Forming method of complex thin-wall sand core

The invention discloses a forming method of a complex thin-wall sand core. The forming method comprises the following steps: (1) adopting a self-solidified furan resin sandy core; (2) arranging a core skeleton according to the shape of the sand core, and adopting steel bars for the core skeleton; simultaneously, adopting a gas discharging rope bundled by fine tying wires as a gas discharging part of the sand core on the core skeleton; pulling out the core skeleton in the clearing process; (3) adding sand-core reinforcing ribs at the easily-broken connecting parts of the sand core, wherein the reinforcing ribs are thread-shaped, placing the reinforcing ribs in the sand core when the sand core is manufactured, melting the parts of the reinforcing ribs, exposed outside the sand core, and a casting piece after casting, and removing the parts buried in the sand core in the clearing process; and (4) designing movable blocks at the parts corresponding to pressure releasing holes in the sand core, adding corresponding graphite rods in the core-manufacturing process, and clearing off the graphite rods in the clearing process; and designing iron-casting rods at the easily-broken parts of the sand core, forming iron-coated sand in the casting process and clearing off the iron-coated sand in the clearing process.