Influence of the Molding Technique on the Bell Casting Geometry

The influence of the technique used to make the casting mold on the geometry and sound of the bell has been analyzed. The starting point was a CAD model of a bell with a geometry designed to obtain the required overtone frequencies that determine the pitch tone of the bell. The frequency of the basic overtones was determined on the basis of the results of the numerical modal analysis. The geometry of the bell was shaped in order to obtain the frequency of natural vibrations, creating a classical bell harmonic system. The developed geometric model was used to make a casting pattern using 3D printing in the FDM technique and a stickle cut on a CNC plotter from steel sheet. The casting molds were made of the same furan molding sand in both cases and were prepared to be poured in the same way, the only difference being the method of making the mould. Both molds were poured during one melting, which almost completely excludes differences in the chemical composition and quality of the liquid alloy. The castings in the raw state were subjected to three-dimensional scanning, which in the next step enabled a precise comparative analysis of their geometry. A spectral analysis of the sound of the tested bells was also performed using the Fourier transform method to determine the frequency of the fundamental overtones. Comparing the results of the geometry analysis with the results of the sound analysis of real bells made it possible to draw conclusions regarding the adoption of assumptions in the design of bells appropriate to the technique of making the mold used in order to obtain the planned tone of the bell sound.