disclosed is a process for the production of a shaped article from a thermoplastic resinous material , comprising the steps of heat plastifying the thermoplastic material ; injecting the heat - plastified plastic material into a forming tool having a first shape configuration and at least one parting plane , to form a pre - form of the thermoplastic material ; subjecting the thermoplastic material pre - form in the forming tool to a cooling phase ; providing at least a partially new second shape configuration to the forming tool containing the pre - form ; and during the cooling phase subjecting the pre - form in the forming tool having the second shape configuration to at least one pressure treatment under elevated pressure to produce a shaped article . also disclosed are several embodiments of apparatus for carrying out the process .