JPS62296982A - Laser welding method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a crater of a weld zone and a lowering of the weld strength by heating first only covering materials until these are vaporized and afterward, projecting a laser beam on base metals to join these metals in case of base metals to be welded which are covered by the covering materials with a lower melting point than the base metals. CONSTITUTION:The covering material 10a of the 1st base metal 10 to be welded and the covering material 12a of the 2nd base metal 12 to be welded are superimposed and positioned so that these materials are faced mutually and a part 18 to be welded is heated by a torch 14 from the upper part of the base metal 12. The heating temperature is selected to the temperature where only the covering materials 10a and 12a are vaporized and the heated part of the covering materials is vaporized and made to a vaporizing body 20 and discharged from between both the base metals to the outside. Next, the laser beam 16a is projected on the part which is heated by the torch 14 by laser welding equipment 16 to join the base metals 10 and 12. Since the covering material of the part to be welded is already removed by the torch 14 in advance, even if the high-temperature laser beam is projected, the explosive vaporization of the covering materials does not take place and the surface without weld defects is obtained.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention The present invention relates to a welding method using a laser beam. When welding them together by superimposing them and irradiating them with a laser beam, it is possible to first heat the low-melting point substance with a torch or the like to vaporize it, and then irradiate the base material with the laser beam to join them. The purpose is to develop a laser welding method that provides a smooth welding surface and a robust welded area.

BACKGROUND ART In recent years, steel sheets coated with coating materials such as zinc and tin have been widely used as exterior members of automobiles in order to enhance the rust prevention effect.

Conventionally, spot welding has been used to join the above-mentioned steel plates, such as galvanized steel plates, by overlapping them. That is, in the spot welding, the galvanized steel sheet that has been polymerized as described above is sandwiched between a pair of electrodes, and the electrodes apply pressure and a current is passed between the electrodes to locally heat and melt the base material. , to join galvanized steel sheets to each other. For this reason, it has been pointed out that there is a problem in that impressions remain on the galvanized fence after welding due to localized pressure and heating.

On the other hand, another welding method for joining coated steel plates as described above is a welding method using a laser. That is, this is a method of welding by polymerizing a workpiece, irradiating the workpiece with a laser beam, and melting the workpiece under the local heating and melting action of the laser beam. However, when this laser welding method is used to weld galvanized steel sheets such as those mentioned above, the zinc, which is a low melting point substance, vaporizes explosively when the laser beam is irradiated, scattering the surrounding molten workpiece. let As a result, there are drawbacks in that sinkholes are formed in the welded area, and pores are formed inside the workpiece even if there is no external problem, resulting in a reduction in welding strength.

Therefore, as a method for solving the above-mentioned drawbacks, there is a method disclosed, for example, in Japanese Patent Application Laid-Open No. 56-62688. That is, when performing laser welding by polymerizing welding base materials, first a recess is formed in one of the welding base materials, and a hollow portion is defined by the welding base metal and the other welding base material. The coating member, which is vaporized explosively by laser beam irradiation, escapes from the hollow portion to the outside.

However, forming a recess in one of the base materials as described above is a complicated process, and furthermore, special equipment must be provided for forming the recess.
The disadvantage is that the economic burden increases.

Further, a different method is disclosed in Japanese Patent Application Laid-Open No. 60-255294. That is, according to this method, a convex portion is provided on one weld base material so that only the convex portion comes into contact with the other weld base material, and as a result, a gap is created between the respective weld base materials. The zinc vaporized by laser beam irradiation is discharged outward from the gap.

However, in this case as well,
Needless to say, this method exposes the same drawbacks as the method shown in No.

The present invention has been made in order to overcome the above-mentioned disadvantages, and when a workpiece coated with a low-melting point substance such as zinc or tin is polymerized and joined by a laser welding method, the low-melting point substance is first applied. is heated with a plasma jet or torch to a temperature at which it melts and vaporizes, and once the low melting point material near the welding area is removed, the heated part is irradiated with a laser beam to join the workpieces. To provide a laser welding method capable of preventing scattering of a molten workpiece caused by explosive vaporization of a low-melting point substance when using a laser beam, and thereby achieving a beautiful finish on a welding surface without welding defects. With the goal.

In order to achieve the above object, the present invention provides a laser welding method in which a welding base material coated with a coating material having a melting point lower than that of the base material is polymerized, and the welding base material is irradiated with a laser beam to perform welding. a first step of heating the welded portion of the welding base material to vaporize the coating material and once removing it; and a second step of irradiating the welded portion with a laser beam to join the welded base materials to each other. It is characterized by consisting of the following steps.

Next, preferred embodiments of the laser welding method according to the present invention will be described in detail with reference to the accompanying drawings.

In FIGS. 1a to 1C, reference numeral 10 indicates a first weld base material 1o, and the surface of the first weld base material 1o is coated with a coating material having a rust-preventing effect, for example, a zinc layer 10a. A second welding base material 12 is superposed on one surface of the first welding base material 10 . In this embodiment, the second
One surface of the weld base metal 12 is also coated with zinc JW 12a as a coating member. In addition, as can be easily understood from the figure, the zinc layer 10a of the first welding base material 1o and the second
The zinc layers 12a of the weld base material 12 are positioned so as to overlap so as to face each other.

Next, when welding the welding base materials laminated as described above, in this embodiment, a torch 14 for vaporizing the zinc layers 10a, 12a and a laser welding device 16 for actually welding are used. be done.

That is, as shown in FIG. 1, the second welding base material 1
The to-be-welded part 18 is heated by the torch 14 from above 2. In this case, reference numeral 18a in the figure indicates a region that is thermally affected by the heating action of the torch 14,
The heating temperature is the coating zinc layer 10a, 12a.
The temperature (approximately 1000° C. to 1400° C.) is selected to allow only vaporization.

As a result, the heated parts of the zinc layers 10a and 12a are vaporized, become a vaporized substance 20, and diffused into the narrow gap between the first welding base material 10 and the second welding base material 12, as shown in FIG. It is discharged to the outside as indicated by the arrow. On the other hand, the zinc layers 10a and 12a near the heating section are heated, but because they are located away from the direct heating action, they are not vaporized and ultimately remain as zinc oxide 22.24.

Then, the zinc oxide 22.24 and the first weld base material 1
0 and the second weld base material 12 define a hollow portion 26 .

Next, as shown in FIG. 1C, the laser beam 16a is irradiated by the laser welding device 16 to the area heated by the torch 14 to join the first weld base material 10 and the second weld base material 12. I do. In this case, the zinc layers 10a and 12a have already been removed by heating the area irradiated with the laser beam 16a with the torch 14 in advance. Therefore, even when the sheet metal is irradiated with a high-temperature laser beam, explosive vaporization of zinc does not occur, scattering of the molten steel plate is prevented, and a welded area 28 with a smooth surface without welding defects is obtained.

In this case, if the laser beam is irradiated immediately after heating with the torch 14, the oscillation output of the laser beam can be lowered, since the higher the surface temperature, the better the absorption rate of the l,-the beam is generally. Therefore, the laser beam oscillator itself can be downsized, and the cost of equipment usage can also be reduced.

As described above, according to the present invention, when performing laser welding by polymerizing the welding base material whose surface is coated with a coating material having a melting point lower than that of the welding base material and irradiating it with a laser beam, first, , a method is used in which the coating material is heated with a plasma jet, a torch, etc. to a temperature at which only the coating material vaporizes, the coating material is removed from the welded part, and then a laser beam is irradiated.

Therefore, in the present invention, the explosive vaporization of the coating material that occurs when the laser beam is irradiated from the beginning, as in the past, is prevented by removing the coating material in advance. The effect is that it is possible to obtain a continuous and good weld area without sinkholes or other irregularities caused by the beam.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design can be made without departing from the gist of the present invention. Of course.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A to 1C are enlarged sectional views of a welded part showing a laser welding method according to the present invention.

Claims (2)

[Claims] (1) In a laser welding method in which a welding base material coated with a coating material having a melting point lower than that of the base metal is polymerized and welding is performed by irradiating the welding base material with a laser beam, the part of the welding base material to be welded is The method is characterized by comprising a first step of heating to vaporize the coating material and once removing it, and a second step of irradiating the welded area with a laser beam to join the weld base materials to each other. Laser welding method. (2) A laser welding method according to claim 1, in which the temperature at which the part to be welded is heated is selected to a temperature at which only the coating material vaporizes.