Particle-Bed 3D Printing by Selective Cement Paste Intrusion (SPI) – Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement
Riegger, Felix; Doctoral researcher;
Wimmer, Andreas; Head of the research group;
All: Technical University of Munich, Institute for Machine Tools and Industrial Management
The main goal of project A02 is the implementation of reinforcement with Wire and Arc Additive Manufacturing (WAAM) in concrete elements produced by Selective Paste Intrusion (SPI) by means of a simultaneously additive manufacturing process.
The combination of SPI and WAAM is accompanied by obstacles that must be overcome to ensure the collaborated functionality. One major challenge occurs from the high energy input of WAAM (temperatures up to 1600 °C), which negatively affects the paste rheology and the resulting concrete strength. Therefore, the overall goal is to minimize heat propagation into the particle bed.
Within A02, the working group Zaeh is researching the WAAM process for the production of reinforcements. The aim is to achieve 3D printable WAAM reinforcements with properties comparable to conventional rebars, validated through experiments and simulation. Therefore, suitable process parameters for producing reinforcement structures by WAAM are identified, and process investigations are conducted with an experimental setup.
Within the last reporting period, the manufacturing strategies for branching and joining nodes were transferred from 2D to 3D. For that, convergent as well as divergent nodes with overhanging angles from 30° to 75° were investigated, as shown in Figure 1.
With the knowledge gained for the manufacturing strategies of the nodes, lattice structures can be planned in a modular way based on so-called unit cells. These lattice structures can then be used as reinforcements.
Therefore, we firstly intensified our research on the role and the impact of automated and robotic systems for in-situ production. We analysed automated and robotics systems (ARS) used for extrusion-based concrete additive manufacturing and classified them. Those automated and robotic systems will have a significant impact on further decisions in the preparation phase, e. g. in how many “printing segments” the building has to be divided due to a limited range of coverage (corresponding publication is accepted and will be published in 12/2022).
Secondly, we continued our research about the prefabrication strategy. Together with A04 and B04, we monitored the production of three walls with different geometric complexity to investigate the productivity of Shotcrete 3D Printing (SC3DP) and to compare it to conventional formwork-based fabrication. Both, the investigation of robotics systems and a plausible comparison of conventional and additive construction will help to bring additive manufacturing out of its niche.
Current state of research
In the combined SPI+WAAM process, the main part of the reinforcements produced with WAAM will be encased in concrete. Therefore, a directed and precise cooling of the reinforcing bars is necessary. A robot-guided cooling system (see Figure 2) was developed for this purpose. The cooling setup enables experiments with cooling strategies such as spray water cooling and is capable to adjust the angle and the distance between the cooling nozzle and the additively manufactured part. With this setup, the influence of these parameters can be investigated and the optimal setup can be determined.
For the evaluation of the different cooling strategies and setups, specimens are produced by the WAAM process. During the experiments, a pyrometer is used to measure the temperature development on the top of the bars. The specimens are examined by mechanical tests regarding their tensile strength and their hardness. Correlations between the cooling rate and the mechanical properties are investigated.