Focus on situation analysis

In the recently completed DNAguss research project, a consortium led by the Fraunhofer LBF, Darmstadt, has linked several software tools into a single software chain in which castability, lightweight construction, operational strength and non-destructive testability of components are optimally coordinated.

The aim of the DNAguss project, which is funded by the BMWK, is the continuous numerical design of cast components along the process chain. Linking the tools into a single chain enables improved structural design, weight reduction - in the project example by 34 % - and reduction of manufacturing costs while ensuring operational stability.

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. This enables a material-saving and strength-optimised design. 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 taken into account 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 using 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.

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 collaboration between the Fraunhofer LBF and Ansbach University of Applied Sciences. This enables targeted weight optimisation while at the same time ensuring operational strength. The use of a local material definition is particularly useful for components with locally different cooling rates, as the microstructure can vary greatly within the component. Different cooling rates result, for example, from different wall thicknesses. A small wall thickness leads to a short cooling time. As a result, a structure 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, which increases due to a lower ferrite content.