Aeronautical engines: reduction of emissions and consumptions with a process simulation study

At the end of 2006, a Marboré VI-C turbojet, dismantled from a target plane which had crashed, was collected and given to the University. The engine had been designed and produced by the French company Turbomeca in the 70’s. After the impact, the propeller was heavily damaged, in particular the front section, seat of the centrifugal compressor. The project included the entire modelling of the turbojet with the help of a CAD software and the reconstruction of the damaged parts. At the end of 2007, the rotor was completed, while the intake casing, originally created with magnesium alloy, was excluded from any analysis, as this study required particular knowledge about the casting process. For this reason, it was necessary to carry out a specific study for this part with the aim to find out all the technological details to plan and perform the casting process.

The first step was a careful CAD modelling which was slightly modified from the original according to the different use and then the project focused on the design of the casting system. After a first sketch of the casting system using CAD, the software MAGMASOFT was used to verify and optimize the casting process. During this step an academic approach permitted to carry out a series of simulations which modified the model as to a careful analysis of the results. This enabled to obtain a single good quality prototype without limits on time and elaboration methods. First of all, the simulations of the initial versions, which were created in agreement with the partners involved in the project, were essential to choose among different possible configuration methods. These versions differed both in the cooling system and in the filters placement.

The first version had a central cast iron chill and three exothermic feeders on top of the component. Solidification results immediately showed that this type of placement was perfect for the bearing support: as a matter of fact, a very quick cooling improved the mechanical characteristics in the most “significant” area of the component. At the same time, isolated liquid bubbles on the external surface during the cooling caused feeding problems.
In the second version there were only exothermic feeders on the top. Just like the previous version, this new one presented both pros and cons during the analysis of the solidification results. The fluid temperature was more homogeneous in the cooling but the cooling front on the bearing support moving upward and the longer time of solidification led to worse mechanical characteristics, especially on the central part.

designed, enabled to obtain a “hybrid” system and simulations showed that this version was definitely better. It was constituted by a central cast iron chill and eight exo-feeders on the top of the component. In addition, the number of ingates increased up to six in order to improve the homogeneity of the input flow and to reduce the temperature gradients, which appeared at the end of the casting process in the previous versions with only four ingates.
Filling and solidification results pointed out that feeding defects decreased in comparison to the previous versions, hence the quality target was reached. Defects could be considered irrelevant due to the precautionary software applied and the particular refining of the casting process.
The sand mold was therefore realized using SLS (Selective Laser Sintering) rapid prototyping techniques. Afterwards, light alloy casting was carried out taking into particular consideration the preparation of the alloy. Finally, some X-ray analyses were performed to verify the integrity of the component and to compare the simulation results with real data. This study enabled to analyse each detail accurately and to follow the transformation from a CAD drawing to a real component. In addition, it pointed out the potentialities of this process, which is suitable both to optimize all the steps using specific software and at the same time, to minimize errors.