JP2007090397A - Lap fillet welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lap fillet welding method composed of a combined welding of a laser beam welding and a gas-metal arc welding to a thin sheet for automobile demanding excellent fatigue characteristic. <P>SOLUTION: The preceding welding is performed with the laser beam welding and the following welding is performed with the gas-metal arc welding, and before solidifying the fused pond with the laser beam welding, an arc discharge of the gas-metal arc welding is performed onto this fused pond. The laser beam diameter D (mm), the laser beam output P (W) and the welding speed V (m/min), satisfy the formula, 120<P/(S×V<SP>2</SP>)<170 (wherein, S=π(D/2)<SP>2</SP>is laser beam irradiating area). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lap fillet welding method composed of a composite welding of laser welding and gas metal arc welding, and more particularly to a lap fillet welding method for a thin steel sheet for automobiles that requires excellent fatigue characteristics.

  High strength materials are used to increase the strength of the welded structure. Looking at the fatigue strength, the fatigue strength of the welded structure is dominated by the welded joint, and the fatigue strength is almost constant regardless of the material strength. Therefore, fatigue strength does not improve even if a strong material is used.

  When repeated stress or load is applied to the arc welded joint, fatigue cracks occur from the weld toe. This is because the weld toe portion is discontinuous in shape and stress is concentrated.

For example, FIG. 4 shows a cross-sectional shape of a lap fillet weld, and if the shape of the weld metal 30 defined by the throat thickness a etc. at the fillet weld consisting of the upper plate 10 and the lower plate 20 is inappropriate, Joint strength decreases.
The fatigue strength of welded joints is governed by the tensile residual stress near the weld and the shape of the weld toe.

As a technique for improving the fatigue strength of welded joints, a method of reducing the tensile residual stress by shot blasting and heating in the vicinity of the welded portion (Non-patent Document 1), using a welding wire made of austenitic stainless steel, Many methods have been proposed, such as a method of reducing the tensile residual stress using the expansion of the martensite structure (Patent Document 1) and a method of remelting and flattening the weld toe with a TIG arc or the like.
JP 2001-246495 A Journal of the Japan Welding Society vol17, No.2 (1999) p319-325 “Effect of local heating on fatigue strength improvement of arc welds of thin steel sheet -Residual stress reduction effect by local heating-”

  However, the above-described method requires another process after welding, which increases man-hours and leads to lower productivity and higher costs. In addition, when a welding wire made of austenitic stainless steel is used, the welded portion becomes a hard and brittle martensite structure, so that the elongation is low and the workability is inferior, and the welding wire is also expensive.

  The present invention was developed to answer such a demand, and in the fillet welding of a thin steel plate by a welding method using both a laser and an arc, the weld toe is smoothed to obtain a bead with excellent fatigue strength. An object of the present invention is to provide a welding method excellent in productivity and cost.

The object of the present invention can be achieved by the following means.
1. In the lap fillet welding method by composite welding in which the preceding welding is laser welding and the subsequent welding is gas metal arc welding, the arc discharge of the gas metal arc welding is performed on the molten pool before the molten pool is solidified by the laser welding. And
A laser beam diameter D (mm), laser output P (W), and welding speed v (m / min) in the laser welding satisfy the following relationship:
120 <P / (S ・ v ² ) <170 (1)
Here, the irradiation area of the laser beam is indicated by S = π (D / 2) ² .

  2. In the laser welding, the target position of the laser beam center is in the range perpendicular to the welding line from the upper plate edge of the lap fillet joint, with the laser beam diameter D being in the range of 0 mm or more and D × 3/4 mm or less. 2. The lap fillet welding method according to 1, wherein the target position of the wire for arc welding is in the range of 0.5 mm or more and 4 mm or less in the direction parallel to the welding line, behind the target position of the center of the laser beam.

  3. The laser irradiation angle in the laser welding and the wire aiming angle θ (deg.) In the gas metal arc welding are 5.0 ≦ θ ≦ 40 with respect to the normal direction of the workpiece in a plane perpendicular to the welding direction. The lap fillet welding method according to 1 or 2, wherein the method is inclined to the plate side.

  According to the present invention, a weld toe is smoothed in fillet welding of a thin steel plate used in an automobile or the like, and a bead having excellent fatigue strength is obtained, which is extremely useful industrially.

  In the present invention, the lap fillet welding is a composite welding in which the preceding welding is laser welding and the subsequent welding is gas metal arc welding, and the timing and individual welding conditions for performing the gas metal arc welding after the laser welding are optimized. It is characterized by that. In the following description, the material to be welded on the upper side of the lap fillet welded joint is the upper plate, and the material to be the lower side is the lower plate.

  In the lap fillet welding according to the present invention, the preceding welding is laser welding, the subsequent welding is gas metal arc welding, and the gas metal arc welding is performed before the molten pool is solidified by the preceding laser welding. Performs arc discharge for gas metal arc welding. When the molten pool formed by laser beam irradiation is irradiated with an arc, arc discharge is stably generated and maintained in the laser irradiation section.

  The molten metal supplied by arc welding relaxes the cooling rate by the melting / heating region formed by laser welding, and the weld toe becomes flat. The arc discharge is not limited to the molten pool as long as it is applied to the region including the molten pool.

In laser welding, it is preferable to obtain a good weld by setting the laser beam diameter D (mm), laser output P (W), and welding speed v (m / min) so as to satisfy the relationship of equation (1). .
120 <P / (S ・ v ² ) <170 (1)
Here, the irradiation area of the laser beam is indicated by S = π (D / 2) ² .

If P / (S · v ² ) is 120 or less, the power density of the laser is too low to heat the lower and upper plates, the arc becomes unstable, and at the same time, the molten metal and the lower and upper plates The welding toe is not flattened.

On the other hand, when it exceeds P / (S · v ²⁾ is 170, the power density of the laser becomes excessive, penetration of the lower plate penetrates too large. Furthermore, since the upper plate is melted excessively, the throat thickness of the welded portion is reduced and the strength of the static joint is reduced.

  FIG. 1 is a schematic diagram for explaining a preferred target position for a lap fillet joint of a laser beam and a gas metal arc welding wire. In the figure, 1 is an upper plate, 2 is a lower plate, 3 is a target position of the laser beam, Reference numeral 4 denotes a target position of arc irradiation in gas metal arc welding, 5 denotes a welding progress direction, 11 denotes an edge portion of the upper plate 1, and D denotes a laser beam diameter.

In laser welding, the target position 3 of the laser beam is the center of the laser beam (indicated by a black dot in the figure), 0 mm or more in the direction perpendicular to the weld line 5 from the upper plate edge 11 of the lap fillet joint, laser beam diameter D × In the range of 3/4 mm or less (indicated as l _{1 in the} figure), the target position 4 of the gas metal arc welding arc irradiation is the wire aiming position (indicated by a black dot in the figure) and behind the laser beam aiming position 3. in, weld line parallel to 0.5mm or more and 4mm or less in the range (in the drawing l ₂ and the display).

  If the laser and gas metal arc welding position is less than 0mm from the upper plate edge to the upper plate, the upper plate will melt too much, and the leg length of the weld will be reduced, reducing the joint strength. On the other hand, if it exceeds D × 3 / 4mm from the upper plate end to the opposite side of the upper plate, the joint will be too far from the upper plate end, the throat thickness will decrease, and the weld joint strength will decrease.

  As described above, when the laser beam center and the wire aiming position are defined, they are aligned in parallel with the weld line, that is, in parallel with the upper plate edge portion 11, and without overlapping the upper plate in large quantities. A joint is obtained and preferable.

  FIG. 2 is a diagram for explaining a preferable irradiation angle of the laser beam and a target angle of the gas metal arc welding wire. In FIG. 2, reference numeral 6 denotes a laser beam central axis and a gas metal arc welding wire center.

  The center axis of the laser beam and the center of the gas metal arc welding wire (symbol 6 in the figure) are 5.0 ≦ θ ≦ 40 with respect to the normal direction of the workpiece (lower plate in the figure) in a plane perpendicular to the welding direction. Then, tilt the lower plate side by an angle θ.

  If the angle θ is less than 5 (deg.) In the plane perpendicular to the welding direction (perpendicular to the welding direction and normal to the steel plate surface), the flank angle of the weld bead (see Fig. 4) is a steep angle Therefore, a welding defect such as a decrease in fatigue strength and slag entrainment occurs.

  On the other hand, when the angle θ exceeds 40 (deg.) In the above-mentioned plane, the weld bead has a insufficient throat thickness, so that not only the fatigue strength but also the static joint strength is lowered.

  Therefore, in order to obtain a weld bead with few defects in the lap fillet welded joint and excellent static and fatigue strength, it is preferable to set the angle θ (deg.) To 5.0 ≦ θ ≦ 40.

  Although the laser oscillator of the present invention is not particularly defined, it is preferably set to an output of 200 watts or more, preferably a kilowatt class for use in welding. As the type of laser, a YAG laser that excites laser light with a halogen lamp or the like using a YAG rod as a laser light generation medium or a type that excites laser light with a laser diode (LD) is preferable. In addition, carbon dioxide laser, slab laser, ruby laser, excimer laser, semiconductor laser, and others can be used.

  It is preferable that the optical system includes an optical system in which a deflecting reflecting mirror and several positive and negative focusing lenses are combined. However, laser light is focused only by a combination of a concave mirror and a convex mirror without using a lens system. May be.

  Since the gas metal arc welding apparatus is intended for welding thin metal plates, it is preferable to use a thin wire with a diameter of 1.2 mm or less as the welding wire. In order to achieve both arc stability and prevention of oxidation of the weld metal, it is preferable to use an inert gas such as argon gas as the shielding gas, but carbon dioxide is contained in the argon gas in the range of 10 to 100%. It is also possible to use a gas in which hydrogen gas or helium gas is mixed in the range of 2 to 20% in the gas mixed in the above and argon gas. Examples of the present invention will be described below.

  Fillet joints were formed and welded using mild steel plates with an upper plate thickness of 1.6 mm and a lower plate thickness of 2.0 mm without any gaps between them. Fillet welding was performed by composite welding with YAG laser welding as the pre-welding and gas metal arc welding as the subsequent welding.

  In YAG laser welding and gas metal arc welding, the distance between the laser beam center position and the wire center is 1 mm, and the irradiation angle is perpendicular to the welding direction and the angle θ (deg.) Is 20 degrees with respect to the normal direction of the steel plate surface. Welding was performed. The YAG laser output P was set to 1kw, 2kW and 3kW at the machining point. The beam diameter D (mm) and welding speed v (m / min) were varied.

  For the quality evaluation of the welded part, the Schenk-type swing swing fatigue test was conducted. The maximum stress range that does not break at a breaking life of 10 million times was defined as the fatigue limit σW, and the condition under which the fatigue limit σW exceeded 200 MPa was judged as good.

Table 1 shows the test conditions and the obtained fatigue strength, and FIG. 3 shows the test results. In a range where 120 <P / (S · v ² <170 is satisfied, the fatigue limit σW exceeds 200 MPa, and it was confirmed that a fillet welded joint having good fatigue characteristics can be obtained by the present invention. S = π (D / 2) ² indicates the laser beam irradiation area.

  The effects of laser aiming position and gas metal arc aiming position on weld quality and the effect of laser irradiation angle on fatigue strength were investigated.

  Lap fillet welding was performed using 0.8 and 1.6 mm and 1.6 and 2.0 mm mild steel plates with upper and lower plate thicknesses with zero gap. Welding was performed by the welding method according to the present invention in which YAG laser welding and gas metal arc welding were combined.

  The welding conditions were as follows: the laser target position and the gas metal arc welding target position were changed from 0.0 mm to 5.0 mm, the laser irradiation angle was changed from 0 to 50 degrees, and the laser output was 1,3 kW.

  For the quality evaluation of welded parts, a Schenck-type swing-bending fatigue test was performed. The maximum stress range where the rupture life was 10 million times and did not rupture was defined as the fatigue limit σW, and this value was obtained. As a result of the evaluation, the condition where the fatigue limit exceeded 200 MPa was judged as good.

  Table 2 shows the test conditions. From the experimental results, the irradiation interval of the laser beam and the arc is in the range of 0.5 mm or more and 4 mm or less, and the irradiation angle of the laser and gas metal arc welding is perpendicular to the welding direction and the normal direction of the stack fillet steel plate surface In contrast, the fatigue limit exceeded 200 MPa when the angle θ (deg.) Was in the range of 5.0 ≦ θ ≦ 40.

  When the laser target position and the gas metal arc target position are set to exceed 4 mm, the distance between the two is too far, and the effect of stabilizing and concentrating the arc by laser irradiation is slightly reduced. Although the number of weld defects is increased, there is no practical problem.

  On the other hand, if the laser target position and the gas metal arc target position are set to less than 0.5 mm, the weld bead becomes discontinuous because the droplets from the arc welding interfere with the laser.

  Therefore, in order to obtain a sound weld, it is preferable to set the distance between the laser target position and the gas metal arc target position to 0.5 mm or more and 4 mm or less.

  When the irradiation angle of laser and gas metal arc welding is 0 deg. Perpendicular to the welding direction and normal to the steel sheet surface, the toe angle of the weld bead becomes a steep angle exceeding 30 degrees, resulting in fatigue strength. Welding defects such as slag entrainment and slag entrainment occur.

  On the other hand, when the irradiation angle of laser and gas metal arc welding exceeds 40 ° with respect to the normal direction of the steel sheet surface perpendicular to the welding direction, the fatigue strength decreases because the throat thickness of the weld bead is insufficient. Of course, the static joint strength also decreases.

  From the above results, in order to obtain a weld bead with few defects in the lap fillet welded joint and excellent in static and fatigue strength, the irradiation angle of laser and gas metal arc welding should be perpendicular to the welding direction. It has become clear that it is preferable to set the angle θ (deg.) With respect to the normal direction so as to be inclined in the opposite direction with respect to the upper plate in the range of 5.0 ≦ θ ≦ 40.

Example of the present invention. Example of the present invention. The figure which shows the influence of the beam diameter D (mm), the laser output P (W), and the welding speed v (m / min) which acts on fatigue strength (Example). The figure which shows the shape of a lap fillet weld part.

Explanation of symbols

1 Upper plate 2 Lower plate 3 Target position of laser beam 4 Target position of arc irradiation of gas metal arc welding 5 Welding direction 6 Laser beam central axis (central axis of gas metal arc welding wire)
11 Upper plate edge D Laser beam diameter

Claims (3)

In the lap fillet welding method by composite welding in which the preceding welding is laser welding and the subsequent welding is gas metal arc welding, the arc discharge of the gas metal arc welding is performed on the molten pool before the molten pool is solidified by the laser welding. And
A laser beam diameter D (mm), a laser output P (W), and a welding speed v (m / min) in the laser welding satisfy the following relationship:
120 <P / (S ・ v ² ) <170 (1)
Where S = π (D / 2) ² In the laser welding, the target position of the laser beam center is in the range perpendicular to the welding line from the upper plate edge of the lap fillet joint, with the laser beam diameter D being in the range of 0 mm or more and D × 3/4 mm or less. The lap fillet welding method according to claim 1, wherein the target position of the wire for arc welding is in the range of 0.5 mm or more and 4 mm or less in the direction parallel to the welding line, behind the target position of the center of the laser beam. The laser irradiation angle in the laser welding and the wire aiming angle θ (deg.) In the gas metal arc welding are 5.0 ≦ θ ≦ 40 with respect to the normal direction of the workpiece in a plane perpendicular to the welding direction. The lap fillet welding method according to claim 1, wherein the lap fillet welding method is inclined to the plate side.

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