Molding device for pulling open elongated holes in pipes or sheets

A molding device that pulls open a desired long hole in a molding target piece such as a pipe or a sheet, comprising:

• an arm that moves in a direction substantially perpendicular to a surface of the molding target piece in which a pilot hole is provided, and is configured to be inserted into an opening portion of the pilot hole, the molding target piece having the pilot hole, which is smaller than but substantially concentric with the elongated hole, provided therein;
• a control unit that controls movement of the arm;
• and
• a plug that is previously arranged on the opposite side of the arm with respect to the surface of the molding target piece in which the pilot hole is provided, configured to engage with and operate integrally with the arm, and has a plane area associated with the elongated hole;
• wherein the arm has a claw configured to engage with the plug, and an operation of the claw is controlled by the control unit, and the claw allows the plug to be coupled with or released from power by a butterfly-like operation thereof.