A structure includes a first part provided in a first plane and second and third parts provided in a second plane located under the first plane. The second and third parts are welded together at a welded seam. The first part has at least one recess configured to receive a welding mechanism that forms the welded seam on the second and third parts. Another structure includes an “n” number of layers, n being at least three. Adjacent layers are in contact with one another and are connected by a welded seam. The structure also includes an outer surface. The layers between the outer surface and the respective welded seam define a recess through which a welding mechanism is configured to be passed as far as the respective layers to be welded to produce the welded seam.