Method of moulding a sheet including the use of heated barrier fluid

Claim 1

A method of moulding an article of complicated shape out of a preformed sheet with the use of a female forming element having an internal surface of complicated shape, comprising: progressively stretching said sheet to a position approaching said internal surface of the forming element by applying pressure to the sheet from the side thereof opposite the female forming element, introducing a heated fluid into the forming element during said stretching in the vicinity of one or more portions of said internal surface of the forming element which would otherwise be first contacted by the sheet in the absence of such a barrier, at a sufficient pressure to act as a continuously flowing thin barrier layer between the stretching sheet and said portion, controlling the pressure and temperature of the heated barrier fluid while the sheet continues to spread over adjacent areas of the forming element still separated by the thin layer of heated barrier fluid until it is stretched into substantially the final shape of the article in close conformity with said internal surface of the forming element while remaining out of contact with said forming element, wherein the pressure and temperature control is selected so as to obtain a predetermined thickness profile in the article which would otherwise be unobtainable given the complicated shape of the internal surface of the forming element, stopping the flow of the barrier fluid, and continuing to apply pressure to the sheet from the side thereof opposite the female forming element whereby to stretch the sheet further to the limits provided by the internal surface of the forming element.

Claim 2

A method of moulding an article of complicated shape out of a preformed sheet with the use of a female forming element having an internal surface of complicated shape, comprising: progressively stretching said sheet to a position approaching said internal surface of the forming element by applying pressure to the sheet from the side thereof opposite the female forming element, introducing a heated fluid into the forming element during said stretching in the vicinity of one or more portions of said internal surface of the forming element which would otherwise be first contacted by the sheet in the absence of such a barrier, at a sufficient pressure to act as a continuously flowing thin barrier layer between the stretching sheet and said portion, controlling the pressure and temperature of the heated barrier fluid while the sheet continues to spread over adjacent areas of the forming element still separated by the thin layer of heated barrier fluid until it is stretched into substantially the final shape of the article in close conformity with said internal surface of the forming element while remaining out of contact with said forming element, wherein the pressure and temperature control is selected so as to obtain a predetermined thickness profile in the article which would otherwise be unobtainable given the complicated shape of the internal surface of the forming element, stopping the flow of the barrier fluid, and continuing to apply pressure to the sheet from the side thereof opposite the female forming element whereby to stretch the sheet further to the limits provided by the internal surface of the forming element.