MANUFACTURE OF HOLLOW BODY WITH BUILT-IN RIB

PURPOSE:To manufacture a hollow body, which is rigid to three-dimensional bending, by a method wherein, firstly, three sheets are arranged at intervals between molding tools opposing to each other; secondly, the molding tools are clamped and finally some portions of two sheets arranged on both sides are abutted against the intermediate sheet by advancing protruding members in facing directions from the inner surfaces of cavities. CONSTITUTION:Firstly, three sheets 2a, 2b and 2c are hangingly extruded from an extruder head 1 in between a left and a right molding tools 3 and 4 with protruding members 7 and 8 in retreated state. Secondly, after the molding tools are clamped, the ejectors 7 and 8 are advanced so as to deform some portions of two sheets 2a and 2c, which locate at the left and right positions, inwards in order to abut the tips of the deformed portions against the intermediate sheet 2b. In addition, the cavities 5 and 6 of the left and the right molding tools 3 and 4 are preferably evacuated during said mold clamping process in order to keep spaces between the left sheet 2a and the intermediate sheet 2b and between the right sheet 2c and the intermediate sheet 2b. Thirdly, after the protruding members 7 and 8 are retreated, pressure fluid is blown in between the respective sheets in order to form lateral ribs 13 and 14 along the lines of retreat of the protruding members 7 and 8 within a hollow body.