Process for manufacturing an automobile interior trim part with an airbag cover and to the associated machine

A process to manufacture a vehicle interior trim with an airbag cover, the process including:

• obtaining an interior trim part,
• creating a weakening line around at least a part of a defined area of said interior trim part said defined area being the airbag cover,
• wherein the weakening line is created by milling along the weakening line a number of holes, the holes being milled by a milling machine having a milling tool and a linear Z-axis for moving the milling tool substantially perpendicularly to a zone of the trim part to be milled, and a linear stitching axis for moving the milling tool along a direction substantially parallel to the Z-axis,
• wherein the linear Z-axis moves the milling tool with an acceleration of less than 4 m/s2 substantially perpendicularly to said zone of the trip trim part to be milled;
• and
• wherein the linear stitching axis moves the milling tool with an acceleration of 4-8 m/s2 substantially perpendicularly to said zone of the trim part to be milled,
• wherein the weakening line is created by milling along the weakening line at least one slot in addition to said holes, using said milling machine, the holes being frustoconical or cylindrical with a circular cross-section, the slots having a shape elongated along the weakening line and different from the shape of the holes, the slots and the holes being spaced from one another along the weakening line and being separated from one another by bridges of material spaced from one another along the weakening line,
• wherein the weakening line has at least a hinge portion, an initial split portion, and a corner, each having a given tear resistance, the respective tear resistance of the initial split portion, of the corner and of the hinge portion increasing in that order, at least the ratio between the number of slots and the number of holes in each portion and a corner being adapted to obtain the respective tear resistance of said portion of the corner.