Research Summary Report A04

Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality

Within this project, basic research on various Shotcrete 3D Printing (SC3DP) strategies, materials, tools and methods will be conducted with regard to enhanced material and process control, reinforcement integration, surface quality and automation. To that end, different reinforcement materials in combination with suitable reinforcement manufacturing and integration concepts will be investigated based on force-flow optimised reinforcement alignment. Besides, design strategies as well as material and process control will be investigated in detail. Furthermore, tools and strategies for precise control of the surface quality and geometric resolution of SC3DP elements are subject of research.

Summary

Research on the SC3DP has been ongoing to improve the process control, process stability and the limitations of the printing process. Furthermore, the automation of SC3DP currently progressed due to the installation of an additional automated concrete mixing plant (Fig 1.), the optimisation of the material flow control system and the accelerator system and end effector design. The implementation of these features aims at establishing a fully automated process, which can produce complex shaped, reinforced concrete construction elements. The automated concrete mixing plant consists of three big bag silos, which are connected to a conical mixer KKM 375/550 with a drive power of 2 x 11KW via pipe screw conveyors. The water, admixture and binder are added via digital weighing and metering devices. Due to the digital control and integration into the DBFL control system, special material mixtures can be prepared as required for additive manufacturing.

The optimisation of the material flow control and accelerator intake system result in streamlining the current end effector and applying several adjustments. Firstly, pipes and connections are adapted to the necessary flow rates during the process. Secondly digitally controllable valves are installed and integrated into the control system for a higher degree of automation. Finally, A04 (Kloft) will continue investigating the process control and especially the limitations of the printing process using the newly implemented features to maximise the accuracy of the printed geometry and minimize the post processing needed to reach the near net shape of the geometry. This technical approach runs hand in hand with the digital approach of path planning to reach and accurate geometry.

Current state of research

Currently research is focused on the automated integration of reinforcement as well as the reduction of material use through optimising the construction elements shape according to the force flow. The aim of these investigations is to reduce the material use by 30% as well as increasing the load bearing capacity of the construction element by 30%. This can be achieved by orienting the reinforcement along the force flow and the above-mentioned shape optimisation. Current studies from A04 show, that by orienting the reinforcement along the force flow, an increase of flexural strength by 60% in beam elements is possible.

A main focus of upcoming studies is the adaption of these results to other large scale construction elements and different load cases combined with the automated integration of force flow oriented reinforcement. Another experiment (Fig 2.) showed the potential of a fully automated combined printing process, where reinforced walls were produced using the DBFL with its two manufacturing units for structural build up and post processing of the reinforced structure.