The fabrication of polymer–metal hybrids in an additive process makes it possible to further improve the geometrical and material adaption in a multi-material design. In this work, PLA is fabricated through a fused filament fabrication process on AlSi10Mg structures manufactured by laser powder bed fusion. The mechanical connection is realised by form fit, for which different geometries are examined through tensile tests. Deep penetration of the PLA into the metallic structures is achieved by optimisation of the process parameters. The penetration depth is assessed through the use of micro-computed tomography. Finally, the interplay of mechanisms leading to a firm connection is discussed.

Additive manufacturing by material extrusion offers innovative potential for component design and is driving advances in many industries. However, fully harnessing these advancements necessitates a thorough comprehension of the process-specific anisotropic structural properties. The complex interactions between process parameters and their direct influence on structural properties often lead to discrepancies between the mechanical properties of tested specimens at the coupon level and the inherent properties of additively manufactured components. In addition, there is no standardized method for preparing specimens that represent the mechanical properties within a given component. This further complicates the comparison of measured properties of different series of measurements and the investigation of manufacturing effects that may occur during the production of a component. Given these challenges, the present work addresses the fundamental question of what aspects need to be considered to ensure that the test specimens reflect the process conditions being tested. The studies look at the requirements for producing representative specimens and for the test methodology to characterize the mechanical properties of additively manufactured structures. The tests are carried out on specimens that were produced directly using the material extrusion process and on specimens that were cut from additively manufactured plates. Water jet cutting, milling, and laser cutting are investigated and compared as cutting methods. The influence of the specimen geometry and the size of the additively manufactured plate is considered. The orientation-dependent mechanical properties, the significance of the individual tests, the measurement scatter, and scanning electron micrographs of the cut edges and fracture surfaces are analyzed. Finally, guidelines for performing representative tests to characterize the mechanical properties of additively manufactured components are proposed.

Technological advances have led to the increased use of plastic-based additive manufacturing processes for the production of consumer goods and spare parts. For this reason, the need for the best possible mechanical properties while maintaining geometric accuracy is becoming increasingly important. One of these additive manufacturing processes is the Arburg Plastic Freeforming process, which differs from the widely used Fused Filament Fabrication process in the way that droplets are discharged along a track instead of continuous extruded tracks. As with all other plastic-based additive manufacturing processes, due to the round shape of the tracks, voids occur between the individual tracks during manufacturing, which effects mechanical properties. In contrast to previous work, which mainly focused on how the mechanical properties change with a change in a single printing parameter, this work focused more closely on the interaction of three relevant printing parameters considered as a parameter set. Their influence on the mechanical properties was investigated by tensile tests, the influence on the residual porosity by density measurements and the influence on the geometric accuracy by surface roughness measurements. It was shown that by considering the parameters as a parameter set, states of high density and therefore high mechanical properties while reaching minimal surface roughness can be achieved for significantly more combinations than previously assumed. However, for these states the residual porosity was slightly different. This difference was explained by a parameter-dependent deformation factor of the droplets, which influences the maximal possible degree of filling during manufacturing. For the optimization of arbitrary parameter sets, an analytical model was derived.

The mechanical properties of plastic-based additively manufactured specimens have been widely discussed. However, there is still no standard that can be used to determine properties such as the interfacial strength of adjacent tracks and also to exclude the influence of varying manufacturing conditions. In this paper, a proposal is made to determine the interfacial strength using specimens with only one track within a layer. For this purpose, so-called single-wall specimens of polylactide were characterised under tensile load and the interfacial area between the adjacent layers was determined using three methods. It turned out that the determination of the interfacial area via the fracture surface is the most accurate method for determining the interfacial strength. The measured interfacial strengths were compared with the bulk material strength and it was found that the bulk material strength can be achieved under optimal conditions in the FFF process. It was also observed that with increasing nozzle temperature, the simultaneous printing of specimens influences the interfacial strength. To conclude, this method allows to measure the interfacial strength without superimposing the influence of voids. However, for example, the interfacial strength within a layer cannot be determined.

This study presents a comprehensive simulation of the fused deposition modeling (FFF) process of polylactic acid (PLA) using the multiphase-field method. Compared to existing works, this work aims to simulate the overall FFF process. It combines temperature evolution, viscous flow, polymer crystallization, and residual strain calculations within the microstructure with mechanical property analysis in a single study. Simulation studies were done in the case of the single layer to study the flowing effect of the filament and the distribution of temperature, viscosity, and relative crystallinity throughout the cooling process. Afterward, a system of layers with three rows and three columns was investigated. The nozzle temperature, bed temperature, viscosity, and layer height were varied, and for each case the porosity was calculated. After running mechanical loading simulations on each case, the effective Young’s modulus was calculated. The simulations show that increasing the nozzle and bed temperatures leads to a decrease in the porosity, while increasing the layer height increases the distortion in the pores’ shapes without significantly affecting the porosity. The decrease in porosity leads to an increase in the effective Young’s modulus of the structure in a linear trend within the investigated porosities. The Young’s modulus–porosity relation was validated with experimental values from the literature within an average error of 3.6 %.

Plastic-based additive manufacturing processes are becoming increasingly popular in the production of structural parts. Based on the idea of lightweight design and the aim of extending the functionality of additive structures, the production of additively manufactured foam structures has emerged as a new field of application. The optical characterisation of these structures is of particular importance for process adjustments and the identification of (unwanted) changes in the foam structure. The degree of foaming and the fineness of a foam structure are of interest at this point. In this context, only the part of a structure dominated by foam pores is considered a foam structure. So far, there are no sophisticated methods for such an optical characterisation. Therefore, in this work, microscope images of manufactured as well as artificially created additively manufactured foam structures were evaluated. On these images, the features porosity, pore size, pore amount and a measure for the textural change were determined in order to obtain information about changes within an additively manufactured foam structure. It is shown that additive structures show changing pore shapes depending on the orientation of the cutting plane, although there are no changes in the foaming behaviour. Therefore, caution is required when identifying changes within the foam structure. It was also found that, owing to the additive process, the total porosity is already set in the slicing process and remains constant even if the degree of foaming of individual tracks is changed. Therefore, the degree of foaming cannot be determined on the basis of the total porosity, but it can be assessed on the basis of the formation of large networks of process-related pores.