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Article
Publication date: 1 March 2005

Jingzhe Pan and H.N. Ch’ng

This paper presents a unified framework to model the sintering process of fine powders. The framework is based on classical virtual power principle and its corresponding…

Abstract

This paper presents a unified framework to model the sintering process of fine powders. The framework is based on classical virtual power principle and its corresponding variational principle. Firstly, the classical models of solid state, viscous and liquid phase sintering are reproduced assuming single matter re‐distribution mechanism and using the virtual power principle as the starting point. Then we demonstrate how to obtain the governing equations for microstructural evolution using the variational principle. These provide a common thread through the existing sintering models. Finally a numerical solution scheme is briefly outlined for computer simulation of microstructural evolution using the variational principle as the starting point. The computer simulation can follow the entire sintering process from powder compact to fully dense solid and deal with fully couple multi‐physics processes involving all the possible underlying matter re‐distribution mechanisms. Several examples are provided to demonstrate the deep insights that can be gained into the sintering process by using the numerical tool.

Details

Multidiscipline Modeling in Materials and Structures, vol. 1 no. 3
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 28 March 2008

Q. Sun, G.M. Rizvi, C.T. Bellehumeur and P. Gu

The purpose of this paper is to investigate the mechanisms controlling the bond formation among extruded polymer filaments in the fused deposition modeling (FDM) process…

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Abstract

Purpose

The purpose of this paper is to investigate the mechanisms controlling the bond formation among extruded polymer filaments in the fused deposition modeling (FDM) process. The bonding phenomenon is thermally driven and ultimately determines the integrity and mechanical properties of the resultant prototypes.

Design/methodology/approach

The bond quality was assessed through measuring and analyzing changes in the mesostructure and the degree of healing achieved at the interfaces between the adjoining polymer filaments. Experimental measurements of the temperature profiles were carried out for specimens produced under different processing conditions, and the effects on mesostructures and mechanical properties were observed. Parallel to the experimental work, predictions of the degree of bonding achieved during the filament deposition process were made based on the thermal analysis of extruded polymer filaments.

Findings

Experimental results showed that the fabrication strategy, the envelope temperature and variations in the convection coefficient had strong effects on the cooling temperature profile, as well as on the mesostructure and overall quality of the bond strength between filaments. The sintering phenomenon was found to have a significant effect on bond formation, but only for the very short duration when the filament's temperature was above the critical sintering temperature. Otherwise, creep deformation was found to dominate changes in the mesostructure.

Originality/value

This study provides valuable information about the effect of deposition strategies and processing conditions on the mesostructure and local mechanical properties within FDM prototypes. It also brings a better understanding of phenomena controlling the integrity of FDM products. Such knowledge is essential for manufacturing functional parts and diversifying the range of application of this process. The findings are particularly relevant to work conducted on modeling of the process and for the formulation of materials new to the FDM process.

Details

Rapid Prototyping Journal, vol. 14 no. 2
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 17 October 2017

Hao Li, Shuai Zhang, Zhiran Yi, Jie Li, Aihua Sun, Jianjun Guo and Gaojie Xu

This work aims to evaluate the influence of rheological properties of building materials on the bonding quality and ultimate tensile strength in the fused deposition…

Abstract

Purpose

This work aims to evaluate the influence of rheological properties of building materials on the bonding quality and ultimate tensile strength in the fused deposition modeling (FDM) process, through the investigation of parts printed by semi-crystalline and amorphous resins. Little information is currently available about the influence of the crystalline nature on FDM-printed part quality.

Design/methodology/approach

Semi-crystalline polyamide 12 and amorphous acrylonitrile butadiene styrene (ABS) were used to assess the influence of rheological properties on bonding quality and the tensile strength, by varying three important process parameters: materials, liquefier temperature and raster orientation. A fractography of both tensile and freeze-fractured samples was also investigated.

Findings

The rheological properties, mainly the melt viscosity, were found to have a significant influence on the bonding quality of fused filaments. Better bonding quality and higher tensile strength of FDM parts printed with semi-crystalline PA12, as compared with amorphous ABS, are suggested to be a result of higher initial sintering rates owing to the lower melt viscosity of PA12 at low shear rates. Near-full dense PA12 parts were obtained by FDM.

Originality/value

This project provides a variety of data and insight regarding the effect of materials properties on the mechanical performance of FDM-printed parts. The results showed that FDM technique allows the production of PA12 parts with adequate mechanical performance, overcoming the greatest limitation of a dependence on amorphous thermoplastics as a feedstock for the production of prototypes.

Details

Rapid Prototyping Journal, vol. 23 no. 6
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 August 2019

Ognjan Luzanin, Dejan Movrin, Vassilis Stathopoulos, Pavlos Pandis, Tanja Radusin and Vera Guduric

This study aims to investigate the impact of layer thickness, extrusion temperature, extrusion speed and build plate temperature on the tensile strength, crystallinity…

Abstract

Purpose

This study aims to investigate the impact of layer thickness, extrusion temperature, extrusion speed and build plate temperature on the tensile strength, crystallinity achieved during fabrication (herein, in-process crystallinity) and mesostructure of Poly(lactic acid) specimens. Both tensile strength and in-process crystallinity were optimized and verified as the function of processing parameters, and their relationship was thoroughly examined.

Design/methodology/approach

The four key technological parameters were systematically varied as factors on three levels, using the statistically designed experiment. Surface response methodology was used to optimize tensile strength and crystallinity for the given ranges of input factors. Optimized factor settings were used in a set of confirmation runs, where the result of optimization was experimentally confirmed. Material characterization was performed using differential scanning calorimetry and X-ray diffraction analysis, while the effect of processing parameters on mesostructure was examined by scanning electron microscopy.

Findings

Layer thickness and its quadratic effect are dominant contributors to tensile strength. Significant interaction between layer thickness and extrusion speed implies that these parameters should always be varied simultaneously within designed experiment to obtain adequate process model. As regards, the in-process crystallinity, extrusion speed is part of two significant interactions with plate temperature and layer thickness, respectively. Quality of mesostructure is vital contributor to tensile strength during FDM process, while the in-process crystallinity exhibited no impact, remaining below the 20 per cent margin regardless of process parameter settings.

Originality/value

According to available literature, there have been no previously published investigations which studied the effect of process parameters on tensile strength, mesostructure and in-process crystallinity through systematic variation of four critical processing parameters.

Details

Rapid Prototyping Journal, vol. 25 no. 8
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 1 March 1989

M.G. Norton

Aluminium nitride (AlN) is currently under investigation as a substrate material for use in microcircuit applications in particular where high thermal conductivity is…

Abstract

Aluminium nitride (AlN) is currently under investigation as a substrate material for use in microcircuit applications in particular where high thermal conductivity is required. Three commercially available substrate materials have been characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The differences in thermal conductivity between the materials and also the difference from the theoretical thermal conductivity have been correlated to the presence of low thermal conductivity second phase regions between grains, defects within the crystal structure, the presence of oxygen impurities and poor sintering behaviour. The highest thermal conductivity substrate obtainable during this study was 140 W7m K. The substrates were identified as comprising hexagonal AIM having a wurtzite type structure. In addition, oxide and oxynitride phases were detected. The surface morphology of the substrates was also investigated, as it is the nature of the surface that will be of importance in determining the adhesion of applied films.

Details

Microelectronics International, vol. 6 no. 3
Type: Research Article
ISSN: 1356-5362

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Article
Publication date: 3 February 2020

Nickolas D. Polychronopoulos and John Vlachopoulos

This study aims to develop mathematical models for the determination of the effects of heating or cooling on neck growth in Selective Laser Sintering (SLS) and Fused…

Abstract

Purpose

This study aims to develop mathematical models for the determination of the effects of heating or cooling on neck growth in Selective Laser Sintering (SLS) and Fused Filament Fabrication (FFF). Two particle shapes are studied: spherical and cylindrical.

Design/methodology/approach

The time required for the coalescence (sintering) process is determined by balancing the work of surface tension forces and viscous dissipation. Heating and cooling effects are studied by incorporating temperature dependence of viscosity in an exponential form. Heating by a laser, convective and/or radiative heat transfer is assumed. It is also assumed that there are no temperature gradients within the coalescing molten polymers (lumped parameter heat transfer analysis).

Findings

The models predict faster sintering with heating and slower with cooling, as expected because of the effect of temperature on viscosity. For the isothermal case of pairs of cylinders, the present model predicts significantly longer time for completion of sintering than a previously developed and frequently cited model by Hopper.

Originality/value

An isothermal sintering model for two spheres was reworked for two long cylinders, and for the first time it has been compared to other models available in the literature. The mathematical models are capable of predicting neck growth under non-isothermal conditions for both spheres and cylinders. They are useful in assessment of bonding in selective laser sintering and fused deposition fabrication.

Details

Rapid Prototyping Journal, vol. 26 no. 4
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 4 September 2019

Nicholas J. Beutell, Jeffrey W. Alstete, Joy A. Schneer and Camille Hutt

The purpose of this paper is to test a model predicting self-employment (SE) personal growth (learning opportunities and creativity) and SE exit intentions (exiting to…

Abstract

Purpose

The purpose of this paper is to test a model predicting self-employment (SE) personal growth (learning opportunities and creativity) and SE exit intentions (exiting to work for someone else and exit likelihood) based on the job demands-resources model.

Design/methodology/approach

SEM was used to examine SE demands and resources, strain, and engagement predicting growth, exit intentions, job satisfaction, and life satisfaction. SE type (owners with employees and independent owners without employees) was a moderator variable. Data were analyzed from a national probability sample (n=464 self-employed respondents for whom SE was their primary work involvement), the National Study of the Changing Workforce.

Findings

Overall support for the model was found. Work–family conflict (demand) and work–family synergy (resource) had the strongest relationships with strain and engagement. Strain was positively related to both growth and exit intentions while engagement was inversely related to exit intentions but positively related to growth. The model was significantly different for business owners and independently self-employed.

Practical implications

These results provide guidance to researchers and educators regarding the challenges of self- employment engagement and strain with implications for selecting business types that minimize exit likelihood while maximizing work engagement and personal growth potential.

Originality/value

This study breaks new ground by testing a structural model of engagement and growth for self-employed individuals while also investigating two types of exit intentions. The authors report findings for growth and exit decisions that have received scant attention in the literature to date. Type of SE was a significant variable.

Details

International Journal of Entrepreneurial Behavior & Research, vol. 25 no. 7
Type: Research Article
ISSN: 1355-2554

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Article
Publication date: 1 December 2003

Nikolay K. Tolochko, Maxim K. Arshinov, Andrey V. Gusarov, Victor I. Titov, Tahar Laoui and Ludo Froyen

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…

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5774

Abstract

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 α‐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.

Details

Rapid Prototyping Journal, vol. 9 no. 5
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 27 October 2020

J.A. Travieso-Rodriguez, R. Jerez-Mesa, Jordi Llumà, Giovanni Gomez-Gras and Oriol Casadesus

The aim of this paper is to analyze the mechanical properties of acrylonitrile-butadiene-styrene (ABS) parts manufactured through fused filament fabrication and compare…

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128

Abstract

Purpose

The aim of this paper is to analyze the mechanical properties of acrylonitrile-butadiene-styrene (ABS) parts manufactured through fused filament fabrication and compare these results to analogous ones obtained on polylactic acid (PLA) and PLA–wood specimens to contribute for a wider understanding of the different materials used for additive manufacturing.

Design/methodology/approach

With that aim, an experimental based on an L27 Taguchi array was used to combine the specific parameters taken into account in the study, namely, layer height, nozzle diameter, infill density, orientation and printing velocity. All samples were subjected to a four-point bending test performed according to the ASTM D6272 standard.

Findings

Young’s modulus, elastic limit, maximum stress and maximum deformation of every sample were computed and subjected to an analysis of variance. Results prove that layer height and nozzle diameter are the most significant factors that affect the mechanical resistance in pieces generated through additive manufacturing and subjected to bending loads, regardless of the material.

Practical implications

The best results were obtained by combining a layer height of 0.1 mm and a nozzle diameter of 0.6 mm. The comparison of materials evidenced that PLA and its composite version reinforced with wood particles present more rigidity than ABS, whereas the latter can experience further deflection before break.

Originality/value

This study is of interest for manufacturers that want to decide which is the best material to be applied for their application, as it derives in a practical technical recommendation of the best parameters that should be selected to treat the material during the fused filament fabrication process.

Details

Rapid Prototyping Journal, vol. 27 no. 1
Type: Research Article
ISSN: 1355-2546

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Article
Publication date: 2 May 2017

Peter Lukacs, Alena Pietrikova and Pavol Cabuk

The purpose of this paper is to find optimal sintering conditions of silver-based nano-inks for achieving the high electrical conductivity of the deposited layers applied…

Abstract

Purpose

The purpose of this paper is to find optimal sintering conditions of silver-based nano-inks for achieving the high electrical conductivity of the deposited layers applied on polyimide foils as well as the influence of ageing on the electrical conductivity. Therefore, the investigation in the field of silver layers deposited by inkjet printing technology is presented in this paper.

Design/methodology/approach

The four-point resistance measurements were realized for a detailed and precise analysis of the resistance of two different silver layers under different sintering conditions depending on the type of nano-ink varied about the recommended values. Highly accelerated stress tests (HASTs) were also applied as an ageing method for confirmation of the high electrical stability of the silver layers.

Findings

The results prove the strong influence of the temperature and the time of the sintering process on the sheet resistance of the investigated silver-based layers deposited by inkjet printing technology on polyimide foils. The HASTs caused significant changes in the electrical conductivity for both nano-inks presented in this paper. The existence of noticeable dependence among the resistivity, thermal treatment and ageing was proved.

Originality/value

The main benefit lays in the optimization of sintering conditions to improve the electrical conductivity of the silver layers. The paper also presents a new approach for a stability analysis of the silver layers by HASTs.

Details

Circuit World, vol. 43 no. 2
Type: Research Article
ISSN: 0305-6120

Keywords

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