Can Manufacturing Method and Device for Carrying Out the Said Method

The present invention has essentially for its object an improved method of manufacture of preserved-food cans or tins. More specifically, the invention relates to the use of laser beam welding for joining the adjacent confronting edges of a tube intended to constitute the body of a preserved-food can or tin.

It is known that the tubular bodies of preserved-food cans are manufactured by soldering the mutually opposite sides of a rectangular metal sheet formed into a ring, cylinder or like shape so as to constitute a tube with adjacent confronting edges. The filler metal (solder) generally employed for the soldering is an alloy of lead and tin. The opposite sides of the metal sheet are either placed together in overlapping relationship or lock-seamed to one another, which necessarily results in a surplus thickness of material at least equal to the thickness of the rectangular base sheet. This surplus thickness makes it very difficult to lock-bead the can bottom at the joint of the tube, so that a lack of tightness is frequently observed at that location. Moreover, there is the risk of the filler metal penetrating the can, resulting in a hazard of contamination by the filler lead, which is toxic.

The present invention allows all the aforementioned drawbacks to be avoided, since the opposite sides of the tube with adjacent confronting edges intended to constitute the can body are assembled edge to edge without surplus thickness and preferably by autogenous welding, i.e. without using a lead-based filler alloy.

More precisely, the invention relates to a can manufacturing method, characterized in that the can body is obtained by forming a metal sheet into a tube with adjacent confronting edges, holding together the said edges and welding them together by means of a laser beam.

The welding is preferably autogenous, and its has been deemed preferable to perform the same by longitudinally displacing the tube-shaped metal sheet in front of a stationary laser beam, thereby ensuring higher welding accuracy.

The invention also relates to a can manufacturing device, more particularly for carrying out the above method, characterized in that it comprises two longitudinal parallel vices, means for uniformly displacing both vices as a whole in their longitudinal direction and a laser generating device placed opposite the said vices in such a manner that the impact of the laser beam produced thereby passes along substantially the middle line between the said vices.

The invention will be better understood and other purposes, details and advantages thereof will appear more clearly from the following explanatory description given solely by way of example with reference to the appended non-limitative drawing wherein:

FIG. 1 is a diagrammatic perspective view of a device for carrying out the method according to the invention;

FIG. 2 diagrammatically illustrates a modification of the device of FIG. 1; and

FIG. 3 illustrates another modification of the device of FIG. 1.

As seen in the appended drawing, a rectangular metal sheet 11 is formed into a tube with adjacent confronting edges, which is held by two longitudinal parallel vices 12 and 13, the opposite sides 14 and 15 of the said metal sheet 11 being placed edge to edge without overlap. Each vice is made up of two parallel clamping bars 16a, 16b, which are assembled and pressed together by means of clamping screws 17. A laser-beam generating device 18 is arranged above the vices 12 and 13 in such a manner that the laser beam 18a passes substantially along the middle line between the said vices and the impact on the metal sheet 11 is located on the junction line between the opposite sides 14 and 15. The clamping bars 16b remotest from the laser device 18 are secured to a support plate 20 on which are mounted the mechanical means for uniformly displacing both vices 12 and 13 as a whole. In the case considered, the said mechanical means are constituted by a dovetail guide slot 21 provided in the lower portion of the support plate and by means of which the latter can slide along a stationary counter-guide 22 of a complementary shape. The uniform displacement is ensured by a quite simple system comprising a bar 23 fixed to and moving jointly with the plate 20 and provided with a tapped hole 24 in which is passed a threaded rod 25. The rotation of the threaded rod 25 causes a longitudinal displacement of the plate 20 along the counter-guide 22, thus ensuring the autogenous welding of the sides 14 and 15 over the whole height of the can body.

FIG. 2 shows a modification of the invention, wherein the bars 16b are done away with. Thus, the sides 14 and 15 of the tube-shaped metal sheet 11 are applied to and directly engage the support plate 20 during the welding, thus overcoming any possibility of collapse of the edges 14 and 15 towards the interior of the cylinder at the time of welding.

FIG. 3 illustrates another modification, closely similar to the foregoing one, wherein a very fine slot 30 is provided in the base plate 20 exactly at the location where the two sides 14 and 15 are placed edge to edge. Heat losses through the support plate are thus avoided, ensuring a better quality of the autogenous weld.

It is thus apparent that with the invention sheet material portions which respectively terminate in the edges 14 and 15 are placed with respect to each other in such a position that these sheet material portions are in edge-to-edge relation, without any overlap, at these edges which thus form a junction line between the sheet material portions. This junction line is situated in a plane illustrated by the vertical center line of FIG. 2 or FIG. 3. The laser-beam generating means 18 is situated with respect to the sheet material portions to direct the laser beam 18a in this plane which contains the junction line formed by the adjacent confronting edges of the sheet material portions toward and into engagement with the edges at this junction line. In order to maintain these sheet material portions in the above edge-to-edge relation, the sheet material portions are clamped to a support means 20 with clamping forces which extend perpendicularly with respect to the sheet material portions in directions parallel to the above plane, and the sheet material portions are held in edge-to-edge relation as set forth above only by way of these clamping forces so that during welding there are no forces pushing the above edges 14 and 15 toward each other, thus avoiding the possibility of creating a surplus thickness at the weld. The laser-beam generating means 18 and the support mean 20 form a pair of means at least one of which is moved with respect to the other for causing the laser beam and junction line to move one with respect to the other in a manner which will cause a weld to be formed between the sheet material portions at the above junction line in a progressive manner progressing longitudinally along the junction line.

Of course the invention is by no means limited to the forms of embodiment described and illustrated which have been given by way of example only. In particular, it comprises all the means constituting technical equivalents to the means described as well as their combinations should the latter be carried out according to its gist and used within the scope of the following claims.