Focus on situation analysis
One of the most important steps in the design process is the situation analysis, in which the installation space, the forces to be transmitted, and other boundary conditions are defined. This serves as the basis for creating the CAD model by means of topology optimisation. With topology optimisation, a material-saving and strength-optimised design can be achieved. In this process, the structural-mechanical simulation is carried out in a finite element programme, e.g. Permas, and the rough shape is determined. The advantage of topology optimisation is that basic requirements for castability and testability can be considered automatically. Alternatively, manual design or the use of a previously designed component is also possible.
After creating the CAD model, the castability of the component made of the material EN-GJS-400-18-LT is ensured by a casting process simulation in Magmasoft. This also calculates the local microstructure composition, which can later be used in the software chain. This is followed by the mould optimisation, in which the fatigue strength is integrated into the mould optimisation loop with the help of the FEMFAT software and used as a tool for the service life calculation. The service life calculation can be carried out either based on a local microstructure composition or with global characteristic values.
Microstructure composition determines service life
Based on the results of Magmasoft, experimental and metallographic data, a correlation equation is used to determine the local fatigue strength as a function of the local microstructure composition. These correlation equations were determined in the project in cooperation between the Fraunhofer LBF and the Ansbach University of Applied Sciences.
The correlation equation enables targeted weight optimisation while simultaneously ensuring operational strength. The use of a local material definition is particularly useful for components with locally different cooling rates, as the microstructure within the component can vary greatly. Different cooling rates result, for example, from different wall thicknesses. A small wall thickness leads to a short cooling time. As a result, a microstructure with a high graphite precipitation density is formed, which leads to higher stressability. In addition to the graphite precipitation density, the ferrite/pearlite ratio has an influence on the stressability. A low ferrite content also leads to higher stressability.
Linking advanced software tools
"The project results show that the design of cast components can be revolutionised by linking advanced software tools," says Felix Reissner, research associate at Fraunhofer LBF and project manager of DNAguss.
By integrating all software tools used in design into a single software chain, castability, lightweight construction, operational strength and non-destructive testability of components are optimally coordinated. This enables improved structural design, weight reduction and lowering of manufacturing costs while ensuring operational stability.
