Laser Welding Method

The present invention relates to a laser welding method for welding materials with a laser beam and to an apparatus for practicing this method. More particularly, the invention relates to a laser welding method in which a plurality of materials to be welded are stacked one on another and welded together and to an apparatus for practicing the method.

A laser welding apparatus of this type is disclosed in Japanese Laid-Open Patent Application No. 47590/1983. In that apparatus, upper and lower rollers are arranged in such a manner that materials to be welded which have been stacked together are held thereby, and the upper roller presses the materials to be welded while being rotated. The welding operation is carried out by applying a laser beam to the materials to be welded, which are moved horizontally while being held between the upper and lower rollers.

In the conventional welding machine constructed as described above, in the case where materials to be welded are coated members formed by plating or coating base plates such as steel plates with zinc or tin, or more specifically, when the materials to be welded are zinc-plated steel plates as shown in FIG. 1, when the zinc-plated steel plates 1 and 2 are rendered molten by a laser beam 3, the zinc deposits 4 through 7 becomes zinc vapor 8 instantaneously because the melting point of the zinc deposits 4 through 7 is much lower than that of the steel base. In this case, as the zinc-plated steel plates 1 and 2 are forced into close contact with each other, the zinc vapor 8 is forced to jet into a hole 9 formed by molten metal 10, thus blowing the molten metal. As a result, the hole 9 become irregular in configuration. Thus, during the welding operation, the molten metal cannot completely fill the hole 9, and therefore many voids 12 are liable to be formed in the solidified metal 11. This is a disadvantage of the conventional welding machine.

The present invention is intended to eliminate the above-described difficulties accompanying a conventional welding machine.

In accordance with this and other objects, the invention provides a laser welding method in which materials to be welded are held in such a manner as to have a suitable air gap therebetween through which the vapor of a covering material such as zinc is released, whereby the resultant weld is excellent, having no defects such as air holes.

FIG. 1 is an explanatory diagram used for a description of a conventional laser welding method;

FIG. 2 is an explanatory diagram showing the arrangement of a welding apparatus constructed in accordance with a preferred embodiment of the invention; and

FIG. 3 is an explanatory diagram used for a description of a laser welding method practiced with the welding apparatus in FIG. 2.

A preferred embodiment of the invention will now be described. As shown in FIG. 2, a material to be welded, namely, a zinc-plated steel plate 2, is placed on a welding table 13 and a spacer 14 having a thickness G is placed on the steel plate 2. Another zinc-plated steel plate 1 is placed on the spacer 14. Under this condition, the steel plates and the spacer are pressed by a clamper 15, as a result of which a predetermined uniform air gap is formed between the confronting surfaces of the overlapping parts of the zinc-plated steel plates 1 and 2 due to the presence of the spacer 14. The spacer 14 and the clamper 15 are connected to driving cylinders 17 and 18, respectively, so as to be moved vertically.

With the predetermined air gap 16 formed between the overlapping parts of the zinc-plated steel plates 1 and 2 as described above, the welding operation is carried out by applying a laser beam 3 to the steel plates as indicated in FIG. 3. In this case, the zinc vapor 8 of the zinc deposits 4 and 5 can flow into the air gap 16, and therefore the configuration of the hole 9 formed by molten metal 10 is maintained satisfactory. Accordingly, as the welding point is moved, the hole 9 is completely filled with the molten metal 10. Therefore, no air holes are formed in the solidified metal 11. Thus, the resultant weld is satisfactory in quality.

An example of the results of a welding operation carried out according to the above-described embodiment will be described. The welding operation was carried out by applying a CO.sub.2 laser to materials as indicated in Table 1. The number of air holes (12) formed in the welds were counted using an X-ray photographing technique. The results of the inspection are as indicated in Table 2. As is apparent from Table 2, no air holes were formed when the thickness of the spacer was 0.1 mm to 0.5 mm.

In the above-described embodiment, zinc-plated steel plates are employed as the materials to be welded. However, the same effect can be obtained with tin-plated steel plates or the like the metal coatings of which have lower melting points than the base materials. In addition, the same effect can be obtained with materials which are coated with a paint which is gasified by the welding heat.

In the above-described embodiment, the materials to be welded are two zinc-plated steel-plates. However, the same effect can be obtained in the case also where more than two materials to be welded are laid one on another.

Furthermore, in the described embodiment, the materials to be welded are covered with metal. However, it should be noted that the same effect can be obtained with materials which are not covered with metal or with materials which are coated by oil or the like which is gasified by the welding heat.

In the described embodiment, a spacer is used to provide the air gap between the materials to be welded. However, the same effect can be obtained by other methods.

As is apparent from the above description, in accordance with the invention, laser welding is carried out with an air gap provided between overlapping parts of materials to be welded. The resultant weld has an excellent quality, having no defects such as air holes.