PSI - Issue 40

Nina A. Bogdanova et al. / Procedia Structural Integrity 40 (2022) 70–74 Nina A. Bogdanova at al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Investment compounds in the form of flake-like irregular-shaped powders are used for manufacture of re-movable porous patterns by means of compression molding (Zhilin, 2018). Spherical granules with the diameter of 10 mm were used, in order to idealize the compression molding process. Metal balls with the diameter of 10 mm made of steel 45 were used for simulation of soluble components of the investment compound, in order to simulate the process of compression molding of a combined removable pattern. The properties of St45 are regulated by GOST 1050- 2013 “Metal Products from Nonalloyed Structural Quality and Special Steels. General Specification” in accordance with this standard, the steel elements have the Young’s modulus of Е = 210 GPa and density of ρ = 7,810 kg/m3 (GOST 1050-2013). In order to visualize the compaction process, the spherical elements were placed in one layer in a mold die with transparent walls which were rigid enough to resist plastic deformation of the investment compound. The inner cavity of the mold is a parallelepiped with the dimensions of 10×50×90 mm. Figure 1 shows the diagrams of spherical element distribution inside the mold die. Non-deformable elastic elements in the form of steel balls are highlighted in dark color in diagrams d and e. The initial conditions of investment compound compaction are given in Table 1. By deformable components we mean the elements of the system, except for the elastic elements in cases d and e. Fraction of the volume occupied by the waxy elements [%] 65 The experimental study was conducted with the use of an AGX plus Shimadzu universal testing machine. A mold die containing the investment compound was installed on the testing machine table; then, the upper crosshead moving at a constant speed was used to compact the investment compound until the compact porosity reached 10%. Simulation of the compression molding process was performed in series with two ram velocities: 0.5 mm/s and 3 mm/s. 3. Experimental study results Figure 1 shows the third order polynomial relations plotted based on the experimental study results: the solid line is the ram velocity of 3 mm/s, while the dashed line is the velocity of 0.5 mm/s. Symbols R 3 2 and R 0.5 2 are the R squared values for the third order polynomial of stress-strain relations at different ram velocities. It can be seen from Figure 1 that the maximum stresses for all the cases of the initial packing of the elements do not exceed 0.9 MPa. The difference between the stress values under different initial compression-molding conditions is less obvious at the first stage of compaction. The second stage of compaction for all the initial-element-packing cases starts at the stress level of about 10%. This stage is characterized by less intensive rise in stresses. The difference be-tween the compaction curves also becomes more obvious as the ram velocity increases. The third stage of compression for all the cases of single-component initial packing starts at the strain of 30%. In case of compounds comprising elastic elements, this stage starts at the strain level of about 25%. At the beginning of the third stage, the plastic deformation is spread over the entire volume of the compact. Table 1. Initial Conditions of Compact Molding. Element arrangement case Volume of the deformable components [cm3] a b c d e 45 45 43.75 40 33.5 445 Bulk density of the elements [kg/m3] 340 445 460 445 Number of waxy elements in the mold die [pcs] 34 40 45 52 45 54 35 59 23