Research Summary Report of A04

[20.01.2023]

David, Martin; Doctoral Researcher, m.david@tu-braunschweig.de,

TU Braunschweig, Institute for Machine Tools and Production Technology (IWF)

Summary

Project A04 aims to investigate cooperative Additive Manufacturing (AM) processes based on Shotcrete 3D Printing (SC3DP) for the production of material-efficient, force-optimised, reinforced, load-bearing concrete components with precise surface quality and geometrical precision. The goal is to produce large-scale concrete elements using significantly lower amounts of reinforcement and concrete as compared to standard concrete construction principles. Hereby, different robot guided end effectors are subject for research in a flexible and automated process chain.

Current state of research

Currently, there are two focal points in the research of Workgroup Dröder.

• Improvement of SC3DP process, reinforcement integration and surface treatment on its own by identifying and expanding the respective process window and end effectors
• Research on planning strategies for combined process chains containing SC3DP, reinforcement integration and surface treatment:

For SC3DP a variation in process parameters and their influence on the resulting strand geometry was investigated. Especially a change in the nozzle outlet diameter led to a significant change in strand geometry and material properties. The SRI-process was improved regarding process time and repeatability. For surface treatment different end effector concepts were developed and tested. Rotating trowels and discs showed promising results regarding surface smoothness and geometrical accuracy. A transfer of these concepts towards freeform surfaces is planned.

The combination of SC3DP with reinforcement integration strategies for rebars and surface finishing is investigated towards the automation capability. For an evaluation an automated process chain was established. Figure 1 shows the results of the small-scale demonstrator study. Hereby, the processes of “Short Rebar Insertion” (SRI) and “Interlayer Rebar placement “(IRP) were combined, while the surface was processed by a rotating disc to improve the surface quality. The post-processing of the surface was conducted in two steps. In a first roughing step, the components shell is reduced to a near-net shape geometry by cutting away large accumulations of concrete. In a second step the surface is finished with a slightly elliptical disc to distribute surplus material into gaps and holes.

Although the process chain showed promising results, a detailed analysis of the process chain regarding the final dimensions of the component and the surface roughness is still pending. The challenges and effects of surface treatment on material properties like durability and porosity of the produced structure will be investigated in the future.