LaserForm ST‐100 material, the ARCAM H13 tool steel material, and the ProMetal material all exhibit responses to compressive loads which make them suitable for use in load bearing situations, whilst the EOS DirectSteel (50 μm) exhibits a small permanent set in compression, making it less suitable in these situations.
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Tiago Czelusniak and Fred Lacerda Amorim
This paper aims to provide a detailed study on influence of the laser energy density on mechanical, surface and dimensional properties of polyamide 12 (PA12) parts produced by…
Abstract
Purpose
This paper aims to provide a detailed study on influence of the laser energy density on mechanical, surface and dimensional properties of polyamide 12 (PA12) parts produced by selective laser sintering (SLS), providing the microstructural and crystallization evolution of the samples produced at different energy densities.
Design/methodology/approach
Making use of a space filling design of experiments, a wide range of laser sintering parameters is covered. Surface morphology is assessed by means of profile measurements and scanning electron microscopy (SEM) images. Mechanical testing, SEM, X-ray diffraction (XRD), differential scanning calorimeter (DSC) and infrared spectroscopy (FTIR) were used to assess the influence of energy density on structural and mechanical properties.
Findings
Results show a high dependency of the properties on the laser energy density and also a compromise existing between laser exposure parameters and desired properties of laser sintered parts. Surface roughness could be associated to overlap degree when using higher scan line spacing values and lower laser speeds improved surface roughness when high scan line spacing is used. Higher mechanical properties were found at higher energy density levels, but excessively high energy density decreased mechanical properties. A transition from brittle to ductile fracture with increasing energy density could be clearly observed by mechanical analysis and SEM. XRD and DSC measurements show a decrease on the crystal fraction with increasing energy densities, which corroborated the plastic behavior observed, and FTIR measurements revealed polymer degradation through chain scission might occur at too high energy densities.
Originality/value
Valuable guidelines are given regarding energy density optimization for SLS of PA12 considering not only quality criteria but also microstructure characteristics. Surface properties are studied based on the concept of degree of overlap between laser scanning lines. For the first time, crystallization behavior of SLS PA12 parts produced at different energy levels was studied by means of XRD measurements. Polymer degradation of SLS PA12 parts was evaluated with FTIR, which is a non-destructive and easy test to be conducted.
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Achille Gazzerro, Wilma Polini and Luca Sorrentino
Selective laser sintering (SLS) has passed other techniques, thanks to its high print resolution, its ability to print microscale geometries without any additional support, its…
Abstract
Purpose
Selective laser sintering (SLS) has passed other techniques, thanks to its high print resolution, its ability to print microscale geometries without any additional support, its surface quality and its long-term thermal stability. However, despite the many advantages of SLS compared to fusion deposition modelling, there are still today some limitations on the materials to be printed. A limit critical from an industrial point of view is the aging of PA12 powder, i.e. the degradation of its physical and chemical performances, due to the high temperatures and the long printing cycles, thus involving a decrease of the mechanical properties of the printed parts. The purpose of this study was to charaterize mechanically and dimensionally specimens printed in PA12 through SLS by means of virgin or aged powder, i.e. powder just used for five printing cycles.
Design/methodology/approach
To achieve this aim, a set of specimens were designed, built, measured and mechanically tested; the obtained results were put into relationship with the values of the process parameters used to print them. Statistical tools to design the experiments and to analyse the obtained results were used.
Findings
The results show that the SLS process carried out through a Sintratec machine on PA12 powder has a good repeatability. To obtain the best dimensional and mechanical performances, it is needed to use virgin powder and place the part in the central zone of the printing area.
Originality/value
There are no scientific articles dealing with the influence of both the aging of the powder and the manufacturing parameters on the dimensional and mechanical characterization of specimens printed with SLS technique in PA12.
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Grazielle de Oliveira Setti, Marcelo Fernandes de Oliveira, Izaque Alves Maia, Jorge Vicente Lopes da Silva and Ednan Joanni
This paper aims to demonstrate the functionalization of polyamide parts made by selective laser sintering (SLS) for application as substrates for chemical analysis by…
Abstract
Purpose
This paper aims to demonstrate the functionalization of polyamide parts made by selective laser sintering (SLS) for application as substrates for chemical analysis by surface-enhanced Raman scattering (SERS).
Design/methodology/approach
Fabrication of Nylon 12 (Duraform PA®) samples using two laser power levels and deposition of a layer of gold-coated zinc oxide nanostructures. Performance of these substrates in the detection of a known compound was tested by Raman spectroscopy.
Findings
The hydrothermal synthesis proved to be a good method for functionalizing the surface of polyamide parts made by the SLS process. By varying the synthesis temperature, ZnO nanoparticles and nanorods attached to the sample surfaces could be obtained. The degree of sample sintering had an effect on the growth of the nanostructures. The gold-coated functionalized surfaces enhanced the Raman signal from crystal violet by more than three orders of magnitude. ZnO nanorods grown on well-sintered SLS parts showed the best performance from the set of samples tested in this work.
Originality/value
ZnO nanostructures were grown directly on untreated surfaces of SLS-made polyamide. These substrates were used for chemical analysis by SERS.
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Keywords
Mattia Mele, Giampaolo Campana and Gian Luca Monti
The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process…
Abstract
Purpose
The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process has not been addressed by any previous research, despite the key role of this process in the AM industry. The aim of this paper is to explore the relationship between irradiance and dimensional accuracy in MJF.
Design/methodology/approach
An experimental activity was carried out to map the relationship between irradiance and dimensional accuracy in the MJF transformation of polyamide 12. Two specimens were used to measure the dimensional accuracy on medium and small sizes. The experiment was run using six different levels of irradiance. For each, the crystallinity degree and part density were measured.
Findings
Irradiance was found to be directly proportional to part density and inversely proportional to crystallinity degree. Higher irradiance leads to an increase in the measured dimensions of parts. This highlights a predominant role of the crystallisation degree and uncontrolled peripherical sintering, in line with the previous literature on other powder-bed AM processes. The results demonstrate that different trends can be observed according to the range of sizes.
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Sangho Ha, Kasin Ransikarbum, Hweeyoung Han, Daeil Kwon, Hyeonnam Kim and Namhun Kim
The purpose of this study is to mitigate the dimensional inaccuracy due to vertical curling/bending deformation of three-dimensional (3D) printed parts produced by selective laser…
Abstract
Purpose
The purpose of this study is to mitigate the dimensional inaccuracy due to vertical curling/bending deformation of three-dimensional (3D) printed parts produced by selective laser sintering (SLS) using PA12 based on dimensional compensation of the computer-aided design (CAD) model.
Design/methodology/approach
To carry out this study, specially designed features are initially produced as references, and the dimensional deviations from the vertical bending deformation of the SLS process are analyzed. Next, the deformation patterns are formulated using a polynomial regression model in the global Cartesian coordinates of the building platform. Then, the compensation algorithm is implemented and the original 3D CAD file is preprocessed with an inverse transformation of the features to compensate the deformation errors.
Findings
It was found that the 3D printed parts from the SLS process have the dimensional inaccuracy due to the vertical bending pattern of the quadratic form. By implementing the compensation algorithm, it was statistically shown to effectively reduce bending deformations of various sample parts, including the automotive components, in SLS.
Research limitations/implications
The position of samples in a batch has a direct impact on not only bending deformation but also on horizontal shape geometry error. However, the application of this algorithm is focused on the vertical bending deformation, which is estimated as a major part of dimensional inaccuracy.
Practical implications
This paper provides a practical case study with a real vehicle part. The algorithm was shown to provide a more realistic solution to the dimensional deformation of printed products, which is not manageable by simply using the constant scale factors provided by SLS 3D printer manufacturers.
Originality/value
This paper suggests that the vertical bending deformation from SLS’s 3D printed complex parts can be improved through the proposed compensation algorithm. The compensation algorithm was constructed by using the predictive regression model created from the bending deformation patterns of reference samples. The proposed compensation algorithm can be further used and applied for other complex samples without making additional reference parts.