Selective laser sintering (SLS) with polymers is currently at the transition to the production of functional components and thus holds great potential to revolutionize conventional production processes. Nevertheless, the application capability is confronted by newly defined requirements regarding reliability and reproducibility. In order to fulfil the requirements and to increase the process stability, the ageing mechanisms in polymers are compensated by recycling strategies. This involves fraction-based mixing of a defined ratio of new powder with recycled powder. Basically, fraction-based mixing must be preceded by the selection of suitable mixing parameters. The work focused on the influence of the mixing process on the powder characteristics for cyclic reuse in SLS. With regard to the powder characteristics, the particle shape and particle size distribution as well as the bulk and tap density of the powder were investigated. The authors found an influence of the mixing process with increasing mixing time on the powder characteristics of a black polyamide 12 sintering material. A mixing time of 1 h and a mixing intensity of 15 rpm proved to be potentially effective for achieving a gentle and homogeneous mixing of the powders.

In Laser Powder Bed Fusion, process material defects such as a lack of fusion, powder inclusions and cavities occur repeatedly by chance. These stochastically distributed defects can significantly reduce the mechanical performance of the components during operation. Possible in situ repair solutions such as multiple remelting of specific layer areas are promising approaches to avoid these defects in the finished component, thus improving the overall properties. In this context, the present study investigates the remelting of artificially introduced defects using the example of M789 tool steel. In the first step, the process parameter settings and mechanical properties were evaluated using a tensile test, and the density of the local repair was examined using X-ray computer tomography and a metallographic analysis. The results demonstrate that the mechanical properties of the tensile test are comparable with those of the reference samples while successfully increasing the component quality. This indicates that defects that arise during the process can be remelted without the loss of mechanical characteristics.

Selective laser sintering (SLS) with polymers is currently in transition to the production of functional components. Nevertheless, the potential to revolutionize conventional production processes is confronted by newly imposed requirements regarding reliability and reproducibility. To ensure that the requirements are fulfilled, the aging mechanisms occurring in polymers are compensated by recycling strategies, such as fraction-based mixing of a defined ratio of new with recycled powder. Although various mixing ratios for the reuse of the material in SLS have been investigated, there is insufficient knowledge of suitable mixing parameters for homogeneous and gentle mixing of the powder fractions. This work therefore focused on the influence of potentially suitable mixing parameters identified in a previous study on the ongoing powder and component properties in SLS using polyamide 12 and a constant refreshing rate. Regarding the powder properties, the intrinsic properties and density of the powders were investigated. Regarding the component properties, mechanical properties, sinter density, and surface quality were investigated. Decreases in the powder density and the component properties were measured by increasing the number of process cycles. Taking into account the determined powder and component properties, the selected mixing parameters enabled a homogeneous and gentle mixing of the powder fractions.

Selective laser sintering (SLS) with polymers is currently at the transition stage for the production of functional components and holds great potential to revolutionize conventional production processes. Nevertheless, its application capability is confronted by newly imposed requirements regarding reliability and reproducibility. To safeguard these requirements, a deeper process understanding of material aging mechanisms in polymeric materials is needed. In order to enable the traceability of the materials as well as the identification of defective components with subsequent tracing of the cause, the use of a material marking process represents an alternative. SLS in combination with material marking is proving to be an efficient option for reproducible, high-quality manufacturing based on an increased understanding of the process. In this study, the idea of a marker-based traceability methodology for the purpose of process optimization is presented. Fundamental to the subsequent experimental investigation of the marking agent suitability, this work first focuses on the systematic selection of a suitable marking agent for use in SLS. Based on an analysis of the sinter material to be marked and a set of marking technologies, as well as using the selection methodology, the modified polymer marking technology was evaluated as the most suitable marking technology.

Selective laser sintering (SLS) is currently in transition to the production of functional components. However, the ability to apply it is confronted with new requirements for reliability and reproducibility. Therefore, an in-depth understanding of aging processes in polymers is essential. Regarding material traceability as well as defective component identification with subsequent cause tracing, the application of a material-inherent marking technology represents a solution. SLS in combination with modified polymers as a marking technology proves to be an efficient opportunity to produce reproducible and high-quality components due to an increased understanding of the process. Based on a selection of modified polymers for use in SLS, which were characterized in part I of the study, this work focuses on the experimental validation of the result. The influence of modified polymers on materials and component properties and the SLS process’s influence on the traceability of modified polymers are examined. Intrinsic and extrinsic material properties as well as mechanical properties, surface quality and sinter density are analyzed. No discernible influences of the modified polymers on the investigated properties could be observed and the traceability of the modified polymers could also be confirmed in the aged powder and component using mass spectroscopy.

Injection molding (IM) is already an established technology for manufacturing polymer products. However, in the course of the increased use of recyclates for economic and ecological reasons, its application capability has been confronted with new requirements for reliability and reproducibility. In addition, the IM process is confronted with regulations regarding a verifiable recycling degree in polymers. With regard to the material identification and storage of manufacturer-, process- or product-related data in polymers, the implementation of a material-inherent marking technology forms a potential answer. The IM process combined with modified polymers (MP) as a marking technology turns out to be a feasible approach to manufacturing reproducibly and offers a high quality based on increased process awareness and fulfilling the required traceability. Therefore, this work focuses on the trial evaluation of MP within the IM process. The influence of MP on the material process behavior and mechanical and thermal component properties, as well as the influence of the IM process and recycling on MP traceability, are investigated. No discernible influences of MP on the investigated properties could be identified, and the traceability from the initial material to a recyclate could be confirmed. MP is suitable for monitoring the aging state of polymers in IM.