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2 2024

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Research of Hybrid Aluminium Castings with the Use of Porous Cores

Brůna M., Medňanský Martin, Oslanec P.

Archives of Foundry Engineering

2024

Vol. 24, iss. 3

18--24

The paper focuses on the research of hybrid aluminium castings produced by overcasting technology. This is an advanced technology for ensuring the lightness of castings by using the principle of overcasting a core with a porous cellular structure produced by foaming. Process parameters in the foaming phase of the material have a great influence on the resulting porous structure. The article focuses on controlling the influence of pressure during the foaming process on the resulting porosity and evaluating by X-ray tomograph and measuring the relative density. Variants using an initial pressure of 0.3 MPa appear to be the most satisfactory. The challenge of this technology is to ensure adequate bonding of the metals at the interface between the porous core and the solidified metal without penetrating the coating layer. For this reason, the surface treatment of foamed cores with various etchants has been proposed to disrupt the oxide layer on their surface. Macrographs of the uncoated sample and samples etched with 0.5% HF and 10% H3PO4 demonstrated the need for core surface treatment to prevent liquid metal penetration. EDX analysis confirmed the presence of AlPO4 at the core/casting interface in the treated sample.

Optimization of 3D Printed Patterns for the Hybrid Investment Casting Technology

Štěpán R., Krutiš V., Jelínek R., Petřík M.

Archives of Foundry Engineering

2024

Vol. 24, iss. 4

63--68

Currently, great emphasis is placed on the production of castings with complex shapes. The hybrid investment casting technology using 3D printed models offers new possibilities in the production of such complex and thin-walled castings. The motivation for this paper was to find a solution to the problem with ceramic shells cracking during the 3D model firing stage. The main factors affecting the shell cracking are the thermal expansion of the model and the shell material, and the newly considered pressure of the gas closed in the ceramic shell cavity. First, thermal analyses were performed of a commercial material used for 3D printing - Polymaker PolyCast™. The characteristics yielded by the measurements helped establish the glass transition temperature, the autoignition temperature and the behaviour of the gas produced by the model burning. Suitable experimental models in the shape of tetrahedrons were designed and used for a number of experiments. The tests confirmed that cracks only occur during shock firing in models printed by the FFF technology with 0% of infill. A solution suggested for further experiments is purposeful venting of the models. Practical testing of the optimization has also been performed. The last step was measurement of the heat transfer through the ceramic shell after being placed in the annealing furnace. There were temperature evolution profiles in the system model-ceramic shell obtained.