JP2008137012A - Laser beam welding method and laser beam welding system for surface treated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam welding method which is made easily applicable to the welding of a panel having a complicated shape by improved the adhesive property or the fixability to a weld base material of itself by using a solid material having a low melting point as spacers for ensuring a prescribed gap between the weld base materials. <P>SOLUTION: The low melting point solid material 1 such as a brazing filler metal, paraffin wax or the like which are molten by thermal effect during welding are arranged like dots in the vicinity of a weld line Lw. Gas in the plating layer of the base material is discharged through the gap G which is physically ensured between the base materials (plated steel sheets, for example) W1, W2 by interposition of the low melting point solid materials 1. It contributes to the improvement of the adhesiveness between mutual base materials W1, W2 that the low melting point solid material 1 is molten by the thermal effect during welding and is extended in the gap G. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a laser welding method for a surface-treated steel sheet and a laser welding system used therefor, and in particular, when performing laser welding under a plate set such that a plated steel sheet such as an alloyed hot-dip galvanized steel sheet is on the lower side, plating is performed. The present invention relates to a laser welding method for a surface-treated steel sheet in which welding is performed in a state in which a predetermined gap is secured between weld base materials in order to prevent secondary problems due to evaporation of layers, and a laser welding system used therefor.

  When laser welding is performed in the form of a so-called lap joint after stacking two or more base materials, if the base material that is at least the lower side is, for example, a galvanized steel sheet, the plating layer evaporates due to heat during welding. This becomes gas (zinc vapor), which remains as bubbles in the weld bead, resulting in a decrease in welding strength. This phenomenon is attributed to the fact that the melting point of zinc is about 420 ° C., which is significantly lower than the melting point of iron, 1535 ° C.

As a countermeasure against this, it is effective to provide a physical gap between the welded base metals and positively discharge the air bubbles generated during welding to the outside. Therefore, for example, as described in Patent Document 1, fine solid particles such as steel beads are interposed in the superposed portion of the welded base materials by means such as welding and fixing, and in that state the fine solid Managing the size of the gap between the welded base materials by pressing the base materials including particles from above and below is performed. Then, welding is performed by irradiating a laser beam with a pressurized state by a known method.
JP 2003-290955 A

  However, in the method of sandwiching fine solid particles such as steel beads between the welded base materials as described above, it is possible to ensure a uniform gap between the welded base materials, but securely fix the fine solid particles to the welded base material. This is difficult, and the shape of the applicable weld base material is limited.

  More specifically, in the technique described in Patent Document 1, fine solid particles dispersed on a welding base material are welded by laser beam irradiation, but the fine solid particles themselves are easy to roll. For example, if the weld base material is a slanted part or a complex three-dimensional body panel having a predetermined curvature, the fine solid particles are deposited or deposited. Until then, the fine solid particles roll, and it is difficult to keep the necessary amount of fine solid particles in a necessary part, and a sufficient effect cannot be expected.

  For example, if the amount of fine solid particles adhering or fixing is small, a gap of the required size cannot be secured between the base materials, and porosity still occurs, and the amount of fine solid particles adhering or fixing If the amount is too large, the weld bead will be perforated and defects such as irregularities will occur, making it impossible to ensure the required welding strength.

  The present invention has been made paying attention to such a problem, and intends to solve the above-mentioned problems of the prior art by using a low-melting-point solid material instead of the fine solid particles that are easy to roll. That is, the present invention uses a low-melting-point solid material as a gap material for securing a predetermined gap between weld base materials, thereby improving the adhesion or fixability to the weld base material itself, and a panel having a complicated shape The present invention provides a laser welding method and a laser welding system that can be easily applied to the welding of a laser beam.

  The present invention is a method of performing laser welding in the form of a lap joint after superposing at least two base materials including the surface-treated steel sheet so that the surface-treated steel sheet is on the lower side. Apply a solid melted low melting point solid that can be melted due to the thermal effect during welding to the joint surface of the base metal, solidify the base materials, and overlap the base materials with each other. Laser welding is performed in a state where a predetermined gap is secured by sandwiching an object.

  According to the present invention, since the low melting point solid is melted on the joining surface of any one of the base materials and solidified by being solidified, the gap material is used regardless of the shape of the base material. The low-melting-point solid that will function as a good fixing retention and can retain the required amount of the low-melting-point solid in the required part, so the gap between the welded base metal due to the low-melting solid Securement can be ensured, and it is possible to prevent the occurrence of porosity and insufficient welding strength and improve the welding quality.

  In addition, since the low melting point solid material melts and spreads due to the thermal effect during welding and fills the gaps between the base materials, even if the surface treatment layer such as the plating layer is peeled or thinned by welding The low-melting-point solid material that melts out rust covers the rust-proof performance and can contribute to the improvement of the rust-proof property.

  1 and the following drawings show a more specific embodiment of the laser welding method according to the present invention, and in particular, FIG. 1 shows an outline of the whole welding system used for the laser welding.

  Here, a case where two base materials W1 and W2 are continuously welded in the form of a lap joint using, for example, an alloyed hot-dip galvanized steel plate as a base material, which is a surface-treated steel plate, is shown. Prior to this, there is a feature in means for securing a minute gap between the two base materials W1, W2.

  And when it presupposes performing continuous welding along the linear welding line Lw in the state which piled up base materials W1 and W2, before superposing upper base material W2 on lower base material W1 On the lower base material W1, the low-melting-point solid material 1 is adhered or fixed and held as a gap material for securing a predetermined gap G (see FIG. 2) between the base materials W1 and W2. More specifically, as shown in FIG. 2, the low-melting-point solid material 1 is placed on the lower base material W1 so as to face each other across the weld line Lw at a plurality of locations near both sides of the weld line Lw. Adhered or fixed in a dot shape.

  The low-melting-point solid material 1 used here is a low-melting-point solid material having a melting point of 80 ° C. or lower, such as a brazing material or paraffin wax, which melts by conduction heat during welding and becomes a liquid while becoming a solid at room temperature Etc.

  As a means for attaching or fixing and holding the low melting point solid 1 on the lower base material W1, the low melting point solid 1 is melted as shown in FIG. 1 (here, the low melting point solid is melted). (Referred to as liquid 1a) is stored in a tank 2 with a heat-retaining function, while a sealing robot 3 that functions as a coating means is provided with a coating gun 4 to melt a low-melting-point solid substance quantitatively supplied from the tank 2 The liquid 1a is applied in the form of dots on the lower base material W1 by the autonomous operation of the sealing robot 3. When the low melting point solid melt 1a is applied, the low melting point solid melt 1a is allowed to stand for a predetermined time, and waits for the low melting point solid melt 1a to solidify or solidify into the low melting point solid 1. Since the low melting point solid 1 is firmly fixed and held in the process of solidifying or solidifying on the lower base material W1, for example, the lower base material W1 has a complicated three-dimensional shape. Even if it is, the movement of the low melting point solid 1 on the base material W1 can be prevented in advance, and the low melting point solid 1 can be stably kept at a predetermined position until the welding. .

  Here, the arrangement position of the low melting point solid 1 is not directly affected by the melting of the base materials W1 and W2 by welding, and starts to melt by the conduction heat generated by welding (as described above, Since the melting point of the low-melting-point solid 1 is 80 ° C. or lower, the position where the temperature rises to 100 ° C. or lower is desirable here. As a result of various experiments conducted by the present inventor, it has been found that a range of approximately m = 5 mm or less is preferable as the distance m from the weld bead Be as the weld line Lw as shown in FIG. In addition, the code | symbol P in the figure has shown the range from which the plating layer of the surface of base material W1, W2 peels or becomes thin with the thermal influence accompanying welding.

  In addition, in order to accurately and easily control the amount of the gap G between the base materials W1, W2 due to the low melting point solid 1, the low melting point solid 1 may be made of, for example, glass beads, titanium oxide, alumina or the like. It is desirable to mix so-called inorganic oxide fine solid particles in advance. In this case, the melting point of the fine solid particles mixed in the low melting point solid 1 is higher than that of the low melting point solid 1. Moreover, if the coating film thickness of the low melting point solid 1 is set to about 100 to 200 μm, for example, it is desirable that the particle size of the fine solid particles such as glass beads and titanium oxide to be mixed is about 50 to 100 μm.

  When the low melting point solid material 1 is fixed and held in a dot-like manner on the lower base material W1, the upper base material W2 is superposed on the lower base material W1 so that the two base materials W1 and W2 are placed between each other. A plurality of point-like low-melting-point solids 1 are interposed. At this time, even if the upper base material W2 is superposed, the plurality of low melting point solids 1 are immobile, and are interposed between the upper and lower base materials W1 and W2 so that the coating thickness of the low melting point solids 1 is increased. A corresponding predetermined gap G is secured between the upper and lower base materials W1, W2.

  In this state, as shown in FIG. 2, the base materials W1 and W2 and the laser processing head 7 are moved relative to each other (the relative movement direction in FIG. 2 is a direction perpendicular to the paper surface). If the fixed side is used, the laser processing head 7 is continuously moved at a predetermined speed along the welding line Lw, and the base materials W1 and W2 are welded together by irradiating the laser beam 8 from the upper base material W2 side. To do. More specifically, as shown in FIG. 1, by moving a laser processing head 7 provided at the tip of an arm 6 of a welding robot 5 as laser welding means continuously along a welding line Lw, a base material W1, Weld W2 together. If necessary, the vicinity of the weld line Lw is pressure-restrained by a clamping means (not shown) or the vicinity of the weld line Lw by a pressure pin or a pressure roller attached to the laser processing head 7 in advance. Shall be restrained under pressure.

  In this case, since the base materials W1 and W2 to be welded are alloyed hot-dip galvanized steel plates, the plating layers on the surfaces of the base materials W1 and W2 are melted as the base materials W1 and W2 themselves melt at the welded portion. As is well known, gas (zinc vapor) is generated by evaporation of these gases, but these gases are smoothly discharged to the outside through a gap G secured in advance between the base materials W1 and W2. Therefore, defects such as porosity and non-welding do not occur in the weld bead Be (see FIG. 3).

  On the other hand, it is known that the welding state becomes unstable at the start and end points of welding (the start and end portions of the weld bead Be), and problems such as poor welding and perforation are likely to occur. When the welding line Lw is changed or when the welding line Lw is short (for example, when the length of the welding line Lw is 30 mm or less), the tendency becomes more remarkable.

  In the present embodiment, since the periphery of the weld bead Be, which is the weld line Lw, is warmed by the influence of heat (conduction heat) generated during welding, a gap G is secured between the base materials W1 and W2 until then. The low-melting-point solid material 1 functioning as a gap material for melting melts and spreads into the gap G, thereby filling the gap G. As a result, the adhesion between the base materials W1 and W2 is improved. Become.

  In addition, since the low-melting-point solid material 1 melts and spreads into the gap G, it covers the start and end portions of the weld line Lw (weld bead Be) that easily causes poor welding. Even when this occurs, the melted low melting point solid material 1 serves to fill the hole. Furthermore, in the part which received the thermal influence at the time of welding as mentioned above in the joint surface of base materials W1 and W2, a plating layer becomes thin or peels, and rust prevention performance falls. 3 is a part marked with a symbol P). On the other hand, since the low melting point solid 1 that has melted as described above covers the portion P where the plating layer is thinned or peeled off, the rust prevention performance is recovered and the rust prevention performance is not reduced. It will be.

  Here, the present inventor tried to find the optimal arrangement of the low-melting-point solid 1 with respect to the weld line Lw from the viewpoint of preventing the occurrence of porosity.

  The base material was an alloyed hot-dip galvanized steel sheet (SP783) with a plate thickness of 1.0 mm, and the two base materials were laser welded in the form of a lap joint. The laser used was a YAG laser with an output of 3.6 kW and a welding speed of 5 m / min.

  As shown in the pattern (1) in FIG. 4A, in the case of a linear weld line Lw (weld bead Be) and the length of the weld line Lw is 10 mm or less, welding is performed. It has been found that no porosity is generated when the low-melting-point solids 1 are arranged at both ends of the line Lw on the extended line or symmetrically arranged across the weld line Lw.

  On the other hand, in the case of the linear weld line Lw and the length of the weld line Lw is as long as about 10 mm to 30 mm, as shown in a pattern (2) in FIG. It has been found that when the low melting point solid 1 is placed symmetrically across the weld line Lw at the center in the longitudinal direction in addition to the both ends of the weld line Lw on the extended line, no porosity is generated. In addition, when the length of the welding line Lw becomes longer to 30 mm or more, it copes with increasing the number of the low melting point solid objects 1 of symmetrical arrangement with a span of 10 to 15 mm. Moreover, arrangement | positioning of the low melting point solid substance 1 shown as a pattern (2) in (A) of FIG. 4 is applicable also when the length of the welding line Lw is 10 mm or less like a pattern (1).

  On the other hand, as shown in (B) of the figure, when the weld line Lw is O-shaped with a diameter of about 8 to 10 mm or C-shaped, the low-melting-point solid material 1 is placed at the center of the circle of the weld line Lw. It was found that there was no porosity when placed. Furthermore, when the circle diameter of the weld line Lw is larger, as shown at the right end of FIG. 4B, when the low melting point solid 1 is arranged at the start and end portions in addition to the center portion of the circle, It was proved effective in preventing the occurrence.

  Also, as shown in (C) of the figure, in the case of a so-called S-shape in which two incomplete circles having a weld line Lw of about 4 to 5 mm are connected, a low melting point is formed at the center of each circle. It has been found that when the solid material 1 is disposed, or the low melting point solid material 1 is disposed at the start and end portions of the weld line Lw in addition to the central portion of each circle, no porosity is generated.

  In the above embodiment, the plate assembly in which the base materials W1 and W2 are both alloyed hot-dip galvanized steel plates has been described. However, at least the lower base material W1 may be a surface-treated steel plate such as a plated steel plate. For example, the present invention can be applied to welding other plate sets.

The schematic explanatory drawing of the whole welding system with which the laser welding of this invention is provided. The principal part expanded sectional explanatory drawing of the welding part in FIG. FIG. 3 is a further enlarged explanatory view of FIG. 2. Explanatory drawing which shows the preferable arrangement | positioning relationship between a welding line and the low melting point solid substance of the vicinity.

Explanation of symbols

1 ... Low melting point solid 3 ... Sealing robot (coating means)
DESCRIPTION OF SYMBOLS 4 ... Coating gun 5 ... Welding robot 7 ... Laser processing head 8 ... Laser beam Be ... Welding bead G ... Gap Lw ... Welding line W1 ... Base material (alloyed hot-dip galvanized steel sheet)
W2 ... Base material (alloyed hot-dip galvanized steel sheet)

Claims (6)

A method of performing laser welding in the form of a lap joint after overlapping at least two base materials including the surface-treated steel sheet so that the surface-treated steel sheet is on the lower side,
Apply and solidify the melted low melting point solid that can be melted by the thermal effect during welding on the joint surface of either one of the base materials,
A laser welding method for a surface-treated steel sheet, characterized in that laser welding is performed in a state in which a predetermined gap is secured by superposing base materials and sandwiching a low melting point solid material between the base materials.   2. The surface according to claim 1, wherein laser welding is performed along the weld line in a state in which a predetermined gap is secured by sandwiching a low-melting-point solid substance at a position in the vicinity of the weld line between the base materials. Laser welding method for treated steel plate.   After the melted low-melting-point solid material is applied onto the lower base material and solidified, the upper base material is overlaid from above, and a laser beam is irradiated from the upper base material side. The laser welding method for a surface-treated steel sheet according to claim 1, wherein laser welding is performed.   The method of laser welding a surface-treated steel sheet according to any one of claims 1 to 3, wherein the low-melting-point solid material is sandwiched between the bases and at least in the vicinity of the start / end portion of the weld line.   The laser-welding method for a surface-treated steel sheet according to any one of claims 1 to 4, wherein fine solid particles having a melting point higher than that of the low-melting-point solid are mixed in the low-melting-point solid in advance. . A laser welding system used for the laser welding method according to claim 1,
A state in which the upper base material is overlaid on the lower base material after the low melting point solid has solidified after the low melting point solid material is applied on the lower base material. And laser welding means for performing laser welding by irradiating a laser beam from the upper base metal side,
The laser welding means performs laser welding along a preset welding line in a state where a gap corresponding to the thickness of the low melting point solid is secured between the upper and lower base materials. A featured laser welding system.

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