JP4470482B2 - Brazing method for lap fillet joints - Google Patents

Description

  The present invention relates to a method for brazing a lap fillet joint used for joining thin steel plates or structures formed of thin steel plates.

  For joining structures formed of thin steel plates, an arc brazing method using a brazing material having a melting point lower than that of the base steel such as silver or copper is mainly used. The arc brazing method is a method in which an arc is generated and joined between a wire and a base material while continuously brazing the wire in an atmosphere of inert gas such as argon, carbon dioxide, or a mixed gas thereof. It is.

  However, the arc brazing method has poor convergence of the heat source, so the brazing speed is slow, the heat input to the thin steel plate structure is excessive, the thermal deformation becomes large, and a burn-out defect occurs. There are problems such as easy.

Recently, for example, a laser brazing method using a laser as a heat source as described in Patent Document 1 has been put into practical use as a brazing method that does not have the above-described drawbacks in the arc brazing method. In the laser brazing method, the brazing material is melted by laser irradiation, the surface layer portion of the base material is melted to a depth of several μm, and a small amount of the base material and the brazing material are diluted and mixed and joined. According to such a laser brazing method, no melt-off defect is generated compared to the arc brazing method or laser welding, and thermal deformation of the steel sheet can be suppressed.
JP 2003-225784 A

  However, in the laser brazing method, most of the laser energy is consumed for melting the brazing material, so that the joining speed is greatly reduced as compared with the laser welding method. Further, in the laser brazing method, it is important to accurately irradiate a brazing material with a laser beam having a diameter of several millimeters or less, and thus it is difficult to obtain a joint having a complicated shape such as a lap fillet joint.

  When brazing a thin steel plate or a lap fillet joint of a structure formed thereby, the above-described prior art has the following various problems.

  In the arc brazing method, the joining speed is slow and the working efficiency is low. In addition, it is difficult to control the amount of heat input, and it is difficult to obtain an appropriate bead width of the brazed portion according to the thickness of the thin steel plate. Furthermore, when the heat input becomes excessive, the brazed objects on the upper and lower sides melt away.

  The laser brazing method does not increase the work efficiency because it takes time to melt the brazing material. In addition, the supply accuracy of the brazing material to the laser beam is severe.

  The present invention has been made to solve the above-described problems, and provides a brazing method for a lap fillet joint that has a high joining speed and can reduce thermal deformation of an object to be brazed by joining with low heat input. For the purpose.

  As a result of diligent research to solve the above problems, the present inventors have combined production of arc brazing using a wire such as copper or silver and laser irradiation to achieve production efficiency, joint strength, gap tolerance, and bead. We obtained the knowledge that all of the shapes improved in a well-balanced manner. The present invention has been made based on such findings.

The method of brazing a lap fillet joint according to the present invention is a method of joining a lap fillet joint of a thin steel sheet structure,
A step (i) of irradiating a laser beam to a joint portion of a lap fillet joint in which the mutual gap S of the overlapping portions of the thin steel plates having a thickness of 1 mm or less is 0.25 mm or more and 1 mm or less ;
An inert gas is supplied to the laser irradiation portion to form a predetermined inert atmosphere, and a wire-like brazing material mainly composed of copper and silver is fed, and the brazing material and the brazing material are fed under the inert atmosphere. A step of generating an arc between the base material at the laser irradiation location and melting the brazing material by an arc with a low heat input, with an arc brazing speed of 2 to 5 m / min in order to reduce thermal deformation ( and ii).

In the step (i), the mutual gap S between the overlapping portions of the thin steel plates having a thickness of 1 mm or less is set to 0.25 mm or more and 1 mm or less. This is because if the mutual gap S of the overlapped portion exceeds 1 mm, melt-off occurs easily during arc brazing, and the overlapped steel plates may not be joined.

In the said process (ii), an arc brazing speed shall be 2-5 m / min. This is because if the brazing speed is less than 2 m / min, the heat input becomes excessive, the bead shape becomes poor, and the melt-off tends to occur. Note that at a slow brazing speed of less than 2 m / min, even if the mutual gap S is made as small as 0.5 to 1.0 mm, it may burn through. In addition, when the brazing speed is low, the amount of heat input becomes excessive, which causes a disadvantage that the arc output cannot be increased. Care must be taken because there is an unclear correlation between the arc brazing speed, the mutual gap S of the overlapping portion, the arc output, and the laser output.

  On the other hand, when the brazing speed exceeds 5 m / min, the amount of heat input becomes insufficient, the melting of the brazing material becomes insufficient, and the joining strength becomes insufficient.

  In the present invention, the part to be joined is first heated by laser irradiation, and predetermined heat energy is preliminarily applied to the base material side, so that the shortage of heat input during subsequent arc brazing is compensated for, The surface layer portion of the base material is quickly melted. For this reason, even if there is some mutual gap in the overlapped portion, it is possible to join without causing melting.

  According to the present invention, by combining laser irradiation and arc brazing, there is no melt-off in the joining of lap fillet joints of structures, high-speed brazing is possible, high strength, and thermal deformation is prevented. No good lap fillet joint is provided.

  The best mode of the present invention will be described below.

  In the present invention, arc brazing using a brazing wire as an electrode is performed after laser irradiation. In the case of arc brazing alone, the heat input is excessive for the thin steel plate structure, and it becomes easy to cause burn-off defects. However, in the present invention, since the arc is concentrated on the laser irradiation portion, the brazing portion is narrowed, and arc brazing with low heat input is possible, so that no melting occurs.

  There is almost no variation in bead width, and a uniform bead is formed. In addition, in laser brazing alone, energy is consumed for melting the brazing, so that the joining speed is significantly lower than the laser welding speed. However, in the present invention, melting of the brazing material is not performed by laser energy but by arc. The same high-speed joining as laser welding is possible. Furthermore, the laser irradiation only melts the surface layer portion from the surface of the steel plate to a depth of several μm and does not require the penetration of the plate thickness.

[Example]
Hereinafter, preferred embodiments of the present invention will be described.

  Two thin steel plates having a width of 200 mm, a length of 300 mm and a thickness of 1.0 mm were stacked, and the fillet joint was brazed.

  The material used for the test is a 440 MPa class cold-rolled steel sheet having a tensile strength TS of 442 MPa and a yield strength YS of 299 MPa. Its composition and mechanical properties are shown in Table 1. A plurality of test pieces were prepared in which the mutual gap S between the upper and lower steel plates was varied in a range from 0.25 mm to 1 mm.

  Brazing was performed by a method in which the following three were combined.

(1) Arc brazing method using copper wire as electrode
(2) Brazing method of copper wire by YAG laser irradiation
(3) Arc brazing method using YAG laser irradiation and copper-based wire as an electrode Each brazing condition is as follows: the arc brazing of (1) and (3) has a current value of 100 A, a voltage of 20 V, an arc length of 5 mm, ( The YAG lasers 2) and (3) have a wavelength of 1.06 μm and an output of 2 kW continuous oscillation.

  The wire used as the brazing material had the composition shown in Table 2 and a diameter of 0.8 mm.

  Table 3 shows the test results. In the evaluation of bondability, the symbol ○ indicates that a stable brazed part has been obtained without spattering or fusing, and the symbol indicating that the brazed part has become uneven due to spatter or fusing. Displayed with ×.

  In thermal deformation evaluation, the amount of deformation in the brazing line direction (300 mm) was measured. A case where the deformation amount exceeds 4 mm is indicated by a symbol x, and a deformation amount which is 4 mm or less is indicated by a symbol ◯. The joint strength was evaluated by a tensile shear test according to a test method defined in JIS Z3136. The case where the joint strength was 200 MPa or less was indicated by symbol x, and the case where the joint strength was 200 MPa or more was indicated by symbol O.

  The shape of the tensile shear test piece is shown in FIGS. The test piece 1 uses two thin steel plates 2 having the same thickness t, length L3, and width L4, overlaps a part thereof, brazes the step of the overlap portion 3, and connects the fillet joint 4 to each other. Formed. A test piece 1 was prepared by placing a brazing bead 4 in a direction perpendicular to the tensile axis. As for the dimensions of each part of the test piece 1, the total length L3 is 170 mm, the width L4 is 30 mm, the length L2 of the overlapping portion is 30 mm, and the plate thickness t is 1.0 mm.

  As is apparent from the results in Table 3, there is no problem of burn-off in the combined laser and arc brazing method (Examples 1 to 9) of the present invention, and since the arc is stabilized by laser irradiation, a healthy brazing portion is obtained. was gotten.

  There is almost no penetration of the brazing material into the base material, it is joined by diffusion mixing (dilution) of the components of the brazing material and the base material, and the anchor effect of a cell of several μm thickness formed at the time of solidification of the interface. There was no problem in strength and thermal deformation was small.

  As described above, according to the laser brazing method of the present invention, it was possible to achieve all of high-speed bonding, avoidance of burn-through, stabilization of the bead shape, and high strength.

[Comparative example]
In the arc brazing method (Comparative Examples 1 to 18), when the output condition is 150 A and 20 V, the heat input becomes excessive at a brazing speed of 0.5 m / min, so the mutual gap S melts at 0.5 mm or more. Drops occurred and the upper and lower steel plates were not connected.

  When the brazing speed was 1 m / min or higher, the arc became unstable and the bead shape had a problem.

  In addition, when the output conditions were 100A and 10V, the arc became unstable due to low heat input, causing a problem in the bead shape. In addition, there was a problem of thermal deformation under this output condition.

In the laser brazing method (Comparative Examples 19 to 27), since the heat input was excessive at a brazing speed of 1 m / min, melting occurred when the mutual gap S was 0.5 mm or more. When the brazing speed is 1 m / min or more, the heat input is too high and the heat input becomes insufficient, and the brazing material is insufficiently melted.

(A) is a side view of a tensile shear test piece, (b) is a plan view of the tensile shear test piece.

Explanation of symbols

2. Steel plate (base material)
3 ... Overlapping part 4 ... Brazed bead (lap fillet joint)

Claims (1)

A method for joining lap fillet joints of thin steel sheet structures,
A step (i) of irradiating a laser beam to a joint portion of a lap fillet joint in which the mutual gap S of the overlapping portions of the thin steel plates having a thickness of 1 mm or less is 0.25 mm or more and 1 mm or less ;
An inert gas is supplied to the laser irradiation portion to form a predetermined inert atmosphere, and a wire-like brazing material mainly composed of copper and silver is fed, and the brazing material and the brazing material are fed under the inert atmosphere. A step of generating an arc between the base material at the laser irradiation location and melting the brazing material by an arc with a low heat input, with an arc brazing speed of 2 to 5 m / min in order to reduce thermal deformation ( ii) and
A method for brazing a lap fillet joint, comprising:

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