Study On Springback Of High Pressure Compaction Sand Molds And The Mechanism Of Springback

With the improvement of casting automation, the technology of high pressure compaction molding has been adopted more and more extensively in practice. To realize the aim of fast, accurate production of high-quality castings, the research of molding sand springback is essential. Springback is a kind of sand mould micro-deformation when the external force is discharged. Foundry green sand is a complicated mixture, in which solid, liquid, and gas exist simultaneously. Green sand has viscosity, elasticity and plasticity concurrently. The deformation of green sand is different from that of the clay, and is also different from that of the merely quartz sand, and this makes the mechanism of molding sand springback very complex.This subject is a part of the project "Research on the Prediction of Springback of High Compaction Sand Mold and its Mechanism" which was supported by the National Natural Science Fund. It is also to supplement the project "Research on the Micro-deformation of foundry molding sand" which was also supported by the National Natural Science Fund. Through the dynamical test of standard sand specimen during the whole process of high pressure compaction, the rule of springback of sand specimen has been resulted, and the constitutive relationship formulations with respect to specific pressure, bentonite content and compactibility have been derived. With the intelligent molding sand multi-property tester, developed by ourselves, the springback potential of standard sand specimen has been measured. As compared with the practical springback value of sand specimen, it has been concluded that both of them have the similar variations with bentonite content, compactibility, and specific pressure. Furthermore, in the paper, the practical springback of high pressure compacted sand molds have been contrasted with the springback potential of standard sand specimen, and it has been concluded that during the process of high pressure sand compaction, the springback potential of sand specimen can qualitatively reflect the magnitude of sand mold springback. This subject is helpful for quality controlling of high compaction sand molds and the improvement of casting precision in foundry production, and can provide a theoretical basis for the forming of high compaction sand molds and its numerical simulation.