METAL JOINT AND MANUFACTURING METHOD THEREFOR

Abstract

The present invention provides a method for manufacturing a metal joint that promotes adhesion between metallic joint surfaces to improve joint strength. Pulse lasers are illuminated to at least surface portions, where riveting is to be implemented, of surfaces of metal plates (1), so that the surface portions are molten and solidified to form surface modification thin films (4); and multiple metal plates (1) are stacked to form a laminated metal plate (5) by facing the surface modification thin films (4) to each other, and pressurized shaping is performed on the laminated metal plate (5) by using a punch (7) and a die (6) to implement riveting.

Claims

1. A metal joint, comprising a laminated metal plate formed by stacking a plurality of metal plates with each other, wherein a recess is formed on a surface of the laminated metal plate, a protrusion is formed on another surface of the laminated metal plate by protruding a recessed portion of the recess, and surface modification thin films brittler than other parts are formed on surfaces opposite to each other of the metal plates, and in the recess, fresh surfaces exposed due to peeling off of a part of the surface modification thin films are adhered to each other.

2. A method for manufacturing a metal joint, comprising: illuminating a high energy beam to at least surface portions, where riveting is to be implemented, of surfaces of a plurality of metal plates, wherein the surface portions are molten and solidified to form surface modification thin films; stacking the plurality of metal plates to form a laminated metal plate by facing the surface modification thin films to each other; and implementing riveting by pertaining pressurized shaping on the laminated metal plate through a tool.

3. The method for manufacturing a metal joint according to claim 2, wherein the high energy beams are pulse lasers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0027] FIG. 1 is a cross-sectional view of state in which surface modification of a surface of a metal plate is performed by means of a pulse laser.

[0028] FIG. 2 is a cross-sectional view of state in which riveting is implemented on laminated metal plates formed by overlapping metal plates after surface modification.

[0029] FIG. 3(A) is a photo obtained by photographing a surface of a rolled material at a magnification of 100. FIG. 3(B) is a photo obtained by photographing the surface of the rolled material at a magnification of 500.

[0030] FIG. 4(A) is a photo obtained by photographing a surface of a metal plate after surface modification at a magnification of 100. FIG. 4(B) is a photo obtained by photographing the surface of the metal plate at a magnification of 500.

[0031] FIG. 5(A) is a photo of a surface of a rolled material before a V-shaped bending test. FIG. 5(B) is a photo of a surface of a bending portion of the rolled material after the V-shaped bending test.

[0032] FIG. 6(A) is a photo of a surface of a metal plate after surface modification before a V-shaped bending test. FIG. 6(B) is a photo of a surface of a bending portion of a metal plate after the V-shaped bending test.

[0033] FIG. 7 is a cross-sectional view of a processed laminated metal plate in an embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0034] Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

1. Surface Modification Processing

[0035] An implementation manner of the present invention is described below with reference to the accompanying drawings. FIG. 1 indicates state in surface modification processing is implemented on a metal plate 1, for example, an aluminum plate. A metal oxide film 2 is formed on a surface of the metal plate 1. When a pulse laser 3 is illuminated to a surface of the metal plate 1, the pulse laser 3 is scanned. Therefore, the metal oxide film 2 is made molten and solidified and surface modification is performed on the metal oxide film 2 to form a surface modification thin film 4. In this case, surface modification is performed seamlessly on a whole surface of a part in which riveting is subsequently implemented. The surface modification thin film 4 is a brittle tissue that includes coarse crystals.

2. Riveted Joint

[0036] Second, as shown in FIG. 2, two metal plates 1 are made overlapped to form a laminated metal plate 5 in a manner of making the surface modification thin films 4 face each other. Pressurized shaping is performed on the laminated metal plates 5 by means of a die 6 with a circular cross section and a recess 6a, and a punch 7 with a circular cross section. The punch 7 can approach to or get far away from the die 6 by means of a driving mechanism not shown in the drawing. A diameter of a front end portion of the punch 7 is a diameter less than that of the recess 6a of the die 6.

[0037] If the punch 7 is moved to a side of the die 6, then the laminated metal plate 5 perform plastic deformation in a manner of protruding downwards. In this case, because the surface modification thin films 4 are brittle, the surface modification thin films 4 generate micro cracks due to deformation of the laminated metal plate 5; each segmented piece is peeled off starting from the cracks; and fresh surfaces of the metal plates 1 are exposed in a large range. Next, the fresh surfaces are adhered to each other due to pressure applied to the fresh surfaces. Therefore, compared with the prior art in which metal oxide films on surfaces are removed by using a wire brush, and the like disclosed in patent document 1 and patent document 2, the technology of the present invention can lead to adhesion in a larger range so as to obtain stronger joint strength.

[0038] In particular, in the implementation manner, the pulse laser 3 is used as a high energy beam, and therefore heat output to surfaces of the metal plates 1 can be controlled to make only extremely thin surfaces molten and solidified to form thin and brittle surface modification thin films. Therefore, even plastic deformation generated by riveting is small, the surface modification thin films 4 are also practically cracked; segmented pieces are peeled off starting from the cracks, so as to make the fresh surfaces exposed in a large ranged. In addition, because the fresh surfaces are adhered to each other, join strength can be improved.

[0039] Further, in the implementation manners, riveted joint can be performed on the laminated metal plate 5 that includes two metal plates 1, and can also be performed on the laminated metal plate 5 that includes three or more metal plates 1. In this case, surface modification is performed by means of the pulse laser 3 on all surfaces that face each other of the metal plates 1.

Embodiments

1. Embodiment 1 (Surface Modification Processing)

[0040] The present invention is described below in more detail with reference to an embodiment.

[0041] FIG. 3 is a photo of a surface of an aluminum (an aluminum alloy manufactured by KOBE STEEL LTD: 6K21) rolled material with a thickness of 1 mm. FIG. 3(A) is a photo photographed at a magnification of 100. FIG. 3(B) is a photo photographed at a magnification of 500. As shown in the drawings, micro traces of a rolling roller remain on the surface of the rolled material.

[0042] Second, a pulse laser apparatus (manufactured by Clean Laser System Company; power: 120 W; focal distance: 150 mm; pulse frequency: 10 kHz; scan frequency: 50 Hz) is used to perform surface modification on the rolled material. Pulse laser scanning is performed seamlessly on a whole surface of a local part of the rolled material.

[0043] FIG. 4 is a photo of a surface of a metal plate after surface modification is performed under the condition. FIG. 4(A) is a photo photographed at a magnification of 100. FIG. 4(B) is a photo photographed at a magnification of 500. According to FIG. 4(A), it is known that scanning is performed seamlessly by using a pulse laser. In addition, according to FIG. 4(B), it is known that the surface of the rolled material is molten and solidified; the traces of the rolling roller disappear, and the surface becomes smooth. That is, formation of a surface modification thin film is confirmed. An average thickness of the surface modification thin film is 7 m.

2. Embodiment 2 (V-Shaped Bending Test)

[0044] According to Japanese Industrial Standards (JIS) Z2248, a V-shaped bending test is performed on the rolled material and the metal plate after surface modification. The V-shaped bending test is the following test, that is, making a male die and a female die that have a press surface bent into a V shape at a specified angle sandwich a sample to bend the sample. In the V-shaped bending test of the metal plate, a part after surface modification is located at an angular side of the V shape.

[0045] FIG. 5(A) is a photo of a surface of a rolled material before a V-shaped bending test. FIG. 5(B) is a photo of a surface of a bending portion of the rolled material after the V-shaped bending test. As shown in FIG. 5(B), large cracks of a metal oxide film are seen on the surface of the bending portion of the rolled material.

[0046] On the other aspect, FIG. 6(A) is a photo of a surface of a metal plate after surface modification before a V-shaped bending test. FIG. 6(B) is a photo of a surface of a bending portion of a metal plate after the V-shaped bending test. As shown in FIG. 6(B), a large quantity of micro cracks of a surface modification thin film are seen on the surface of the bending portion of the metal plate. Therefore, it is derived that if riveting is performed on the foregoing metal plates, then the surface modification thin films generate micro cracks, and each segmented piece is peeled off starting from the cracks, and fresh surfaces are exposed in a large range. Upon comparison, it is derived that it is difficult to peel off each segmented piece of a rolled plate on which surface modification is not performed because cracks of metal oxide films are large. This case also applies to the technology disclosed in patent document literature 4.

[0047] In addition, in patent document literature 4, surface modification is performed on an aluminum ingot by using a tungsten insert gas (TIG) arc welding. This technology is to cast an ingot with a thickness of more than 300 mm, and then cool to 200 C., and make a whole surface molten by means of the TIG arc welding. Then, a trace of alloy elements is added into the molten surface, and therefore a molten tissue is micronized. Or, a shield gas (shield gas) during melting is made to contain oxygen or nitrogen, and therefore an oxide or a nitride is generated to improve abrasion resistance. A thickness of a surface modification layer in this technology is about 1/10 to 1/100 of that of the ingot. Therefore, for the technology in patent document 4, because a tissue of the surface modification layer is micro and hard, and the surface modification layer is thick, in the V-shaped bending test, the surface modification layer is not easily cracked, and therefore it is derived that when riveting is implemented, it is difficult to peel off the surface modification layer.

[0048] Further, for the present invention, if in a surface modification process, a pulse laser is repeatedly scanned, then the thickness of the surface modification thin film is increased, and consequently, a problem the same as in patent document 4 is also generated. Therefore, ideally, the pulse laser is scanned seamlessly without increasing the thickness, and therefore, the thickness of the surface modification thin film is set to be less than 100 m.

3. Embodiment 3 (Riveted Joint)

[0049] Metal oxide films of single surfaces of the rolled material used in Embodiment 1 are removed by using a wire brush, and two rolled materials are made overlapped to form laminated metal plate in a manner of making the surfaces face each other. In addition, two metal plates are made overlapped to form laminated metal plates in a manner of surface facing of surface modification performed in Embodiment 1. In this case, the rolled materials and the metal plates are set to be reed-shaped, and the rolled materials and the metal plates are staggered from each other to form laminated metal plates. A riveting apparatus (manufactured by TOX company) shown in FIG. 7 is used to shape the laminated metal plate into a shape shown in FIG. 7, and riveted joint is performed. The riveting apparatus is an apparatus having the following structure, that is, a die 6 with a recess 6a, and a punch 7, and the punch 7 is made to approach or far away from the die 6. A lower low-lying part is Mimed on a periphery of a bottom part of the recess 6a, so that material of the shaped laminated metal plate enters the low-lying part and riveting shaping is performed on a boundary portion of the materials by means of engagement.

[0050] A diameter of the punch 7 for riveted joint is set as 5.6 mm; a diameter of the die 6 is set as 8 mm; and a depth of the recess 6a of the die 6 is set as 1.0 mm. In addition, a location of a bottom dead center of the punch 7 is adjusted, so that a plate thickness t after the punch 7 is pressed into the laminated metal plate reaches 0.9 mm to 1.4 mm. Shear strength of each laminated metal plate of each pressed plate thickness tis indicated in Table 1. Further, a tensile test is performed on a separation direction of two end portions of the laminated metal plate which are riveting shaped is performed, so as to measure the shear strength.

TABLE-US-00001 TABLE 1 Pressed plate thickness (mm) 0.9 1 1.2 1.4 Shear strength (kN) Example of the present 2.35 2.13 1.46 1.16 invention Existing example 2.04 1.27 1.01 0.00

[0051] If a press degree of the punch 7 is increased, then a press amount is increased, and the pressed plate thickness is reduced. On the contrary, if the pressed plate thickness is increased, then pressurization performed by the punch is insufficient, and a riveting shaping portion cannot be completely shaped. Compared with the existing example, in the example of the present invention, a press depth and the shear strength are both higher. When the pressed plate thickness is 1.4 mm, for the existing example, the riveting shaping is insufficient, and the laminated metal plates 1 are not adhered to each other, and therefore, the shear strength is not reflected. However, for the example of the present invention, in a bottom surface area wrapped and sandwiched between the punch 7 and the die 6, fresh surfaces are adhered, and therefore, the shear strength is reflected.

[0052] In this way, in the existing example in which oxide films are removed by using a wire brush, during processing, a reach to a large depth of a groove formed by the wire brush indicates a difficult attempt to cause a sufficient plastic flow, and adhesion between materials becomes insufficient, and joint strength is insufficient. Upon comparison, in the example of the present invention, as shown in Embodiment 2, the surface modification thin films generate micro cracks, and each segmented piece is peeled off starting from the cracks, and flat fresh surfaces are exposed in a large range. Therefore, adhesion is easy during deformation, and as a result, a large adhesion area can be ensured to improve joint strength.

[0053] Further, for the technology disclosed in patent document 4, because the thickness of the surface modification layer is large, it is not considered that the surface modification layer is made to generate micro cracks by means of riveted joint as in the example of the present invention, and therefore, it is derived that the obtained shear strength is equal to or less than that of the existing example.

Industrial Applicability

[0054] The present invention can use a technology that performs riveting on multiple metal plates to make the metal plates jointed, and is, in particular, applicable to usage when an area or a depth of a joint portion is limited.

[0055] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.