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Since pulsed lasers are mainly used in selective laser sintering (SLS) – contrarily to selective laser melting (SLM) – only the exterior of the powder particles is molten while their core stays solid. The purpose of this paper is to investigate the binding mechanism between two particles of titanium powder.

A dedicated experimental setup is used to isolate the particles. They are then irradiated by the laser. SEM micrographs are taken at each step and image analysis is performed. The obtained results are compared with the predictions of a thermal model allowing for the incorporation of the latent heat of fusion and for a realistic surrounding. The absorbed laser intensity is modeled by means of the Mie theory.

The growing of the interparticular necks and the volume of liquid formed for different repetition rates are measured and compared with numerical simulations. A good agreement is found. A new method to easily find the absorption coefficient of the laser into the grain and the heat exchange coefficient with the exterior is developed.

This paper leads to a better understanding of the necking phenomena involved in the SLS consolidation process. An experimental set‐up has been developed to observe and quantify the final state of a small amount of laser sintered grains. This process has been shown to be replicable and trustful. The thermal model leads to good predictions of the particle final sintering state.

In binder jetting, the interaction between the liquid binder droplets and the powder particles defines the shape of the printed primitives. The purpose of this study is to explore the interaction of the relative size of powder particles and binder droplets and the subsequent effects on macro-scale part properties.

The effects of different particle size distribution (5–25 µm and 15–45 µm) of stainless steel 316 L powders and droplet sizes (10 and 30 pL) on part density, shrinkage, mechanical strength, pore morphology and distribution are investigated. Experimental samples were fabricated in two different layer thicknesses (50 and 100 µm).

While 15–45 µm samples demonstrated higher green density (53.10 ± 0.25%) than 5–25 µm samples (50.31 ± 1.06%), higher sintered densities were achieved in 5–25 µm samples (70.60 ± 6.18%) compared to 15–45 µm samples (65.23 ± 3.24%). Samples of 5–25 µm also demonstrated superior ultimate tensile strength (94.66 ± 25.92 MPa) compared to 15–45 µm samples (39.34 ± 7.33 MPa). Droplet size effects were found to be negligible on both green and sintered densities; however, specimens printed with 10-pL droplets had higher ultimate tensile strength (79.70 ± 42.31 MPa) compared to those made from 30-pL droplets (54.29 ± 23.35 MPa).

To the best of the authors’ knowledge, this paper details the first report of the combined effects of different particle size distribution with different binder droplet sizes on the part macro-scale properties. The results can inform appropriate process parameters to achieve desired final part properties.

The purpose of this paper is to investigate the fundamentals of the selective inhibition sintering (SIS) process for fabricating dense metallic parts.

A SIS‐Metal process based on the microscopic mechanical inhibition is developed. In the process, salt solution is printed in the selected area of each powder layer; the salt re‐crystallizes when water evaporates; salt crystals decompose and grow rapidly prior to sintering; the generated salt particles spread between metal powder particles and prevent the fusing of these particles together, hence inhibiting the sintering process in the affected regions.

The SIS‐Metal process has numerous advantages. An inhibition of sintering mechanism is established for the future development of the technology. Through chemical and visual analysis using STM the mechanism for the inhibition phenomenon has been identified.

Only bronze powder has been used in the research. Accordingly, the inhibition chemical has been engineered for this material choice. The approach should be feasible for other metals but a proper inhibitor would need to be found for each material choice.

The only limitation envisioned for the process may be the removal after sintering of inhibited sections in hard‐to reach areas using physical means such as scraping or vibration. Chemical removal of such sections should be possible, however.

The paper illustrates a new additive manufacturing technology for metallic parts fabrication.

The purpose of this paper is to fundamentally develop a mathematical model for predicting the particle size distribution (PSD) in fluidized beds because their hydrodynamics depend on the PSD and its evolution during operation. To predict the gradual PSD change in a fluidized bed by using the population balance method (PBM), the kinetic parameter for agglomerate formation should be known and this parameter, in this work, is determined by the results of computational fluid dynamic–discrete element method (CFD-DEM) simulation.

Momentum and energy conservation equations and soft-sphere DEM are used to simulate the agglomeration phenomenon at high temperature in a two-dimensional air-polyethylene fluidized bed in bubbling regime. The Navier–Stokes equations for motion of gas are solved by the SIMPLE algorithm. Newton’s second law of motion is applied to describe the motion of individual particles. Collision between particles is detected by the no-binary search algorithm.

A correlation is proposed for estimating the kinetic parameter for agglomerate formation based on collision frequency, collision efficiency and inlet gas temperature. Based on the corrected kinetic parameter, the PBM is able to predict the PSD evolution in the fluidized bed in a fairly good agreement with the results of the CFD-DEM.

The results of the agglomeration process cannot be compared quantitatively with experimental results. Because three-dimensional fluidized bed mostly contains millions of particles and simulating them takes a long computing time in DEM. As far as temperature is a dominant parameter in the agglomeration process, effects of inlet gas temperature are examined on the kinetic parameter. On the other hand, wider and deeper insights in which the effect of other parameters, such as velocity and so on will be studied, is one of the goals in the authors’ next works to compensate for the shortcomings in this work.

This study helps to understand the effect of the inlet gas temperature during the agglomeration process on the kinetic parameter and provides fundamental information in dealing with kinetic parameter to attain PSD in fluidized bed by the PBM.

The purpose of this paper is to acquire thermal conductivities of both fresh and preheated polyamide 12 powder under various conditions to provide a basis for effective and accurate control during the laser sintering (LS) process.

A Hot Disk® TPS 500 thermal measurement system using a transient plane source (TPS) technology was employed for thermal conductivity measurements. Polyamide 12 powder was packed at different densities, and different carrier gases were used. Tests were also performed on fully dense laser sintered polyamide 12 to establish a baseline.

Polyamide 12 powder thermal conductivity varies with packing density and temperature, which is approximately one-third bulk form thermal conductivity. Inter-particle bonding is the primary factor influencing polyamide 12 thermal conductivity.

Limited ranges of density were tested, and the carrier gas needed carefully control to prevent powder oxidation. Thermal properties obtained were not tested in the LS process.

This experimental result could be used to enhance thermal control during the LS process.

During the operation of nickel-based alloys as blades and discs in turbines, the sliding activity between metallic surfaces is subjected to structural and compositional changes. In as much as friction and wear are influenced by interacting surfaces, it is necessary to investigate these effects. This study aims to understand better the mechanical and tribological characteristics of Ni-17Cr-10X (X = Mo, W, Ta) ternary alloy systems developed via spark plasma sintering (SPS) technique.

Nickel-based ternary alloys were fabricated via SPS technique at 50 MPa, 1100 °C, 100 °C/min and a dwell time of 10 mins. Scanning electron microscopy, X-Ray diffraction, energy dispersive X-ray spectroscopy, nanoindentation techniques and tribometer were used to assess the microstructure, phase composition, elemental dispersion, mechanical and tribological characteristics of the sintered nickel-based alloys.

The outcome of the investigation showed that the Ni-17Cr10Mo alloy exhibited the highest indentation hardness value of 8045 MPa, elastic modulus value of 386 GPa and wear resistance. At the same time, Ni-17Cr10W possessed the least mechanical and wear properties.

It can be shown that the SPS technique is efficient in the development of nickel-based alloys with good elemental distribution and without defects such as segregation of alloying elements, non-metallic inclusions. This is evident from the scanning electron microscopy micrographs.

The purpose of this paper is to evaluate the effect of copolymer and starting material concentrations in homogeneous precipitation synthesis of Yttria nanoparticles and red‐emitting nanophosphors Y₂O₃:Eu³⁺. N‐isopropylacrylamide and acrylic acid (NIPAM/AAc) and urea are used.

To optimise synthesis condition of Y₂O₃:Eu³⁺ nanophosphor NIPAM/AAc copolymer was used as a modifier and the effect of various concentration of yttrium ions, urea and precipitation time on size, morphology and emission spectra were investigated.

Using NIPAM/AAc copolymer shows significant improvement on size and dispersion of nanoparticles. It is found that yttrium concentration, varying between 0.006 and 0.03 M, has a profound impact on the average size of particles, which systematically increases from 65 to over 165 nm. The rate of precipitation reaction, however, is shown to be independent of yttrium concentration. In contrast, as urea concentration increases from 0.2 to 5 M, the average particle size exhibits a gradual decrease from 183 to 70 nm. At extremely high urea concentration such as 5 M, a significant level of inter‐particle agglomeration is observed.

Based on this paper, the authors have successfully prepared some promising nanophosphors. The nanoparticles are studied by X‐ray diffraction, transmission electronic microscopy, zeta sizer, Infra red and photoluminescence spectroscopy.

The purpose of this paper is to prepare nano size micro-emulsion co-polymer particles based on butyl acrylate (BA)/acrylic acid (AAc) with high monomer/surfactant ratio. The study involved the application of the prepared micro-emulsions co-polymers as textile pigment printing binders.

The micro-emulsion co-polymerisations processes were carried out with different mixtures of BA and AAc using modified process. Sodium dodecyl sulphate (SDS) and potassium peroxy disulphate/glucose were used as emulsifier and redox initiator, respectively. The prepared emulsion co-polymer was characterized via spectroscopic measurements, FT-IR, 1H-NMR and transmission electron microscope (TEM), in addition to thermal analysis. The prepared micro-emulsion co-polymers were applied as binders for pigment printing process onto cotton fabric, polyester and cotton/polyester blend by using flat screen technique. The optimum curing conditions were determined, colour strength and fastness properties of pigment printed areas to light, washing, perspiration and rubbing were evaluated. In addition, stiffness of the prints was studied.

The achieved results indicated that particle size and homogeneity of the prepared micro-emulsions depend on monomers weight ratio, initiator and emulsifier concentrations. On the other hand, the prints obtained using the prepared binders with optimum conditions have satisfactory fastness, good handle and high colour yield.

Monomers were continuously and slowly added into the polymerising system with mild stirring to avoid disturbing the stability of the micro-emulsion. Also, emulsifier and initiator concentrations should be controlled to avoid coagulation.

The research provides textile pigment printing binder with nano particle size within the range of 24-48 nm. Using the prepared nano binders in pigment printing enhances the stiffness, handle, and fastnesses properties of the prints.

The prepared co-polymer binders showed high-performance physico-mechanical properties; in addition, the ultimate goal of this study is to prepare a nano size binder with high monomer/surfactant ratio using a modified micro-emulsion process.

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).

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.

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.

The range of techniques (DSC, oxidative induction time and TGA) form an effective analytical package with which to consider new polymeric materials for SLM.

High-Mw PP polymers, in tape or powder form, have potential use in SLM processes, providing scope to enhance part properties in future.

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.

The macroscopic properties of dried sand can be correctly modelled when the accurate determination of the microscopic properties is available. The microscopic properties between the particles such as the coefficients of rolling (µ _r) and sliding (µ _s), are numerically determined in two different ways: with and without considering the fluid effect. In an earlier study, the microscopic properties were determined by discrete element method (DEM) and without considering the air effect on the macroscopic properties such as the Angle of Repose. The purpose of this paper is to recalibrate the microscopic properties through a coupling between the DEM and computational fluid dynamics (CFD).

The first step is dedicated to the calibration of the CFD-DEM model through modelling a single particle sedimentation within air, water, and silicon oil. The voidage and drag models, the grid size ratio (D/dx), the domain size ratio (W/D), and the optimum coupling interval between the CFD and DEM were investigated through comparing the CFD-DEM results with the analytical solution and experimental data. The next step is about modelling an Hourglass with the calibrated CFD-DEM model to recalibrate the µ _r and µ _s of dried sand particles.

It was concluded that the air has a minor effect on the macroscopic properties of the dried sand and the µ _r and µ _s that were obtained with the DEM can be utilized in the CFD-DEM simulation.

Utilizing the granulometry of dried quartz sand in the calibration process of the CFD-DEM method has raised the possibility of using the µ _r and µ _s for other applications in future studies.