POLYAMIDES, MECHANICAL behavior of materials, MATHEMATICAL optimization, RAPID prototyping, SINTERING, and RESPONSE surfaces (Statistics)
Selective laser sintering (SLS) is one of the widely used rapid prototyping (RP) processes. The main challenge of this process is to choose the correct working parameters to attain the desired shape, size, and strength of different products. Therefore, this article pertains to an experimental study carried out to understand mechanical properties of selective laser sintered polyamide parts. Experiments were established based on face-centered central composite design (CCD) of response surface methodology (RSM). The effect of various process parameters on different properties (i.e., ultimate tensile strength, % elongation, yield strength, and Young's modulus) was analyzed. Analysis of variance was employed to check the adequacy of the developed models. Furthermore, the optimal combination of these process parameters has been evaluated. Considering ultimate tensile strength, % elongation, yield strength, and Young's modulus simultaneously, the optimum values of different process parameters have been obtained as: laser power, 32 W; scan spacing, 0.17 mm; bed temp, 178°C; and scan count, 2. [ABSTRACT FROM AUTHOR]
SINTERING, LASER sintering, POLYAMIDES, LITHOPHANES (Ceramics), and THREE-dimensional printing
Purpose – This paper aims to analyze the additive manufacturing orientation effect of laser sintered polyamide 12 (PA 12) optically translucent parts. Design/methodology/approach – Plates with small features, wedges and lithophanes were laser sintered on a SinterStation HiQ™ in different orientations using PA 12. Lithophane performance was assessed using a Picker 240050 X-ray view/light box. All parts were examined using stereomicroscopy to capture the small features. Findings – The quality of the lithophane image was substantially improved by orienting the flat plate side to the incident backlit light. Sintering in the ZX/ZY plane significantly increased the contrast and resolution compared to sintering in the XY plane. The thinnest feature thickness possible in the SinterStation HiQ is in the XY plane 0.13 mm, and it is 0.57 mm when manufacturing in the ZX/ZY plane. Research limitations/implications – The laser spot size and other machine parameters were not changeable, which limited the manufacturing resolution. Oblique, non-orthogonal orientations were not investigated. Originality/value – This is a first effort to investigate the manufacturing orientation effect of laser sintered polyamide optically translucent parts. The manufacturing resolutions on different planes were defined. [ABSTRACT FROM AUTHOR]
VISCOSITY, SINTERING, POLYMERS, RHEOLOGY, MOLECULAR weights, and POLYAMIDES
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. [ABSTRACT FROM AUTHOR]
HYDROXYAPATITE, POLYMERS, MACROMOLECULES, POLYAMIDES, and BIOMATERIALS
Purpose – Hydroxyapatite-polymer composite materials are being researched for the development of low-load bearing implants because of their bioactive and osteoconductive properties, while avoiding modulus mismatch found in homogenous materials. For the direct production of hydroxyapatite-polymer composite implants, selective laser sintering (SLS) has been used and various parameters and their effects on the physical properties (micro and macro morphologies) have been investigated. The purpose of this paper is to identify the most influential parameters on the micro and macro pore morphologies of sintered hydroxyapatite-polymer composites. Design/methodology/approach – A two-level full factorial experiment was designed to evaluate the effects of the various processing parameters and their effects on the physical properties, including open porosity, average pore width and the percentage of pores which could enable potential bone regeneration and ingrowth of the sintered parts. The density of the sintered parts was measured by weight and volume; optical microscopy combined with the interception method was used to determine the average pore size and proportion of pores suitable to enable bone regeneration. Findings – It was found that the effect of build layer thickness was the most influential parameter with respect to physical and pore morphology features. Consequently, it is found that the energy density equation with the layer thickness parameter provides a better estimation of part porosity of composite structures than the energy density equation without the layer thickness parameter. However, further work needs to be conducted to overcome the existing error of variance. Originality/value – This work is the first step in identifying the most significant SLS parameters and their effects on the porosity, micro and macro pore morphologies of the fabricated parts. This is an important step in the further development of implants which may be required. [ABSTRACT FROM AUTHOR]
COMPOSITE materials research, POLYAMIDES, ALUMINUM oxide, SINTERING, SCANNING electron microscopes, and MICROMECHANICS
The article presents a study which characterized the composite of polyamide (PA)-aluminum oxide (Al2O3) for selective laser sintering (SLS). Tension test was used to determine the mechanical characteristics of the specimens used in the study. It also analyzed the failure and joining micromechanisms that rule the composite materials' macroscopic characteristics using optical and scanning electron microscope (SEM).
POLYAMIDES, SINTERING, POLYMER research, POLYMER melting, and MATERIALS
The article presents a research paper which investigates polyamide 12 (PA12) powder recycling in the laser sintering (LS) process. It mentions that samples of recycled grades of PA2200 powder were artificially aged in a temperature-controlled oven. It says that polymers were the first engineering materials due their ability to be processed easily by melting. It states that melt flow rate (MFR) index can provide a fast and inexpensive way to measure powder degradation.