Vacuum forming method

Abstract

Mainly, local wall thinning is prevented. The invention relates to a vacuum forming method for fabricating a resin-molded article. The vacuum forming method includes pressing a thermoplastic resin sheet 201 softened by heating into a vacuum forming mold 202 using a core mold 203 to stretch and deform thermoplastic resin sheet 201 at the same time, and bringing the thermoplastic resin sheet 201 into intimate contact with the vacuum forming mold 202 by vacuum suction to shape the thermoplastic resin sheet 201 . In the process of closing the vacuum forming mold 202 and the core mold 203 , at least part of the thermoplastic resin sheet 201 is preshaped using air pressure in such a way that the at least part of the thermoplastic resin sheet 201 is locally stretched and deformed at the same time and thus brought into intimate contact with the core mold 203 . Then, the thermoplastic resin sheet 201 is final-shaped by closing the vacuum forming mold 202 and the core mold 203 and performing vacuum suction through the vacuum forming mold 202.

1 . A vacuum forming method for fabricating a resin-molded article, comprising:
 pressing a thermoplastic resin sheet softened by heating into a vacuum forming mold using a core mold to stretch and deform the thermoplastic resin sheet at the same time; and   bringing the thermoplastic resin sheet into intimate contact with the vacuum forming mold by vacuum suction to shape the thermoplastic resin sheet,   wherein at least part of the thermoplastic resin sheet is preshaped using air pressure in the process of closing the vacuum forming mold and the core mold in such a way that the at least part of the thermoplastic resin sheet are locally stretched and deformed at the same time and thus brought into intimate contact with the core mold, and   the thermoplastic resin sheet is then final-shaped by closing the vacuum forming mold and the core mold and performing vacuum suction through the vacuum forming mold.   
     
     
         2 . The vacuum forming method according to  claim 1 , wherein the at least part of the thermoplastic resin sheet which is preshaped comprises a portion which would be locally stretched to a great extent and thin-walled if only final shaping is performed without preshaping, and a portion around the foregoing portion. 
     
     
         3 . The vacuum forming method according to  claim 2 , wherein the at least part of the thermoplastic resin sheet which is preshaped comprises a portion around a deep draw portion, an undercut portion, or another portion in the vacuum-formed resin-molded article. 
     
     
         4 . The vacuum forming method according to  claim 1 , wherein the vacuum forming mold has a projecting portion or a recessed portion formed therein for forming a deep draw portion, and the core mold has a recessed portion or a projecting portion formed therein for forming the deep draw portion. 
     
     
         5 . The vacuum forming method according to  claim 4 , wherein the projecting portion and the recessed portion are configured to have such sizes and shapes as to be almost fittable to each other with a required space left therebetween. 
     
     
         6 . The vacuum forming method according to  claim 1 , wherein the vacuum forming mold has a large number of vacuum holes formed therein and configured to allow vacuum suction to be performed therethrough, and the core mold has a vacuum hole formed therein and configured to allow any one of vacuum suction and air blowing to be performed therethrough. 
     
     
         7 . The vacuum forming method according to  claim 6 , wherein a vacuum source and a pressure source are switchably connected to the vacuum holes of the vacuum forming mold, and air is blown from the vacuum holes toward the thermoplastic resin sheet in the preshaping. 
     
     
         8 . The vacuum forming method according to  claim 6 , wherein the core mold is formed to be suitable for the preshaping by being provided with one or a very small number of vacuum holes at an approximately central position of a bottom surface of a recessed portion, and provided with a vacuum groove around apertures of the vacuum holes, the vacuum groove communicating with the vacuum holes and extending over the entire bottom surface of the recessed portion. 
     
     
         9 . The vacuum forming method according to  claim 8 , wherein the vacuum groove includes: radial portions radially extending from the apertures of the vacuum holes in a cross-like shape or another shape; and a closed-loop circumferential portion extending along a peripheral portion of the bottom surface of the recessed portion while connecting tip portions of the radial portions. 
     
     
         10 . The vacuum forming method according to  claim 7 , wherein the air pressure for locally stretching the at least part of the thermoplastic resin sheet  201  is applied by using any one of evacuation of air through the vacuum holes of the core mold, and blowing of air from a top portion of a projecting portion toward the thermoplastic resin sheet by connecting the pressure source to the vacuum holes or a blowing hole of the vacuum forming mold. 
     
     
         11 . The vacuum forming method according to  claim 10 , wherein the any one of the evacuation of air through the vacuum holes and the blowing of air using the vacuum holes is started slightly before the top portion of the projecting portion and an edge portion of a recessed portion provided in the vacuum forming mold and the core mold come to approximately the same level of height and contact the thermoplastic resin sheet. 
     
     
         12 . The vacuum forming method according to  claim 1 , wherein the preshaping is performed while stopping closing the vacuum forming mold and the core mold or without stopping closing the molds. 
     
     
         13 . The vacuum forming method according to  claim 11 , wherein any one of the evacuation and blowing of air for the preshaping is stopped when the vacuum forming mold and the core mold come closest to each other with the projecting portion and the recessed portion fitting to each other with a required space left therebetween upon completion of closing the molds. 
     
     
         14 . The vacuum forming method according to  claim 1 , wherein start of the vacuum suction for the final shaping through the vacuum forming mold is approximately simultaneous with any one of completion of closing the molds and stoppage of any one of the evacuation and blowing of air for the preshaping.