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

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.