JP2008194730A - Fuel tank manufacturing method and fuel tank - Google Patents

Abstract

The present invention provides a welding method that increases energy efficiency while suppressing contact defects when manufacturing a fuel tank for automobiles from hexavalent chromium-free plated steel sheets.
SOLUTION: A hexavalent chromium-free plated steel sheet such as a tin-zinc (Sn-Zn) plated steel sheet is subjected to a drawing process, and a pair of halves each having a flange portion formed along the outer periphery of a recess by the drawing is formed. A pair of halves face each other on the inner surface side, and the flanges face each other and are welded by laser beams along the opposed flanges. During welding, the welding beam moves while drawing a triangle. l1, l2, l3 and a sawtooth weld P is formed along the flange.
[Selection] Figure 4

Description

  The present invention relates to a method for manufacturing a fuel tank for automobiles or the like from hexavalent chromium-free plated steel sheets.

  As a measure against environmental pollution, there has been a demand for hexavalent chromium-free steel plates for fuel tanks for automobiles. That is, as a material for the fuel tank, a steel plate is used after being plated with a corrosion-resistant film, but a material containing hexavalent chromium as a plating solution has been used in the past, but the environment caused by elution of hexavalent chromium ions from the plating layer Due to concerns about contamination, hexavalent chromium-free plated steel sheets such as tin-zinc (Sn-Zn) -plated hexavalent chromium-free plated steel sheets have attracted attention as those having a surface treatment layer that does not cause elution of these ions.

  The fuel tank is usually formed by drawing the upper and lower flanged halves from the plated steel plate, and the upper and lower half flanges are integrated by welding. As a welding method, seam welding has been most commonly used, but laser welding has also been proposed. In both seam welding and laser welding, the welding beam is usually moved forward along the overlapping flange portion (Patent Document 1).

  Conventionally, the welding beam is moved forward along the flange portion to obtain a weld portion along the flange portion. Since the welding beam only moves forward, there is only one heat input by the welding beam at the weld, and after the heat input, the temperature of the weld only decreases monotonically, and the solidification rate is fast, so during the combustion Since the gas generated by the combustion of the plating material such as zinc generated is not released to the atmosphere but remains in the bead, it becomes a welding defect and is not suitable for a plated steel sheet. Therefore, the material is limited to a material such as a stainless material that does not have a problem of gas generation as described in Patent Document 1, and the material is expensive, leading to an increase in cost.

In view of this, there has been proposed a technique in which a laser beam is moved while being circularly moved to obtain a coil-shaped weld along the flange (Patent Document 2). By moving while drawing a circle, once the heat input part is reheated (heated) before solidification, the solidification rate slows down, so it is easy for gas to be released into the atmosphere, and blowholes and porosity The risk of occurrence is reduced.
Japanese Patent Laid-Open No. 2003-2102 Japanese Patent No. 3238977

  Moving the welding beam in a circular motion slows the solidification rate, and even a fuel tank made from hexavalent chromium-free plated steel plate is a countermeasure against environmental pollution, but moves the welding beam in a circular motion. If it does, there will be a problem that the welding path is relatively extended, the amount of energy entering is increased, and the manufacturing cost is deteriorated accordingly.

  An object of the present invention is to increase energy efficiency while suppressing welding defects when manufacturing a fuel tank from a hexavalent chromium-free plated steel sheet.

  In the fuel tank manufacturing method of the present invention, a hexavalent chromium-free plated steel sheet is subjected to drawing, and a pair of halves each having a flange portion formed along the outer periphery of the recess formed by the drawing is formed. The recesses face each other on the inner surface side, and the respective flange portions are opposed to each other and welded along the opposed flange portions. During welding, the welding beam is moved along the flange portion while drawing a triangle.

  Here, as the hexavalent chromium-free plated steel sheet, there is a tin-zinc (Sn-Zn) hexavalent chromium-free plated steel sheet. However, the present invention can be realized not only in the tin-zinc plated steel sheet but also in other hexavalent chromium-free plated steel sheets.

  Since the laser beam is moved along the flange contact portion while drawing a triangle, the weld bead is basically formed in a sawtooth shape, but in the adjacent triangle portion, the weld bead is temporarily retracted with respect to the welding direction. It has a bent shape and a triangular local loop at this site. Therefore, since re-entry heat before solidification of the part cooled after heat input first is obtained and the solidification rate becomes relatively slow, even in welding hexavalent chromium-free plated steel sheets such as tin-zinc plated steel sheets Gases are easily released into the atmosphere, and the risk of blowholes and porosity is reduced.

  The movement of the triangle of the laser beam provides the same weld defect prevention effect as the re-entry circular motion before solidification, and the movement length of the laser beam is relatively shortened compared to the circular motion, resulting in energy efficiency. Can be increased.

  In the embodiment of the present invention, the fuel tank is formed of a hexavalent chromium-free plated steel plate such as a Sn—Zn (tin-zinc) plated steel plate. Sn-Zn-plated steel sheet is a cold-rolled steel sheet with a thickness of 0.7-1.0mm, plated with Sn-Zn alloy. Eutectic composition so that Zn is finely dispersed with respect to Sn in the plating layer. I am doing. The weight ratio of Sn and Zn in the plating layer is 5 to 10 wt%.

  FIG. 1 schematically shows the structure of a fuel tank, which includes upper and lower halves 10 and 12. The halves 10 and 12 are recessed by subjecting the Sn-Zn plated steel sheet to a drawing process using a press machine (the recessed portions are indicated by 10A and 12A in FIG. 2), and the flange portions 10-1, 12-1 (FIG. 2) is formed. As shown in FIG. 2, the recesses 10A and 12A are opposed to each other and the flanges 10-1 and 12-1 are opposed to each other (in the case of laser welding, a small gap is formed between the opposed flanges 10-1 and 12-1). And welding is performed along the entire circumference of the facing portion.

  The half tanks 10 and 12 are opposed to each other by the flanges 10-1 and 12-1 so that the depressions 10A and 12A are opposed to each other, and welding is performed along the facing surface. In the form, the fuel tank has a recessed portion 10 'on the side surface. Therefore, the welding line is also recessed in the recessed portion 10 'at the opposing portion of the flange portions 10-1, 12-1, and in the case of seam welding, the electric plate wheel is in the flange portion 10-1, in the recessed portion 10'. There is a concern that welding will be impossible due to interference at the opposing part of 12-1. Therefore, it is preferable to employ laser welding in the case of the fuel tank having the shape shown in FIG. That is, in laser beam welding, a CO2 or YAG laser beam is used as a heat source, and the laser beam is applied to the flange portions 10-1 and 12-1 from the upper surface as indicated by an arrow f in FIG. In the case of laser welding, there is no concern of mechanical interference as in the case of the electric plate wheel in the case of seam welding, and the opposing portions of the flange portions 10-1 and 12-1 also in the recessed portion 10 'on the side surface of the fuel tank , The welding beam f can be moved without interfering with the recessed portion 10 ′. As is well known, in laser welding, it is indispensable to maintain a gap between the welded portions. When laser welding is employed as the welding method, the flange portions 10-1, 12 that are welded portions are used. It is necessary to perform the welding operation while maintaining a strictly predetermined gap between -1.

  In the present invention, as shown in FIG. 3, the laser beam has a triangular shape along flange portions 10-1 and 12-1 that are opposed to each other at a predetermined minute gap in the upper and lower fuel tank halves 10 and 12, which are welded portions. It is moved like an arrow while drawing a trajectory. That is, the movement of the laser beam is composed of a combination of a closed triangular movement and a linear movement along the welded portion. Therefore, although the locus of the laser beam is basically a sawtooth shape as shown in FIGS. 3 and 4, the connection portion of the adjacent chevron portion in the sawtooth shape is welded by the laser beam retreating once and re-advancing. It intersects with the part of. That is, considering the heat input / output in the region indicated by P in FIG. 4, the heat is input at the line 11, retreats at the line 12, and the heat input portion of the 11 is cooled once, but is re-established at the line 13 while being unsolidified. Heat input. That is, at each welding site, re-entry heat before solidification after heat input is obtained, and the solidification rate is relatively slow, so that gas is easily released to the atmosphere, and blow holes and porosity are generated. There is less fear.

  As an embodiment of the present invention, welding can be performed by laser-arc hybrid welding. In this case, the welding beam of the present invention refers to a combination of a laser beam and an arc. FIG. 5 shows a schematic configuration of laser-arc hybrid welding, 22 is a laser head, a condenser lens 24 for laser light is provided inside, and a laser beam 26 is applied to the surface to be welded in an orthogonal direction. . On the other hand, 28 is a MIG torch, and its arc welding wire 30 is provided with a slight inclination with respect to the laser beam 26. In this embodiment, the laser beam 26 is first applied to the welding direction indicated by the arrow. Then, the arc beam can be applied with a slight delay. However, the present invention also includes a method in which an arc is first applied and a laser beam is applied subsequently. The laser head and the MIG torch are moved along the flange portion while drawing a triangle in the same manner as in FIG. Therefore, the laser-arc hybrid beam is moved along the flange portion while drawing a triangle, and as a result, a saw-tooth welded portion (FIGS. 3 and 4) in which adjacent triangular portions are folded is obtained. Since re-entry heat before solidification is obtained and the solidification rate is relatively slow, gas can be easily released into the atmosphere, and an equivalent effect of reducing the possibility of blowholes and porosity is obtained. Further, by adopting a laser / arc hybrid beam, even if the flange portions 10-1 and 12-1 which are welded portions are brought into close contact with each other, welding defects are hardly generated, which is an advantage over simple laser welding. In other words, when using tin-galvanized steel sheet, laser welding requires strict control of the gap between the steel sheets in the case of lap welding of the steel sheets. In addition, blowout of the weld metal due to the evaporation of zinc and blowholes and porosity due to the residue in the weld metal were generated, which was likely to cause welding defects, and strict clearance management was required. On the other hand, with the laser / arc hybrid beam, such gap management is unnecessary, it is difficult to produce welding defects even in the state of close contact, the yield of the welding process is increased, and efficiency and cost reduction can be realized. .

FIG. 1 is a schematic perspective view of a fuel tank. FIG. 2 is a cross-sectional view of the flange welded portion of the fuel tank. FIG. 3 is a diagram showing the movement trajectory of the welding beam along the flange surface. FIG. 4 is a partially enlarged view of the movement trajectory of the welding beam. FIG. 5 is a diagram showing a schematic configuration of laser-arc hybrid welding.

Explanation of symbols

10, 12 ... upper and lower half
10A, 12A ... depression
10-1, 12-1 ... Flange 22 ... Laser head 24 ... Condensing lens 26 ... Laser beam 28 ... MIG torch 30 ... Arc welding wire
31, 32… Electrode wheel
l1, l2, l3 ... welding line P ... welded part

Claims (3)

  Subjecting the hexavalent chromium-free plated steel sheet to drawing, forming a pair of halves formed with flanges along the outer periphery of the recesses by drawing, each pair of halves facing each other on the inner surface side, and A method of manufacturing a fuel tank, wherein the flange portions are opposed to each other, welded along the opposed flange portions, and the welding beam is moved along the flange portion while drawing a triangle.   A pair of halves that have been drawn from a hexavalent chromium-free plated steel plate and formed a flange along the outer periphery of the recess by drawing are opposed to each other so that each recess faces the inner surface. A fuel tank comprising a welded portion along an opposed flange portion, wherein the welded portion is obtained by moving a welding beam while drawing a triangle along the contact flange portion.   A pair of halves that have been drawn from a hexavalent chromium-free plated steel plate and formed a flange along the outer periphery of the recess by drawing are opposed to each other so that each recess faces the inner surface. A fuel tank comprising a welded portion along the abutted flange portion, wherein the welded portion has a sawtooth shape in which adjacent chevron portions are folded at the connecting portion.

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