Mandrel structure of sand core

The utility model relates to a mandrel structure of a sand core. The mandrel structure comprises a mandrel main rod located on a sand core axis. The upper end of the mandrel main rod is provided with a main rod upper guide sleeve, and the lower end of the mandrel main rod is provided with a main rod lower guide sleeve. The main rod upper guide sleeve is connected with a mandrel concave end, and the main rod lower guide sleeve is connected with a mandrel convex end. The mandrel convex end and the mandrel concave end are in interference fit with the mandrel main rod respectively. A cone hole concave downward of the mandrel concave end is formed in the center of an upper end face of the mandrel concave end. The lower end of the mandrel convex end is provided with a cone head of the mandrel convex end. The cone head of the mandrel convex end can be in interference fit with the cone hole of the mandrel concave end. A plurality of core bar clamping grooves are uniformly and symmetrically arranged on two sides of the middle portion of the mandrel main rod in the height direction. Main core bars are inserted in the core bar clamping grooves respectively and are in interference fit with the core bar clamping grooves. The upper portions of each layer of the main core bars are in lap joint with auxiliary core bars perpendicular to the main core bars respectively. The mandrel structure can bear the weight of large sand cores, and the weight of the upper sand cores can be transferred to a sand core base.