JP2011115836A - Method of laser welding metal plated plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method which dispenses with a special mechanism for forming minute gaps between metal plated plates and which ensures welding quality. <P>SOLUTION: A laser head 13 is prepared that emits a laser beam 18 through a condensing lens 16 to converge the laser beam 18 at the focal position P of the condensing lens 16. Galvanized steel plates 11, 12 are superimposed closely without a gap. Then, the surface of the galvanized steel plate 12 in the superimposed part is irradiated with the laser beam 18 by the laser head 13, so that the steel plate portion in the laser irradiation region 19 is fused to form a welded joint. In this instance, for the purpose of making the irradiation region 19 of the laser beam 18 be the size in which no welding defect is generated in the weld zone by the jetting of zinc gas, the focal position P of the laser beam 18 is shifted upward from the surface of the galvanized steel plate 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for laser welding an overlapped portion of a plurality of metal plated plates.

  A galvanized steel sheet is a steel sheet material in which the surface of a steel sheet, which is a base metal sheet, is galvanized for rust prevention, and is often used as a structural material for automobile bodies. In the case of forming a vehicle body or the like, a laser welding method is known in which two galvanized steel plates are superposed and the superposed portion is irradiated with laser light to melt and bond the steel plates.

  When the laser welding is performed, it is known that welding defects occur due to the boiling point of zinc (about 900 ° C.) being lower than the melting point of steel plate (iron) (about 1500 ° C.). That is, by irradiating the overlapped portion with laser light, the steel sheet is melted. At this time, the zinc on the overlapped surface is gasified. And zinc gas tends to escape outside through the molten steel plate. As a result, a part of the molten steel sheet is blown away, or a part of the zinc gas remains inside the steel sheet, forming pores called blow holes, deteriorating the welding strength, and the appearance is deteriorated. (See Patent Document 1)

  In order to prevent such welding defects such as blow holes, Patent Documents 2 and 3 disclose a method of forming a minute gap for plating metal gas escape between stacked metal plating plates. Yes.

JP 2009-262187 A JP 2001-162387 A JP 2007-038269 A

  However, in the method of forming a minute gap for escaping the plating metal gas between the metal plating plates stacked as described above, it is necessary to use a special mechanism for forming the minute gap. Such a mechanism is more complicated than a mechanism in which metal-plated plates are brought into close contact with each other.

  Accordingly, an object of the present invention is to provide a laser welding method for a metal plating plate that ensures welding quality without using a special mechanism for forming a minute gap.

  The present invention superimposes a plurality of metal plating plates formed by plating a metal having a boiling point lower than the melting point of the base metal plate on the surface of the base metal plate, and lasers the overlapped portion of the metal plating plate. In a laser welding method of a metal plating plate in which a plurality of the metal plating plates are welded by irradiating light, a laser head that emits laser light through a condenser lens and condenses the laser light at a focal position of the condenser lens Preparing and laminating the plurality of metal plated plates in close contact with each other, and irradiating a laser beam on the surface of the metal plated plate in the overlapped portion by the laser head to form a base metal in a laser irradiation region. A step of melting and forming a weld joint, and the irradiation region of the laser beam is large enough to prevent a weld defect caused by ejection of a plating metal gas at the weld joint. So that is, it is characterized in that shifting the focal position of the laser light from the surface of the metal plating plate.

  According to the present invention, since the laser irradiation is performed in a state where a plurality of metal plating plates are closely adhered and overlapped without gaps, a mechanism of a jig for fixing the metal plating plates can be simplified.

  And according to the present invention, since the laser beam is defocused and irradiated so that the area of the laser irradiation region is increased to some extent, the area of the molten pool formed by melting the base metal in the laser irradiation region The plating metal gas can be released to the outside stably at a low pressure through the molten pool. Thereby, it is possible to prevent the molten metal from being blown out by the plating metal gas and welding defects such as blow holes.

  According to the present invention, the laser beam irradiation is performed in a state where the metal plated plates are in close contact with each other, so that a special mechanism for forming a minute gap between the metal plated plates is not required, and the welding quality is ensured. Can do.

It is a figure which shows the structure of the laser processing apparatus of embodiment of this invention. It is a perspective view which shows the circular welding part formed by the laser welding method of embodiment of this invention. It is sectional drawing of the overlapping part of the galvanized steel plate explaining the laser welding method of embodiment of this invention. It is a figure which shows the other structure of the laser processing apparatus of embodiment of this invention. It is a perspective view which shows the line-shaped welding part formed by the laser welding method of embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described. First, the configuration of the laser processing apparatus will be described with reference to FIG. As shown in the drawing, two galvanized steel plates 11 and 12 are placed on the laser processing table 10 in an overlapped state.

A laser head 13 is arranged above the laser processing table 10 on which the galvanized steel plates 11 and 12 are placed. A laser beam 18 generated by a fiber laser oscillator 17 via an optical fiber 14 is placed on the laser head 13. Is output. Instead of the fiber laser oscillator 17, another type of laser oscillator such as a YAG laser oscillator or a CO ₂ laser oscillator may be used.

  The laser head 13 houses a collimation lens 15 and a condenser lens 16. The laser light 18 from the fiber laser oscillator 17 is first converted into parallel rays by the collimation lens 15, and the parallel rays are emitted through the condenser lens 16 and condensed at a predetermined focal position P.

  Further, the laser head 13 can be moved in the X and Y directions within the surface of the upper galvanized steel sheet 12 and in the Z direction perpendicular to the surface of the galvanized steel sheet 12 by moving means such as a laser processing robot. It is configured. Further, the angle of the laser beam 18 emitted from the laser head 13 with respect to the Z direction is configured to be adjustable. For example, the rotation axis of the laser head 13 is adjusted so that the angle can be adjusted within a range of ± 15 °. You may comprise so that rotation is possible at the center.

  Therefore, by moving the laser head 13 in the Z direction, the focal position P of the laser beam 18 emitted from the laser head 13 is moved in the Z direction, and the irradiation area 19 (circular when viewed from the direction perpendicular to the galvanized steel sheet 12) is obtained. Can be changed. The energy density of the laser beam 18 is the energy per unit area of the irradiation region 19. If the output of the fiber laser oscillator 17 is constant, the energy density of the laser beam 18 is inversely proportional to the area of the irradiation region 19.

  Hereinafter, the laser welding method of the galvanized steel sheet according to the present embodiment will be described. First, as shown in FIG. 1, two galvanized steel plates 11 and 12 are placed on a laser processing table 10 in a state of being overlaid. In this case, the galvanized steel plates 11 and 12 are pressed by a fixing jig from above and below, so that the overlapping portions of the galvanized steel plates 11 and 12 are brought into close contact with no gap. In this case, the galvanized steel plate 11 is a lower plate and the galvanized steel plate 12 is an upper plate.

  Next, the laser head 13 is moved in the X, Y, and Z directions by the laser processing robot and is positioned on the overlapping portion of the galvanized steel plates 11 and 12. And, by irradiating the laser beam 18 from the surface of the galvanized steel sheet 12 of the overlapping portion toward the inside for a predetermined time, the steel material portions of the galvanized steel sheets 11 and 12 in the irradiation region 19 of the laser beam 18 are heated and melted, Thereafter, natural cooling is performed to form a circular welded joint 20 as shown in FIG.

  At this time, as shown in FIGS. 1 and 3, the irradiation region 19 of the laser beam 18 has a focal position P of the laser beam so that a welding defect due to zinc gas ejection does not occur in the weld joint 20. Is shifted upward from the surface of the galvanized steel sheet 12. That is, the area of the irradiation region 19 is increased by defocusing the laser beam from the irradiation surface (the surface of the galvanized steel sheet 12).

  Thereby, as shown in FIG. 3, the planar area of the molten pool 23 formed when the steel material part of the galvanized steel plates 11 and 12 melts increases to some extent. By heating by the irradiation of the laser beam 18, the plated zinc is vaporized and the zinc gas 22 is generated from the irradiation region 19 and the zinc gas generation region 21 on the contact surface of the galvanized steel plates 11 and 12 in the vicinity thereof. Then, the zinc gas 22 generated from the zinc gas generation region 21 escapes to the outside through a large molten pool 23 with a low pressure. Thereby, it is possible to prevent the molten steel material from being blown off by the zinc gas 22 and welding defects such as blow holes.

  Moreover, according to this embodiment, since it can weld in a short time by one laser irradiation, there also exists an advantage that productivity is high.

  The inventor conducted an experiment for demonstrating the effect of the present invention using the laser processing apparatus of FIG. In this case, the galvanized steel plates 11 and 12 were irradiated with the laser beam 18 in a state of being in close contact with each other as described above. The laser head 13 was kept stationary with respect to the galvanized steel plates 11 and 12 during the irradiation of the laser beam 18. The experimental results are shown in Table 1.

先ず、２枚の亜鉛メッキ鋼板１１，１２の厚さが各０．７ｍｍの場合、レーザー光１８の照射領域１９のスポット口径を６〜８ｍｍとし、０．５秒間のレーザー照射を行った。レーザー光出力は３ｋＷキロワットであった。

First, when the thickness of the two galvanized steel sheets 11 and 12 was 0.7 mm, the spot diameter of the irradiation region 19 of the laser beam 18 was set to 6 to 8 mm, and laser irradiation was performed for 0.5 seconds. The laser light output was 3 kW kilowatts.

In addition, when the thickness of the galvanized steel plates 11 and 12 is relatively thick at 1.2 mm each,
The laser irradiation time was set a little longer to 0.8 seconds and the output power of the laser beam 18 was set to 4 kW, but the spot diameter of the laser beam irradiation region 19 was set to 6 to 8 mm. According to these experiments, there was no welding defects such as blown molten steel and blowholes, and the welding quality was good.

  On the other hand, conventional laser welding conditions Conventional technology, that is, when the spot diameter is about 0.5 to 1.0 mm, blown molten steel or weld defects such as blow holes occur, resulting in welding quality. Was bad.

  That is, in the prior art, when the galvanized steel plates 11 and 12 are brought into close contact with each other, it is difficult to prevent welding defects. This is because if the area of the irradiation region 19 of the laser beam 18 is small, the area of the molten pool 23 also decreases, and the pressure in the molten pool 23 of the zinc gas 22 trying to escape through the molten pool 23 increases.

  In contrast, the present inventor has found that welding defects can be prevented by intentionally shifting the focal position P of the laser beam 18 from the surface of the galvanized steel sheet 12 to increase the irradiation region 19 of the laser beam 18. It was. This is because the pressure in the molten pool 23 of the zinc gas 22 is lowered by increasing the planar area of the molten pool 23.

  In this case, how much the focal position P of the laser beam 18 is shifted in order to prevent welding defects depends on various conditions such as the thickness of the galvanized steel plates 11 and 12, the output power of the laser beam 18, and the irradiation time. First, under various conditions, the focal position P of the laser beam 18 (the size of the irradiation region 19 of the laser beam 18) is experimentally determined using test samples of the galvanized steel plates 11 and 12, and then The laser welding of the actual galvanized steel sheets 11 and 12 is preferably performed under the determined focal position P of the laser beam 18 (the irradiation area 19 of the laser beam 18 is large).

  In the embodiment described above, the focal position P of the laser beam 18 is shifted upward from the surface of the galvanized steel sheet 12 by fixing the laser head 13 at a position raised in the Z direction. As a result, the secondary effect of preventing interference between the fixing jig 13 and the fixing jig of the galvanized steel sheet 12 can be obtained.

  When there is no possibility of such interference, the laser beam 18 may be defocused by bringing the laser head 13 close to the surface of the galvanized steel sheet 12 as shown in FIG. That is, the focal position P of the laser beam 18 is shifted downward from the surface of the galvanized steel sheet 12. Also in this configuration, since the area of the irradiation region 19 of the laser beam 18 can be increased, the effect of preventing welding defects can be obtained as in the above-described embodiment.

  In the above-described embodiment, the laser head 13 is stationary with respect to the galvanized steel plates 11 and 12 to form the circular weld joint 20 during the irradiation of the laser beam 18. By moving X in the X direction or the Y direction, the defocused irradiation region 19 can be moved to form the line-shaped weld joint 24.

  Although the irradiation region 19 is set in the overlap portion of the galvanized steel plates 11 and 12 in FIG. 5, it may be set in a boundary portion of the overlapped galvanized steel plates 11 and 12. According to the inventor's experiment, in order to prevent welding defects, the moving speed of the irradiation region 19 of the laser beam 18 is 1.4 m / min, which is lower than that of the normal laser welding of about 5 m / min. There was a need. Also in this case, as described above, it is preferable to set conditions such as the moving speed in advance using test samples of the galvanized steel plates 11 and 12.

  Moreover, in the said embodiment, although laser welding is performed in the state which piled up the two galvanized steel plates 11 and 12, this invention is laser welding in the state which piled up three or more galvanized steel plates. It can also be applied to the case where This is because the pressure of the zinc gas 22 can be lowered by forming a large molten pool even in such a case.

  Furthermore, the metal plating plate to be laser welded according to the present invention is not limited to a galvanized steel plate, but a metal having a boiling point lower than the melting point of the steel plate, such as aluminum or tin, is plated on the surface of the steel plate. The metal plating board which becomes may be sufficient. Further, the material of the base metal plate is not limited to iron, and may be, for example, an alloy of iron and other elements.

DESCRIPTION OF SYMBOLS 10 ... Laser processing table 11 ... Galvanized steel plate 12 ... Galvanized steel plate 13 ... Laser head 14 ... Optical fiber 15 ... Collimation lens 16 ... Condensing lens 17 ... Fiber Laser oscillator 18... Laser beam 19... Laser beam irradiation area 20... Circular weld joint 21... Zinc gas generation area 23. Line-shaped weld joint

Claims (4)

A plurality of metal plating plates formed by plating a metal having a boiling point lower than the melting point of the base metal plate are superposed on the surface of the base metal plate, and a laser beam is irradiated to the overlap portion of the metal plating plate. In the laser welding method of the metal plating plate for welding a plurality of the metal plating plates,
Prepare a laser head that emits laser light through a condenser lens and collects the laser light at the focal position of the condenser lens.
A step of closely adhering the plurality of metal plated plates without gaps; and
Irradiating a laser beam on the surface of the metal plating plate of the overlapped portion by the laser head, thereby melting a base metal plate in a laser light irradiation region to form a weld joint,
The laser beam focus position is shifted from the surface of the metal plating plate so that the irradiation region of the laser beam has such a size that a welding defect due to the ejection of plating metal gas does not occur in the weld joint. Laser welding method for metal plated plate.   The laser welding method for a metal plated plate according to claim 1, wherein the focal position of the laser beam is shifted upward from the surface of the metal plated plate.   3. The method of laser welding a metal plated plate according to claim 1, wherein the laser head is stationary with respect to the metal plated plate while the laser beam is irradiated.   4. The metal plated plate according to claim 1, wherein the base metal plate is steel, and the metal plated on the surface of the base metal plate is zinc or aluminum. 5. Laser welding method.

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