JPH04258391A - Joining method for galvanized steel sheets - Google Patents

Abstract

PURPOSE:To furnish the joining method capable of performing satisfactory joining of the galvanized steel sheets without being affected by gasified zinc gas, CONSTITUTION:In the joining method of the galvanized steel sheets where the galvanized steel sheets 1 and 2 are superposed on each other and irradiated with a laser beam to perform welding, it is characterized to constitute this joining method of a first stage where while parts to be joined of the above- mentioned steel sheets 1 and 2 being held and press-contacted between a couple of rollers 3 and 4, energizing is executed between the rollers 3 and 4 and heat is generated by contact resistance between the above-mentioned steel sheets 1 and 2 to gasify and remove zinc and a second stage where the parts to be joined of the above-mentioned steel sheets 1 and 2 are irradiated with the laser beam to perform welding.

Description

Description: [0001] The present invention relates to a method for joining galvanized steel plates, which involves stacking galvanized steel plates and welding them by irradiating them with a laser beam. BACKGROUND OF THE INVENTION When galvanized steel plates are layered without any gaps and welded using a laser beam, zinc, which has a low boiling point, vaporizes and blows away the molten iron, resulting in poor surface appearance. As a means to solve this problem, as described in Japanese Patent Application Laid-Open No. 60-255294, a protrusion is formed on either side of the galvanized steel plate, and the protrusion is sandwiched between the two plates. A laser welding method is known in which steel plates are stacked one on top of the other, a predetermined gap is provided between them, and a discharge path for zinc vaporized by laser beam irradiation is formed. On the other hand, if the gap between the two steel plates is too wide, a bridge will not be formed due to burn-through of the steel plates and welding will not be possible. In order to solve this problem, methods are being considered, such as increasing the number of clamps that hold both steel plates together, and using a roll spot welder to smooth out the gaps between welding points by applying pressure. [0004] In the above-mentioned prior art, it is necessary to increase the number of processing steps in order to provide protrusions and grooves in the joint portions of galvanized steel sheets. In addition, there were many unstable factors such as deformation of the steel plate when clamping and pressurizing the steel plate, or difficulty in joining curved parts of the steel plate, making it difficult to put it into practical use. . [0005] Furthermore, when the gap between the steel plates is too wide, if the gap is corrected by the method described above, there is a risk that the gap will become too narrow and welding cannot be performed. The present invention has been made in view of the above points, and an object of the present invention is to provide a method for joining galvanized steel sheets that can perform good joining without generating vaporized zinc gas during laser beam irradiation. With the goal. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for joining galvanized steel plates, in which galvanized steel plates are stacked and welded by irradiating the steel plates with a laser beam. A first step in which the part to be welded is held and pressed between a pair of rollers and electricity is applied between the rollers to generate heat due to the contact resistance between the steel plates to vaporize and remove zinc; The second step is to perform welding by irradiating the beam.
It is characterized by consisting of the following steps. [Operation] According to the above method, by sandwiching and press-welding the stacked galvanized steel plates with a pair of rollers, a gap of an appropriate distance is uniformly formed between the two steel plates, and at the same time, electricity is applied between the rollers. As a result, the pressed portion generates heat due to the contact resistance between the two steel plates, and the zinc in that portion is vaporized and discharged to the outside through the gap. If that part is then irradiated with a laser beam, good bonding is possible since no vaporized gas is generated. [Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of the device used in this example. A roll heating device 5 consisting of a pair of rollers 3 and 4 that clamps two stacked galvanized steel plates 1 and 2, which are members to be welded, is provided on the workpiece conveyance line. A predetermined voltage is applied between the rollers 3 and 4 by a power source (not shown), and a predetermined pressing force is applied by a pressure means (not shown). Further, a laser processing device 6 is provided downstream of the roll heating device 5 in the transport direction. Next, a method for joining galvanized steel plates 1 and 2 using the apparatus having the above configuration will be explained. 2 superimposed objects flowing in the direction shown by arrow A on the workpiece conveyance line
The galvanized steel plates 1 and 2 are sandwiched and pressed between rolls 3 and 4 of a roll heating device 5, so that a uniform and appropriately spaced gap is formed between the steel plates 1 and 2 at the welded portion. At the same time, since a voltage is applied between the rolls 3 and 4, a predetermined current flows. Therefore, the contact resistance between the steel plates 1 and 2 generates heat in the welded portion, and the zinc in that portion is vaporized. This vaporized zinc gas is removed to the outside through the gap. Next, the steel plates 1 and 2 move along the workpiece conveyance line in the direction of arrow A, and a laser beam is irradiated by the laser processing device 6 onto the welded parts from which zinc has been removed. As a result, a good welding beat can be obtained without being affected by vaporized zinc gas. Next, the results of experiments conducted using the method according to this example are shown in Tables 1 and 2 below. [Table 1] [Table 2] [0014] In the experiment shown in Table 1, galvanized steel sheets (SGAC60/60) with a thickness of 1 mm were stacked and heat welded, and good welding was performed. A bead was obtained. Also Table 2
According to the current conditions shown in , similarly good weld beads were obtained in various combinations of plate thicknesses. Furthermore, when using a laser processing device 6 that can use optical fibers such as a YAG laser for welding, welding can be performed without tacking by installing a welding nozzle immediately after the roll heating device 3. It is possible. In addition, when using a laser processing device such as a carbon dioxide laser that cannot use optical fibers, it is also possible to perform zinc removal using the roll heating device 3 and welding using the laser processing device 6 after tack welding by roll spot welding in a separate process. It is possible. Further, when a roll spot welding machine is used as the roll heating device 3, the pressing force is the same as the pressing force when moving between dots during spot welding for temporary attachment. In other words, there is no need for a special process to remove zinc, and when tacking is done using a roll spot welder,
Only a weak current needs to be passed during movement between dots, and the damage to the electrodes is minimal. [0017] According to the present invention as described above, after a galvanized steel plate is sandwiched between rollers and pressed together and electricity is applied to vaporize and remove the zinc, a laser beam is irradiated onto the part to be welded to perform welding. As a result, good bonding can be performed without being affected by vaporized zinc gas.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a schematic configuration of an apparatus used in an embodiment of the present invention.

[Explanation of symbols]

1 Galvanized steel sheet 2 Galvanized steel sheet 3 Roller 4 Roller 5 Roll heating device 6 Laser processing equipment

Claims (1)

[Claims] 1. A method for joining galvanized steel sheets in which galvanized steel sheets are stacked one on top of the other and welded by irradiating the steel sheets with a laser beam, wherein the parts to be joined of the steel sheets are sandwiched and pressure-welded between a pair of rollers while electricity is applied between the rollers. and a first step of vaporizing and removing zinc by generating heat due to contact resistance between the steel plates, and a second step of welding by irradiating the part of the steel plates to be joined with a laser beam. A method for joining galvanized steel sheets.