The invention relates to a gas shielding device for use during a step comprising the welding of a sound attenuation panel (100) under a controlled atmosphere, said device including means for injecting an inert gas onto the panel (100) and means for receiving a welding torch (40). The device is characterised in that the inert gas injection means comprise an inert gas diffuser (54) mounted on the periphery of the welding torch (40) receiving means.
