PURPOSE: An expandable core for insert injection molding of shaft type and an injection molding device having the expandable core are provided to secure the dimensional stability of high precision by efficiency centering the insert in a molding process. CONSTITUTION: An expandable core for insert injection molding of shaft type comprises a cylinder(20) and an extension unit(30). The internal space of cylinder is composed an insertion hole(210) and a through-hole(220). The insertion hole has an inner diameter having a wide upside and a narrow lower side. The through-hole is communicated with the end of the insertion hole. The elastic member has the elasticity in order to partition a wedge-shaped division head. Wedge-shaped division heads are unified by inserting the extension unit into the cylinder in the closing of a mold.
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