Abstract: The device of the invention allows a hair-pin spring with two legs to be inserted astride a plate having windows for locally welding the legs together. This device receives one plate at a time and moves it lengthwise, and a corridor guides each spring in turn, the spring being moved along the corridor towards its insertion position. A mask movable parallel to the plane of the plate from the edge furthest from the zone through which the introduction takes place allows the window to be covered furthest from the zone through which the introduction takes place so as to avoid jamming.

Abstract: For welding a grid formed by sets of plates disposed orthogonally and whose endmost parts are secured to a surround, it is placed in a shaping and mechanically holding frame allowing access to the point to be welded. The frame containing the grid is then placed on a revolving device belonging to a roundabout, at a first welding position and welding is carried out therein on at least one face of the grid by means of a welding member movable in two perpendicular directions for bringing it at right angles to each of the welding points on the face. The frame is then brought to a second welding position in which the plates are welded to the surround by means of a second welding member movable in only one direction, after rotation through 90.degree. of the frame by means of the revolving device; and the operations are repeated as necessary until the whole of the welds have been executed.