Advancing sustainable casting through cryogenic gradient forming of frozen sand molds: design, error control, and experimental validation

Owing to its exceptional casting performance, substantial utilization of recycled sand, and environmentally sustainable characteristics, frozen sand mold casting technology has found extensive application across diverse sectors, including aerospace, power machinery, and the automotive industry. The focus of the present study was on the development of frozen sand mold formulations tailored for efficient machining, guided by the performance and cutting fracture mechanism of frozen sand molds. A regional temperature control device was developed for the purpose of conducting cryogenic cutting experiments on frozen sand molds with varying geometrical characteristics and molding materials. The impact of milling process parameters on the dimension accuracy of both sand molds and castings, as well as castings' surface roughness, were systematically investigated by a whole-process error flow control method. The findings indicate that precise and efficient processing of complicated sand molds was achievable by using sand particles with sizes ranging from 106 to 212 μm, and water content between 4 and 5 wt.%, freezing temperature below –25°C, and cutting temperature within the range of –5 to 0 ℃. Through the frozen-casting of representative components, it was validated that the machining error of the frozen sand mold was within ± 0.25 mm. Additionally, the dimensional accuracy of the flywheel shell casting conformed to the CT8 specifications. This study provides theoretical guidance for the selection of frozen-casting sand formulations and close-loop control of process size chains for complex metal parts, as well as an overall solution for the realization of sustainable development of green casting.