JP2021091009A - Method of welding hot press molding - Google Patents

Abstract

To provide a method of welding a hot press molding that can stabilize quality of a weld zone when spot welding is performed.SOLUTION: A fiber laser oscillator 51a is used to irradiate, with laser light L1, welding predetermined regions A1 surrounding a plurality of dotting predetermined parts X1 of spot welding on a surface of a hot press molding P1 respectively in a rectangular shape, and thus an oxide coating W1 sticking on the welding predetermined region A1 is vaporized to reduce the film thickness, so that the film thickness of the oxide coating sticking on the welding predetermined region is less than the film thickness of the oxide coating sticking on regions except the welding predetermined region, and also left as thick as a predetermined quantity.SELECTED DRAWING: Figure 3

Description

The technique disclosed herein belongs to the technical field relating to a method of welding a hot press molded article obtained by hot pressing.

Conventionally, it is generally known that when a hot press molded product is obtained by hot press molding from a steel sheet having a zinc plating layer or an alloyed zinc plating layer on the surface, an oxide film is formed on the surface thereof. Since the oxide film adhering to the surface of the hot press molded product may reduce the adhesion of the coating film, for example, in Patent Document 1, the surface of the hot press molded product is irradiated with a laser beam to form the oxide film. After removing by vaporization, the adhesion of the coating film is improved by performing a painting treatment.

Japanese Unexamined Patent Publication No. 2015-105422

By the way, when a hot press molded product is welded by spot welding, if an oxide film is attached to the surface of the hot press molded product, the electrode tip is used to pressurize and hold the hot press molded product to energize. The electrical resistance between the tip surface of the hot press and the hot press molded product is increased by the oxide film. Therefore, the energization path becomes unstable and divergence occurs, and the quality of the formed welded portion varies.

In order to deal with this, the quality of the welded portion is stabilized by performing spot welding after removing the oxide film adhering to the surface of the hot press molded product by a method of irradiating a laser beam as in Patent Document 1. Can be considered.

However, although Patent Document 1 describes how to remove the oxide film with a laser beam to improve the adhesion of the coating film, the laser beam for stabilizing the quality of the welded portion formed by spot welding is used. Naturally, no consideration is given to how to reduce the oxide film.

The technique disclosed here has been made in view of these points, and the purpose thereof is a welding method for a hot press molded product capable of stabilizing the quality of the welded portion when spot welding is performed. Is to provide.

In order to solve the above-mentioned problems, in the technique disclosed here, only a part of the oxide film adhering to the surface of the hot press molded product is reduced by the laser beam, and the area where the oxide film is reduced and other areas are reduced. It is characterized in that a step is formed between the region and the region.

That is, the first aspect of the technique disclosed herein is to obtain a hot press molded product by hot press molding from a steel plate having a zinc plating layer or an alloyed zinc plating layer on the surface, and then the surface of the hot press molded product. An oxide film adhering to the planned welding region is formed by irradiating the planned welding region, which encloses the planned spot welding spots of the plurality of spot welds in a rectangular shape or a circular shape, with a laser beam using a laser oscillator. By vaporizing, the film thickness of the oxide film is reduced so that the film thickness of the oxide film adhering to the planned welding region becomes thinner than the film thickness of the oxide film adhering to the region other than the planned welding region. It is characterized in that a predetermined amount of thickness remains, and then another press-formed product or steel plate is superposed on the hot-press-formed product, and spot welding is performed on the planned spot welding portion in each of the planned welding regions. To do.

A second aspect of the technique disclosed herein is characterized in that, in the first aspect, the output of the laser beam irradiating the oxide film is 60 W to 140 W.

A third aspect of the technique disclosed herein is, in the first or second aspect, when reducing the oxide film adhering to the planned welding region, the laser beam is emitted in a state where the oxide film is irradiated with the laser light. It is characterized in that it scans in a zigzag manner at a scanning speed of 60 mm / sec or less.

In the first aspect, the amount of the oxide film adhering to each planned welding region on the surface of the hot press molded product is reduced, so that a step is generated between each planned welding region and the other region on the surface of the hot press molded product. become. Then, when the hot press molded product is pressurized and held by the electrode tip to energize, the electrical resistance between the tip surface of the electrode tip and the hot press molded product becomes smaller, and each welding of the hot press molded product surface is scheduled. Since the difference in electrical resistance between the region and the other region becomes large, it becomes possible to prevent the diversion during energization, and it is possible to stabilize the quality of the welded portion.

Further, by irradiating the laser beam so that a predetermined amount of the oxide film adhering to the planned welding region remains, the laser beam does not directly hit the galvanized layer, the alloyed zinc-plated layer, or the base metal. Therefore, it is possible to prevent the galvanized layer or the alloyed galvanized layer from being damaged or the hardness of the base metal from being affected, and the corrosion resistance, rust prevention, and rigidity are high even after spot welding. It can be a hot press molded product.

FIG. 1 is a layout diagram of a production line to which the welding method according to the first embodiment is applied. FIG. 2 is a block diagram of a production line to which the welding method according to the first embodiment is applied. FIG. 3 is a view taken along the line III of FIG. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. FIG. 5 is a photograph showing a cross section of a hot press molded product before removing the oxide film. FIG. 6 is a photograph showing a cross section of a hot press molded product after removing the oxide film. FIG. 7 is a graph showing the hardness of the base material before and after removing the oxide film in the hot press molded product. FIG. 8 shows various oxide film removal conditions when the oxide film is removed while changing the laser output for a hot press molded product molded under the maximum heating conditions, and hot with the oxide film removed under the various oxide film removal conditions. It is a graph which showed the relationship with the resistance value between electrode chips when a press-molded article was pressurized and held by a pair of electrode chips. FIG. 9 shows various oxide film removal conditions when the oxide film is removed while changing the laser output for a hot press molded product molded under the minimum heating conditions, and hot with the oxide film removed under the various oxide film removal conditions. It is a graph which showed the relationship with the resistance value between electrode chips when a press-molded article was pressurized and held by a pair of electrode chips. FIG. 10 shows various oxide film removing conditions when the oxide film is removed while changing the processing speed of the hot press molded product molded under the maximum heating condition, and hot with the oxide film removed under the various oxide film removing conditions. It is a graph which showed the relationship with the resistance value between electrode chips when a press-molded article was pressurized and held by a pair of electrode chips. FIG. 11 shows various oxide film removal conditions when the oxide film is removed while changing the processing speed of a hot press molded product molded under the minimum heating conditions, and hot with the oxide film removed under the various oxide film removal conditions. It is a graph which showed the relationship with the resistance value between electrode chips when a press-molded article was pressurized and held by a pair of electrode tips. FIG. 12 is a graph showing the relationship between the current value when spot welding is performed on a hot press molded product to which an oxide film adheres and the nugget diameter of the welded portion. FIG. 13 is a graph showing the relationship between the current value and the nugget diameter of the welded portion when spot welding is performed on the hot press molded product from which the oxide film has been removed. FIG. 14 is a diagram corresponding to FIG. 4 according to the second embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiment is essentially merely an example.

<< Embodiment 1 of the invention >>
FIG. 1 shows a production line 1 according to the first embodiment of the present invention. The production line 1 is designed to produce a vehicle body frame B1, and as shown in FIG. 2, has a zinc plating layer G1 (or an alloyed zinc plating layer) on the surface in order from the upstream side of the production line 1. A hot press molded product P1 is formed from a carry-in step 2 for storing a plurality of steel plates S1, a heating step 3 for heating the steel plate S1 carried in from the carry-in step 2, and a steel plate S1 heated in the heating step 3. Hot press step 4 to remove the oxide film W1 (see FIG. 4) adhering to the surface of the hot press molded product P1 during hot press molding, and the film removing step 5 to remove the oxide film, and the hot press molded product after removing the oxide film. The welding step 6 for obtaining the vehicle body frame B1 by integrating P1 and the flat plate-shaped press plate P2 (steel plate) by spot welding is arranged on a straight line.

As shown in FIG. 1, the carry-in step 2 has a pallet 20 on which a plurality of steel plates S1 are stacked and placed.

Between the carry-in step 2 and the heating step 3, a first robot R1 that sequentially carries a plurality of steel plates S1 stacked on the pallet 20 into the heating step 3 is arranged.

The heating step 3 includes a heating furnace 30 extending from the upstream side to the downstream side of the production line 1, and the heating furnace 30 includes a lower furnace body 30a installed on the floor and an upper side of the lower furnace body 30a. It has an upper furnace body 30b arranged opposite to the position of.

The lower furnace body 30a is provided with a plurality of transfer rollers (not shown) for transporting the steel plate S1, while the upper furnace body 30b has an atmosphere between the upper furnace body 30b and the lower furnace body 30a. A heater (not shown) for raising the gas is attached, and the heating furnace 30 raises the temperature of the steel plate S1 to about 800 to 1000 ° C. when the steel plate S1 is conveyed.

A second robot R2 that conveys the steel plate S1 heated in the heating furnace 30 to the hot pressing step 4 is arranged between the heating step 3 and the hot pressing step 4.

The hot press step 4 includes a mold 40 for hot press molding having an upper mold 41 and a lower mold 42, and a servomotor-controlled hydraulic press 43, and the hydraulic press 43 lowers the upper mold 41. It is designed to move up and down with respect to 42.

The upper mold 41 is formed with an upper pressure surface 41a having a substantially concave cross section, while the lower mold 42 is formed with a lower pressure surface 42a having a substantially convex cross section corresponding to the upper pressure surface 41a.

Then, by setting the heated steel plate S1 on the lower pressure surface 42a of the lower mold 42 and lowering the upper mold 41 to the lower dead point, the steel plate S1 is along the upper pressure surface 41a and the lower pressure surface 42a. The molded product is molded into a molded product having a substantially hat-shaped cross section, and the molded product is pressed and held by the upper mold 41 and the lower mold 42 to be cooled so that the molded product is hardened to obtain a hot press molded product P1. It has become.

Between the hot press step 4 and the film removing step 5, a third robot R3 that sequentially conveys the hot press molded product P1 formed in the hot press step 4 to the film removing step 5 is arranged.

The film removing step 5 includes a mounting table 50 on which the hot press molded product P1 can be placed, and a film removing device 51 arranged on the side of the mounting table 50.

The film removing device 51 is connected to the fourth robot R4, which is an industrial robot, the fiber laser oscillator 51a arranged on the side of the fourth robot R4, and the fiber laser oscillator 51a via a fiber cable 51b. The galvano scanner head 51c attached to the tip of the arm of the fourth robot R4 is provided, and the galvano scanner head 51c can scan the laser beam L1 excited by the fiber laser oscillator 51a with respect to the object. It has become.

As shown in FIG. 3, a plurality of spot welding spots scheduled to be implemented X1 are preset on the flange portion F1 of the hot press molded product P1 mounted on the mounting table 50, and the film removing device 51 As shown in FIG. 4, the oxide film W1 adhering to each planned welding region A1 is irradiated by irradiating the planned welding region A1 that encloses each planned spot welding portion X1 in a rectangular shape while scanning the laser beam L1. Is designed to be vaporized and removed.

The hot-press molded product P1 after removing the oxide film is conveyed to the welding step 6 by an industrial robot (not shown).

As shown in FIG. 1, the welding step 6 is arranged on the side of a jig 61 capable of superimposing and positioning the hot press molded product P1 and the press plate P2 after removing the oxide film, and the tip of the arm. A fifth robot R5 to which a welding gun T1 is attached is provided, and spot welding is performed on each planned spotting portion X1 using the welding gun T1 to integrate the hot press molded product P1 and the press plate P2. The body frame B1 is obtained.

Next, the work of removing the oxide film W1 in the hot press molded product P1 and the work of welding the hot press molded product P1 after removing the oxide film W1 will be described in detail.

As shown in FIG. 5, an oxide film W1 having a film thickness of about 2 to 5 μm is attached to the surface of the hot press molded product P1 obtained in the hot press step 4.

When the hot press molded product P1 to which the oxide film W1 adheres is placed on the mounting table 50 in the film removing step 5, the fourth robot R4 moves the galvano scanner head 51c above the flange portion F1 of the hot press molded product P1. ..

Next, when the galvano scanner head 51c reaches above the predetermined welding planned region A1 before removing the oxide film W1 in the flange portion F1, the laser beam L1 excited by the fiber laser oscillator 51a is welded from the galvano scanner head 51c. It is irradiated toward the planned area A1. Specifically, as shown in FIGS. 3 and 4, the scanning width is 30 mm and the processing speed (moving speed in the direction of arrow Z1 in FIG. 3 in the laser beam L1) is set with respect to the planned welding area A1 having an area of 30 mm × 30 mm. The laser beam L1 having an output of 100 W is scanned at 30 mm / sec. Then, as shown in FIG. 6, the oxide film W1 adhering to the surface of the hot press molded product P1 is removed. The planned welding area A1 may have another size.

Next, when the work of removing the oxide film W1 in the predetermined welding planned area A1 in the galvano scanner head 51c is completed, the fourth robot R4 moves the galvano toward the upper side of the welding planned area A1 in which the oxide film W1 is removed next. The scanner head 51c is moved. In this way, the work of removing the oxide film W1 in all the planned welding regions A1 is performed in order.

When the work of removing the oxide film W1 in all the planned welding regions A1 is completed, as shown in FIG. 1, the hot press molded product P1 after removing the oxide film W1 is conveyed to the welding step 6 by a robot (not shown), and the jig 61. It is superposed on the press plate P2 set on the top and positioned on the jig 61.

Then, the fifth robot R5 moves the welding gun T1 to perform spot welding on each spot welding planned portion X1 in the hot press molded product P1. Then, the hot press molded product P1 and the press plate P2 are integrated to obtain the vehicle body frame B1.

Next, the hardness evaluation of the hot press molded product P1 after the removal work of the oxide film W1 will be described.

FIG. 7 is a graph showing the results of measuring the hardness before and after removing the oxide film W1 in the planned welding region A1 in the hot press molded product P1, and the horizontal axis is the hot press molded product P1. The depth from the surface and the vertical axis are the hardness. From this result, there is no change in the hardness of the base metal before and after removing the oxide film W1 in the hot press molded product P1, and the work of removing the oxide film W1 in the film removing step 5 of the present invention is hot press molding. It was confirmed that it did not affect the quenching effect at the time.

Next, the hot press molded product P1 obtained by hot press molding with the heating conditions in the heating step 3 set to 910 ° C., and the hot press molded product obtained by hot press molding with the heating conditions set to 890 ° C. in the heating step 3 An experiment in which the oxide film W1 in each planned welding region A1 is removed under various oxide film removal conditions will be described with reference to P1.

The oxide film W1 is removed under the conditions A to F in which the combination of the output, processing speed, and frequency of the laser beam L1 emitted from the galvano scanner head 51c is changed, and the area to be welded after the oxide film W1 is removed. A1 was sandwiched between a pair of electrode tips and pressurized with a pressing force of 5.88 kN, and the work of checking the resistance value between the electrode tips was performed a plurality of times. The thickness of each of the hot press molded product P1 and the press plate P2 is 1.8 mm.

Then, when the processing speed and frequency of the laser beam L1 are set to the same conditions and the output is changed, as shown in FIGS. 8 and 9, both hot press molded products P1 having different heating conditions have the laser beam L1. It was found that the resistance value between the electrode chips was low and became a stable value when the output of was 100 W.

Further, when the output and frequency of the laser beam L1 are set to the same conditions and the processing speed is changed, as shown in FIGS. 10 and 11, both hot press molded products P1 having different heating conditions have the laser beam L1. It was found that the resistance value between the electrode chips was low and became a stable value when the processing speed was 30 mm / sec.

Next, an experiment in which spot welding is performed on each of the hot press molded products P1 before and after removing the oxide film W1 will be described.

Spot welding was performed while changing the current value of energizing the hot press molded product P1, and the nugget diameter of each welded portion was measured. Other welding conditions for spot welding were a pressing force of 5.88 kN, an electrode tip diameter of φ6R40 mm, an energizing time of 24 cycles, and a holding time of 2 cycles.

As shown in FIG. 12, when spot welding is performed on the hot press molded product P1 before removing the oxide film W1, a range of current values (appropriate current range) that satisfies the reference value of the nugget diameter that can ensure welding quality. Turned out to be very narrow.

On the other hand, as shown in FIG. 13, when spot welding is performed on the hot press molded product P1 after removing the oxide film W1, a range of current values (appropriate current) that satisfies the reference value of the nugget diameter that can ensure welding quality. It turned out that the range) can be widened.

From the above, according to the first embodiment of the present invention, the oxide film W1 adhering to each planned welding region A1 on the surface of the hot press molded product P1 disappears, and as shown in FIG. 4, each on the surface of the hot press molded product P1. A step will be generated between the planned welding region A1 and the other region. Then, when the hot press molded product P1 is pressurized and held by the electrode tip to be energized, the electrical resistance between the tip surface of the electrode tip and the hot press molded product P1 becomes small, and the surface of the hot press molded product P1 surface. Since the difference in electrical resistance between each planned welding region A1 and the other regions becomes large, it becomes possible to prevent the diversion at the time of energization, and it is possible to stabilize the quality of the welded portion.

<< 2nd Embodiment of the Invention >>
FIG. 14 shows a state in which the oxide film W1 is removed from the surface of the hot press molded product P1 in the film removing step 5 of the production line 1 according to the second embodiment of the present invention. In the second embodiment, the method of removing the oxide film W1 is different from that of the first embodiment, and the other parts are the same as those of the first embodiment. Therefore, the same parts as those of the first embodiment are designated by the same reference numerals. , Only the different parts will be explained in detail.

The planned welding region A1 of the second embodiment has a circular shape corresponding to the tip surface of the electrode tip used at the time of spot welding.

Further, in the second embodiment, when the planned welding region A1 is irradiated with the laser beam L1, the film thickness H1 of the oxide film W1 adhering to the planned welding region A1 on the surface of the hot press molded product P1 excludes the planned welding region A1. The thickness of the oxide film W1 adhering to the region is made thinner than the film thickness H2, and a predetermined amount of thickness remains.

From the above, according to the second embodiment of the present invention, when the hot press molded product P1 is pressure-held by the electrode tip in the planned spotting portion X1, the peripheral edge portion of the tip surface of the electrode tip corresponds to the stepped portion of the oxide film W1. It will be in the position where it was. Therefore, when a current is passed between the tip surface of the electrode tip and the hot press molded product P1, the current flow is concentrated on the planned spotting portion X1 and the diversion can be reliably prevented. The quality of the welded part can be further stabilized.

Further, since the laser beam L1 is irradiated so that a predetermined amount of the oxide film W1 adhering to the planned welding region A1 remains, the laser beam L1 does not directly hit the galvanized layer G1 and the base material. Therefore, it is possible to prevent the galvanized layer G1 from being damaged or the hardness of the base metal from being affected, and the hot press molded product P1 having high corrosion resistance, rust prevention, and rigidity even after spot welding. Can be.

In the first and second embodiments of the present invention, the flat plate-shaped press plate P2 is superposed on the hot-press molded product P1 and integrated by spot welding, but the non-flat-shaped press-molded product is a hot-press molded product. It may be overlapped with P1 and integrated by spot welding.

Further, in the first and second embodiments of the present invention, the fiber laser oscillator 51a is used as the oscillator that oscillates the laser beam L1, but the laser beam L1 may be oscillated by using the YAG laser oscillator.

Further, in the first and second embodiments of the present invention, the galvano scanner head 51c is used to irradiate the planned welding region A1 with the laser beam L1, but another laser processing head is used to irradiate the planned welding region A1 with the laser beam L1. May be irradiated.

The present invention is suitable for a method of welding a hot press molded product obtained by hot pressing.

A1 Planned welding area G1 Galvanized layer L1 Laser beam P1 Hot press molded product P2 Press plate (steel plate)
S1 Steel plate W1 Oxide film X1 Dotting planned part

Claims (3)

After obtaining a hot press molded product by hot press molding from a steel plate having a zinc plating layer or an alloyed zinc plating layer on the surface, is the planned spot welding portion of a plurality of spot welds on the surface of the hot press molded product rectangular in shape? Alternatively, by irradiating the planned welding region surrounded by a circular shape with laser light using a laser oscillator, the oxide film adhering to the planned welding region is vaporized to reduce the film thickness of the oxide film, and the welding is performed. The film thickness of the oxide film adhering to the planned area is made thinner than the film thickness of the oxide film adhering to the area other than the planned welding area, and a predetermined amount of thickness remains, and then the hot press is performed. A method for welding a hot press molded product, which comprises superimposing another press molded product or a steel plate on the molded product and performing spot welding on the planned spot welding portion in each of the planned welding regions. In the method for welding a hot press molded product according to claim 1,
A method for welding a hot press molded product, wherein the output of the laser beam irradiating the oxide film is 60 W to 140 W. In the method for welding a hot press molded product according to claim 1 or 2.
When reducing the oxide film adhering to the planned welding region, the hot press molded product is characterized in that the laser beam is scanned in a zigzag manner at a scanning speed of 60 mm / sec or less while the oxide film is irradiated with the laser beam. Welding method.

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