Sustainability, efficiency and digitalization are regarded as benchmarks for modern manufacturing processes and go hand in hand with a positive productivity trend in many areas of the manufacturing industry. However, the construction industry lacks new key technologies to implement these principles within one of Germany's largest economic sectors. In the absence of new concepts, tried and tested manufacturing processes are leading to stagnating productivity and a high demand for resources. In particular, the considerable amount of post-processing required to integrate supply technology and a high proportion of manual activities represent significant potential for optimization.

Based on current developments, additive manufacturing processes offer a suitable solution to counter the three challenges mentioned above in the long term. As part of the Collaborative Research Center TRR 277, which has been funded by the DFG since 2020, the foundations for enabling additive manufacturing processes for use in the construction industry are therefore being investigated. The research focus at the Institute of Assembly Technology (match) within TRR 277 is on the development of adaptive path planning and control concepts for the additive manufacturing of concrete components using industrial robots with an extended degree of freedom. The use of such robot systems offers new possibilities for expanding the workspace and avoiding collisions. At the same time, however, new research questions arise in the areas of control and regulation. In particular, a constant path speed and the generation of reproducible paths between two target points are a key aspect of developments at match.

In addition, methods for integrating the dynamic material behavior of fresh concrete into the path planning algorithms are being investigated. Initial approaches focus on a priori optimization by coupling a finite element model to the path planner. Based on an initial pressure path, the deformations are simulated during the production process, taking into account the time-dependent material behaviour, and then minimized. Two compensation mechanisms are available for additive manufacturing with concrete. The first mechanism makes use of the targeted adaptation of the strand geometry. For this purpose, the cross-section of the strand of the material applied close to the floor is adjusted in such a way that the final shape is only created by the load from the layers above. The second mechanism intervenes in the material behavior by adding a curing accelerator. Both compensation mechanisms require a targeted adjustment of the strand geometry in order to be able to manufacture close to the final contour, which inevitably requires a suitable model for the relationships between process parameters and process result. Previous investigations have shown that empirical model approaches are significantly more robust than analytical description methods.

The typical component dimensions in the construction industry and production on the construction site cause varying environmental conditions over the production period. As a result, the high sensitivity of material properties to temperature and humidity fluctuations poses a particular challenge for modeling and process control. Initial investigations show that in non-air-conditioned working environments, extensive calibration of the process model is required before each production order. The additional integration of a 2D laser profile sensor in the 3D print head, adapted to conditions similar to those on construction sites, makes it possible to record profile data of the applied material during the printing process. The resulting cross-section data can be used in combination with the recorded process parameters for online model adaptation and reduce the calibration effort.

Lukas Lachmayer, M.Sc. / dsc

Briefly explained: The match

The Institute of Assembly Technology (match) at Leibniz Universität Hannover was founded in 2013 with the appointment of Prof. Dr. Annika Raatz. Since then, match has stood for innovative basic research in the field of automated and robot-assisted assembly and handling. The scientific work of the institute can be summarized under the main research areas of robot-assisted handling processes, innovative robot systems for human-robot or robot-robot cooperation and precision assembly processes.

Briefly explained: The MHI e.V.

The Wissenschaftliche Gesellschaft für Montage, Handhabung und Industrierobotik e.V. (MHI e.V.) is a network of renowned university professors - institute directors and chair holders - from German-speaking countries. The members conduct both fundamental and application-oriented research on a wide range of current topics in the fields of assembly, handling and industrial robotics. Further information on the society, its members and activities: www.wgmhi.de