Patent Description:
MIG welding, laser welding, hybrid welding, and the like have been known as methods of forming a lap joint by welding an inner corner portion formed by overlapping metal members. MIG welding has an advantage of a wider margin for the clearance at the welding portion and misalignment of the target position because the welding is performed with a filler material being supplied. On the other hand, MIG welding has disadvantages of a slow welding speed and a shallow penetration depth. In MIG welding, there is a disadvantage that when the welding speed is set high, a deposited metal (throat thickness) shortage occurs at the inner corner portion, decreasing the joint strength.

Laser welding has an advantage that the welding speed is faster than that in arc welding such as MIG welding. On the other hand, laser welding has a disadvantage that the margin for the clearance in the welded portion is significantly small because no filler material is added.

Document <CIT> describes a hybrid welding using a hybrid welding machine including a preceding laser welding unit and a following MIG welding unit for welding. <FIG> is a schematic cross-sectional view illustrating conventional hybrid welding. In this hybrid welding, the inner corner portion formed by the front surface 1b of a first metal member <NUM> and an end surface 2a of a second metal member <NUM> is welded. In this hybrid welding, the target positions of a preceding laser beam LB and a following MIG arc <NUM> are both set to be at the corner portion P where the front surface 1b of the first metal member <NUM> and the end surface 2a of the second metal member <NUM> intersect with each other.

Document <CIT> describes a method of big light spot laser and arc composite heat source for joining heterologous metals. A filler metal matched with the heterologous metal is used as solder of high-melting carbon steel / alloyed steel and as flux solder of low-melting nonferrous metal. A connecting piece heat input control is realized by adjusting laser power and adopting large scale laser light spot, at the one side of low-melting nonferrous metal forming fusion welding connect, and at one side of high-melting carbon steel and alloyed steel forming self-brazing connect.

Document <CIT> describes a dissimilar material joining method for obtaining a composite structure of an aluminum-based material and an iron-based material used as various structural materials for automobiles. An overlapping joint is formed with an aluminum plate (upper plate) and a steel plate (underneath plate) having an aluminum coating layer on the surface. A laser beam is irradiated to an overlapping part located on the upper surface of the aluminum plate at their edge parts for joining the plates.

Document <CIT> describes a method for joining a different material using laser welding. An overlapping joint is formed by overlapping an end portion of an aluminum plate to a steel plate having a zinc coating layer on the surface. A laser beam from a preceding first heat source is irradiated to a surface of a steel plate vicinity of the overlapping joint. A molten portion is formed by melting the coating layer coating the surface of the steel plate. Then, a molten portion is formed by melting the aluminum plate by providing a second heat source to the aluminum plate, thereby a joining joint is obtained.

<CIT> discloses a joining method according to the preamble of claim <NUM>.

The above-described hybrid welding provides welding compensating the disadvantages of the laser welding and the MIG welding. However, hybrid welding still has a problem that when the welding speed is set high, the phenomenon of a deposited metal (throat thickness) shortage still occurs at the inner corner portion, decreasing the joint strength of the lap joint and robustness for allowing a clearance and misalignment of the target position. In these days, a weld length is increased along with an increase in the size of a welding target, and therefore an increase in the welding speed and an improvement in the robustness are required.

In view of the above, an object of the present invention is to provide a joining method that achieves an increase of the welding speed and also improve the robustness for allowing the clearance between metal members and misalignment of the welding target position.

To solve the above problems, the present invention includes: an overlapping step of overlapping a first metal member and a second metal member such that a front surface of the first metal member is opposed to a back surface of the second metal member; and a welding step of performing a laser welding and a MIG welding by using a hybrid welding machine including a preceding laser welding unit for a preceding welding and a following MIG welding unit for a following welding, in which laser welding is performed by emitting a laser beam onto a front surface of the second metal member, MIG welding is performed on an inner corner portion formed by the front surface of the first metal member and an end surface of the second metal member, and the welding step includes setting a target position for the laser beam from the laser welding unit such in a way that the target position is located against the second metal member relative to a target position for a MIG arc by the MIG welding unit.

According to the joining method, by emitting the laser beam onto the front surface of the second metal member, a part of the second metal member melted by the preceding laser beam serves as deposited metal for the following MIG welding, and thus it is possible to increase the amount of the deposited metal (throat thickness) at the inner corner portion. Therefore, it achieves both an increase in the welding speed and an improvement in the joint strength. Additionally, with the amount of the deposited metal (throat thickness) increased, it improves the robustness for allowing the clearance between the metal members and misalignment of the welding target position.

In the welding step, a rotation angle, when viewed from above, between a reference line parallel to a direction of movement of the hybrid welding machine and an imaginary line connecting distal ends of the laser welding unit and the MIG welding unit, is set to <NUM>° to <NUM>°. In the welding step, it is preferable that a distance between the target position of the preceding laser beam and the target position of the following MIG arc is set to <NUM> to <NUM>. In the welding step, it is preferable that a target angle of the MIG arc is set to <NUM>° to <NUM>°. In the welding step, it is preferable that an angle of advance of the MIG arc is set to <NUM>° to <NUM>°. In the overlapping step, it is preferable that a clearance between the front surface of the first metal member and the back surface of the second metal member is set to <NUM> to <NUM>. In the welding step, it is preferable that the laser beam is emitted perpendicularly to the front surface of the second metal member.

The joining method according to the present invention increases the welding speed and improves the robustness for allowing the clearance between metal members and misalignment of the welding target position.

A joining method according to an embodiment of the present invention is described in detail with reference to drawings. As illustrated in <FIG>, in the joining method according to this embodiment, a second metal member <NUM> is overlapped on a first metal member <NUM>, and then the first metal member <NUM> and the second metal member <NUM> are joined with each other by welding to form a lap joint. In the joining method according to this embodiment, an overlapping step and a welding step are performed. Note that, a "front surface" in the specification means a surface on the opposite side of a "back surface".

As illustrated in <FIG>, the overlapping step is a step of overlapping the second metal member <NUM> on the first metal member <NUM>. The first metal member <NUM> and the second metal member <NUM> may have any shape; in this embodiment, both have a plate shape. The first metal member <NUM> and the second metal member <NUM> are properly selected from weldable metals such as aluminum, aluminum alloys, copper, copper alloys, titanium, titanium alloys, iron steels, and stainless steels.

In the overlapping step, the first metal member <NUM> and the second metal member <NUM> are overlapped such that the front surface 1b of the first metal member <NUM> is opposed to the back surface 2c of the second metal member <NUM>. The front surface 1b of the first metal member <NUM> and an end surface 2a of the second metal member <NUM> form an inner corner portion. A point at which the front surface 1b of the first metal member <NUM> and the end surface 2a of the second metal member <NUM> intersect with each other is called a corner portion P.

The welding step is a step of welding the inner corner portion by using a hybrid welding machine <NUM> as illustrated in <FIG>. In <FIG>, <FIG>, the hybrid welding machine <NUM> is moved from the right side to the left side. In <FIG>, the hybrid welding machine <NUM> is moved from the far side to the near side. The hybrid welding machine <NUM> includes a connecting portion <NUM>, a laser welding unit <NUM>, and a MIG welding unit <NUM>. The connecting portion <NUM> is, for example, attached to a distal end of an arm robot. The laser welding unit <NUM> includes a laser head <NUM> and is formed on one end of the connecting portion <NUM>. The laser head <NUM> emits a laser beam LB.

The MIG welding unit <NUM> includes an arc torch <NUM> and is placed on the other end of the connecting portion <NUM>. The arc torch <NUM> supplies a filler material <NUM> and also generates a MIG arc <NUM> (see <FIG>) at its distal end.

As illustrated in <FIG>, the angle of advance θ1 of a shaft portion of the laser head <NUM> is set to <NUM>°, for example. The angle of advance is the tilt angle of the shaft portion of the laser head <NUM> with respect to the vertical axis when the hybrid welding machine <NUM> is viewed from the side. The angle of advance θ1 may be set properly between -<NUM>° to <NUM>° with respect to the vertical axis. As illustrated in <FIG>, the target angle θ3 of the shaft portion of the laser head <NUM> is set to <NUM>°, for example. That is, the laser beam LB is emitted perpendicularly to the front surface 2b of the second metal member <NUM>. The target angle θ3 is the opening angle from the front surface 2b of the second metal member <NUM> to the shaft portion of the laser head <NUM>. The target angle θ3 may be set properly between <NUM>° to <NUM>°.

As illustrated in <FIG>, the target position Q1 of the laser beam LB emitted from the laser head <NUM> is set to the position <NUM> away from the end surface 2a in this embodiment. The target position Q1 may be properly set according to the plate thickness of the second metal member <NUM>. For example, it may be set within a range of <NUM> < L1 ≤ <NUM> (mm), where L1 is the distance from the end surface 2a of the second metal member <NUM> to the target position Q1. The target position Q1 is set on the front surface 2b of the second metal member <NUM> and placed closer to the center of the surface of the second metal member <NUM> (placed away from the end surface 2a) relative to the target position Q2 of the MIG arc <NUM> described later.

As illustrated in <FIG>, the angle of advance θ2 of a shaft portion of the arc torch <NUM> is set to <NUM>°, for example. The angle of advance θ2 may be set properly between <NUM>° to <NUM>°. As illustrated in <FIG>, the target angle θ4 of the shaft portion of the arc torch <NUM> is set to <NUM>°, for example. The target angle θ4 is the opening angle from the front surface 1b of the first metal member <NUM> to the shaft portion of the arc torch <NUM>. The target angle θ4 may be set properly within a range of <NUM> to <NUM>°. The target position Q2 of the MIG arc <NUM> (see <FIG>) generated from the arc torch <NUM> is set to be at the corner portion P.

As illustrated in <FIG>, when the hybrid welding machine <NUM> is viewed from above, the opening angle (rotation angle θ5) between the imaginary line M1 connecting the distal end of the laser head <NUM> and the distal end of the arc torch <NUM> and a reference line M2 parallel to the direction of the movement of the hybrid welding machine <NUM> is set to <NUM>°, for example. In this embodiment, the reference line M2 is the same as the in-plane direction of the end surface 2a of the second metal member <NUM>. The rotation angle θ5 may be set properly between <NUM>° to <NUM>°. The distance L2 from the target position Q1 of the laser beam LB to the target position Q2 of the MIG arc <NUM> on the imaginary line M1 is set to about <NUM>. The distance L2 may be set properly within a range of <NUM> < L2 ≤ <NUM> (mm).

In the welding step, laser welding is performed by the laser beam LB emitted from the preceding laser head <NUM> as illustrated in <FIG>. The target position Q1 of the laser beam LB is set to a position away from the end surface 2a of the second metal member <NUM>, and an end portion of the second metal member <NUM> is melted substantially parallel to the end surface 2a. For this process, it is preferable to set the output of the laser beam LB to a degree that allows a keyhole KH formed by the laser welding to be formed in the first metal member <NUM> as illustrated in <FIG>. With this, the end portion of the second metal member <NUM> is cut and melted by the laser beam LB.

In the welding step, MIG welding is performed by the arc torch <NUM> following the laser head <NUM> as illustrated in <FIG>. The target position Q2 of the arc torch <NUM> is set to overlap the corner portion P. As also illustrated in <FIG>, the following MIG arc <NUM> is guided to a cathode spot (laser-induced plasma LP generated around the distal end of the laser beam LB) generated by the laser welding. A weld pool WP formed by the MIG arc <NUM> is fused with the end portion of the second metal member <NUM> melted (cut) by the laser beam LB, and a weld metal W is formed at the inner corner portion as illustrated in <FIG>.

Note that, although the output of the laser beam LB is set as described above in the welding step, the output of the laser beam LB may be set to a depth at which the end portion of the second metal member <NUM> is not completely cut.

According to conventional hybrid welding, the target position of the laser beam LB and the target position of the MIG arc <NUM> are both at the corner portion P as illustrated in <FIG>. This method has a disadvantage that the deposited metal becomes small when the welding speed is increased. Additionally, since the deposited metal becomes small, there is a problem of low robustness for allowing a clearance between the metal members and misalignment of the welding target position.

In contrast, in the joining method according to this embodiment, the laser beam LB is emitted to the front surface 2b from above the second metal member <NUM>, and thereby a part of the second metal member <NUM> melted by the preceding laser beam LB serves as a deposited metal of the following MIG welding. Thus, it is possible to increase the amount of the deposited metal in the inner corner portion (throat thickness Wd: see <FIG>) in combination with the filler material <NUM>. Therefore, the welding speed increases as well as the joint strength improves. Additionally, with the increase in the amount of the deposited metal, it is possible to improve the robustness for allowing a clearance between the metal members and misalignment of the welding target position.

Moreover, according to the invention, the rotation angle of the reference line M2 that is parallel to the direction of movement of the hybrid welding machine <NUM> and the imaginary line M1 connecting the distal ends of the laser welding unit <NUM> and the MIG welding unit <NUM> is set to <NUM>° to <NUM>°, when viewed from above. Furthermore, like the welding step in this embodiment, it is preferable to set the distance L2 between the target position Q1 of the preceding laser beam LB and the target position Q2 of the following MIG arc <NUM> to <NUM> to <NUM>. If the distance L2 is shorter than <NUM>, the distance between the laser head <NUM> and the arc torch <NUM> is too close, and it is difficult to make proper joining. If the distance L2 exceeds <NUM>, the cathode spot of the laser welding does not induce the MIG arc <NUM>, which results in that the deposited beads (deposited metal W) may meander.

Additionally, in the overlapping step, it is preferable to set a clearance between the front surface 1b of the first metal member <NUM> and the back surface 2c of the second metal member <NUM> to <NUM> to <NUM>. If the clearance exceeds <NUM>, there is a possibility of a decrease in the joining strength. Moreover, in the welding step, it is preferable to set the target angle θ4 of the MIG arc <NUM> to <NUM>° to <NUM>°. Furthermore, in the above-described welding step, it is preferable to set the angle of advance θ2 of the MIG arc <NUM> to <NUM>° to <NUM>°.

Next, examples according to this embodiment are described. Here, the first metal member <NUM> was joined with the second metal member <NUM> by using the hybrid welding machine <NUM> to form a lap joint, and a tensile test was conducted for the lap joint. The first metal member <NUM> of an aluminum alloy A5052-H34 with a thickness of t = <NUM> was used for both a group of comparative examples and a group of examples. The second metal member <NUM> of an aluminum alloy A6061-T6 with a thickness of t = <NUM> was used for both the group of comparative examples and the group of examples.

As indicated in <FIG>, the welding speeds were set to <NUM> (m/min) in the comparative examples and the examples. The laser outputs were set to <NUM> (kW) in the comparative examples and set to <NUM> (kW) in the examples. A welding currents of the MIG arc were set to <NUM> (A) in the comparative examples and set to <NUM> (A) in the examples. Other conditions were as indicated in <FIG>.

As indicated in <FIG>, the angles of advance θ1 of the laser head <NUM> were set to <NUM>° for both the group of comparative examples and the group of examples, and the angles of advance θ2 of the arc torch <NUM> were set to <NUM>° for both sets. The target angles of the laser head <NUM> in the comparative examples were set to <NUM>°, and the target angles θ3 of the laser head <NUM> in the examples were set to <NUM>°. The target angles of the MIG arc <NUM> in the comparative examples were set to <NUM>°.

In the comparative examples, the target positions Q1 of the laser beam LB and the target positions Q2 of the MIG arc <NUM> were both set to be at the corner portion P of the inner corner portion. The distances L2 in the comparative examples were set to <NUM>.

Unlike the above setting, the target positions Q1 of the laser beams LB in the examples were set to three kinds of positions: a position <NUM> away from the end surface 2a of the second metal member <NUM> which is used as a reference position (offset distance <NUM>), a position -<NUM> which is placed toward the end surface 2a from the reference (offset distance -<NUM>), and a position +<NUM> which is placed away from the end surface 2a (offset distance <NUM>). The target positions Q2 of the MIG arc <NUM> in the examples were set to be at the corner portion P of the inner corner portion. The rotation angles θ5 in the examples were set to <NUM>°, and the distances L2 therein were set to <NUM>.

Additionally, the clearances between the first metal member <NUM> and the second metal member <NUM> in both the group of comparative examples and the group of examples were set to three kinds, <NUM>, <NUM>, and <NUM>, for each of the above-described offset distances. Consequently, Nos. <NUM> to <NUM> test specimens were obtained as the comparative examples, and Nos. <NUM> to <NUM> test specimens were obtained as the examples.

For both the group of comparative examples and the group of examples, a tensile test was performed on each specimen, and the joint efficiency (%) was calculated according to the following formula (<NUM>). Joint efficiencies having over <NUM>% were regarded as "favorable" results. <NUM>] <MAT>.

As indicated in <FIG>, the largest joint strength in the comparative examples was <NUM> (N/mm) exhibited by NO. <NUM>, and the joint efficiencies were all below <NUM>%. Also, the deposited metal W was thin and dented toward the inner corner portion.

In contrast, as indicated in <FIG>, the joint strengths in the examples were <NUM> to <NUM> (N/mm), and the joint efficiencies were all over <NUM>%. Also, the deposited metal W was formed to have a great throat thickness and to be convex in the direction away from the inner corner portion. The average cross-section area of the deposited metals W of the examples was about three times greater than the average cross-section area of the deposited metals W of the comparative examples.

It was found that the joint strengths and the joint efficiencies in the examples are high even if the clearances between the front surface 2b of the first metal member <NUM> and the back surface 2c of the second metal member <NUM> are <NUM> to <NUM>. Additionally, it was found that the joint strengths and the joint efficiencies in the examples are high even if the positions of the laser beam LB are shifted from the target position by ±<NUM>. That is to say, according to the examples, a thickness of the deposited metal W became large even under a situation of a fast welding speed, resulting in improvement of the robustness for allowing a clearance between metal members and misalignment of the welding target position.

Claim 1:
A joining method comprising:
an overlapping step configured to overlap a first metal member (<NUM>) and a second metal member (<NUM>) with each other such that a front surface (1b) of the first metal member (<NUM>) is opposed to a back surface (2c) of the second metal member (<NUM>); and
a welding step configured to perform a laser welding and a MIG welding by using a hybrid welding machine (<NUM>) including a laser welding unit (<NUM>) for a preceding welding and a MIG welding unit (<NUM>) for a following welding,
characterized in that
the welding step includes:
performing the laser welding by emitting a laser beam (LB) onto a front surface (2b) of the second metal member (<NUM>);
performing the MIG welding on an inner corner portion formed by the front surface (1b) of the first metal member (<NUM>) and an end surface (2a) of the second metal member (<NUM>);
setting a target position (Q1) for the laser beam (LB) from the laser welding unit (<NUM>) such in a way that the target position (Q1) is located against the second metal member (<NUM>) relative to a target position (Q2) for a MIG arc (<NUM>) by the MIG welding unit (<NUM>);
setting a reference line (M2) parallel to a direction in which the hybrid welding machine (<NUM>) moves;
setting an imaginary line (M1) connecting a distal end of the laser welding unit (<NUM>) and a distal end of the MIG welding unit (<NUM>); and
setting a rotation angle θ5 between the reference line (M2) and the imaginary line (M1) to <NUM>° to <NUM>° in a view from above.