Method and apparatus of making air bag cover having a visually perceptible tear seam

A method of making an air bag cover for an inflatable air bag system in a plastic injection mold having first and second mold halves which provide a cover-defining cavity with a restricted-flow, tear seam-defining portion in a closed position of the mold, the air bag cover having front and back surfaces and having a tear seam visually perceptible from the front surface, the method comprising the steps of:

• injecting molten thermoplastic into the cover-defining cavity of the mold in the closed position of the mold;
• allowing the tear seam of the air bag cover to sink before the molten thermoplastic completely solidifies to form the visually perceptible tear seam having a visually perceptible concave exterior surface having a width substantially perpendicular to the thickness of the tear seam and a flat inner surface defining a break portion of the tear seam and a pair of walls extending at an angle of 90 degree to 95 degree from the flat inner surface and spaced a substantially uniform distance apart and wherein the width of the concave exterior surface is greater than the substantially uniform distance between the pair of walls;
• permitting the resulting air bag cover to cool to a temperature beneath the softening point of the plastic;
• and
• removing the completed air bag cover from the mold.

A thermoplastic injection mold for making an air bag cover for an inflatable air bag system, the air bag cover having front and back surfaces and having a tear seam visually perceptible from the front surface, the mold comprising:

• a first mold half;
• and
• a second mold half, the first and second mold halves having first and second surfaces, respectively, which provide a cover-defining cavity, the first surface having an outwardly extending projection and the second surface being relatively smooth to provide a restricted-flow, tear seam-defining portion of the cover-defining cavity in a closed position of the mold, the projection being sized and shaped and spaced away from the second surface sufficiently in the closed position of the mold, the projection having a flat top surface and side surfaces extending at an angle of about 90 degree to 95 degree from the flat top surface, the side surfaces being spaced a substantially uniform distance apart to form the tear seam having a visually perceptible concave exterior surface having a width substantially perpendicular to the thickness of the tear seam, the tear seam having a flat inner surface defining a break portion of the tear seam and a pair of walls extending at an angle of 90 degree to 95 degree from the flat inner surface, the pair of walls being spaced a substantially uniform distance apart and wherein the width of the concave exterior surface is greater than the substantially uniform distance between the pair of walls.