Research Summary Report of A02

Riegger, Felix; Doctoral researcher;   Felix.Riegger@iwb.tum.de
Baehr, Siegfried; Head of the research group;  Siegfried.Baehr@iwb.tum.de

All: Technical University of Munich, Institute for Machine Tools and Industrial Management

Main Goal

To enable selective paste intrusion (SPI) for practical applications, the inclusion of reinforcement is mandatory. The focus of the first funding period was set on implementing reinforcements in SPI parts by using wire arc additive manufacturing (WAAM). During the first funding period, two main issues were identified: the need for increased ecological sustainability for the combined process of SPI+WAAM and accelerated process velocities to improve the economic efficiency. Therefore, the main goals of the project A02 for the second funding period are the ecological material optimisation of SPI and the reduction of the required number of (time-consuming) welding operations within the WAAM process.

Summary 

Within A02, the working group (WG) Zaeh is researching the use of semi-finished products to replace reinforcement sections with low geometrical complexity (e.g., straight rebar sections). The complex geometrical sections (e.g., the nodes) are manufactured with WAAM. Stud welding, which is characterised by coaxial welding, is used to join the semi-finished products to the WAAM sections. The use of semi-finished products and the resulting reduction of welding operations increases the building rate and sustainability and leads to less heat generation, reducing the risk of detrimental effects on the concrete. Suitable process parameters and strategies are identified, supported by a numerical thermal model and feature-based computer-aided manufacturing.

Current state of research

To showcase the feasibility of this novel approach, a ™proof of concept was conducted with a robotic test setup, as shown in Figure 1.

The new combined AM process consisting of WAAM and drawn arc stud welding (DASW) is referred to as stud and wire arc additive manufacturing (SWAAM). The SWAAM process is especially suitable for metallic lattice structures. Different machine configurations for this process were discussed. One of the concepts, the concept of two robots, each with one mounted tool, was investigated further. The chosen concept can be used for separated, sequential, and simultaneous hybrid production. To investigate the potential of the combined process, the novel process was benchmarked against the WAAM process, as shown in Figure 2. The temperature development was measured by thermocouples, and the production times were determined.

The structures manufactured with the combined process showed lower maximum temperatures in comparison with the first layer produced with WAAM. With the second and third WAAM layers, the maximum temperatures were increased even further. The comparison of the overall production times, depicted in Figure 3, showed a reduction of 57.7 % for the combined process relative to the WAAM process. In addition, we found that DASW reaches higher volumetric deposition rates than WAAM since the DASW process accounts for 66.7 % of the total specimen volume in only 1.4 % of the overall production time. If longer studs and smaller WAAM sections are used, the heat input into the manufactured structures can be reduced further, and lower overall production times can be achieved.

For further information and details on the results, the reader is referred to the associated open-access article [1].