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Whether for producing prototypes or functional parts by additive manufacturing, the fused deposition modeling is the most commonly used technique. Nevertheless, not only the hobbyist but also the industrial three-dimensional printers produce parts that suffer from anisotropy in their mechanical properties imposing important limitations on the strength of the manufactured piece. The aim of this work is to propose a strategy for determining the optimal build surface orientation of three-dimensional truss-like structures manufactured using fused deposition modeling. This can be achieved by minimizing the norm of the dot products of the normal direction of the deposition plane (build surface plane) and the directions of the tensile forces. Since three-dimensional trusses are subjected to tensile forces in different directions, a multi-objective cost function was proposed. Moreover, these structures might present rotational symmetry, which should be considered as design constraints. In this work, two three-dimensional truss-like structures were investigated. The nature of the optimization is case dependent and solvers were selected accordingly. Experimental campaigns were carried out for evaluating the specimens manufactured using fused deposition modeling. It could be concluded that higher yield tensile strength could be achieved by adopting the optimal deposition plane. This result demonstrates the applicability of optimization techniques for improving additive manufacturing results.

Additive manufacturing processes have been developed over the last decades, especially vat photopolymerization (VP) processes, due to its simplicity and speed. The objective of this paper is to characterize commercial VP resins widely used for technical applications. Thus, test specimens were printed by Digital Light Processing and subjected to tensile, compression, flexural, hardness, and inorganic composition analyses. The resin with the highest resistance and hardness (containing 0.6 vol% of inorganics load) reached 53 MPa in tension, 110 MPa in compression, 79 MPa in bending, and 82.3 Shore D, which is comparable to injected polymers. A case study was made, replacing the injected gears of a reducer by printed ones and comparing the finite element analysis with resin properties. The characterization and case study results encourage the expansion of VP processes in the manufacturing of products in several industries and service sectors, as well as the development of new composite resins.

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The design of modern mechanical components often requires the use of low-density and high-strength parts. Additive manufacturing presents competence in obtaining format complexity internally (voids, ducts, channels) and externally (shape, holes). However, parts obtained by material extrusion additive manufacturing are highly anisotropic and relatively weak. This paper aims to present a new mechanical design technique that combines the high geometry flexibility of additive manufacturing with internal structuring reinforcement by high-strength materials, which enables optimized parts with reinforcement in the most mechanical stressed areas during service, through adopting structured internal geometry filled with reinforcement material. Dense test specimens and test specimens with internal structural canals filled with reinforcement material (epoxy resin and carbon fibers) were designed, fabricated and tested physically and virtually. The obtained results provide property values for 3D-printed acrylonitrile butadiene styrene (typical material of additive manufacturing) and for this polymer reinforced with various reinforcement material configurations (useful for mechanical design). The reinforcement decreased anisotropy and improved mechanical properties. Optimized parts filled with resin and long carbon fibers had maximum flexural resistance of 112 MPa, with a specific weight of 1.1 g/cm3. This reinforcement provided parts with specific flexural strength similar to structural aluminum alloys, preserving the geometry and external dimension of the printed parts. The technique presented here shows the possibility of new conceptions in mechanical components design and strength optimization by internal reinforcement canals in parts. The technique is useful for mechanical design activity and allows for new product conceptions based on additive manufacturing.

Additive manufacturing (AM) has provided huge versatility in geometry and materials, allowing new products and processes in several areas to be created. Laser Engineered Net Shaping (LENS) is an additive manufacturing process created in 1995 that allows building high-density metals and ceramics parts with no need for further operation. This manuscript aims to study the scientific literature about the process of Laser Engineered Net Shaping related to ceramics. After a systematic review, the articles were grouped into three categories: ceramic coating and AM of ceramics and AM of composites with ceramic reinforcement. Raw materials, substrates, applications, process parameters, and the obtained properties were analyzed and summarized for each group. Most of the additive manufacturing of ceramic parts are related to alumina, which present similar properties when compared to the traditionally manufactured ones. Recent works have the aid of an ultrasonic vibration to homogenize the in-process material, reduce cracks and improve mechanical properties. The additive manufacturing of composites with ceramic reinforcement has been used to create functionally graded composites materials with increased hardness, while the ceramic coating has been employed to manufacture biocompatible coating with increased hardness and low wear rate. Moreover, an additive manufacturing timeline including Laser Engineered Net Shaping landmarks is presented.

The development of photosensitive ceramic slurries for vat photopolymerization (stereolithography or digital light processing) has received much effort in recent years. However, many of these ceramic suspensions have high viscosity and they are suitable for use only on equipment, specialized in ceramic additive manufacturing. In this work, ceramic manufacturing using photocurable slurries was tested in a low-cost vat photopolymerization printer and in silicone moulds for UV-casting replication, with the latter approach still scarcely explored in the literature. Both processes were able to produce ceramic parts. The UV-casting replication was able to work with more viscous photocurable ceramic slurries and proved more suitable for the manufacturing of ceramic parts with larger cross-sections, providing pieces with improved flexural strength to those produced by additive manufacturing. This work presents the possibility of UV-casting photosensitive slurries to manufacture ceramics, an approach that could be easily adopted without high equipment costs.

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