Modeling and simulation
Head of the Working Group
Dr. rer. nat. Markus Apel
Access e. V.
Within the SFB, the working group Modeling and Simulation deals with simulation models and numerical methods used for quantitative modeling of the various melt-based processes. The simulation approaches cover different length and time scales, from a sub-micrometer scale for the microstructure description, over the micrometer scale, e.g. for the description of individual particles in plasma spraying or for the calculation of the melt film dynamics in laser beam cutting, up to the macroscopic component scale, which, e.g. in plastic injection molding, includes both the component and the cavity. On the time scale, on the one hand, highly dynamic processes (milliseconds), as in the formation of the vapor capillary in laser beam welding, and on the other hand, rather slow processes (~10 s), such as the solidification of a solid aluminum part in permanent mold casting, are captured by different models. Examples of different problems and scales are shown in .
While in the individual subprojects the models are developed and applied rather specifically with regard to the respective problem, in the working groups a cross-material and cross-process consideration takes place. On the one hand, this opens up synergies, e.g. through the transfer of already developed model approaches to new problems, but also cross-material findings. One example of this is the iterative multi-scale simulation, which was initially developed for the permanent mold casting of an Al component and whose transferability to plastic injection molding was discussed in AK M3. Another important aspect of the AKG is therefore the linking and data exchange between different model approaches. While in the course of the SFB so far the focus has been on the development of novel, demand-oriented process models, in the third phase it is on the use of these methods to increase precision in the various processes, e.g. by numerically supporting compensation measures. The aspect "short computation time" plays an important role, i.e. the models used so far are continuously investigated and further developed also with regard to computation time aspects. An example for this are approaches of model reduction or the newly included SPH method from SP A13 (N). The new focus led to a new division and reorientation of the contents, which is reflected in a partial renaming of existing working groups. In the third phase, the AKG Modeling and Simulation is divided into four working groups, which are described below.
M1: Control of energy transfer at interfaces
This working group deals with the modeling of heat transfer between melt and environment, especially at free melt surfaces. The heat flow across interfaces controls both the melting process and the solidification. In the first two phases, the focus was on modeling "passive" heat transfer. This includes a model for heat transfer with gap formation in which both heat conduction and convection in the gas-filled gap as well as thermal radiation are taken into account. The gap formation itself was modeled in a thermomechanical contact model. In the third phase, the working group will focus on "active" heat transfer. This includes the modeling of energy coupling via heating layers. With the help of the simulation, a better understanding of the local temperature conditions in the area of the interfaces and in particular of their dynamics is to be developed. The work supports the design of compensation measures for different processes and materials and is an important contribution to the implementation of control concepts such as in SP B03. An important aspect in this work group is the comparison of the thermal behavior of partially crystalline plastics and metals during energy coupling or active insulation via heating layers.
M2: Melt pool dynamics and multiphase modeling of the melt.
The working group Melt Pool Dynamics and Multiphase Modeling of the Melt brings together subprojects that focus on the simulation of the flow in the melt. The melting behavior is addressed, e.g. the formation of the melt pool during welding and in the LPBF process, as well as the drive of the melt, e.g. by the gas jet during laser cutting. In addition, aspects of surface tension and evaporation at the melt surface are discussed. Similarly, solidification of the melt is modeled on a scale typical of the process (micro to millimeter). The development of reduced models is also being pursued in this AK together with AK M4. By reducing the numerical effort, model reduction enables the creation of process maps for the analysis of technical processes and opens up perspectives for the application of simulation in active control loops.
M3: Solidification/phase transformation: material models for distortion and residual stresses
This working group deals with models and simulation methods that can be used to describe the solidification process and phase transformations along cooling. Both metals and plastics are covered in this working group. The models discussed in the working group describe the processes on both the microstructure and continuum scales. One focus of work for the third phase will be material models for mechanical behavior to correctly describe distortion and residual stresses in metals and plastics, so that simulation can support the design of compensation measures. A second focus will be the topic of "hot cracking criteria". The common goal is the further development of process and material sensitive hot cracking criteria and their application to the casting and welding processes represented in the working group.
M4: Efficient numerical methods
The working group Efficient Numerical Methods focuses on numerical methods. Topics in this working group include (1) methods for model reduction, (2) modern discretization methods such as the discontinuous Galerkin method or spacetime discretization, and (3) approaches and methods for solving inverse problems. In the second phase, common benchmarks were defined, e.g. Stokes flow around an orbiting sphere, which were calculated using different approaches. A new addition is the SPH method, which was evaluated in the framework of a companion project and is now to become an essential part of the newly applied for SP A13 (N). To evaluate the SPH approach, several examples (e.g. heat conduction, solidification rate of a planar front, detaching melt drop) were defined as benchmarks. The results of the SPH method show in many cases a good agreement with the results of other approaches, e.g. classical FEM, with significantly reduced computation time. Another example from the second phase is the comparison between the enthalpy-porosity model and the viscosity approach in the calculation of the weld pool geometry in the welding process. Here, it was shown that the enthalpy-porosity approach provides better agreement between simulation and experiment. Meanwhile, the enthalpy-porosity method is used in several subprojects.