Novel design strategy of insulation cotton for regulating temperature gradient during investment casting based on simulation visualization and experiment results

To meet the high demand for precision castings in the aviation field, we innovatively adopt a two-stage optimization strategy of 'process parameter-solidification process control'. Firstly, the influence of shell thickness and cooling rate regulation method to the casting quality were studied by orthogonal experiments of two factors and three levels. The optimum process was determined as the shell thickness of 10 mm and the cooling interfacial heat transfer coefficient of 30 W/(m²·K). We used multi-physical fields coupled simulation and experimental analysis to reveal that the balance the cooling rate and feeding efficiency is of great significance to control the defect and the grain size. Based on these analyses, the novel idea of gradient layered insulation cotton design was proposed. Through the simulation results of the temperature field, we calculated the formula of the thermal insulation cotton gradient thickness. Combining with multi-physical field coupling simulation and experimental verification, we revealed the traditional uniform heat preservation process is easy to cause thermal stress concentration and shrinkage porosity due to the uneven temperature gradient distribution, while the new gradient layered insulation cotton can balance the solidification sequence of different parts by regulating the cooling rate and suppresses thermal stress. The results show that the shrinkage volume is reduced from 0.096 cm³ to 0.058 cm³. This study not only established a quantitative casting defects prediction model but also achieved fine control of defects, which provides a valuable solution for improving the performance of precision castings.