Patent Description:
Low specific gravity and high strength metal referred to as high tension steel is used to reduce weight and improve safety of vehicles. Although the high tension steel is effective in reducing weight and improving safety, the high tension steel is heavier than lower specific gravity material such as aluminum. In addition, when high tension steel is used, the high strength causes problems such as a decrease in formability, an increase in forming load, and a decrease in dimensional accuracy. In order to solve these problems, in recent years, multi-materialization of using, in combination with steel parts, extrusion-molded products, cast products, and press-molded products that use aluminum having a lower specific gravity than steel has been performed.

The problem with multi-materialization is the joining of dissimilar metals such as steel parts and aluminum parts. Generally, it is difficult to join dissimilar metals having different properties as described above, but, for example, Patent Document <NUM> and Patent Document <NUM> disclose methods for joining members of enabling dissimilar metals to be joined in multi-materialization with utilizing an elastic body. Specifically, in methods for joining members of Patent Document <NUM> and Patent Document <NUM>, a pipe body is inserted into a hole portion of a wall surface body (plate member), an elastic body (urethane rubber member) is inserted inside the pipe body (pipe member), and the elastic body is pressed to be deformed, whereby the pipe body is expanded, and the wall surface body and the pipe body are joined together by press-fitting.

A conventional joined body according to the preamble of claim <NUM> is shown in Patent Document <NUM>. A further conventional joined body is shown in Patent Document <NUM>.

In the joining methods of Patent Document <NUM> and Patent Document <NUM>, a detailed examination on the material of the members to be joined has not been made, and there is room for improving the joining strength by examining the material.

An object of the present invention is to improve the joining strength between a first member and a second member in a joined body including the first member and the second member and a method for manufacturing the joined body.

The present invention solves the problem by a joined body comprising all features of claim <NUM>.

Advantageous further developments are subject-matter of the dependent claims.

According to this configuration, since the spring-back amount of the cylindrical flange portion arranged outside the first member is larger than the spring-back amount of the first member, the flange portion tightens the first member, so that the joining strength can be improved. Here, the spring-back amount means the restoration amount when the material is deformed, and the deformation may be either elastic deformation or plastic deformation.

According to the configuration of claim <NUM>, the inner circumferential surface of the flange portion does not abut on the outer circumferential surface of the first member in the mode of line contact (point contact in the cross section in the direction in which the flange portion protrudes), but the curved surface portion having a protruding shape abuts on the outer circumferential surface of the first member in the mode of surface contact (line contact in the cross section in the direction in which the flange portion protrudes). Therefore, the contact area between the first member and the second member increases. Due to the increase in the contact area, the contact pressure between the first member and the second member when a load is applied to the joined body can be reduced, and the durability of the joined body can be improved.

With the configuration of claim <NUM>, the area of the curved surface portion can be increased, and the contact area between the first member and the second member is further increased, whereby the durability of the joined body can be further improved.

According to the configuration of claim <NUM>, the mechanical engineering material characteristics can define the materials of the first member and the second member. In particular, since the tensile strength is a factor that greatly affects the spring-back amount of the material, the tensile strength is significant in selecting the material from the viewpoint of the spring-back amount.

According to the configuration of claim <NUM>, the mechanical engineering material characteristics can define the materials of the first member and the second member. In particular, since Young's modulus is a factor that greatly affects the spring-back amount of the material, Young's modulus is significant in selecting the material from the viewpoint of the spring-back amount.

According to the manufacturing method of claim <NUM>, since the spring-back amount of the cylindrical flange portion arranged outside the first member is larger than the spring-back amount of the first member and the flange portion tightens the first member, the joining strength can be improved. In addition, the joining by pipe-expanding does not give a thermal strain as compared with the joining by welding, so that high dimensional accuracy can be secured.

According to the present invention, in a joined body including the first member and the second member and a method for manufacturing the joined body, it is possible to improve the joining strength by defining the materials of the first member and the second member with spring-back amounts.

Referring to <FIG>, the joined body <NUM> of the present embodiment includes a pipe-shaped first member <NUM> and a plate-shaped second member <NUM>. The joined body <NUM> is configured by joining the first member <NUM> and the second member <NUM>.

The first member <NUM> of the present embodiment is a substantially circular pipe-shaped member and is made of mild steel. Referring also to <FIG>, the first member <NUM> includes a circular pipe-shaped main body <NUM> and bulging portions 12A and 12B extending over the circumferential direction of the main body <NUM> and bulging radially outward. The bulging portions 12A and 12B are arranged on both sides in the axial direction (upper side and lower side in <FIG>) of the main body <NUM> with respect to the second member <NUM>.

Referring to <FIG>, the second member <NUM> is a substantially annular member and is made of high tension steel. Referring also to <FIG>, the second member <NUM> includes a plate-shaped lower wall (wall portion) <NUM>, and a cylindrical flange portion <NUM> formed in the central portion of the lower wall <NUM> and extending toward one side (upper side in <FIG>). The flange portion <NUM> is integrally formed with the lower wall <NUM> by burring and is continuous in the circumferential direction. The lower wall <NUM> includes an upper surface (first surface) 21a from which the flange portion <NUM> protrudes and a lower surface (second surface) 21b facing the upper surface <NUM>.

The flange portion <NUM> includes an insertion hole 122a, through which the first member <NUM> is inserted, the insertion hole 122a opening at both ends. The insertion hole 122a of the flange portion <NUM> has a shape corresponding to the outer shape of the first member <NUM>. Specifically, the insertion hole 122a of the flange portion <NUM> has a shape similar to the outer shape of the first member <NUM> in a cross section orthogonal to the axial direction of the flange portion <NUM>.

The inner circumferential surface of the flange portion <NUM> includes a curved surface portion 122b on the base end side, that is, on the lowermost surface 21a side of the lower wall <NUM>, and a tip portion 122d (abutting portion) separated from the outer circumferential surface of the first member <NUM> on the tip side.

The curved surface portion 122b is formed by making a connected portion between the inner circumferential surface of the flange portion <NUM> and the lower surface <NUM> of the lower wall <NUM> into a protruding shape that expands toward the lower surface <NUM>.

The tip portion 122d extends toward one side in the axial direction and toward the outside in the radial direction of the flange portion <NUM>. That is, at the tip portion 122d, the inner circumferential surface of the flange portion <NUM> expands in diameter. The tip portion 122d is formed by chamfering the inner circumferential surface of the end portion on one side of the flange portion <NUM> into a C-plane shape, for example.

The inner circumferential surface of the flange portion <NUM> includes an intermediate portion 122c (separation portion) between the curved surface portion 122b and the tip portion 122d.

In the joined body <NUM>, the first member <NUM> is pipe-expanded in a state where the first member <NUM> is inserted into the insertion hole 122a of the second member <NUM>, whereby the first member <NUM> and the second member <NUM> are joined together by press-fitting. In this state, the flange portion <NUM> of the second member <NUM> is fitted between the bulging portions 12A and 12B of the first member <NUM> and is prevented from coming off in the axial direction.

In the following, a method for manufacturing the joined body <NUM> according to the present embodiment will be described with reference to <FIG>.

As shown in <FIG>, in the method for manufacturing the joined body <NUM> according to the present embodiment, first, the first member <NUM> is inserted into the insertion hole 122a of the flange portion <NUM> of the second member <NUM>. In this state, the first member <NUM> and the second member <NUM> are not pipe-expanded or deformed, and the first member <NUM> is relatively linearly movable in the axial direction of the first member <NUM> with respect to the second member <NUM>. Specifically, the first member <NUM> has substantially constant cross-sectional shapes orthogonal to the axial direction of the first member <NUM> over the entire length in the axial direction of the first member <NUM>. The insertion hole 122a of the flange portion <NUM> of the second member <NUM> is slightly larger than the outer shape of the first member <NUM>.

In this state, a rubber member <NUM> is inserted into the first member <NUM>. Here, the order of insertion is not particularly limited. That is, the rubber member <NUM> may be inserted into the first member <NUM>, and then in that state, the first member <NUM> may be inserted into the insertion hole 122a of the flange portion <NUM> of the second member <NUM>. The rubber member <NUM> has a cylindrical shape and has a size insertable into the first member <NUM>. The outer shape of the rubber member <NUM> is similar to the inner shape of the first member <NUM> in a cross section perpendicular to the axial direction of the first member <NUM>, and is preferably as large as possible. The rubber member <NUM> has flat surfaces orthogonal to the axial direction of the first member <NUM> at both ends in the longitudinal direction. The material of the rubber member <NUM> is preferably any one of urethane rubber, chloroprene rubber, CNR rubber (chloroprene rubber + nitrile rubber), and silicone rubber, for example. In addition, the hardness of the rubber member <NUM> is preferably <NUM> or more in Shore A.

Next, pushers <NUM> are arranged at both ends of the rubber member <NUM>. Each pusher <NUM> includes a pressing portion <NUM> that presses the rubber member <NUM>. The pressing portion <NUM> has a cylindrical shape, and the end surface of the pressing portion <NUM> is a flat pressing surface. The pusher <NUM> is attached to a press device (not shown) or the like, and is driven by this press device to compress the rubber member <NUM> in the axial direction of the first member <NUM> as shown in <FIG> (see arrow A in <FIG>). Along with this compression, the rubber member <NUM> swells toward the outside in the radial direction of the first member <NUM> (see arrow B in <FIG>). The swell of the rubber member <NUM> pipe-expands the first member <NUM>, and also pipe-expands the cylindrical flange portion <NUM> of the second member <NUM>, so that the first member <NUM> and the second member <NUM> are joined together by press-fitting. At this time, the bulging portions 12A and 12B are formed on both sides in the axial direction of the first member <NUM> with respect to the second member <NUM>.

After the first member <NUM> and the second member <NUM> are joined together by press-fitting, as shown in <FIG>, the pressing device (not shown) is driven to release the compression of the rubber member <NUM> by the pusher <NUM>. Since the rubber member <NUM> from which the compressive force of the pusher <NUM> has been removed is restored to its original shape due to the elasticity of the rubber member <NUM> itself, the rubber member <NUM> is easily removed from the first member <NUM>. At this time, a spring-back phenomenon occurs in the first member <NUM> and the second member <NUM> from which the pipe-expanding force of the rubber member <NUM> has been removed. That is, the first member <NUM> and the second member <NUM> slightly pipe-contract radially inward (see arrow C in <FIG>).

Comparing the first member <NUM> and the second member <NUM> from the viewpoint of the spring-back amount, the material of the second member <NUM> arranged outside (high tension steel) has a larger spring-back amount than the material of the first member <NUM> arranged inside (mild steel). Therefore, the second member <NUM> on the outer side pipe-contracts more greatly than the first member <NUM> on the inner side, and the second member <NUM> tightens the first member <NUM> more strongly, whereby the joining strength of the jointing by press-fitting is further improved. Here, the spring-back amount means the restoration amount when the material is deformed, and the deformation may be either plastic deformation or elastic deformation.

<FIG> is a stress-strain diagram showing spring-back amounts S1 and S2. The horizontal axis represents the pipe-expansion amount (strain), and the vertical axis represents the stress. The spring-back amount S1 denotes the spring-back amount of the first member <NUM>, and the spring-back amount S2 denotes the spring-back amount of the flange portion <NUM> of the second member <NUM>. The first member <NUM> (mild steel) and the second member <NUM> (high tension steel) are steel-based materials of the same kind, and as shown by the slopes of the left side straight line portions in the graph, the Young's modulus E1 of the first member <NUM> and the Young's modulus E2 of the second member <NUM> are substantially the same. In addition, the tensile strength Ts1 of the first member <NUM> is smaller than the tensile strength Ts2 of the second member <NUM>. In particular, the difference between the spring-back amount S1 and the spring-back amount S2 in the present embodiment is mainly caused by the difference between the tensile strengths TS1 and Ts2. Generally, the greater the tensile strength, the greater the spring-back amount. It should be noted that the reason why the stress-strain curve of the second member <NUM> does not set the origin as the starting point is due to the clearance existing between the first member <NUM> and the second member <NUM>. That is, this means that the first member <NUM> on the inner side is pipe-expanded by the amount of this clearance, and then the second member <NUM> is pipe-expanded. In addition, the spring back is schematically shown by the broken line in the diagram up to the position where the stress becomes zero, but actually, the stress generated between the first member <NUM> and the second member <NUM> reaches an equilibrium state and the pipe contraction is completed. In consideration of these, the spring-back amount S1 of the first member <NUM> is smaller than the spring-back amount S2 of the second member <NUM>. Therefore, the flange portion <NUM> of the second member <NUM> on the outer side pipe-contracts more greatly than the first member <NUM> on the inner side, and the flange portion <NUM> of the second member <NUM> tightens the first member <NUM> more strongly, so that the joining strength of the joining by press-fitting is further improved.

According to the present embodiment, since the spring-back amount of the cylindrical flange portion <NUM> of the second member <NUM> arranged outside the first member <NUM> is larger than the spring-back amount of the first member <NUM>, the flange portion <NUM> tightens the first member <NUM>, so that the joining strength can be improved.

The inner circumferential surface of the flange portion <NUM> abuts on the outer circumferential surface of the first member <NUM> at the curved surface portion 122b. In addition, the inner circumferential surface of the flange portion <NUM> abuts on the outer circumferential surface of the first member <NUM> at a corner portion 122e formed by the lower end of the tip portion 122d and the upper end of the intermediate portion 122c. The intermediate portion 122c between the curved surface portion 122b and the tip portion 122d is separated from the outer circumferential surface of the first member <NUM>.

At the curved surface portion 122b, the inner circumferential surface of the flange portion <NUM> abuts on the outer circumferential surface of the first member <NUM> in the mode of surface contact (line contact in the cross section in the direction in which the flange portion protrudes), not in the mode of line contact (point contact in the cross section in the direction in which the flange portion protrudes). Therefore, the contact area between the first member <NUM> and the second member <NUM> increases. Due to the increase in the contact area, the contact pressure between the first member and the second member when a load is applied to the joined body can be reduced, and the durability of the joined body can be improved.

In the present embodiment, in addition to the curved surface portion 122b, the corner portion 122e also abuts on the outer circumferential surface of the first member <NUM>. However, the contribution of the abutment of this portion to the joining strength between the first member <NUM> and the second member is small. In addition, in the present embodiment, the protrusion amount h, from the upper surface 21a, of the lower wall <NUM> of the flange portion <NUM> is set to be larger than the dimension of the lower wall <NUM> in the thickness direction, but the contribution of this protrusion amount h to the joining strength between the first member <NUM> and the second member is small.

According to the present embodiment, the mechanical engineering material characteristics can define the materials of the first member <NUM> and the second member <NUM>. In particular, since the tensile strength is a factor that greatly affects the spring-back amount of the material, the tensile strength is significant in selecting the material from the viewpoint of the spring-back amount.

In addition, as a modified example of the present embodiment, the material of the first member <NUM> may be high tension steel, and the material of the second member <NUM> may be an aluminum alloy.

<FIG> is a stress-strain diagram showing spring-back amounts S1 and S2. The horizontal axis represents the pipe-expansion amount (strain), and the vertical axis represents the stress. The spring-back amount S1 denotes the spring-back amount of the first member <NUM>, and the spring-back amount S2 denotes the spring-back amount of the flange portion <NUM> of the second member <NUM>. As shown by the slopes of the left side straight line portions in the graph, the Young's modulus E1 of the first member <NUM> (high tension steel) is larger than the Young's modulus E2 of the second member <NUM> (aluminum alloy). In addition, the tensile strength Ts1 of the first member <NUM> is smaller than the tensile strength Ts2 of the second member <NUM>. In particular, the difference between the spring-back amount S1 and the spring-back amount S2 in the present embodiment is mainly caused by the difference in Young's modulus and the difference in tensile strength. Generally, the smaller the Young's modulus, the larger the spring-back amount. In addition, as described above, generally, the greater the tensile strength, the greater the spring-back amount. In addition, the spring back is schematically shown by the broken line in the diagram up to the position where the stress becomes zero, but actually, the stress generated between the first member <NUM> and the second member <NUM> reaches an equilibrium state and the pipe contraction is completed. In consideration of these, the spring-back amount S <NUM> of the first member <NUM> is smaller than the spring-back amount S2 of the second member <NUM>. Therefore, the second member <NUM> on the outer side pipe-contracts more greatly than the first member <NUM> on the inner side, and the second member <NUM> tightens the first member <NUM> more strongly, so that the joining strength of the joining by press-fitting is further improved.

According to this modified example, specifically, the tensile strength and Young's modulus being mechanical engineering material characteristics can define the materials of the first member <NUM> and the second member <NUM>. In particular, since the tensile strength and Young's modulus are factors that greatly affect the spring-back amount, the tensile strength and Young's modulus are significant in selecting the material from the viewpoint of the spring-back amount.

<FIG> show various alternatives to the shape of the flange portion.

In the alternative shown in <FIG>, the curved surface portion 222b of the inner circumferential surface of the flange portion <NUM> spreads from the lower surface 21b to the tip portion 222c of the lower wall <NUM>. In other words, in this alternative, the intermediate portion 222a of the inner circumferential surface of the flange portion <NUM> also constitutes the curved surface portion 222b. With this configuration, with this configuration, the area of the curved surface portion 222b can be increased, and the contact area between the first member <NUM> and the second member <NUM> is further increased, whereby the durability of the joined body can be further improved.

As shown in <FIG>, the tapered tip portion 122d may be eliminated from the flange portion <NUM> of the present embodiment. In addition, as shown in <FIG>, the tapered tip portion 222d may be eliminated from the flange portion <NUM> of the alternative in <FIG>.

In the alternative in <FIG>, in addition, the inner circumferential surface of the flange portion <NUM> includes a base portion 22b connected to the lower wall <NUM>, an intermediate portion 22c, and a tip portion 22d connected to the intermediate portion 22c.

The base portion 22b contracts in diameter upward in the drawing from the lower surface 21b side of the lower wall <NUM>. The base portion 22b is formed by chamfering the inner circumferential surface of the flange portion <NUM> into a C-plane shape. The tip portion 22d of the flange portion <NUM> expands in diameter toward the tip of the flange portion <NUM>. The tip portion 22d is formed by chamfering the inner circumferential surface of the flange portion <NUM> into a C-plane shape. The intermediate portion 22c is separated from the outer circumferential surface of the first member <NUM>.

The inner circumferential surface of the flange portion <NUM> abuts on the outer circumferential surface of the first member <NUM> at a corner portion 22e formed between the base portion 22b and the intermediate portion 22c. In addition, the inner circumferential surface of the flange portion <NUM> abuts on the outer circumferential surface of the first member <NUM> at a corner portion 22f formed between the intermediate portion 22c and the tip portion 22d. Any of the angles θd and θp of the corners 22e and 22f is an obtuse angle, whereby, as compared with the case where these angles θd and θp are right angles, that is, the case where the base portion 22b and the tip portion 22d are not tapered, the contact pressure between the outer circumferential surface of the first member <NUM> and the inner circumferential surface of the flange portion <NUM> can be reduced.

The alternative in <FIG> is different from the alternative in <FIG> in that the intermediate portion 22c abuts on the outer circumferential surface of the first member <NUM>. The dimension l in the axial direction of the intermediate portion 22c is larger than the dimension d in the thickness direction of the wall portion <NUM>. Therefore, as compared with the case where the second member <NUM> abuts on the outer circumferential surface of the first member <NUM> through the inner circumferential surface of the wall portion <NUM>, the contact area between the first member <NUM> and the second member <NUM> increases. The contact pressure between the first member <NUM> and the second member <NUM> when a load is applied to the joined body <NUM> can be reduced, and the durability of the joined body can be improved.

In the second embodiment described below, the same or similar elements as in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Furthermore, in the second embodiment, the same action and effect as those of the first embodiment are produced, except for the points particularly mentioned.

Referring to <FIG>, the second member <NUM> of the present embodiment is a hollow member, and the first member <NUM> and the second member <NUM> are joined together by press-fitting at two places.

Referring to <FIG> and <FIG>, the first member <NUM> of the present embodiment includes a circular pipe-shaped main body <NUM> and bulging portions 12A, 12B, 12C, and 12D extending over the circumferential direction of the main body <NUM> and bulging radially outward.

The second member <NUM> includes a rectangular plate-shaped lower wall <NUM>, and a cylindrical flange portion <NUM> formed in the central portion of the lower wall <NUM> and extending toward one side (lower side in <FIG>). In addition, the second member <NUM> of the present embodiment includes a rectangular plate-shaped upper wall (wall portion) <NUM> arranged to face the lower wall <NUM>, and a cylindrical flange portion <NUM> formed in the central portion of the upper wall <NUM> and extending toward the other side (upper side in <FIG>). The second member <NUM> includes a pair of side walls 25A and 25B mechanically connecting the end portion of the lower wall <NUM> and the end portion of the upper wall <NUM>. Since the flange portion <NUM> of the upper wall <NUM> has the same configuration as the flange portion <NUM> of the lower wall <NUM>, a detailed description thereof will be omitted. The flange portion <NUM> and the flange portion <NUM> of the second member <NUM> of the present embodiment are formed to point toward the outside of the second member <NUM>.

In the present embodiment, the first member <NUM> is pipe-expanded in a state where the first member <NUM> is inserted into the insertion hole 122a of the flange portion <NUM> and the insertion hole 124a of the flange portion <NUM> of the second member <NUM>, whereby the first member <NUM> and the second member <NUM> are joined together by press-fitting. The flange portion <NUM> of the lower wall <NUM> of the second member <NUM> is fitted between the bulging portions 12A and 12B of the first member <NUM>, and the flange portion <NUM> of the upper wall <NUM> is fitted between the bulging portions 12C and 12D of the first member <NUM>, whereby the first member <NUM> is prevented from coming off in the axial direction.

As shown in <FIG>, in the method for manufacturing the joined body <NUM> according to the present embodiment, first, the first member <NUM> is inserted into the insertion hole 122a of the flange portion <NUM> and the insertion hole 124a of the flange portion <NUM> of the second member <NUM>. In this state, the first member <NUM> and the second member <NUM> are not pipe-expanded or deformed, and the first member <NUM> is relatively linearly movable in the axial direction of the first member <NUM> with respect to the second member <NUM>. Specifically, the first member <NUM> has substantially constant cross-sectional shapes orthogonal to the axial direction of the first member <NUM> over the entire length in the axial direction of the first member <NUM>. The insertion hole 122a of the flange portion <NUM> and the insertion hole 124a of the flange portion <NUM> of the second member <NUM> are slightly larger than the outer shape of the first member <NUM>. Next, a rubber member <NUM> is inserted into the first member <NUM>. Here, the order of insertion is not particularly limited. That is, the rubber member <NUM> may be inserted into the first member <NUM>, and then in that state, the first member <NUM> may be inserted into the insertion hole 122a of the flange portion <NUM> and the insertion hole 124a of the flange portion <NUM> of the second member <NUM>. Here, in the present embodiment, the rubber member <NUM> is divided into two, and a columnar plate <NUM> is arranged between the rubber members <NUM>.

Next, pushers <NUM> are arranged on both sides across the rubber members <NUM>. The pusher <NUM> is attached to a press device (not shown) or the like, and is driven by this press device to compress the rubber member <NUM> in the axial direction of the first member <NUM> as shown in <FIG> (see arrow A in <FIG>). Along with this compression, the rubber member <NUM> swells toward the outside in the radial direction of the first member <NUM> (see arrow B in <FIG>). The swell of the rubber member <NUM> pipe-expands the first member <NUM>, and also pipe-expands the cylindrical flange portion <NUM> and flange portion <NUM> of the second member <NUM>, so that the first member <NUM> and the second member <NUM> are joined together by press-fitting. At this time, bulging portions 12A and 12B are formed on both sides in the axial direction of the first member <NUM> with respect to the lower wall <NUM> of the second member <NUM>, and bulging portions 12C and 12D are formed on both sides in the axial direction of the first member <NUM> with respect to the upper wall <NUM> of the second member <NUM>.

In the following, a modified example of the second embodiment will be described with reference to <FIG>.

In the modified example shown in <FIG>, the flange portion <NUM> and the flange portion <NUM> of the second member <NUM> are formed to point toward the inside of the second member <NUM>. Specifically, the flange portion <NUM> is formed to extend from the central portion of the lower wall <NUM> toward one side (upper side in <FIG>), and the flange portion <NUM> is formed to extend from the central portion of the upper wall <NUM> toward the other side (lower side in <FIG>).

In the second embodiment and its modified example, the flange portion may have forms as the alternatives shown in <FIG>.

Although the present invention has been described above with the preferred embodiments, the present invention is not limited to the specific embodiments, and various modifications may be made within the scope of the appended claims.

For example, the flange portion <NUM>, <NUM>, or <NUM> has an annular cross-sectional shape in the cross section orthogonal to the axial direction of the flange portion <NUM>, <NUM>, or <NUM> in the first and second embodiments, but may have a polygonal cross-sectional shape.

In addition, the flange portion <NUM> does not have to be continuous in the circumferential direction.

Claim 1:
A joined body comprising:
a first member (<NUM>) having a pipe shape; and
a second member (<NUM>) including a wall portion (<NUM>) having a plate shape, and a flange portion (<NUM>, <NUM>, <NUM>) having a cylinder shape and provided with an insertion hole (22a, 122a) through which the first member (<NUM>) is inserted,
wherein in a state where the first member (<NUM>) is inserted into the insertion hole (22a, 122a) of the flange portion (<NUM>, <NUM>, <NUM>) of the second member (<NUM>), the first member (<NUM>) and the second member (<NUM>) are joined with the first member (<NUM>) pipe-expanded,
characterized in that
a material of the second member (<NUM>) is larger than a material of the first member (<NUM>) in a spring-back amount.