METHOD OF MOLDING SYNTHETIC RESIN WITH HIGH ACCURACY

PURPOSE:To manufacture moldings of high planar accuracy with the low cost, which are useful for optical parts such as mirrors and lenses and have a shape faithfully profiling the shape of molds, by a method wherein resin is injected into the molds and molding is then performed while pressurizing the resin with movable parts of the molds. CONSTITUTION:Molds D1, D2 are held integral by a mold fastening force P and then heated up to injection temperatures. A given amount of resin is poured into a cavity C from an injection cylinder A. Next, a pressurizing piston Po is advanced to close a gate B, and the molds are heated to melt the injected resin and then cooled. At this time, pressurizing of the piston Po imparts pressure Pc against a movable core E of the mold to transmit a pressure to the cavity C. When the resin is hardened under continuous pressurizing in this way, the movable core E serves to reduce the volume of the cavity C attendant on volume reduction resulted from hardening, thus making it possible to manufacture moldings without sink mark.