| Ingot moulds are important equipment in the production process of casting. The ingot molds are influenced by high temperature and thermal-stress during casting of ingots and easy to fail due to thermal fatigue and hot cracking, so, thermal fatigue is the most common failure modes of ingot molds. It not only shortens the mold life, but also reduces the surface quality of castings. Therefore, to study the variations of the temperature field and stress field of the mold during casting process has important practical value. However, it is difficult to get the temperature field and stress field just through experiment research. With the development of computer numerical simulation technology, it is possible to apply computer simulation technique to calculate the temperature field and stress field of ingot mold, so as to optimize the structure of ingot mold to control and ensure the quality of castings and prolong the service life of ingot mold, reduce production cost and enhance the competitive ability of enterprise. This paper first carried out thermal fatigue tests of different graphite shape of cast iron to determine the lead ingot mold's material, then simulated the thermal-stress coupling of lead ingot mold in working process using finite element method based on the actual production process of lead ingots. On the base of this analysis, the structure of lead ingot mold was optimization.Thermal fatigue performance of different graphite contained cast iron was investigated by heat-colding recycle tests in the range of 20℃-650℃. The results show that micro-cracks always initiated at graphite phase during the thermal cycle process. The main crack often propagated along graphite and the matrix between two nearest graphite particles. The thermal fatigue resistance of nodular graphite iron is the best, vermicular graphite iron is moderate, and the flake graphite iron is the worst under the same heat-coding recycle condition. According to thermal fatigue test results, nodular graphite iron was choose as lead ingot mold's material. So the thermal physical parameters of a nodular graphite iron, QT600 were chosen during next numerical simulations of the thermal field and stress field.The finite element theory about thermal analysis and stress calculation in the numerical simulation was reviewed. The mathematical of an ingot mold model of the transient temperature field and thermal elastic-plastic stress field in the solidification process was established according to actual process of a lead ingot product. Then, the transient temperature field of lead ingot mold during casting was simulated using ANSYS software. Temperature and its variation with time of key points of lead ingot mold and the center position of lead ingot were verified by experimental method, and the simulation results are identical with experiment. Furthermore, lead ingot mold's stress field distribution and its variation in lead ingot solidification process were simulated and analyzed by the import temperature field simulation results as body load. The results shows that the maximum stress appears at two intersect surfaces. And so, it is inferred that the fatigue failure easily occurs at the intersect faces of mold.When the draft is 20 degree, temperature field and stress field of lead ingot molds wall thickness of 15mm,25mm,35mm and 45mm were simulated respectively, the stress of ingot mold whose wall thickness is 25 mm is the minimum. When the wall thickness is 25 mm, stress fields of lead ingot molds draft of 8,12 and 20 degree were simulated respectively. In the same wall thickness, the draft has little influence on the ingot mold stress. Considering the service life of lead ingot mold and ingot surface quality, and finally determined that the wall thickness of lead ingot mould for 25mm, draft of 12 degrees. |
PDF Full Text Request