JP2010247232A - Method for manufacturing welded structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a welded structure capable of executing the welding without discoloring a coating surface of a coated metal sheet when manufacturing the welded structure by abutting a non-coated metal sheet on a non-coating surface of the coated metal sheet, executing the welding by applying laser beam from the non-coated metal sheet side. <P>SOLUTION: A coated metal sheet with its first surface being coated, and a non-coated metal sheet are prepared. A first surface of the non-coated metal sheet is abutted on a second surface opposite to the first surface of the coated metal sheet, and laser beam is applied to execute the welding to the second surface opposite to the first surface of the non-coated metal, the laser beam satisfying inequalities R≥t<SB>1</SB>and t<SB>2</SB>/1.05≥R (wherein R denotes the laser beam spot diameter (mm); t<SB>1</SB>denotes the thickness (mm) of the non-coated metal sheet; and t<SB>2</SB>denotes the thickness (mm) of the coated metal sheet). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a welded structure by laser welding metal plates to each other, and more specifically, laser welding a painted metal plate that has been previously painted on one side and a non-coated metal plate. The present invention relates to a method for manufacturing a welded structure.

  Furniture, such as desks, bookcases, cabinets, etc., is designed with a good appearance after laser welding of non-painted metal plates (for example, steel plates) together and assembling to ensure strength. In order to enhance, the surface is painted by spraying or brushing. However, when painting after welding, it is necessary to perform a degreasing treatment or a chemical conversion treatment before painting, and the operation becomes complicated.

  On the other hand, in order to improve productivity and reduce costs, a pre-painted metal plate (sometimes called a pre-coated metal plate) pre-painted on one side and a non-painted metal plate are joined together by laser welding. It is possible. However, when the coated metal plate is laser welded, the periphery of the welded portion is affected by heat and the coating film is thermally damaged, and the appearance is remarkably impaired. For example, Patent Literature 1 proposes a technique for solving such a problem. This document discloses a method of welding an uncoated surface of a single-side precoated steel plate coated on one side with an insulating polymer film to a metal surface of another metal plate. In this welding method, the welded part on the uncoated surface of the single-sided precoated steel sheet and the welded part on the metal surface are brought into close contact with each other, and the precoated steel sheet is bent into a substantially U shape so that the coated surface is on the outer side at the contacted part. A V-shaped groove is formed, and a laser beam is irradiated toward the inner back of the groove. However, in this welding method, it is necessary to bend the precoated steel sheet in order to expose the uncoated surface of the single-sided precoated steel sheet. The close contact portion is irradiated with a laser beam from a direction of about 45 °.

  On the other hand, although it is not a technique for joining a painted metal plate and a non-painted metal plate, Patent Document 2 proposes a weld joint made of a stainless steel plate having a titanium oxide layer on the front surface. In this document, it is pointed out that when the temperature of the titanium oxide-coated part is increased by heat conduction from the molten metal part, a temper color is produced and the design property is inferior. And in order to prevent the designability deterioration, it is disclosed that the penetration depth of the welded portion is 20 to 80% or less of the plate thickness from the back surface.

JP-A-4-41089 JP 2002-103074 A

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to bring a non-painted metal plate into contact with the non-painted surface of the painted metal plate and apply a laser from the non-painted metal plate side. An object of the present invention is to provide a method of manufacturing a welded structure that can be welded and joined without discoloring the painted surface of the coated metal plate when the welded structure is manufactured by welding.

The manufacturing method of the welded structure according to the present invention that has solved the above-mentioned problems is a method of manufacturing a welded structure by laser welding the metal plates to each other. Preparing a non-painted metal plate, contacting a first surface of the non-painted metal plate with a second surface opposite to the first surface of the painted metal plate, Has a gist in that the second surface on the opposite side is welded by applying a laser so as to satisfy the following equations (1) and (2). In the following formula, R is the laser spot diameter (mm), t ₁ is the thickness (mm) of the unpainted metal plate, and t ₂ is the thickness (mm) of the painted metal plate.
R ≧ t ₁ (1)
t ₂ /1.05≧R (2)

On the second surface of the coated metal plate, a resin thin film may be provided with an adhesion amount of less than 4 g / m ² (not including 0 g / m ² ). The laser spot diameter R is, for example, 0.8 mm or more. A thickness t ₁ of the non-painted metal plate is, for example, 0.6 mm or more, and a thickness t ₂ of the painted metal plate is, for example, 0.8 mm or more. The base material of the painted metal plate and / or the non-painted metal plate is preferably a steel plate. The base metal of the painted metal plate and / or the non-painted metal plate may be a galvanized steel plate. The coating film provided on the painted metal plate is, for example, a thermosetting resin film. The present invention also includes furniture including the above welded structure.

According to the present invention, when the non-painted metal plate is brought into contact with the non-painted surface of the painted metal plate and welding is performed by applying a laser from the non-painted metal plate side, the thickness (t ₁ and t ₂ ) and the laser spot diameter (R) are appropriately controlled, so that the coated metal plate can be prevented from being overheated locally during welding. As a result, it is possible to prevent welding heat from being conducted through the painted metal plate to the painted surface and discoloring the coating film due to the thermal influence, and it is possible to provide a welded structure excellent in design.

FIG. 1 is a longitudinal sectional view for explaining a state during laser welding. FIG. 2 is another longitudinal cross-sectional view for explaining the state during laser welding. FIG. 3 is a perspective view for explaining a state during laser welding. FIG. 4 is another perspective view for explaining a state during laser welding.

The inventors of the present invention have provided a coating film provided on a coated metal plate when a coated metal plate coated on one side (that is, a metal plate provided with a coating film) and a non-painted metal plate are laser-welded. Has been intensively studied on a method for producing a welded structure having a good design property by preventing discoloration due to thermal influence during welding. As a result, if the spot diameter R of the laser applied to the non-coated metal plate is appropriately controlled according to the thickness t ₁ of the non-coated metal plate and the thickness t ₂ of the painted metal plate, the coating film provided on the painted metal plate The present inventors have found that a welded structure in which a painted metal plate and a non-painted metal plate are welded and joined can be manufactured without affecting heat, and the present invention has been completed.

  Hereinafter, the method for producing a welded structure according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the illustrated examples, and may be changed within a range that can be adapted to the purpose described above and below. It is also possible to carry out by adding any of these, and they are all included in the technical scope of the present invention.

  FIG. 1 is an explanatory view schematically showing a state when a welded structure according to the present invention is manufactured, and is shown in a longitudinal sectional view. In the figure, 1 is a non-painted metal plate, 2 is a painted metal plate, and 3 is a laser output unit. The coated metal plate 2 is coated on one side of the base material 2a, and 2b indicates a coating film. In this specification, the coated surface is defined as a first surface 2c, and the surface opposite to the first surface is defined as a second surface (non-coated surface) 2d. Moreover, in this specification, among the non-painted metal plates 1, the surface that contacts the second surface 2d of the painted metal plate 2 is the first surface 1a, and the surface opposite to the first surface 1a is the second surface 1b. And In the figure, reference numeral 3a denotes a laser irradiated from the laser output unit 3, and R is a spot diameter drawn on the second surface 1b of the unpainted metal plate 1 by the laser 3a.

In the present invention, as shown in FIG. 1, a painted metal plate 2 having a first surface coated and a non-painted metal plate 1 are prepared, and the first surface 1a of the non-painted metal plate 1 is coated with a painted metal plate. 2 is brought into contact with the second surface 2d to form a laminate. And the laser beam 3a is irradiated to the 2nd surface 1b of the non-coating steel plate 2, and welding is performed. In the present invention this time, according to the thickness t ₂ of the coated metal plate 2 and the thickness t ₁ of the non-coated metal plate 1, the following equation (1), important to laser 3a irradiated so as to satisfy the expression (2) It is. In the formula, R represents the laser spot diameter (mm), t ₁ represents the thickness (mm) of the unpainted metal plate, and t ₂ represents the thickness (mm) of the painted metal plate.
R ≧ t ₁ (1)
t ₂ /1.05≧R (2)

[About equation (1)]
Above (1) shows the relationship between the non-coated metal plate thickness t ₁ and the laser spot diameter R, the present invention is a laser spot diameter R becomes the non-coated metal plate thickness t ₁ or more Irradiate with laser. Since the energy can be concentrated by reducing the laser spot diameter R, the nugget passes between the metal plate on the laser irradiation side and reaches the lower metal plate, melts the lower metal plate, and the nugget is formed between the metal plates. It is formed. As a result, the metal plates can be firmly joined by laser welding. However, if the laser spot diameter R is too small, the energy is concentrated too much and the laser reaches deep inside the lower metal plate. For this reason, the lower metal plate is heated to a high temperature, and No. 1 in Table 1 below will be described. As shown in FIG. 3, the painted surface 2c of the painted metal plate 2 is discolored under the influence of heat. On the other hand, in order to prevent discoloration of the painted surface 2c of the coated metal plate 2 while reducing the laser spot diameter R, it is conceivable to reduce the machining output and shorten the oscillation time among the laser welding conditions. However, when such conditions are employed, sufficient nuggets are not formed at the interface between the metal plates, and welding cannot be performed (see Nos. 1 and 2 in Table 1 below).

On the other hand, in the present invention, welding is performed with the laser spot diameter R equal to or greater than the thickness t ₁ of the unpainted metal plate 1 as shown in the above equation (1). When the laser spot diameter R is increased, it is generally considered that the bonding strength is reduced. However, the present inventors have examined that the above equation (1) is satisfied according to the thickness t ₁ of the unpainted metal plate 1. Thus, it has been clarified that the bonding strength can be unexpectedly ensured by adjusting the laser spot diameter R. In the present invention, the relationship between the non-coated metal plate thickness t ₁ and the laser spot diameter R may satisfy the following (1a) formula.
R ≧ 1.1 × t ₁ (1a)

[About equation (2)]
Equation (2) shows the relationship between the thickness t ₂ and the laser spot diameter R of the coated metal plate 2, in the present invention, the laser spot diameter R is, the thickness t ₂ of the coated metal plate 2, t Irradiate the laser so that it is _{2 /} 1.05 or less. When the laser spot diameter R exceeds t ₂ /1.05 with respect to the thickness t ₂ of the coated metal plate 2, the laser reaches deep inside (the painted surface side) of the painted metal plate 2 and is heated to a high temperature. Therefore, the painted surface is discolored under the influence of heat. The coefficient “1.05” is a value determined by the present inventors as a result of repeating various experiments. In the present invention, the relationship between the thickness t ₂ of the coated metal plate 2 and the laser spot diameter R preferably satisfies the following formula (2a), and more preferably satisfies the following formula (2b).
t ₂ /1.15≧R (2a)
t ₂ /1.25≧R (2b)

In this way, by controlling the laser welding conditions according to the thickness t ₁ of the non-painted metal plate 1 and the thickness t ₂ of the painted metal plate 2, it is possible to prevent the coated metal plate 2 from being overheated locally. The concentration of heat transferred from the second surface 2d side of the painted metal plate 2 through the base material 2a to the first surface (painted surface) 2c is reduced. As a result, the coating film 2b provided on the coated metal plate 2 is hardly affected by heat, and the design of the first surface (painted surface) 2c remains good.

  The laser spot diameter R is, for example, 0.8 mm or more. By setting the laser spot diameter R to 0.8 mm or more, an appropriate nugget can be formed at the interface between the painted metal plate 2 and the non-painted metal plate 1, so that the bonding strength can be increased.

The present invention is characterized in that the laser spot diameter R is adjusted to an appropriate range in accordance with the thicknesses of the painted metal plate and the unpainted metal plate. The other laser welding conditions are that of the painted metal plate and the unpainted metal plate. For example, the processing output and the oscillation time may be adjusted according to the thickness and the laser spot diameter. The machining output is, for example, about 0.9 to 1.3 kW, and the oscillation time is, for example, about 0.1 to 0.2 seconds. Processing the output and the oscillation time, the thickness t ₁ of the non-coated metal plate, a coated metal plate having a thickness t _2, may be determined according to the laser spot diameter R, e.g., as recommended to set within the following range .

(A) When the thickness t ₁ of the non-painted metal plate is 0.8 mm, the thickness t ₂ of the painted metal plate is 1.0 mm, and the laser spot diameter R is 0.8 mm Processing output: 1.0 to 1.3 kW
Oscillation time: 0.1 to 0.2 seconds (b) When the thickness t ₁ of the unpainted metal plate is 0.8 mm, the thickness t ₂ of the painted metal plate is 1.0 mm, and the laser spot diameter R is 0.92 mm Output: 0.9-1.1kW
Oscillation time: 0.1 to 0.16 seconds (c) When the thickness t ₁ of the unpainted metal plate is 0.8 mm, the thickness t ₂ of the painted metal plate is 1.2 mm, and the laser spot diameter R is 0.92 mm Output: 1.0-1.5kW
Oscillation time: 0.1 to 0.15 seconds

  The adjustment of the laser welding conditions can be performed, for example, by changing the number of modules to be used among the total number of modules provided in the apparatus.

  Although the raw material of the said non-coating metal plate 1 is not specifically limited, It is preferable to use a steel plate from the surface of intensity | strength and cost. The non-painted metal plate 1 is usually used as a backing plate for reinforcing the painted metal plate 2.

  The steel plate may be a hot-rolled steel plate or a cold-rolled steel plate, but may also be a steel plate with a plated surface (for example, galvanized or hot-dip galvanized), or a steel plate with a plated layer alloyed. (For example, alloyed galvanized steel sheet, galvannealed steel sheet, etc.) may be used. Moreover, in order to improve corrosion resistance, you may give chemical conversion treatment. Examples of the chemical conversion treatment include phosphate treatment and chromate treatment. Further, a thin film (clear film) for improving fingerprint resistance may be formed.

The thickness t ₁ of the non-painted metal plate 1 may be 0.6 mm or more, for example. If it is too thin, the reinforcing effect cannot be obtained. Accordingly, the thickness t ₁ is 0.6 mm or more, preferably 0.8 mm or more. However, if the unpainted metal plate 1 becomes too thick, an excessive amount of energy is required to penetrate the unpainted metal plate 1. Therefore, the upper limit of the thickness t ₁ is about 1 mm.

  On the other hand, the coated metal plate 2 only needs to be provided with the coating film 2b on one surface (first surface) of the non-coated metal plate, and may be formed with a resin film. As the resin film, a thermosetting resin film may be formed.

  As the thermosetting resin film, for example, urethane resin film, aminoplast resin film, silicone resin film, epoxy resin film, acrylic resin film, etc. A thermosetting resin film that is cured by a curing agent such as a resin film, a polyester resin film, an acrylic resin film, or an epoxy resin film can be used.

  The resin film may be a single layer or a multilayer of two or more layers.

  In addition to the color pigment for design, the resin film may contain inorganic particles. Examples of the inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, zeolite, Examples include molybdenum sulfide and mica.

  The thickness of the said coating film (resin film) is not specifically limited, When using the said coating metal plate 2 as a raw material of furniture, for example, what is necessary is just about 10-30 micrometers.

  The non-painted surface (second surface) of the painted metal plate 2 may be hot rolled or cold rolled. However, as with the non-coated metal plate 1, plating (for example, galvanizing or hot dip galvanizing) ) May be given. Moreover, the plating layer may be alloyed. Moreover, in order to improve corrosion resistance, chemical conversion treatment may be performed. Examples of the chemical conversion treatment include phosphate treatment and chromate treatment as described above.

  A resin thin film may be provided on the non-painted surface (second surface) of the painted metal plate 2 in order to improve corrosion resistance, scratch resistance, or fingerprint resistance. The resin thin film is sometimes called a clear thin film or a service coat.

  The resin thin film may be formed by thinly forming a resin that may be the same as or different from the coating film 2b. As the resin, specifically, the thermosetting resin exemplified above may be provided.

The adhesion amount of the resin thin film is, for example, less than 4 g per unit area (1 m ² ) of the second surface of the coated metal plate. When the amount of adhesion becomes excessive, the resin thin film is caught in the joint, the joint strength is lowered, and joint failure occurs. The adhesion amount is more preferably 3 g / m ² or less, still more preferably 2 g / m ² or less. The film thickness of the resin thin film when the adhesion amount is 4 g / m ² is about 2.5 μm, and the film thickness of the resin thin film when the adhesion amount is 2 g / m ² is about 1.2 μm.

The thickness t ₂ of the coated metal plate 2 may be 0.8 mm or more, for example. The thicker the metal plate, the higher the rigidity. Moreover, since it becomes difficult to propagate welding heat to the 1st surface (painted surface) of the coating metal plate 2 so that it becomes thick, it can prevent that this 1st surface (painted surface) receives a thermal influence and the designability deteriorates. Therefore, the thickness t ₂ of the coated metal plate 2 is 0.8 mm or more, preferably 1 mm or more, more preferably 1.2 mm or more. However, if the coated metal plate 2 is too thick, the welded structure becomes too heavy, making it difficult to use as a furniture material, for example. Therefore, the upper limit of the thickness is about 1.5 mm. In the case where the resin thin film provided on the second side surface of the coated metal plate 2, also including the thickness of the resin thin film thickness t ₂ of the coated metal plate 2.

  The base metal of the non-painted metal plate 1 and the base metal of the painted metal plate 2 may be the same or different.

  In welding the laminate, a cushion material is laid under the first surface (painted surface) 2c in order to prevent the first surface (painted surface) 2c of the painted metal plate 2 from being scratched. It is preferable. By preventing scratches, it is possible to prevent the design quality of the painted surface 2c from deteriorating.

  As said cushion material, what has heat resistance can be used so that it may not receive the heat influence by welding heat, For example, what is necessary is just to use resin-made films. Examples of the film material include polyvinyl chloride, polyvinylidene chloride, saturated polyester, polyamide, polycarbonate, polyolefin such as polyethylene and polypropylene, EVOH resin, EVA resin, acrylic resin, fluororesin, AS resin, ABS resin, polyphenylene ether. , Polyphenylene sulfide, polyarylate, polysulfone, polyether ether ketone and the like. Further, any of these copolymers, blends, grafts, and the like can be used.

  The cushion material may be laid between the first surface (painted surface) 2c of the painted metal plate 2 and the floor surface during welding, and the surface of the first surface (painted surface) 2c is, for example, adhesive. The resin film may be attached in advance.

  As described above, according to the method for manufacturing a welded structure according to the present invention, a welded structure obtained by welding and joining a painted metal plate and a non-painted metal plate without deteriorating the design of the painted surface of the painted metal plate. Can be provided. Therefore, the manufacturing method of this invention can be employ | adopted when manufacturing furniture, such as a desk, a bookshelf, and a cabinet, for example.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

[Experimental Example 1]
Prepare a painted metal plate with a coating on the first surface and a non-painted metal plate. As shown in FIG. 1, the first surface of the uncoated metal plate is the first surface (painted surface) of the painted metal plate. Was laminated in contact with the second surface (non-painted surface) on the opposite side. About this laminated body, it welded by applying the laser which goes to the coating metal plate on the 2nd surface on the opposite side to the 1st surface of a non-coating metal plate, and produced the welding structure.

  In FIG. 1, 1 is a non-painted metal plate, 2 is a painted metal plate, and 3 is a laser output unit. Reference numeral 1 a denotes a first surface of the non-painted metal plate 1, and reference numeral 1 b denotes a second surface of the non-painted metal plate 1. The painted metal plate 2 is provided with a coating film 2b on the surface of a base material 2a, 2c indicates a first surface (painted surface), and 2d indicates a second surface (non-coated surface). From the laser output unit 3, the laser 3a is irradiated. Let the diameter when the laser 3a is projected on the second surface 1b of the non-painted metal plate 1 be a laser spot diameter R.

  The unpainted metal plate 1 and the painted metal plate 2 used in this experimental example are as follows.

As the unpainted metal plate 1, an electrogalvanized steel plate having a thickness t ₁ of 0.8 mm was used. The electrogalvanized layer is formed on both surfaces of the base material.

  The coated metal plate 2 was formed with a two-layered coating film 2b on one side of the electrogalvanized steel sheet by the following procedure.

First, an undercoat paint was applied to one side of an electrogalvanized steel sheet with a bar coater so as to have a film thickness of 8 μm, then placed in a baking furnace and heated to reach a reached plate temperature of 230 ° C. at this temperature. Baking was carried out for 2 seconds. As an undercoat paint, 20 parts by mass of a melamine resin (manufactured by Sumitomo Chemical Co., Ltd., “Sumimar M-40ST (trade name)”) is added to 100 parts by weight of a polyester resin (Toyobo, “Byron 29XS (trade name)”). Was used. Next, after applying a top coating with a bar coater to a film thickness of 20 μm, it is placed in a baking furnace, heated to reach a reached plate temperature of 230 ° C., and held at this temperature for 60 seconds for baking. A coated metal plate 2 was produced. As a top coat, 20 parts by mass of melamine resin (manufactured by Sumitomo Chemical Co., Ltd., “Sumimar M-40ST (trade name)”) is added to 100 parts by weight of a polyester resin (Toyobo, “Byron 29XS (trade name)”). Was added as a binder resin, and 50% by mass of titanium dioxide (manufactured by Teika, “JR-603 (trade name)”, average particle diameter: 0.28 μm) was further added. Table 1 below shows the thickness t ₂ of the coated metal plate. In Table 1 below, the value (t ₂ /1.05) on the right side of the equation ( ₂ ) is calculated and shown together.

  The prepared coated metal plate 2 and the non-coated metal plate 1 were overlapped as shown in FIG. 1 and welding was performed under the following conditions.

  A fiber laser manufactured by US IPG Photonics was used as the welding tester. Table 1 below shows the laser spot diameter R when the unpainted metal plate 1 is irradiated with the laser 3a. Table 1 below shows the processing output (kW) and oscillation time (seconds) during laser irradiation. Laser welding was performed at one place for each sample, and welding was performed using 18 modules out of all modules (18 modules).

  About the welded structure obtained by welding the said laminated body, the designability was evaluated by observing visually whether the joining was possible and the presence or absence of the discoloration in the 1st surface (coating surface) 2c of the coating metal plate 2. FIG.

《Joinability》
Whether the metal plates are not separated even when a load of about 1 kg is applied to the welded structure is acceptable (shown as “Yes” in Table 1), and the metal plates are simply lifted up. Or the case where the metal plates separated when a load of about 1 kg was applied was evaluated as a failure (shown as “No” in Table 1). The evaluation results are shown in Table 1 below.

<Presence of discoloration>
The presence or absence of discoloration on the first surface (painted surface) 2c of the painted metal plate 2 passes the case where no discoloration is observed when the first surface (painted surface) 2c is visually observed ("None" in Table 1). The case where discoloration was observed was evaluated as a failure (shown as “Yes” in Table 1). The evaluation results are shown in Table 1 below. The painted surface before welding is white, and when it is affected by heat during welding, the painted surface changes color from cream to yellow to brown.

  The following table 1 can be considered as follows. No. Nos. 4-6, 10-13, 15, 17-19, and 21 are examples satisfying the requirements defined in the present invention, and welding is performed by applying a laser so as to satisfy the above formulas (1) and (2). Therefore, the non-painted metal plate 1 and the painted metal plate 2 can be welded together without changing the color of the first surface (painted surface) 2c of the painted metal plate 2.

  On the other hand, no. 1 to 3 and 7 are examples that do not satisfy the requirements defined in the present invention, and the laser welding conditions do not satisfy the above formula (1) or (2). ) 2c is discolored or the painted metal plate 2 and the unpainted metal plate 1 are not welded.

No. 8,9,14,16,20 are reference examples, the thickness t ₁ of the non-coated metal plate, laser welding condition is sufficiently controlled with respect to the relationship thickness t _2, and the laser spot diameter R of the coated metal plate It has not been. That is, no. No. 8 is not welded because the processing output during laser welding is too small. No. In 9, 14, and 20, since the processing output during laser welding was too large, discoloration was observed on the first surface (painted surface) 2c after welding. No. In No. 16, since the oscillation time during laser welding was too long, discoloration was observed on the first surface (painted surface) 2c after welding.

[Experiment 2]
With respect to the welded structures (No. 10 and No. 17) obtained in Experimental Example 1, the breaking load and the breaking mode were examined.

  For the breaking load, a tensile test was performed at a tensile speed of 10 mm / min, and the load when the welded structure was broken was measured. The measurement was performed twice. The measurement results are shown in Table 2 below.

  It was visually observed whether the fracture mode was a weld fracture (break in the nugget) or peeling at the interface between the nugget and the base material (painted metal plate or non-painted metal plate). The observation results of the fracture mode are shown in Table 2 below. In the present invention, the welded portion fracture is accepted, and the peeling at the interface between the nugget and the base material is rejected.

  Moreover, the nugget diameter D currently formed in the said welded structure was measured after the fracture | rupture. The nugget diameter D was measured from a photographed image obtained by photographing a fracture surface with a digital microscope “VHX-100F (device name)” manufactured by Keyence. The measurement results of the nugget diameter D are shown in Table 2 below.

  It can be considered as follows from Table 2 below. No. 10 and no. It can be seen that all of the welded structures obtained in No. 17 have a large fracture load and are fractured at the welds, so that they can be welded well.

[Experiment 3]
In the experimental example 1, instead of the painted metal plate, a painted metal plate having a first surface coated and a resin thin film provided on the second surface was prepared. As shown in FIG. The first surface of the plate was laminated in contact with the second surface (resin thin film forming surface) opposite to the first surface (painted surface) of the coated metal plate. About this laminated body, it welded by applying the laser which goes to the coating metal plate on the 2nd surface on the opposite side to the 1st surface of a non-coating metal plate, and produced the welding structure. In FIG. 2, the same portions as those in FIG. 1 are denoted by the same reference numerals, and 2e indicates a resin thin film (service coat).

The non-painted metal plate 1 and the painted metal plate 2 used in this experimental example are specifically as follows.
As the non-painted metal plate 1, the same one as in Experimental Example 1 was used.

  The coated metal plate 2 has a two-layered coating film 2b formed on one side of the electrogalvanized steel sheet by the same procedure as in Experimental Example 1, and a resin thin film formed on the other surface of the electrogalvanized steel sheet by the following procedure. Formed.

For the resin thin film, the top coating used in Experimental Example 1 was applied so that the amount of adhesion was 2 g / m ² or 4 g / m ² , then placed in a baking furnace and heated so that the ultimate temperature was 230 ° C. Then, it was formed by baking at this temperature for 60 seconds. Table 3 below shows the thickness t ₂ of the coated metal plate. In Table 3 below, the value (t ₂ /1.05) on the right side of the equation ( ₂ ) is calculated and shown together. In addition, No. 37 shows an example in which a resin thin film is not formed.

  The prepared non-painted metal plate 1 and painted metal plate 2 were superposed as shown in FIG. 2 and welded under the conditions shown in Table 3 below in the same manner as in Experimental Example 1. FIG. 3 shows the external appearance when they are overlaid as shown in FIG. In addition, No. shown in Table 3 below. For 36 and 37, the ends of the non-painted metal plate 1 and the painted metal plate 2 are bent at 90 °, and the first surface 1s of the non-painted metal plate 1 and the second of the painted metal plate 2 as shown in FIG. The surfaces (resin thin film forming surface) 2d were overlapped so as to be a flat surface.

  Laser welding was performed at three locations at 10 mm intervals when stacked as shown in FIG. 3, and at 10 locations at 10 mm intervals when stacked as shown in FIG. When stacked as shown in FIG. 3, welding is performed using 13 of all the modules (18), and when stacked as shown in FIG. 4, 14 of all the modules (18) are welded. Welding was performed using pieces. As shown in FIG. 3 and FIG. 4, since a plurality of continuous welds are easily noticeable in appearance, they are tested under more severe conditions.

  About the welded structure obtained by welding a laminated body, the design property was evaluated by visually observing the possibility of welding and the presence or absence of the discoloration in the 1st surface (painted surface) 2c of the coating metal plate 2. FIG. The evaluation procedure is the same as in Experimental Example 1, and the evaluation results are shown in Table 3 below. In addition, regarding designability, discoloration was recognized when discoloration was recognized even at one location out of 3 or 10 locations (shown as “Yes” in Table 3), and discoloration was recognized at all welding positions. The case where it was not accepted was judged as pass (shown as “None” in Table 3).

  From Table 3 below, it can be considered as follows. No. 31 to 33, 36, and 37 are examples that satisfy the requirements defined in the present invention. A resin thin film (service coat) is provided on the painted metal plate 2 and the interface between the painted metal plate 2 and the non-painted metal plate 1 is provided. Even if the resin thin film is interposed, the non-painted metal plate 1 and the painted metal plate 2 can be welded together without changing the color of the first surface (painted surface) 2c of the painted metal plate 2.

  On the other hand, no. Reference numerals 34 and 35 are reference examples, and are examples in which the amount of the resin thin film provided on the second surface of the coated metal plate 2 is too large. Since the resin thin film is too thick, welding joining of the non-painted metal plate 1 and the painted metal plate 2 is obstructed.

1 Non-painted metal plate 2 Painted metal plate 2a Base material 2b Paint film 2c Painted surface 2d Non-painted surface 3 Laser output unit 3a Laser R Laser spot diameter

Claims (8)

A method of manufacturing a welded structure by laser welding metal plates together,
Prepare a painted metal plate with a coating on the first side and a non-painted metal plate,
Contacting the first surface of the non-painted metal plate with the second surface opposite to the first surface of the painted metal plate;
A welding structure characterized in that welding is performed by applying a laser to the second surface opposite to the first surface of the unpainted metal plate so as to satisfy the following formulas (1) and (2): Production method.
R ≧ t ₁ (1)
t ₂ /1.05≧R (2)
[In the formula, R is the laser spot diameter (mm), t ₁ is the thickness (mm) of the unpainted metal plate, and t ₂ is the thickness (mm) of the painted metal plate. ] The process according to claim 1 in which the resin thin film on the second surface a surface of the coated metal plate is provided below attachment amount ^{4g / m 2 (0g / m} 2 exclusive). The manufacturing method according to claim 1 or 2, wherein the laser spot diameter R is 0.8 mm or more. The manufacturing method according to claim 1, wherein a thickness t ₁ of the non-painted metal plate is 0.6 mm or more, and a thickness t ₂ of the painted metal plate is 0.8 mm or more. The manufacturing method according to any one of claims 1 to 4, wherein a base material of the painted metal plate and / or the non-coated metal plate is a steel plate. The manufacturing method according to any one of claims 1 to 4, wherein a base material of the painted metal plate and / or the non-coated metal plate is a galvanized steel plate. The manufacturing method according to claim 1, wherein the coating film provided on the coated metal plate is a thermosetting resin film. The furniture containing the welded structure obtained by the manufacturing method in any one of Claims 1-7.