© A. Otto

a coupled fluid and solid mechanics simulation of a single track conduction mode weld track

Figure: Preliminary results of a coupled fluid and solid mechanics simulation of a single track conduction mode weld track (domain cut along weld bead centerline); showing liquid melt pool colored by temperature and hydrostatic solid body stress (top), axial and vertical solid body displacement (bottom).

Supervisor: A. Otto

Co supervisor: I. Miladinovic

PhD student: C.Zenz

Objectives: Additive manufacturing processes provide the possibility to produce physical parts directly from CAD. Many different processes like e.g. laser powder bed fusion (L-PBF) or laser direct energy deposition (L-DED) have been developed and industrialized in the past years. However, it is still very difficult to find the correct processing parameters for every single part to be produced. The thermal and thermo-mechanical as well as the metallurgical behaviour of a part during the building process are not only strongly influenced by the processing strategy but also by its geometry and material. This often leads to distortion or cracks, to overheated areas and to many other processing failures to be avoided. Thus, producing first-time-right parts, obviously strongly desired by industry, is still an exception and demands for skilled experts.

Process simulations provide the possibility to study the effects that lead to processing failures and are in principle an appropriate tool for supporting the process design. However, those simulations are very demanding as they exhibit both multiscale and metaphysical characteristics:

• Multiscale, both from the temporal and spatial point of view: typical building times for a part with dimensions of a few cubic centimetres are a few hours, typical fluctuation times on the process scale that may also lead to failures are a few microseconds and they take place on the µm-range.
• Multiphysical, as a correct process description involves optics, heat conduction including phase transitions, fluid dynamics, powder physics, solid mechanics, material science and so on.

Currently there are no simulation tools available covering all these multiscale and multiphysical aspects. Thus, a major objective of future research work in this field of additive manufacturing must be the development of tools and strategies that enable the simulation of laser-assisted additive manufacturing processes. This will be the prerequisite for the desired first-time-right production.

Based on previous work at TUW concerning the mechanistic simulation of the L-PBF process the PhD project aims at the implementation of several new features into the existing simulation tool. These include:

• Coupling of the existing model (based on discrete element method and fluid dynamics) and thermo-mechanics.
• Implementation of a grain growth models and other metallurgical aspects.
• Development of a simplified model for L-PBF in order to reduce the simulation time.
• Derivation of strategies to couple the mechanistic and the simplified model.

TU Wien will lead this PhD project by providing supervision and access to the in-house software for simulating laser material processing that has been developed within the last decade. The project will be embedded in the research group “Laser Process Simulation” providing strong expertise in programming and physics with respect to laser material processing.