Sebastian-Paul Kopp

It is well known that scan strategies have an essential role in powder bed fusion (PBF). For the comparison of different scan strategies, however, it is usually necessary to evaluate manufactured samples or run simulations. Given the typically lengthy nature of these processes, this study focuses on finding a rapid preprocess evaluation method for scan strategies using geometrical approaches: line buffer‐based calculations and a point density field. Both approaches only depend on the geometry of the scan strategy. While these calculations should apply to most PBF processes, this study uses the evaluation methods to predict the differences that four unique scanning strategies have in PBF of polymers using an near‐infrared laser source. Polyamid 12 powder with Lanthanum hexaboride nanoparticles and a commercial black‐dyed Polyamid 12 powder are used for processing. The calculation of the line buffer‐based surface energies of these scanning strategies correctly predicted the sequence in which the scanning curve appeared to have received the laser energy. Moreover, the defects observed in the manufactured samples appear to be related to the variation in point density of the scanning strategies. These promising results are the first step towards new preprocess evaluation methods, leading to improved predictability of different scan strategies.

The feedstock in laser beam powder bed fusion of plastics (PBF‐LB/P) is typically limited to a few materials with strict flowability requirements and low recycling rates, compromising its economic efficiency and sustainability. Polymer nanoadditivation gains attraction to tailor their physiochemical properties by incorporating nanoadditives. Herein, a new approach is introduced to functionalize polymer part surfaces via electrophotographic powder application (EPA). Polyamide 12 (PA 12) microparticles decorated with laser‐synthesized silver nanoparticles (Ag NPs) are printed as thin layers on bulk PA 12 parts. The coating provides bactericidal functionality to the printed part with reduced nanoadditive employment. Indeed, only two Ag‐PA 12 layers accounting for a 140 µm thick coating inhibit S. aureus and E. coli bacteria growth. As a result of the low coating thickness and Ag NP loading of only 0.1 wt.%, the mechanical and calorimetric properties remain unaffected. Owing to its versatility, the proposed approach is envisioned to facilitate selective surface functionalization toward graded materials printing at reduced costs and waste generation.

Laser-based directed energy deposition of polymers (DED-LB/P) is a highly flexible additive manufacturing process capable of fabricating three-dimensional structures with a high degree of customization on free-form surfaces. In this article, the manufacturability of polyamide 12 bulk structures using DED-LB/P in combination with a thulium laser operating at a wavelength of 1.94 μm is investigated for the first time. The typical absorption bands at this wavelength eliminate the need for additives such as carbon-based nanoparticles, which would limit the range of applications. The generated structures were analyzed regarding porosity, thermal behavior, and mechanical properties to evaluate the potential of DED-LB/P with a thulium laser. As a consequence of the evaporation of absorbed moisture or ethanol residues resulting from powder preparation, a thermal pretreatment of the polymer powder reduced the porosity of the DED-LB/P structures to 0.9%. Depending on the processing parameters, the crystallinity of the produced structures ranged from 25.6% to 29.9%. For the tensile tests, the required geometries were milled from the DED-LB/P bulk structures. The results show that an ultimate tensile strength of up to 52 MPa, an elongation at break of up to 58%, and Young's modulus of up to 1590 MPa can be achieved. These remarkable mechanical properties are primarily attributed to the complete melting of the powder particles in DED-LB/P and the improved surface quality resulting from the milling process.

The trajectory of metal additive manufacturing is transitioning from rapid prototyping toward on-demand and serial production. Consequently, the paramount objective remains the enhancement of additive manufacturing processes like laser-based powder bed fusion of metals (PBF-LB/M) to meet modern manufacturing needs and reduce environmental impact. Shielding gas flow significantly influences the mechanical properties in PBF-LB/M by protecting the metal from oxidation and removing process by-products from the powder melting zone. Accordingly, an improper shielding gas flow distribution can result in poor part quality, excessive inert gas consumption, and contamination of the building chamber. Presently, a lack of consensus remains regarding which configuration of shielding gas supply is the most appropriate in terms of process efficiency. This is the comprehensive investigation of a localized and vertically directed shielding gas flow and its effects on the properties of parts, also taking into account the reduction of inert gas consumption. In contrast to previous investigations, it is shown that enhanced surface roughness and relative density of the parts, as well as minimized contamination of the optics inside the building chamber is achieved through more efficient removal of metal plume particles from the processing zone by localized gas flow. Moreover, the developed computational fluid dynamics simulation model enabled the efficient determination of particularly promising gas flow configurations. Furthermore, the validation of the simulation model is demonstrated in an experimental environment. Finally, by localizing shielding gas flow, energy consumption can be reduced by almost half.

Multi-material additive manufacturing (AM) attempts to utilize the full benefits of complex part production with a comprehensive and complementary material spectrum. In this context, this research article presents new processing strategies in the field of polymer- and metal-based multi-material AM. The investigation highlights the current progress in powder-based multi-material AM based on three successfully utilized technological approaches: additive and formative manufacturing of hybrid metal parts with locally adapted and tailored properties, material-efficient AM of multi-material polymer parts through electrophotography, and the implementation of UV-curable thermosets within the laser-based powder bed fusion of plastics. Owing to the complex requirements for the mechanical testing of multi-material parts with an emphasis on the transition area, this research targets an experimental shear testing set-up as a universal method for both metal- and polymer-based processes. The method was selected based on the common need of all technologies for the sufficient characterization of the bonding behavior between the individual materials.

Generating multimaterial parts, reaching higher efficiency in powder consumption, and decoupling of powder application behavior from powder properties such as powder flowability are key aspects for using electrophotographic powder application (EPA) in laser-based powder bed fusion of polymers (PBF-LB/P). Moreover, EPA allows the layer thickness to be reduced from around 100–150 μm, depending on respective particle size distribution, in the case of conventional doctor blade or roller-based powder application methods to the diameter of the applied polymer particles (typically between 50 and 130 μm). This can have positive effects on the interlayer connection and, therefore, the mechanical properties of the additively manufactured part because less powder volume has to be fused with the already generated underlying part. Moreover, due to the above-mentioned independence of EPA from powder flowability, the addition of flow aids, such as nano silica, can be reduced to a minimum or even avoided completely. This is the first comprehensive study on resulting properties of parts generated by PBF-LB/P using EPA taking into account both the reduction in layer thickness and reduced addition of flow aids. In addition to improving mechanical properties of generated parts, the independence of powder flowability, in particular, offers the possibility of qualifying currently unsuitable materials for PBF-LB/P. For this purpose, besides widely employed polyamide 12 (PA12), a polypropylene (PP) powder is used that is very difficult to process in conventional PBF-LB/P and can only be applied there with the help of flow aids.

Charge control substances (CCS) as additives for polymer powders are investigated to make polymer powders suitable for the electrophotographic powder deposition in powder-based additive manufacturing. The use of CCS unifies the occurring charge of a powder, which is crucial for this novel deposition method. Therefore, commercially available polymer powder is functionalized via dry coating in a shaker mixer with two different CCS and analyzed afterwards. The flowability and the degree of coverage of additives on the surface are used to evaluate the coating process. The thermal properties are analyzed by use of differential scanning calorimetry. Most important, the influence of the CCS on the powder charge is shown by measurements of the electrostatic surface potential at first and the powder deposition itself is performed and analyzed with selected formulations afterwards to show the potential of this method. Finally, tensile strength specimens are produced with the conventional deposition method in order to show the usability of the CCS for current machines.