Method for thermoforming plastic sheets
 A cup-shaped deep-draw-formed article is formed by thermoforming a thermoplastic resin sheet characterized in that a concave forming mold and an ancillary mold which are in opposition to each other are used, said ancillary mold being equipped with a molding assist movable vertically to the opening face of the ancillary mold; the molding assist is first moved toward the opening of the ancillary mold; a preheated thermoplastic resin sheet interposed between said forming mold and ancillary mold is then expanded into the ancillary mold while moving the molding assist in contact with the sheet by introducing a pressured fluid into the forming mold; and when the molding assist reaches a predetermined position, a pressured fluid is introduced into the ancillary mold to press the sheet against the interior surface of the forming mold, thereby forming the sheet into the desired shape. This method can be applied to deep draw forming where the depth to opening diameter ratio is greater than 0.2, to obtain easily a shaped article with a favorable thickness distribution and a high strength or stiffness. 
Sumitomo Bakelite Company Limited
B
B29C
inventional
Kyosuke Masahiro
Miki Takeuchi