Photopolymerization of Ceramic Resins by Stereolithography Process: A Review

Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process

A357 alloy by LPBF for Industry Applications

The aim of this study is to define the process parameters to build components for industrial applications in A357 alloy by Laser Powder Bed Fusion (LPBF) and to evaluate the effects of post-processing heat treatments on the microstructure and mechanical properties in order to obtain the highest hardness and strength. First, process parameters values were defined to obtain full dense components with highest productivity. Then samples were built for microstructural, hardness, and tensile strength investigation in different conditions: as-built, after a stress-relieving treatment, and after a T6 precipitation hardening treatment. For this latest treatment, different time and temperatures for solution and ageing were investigated to find the best in terms of final hardness achievable. It is demonstrated that samples in A357 alloy can be successfully fabricated by LPBF with a density of 99.9% and a mean hardness value achievable of 116 HV0.1, in as-built condition. However, for production purposes, it is fundamental to reduce the residual stresses typical of LPBF. It was shown that a similar hardness value could be obtained after a stress-relieving treatment followed by a proper T6 treatment, together with a coarser but more isotropic microstructure

Accuracy of complex internal channels produced by laser powder bed fusion process

Additive manufacturing (AM) technology has great potential in manufacturing complex internal channels for several applications such as satellite-communication microwave systems. These systems can have complex shapes and make traditional finishing processes a challenge for additive parts. Therefore, it is desirable that the internal surfaces are as close as possible to the tolerance of the field of application. In this study, a complex component, a unique waveguide device with bending, twisting and filtering functionalities, has been designed and manufactured in AlSi10Mg alloy through laser powder bed fusion (L-PBF) process. Three different prototypes with three different curvature (R of 50 mm, 40 mm and 30 mm), operating in Ku/K band, have been manufactured and tested showing a very good agreement with the desired performances. Using 3D scan data, the internal deviations from the CAD model have been evaluated showing an average deviation of the internal areas of about 0.08 mm, 0.046 mm and 0.023 mm from the CAD model for the R of 50 mm, 40 mm and 30 mm respectively The surface roughness measured in the internal channel is about Ra (arithmetic average roughness) of 8 μm ± 1.3 μm and Rz (average maximum height of the roughness profile) of 62.3 μm ± 0.34 μm

In Situ Thermal Generation of Silver Nanoparticles in 3D Printed Polymeric Structures

Polymer nanocomposites have always attracted the interest of researchers and industry because of their potential combination of properties from both the nanofillers and the hosting matrix. Gathering nanomaterials and 3D printing could offer clear advantages and numerous new opportunities in several application fields. Embedding nanofillers in a polymeric matrix could improve the final material properties but usually the printing process gets more difficult. Considering this drawback, in this paper we propose a method to obtain polymer nanocomposites by in situ generation of nanoparticles after the printing process. 3D structures were fabricated through a Digital Light Processing (DLP) system by disolving metal salts in the starting liquid formulation. The 3D fabrication is followed by a thermal treatment in order to induce in situ generation of metal nanoparticles (NPs) in the polymer matrix. Comprehensive studies were systematically performed on the thermo-mechanical characteristics, morphology and electrical properties of the 3D printed nanocomposites

Experimental testing of 3D printed polymeric heat exchangers

Unlike conventional manufacturing technologies, additive manufacturing and 3D printing empower engineers with much more design freedom. Heat exchangers with complex internal channels or lattice structures can be designed for layerwise manufacturing by maximizing the surface to volume ratio. Low-weight polymeric heat exchangers are employed in aviation and aerospace applications. For increasing the thermal performance of polymers, additives can be used such as graphene. In this study, a Grafylon filament is used for the production of a simple heat exchanger by 3D printing. The heat exchanger is composed of two external shells and an interior duct with a two-stage 45-degree bend. For watertight purposes, the duct is manufactured by selective laser sintering of polyamide powder. Two replicas of the shells are fabricated by 3D printing of Grafylon and acrylonitrile butadiene styrene (ABS) respectively. The thermal performance of the two materials is experimentally tested and compared also to numerical simulations. The results of the study show that the Grafylon filament provides enhanced thermal performance to 3D printed heat exchangers of polymeric material

Experimental assessment of compensated distortion in selective laser melting of Ti6Al4V parts

Selective laser melting (SLM) is a well-established Additive Manufacturing technique for the fabrication of end-use metal components. Process reliability and maximum product quality are ensured by 20 years of technology development. Nevertheless, depending on the complexity of the part geometry and on the operator experience, different trials are often needed before getting a part first time right. To reduce the number of failed jobs, simulation software packages predict residual stresses and related distortions in SLM parts and propose a compensated geometry for the “right first time” production of the product. In this works, the simulation routines of Amphyon software by Additive Works are experimentally calibrated and validated for the fabrication of a reference geometry by means of an EOSINT M270 machine and Ti6Al4V powder. The calibration of Amphyon is performed using three cantilever specimens and the calibrated SLM simulation is then used to compute the compensated shape of the reference part. The validation of the compensated shape by comparison to the real part geometry shows that Amphyon routines have good prediction capability and dimensional accuracy

Failure mode analysis on compression of lattice structures with internal cooling channels produced by laser powder bed fusion

Conformal cooling coils have been developed during the last decades through the use of additive manufacturing (AM) technologies. The main goal of this study was to analyze how the presence of an internal channel that could act as a conformal cooling coil could affect compressive strength and quasi-elastic gradient of AlSi10Mg lattice structures produced by laser powder bed fusion (LPBF). Three different configurations of samples were tested in compression at 25 °C and 200 °C. The reference structures were body centered cubic (BBC) in the core of the samples with vertical struts along Z (BCCZ) lattices in the outer perimeter, labelled as NC samples. The main novelty consisted in inserting a straight elliptical channel and a 45° elliptical channel inside the BCCZ lattice structures, labelled as SC and 45C samples respectively. All the samples were then tested in as-built (AB) condition, and after two post process heat treatments, commonly used for AlSi10Mg LPBF industrial components, a stress relieving (SR) and a T6 treatment. NC lattice structures AB exhibited an overall fragile fracture and therefore the SC and 45C configuration samples were tested only after thermal treatments. The test at 25 °C showed that all types of samples were characterized by negligible variations in their quasi-elastic gradients and yield strength. On the contrary, the general trend of stress-strain curves was influenced by the presence of the channel and its position. The test at 200 °C showed that NC, SC and 45C samples after SR and T6 treatments exhibited a metal-foam like deformation

Additive Manufacturing Technology for High Performances Feed Horn

In this work the design and manufacturing through selective laser melting technology of single-band dual circular feed-system operating in Ka-band is reported. In the feed design an AM oriented architecture has been employed. The measured performances confirms the good manufacturing of the system that satisfies very stringent requirements in terms of polarization purity

Butyrate modulating effects on pro-inflammatory pathways in human intestinal epithelial cells

Butyrate acts as energy source for intestinal epithelial cells and as key mediator of several immune processes, modulating gene expression mainly through histone deacetylation inhibition. Thanks to these effects, butyrate has been proposed for the treatment of many intestinal diseases. Aim of this study was to investigate the effect of butyrate on the expression of a large series of target genes encoding proteins involved in pro-inflammatory pathways. We performed quantitative real-time-PCR analysis of the expression of 86 genes encoding proteins bearing to pro-inflammatory pathways, before and after butyrate exposure, in primary epithelial cells derived from human small intestine and colon. Butyrate significantly down-regulated the expression of genes involved in inflammatory response, among which nuclear factor kappa beta, interferon-gamma, Toll like 2 receptor and tumour necrosis factor-alpha. Further confirmations of these data, including studies at protein level, would support the use of butyrate as effective therapeutic strategy in intestinal inflammatory disorders

Experimental research activity on additive manufacturing of microwave passive waveguide components

All metal passive waveguide components are key building-blocks of several RF systems used for telecommunications, navigation, imaging, radio-astronomy, and cosmology. The accurate manufacture of these devices in Additive Manufacturing (AM) technologies can open the way to a high integration level of microwave functionalities with a significant cost and mass reduction. In the paper, after an introduction on the most common AM technologies with particular detail on selective laser melting (SLM) and stereo-lithography apparatus (SLA) processes, the results on the on-going research activity are discussed. Measured performances are reported for AM prototypes of Ku/K/Ka-band rectangular and circular waveguide lines, microwave filters and a smooth wall horn