| 摘要 |
PURPOSE:To mold a sheet inexpensively using a mold having a simple structure by preforming the sheet into such a state that the acute-angle bent part of an undercut part is opened so as to have an obtuse angle and subsequently forming the obtuse-angle bend part of the preformed sheet into the acute-angle bent part by folding processing to form the undercut part. CONSTITUTION:One sheet 16 is molded into an objective shape having an undercut part 16A. Subsequently, the molded sheet 16 is stretched to a state having no undercut part. In this state, the acute-angle bent parts 16B, 16C forming the undercut part 16A are opened to become obtuse-angle bent parts 16'B, 16'C. Next, a mixture consisting of casting sand, water and a binder is applied to the under surface of the stretched sheet 16 to prepare a casting mold 17 in the shape of the stretched sheet. The upper mold 11 of a mold 13 is cast using the casting mold 17. A casting mold for casting a lower mold is prepared using the upper mold 11 to cast the lower mold 12. The sheet 16 is preformed using the mold 13 thus prepared and the preformed sheet 16 is further subjected to folding processing to form a mold sheet 16 having an objective shape having the undercut part 16A. |
