In the post-processing results of stress field in ProCAST software, there is an option to judge the hot crack trend in the “stress” option. After starting this option, the analysis diagram of solidification hot crack trend of sand mold casting as shown in Figure 1 can be seen in the post-processing program. It can be seen that the root of the two large risers is the hot spot concentration position, and its hot crack trend is large; The trend is relatively small at the root of the small riser and the fillet of the column window.
For the analysis of hot crack in the solidification process of sand casting, the solidification mechanical criterion of sand casting by ZHANGJIAQUAN et al is used as the hot crack criterion. The two-phase zone in the solidification front of sand mold casting is divided into solid phase zone and quasi solid phase zone, which is based on the critical solid rate FTS. The physical quantity of equivalent stress / yield strength ratio reflects the above criteria. In the solid region, yield occurs when the equivalent stress is greater than the yield stress, that is, the ratio is greater than 1; In the quasi solid region, that is, the crack sensitive region, when the ratio is greater than 1, it is easy to produce microcracks and eventually lead to hot cracks.
As shown in figure a in Figure 2. In the solid-liquid temperature range of sand casting, four parts with large equivalent stress in sand casting are selected: the root a of left large riser, the fillet B of inner window, the root c of small riser and the root D of right large riser. One node is taken for hot crack analysis.
The critical solid rate fts = 0.75 is taken as the quasi solid zone for simulation analysis. The temperature corresponding to the critical solid rate is t’s = 1476 ℃, so the temperature range corresponding to the quasi solid zone is 1438-1476 ℃. As shown in Figure 2, the point is the position with large stress value in the solidification process of sand mold casting, which is the key inspection position. It can be seen that the stress at the root of the two large risers is large, and the stress at the root of the small riser and the transition fillet of the inner window is also in the dangerous area. The stress at these four positions has always been at a high level. In the corresponding temperature range of the quasi solid phase zone, the ratio of the equivalent stress at four positions to the tensile yield strength of the material is always less than 1, the ratio of the root nodes a and B of the two large risers is between 0.5-0.7, and the ratio of the other two nodes is between 0.3-0.4. Therefore, there is little tendency for the sand mold casting to produce hot cracks in the casting solidification process.