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This paper reports the results of a comparison study between objects printed with a large-format 3D printing machine and a conventional fused filament fabrication (FFF) printer. A pellet extrusion head was developed and integrated into a cartesian 3D printing platform, obtaining a large-format 3D printing system based on the FFF technique. This integration allows to use polymerised pellets as raw material and printing with a larger stroke through bigger nozzles than conventional FFF nozzles. In addition, this integration enables printing pieces with considerably thicker layers compared with a traditional FFF process. One of the concerns addressed in this study was the mechanical performance of the objects obtained by the large-format 3D printer. Hence, a comparison of the surface's roughness, maximal tensile stress, tensile modulus, and deformation were made between pieces printed in a large-format 3D printer and a conventional FFF printer. The results reveal that large-format 3D printing has important benefits, such as reducing the time required to print objects, improving the mechanical performance of the printed pieces, and enabling the use of composite materials in additive manufacturing. However, some drawbacks are noticed, e.g. the low resolution and poor surface finish obtained. [ABSTRACT FROM AUTHOR]

The high volume of plastic waste and the extremely low recycling rate have created a serious challenge worldwide. Local distributed recycling and additive manufacturing (DRAM) offers a solution by economically incentivizing local recycling. One DRAM technology capable of processing large quantities of plastic waste is fused granular fabrication, where solid shredded plastic waste can be reused directly as 3D printing feedstock. This study presents an experimental assessment of multi‐material recycling printability using two of the most common thermoplastics in the beverage industry, polyethylene terephthalate (PET) and high‐density polyethylene (HDPE), and the feasibility of mixing PET and HDPE to be used as a feedstock material for large‐scale 3‐D printing. After the material collection, shredding, and cleaning, the characterization and optimization of parameters for 3D printing were performed. Results showed the feasibility of printing a large object from rPET/rHDPE flakes, reducing production costs by up to 88%. Highlights: Study: multi‐material recycling printability of PET‐HDPE.Large‐scale fused particle‐based 3‐D printing technically possible.Direct waste 3‐D printing rPET/rHDPE flakes, reducing production costs up to 88%. [ABSTRACT FROM AUTHOR]

Due to the development of printing materials, light-cured 3D printing is playing an increasingly important role in industrial and consumer markets for prototype manufacturing and conceptual design due to its advantages in high-precision and high-surface finish. Despite its widespread use, it is still difficult to achieve the 3D printing requirements of large volume, high resolution, and high speed. Currently, traditional light-cured 3D printing technologies based on stereolithography, such as regular DLP and SLA, can no longer meet the requirements of the processing size and processing rate. This paper introduces a dynamic projection of 3D printing technology utilizing a digital micro-mirror device (DMD). By projecting the ultraviolet light pattern in the form of "animation", the printing resin is continuously cured in the exposure process to form the required three-dimensional structure. To print large-size objects, the three-dimensional model is sliced into high-resolution sectional images, and each layer of the sectional image is further divided into sub-regional images. These images are dynamically exposed to the light-curing material and are synchronized with the scanning motion of the projection lens to form a static exposure pattern in the construction area. Combined with the digital super-resolution, this system can achieve the layering and fine printing of large-size objects up to 400 × 400 × 200 mm, with a minimum feature size of 45 μm. This technology can achieve large-size, high-precision structural printing in industrial fields such as automobiles and aviation, promoting structural design, performance verification, product pre-production, and final part processing. Its printing speed and material bending characteristics are superior to existing DLP light-curing 3D printing methods. [ABSTRACT FROM AUTHOR]

DcAFF (discontinuous aligned fibre filament) is a novel material for fused filament fabrication (FFF) 3D printing made of highly aligned discontinuous fibres produced using high performance discontinuous fibre (HiPerDiF) technology. It reinforces a thermoplastic matrix to provide high mechanical performance and formability. Accurate printing of DcAFF poses a challenge, especially for complex geometries, because: (i) there is a discrepancy between the path where the filament experiences the adhering pressure from the filleted nozzle and the nozzle path; and (ii) the rasters display poor adhesion to the build platform immediately after deposition, which causes the filament to be dragged when the printing direction changes. This paper explains the implication of these phenomena on steering capabilities and examines the techniques for improving DcAFF printing accuracy. In the first approach, the machine parameters were adjusted to improve the quality of the sharp turning angle without changing the desired path, but this showed insignificant effects in terms of precision improvements. In the second approach, a printing path modification with a compensation algorithm was introduced. The nature of the inaccuracy of the printing at the turning point was studied with a first-order lag relationship. Then the equation to describe the deposition raster inaccuracy was determined. A proportional–integral (PI) controller was added to the equation to calculate the nozzle movement in order to bring the raster back to the desired path. The applied compensation path is shown to give an accuracy improvement in curvilinear printing paths. This is particularly beneficial when printing larger circular diameter curvilinear printed parts. The developed printing approach can be applied with other fibre reinforced filaments to achieve complex geometries. [ABSTRACT FROM AUTHOR]

In this research, the effects of fumed silica (FS) on the Ultraviolet (UV)-ink rheological behavior and processing windows were discussed. Objects using different concentrations of FS inks were printed by the modified UV-Direct ink writing (DIW) printer. The function of fumed silica in the ink-based system has been verified, and the processing scope has been expended with a suitable amount of FS combined with the UV light. The results show that the combination of a suitable amount of FS with the UV-DIW system reaches fast and accurate printing with a larger processing window compared to the non-UV system. However, an excessively high concentration of FS will increase the yield stress of the ink, which also increases the requirement of extrusion unit and the die-swelling effects. [ABSTRACT FROM AUTHOR]

[Display omitted] • SLM-manufactured lattice structure geometries exhibit distortion and cluttering. • The lattice distortion is pronounced in upright printed slender geometries. • Unit cells with high nodal connectivity and obtuse angles increase both deficiencies. • The heuristic of reinforcement walls significantly reduces the lattice distortion. • Curvilinear, bio-inspired unit cells diminish both lattice distortion and cluttering. The rapid growth of the geriatric population in industrial societies is expected to increase the demand for prosthetic implants. Unfortunately, current products exhibit shortcomings such as inadequate sizing or excessive material strength both of which hamper the recovery of fractures. Selective laser melting (SLM), as a manufacturing method, is highly suited for optimizing the geometry and topology of products. However, SLM however, seems to restrict the manufacturing precision to mostly horizontal printing which is inefficient when considering the build envelope. Additionally, certain elongated geometries are subject to warpage when printed horizontally. To address these issues, our study investigated the feasibility of vertically oriented porous structures using SLM. It will report on two specific deficiencies, namely slanting and cluttering, that were revealed through X-ray computer tomography. To facilitate the manufacturing of slender, porous structures, the paper will offer and examine heuristics that minimize the defects. The preliminary results indicate that structures such as shell reinforcements and bio-inspired unit cells reduce the occurrence of slanting and cluttering and might serve as interim solutions for the printing of large filigree structures. The general findings suggest that more dedicated research is necessary to understand the relationship between geometrical features and manufacturing precision in SLM. [ABSTRACT FROM AUTHOR]