Fused filament fabrication is a technology of additive manufacturing that uses molten thermoplastics for building parts. Due to the convenient shape of the raw material, a simple filament, the market offers a great variety of materials from simple to blends of compatible materials. However, finding a material with the desired properties can be difficult. Making it in-house or using a material manufacturer can be costly and time-consuming, especially when the optimum blend ratios are unknown or new design perspectives are tested. This paper presents an accessible method of producing core-shell filaments using material extrusion 3D printing. The printed filaments are characterised by a polycarbonate (PC) core and acryl butadiene styrene (ABS) shell with three material ratios. Their performance was investigated through printed samples. Additionally, the material mixing degree was studied by varying the extrusion temperature, nozzle feeding geometry, and layer thickness. The influence of all four factors was evaluated using a graphical representation of the main effects. The results showed that a core-shell filament can be processed using a 3D printer with a dual extrusion configuration and that the mechanical properties of the samples can be improved by varying the PC–ABS ratio. This research provides an accessible method for developing new hybrid filaments with a predesigned structure using a 3D printer.

The strength of a joint between the ends of one or more strips can be improved by making the contours of the joint into the shape of either the Greek letter omega or of a dovetail. From the point of view of industrial practice, it is of interest to study the behavior of these joints under stretching demands. The emergence and development of additive manufacturing processes for parts made of polymeric materials has led to the idea of conducting experimental tests to highlight the behavior of omega and dovetail-type joints during the tensile test. For the tensile testing of some test samples in which omega and dovetail joints were used, a Taguchi array of type L18 was employed, with eight independent variables, one variable with a two-level variation, and seven variables with variations on three levels. As independent variables, the type of joint, the couple of polymer materials used to make the two components of the joint, some characteristic dimensions of the joint contours, and some input factors in the 3D printing process were established. The values of average force and average displacement at the peak were considered output parameters. The experimental results were mathematically processed, determining empirical mathematical models of the second-degree polynomial type. These models highlight the influence exerted by the considered input factors on the values of the output parameters.

The development of 3D Printing technologies introduced new possibilities regarding multi-material part production. Fused Filament Fabrication (FFF) is one of those technologies suitable for multi-material 3D printing. Usually, multi-material parts are manufactured from different blends of the same material, also known as multi-colour 3D printing, or from materials with good chemical compatibility. Conventionally, a simple face-to-face bond interface between parts’ bodies and a chemical bond between thermoplastics define the mechanical performance of multi-material components. In this regard, the paper aimed to investigate the strength of the contact interface of multi-material specimens using a geometrical approach. Therefore, multiple interlocking interfaces were investigated, such as omega shape, T-shape, dovetail, and others for samples made of low-compatibility thermoplastic materials, acrylic styrene-acrylonitrile (ASA), thermoplastic polyurethane (TPU). The results showed that macroscopic inter-locking interfaces are significantly increasing the mechanical properties.

The development of 3D printing technologies has introduced new possibilities in producing multi-material parts, and Fused Filament Fabrication (FFF) is one of these technologies. Typically, multi-material parts are made of different blends of the same material, also known as multi-color 3D printing, or from materials with good chemical compatibility. Conventionally, a simple face-to-face bonding interface between part components and chemical bonding between thermoplastics define the mechanical performance of multi-material components. In this regard, the paper aimed to investigate the contact interface strength of multi-material specimens using a geometric approach. Therefore, several geometrical interfaces, such as dovetail, omega, T-shape, and others, were used to interlock pars of low-compatibility thermoplastic polymers, styrene-acrylonitrile acrylic (ASA), and thermoplastic polyurethane (TPU). In the case of one of these interfaces, modeling by the finite element method was resorted to obtain additional information regarding the processes that develop at the interface level between the two components of the joint during the tensile loading. The results showed that the macroscopic interlocking interfaces significantly improved the mechanical properties of the multi-material specimens.

Multi-material 3D printing offers new possibilities regarding product development, allowing design freedom and multiple materials choices in terms of colour and polymer type. Material extrusion technologies are among the most popular options for multi-material printing due to their low equipment cost and various thermoplastic materials. However, polymers’ compatibility and bond interface must be considered for multi-material components. Material Extrusion creates the parts layer by layer, and each layer is characterised by multiple lines of extruded thermoplastic at a defined width. Therefore, regardless of the 3D model’s surfaces, they are composed of numerous lines of material and voids. Depending on the 3D Printing process setup, the bonding mechanism between materials can be influenced due to the different characteristics of horizontal and vertical contact interfaces. For this reason, this paper aims to study the influence of process parameters over horizontal interface through lap-shear tests for multimaterials samples made of acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), and polycarbonate (PC). The results show that bond interface strength can be improved by creating ways for the mechanical interlock of the materials.