Invisible tear seam for an air bag deployment opening cover

A method and apparatus is disclosed for forming a cover for an air bag deployment opening, the cover having a tear seam defined by a reduction in thickness of the cover. The cover can be formed as an unitary part of an outer skin layer for an automobile interior trim structure. The apparatus includes a thin shell having an inner surface upon which a thermoplastic material is cast to form the outer skin. A multiplicity of pins are disposed on and extend away from a backside thereof to transfer heat to the inner surface. The density of the pins is reduced on the portion of the backside of the shell proximate the portion of the inner surface upon which the tear seam of the outer skin is to be formed. The shell can be heated or cooled by using a plurality of nozzles to impinge heated or cooled air onto predetermined locations of the backside. A cover and tear seam construction is also disclosed.