Research Summary Report A06

Laser Powder-Bed Fusion (LPBF) of Steel Elements for Construction – Basics of Design and Mechanical Resilience

Wenzler, David; Doctoral researcher; david.wenzler@tum.de

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

Diller, Johannes; Doctoral researcher; johannes.diller@tum.de,

Siebert, Dorina; Doctoral researcher; dorina.siebert@tum.de

Technical University of Munich, Chair of Metal Structures

The project A06 aims to explore and evaluate the factors influencing the manufacturing of safe and durable structural steel elements by Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M). Thereby, the PBF-LB/M process, the post-treatment, and the geometrical aspects in terms of microstructure and mechanical properties will be investigated and correlations will be determined. In the first funding period, the project is focused on analyzing small-scale specimens and complex facade elements with multiaxial stress states. Based on the results, a first methodology for a qualified design of safe and durable structural steel elements by means of additive manufacturing (AM) will be derived.

Summary

The first large-scale demonstrator of the TRR 277 is now completed. The tensegrity structure will be a permanent exhibit at the Deutsches Museum in Munich (see Fig 1). The bridge-building exhibition hall will reopen at the end of July 2022. The initial design of the 18 nodes was done by A06. The shape optimization was conducted by C02. After the optimization process, A06 manufactured the nodes. Finally, the nodes were heat treated, followed by vibratory grinding to achieve a surface finish of R_a < 0.2 µm. To investigate the mechanical behavior of the nodes, tensile and fatigue tests were performed. The visitors can push and pull at one of the tension cables of the tower. This external force is measured by a load cell, which is installed in the tower.

A digital animation on a screen shows the resulting stresses in the tensegrity tower during pushing and pulling at the cables. Thus, the visitors gain an interactive learning experience on how a tensegrity structure behaves under external loading.

Current state of research

For safety-relevant applications, such as in the construction industry, the quality control of the PBF-LB/M manufactured components is very important. Defects, such as cavities, can result from instabilities during the manufacturing process. Process monitoring systems can detect these instabilities. In a recent work of A06, a methodology to determine melt pool anomalies by means of process monitoring and sensor data fusion was developed and tested. Using a thermography camera, the detection of these melt pool instabilities and the ejection of spatters were enabled (see Fig 2).

The process anomalies were correlated with the defects detected in single melt tracks. The data fusion enabled an increase of the sensitivity of the detection by up to 20%. Moreover, the methodology provides information on the suitability of specific process monitoring systems and signals for the defect detection. The methodology was validated by single melt tracks. The next step is the application of the methodology to 2D layers and 3D components. For further information on this, the reader is kindly referred to the open‑access article. [1]