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1 – 10 of 796J.P. Kruth, X. Wang, T. Laoui and L. Froyen
Selective laser sintering (SLS) is one of the most rapidly growing rapid prototyping techniques (RPT). This is mainly due to its suitability to process almost any material…
Abstract
Selective laser sintering (SLS) is one of the most rapidly growing rapid prototyping techniques (RPT). This is mainly due to its suitability to process almost any material: polymers, metals, ceramics (including foundry sand) and many types of composites. The material should be supplied as powder that may occasionally contain a sacrificial polymer binder that has to be removed (debinded) afterwards. The interaction between the laser beam and the powder material used in SLS is one of the dominant phenomena that defines the feasibility and quality of any SLS process. This paper surveys the current state of SLS in terms of materials and lasers. It describes investigations carried out experimentally and by numerical simulation in order to get insight into laser‐material interaction and to control this interaction properly.
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Barry Haworth, Neil Hopkinson, David Hitt and Xiaotao Zhong
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…
Abstract
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 melt flow rate (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.
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Yifan Guo, Yanling Guo, Jian Li, Yangwei Wang, Deyu Meng, Haoyu Zhang and Jiaming Dai
Selective laser sintering (SLS) is an essential technology in the field of additive manufacturing. However, SLS technology is limited by the traditional point-laser sintering…
Abstract
Purpose
Selective laser sintering (SLS) is an essential technology in the field of additive manufacturing. However, SLS technology is limited by the traditional point-laser sintering method and has reached the bottleneck of efficiency improvement. This study aims to develop an image-shaped laser sintering (ISLS) system based on a digital micromirror device (DMD) to address this problem. The ISLS system uses an image-shaped laser light source with a size of 16 mm × 25.6 mm instead of the traditional SLS point-laser light source.
Design/methodology/approach
The ISLS system achieves large-area image-shaped sintering of polymer powder materials by moving the laser light source continuously in the x-direction and updating the sintering pattern synchronously, as well as by overlapping the splicing of adjacent sintering areas in the y-direction. A low-cost composite powder suitable for the ISLS system was prepared using polyether sulfone (PES), pinewood and carbon black (CB) powders as raw materials. Large-sized samples were fabricated using composite powder, and the microstructure, dimensional accuracy, geometric deviation, density, mechanical properties and feasible feature sizes were evaluated.
Findings
The experimental results demonstrate that the ISLS system is feasible and can print large-sized parts with good dimensional accuracy, acceptable geometric deviations, specific small-scale features and certain density and mechanical properties.
Originality/value
This study has achieved the transition from traditional point sintering mode to image-shaped surface sintering mode. It has provided a new approach to enhance the system performance of traditional SLS.
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Hui Zhang, Yanling Guo, Kaiyi Jiang, David Bourell, Jian Li and Yueqiang Yu
A new kind of polymer mixture (co-PA-PES) was prepared in different mass ratios, by mixing polyether sulfone hot-melt adhesive (PES-HmA) and copolyamide B249 (PA-B249). This study…
Abstract
Purpose
A new kind of polymer mixture (co-PA-PES) was prepared in different mass ratios, by mixing polyether sulfone hot-melt adhesive (PES-HmA) and copolyamide B249 (PA-B249). This study aims to investigate its characteristics of laser sintering and get the optimal process parameters.
Design/methodology/approach
The effect of mass ratio of co-PA-PES on thermal behavior was analyzed using a simultaneous thermal analyzer, and the density and mechanical properties of sintered parts were tested to evaluate the performance of the polymeric system. Scanning electron microscopy and Fourier transform infrared spectroscopy were performed to characterize the microstructure and binding mechanism of sintered co-PA-PES parts. Specifically, mechanical properties of the mixture with 20 Wt.% PA-B249 were optimized based on a design of experiment methodology, along with the restriction of maximum absorbable laser energy density.
Findings
Liquid phase fusion was considered as the main sintering mechanism for co-PA-PES, and mechanical interlocking was the dominant binding mechanism. The effects of mass ratios of this material on the thermal properties, density and mechanical properties were obtained via data results. Additionally, compared to neat PES-HmA, co-20 Wt.% PA-PES showed a 71.7 per cent increase in tensile strength, 24.4 per cent increase in flexural strength and 102.1per cent increase in impact strength.
Originality/value
This paper proposed a new kind of polymer mixture as the feedstock for laser sintering with the advantages of low price and easy processing. The filler of PA-B249 effectively improved the performance of the polymer mixture, including but not limited to mechanical properties.
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Neal K. Vail, Badrinarayan Balasubramanian, Joel W. Barlow and Harris L. Marcus
Reports that measurable amounts of polymer degradation occur during the fabrication of objects from polymer coated ceramic powders by selective laser sintering (SLS). Argues that…
Abstract
Reports that measurable amounts of polymer degradation occur during the fabrication of objects from polymer coated ceramic powders by selective laser sintering (SLS). Argues that because the binder is important in achieving strong green parts that can be handled with minimal breakage during post‐processing operations, it is essential to minimize the extent of binder losses. As the first step towards understanding the mechanisms of binder degradation, this paper presents a thermal model of the physical system, noting that the agreement between theory and experiment are good. The model is used to help determine the most influential parameters affecting binder losses during fabrication from polymer coated powders. Predicts that adjustments to laser beam diameter, laser scanning distance and gaseous environment will strongly affect polymer binder degradation during processing. Further predicts correctly that polymer degradation during SLS processing is not sensitive to the inherent degradation kinetics of the polymer.
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Kamatchi Subramanian, Neal Vail, Joel Barlow and Harris Marcus
The selective laser sintering (SLS) process is used to prepare test bars from Al2O3/polymer binder powders. Finds that binder‐coated A12O3 particles formed bars that were…
Abstract
The selective laser sintering (SLS) process is used to prepare test bars from Al2O3/polymer binder powders. Finds that binder‐coated A12O3 particles formed bars that were approximately twice as strong as could be formed from mixtures of alumina and polymer binder at the same binder level and processing conditions. In mixed systems, bar strengths increased nearly in proportion to increases in polymer binder content over the 20‐40 per cent volume binder range. Parts made in any particular laser scanning mode showed optimum values for strength and density as the laser energy density was systematically increased from 2‐8cal/cm2. Suggests that optima result from the counteracting influences of energy density on binder fusion and thermal degradation. The optimum energy density is mode or geometry sensitive and shifts to lower values as the laser scanning vector is reduced. Concludes that this behaviour is probably the result of the lower heat losses. Equivalently better utilization of laser energy is associated with the shorter scan vectors. Some of the SLS fabricated bars were infiltrated with colloidal alumina, fired to remove the binder, and sintered at 1,600°C to achieve alumina bars with 50 per cent relative densities, interconnected porosity, and strengths between 2 and 8MPa.
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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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Ana Pilipović, Bogdan Valentan and Mladen Šercer
The purpose of this paper is the selection of production parameters in selective laser sintering – SLS for the production of quality products (e.g. good mechanical properties)…
Abstract
Purpose
The purpose of this paper is the selection of production parameters in selective laser sintering – SLS for the production of quality products (e.g. good mechanical properties). The manufacturing procedure affects the properties, which is especially significant in additive procedures, as the products are not cheap and the procedure and material need to be optimally selected.
Design/methodology/approach
The paper presents an analysis of the fabrication parameters in selective laser sintering (SLS) that affect the flexural properties of the finished product.
Findings
The influence of a new parameter has been found, the overlay ratio, and using the mathematical and scheme method, the selection of parameters for obtaining the optimal flexural properties has been proposed.
Originality/value
The paper presents a new mathematical model for the calculation of the processing parameters in SLS of polymer products and gives a diagram for the determination of which parameters are the best to use for practical purposes.
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Yi Fu, Chunze Yan, Xiao Yang, Zhufeng Liu, Peng Chen and Zhaoqing Li
The purpose of this paper is to prepare metal/polymer composite materials prepared by additive manufacturing (AM) technology.
Abstract
Purpose
The purpose of this paper is to prepare metal/polymer composite materials prepared by additive manufacturing (AM) technology.
Design/methodology/approach
The effect of sintering parameters including laser power, scanning speed and slice thickness on strength and accuracy of selective laser sintering (SLS) parts were analyzed experimentally. Then, the laser sintering mechanism of nylon-12 coated copper was discussed through analyzing the interfacial reaction of nylon-12 and copper. The SLS parts were infiltrated with epoxy resin to meet the strength requirements of injection molding.
Findings
In this study, mechanical mixed nylon-12/copper and nylon-12 coated copper composite powders were investigated and compared as SLS materials. An effective dissolution–precipitation method was proposed to prepare nylon-12 coated copper powders with better processing and mechanical properties. The bending strength and modulus of fabricated parts after infiltration with epoxy reach 65.3 MPa and 3,200 MPa, respectively.
Originality/value
The composite materials can be used in the manufacture of injection molds with a conformal cooling channel for the production of common plastics in prototype quantities, showing a broad application prospect in rapid tooling.
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Ryuichi Kobayashi, Takashi Kigure and Ming Yang
This paper aims to describe a new process for suppressing the formation of orange peel, which is a polymer laser sintering (LS) process error.
Abstract
Purpose
This paper aims to describe a new process for suppressing the formation of orange peel, which is a polymer laser sintering (LS) process error.
Design/methodology/approach
The target for controlling the suppression of orange peel is securing the contact between the molten polymer and the surrounding powder. The authors set the powder bed temperature closer to the melting temperature than that for a typical LS. Alternatively, the authors use a low-power laser to irradiate the powder bed surrounding the parts being built. The surface finish of the built parts was evaluated using a three-dimensional scanner.
Findings
Both approaches were effective in suppressing orange peel. From the viewpoint of reusability of the used powder, the process that includes low-power laser irradiation is practical. The presence or absence of contact between the surrounding powder and the molten polymer determines whether the orange peel is formed.
Research limitations/implications
The authors have not tested orange peel suppression for complex shapes.
Originality/value
The authors have demonstrated a concrete process that can suppress orange peel formation even for powders with low melt-flow rates. Furthermore, a mechanism for the formation/suppression of orange peel based on the experimental results was proposed.
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