Method to produce a weakened line in an air bag cover using a sonotrode

The present invention relates to a procedure for obtaining a weakened line for an airbag outlet in a textile lining, wherein the textile lining (1.5) is the finish for plastic parts (1) used in the interior of vehicles, making use of sonotrodes (2.4) to apply mechanical vibrations in the ultrasound range to obtain the weakened line (1.1) on the textile lining of the plastic part (1). Applying this procedure produces a weakened line (1.1) in a very short time, maintaining the pattern of the textile lining and creating a window that breaks at the weakened area in a correct manner when the airbag device is deployed.