Research Summary Report of A04

Main Goal:

Project A04 aims to investigate innovative Additive Manufacturing (AM) processes based on Shotcrete 3D Printing (SC3DP) for the production of material-efficient, force-optimised, reinforced, loadbearing concrete components with a precise surface quality and geometrical precision. The goal is to enable the production of large-scale concrete elements with a reduced necessity for reinforcements and concrete compared to conventional concrete construction principles. For this purpose, different robot guided end effectors are subject to research in a flexible and automated process chain.

Within this scope, the development of end effectors for the processing of free-from concrete surfaces is currently a key point of research.

The primary research topics for the Institute of Machine Tools and Production Technology (IWF) in the project A04 are the processes and robot-guided end effectors. The SC3DP process facilitates the fabrication of reinforced concrete components. To achieve a consistent quality, it is imperative to monitor and regulate the process and especially the volume flows of the media. Consequently, research is being conducted on the development of sensor concepts for measuring the flow of concrete, air and accelerator through experimental evaluation. The measurement of concrete is a challenging process, primarily due to its high viscosity.
On a larger scale, the manufacturing of reinforced elements with precise surface quality encompasses the integration of reinforcements as well as the surface finishing. The utilisation of a screwing motion is investigated for the-process integration of steel reinforcements [1]. Especially the utilisation of vibrations as a replacement for a screwing motion results in an enhanced bond between rebar and concrete, as evidenced by [2].
For achieving a smooth final surface of SC3DP elements, a rotating trowel was investigated. It was shown, that the time between printing and surface processing significantly influences the achieved surface quality [3]. However, without further adaptations, this tool is not able to smooth concave surfaces, which might result from the design freedom of AM processes (see Fig. 1).

Furthermore, the IWF investigates process adaptations for scaling aforementioned process from laboratory environments to on-site applications. For instance, environmental factors such as uneven terrain or solar exposure can impact robotic systems, SC3DP and the other previously presented processes. Without proper adaptations, the unlevel ground has the potential to induce a shift in the local coordinate system relative to the coordinate system of the printed part. This, in turn, can result in inaccurate component geometries. Sunlight can also present a significant challenge for camera-based systems.

As demonstrated in Fig. 1, automated tools, such as plates or discs, are unable to access the entire surface in the instance of concave curvatures. In [4], David et al. propose a deformable trowel concept. This tool is capable of forming a defined surface by approximating a spline. A prototypical trowel was manufactured from polyurethane, a polymer characterized by a high breaking elongation. The trowel is supported by four joints: two fixed joints on the exterior and two linearly actuated joints. This configuration enables it to conform to different curved surfaces. Furthermore, as demonstrated in Fig. 2, the implementation of an elongation compensation technique yields an enhancement of the adaptability of the trowel.

The usage of this tool with a robot enables a usage either in parallel to the build-up of components or after printing for double curved surfaces.

 

[1] Dörrie, R., David, M., Freund, N., Lowke, D., Dröder, K., & Kloft, H. (2023). In-Process Integration of Reinforcement for Construction Elements During Shotcrete 3D Printing. Open Conference Proceedings,3.
https://doi.org/10.52825/ocp.v3i.224

[2] Freund, N., David, M., Dröder, K., Lowke, D. (2024). Vibrated Short Rebar Insertion – The Effect of Integration Time on the Resulting Bond Quality. In: Lowke, D., Freund, N., Böhler, D., Herding, F. (eds) Fourth RILEM International Conference on Concrete and Digital Fabrication. DC 2024. RILEM Bookseries, vol 53. Springer, Cham.
https://doi.org/10.1007/978-3-031-70031-6_38

[3] Dörrie, R., David, M., Freund, N., Lowke, D., Dröder, K., Kloft, H. (2024). Surface Processing of Shotcrete 3D Printed Concrete Elements Using a Rotating Trowel Disc – Influence of Timing on Resulting Surface Quality. In: Lowke, D., Freund, N., Böhler, D., Herding, F. (eds) Fourth RILEM International Conference on Concrete and Digital Fabrication. DC 2024. RILEM Bookseries, vol 53. Springer, Cham.
https://doi.org/10.1007/978-3-031-70031-6_46

[4] David, M., Dröder, K. (2024). Robot-Guided End Effector for an Automated Finishing of Concrete Free-Form Surfaces. In: Lowke, D., Freund, N., Böhler, D., Herding, F. (eds) Fourth RILEM International Conference on Concrete and Digital Fabrication. DC 2024. RILEM Bookseries, vol 53. Springer, Cham.
https://doi.org/10.1007/978-3-031-70031-6_7