TW202026083A - Method for welding stainless steel foils, and welded structure - Google Patents

Abstract

In the case of laser welding of stainless steel foils, the present invention inhibits generation of holes at the time of welding and allows continuous and stable welding. Overlap parts of stainless sheet foils (2a, 2b) are laser-welded so that a sheet-to-sheet gap G between two layers of the stainless steel foils included in the overlap parts satisfies G ≤ 1t and a width W of a laser welding part (15a) on a surface (S1) of a stainless steel foil on the side irradiated with a laser beam satisfies 1t ≤ W ≤ 10t (t is the thickness of the stainless steel foil on the side irradiated with the laser beam).

Description

Stainless steel foil welding method and welding structure

The present invention relates to a welding method and welding structure of stainless steel foil.

In order to reduce the weight of various machines and save space, the weight and thickness of stainless steel plates are sought. As one of the methods of reducing the weight and thickness of the stainless steel sheet, for example, the use of stainless steel foil is mentioned.

Patent Document 1 discloses a method of stacking metal foil on a copper backing plate, and performing a laser in a state where the metal foil is pressed by the edge of a block fixing jig and a strip-shaped elastic body. Welding or plasma welding.

Patent Document 2 discloses a method in which laser irradiation is performed twice at the overlapping portion of two thin plates to perform welding.

[Prior Technical Literature] [Patent Literature] [Patent Document 1] Japanese Patent Publication "Japanese Patent Laid-Open No. 5-8089" [Patent Document 2] Japanese Patent Publication "JP 2010-23047 A"

[Problems to be solved by the invention] However, when laser welding is performed on each stainless steel foil, the stainless steel foil is deformed due to the local heat applied during laser welding. Next, because the stainless steel foil is deformed, there is a risk of welding defects such as perforations. Therefore, it is difficult to perform welding continuously and stably.

In one aspect of the present invention, when laser welding is performed on stainless steel foil, the purpose is to suppress the occurrence of perforations and to perform welding continuously and stably.

[Means for solving the problem] In order to solve the above-mentioned problems, one aspect of the welding method of the present invention is a welding method of welding the stainless steel foil by irradiating the overlapped part of the stainless steel foil with a laser, which includes: Among the two layers of stainless steel foil constituting the aforementioned overlapping portion, the stainless steel foil on the laser irradiation side is used as the first stainless steel foil, and the stainless steel foil on the other side is used as the second stainless steel foil; Among them, laser welding is performed under the following conditions: The plate gap G between the first stainless steel foil and the second stainless steel foil satisfies the following formula (1); and As the width in the direction perpendicular to the extending direction of the laser welding part formed by the laser irradiation, the width W of the laser welding part on the surface of the first stainless steel foil satisfies the following formula (2) ； G≦1t･･･(1); 1t≦W≦10t･･･(2); In the above formula, t is the thickness of the aforementioned first stainless steel foil.

In order to solve the above-mentioned problems, a welded structure according to one aspect of the present invention is a welded structure in which the superimposed portion of the stainless steel foil is provided with a welded portion to be laser welded, which includes: Among the two layers of stainless steel foil constituting the aforementioned overlapping portion, the stainless steel foil on the laser irradiation side is used as the first stainless steel foil, and the stainless steel foil on the other side is used as the second stainless steel foil; The aforementioned welded portion is formed in a manner that simultaneously satisfies the following conditions: In a cross section cut with a plane perpendicular to the extending direction of the welded portion, the plate gap G between the first stainless steel foil and the second stainless steel foil near the welded portion satisfies the following formula (1); and As a width in a direction perpendicular to the extending direction of the welding portion, the width W of the welding portion on the surface of the first stainless steel foil satisfies the following formula (2); G≦1t･･･(1); 1t≦W≦10t･･･(2); In the above formula, t is the thickness of the aforementioned first stainless steel foil.

[Effects of the invention] According to one aspect of the present invention, even in the case where the stainless steel foil is laser-welded, it is possible to suppress the occurrence of perforations and continuously and stably perform welding.

[Embodiment 1] Hereinafter, a welding method in which each stainless steel foil is overlapped and laser-welded according to an embodiment of the present invention will be described. In addition, the following description is for making the reader understand the gist of the present invention more, and as long as it is not specified, it is not intended to limit the present invention. In addition, as long as there is no special description in this specification, "A to B" indicating the numerical range means "A or more and B or less". The shapes and dimensions (length, depth, width, etc.) of the structures disclosed in the drawings of this application do not reflect the actual shapes and dimensions, etc., and can be appropriately changed for clarity and simplification of the drawings.

First, referring to FIG. 1, the method of extending each stainless steel foil to a long distance (for example, a length of 100 mm or more) and continuously performing laser welding will be described on the knowledge of the present invention discovered by the present inventors. Fig. 1 is a perspective view schematically showing the structure of a welded structure 1 according to an embodiment of the present invention.

As shown in Figure 1, the welded structure 1 is formed by superposing a stainless steel foil (first stainless steel foil) 2a and a stainless steel foil (second stainless steel foil) 2b with a plate thickness of 100μm or less, and irradiating the stainless steel foil 2a with a laser. Construct. The stainless steel foil 2a and the stainless steel foil 2b of the welded structure 1 each have a welded portion 3 formed by laser welding. The shape of the stainless steel foil 2a and the stainless steel foil 2b in plan view is rectangular, and the dimension in the longitudinal direction is 100 mm or more. Similarly, the shape of the welded structure 1 in plan view is also rectangular.

The welding part 3 is formed on three sides of the welding structure 1, for example, at a position 10 mm from the end, and the welding part 3 is formed over a length of 100 mm or more.

In addition, in this embodiment, although the welded structure 1 shown in FIG. 1 is used for description, the welded structure formed using the stainless steel foil welding method of one aspect of the present invention is not necessarily limited to this. The welding method of the stainless steel foil of one aspect of the present invention can be applied to the case where each stainless steel foil having a thin plate thickness (for example, a plate thickness of about 100 μm or less) is superimposed and laser welding is performed. Particularly, it is more suitable for the case where a welded portion with a length of about 100 mm or more is formed. The welding structure of one aspect of the present invention is not particularly limited as long as it has a welding part formed by such a welding method.

(Summary of invention knowledge) Because the above-mentioned stainless steel foils 2a, 2b have a thinner plate thickness than a general stainless steel plate, they are very prone to wrinkles and are greatly affected by thermal deformation. Next, when the stainless steel foil is deformed, it is easy to form welding defects such as perforations in the welded portion. Conventionally, it has been difficult to form the welded portion 3 stably by overlapping and laser welding such stainless steel foils 2a, 2b, and it is more difficult to form the welded portion 3 stably over long distances.

After in-depth research, the inventors obtained the following knowledge and completed the present invention. The knowledge of the present invention and the discussion process are described together below.

Even if the stainless steel foils 2a, 2b are pressed by a jig or the like, wrinkles may occur due to thermal deformation during laser welding. When wrinkles are generated, the plate gap becomes larger, and poor welding such as perforation may occur in the welded portion 3.

On the other hand, the molten metal formed by the melting of the stainless steel foil on the side irradiated with the laser is filled between the plate gaps of each stainless steel foil. However, if the plate gap is too large, the problem of perforation (burn-through) is likely to occur. In particular, compared to iron and aluminum, stainless steel has a lower thermal conductivity and is prone to local temperature changes, and therefore is prone to wrinkles caused by thermal deformation. In addition, in the case of using, for example, austenitic stainless steel of SUS304, since the thermal expansion coefficient is relatively large, the thermal deformation when heated by the laser may become larger.

The idea of the inventors is as follows. In other words, the inventors discovered that if the width of the welded portion formed by laser welding (hereinafter also referred to as welding width) is wide, the amount of molten metal will also increase, and problems such as burn-through can be prevented . On the other hand, if the welding width is too wide, wrinkles caused by thermal deformation are likely to be generated near the welding part, which may be an important factor for locally increasing the plate gap. When welding thin stainless steel foils 2a, 2b by laser as described above, in order to prevent burn-through and perforation during welding, it is important not only to control the plate gap, but also to appropriately manage the welding width.

Therefore, the present inventors conducted an experiment as shown in FIG. 2 and discussed appropriate conditions for the plate gap and welding width. Figure 2 is a diagram for explaining the laser welding test with the plate gap adjustable while fixing two stainless steel foils using a plate clamp.

As shown in Fig. 2, on the support table 11, a lower pressing plate jig 12b, a stainless steel foil 10b, a backing plate 13, a stainless steel foil 10a, and an upper pressing plate jig 12a are placed in this order. The backing plate 13 is sandwiched between the stainless steel foil 10a and the stainless steel foil 10b, and by changing the thickness of the backing plate 13, the distance between the stainless steel foil 10a and the stainless steel foil 10b (plate gap G1) can be adjusted. In addition, in order to control the plate gap G1 to the thickness of the backing plate 13, the stainless steel foil 10a and the stainless steel foil 10b used in this test were stainless steel foils without wrinkles. Therefore, the plate gap G1 is approximately equal to the thickness of the backing plate 13.

A groove 14a for irradiating the stainless steel foil 10a with the laser beam LB1 is formed on the upper platen jig 12a. A groove 14b is formed at a position corresponding to the groove 14a of the lower pressing plate clamp 12b. The groove 14b on the lower side prevents the lower platen clamp 12b from melting due to the thermal conduction of the irradiation heat of the laser beam LB1. In addition, in reality, the groove 14a and the groove 14b are continuously formed from the front side to the back side in the direction penetrating the paper surface (when viewed in the cross section of FIG. 2, they are rectangular openings).

By irradiating the stainless steel foil (first stainless steel foil) 10a with the laser beam LB1, the stainless steel foil 10a and the stainless steel foil (second stainless steel foil) 10b can be laser-welded to each other, and between the two backing plates 13 in the figure The part forms a welding part (not shown). Here, in this specification, on the surface of the stainless steel foil 10a irradiated by the laser beam LB1, the width of the welding portion in the direction perpendicular to the extending direction of the welding portion is referred to as the welding width.

The inventors of the present invention conducted experiments under various conditions and found that in order to control the increase in the plate gap G1 during laser welding, thermal deformation must be reduced and the upper limit of the welding width must be controlled. On the other hand, it has also been found that if the welding width is too narrow, burning through of the stainless steel foil 10a (upper plate) is likely to occur.

Next, after further investigation, it was found that if the plate thickness of the stainless steel foil 10a is taken as t, the plate gap G1 is set to 1t or less, and the welding width after laser welding is managed by the range of 1t to 10t. The conditions of laser welding can stably form the welded part.

＜Welding method＞ The welding method of the stainless steel foil of this embodiment will be described below using FIG. 3. Fig. 3 is a diagram showing an example of a laser welding device used in a welding method of stainless steel foil according to an embodiment of the present invention.

As shown in FIG. 3, the laser welding device 20 of this embodiment places a lower platen clamp 22 on a support table 21, and the stainless steel foil 10a is clamped by the lower platen clamp 22 and platen rollers 23, 24. In the state of 10b, the laser beam LB2 is irradiated.

The platen roller 24 is separated from the platen roller 23 and arranged so as to form an optical path for irradiating the laser beam LB2 to the stainless steel foil 10a.

In the cross section shown in FIG. 3, the distance between the contact position of the platen roller 23 and the stainless steel foil 10a and the contact position of the platen roller 24 and the stainless steel foil 10a (the distance between the platens) X can be appropriately set, for example, 2.5mm. In addition, the distance X between the pressing plates may be 1 mm or more and 5 mm or less.

In addition, the platen roller 23 and the platen roller 24 can be pressed by an elastic body 25 such as a spring or rubber. Alternatively, the platen roller 23 and the platen roller 24 may be used as an alternative to the elastic body 25 or combined with the elastic body 25 and connected to a hydraulic cylinder or a pneumatic cylinder not shown in the figure. In this case, the hydraulic cylinder or the pneumatic cylinder applies force to press the stainless steel foil 10a against the platen rollers 23, 24.

Next, the pressing force of the platen roller 23 and the platen roller 24 can be adjusted by changing the pressing amount or spring constant of the elastic body 25 such as a spring or rubber. Or, in the case of using a hydraulic cylinder or a pneumatic cylinder, a pressure adjusting valve is used to adjust the pressing force of the hydraulic cylinder or the pneumatic cylinder. Therefore, the plate gap G can be adjusted by adjusting the pressing force.

The welding method of the stainless steel foil of this embodiment is a method of laser welding the overlapping parts of the stainless steel foils 10a, 10b using a laser beam LB2, and the plate gap G between the stainless steel foil 10a and the stainless steel foil 10b meets the following requirements In the method of formula (1), laser welding is performed. G≦1t･･･(1); In the formula, t is the thickness of the aforementioned first stainless steel foil.

Next, the welding method of the stainless steel foil of this embodiment satisfies the above formula (1) and also satisfies the following formula (2) to perform laser welding. 1t≦W≦10t･･･(2); Here, W is the width in the direction perpendicular to the extending direction of the aforementioned welded portion, and is the width of the welded portion on the surface of the stainless steel foil 10a.

With the above configuration, when laser welding is performed, the plate gap G can be filled with an appropriate amount of molten metal, and the welded portion can be formed more stably.

In the welding method of this embodiment, instead of performing multiple laser irradiations, laser welding is performed by one laser irradiation, and a welded portion is formed.

In addition, the above-mentioned laser welding device is only an example, and as for the welding method of one aspect of the present invention, it is sufficient that laser welding can be performed under the conditions of the above-mentioned plate gap and welding width. The specific aspect of the laser welding device is not particularly limited.

(Stainless steel foil) The stainless steel foils 10a, 10b may be ferritic stainless steel, or may be other types of stainless steel. From the viewpoint of strength and formability, the stainless steel foils 10a, 10b are preferably austenitic stainless steel such as SUS304. Since the austenitic stainless steel has a relatively large coefficient of thermal expansion, it is greatly affected by thermal deformation. According to this welding method, even for each stainless steel foil of such austenitic stainless steel, laser welding can be performed stably.

Also, from the viewpoint of strength, the thickness of the stainless steel foils 10a, 10b is preferably 20 μm or more, more preferably 30 μm or more, and particularly preferably 40 μm or more. In addition, from the viewpoint of weight reduction and welding stability, the thickness of the stainless steel foils 10a, 10b is preferably 100 μm or less, more preferably 70 μm or less, and particularly preferably 50 μm or less. The thickness of the stainless steel foils 10a, 10b is preferably 20 μm or more and 100 μm or less.

More specifically, from the viewpoints of strength, chemical stability, and formability, the stainless steel foils 10a, 10b are preferably austenitic stainless steels having a tensile strength of 700 MPa or more and an elongation of 45% or more.

From the viewpoint of the above-mentioned strength, the tensile strength of the stainless steel foils 10a, 10b is preferably 700 MPa or more, and more preferably 750 MPa or more. In addition, the upper limit of the tensile strength of the stainless steel foils 10a, 10b can be appropriately determined from the viewpoint of ease of acquisition and realization; for example, it is preferably 900 MPa or less, and more preferably 800 MPa or less. The tensile strength of the stainless steel foils 10a, 10b can be measured by a tensile test, for example, can be adjusted by annealing or tempering rolling.

From the viewpoint of the above-mentioned formability, the elongation of the stainless steel foils 10a, 10b is preferably 45% or more, more preferably 55% or more. In addition, the upper limit of the elongation of the stainless steel foils 10a, 10b can be appropriately determined from the viewpoints of ease of acquisition and realization; for example, it is preferably 75% or less, and more preferably 70% or less. The elongation of the stainless steel foil 10a, 10b can be measured by a tensile test. For example, it can be improved by annealing in a rare gas or non-oxidizing gas (for example, hydrogen, etc.) atmosphere after rolling.

In addition, from the viewpoint of welding stability, it is preferable that the stainless steel foils 10a, 10b do not have a resin layer such as a laminate on the surface.

(Welding conditions) Among the stainless steel foil 10a irradiated by the laser beam LB1, the stainless steel foil 10a melted by the laser beam LB1 (the part of the stainless steel foil 10a melted by the laser beam LB1 is called molten metal) is caused to sag due to gravity. It is in contact with the stainless steel foil 10b. Then, the heat generated by the irradiation of the laser beam LB1 is transferred to the stainless steel foil 10b by the molten metal, and the stainless steel foil 10a and the stainless steel foil 10b are fused. After that, it is rapidly cooled and welded by solidification and shrinkage. Therefore, in the case where the amount of molten metal is less than the size of the plate gap, the molten metal burns through the stainless steel foil 10a before coming into contact with the stainless steel foil 10b and becomes an important factor in forming perforations.

In the welding method of this embodiment, by setting the plate gap G to be less than the plate thickness t of the stainless steel foil 10a, it is possible to cause the phenomenon that the molten metal bends downwards and drips and contacts the stainless steel foil 10b (lower plate) , It can improve stability.

In addition, when the welding width W is less than 1.0 times the plate thickness t of the stainless steel foil 10a, the welding portion becomes too narrow because the laser is locally irradiated, and it is difficult to generate molten metal for filling the plate gap. Next, if the welding width W is greater than 10 times the plate thickness t of the stainless steel foil 10a, thermal deformation will cause deep wrinkles. Therefore, if the plate gap becomes too large, it may cause perforation of the stainless steel foil 10a. Therefore, the welding width W should be 1.0 times or more and 10 times or less the thickness t of the stainless steel foil 10a.

In such a manner that the conditions of the plate gap G and the welding width W are satisfied at the same time as described above, and by performing laser welding, the laser welding portion can be formed stably.

＜Welding structure＞ The welded structure 1 will be described below using Fig. 1 and Fig. 4(a). Fig. 4(a) is an enlarged cross-sectional view showing the direction in which the welded portion 3 extends (the extending direction of the welded portion 3), and the cross-section when cut in a vertical plane is enlarged.

As shown in FIG. 4(a), the boundary between the surface S1 of the stainless steel foil (first stainless steel foil) 10a on the laser irradiation side and the welded portion 3 in the cross section can be defined as two points. The distance between the defined boundaries is the welding width W1 of the welding portion 3.

In addition, the plate gap G1 of the welded structure 1 is defined as the distance between the stainless steel foils 10a, 10b in the vicinity of the welded portion 3. This is because after laser welding is performed, the plate gap of the stainless steel foil 10a, 10b during laser welding can no longer be directly known.

In addition, the vicinity of the welded portion 3 refers to a position away from the welded portion 3 by 40 to 80 μm, for example. Although this position exists on both sides of the welding part 3, when the plate gap at each position is different, a gap with a larger value can be used as the plate gap G before laser welding. It is possible to directly measure the plate gap G1 by observing the above-mentioned cross-section. It is also possible to reduce the total thickness of the stainless steel foil 10a, 10b from the measured value obtained by measuring the vicinity of the welded portion 3 using a non-contact optical thickness meter. To measure the plate gap G1. The plate gap G1 may be an average value obtained by measuring a plurality of positions away from the welding portion 3 in the range of 40 to 80 μm, and averaging the results. Alternatively, the plate gap G1 may adopt the maximum value among the measurement results in the above range.

(Modification 1) In the stainless steel foil welding method of the above-mentioned embodiment, the stainless steel foil at the laser irradiation position has a two-piece structure. However, the welding method of the stainless steel foil in one aspect of the present invention is not limited to this. The welding method of the stainless steel foil in one aspect of the present invention can be applied to the superimposed portion composed of two layers of stainless steel foil.

For example, the welding method of the stainless steel foil of a modified example can also be applied to the case where the overlapping part formed by bending or bending a piece of stainless steel foil into a cylindrical shape is welded. The overlapped portion is formed by overlapping the vicinity of the first end portion of one side of a sheet of stainless steel foil with the vicinity of the second end portion located on the opposite side of the first end portion. At this time, the vicinity of the first end portion serves as a first stainless steel foil, and the vicinity of the second end portion serves as a second stainless steel foil.

[Example] The embodiments of the present invention are described below. As the stainless steel foil, a SUS304 BA material with a size of 165mm × 220mm and a thickness of 20, 40, 60, 80, and 100 μm is used. (Example 1) The results of the laser welding test (refer to FIG. 2) performed by changing the plate gap before welding will be described with reference to FIG. 4. Fig. 4 is a schematic diagram showing the observation sample after the cross section of the welded portion is processed to be observable, and the appearance of the cross section is observed using an optical microscope. (A) to (c) of FIG. 4 are graphs showing the results when the stainless steel foil 10a and the stainless steel foil 10b having a plate thickness of 40 μm are used, and the respective plate gaps G1 are 10 μm, 80 μm, and 40 μm. Moreover, FIG. 4(d) is a figure which shows the result of the reference example when the stainless steel foil 18a and the stainless steel foil 18b with a plate thickness of 400 micrometers are used, and the plate gap G1 is 120 micrometers. Here, the cross-section shown in FIG. 4 is a cross-section when the laser welding portion is cut in a vertical plane along the branch direction (extending direction). In addition, in FIG. 4, the shaded part is the part that is melted by laser welding in the stainless steel foil.

As shown in Fig. 4(a), the plate gap G1 is set to 10 μm (the plate thickness ratio of the plate gap to the plate thickness t of the stainless steel foil 10a is 0.25t). As a result of the test, it has a uniform and neat shape The laser welding part 15a. As shown in Fig. 4(c), the plate gap G1 is set to 40 μm (the plate thickness ratio of the plate gap to the plate thickness t of the stainless steel foil 10a is 1.0t). As a result of the test, a laser welded portion is formed 16b. On the other hand, as shown in Fig. 4(b), the plate gap G1 is set to 80 μm (the plate thickness ratio of the plate gap to the plate thickness t of the stainless steel foil 10a is 2.0t). 10a was burned through and the laser welding part could not be formed. This is because the plate gap G1 exceeds the range that the molten metal can extend, causing the molten metal to burn through. In other words, the boundary points 17a, 17b of the display boundary between the laser welded portion 16b and the surface S1 of the stainless steel foil 10a as shown in FIG. 4(c) are unable to support the molten metal and cause the molten metal to burn wear. In addition, in the reference example using the stainless steel foil 18a and the stainless steel foil 18b having a plate thickness of 400 μm, as shown in (d) of FIG. 4, perforations are generated by laser welding. At this time, the plate gap G1 is 120 μm, and the plate thickness ratio of the plate gap with respect to the plate thickness t of the stainless steel foil 18a is 0.3 t. In this reference example, since the plate thickness is 400 μm, the heat capacity of the stainless steel foil is large. Therefore, when laser welding is performed, the molten state can continue for a long time, and the molten metal will drip and form perforations. Comparing the example shown in Fig. 4(a) with the reference example shown in Fig. 4(d), it can be seen that even if the plate thickness ratio is the same, when the plate thickness is small, it will not burn through but can A good weld is formed. On the other hand, in the case of a stainless steel foil with a plate thickness of 400 μm, perforations may occur. (Example 2) Use the aforementioned laser welding device (refer to FIG. 3) and perform laser welding to form a welded portion. The laser beam LB2 is focused on the surface of the stainless steel foil 10a, and the laser spot diameter is φ30, 100, 200 μm, and the laser output is 300W or less. The maximum welding speed is 12.5 m/min. The distance between the pressing plates is 2.5mm.

Table 1 is a table showing the relationship between the welding width W1 and the thickness t of the stainless steel foil plate when the plate gap G1 is fixed at 1t.

The adjustment of the welding width W1 is performed as follows. In other words, while changing the laser spot diameter of the laser beam LB1 to φ30μm, 100μm, and 200μm, the laser output is 300W or less, and the welding speed is 12.5 m/min or less. Adjustment.

[Table 1] Board thickness t (μm) Welding width W1(μm) 10 20 30 40 60 80 100 200 300 400 500 600 700 800 900 1000 1100 20 x 0.5t ○ 1t ○ 1.5t ○ 2t ○ 3t ○ 4t ○ 5t ○ 10t x 15t x 20t - - - - - - - 40 x 0.3t x 0.5t x 0.75t ○ 1t ○ 1.5t ○ 2t ○ 2.5t ○ 5t ○ 7.5t ○ 10t x 12.5t x 15t x 17.5t - - - - 60 - x 0.3t x 0.5t x 0.66t ○ 1t ○ 1.3t ○ 1.7t ○ 3.3t ○ 5t ○ 6.7t ○ 8.3t ○ 10t x 11.7t - - - - 80 - x 0.3t x 0.38t x 0.5t x 0.75t ○ 1t ○ 1.3t ○ 2.5t ○ 3.8t ○ 5t ○ 6.3t ○ 7.5t ○ 8.8t ○ 10t x 11.3t - - 100 - - x 0.3t x 0.4t x 0.6t x 0.8t ○ 1t ○ 2t ○ 3t ○ 4t ○ 5t ○ 6t ○ 7t ○ 8t ○ 9t ○ 10t x 11t

In the above-mentioned Table 1, the mark × refers to the conditions under which the stainless steel foil 10a, which is the plate (upper plate) on the laser irradiation side, is perforated or burned through. In addition, the condition in the case where a laser welding portion can be formed without forming a perforation in the stainless steel foil 10a may be marked with ○. In addition, the ratio of the length of the welding width to the plate thickness (plate thickness ratio) is shown.

In any condition of plate thickness t, it is not appropriate for the welding width W1 to be greater than 10t. This system is considered to be because when deep wrinkles are generated due to thermal deformation, the plate gap becomes too large, thereby generating perforations in the stainless steel foil 10a. In addition, it is also inappropriate that the welding width W1 is less than 1t. This system is considered to be because when the welding part becomes too narrow due to the partial laser irradiation, the welding metal for filling the plate gap 1t cannot be generated, and perforations are generated in the stainless steel foil 10a.

(Example 3) Next, with respect to the stainless steel foil 10a having a plate thickness t of 20, 40, 60, 80, and 100 μm, the plate gap G at each position of the welded portion was measured, and the presence or absence of perforations was investigated. In addition, as a reference example, a test was also performed on the stainless steel foil 18a having a plate thickness t of 400 μm to evaluate whether there is a perforation. The results are collated and shown in Table 2.

[Table 2] category No. Board thickness (μm) Board gap after welding Perforation Gap (μm) Relative to plate thickness ratio Example of the invention 1 20 8 0.4t no 2 14 0.7t 3 20 1.0t Comparative example 4 twenty three 1.2t Have Example of the invention 5 40 8 0.2t no 6 30 0.75t 7 40 1.0t Comparative example 8 44 1.1t Have 9 50 1.25t Example of the invention 10 60 18 0.3t no 11 48 0.8t 12 58 0.96t Comparative example 13 64 1.07t Have 14 70 1.17t Example of the invention 15 80 16 0.2t no 16 70 0.88t 17 80 1.0t Comparative example 18 92 1.15t Have Example of the invention 19 100 44 0.44t no 20 96 0.96t Comparative example twenty one 108 1.08t Have Example of the invention twenty two 400 320 0.8t Have twenty three 460 1.15t Have

As shown in Table 2, when the plate gap G is 1t or less, burn-through of the upper plate is not generated, and no perforation is generated (example of the present invention). On the other hand, if the plate gap G is greater than 1t, burn-through of the upper plate occurs and perforation occurs (comparative example).

In addition, when a stainless steel foil having a plate thickness t of 400 μm (reference examples of Nos. 22 and 23) was used, perforations occurred even under the condition that the plate gap G was 0.8t. This is because it is different from the case of the stainless steel foil having a plate thickness t of 20 to 100 μm as an example of the present invention. In the example of the present invention, even if the plate gap G is 0.8t, welding can be performed normally.

The reason is that when the plate thickness in the reference example is thicker, because the heat capacity becomes large and it is difficult to remove the heat during laser welding, the duration of the molten state of the metal is longer than in the example of the present invention, so the molten metal is likely to drip and cause Produce perforations.

(Reference example: plate gap) In addition, in order to compare with the present invention, for a reference example with a plate thickness t of 400 μm, a test was also conducted to investigate whether there is a perforation in the laser welding portion when the plate gap is smaller. Specifically, under the condition that the welding width W is 3.5t, the test is conducted when the plate gap is 110 μm to 200 μm, that is, the plate thickness ratio is 0.28t to 0.5t. The results are shown in Table 3.

[table 3] category No. Board thickness (μm) Board gap after welding Perforation Gap (μm) Relative to plate thickness ratio Reference example 31 400 110 0.28t no 32 150 0.38t Have 33 170 0.43t 34 200 0.5t

As shown in Table 3, when a stainless steel foil with a plate thickness t of 400 μm is used, although no perforation occurs when the plate thickness ratio is 0.28t (No. 31), when the plate thickness ratio exceeds 0.28t, perforation occurs (No. .32~34).

If the above results are summarized, it is because in the example of the present invention, thin materials with a thickness of 20-100 μm are used as the object, and the heat capacity in the molten state is small, the cooling of the molten metal is fast, and the heat-affected part is accompanied by The shrinkage produces solidification and forms a laser weld. Therefore, even when the plate thickness ratio of the plate gap G is as large as 1.0 t, and even when the welding width W is as large as 10 t, it is possible to form the laser welded portion without generating perforations. In other words, in the example of the present invention, due to reasons such as a small heat capacity due to a thin plate thickness, a phenomenon that is significantly different from the case of using a stainless steel foil having a plate thickness of 400 μm, for example, occurs. Therefore, we can know that based on the conventional technology, the condition range of the plate gap and welding width of the present invention (technical idea) cannot be easily thought of.

(Evaluation of air tightness) Three sides were laser welded into a bag-shaped welded structure 1 (see Fig. 1), and no problem (no perforation) was found in the visual inspection as the test material. Fill the inside of the test material with red penetrant and check for leaks. As a result, it was confirmed that the test material for which no problem was found in the visual inspection did not leak even after 1 hour passed, and the welded portion had airtightness.

[Industrial availability] The present invention can be applied to secondary batteries such as lithium ion batteries. For example, it can be used for secondary batteries mounted on vehicles such as electric cars, secondary batteries mounted on various electronic devices, and the like.

1: Welding structure 2a, 2b, 10a, 10b, 18a, 18b: stainless steel foil 3: Welding department 11, 21: Support table 12a: Upper pressure plate fixture 12b, 22: Lower pressure plate fixture 13: Pad 14a, 14b: groove 15a, 16a: Laser welding part 17a, 17b: boundary point 20: Laser welding device 23, 24: platen roller 25: elastomer G, G1: plate gap LB1, LB2: laser beam S1: Surface of stainless steel foil 10a t: board thickness W1: welding width X: Distance between pressure plates

Fig. 1 is a perspective view schematically showing the structure of a welded structure according to an embodiment of the present invention. [Fig. 2] It is a diagram for explaining the laser welding test in the state where the gap between the plates can be adjusted while fixing two stainless steel foils using a plate clamp. Fig. 3 is a diagram showing an example of a laser welding device used in a welding method of stainless steel foil according to an embodiment of the present invention. [Figure 4] is a schematic diagram showing the appearance of the cross-section of the laser welded part observed with an optical microscope; (a)~(c) shows that the thickness of the stainless steel foil is 40μm, and the respective plate gaps are 10μm, 80μm, 40μm (D) is a graph showing the results when the plate thickness of the stainless steel foil is 400 μm and the plate gap is 120 μm.

1: Welding structure

2a, 2b: stainless steel foil

3: Welding department

Claims (4)

A welding method, which is a welding method of welding the stainless steel foil by irradiating the overlapping part of the stainless steel foil with a laser, which includes: Among the two layers of stainless steel foils constituting the aforementioned overlapping portion, the stainless steel foil on the laser irradiation side is used as the first stainless steel foil, and the stainless steel foil on the other side is used as the second stainless steel foil; wherein, Perform laser welding under the following conditions: The plate gap G between the first stainless steel foil and the second stainless steel foil satisfies the following formula (1); and As the width in the direction perpendicular to the extending direction of the laser welding part formed by the laser irradiation, the width W of the laser welding part on the surface of the first stainless steel foil satisfies the following formula (2) ； G≦1t･･･(1); 1t≦W≦10t･･･(2); In the above formula, t is the thickness of the aforementioned first stainless steel foil. The welding method according to claim 1, wherein the thickness of the first stainless steel foil and the thickness of the second stainless steel foil are 20 μm or more and 100 μm or less. A welded structure, which is a welded structure in which the overlapping part of a stainless steel foil is provided with a welded part to be welded by laser, which includes: Among the two layers of stainless steel foils constituting the aforementioned overlapping portion, the stainless steel foil on the laser irradiation side is used as the first stainless steel foil, and the stainless steel foil on the other side is used as the second stainless steel foil; wherein, The aforementioned welded portion is formed in a manner that simultaneously satisfies the following conditions: In a cross section cut with a plane perpendicular to the extending direction of the welded portion, the plate gap G between the first stainless steel foil and the second stainless steel foil near the welded portion satisfies the following formula (1); and As a width in a direction perpendicular to the extending direction of the welding portion, the width W of the welding portion on the surface of the first stainless steel foil satisfies the following formula (2); G≦1t･･･(1); 1t≦W≦10t･･･(2); In the above formula, t is the thickness of the aforementioned first stainless steel foil. The welded structure according to claim 3, wherein the thickness of the first stainless steel foil and the thickness of the second stainless steel foil are 20 μm or more and 100 μm or less.

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