JP2020157346A - Resistance welding method of welding object having insulation coating film - Google Patents

Abstract

To provide a resistance welding method capable of simply executing work before welding when applying resistance welding to a welding object having an insulation coating film and capable of also applying to a welding object having an insulation coating film on both surfaces.SOLUTION: A resistance welding method includes a first process of forming an assembly by superposing a plurality of welding objects having an insulation coating film on a surface, a second process of imparting damage to the inside insulation coating film of the assembly by heating means via an area for contacting a welding electrode with the assembly and a third process of executing resistance welding by electrically conducting by contacting a pair of welding electrodes with an opposed position by sandwiching the assembly on a surface of the damage-imparted assembly.SELECTED DRAWING: Figure 4

Description

The present invention relates to a resistance welding method for an object to be welded having an insulating film on the surface of a base metal.

Various heating means are used as a method of welding metal members to each other. Among them, in resistance welding, the overlapped objects to be welded are sandwiched between resistance weld electrodes, a welding current is applied from the resistance weld electrodes through the surface of the objects to be welded, and Joule heat is generated to generate Joule heat near the joint surface of the objects to be welded. Is a method of heating and welding. The resistance welding method is used in many fields because it can be welded efficiently in a short time.

When the object to be welded has an electrically insulating film (referred to as "insulating film" in the present specification) on the surface, when the resistance welding method is applied to the film, a welding current is passed through the object to be welded. It is not possible to secure a sufficient energization path. Therefore, the joint surface of the object to be welded cannot be sufficiently heated, and it is difficult to perform resistance welding. Further, if the amount of energization is excessively increased in order to obtain the required amount of heat generation resistance, spatter may occur, resulting in poor appearance and deterioration of the working environment.

In order to solve the above problem, a method has been proposed in which the insulating film on the surface of the work piece is removed in advance by irradiation with a laser beam (see Patent Document 1). FIG. 5 of Patent Document 1 describes the third embodiment in which an aluminum alloy object to be welded having an anodic oxide film on one side is used as an example. After superimposing the two objects to be welded so that the insulating anodic oxide film was located on the outside, the surface of the objects to be welded was irradiated with a laser beam to remove the anodic oxide film. Next, the resistance welding electrode was brought into contact with the portion from which the anodic oxide film was removed to sandwich the object to be welded, and welding was performed at the joint surface of the object to be welded.

Japanese Unexamined Patent Publication No. 10-225770

In the method of Patent Document 1, it is necessary to remove the insulating film before welding at the portion where the resistance welding electrode is brought into contact, and the work for that purpose is troublesome. Further, the method of Patent Document 1 cannot be applied to an object to be welded having an insulating coating on both sides. Therefore, when applying resistance welding to an object to be welded having an insulating coating, it is desirable to simplify the work before welding. Further, it is desired to apply it to an object to be welded having an insulating film on both sides.

When resistance welding is applied to an object to be welded having an insulating film, the present invention can simplify the work before welding and can be further applied to an object to be welded having an insulating film on both sides. It is an object of the present invention to provide a resistance welding method.

As a result of studies to achieve the above object, the present inventors ensure the electrical conductivity required for resistance welding by damaging the insulating film on the joint surface side on which the objects to be welded are overlapped. We have found what we can do and have completed the present invention. Specifically, the present invention provides the following.

(1) The present invention comprises a first step of superimposing a plurality of objects to be welded having an insulating coating on the surface to form an assembly, and means for heating the assembly through a region where the welding electrode is brought into contact with the assembly. A pair of welding electrodes are brought into contact with each other at positions facing each other across the assembled assembly on the surface of the damaged assembly and the second step of damaging the insulating coating inside the assembly. This is a resistance welding method including a third step of performing resistance welding.

(2) In the second step of the present invention, the area of damaging the insulating coating inside the assembly is equal to or greater than the value indicated by 0.3 × 4πt (t: plate thickness) (1). ) Is the resistance welding method.

(3) The present invention is the resistance welding method according to (1) or (2), wherein the heating means in the second step is irradiation with a laser beam.

(4) The present invention describes any one of (1) to (3), wherein the insulating coating is an oxide coating containing at least one of zinc (Zn), aluminum (Al), and magnesium (Mg). This is a resistance welding method.

According to the present invention, when resistance welding is applied to an object to be welded having an insulating film, the work before welding can be simplified, and further, it is applied to an object to be welded having an insulating film on both sides. Can be done.

It is a figure for demonstrating the aspect by the double-sided plated steel sheet in the 1st step of this embodiment. It is a figure for demonstrating the aspect which irradiates a laser beam in the 2nd step of this embodiment. It is a figure for demonstrating the solidified part and the damaged part of the object to be welded formed by the irradiation of the laser beam of FIG. It is a figure for demonstrating the mode in which the resistance welding electrode was brought into contact with each other in the 3rd step of this embodiment. It is a figure which shows the example which applied this embodiment to a single-sided plated steel sheet, and made the plated surface face each other. It is a figure which shows the example which applied this embodiment to a single-sided plated steel sheet, and made the plated surface and the non-plated surface face each other. It is a figure which shows the damaged part of the object to be welded formed by the laser irradiation of this embodiment.

Hereinafter, embodiments according to the present invention will be described. The present invention is not limited to the following description.

Depending on the application, an assembly is formed by superimposing objects to be welded such as double-sided plated steel plates with an insulating coating, and then resistance welding such as spot welding is performed by sandwiching a pair of welding electrodes to join them. Be given. The electrical conductivity of the current supplied from the weld electrode is reduced by the insulating coating. Therefore, as in the prior art, removing the edge coating in the region in contact with the welding electrode before welding is effective in improving the electrical conductivity of resistance welding. However, sufficient electrical conductivity could not be obtained only by removing the insulating film in the region in contact with the weld electrode.

Since the joint portion by welding is a region where the insulating coating of the object to be welded faces, the present inventors paid attention to the electrical conductivity in this facing region. In the case of an assembly in which two double-sided plated steel sheets are laminated, the insulating coatings of the respective plated steel plates face each other, and the double insulating coatings are arranged at the joints, so that the electrical conductivity is greatly impaired. .. Therefore, we tried to form an energization path by removing a part of the insulating film in this facing region. As a result, they have found that even if an insulating film remains on the surface in contact with the welding electrode, good weldability can be obtained by ensuring the electrical conductivity between the steel plates.

The resistance welding method according to the present embodiment heats through a first step of superimposing a plurality of objects to be welded having an insulating coating on the surface to form an assembly and a region where the welding electrode is brought into contact with the assembly. The second step of damaging the insulating coating inside the assembly and the pair of welding electrodes are brought into contact with each other at positions facing each other across the assembled assembly on the surface of the damaged assembly. It includes a third step of performing resistance welding by energizing and energizing.

(First step)
The work piece has an insulating coating on the surface of the base metal. In the first step of the present embodiment, a plurality of objects to be welded are superposed to form an assembly. It is preferable to fix the assembly with a jig (not shown). The object to be welded is not particularly limited as long as it is an article having an electrically insulating coating on its surface, such as a plate material, a profile material, and a pipe material. A double-sided plated steel sheet or a single-sided plated steel sheet having a plated layer on the surface of the steel sheet is preferable. It may be applied to a steel plate having a plate thickness of 0.4 to 2.3 mm.

The insulating coating according to the present embodiment is not limited to the one in which the entire coating has an insulating property. The case where the front surface side portion has an insulating property and the inner surface portion has a conductive film is also included.

FIG. 1 is a diagram schematically showing the first step of the present embodiment. This is an example in which a double-sided plated steel sheet 3 having an insulating coating 2 on both sides of the steel sheet 1 is used as the object to be welded. The assembly 4 is formed by superimposing two double-sided plated steel plates 3. Inside the assembly 4, the insulating coatings 2 of the plated steel sheets 3 are in contact with each other so as to face each other. The outer surface of the assembly 4 also has an insulating coating 2.

Examples of using a single-sided plated steel sheet having an insulating coating on one side of the steel sheet as the object to be welded are shown in FIGS. 5 and 6. In the example shown in FIG. 5, the plated surfaces of the single-sided plated steel sheets 5 face each other, and the insulating coating 2 is arranged inside the assembly 4. In FIG. 6, the plated surface and the non-plated surface face each other, the insulating coating 2 of one single-sided plated steel sheet 5 is arranged inside the assembly 4, and the insulating coating 2 of the other single-sided plated steel sheet 5 is the assembly. It is a form arranged on the outer surface of the solid body 4.

The resistance welding method of the present embodiment can be applied to an article containing an insulating plating film having an insulating surface on both sides or one side of the base material. It may be applied to a plated steel sheet in which the amount of the insulating plating film adhered is in the range of 30 to 350 g / m ² per both sides or one side.

(Second step)
2 and 3 are diagrams schematically showing the second step of the present embodiment. In the second step of the present embodiment, the means 6 for heating the assembly 4 through the region where the welding electrode 9 is brought into contact with the assembly 4 is used to damage the insulating coating 2 inside the assembly 4. In the third step, the welding electrode is brought into contact with the surface of the assembly to perform resistance welding. Therefore, in the second step, as a pretreatment thereof, the inside of the test piece is heated through the region where the welding electrode is in contact. By locally heating the assembly, a portion of the insulating coating contained inside the assembly can be removed, thereby forming an energizing path inside the assembly.

In the second step of the present embodiment, it is preferable that the area of damaging the insulating coating inside the assembly is equal to or larger than the value indicated by 0.3 × 4πt (t: plate thickness). The diameter (nugget diameter) of a nugget, which is a melted / solidified portion generated at a joint by welding, is generally represented by 4√t (t: plate thickness), and the nugget area is represented by 4πt. The above "0.3 x 4πt" indicates the ratio of the damaged area to the nugget area, and since the damaged part in the nugget provides an energizing path, the area of the damaged part is the nugget area (4πt). When it is 30% or more, sufficient electrical conductivity can be obtained. On the other hand, if the area ratio of the damaged portion is smaller than 30%, an excessive current density is required, which may affect the nugget diameter and the joint strength.

As the heating means, a method of irradiating a laser beam is preferable. As shown in FIG. 2, the laser beam 6 is irradiated to the region where the welding electrode 9 is brought into contact in the third step toward one surface of the assembly 4. When the laser beam 6 is irradiated for a predetermined time, as shown in FIG. 3, the insulating coating 2 on the surface to which the laser beam 6 of the assembly 4 is irradiated and passes is locally heated. The portion melts and solidifies to form a region 7 from which the insulating film has been removed. In the present specification, this region 7 is referred to as a “coagulation portion”. The solidifying portion 7 forms an energizing path for applying a welding current from the surface of the assembly 4.

Further, when the laser beam is irradiated under appropriate conditions such as setting the focus of the laser beam near the insulating coating 2 inside the assembly 4, the insulating coating 2 is locally heated. By the heating, the insulating coating 2 is melted or evaporated, and a part of the insulating coating 2 is removed and damaged. As described above, the description of "damage" in the second step of the present embodiment means a state in which a part of the insulating coating is removed. The damaged portion 8 in the insulating coating 2 inside the assembly 4 is referred to as a “damaged portion”. By forming the damaged portion 8, it is possible to secure an energization path between the plates in which the insulating coating 2 is overlapped in two layers.

As conditions for irradiating the laser beam, for example, the irradiation output can be 600 W and the irradiation time can be 500 ms.

As the heating means in the second step, in addition to laser light irradiation, means that enable local heat input such as induction heating and eddy current may be used.

(Third step)
FIG. 4 is a diagram schematically showing the third step of the present embodiment. As shown in FIG. 4, in the third step of the present embodiment, a pair of welding electrodes 8 are brought into contact with each other at positions facing each other across the assembly 4 on the surface of the damaged assembly 4 to energize. Then, resistance welding such as spot welding is performed. By the heat treatment in the second step, in addition to forming the solidified portion 7 on the surface of the assembly 4, the damaged portion 8 of the insulating coating 2 is formed inside the assembly 4, so that sufficient energization is performed. A path is formed. Therefore, when the welding electrode 9 is brought into contact with the surface of the assembly 4 and energized, resistance welding can be performed under appropriate conditions without applying an excessive voltage.

For resistance welding, known welding means such as spot welding can be used. The assembly is sandwiched between welding electrodes, a predetermined pressing force is applied, and a predetermined current is applied to locally heat the assembly to form a point-shaped welded portion (nugget). As the welding conditions, for example, energization time: 12/60 seconds, current: 8.0 kA, and pressing force: 2.0 kN can be used.

The resistance welding method according to the present embodiment can be applied to an object to be welded having an insulating film which is an oxide film containing at least one of zinc (Zn), aluminum (Al), and magnesium (Mg). For example, a black hot-dip galvanized steel sheet can be mentioned. This steel sheet uses a plated steel sheet having a molten Zn plating layer containing Al: 1.0 to 22.0% by mass and Mg: 1.3 to 10.0% by mass as the original plate, and seals the plated steel sheet in a sealed container. It is a black-plated steel sheet obtained by subjecting it to contact with water vapor. By the treatment of contacting with water vapor, an oxidation reaction of Zn, Al and Mg occurs from the surface of the plating layer, and as a result, a black oxide is formed in the plating layer to obtain a black hot-dip galvanized steel sheet. Since the black oxide is an insulating substance, the surface side portion of the black hot-dip galvanized layer exhibits insulating properties, and the inner portion thereof has conductivity. This black hot-dip galvanized layer is formed on both sides or one side of a steel sheet and corresponds to an insulating film.

Hereinafter, examples of the present invention will be described. The present invention is not limited to the following examples.

<Example>
(1) Measurement of Inter-plate Coating Damage Area Ratio A test piece composed of an upper plate and a lower plate was prepared by superimposing two black hot-dip galvanized steel plates having a plate thickness of 0.8 mm. The plated steel sheet used was a double-sided plated steel sheet having a plating layer having a Zn-6% Al-3% Mg composition in mass%, and had dimensions of 100 mm × 30 mm and a plating adhesion amount of 60 to 80 g / m ² . .. The surface side portion of the plated layer of the plated steel sheet exhibits insulating properties, and the inner portion thereof has conductivity. A laser beam was irradiated to the outer surface of the upper plate of the test piece with a 1 kW laser welder to partially damage the insulating coating on the side where both the upper plate and the lower plate face each other.

For the irradiation of the laser beam, the focus of the laser welder was fixed at 245 mm (just focus 225 mm + 20 mm), the irradiation output was 200 W to 800 W, and the irradiation time was within the range of 200 ms to 1000 ms.

Next, the damaged area of the damaged portion of the insulating coating on the upper plate and the lower plate of the test piece was measured. Since the laser beam is applied to the upper and lower plates that are overlapped with each other, it is considered that the same degree of damage is caused to both the upper plate and the lower plate. Therefore, the damaged area of the upper plate was measured. However, since the reference nugget area depends on the plate thickness, when the two plate thicknesses are not the same, the damaged area of the thinner plate is measured.

After separating the upper plate and the lower plate, the damaged area of the insulating coating on the surface of the upper plate facing the lower plate was measured. Using the image observed with the microscope, the remaining plating portion and the removing plating portion can be distinguished by different colors. An example thereof is shown in FIG. In FIG. 7, the remaining plating portion is displayed in black, and the plating removal portion is displayed in silver white.

The area of the plating-removed portion was measured in the region corresponding to the nugget area (4πt), and the total value was taken as the damaged area. The ratio (%) of the damaged area to the nugget area (4πt) was calculated. The ratio is called the "inter-plate coating damage area ratio". Since the test piece used in Example 1 has a plated steel plate thickness of 0.8 mm, the nugget area (4πt) based on the reference nugget diameter (4√t) corresponds to about 10.1 mm ² .

(2) Evaluation of weldability According to the same procedure as the test piece used for measuring the area ratio of the coating film damaged between the plates in (1) above, the test piece No. 1-No. No. 9 was prepared, and the test piece was irradiated with a laser beam. Next, the obtained test piece was subjected to resistance welding by spot welding using a single-phase AC welding machine (AC frequency 60 Hz) at a location irradiated with laser light.

Spot welding was performed at an initial pressurizing time of 35 cycles, an energizing time of 12 cycles, a current value of 7.0 kA, a pressing force of 2.0 kN, and a cooling water amount of 3 L / min. As the welding electrode, a 6DR type (dome radius type JIS C9304) electrode made of chrome copper was used. The initial pressurization time and energization time correspond to the time obtained by dividing the cycle value by the frequency of 60 Hz. For example, 12 cycles correspond to 0.2 s (= 12/60).

As a conventional example, a test piece No. made of a double-sided plated steel sheet that has not been irradiated with a laser beam. 10 was prepared and spot welded under the same conditions as other test pieces. Specimen No. The double-sided plated steel sheet of No. 10 has a test piece No. 1-No. The same double-sided galvanized steel sheet as in No. 9 was used.

In order to evaluate the weldability of the joint, a tensile shear test conforming to JIS Z3140 was performed using a test piece subjected to spot welding, and the tensile shear strength (kN) was measured. The measurement results are shown in Table 1. In the test specimens indicated by "-" in Table 1, the tensile shear strength could not be measured because the joints were separated before being attached to the tensile shear tester.

According to JIS Z3140, the tensile shear strength of JIS A class in steel corresponds to 3.62 kN when the plate thickness is 0.8 mm. Therefore, when the tensile shear strength of the test piece exceeds 3.62 kN, the test piece is judged to have good weldability (◯). When it was 3.62 kN or less or when it was not joined, the test piece was judged to have poor weldability (x). The evaluation results are shown in Table 1.

The inter-plate coating damage area ratio (%) in Table 1 is a numerical value calculated by measuring the test piece before spot welding. Specimen No. that was spot welded. 1-No. It can be estimated that even in No. 9, it has the same level of inter-plate coating damage area ratio as those measurement results.

As shown in Table 1, Specimen No. 1-No. In No. 5, since the damage area ratio between the plates of the insulating coating was 30% or more, good weldability was obtained in each case. On the other hand, the test piece No. 7 to No. In No. 9, the weldability was poor because the area ratio of the coating between the plates was less than 30%.

<Example 2>
Using double-sided plated steel sheets having different plating adhesion amounts, the test piece No. was used in the same procedure as in Example 1. 21-No. 25 was produced, laser light irradiation and spot welding were performed, the inter-plate film damage area ratio and tensile shear strength were measured, and the weldability was evaluated. Specimens were prepared by changing the amount of plating on the steel sheet in the range of 30 to 350 g / m ² . Laser irradiation and spot welding were performed under the same conditions as in Example 1. The tensile shear strength of the test piece subjected to spot welding was measured, and the weldability was evaluated according to the same criteria as in Example 1. The results are shown in Table 2.

As shown in Table 2, for samples with an adhesion amount of 30 to 350 g / m ² , test specimens having an inter-plate coating damage area ratio of 30% or more were obtained, and good welding was obtained in all cases, which was practical. It was possible to apply spot welding.

<Example 3>
Using double-sided plated steel sheets having different plate thicknesses, the test piece No. was used in the same procedure as in Example 1. 31-No. 35 was produced, laser light irradiation and spot welding were performed, the inter-plate film damage area ratio and tensile shear strength were measured, and the weldability was evaluated. Specimens were prepared by changing the thickness of the double-sided plated steel sheet in the range of 0.4 to 2.3 mm. The dimensions and the amount of plating adhesion of the double-sided plated steel sheet are the same as in Example 1.

The laser beam irradiation had an output of 200 to 1000 W and an irradiation time of 200 to 2000 ms, and other conditions were the same as in Example 1.

In spot welding, the energizing time was 6 to 30 cycles, the current value was 6.0 to 13.0 kA, the pressing force was 1.5 to 5.0 kN, and other conditions were the same as in Example 1. The tensile shear strength of the test piece subjected to spot welding was measured, and the weldability was evaluated by the same procedure as in Example 1. The results are shown in Table 3.

As shown in Table 3, for a test piece having a plate thickness of 0.4 to 2.3 mm, a test piece having an inter-plate coating damage area ratio of 30% or more was obtained, and good welding was obtained in each case, which was practically used. It was possible to perform the above spot welding.

Examples 1 to 3 show the test results using the double-sided plated steel sheet. As shown in FIG. 5, two layers of insulating coatings are overlapped and arranged inside the assembly in which the single-sided plated steel plates are laminated, and as shown in FIG. In addition, there is a form in which one layer of an insulating film is arranged, and it can be said that the thickness of the insulating film inside the assembly is about the same as or thinner than that of the test pieces of Examples 1 to 3. Therefore, if the laser beam irradiation treatment and spot welding are performed by using these single-sided plated steel sheet assemblies in the same procedure as in Examples 1 to 3, the inter-plate coating damage is performed as in Examples 1 to 3. When the ratio is 30% or more, good weldability can be obtained.

1 Steel plate 2 Plating layer (insulating film)
3 Double-sided galvanized steel sheet (workpiece)
4 Assembly 5 Single-sided galvanized steel sheet (workpiece)
6 Laser beam 7 Solidified part 8 Damaged part 9 Welded electrode

Claims (4)

The first step of superimposing a plurality of objects to be welded having an insulating coating on the surface to form an assembly, and
A second step of damaging the insulating coating inside the assembly by means of heating through a region that contacts the weld electrode with the assembly.
A resistance welding method comprising a third step of performing resistance welding by bringing a pair of welding electrodes into contact with each other at positions facing each other on the surface of the damaged assembly so as to sandwich the assembly. The resistance welding method according to claim 1, wherein in the second step, the area that damages the insulating coating inside the assembly is equal to or larger than a numerical value indicated by 0.3 × 4πt (t: plate thickness). .. The resistance welding method according to claim 1 or 2, wherein the heating means in the second step is irradiation of a laser beam. The resistance welding method according to any one of claims 1 to 3, wherein the insulating coating is an oxide coating containing at least one of zinc (Zn), aluminum (Al), and magnesium (Mg).