FIG. 3). In the case of a helical angle 90°, the helical groove 3b circles the first shaft portion 3 a quarter of a turn, and in the case of a helical angle 720°, the helical groove 3b circles the first shaft portion 3 two turns. FIGS. 1 to 4 show the case of a helical angle 180°, and the helical groove 3b circles the first shaft portion 3 a half a turn. An appropriate value of the helical angle β of the helical groove 3b is described later.

The cross-sectional shape, width, and depth of the helical groove 3b can be set as appropriate within a scope in which the helical groove 3b can perform its role of digging into the members to be fastened. As shown in FIG. 4, the helical groove 3b in this example has a substantially arc shape in a cross-sectional view, and is tapered toward the tip end side (shape that becomes narrower and shallower toward the tip end side). Note that the helical groove 3b may be provided in part of the main body portion 3a. Moreover, multiple helical grooves 3b may be provided in the main body portion 3a.

The second shaft portion 4 extends from the center portion 2a of the head portion 2 in the opposite direction to the first shaft portion 3, and is a portion having, for example, a substantially cylindrical shape.

FIG. 5 shows a rivet 1b that is a modified example of the rivet 1a described above. The rivet 1b is different from the rivet 1a in the following point. The thickness of the peripheral edge portion 2b of the head portion 2 in the rivet 1a is substantially constant, while the thickness of the peripheral edge portion 2b in the rivet 1b has a tapered shape as shown in FIG. 5 in which part of the head portion 2 is cut away. Other configurations are the same as those of the rivet 1a described above, and detailed explanation is omitted by denoting the configurations in FIG. 5 with the same reference signs as those in FIGS. 1 to 4.

Regarding To-be-Fastened Members

The to-be-fastened members 30 shown in FIG. 6 are members to be fastened to each other by the rivet 1a or the rivet 1b described above. The to-be-fastened members 30 include a first to-be-fastened member 40 and a second to-be-fastened member 50. Specifically, the first to-be-fastened member 40 and the second to-be-fastened member 50 are fastened to each other by driving the rivet 1a or the rivet 1b therein. The first to-be-fastened member 40 and the second to-be-fastened member 50 are fastened to each other with the rivet 1a or the rivet 1b in a state where a back surface 50a of the second to-be-fastened member 50 is laid on a front surface 40a of the first to-be-fastened member 40 having the prepared hole 41.

In the present embodiment, the first to-be-fastened member 40 is a block material with a quadrilateral prism shape. The shape of the first to-be-fastened member 40 is not limited to a particular shape as long as the first to-be-fastened member 40 is a member that has a thickness large enough to provide at least the prepared hole 41 to be described later, and may be another shape. For example, the first to-be-fastened member 40 is a column-shaped member having a cross section with a circular, elliptical, polygonal, or indefinite shape. The length of the first to-be-fastened member 40 is preferably larger than the length of the first shaft portion 3 in a direction in which the rivet 1a or 1b is inserted. Moreover, the first to-be-fastened member 40 may be a member made to have a large thickness by laying two or more plate members one on top of another.

The prepared hole 41 includes an opening portion 42 opened on the front surface 40a of the first to-be-fastened member 40 and a hole portion 43 continuous with the opening portion 42. The hole portion 43 includes an inner wall surface with a substantially cone shape or a substantially truncated cone shape that is a tapered shape. The opening portion 42 is formed in a substantially cone shape whose inner wall surface forms a taper angle θ2 and whose diameter decreases from the front surface 40a side toward an inner portion of the first to-be-fastened member 40. The hole portion 43 is formed in a substantially cone shape or a substantially truncated cone shape whose inner wall surface forms a taper θ3 and whose diameter decreases from the front surface 40a side toward the inner portion of the first to-be-fastened member 40. The depth of the hole portion 43 is larger than the length of the first shaft portion 3 described above. The opening diameter φ1 of the hole portion 43 is larger than the diameter φ2 (FIG. 2) of the base end portion 3a2 of the first shaft portion 3. Moreover, the depth of the prepared hole 41 may be the same as the length of the first shaft portion 3 or smaller than the length of the first shaft portion 3. In the case where the depth of the prepared hole 41 is larger than the length of the first shaft portion 3, the rivet 1a can be smoothly inserted. In the case where the depth of the prepared hole 41 is smaller than the length of the first shaft portion 3, the tip end of the first shaft portion 3 is driven into a bottom portion of the prepared hole 41, and the joint strength increases. However, the depth and the length are preferably set to such depth and length that insertion is not hindered. The prepared hole 41 may be formed to be provided in formation of the first to-be-fastened member 40, or may be formed by performing tapered hole opening processing on the first to-be-fastened member 40 with a tool such as a drill, a reamer, or an end mill.

In the present embodiment, the second to-be-fastened member 50 is a plate member with a flat plate shape. The second to-be-fastened member 50 may have any shape or the like as long as the second to-be-fastened member 50 has such a thickness that at least the first shaft portion 3 can penetrate the second to-be-fastened member 50, and is, for example, a plate-shaped member that has a thickness smaller than the length of the first shaft portion 3. The material of the first to-be-fastened member 40 and the second to-be-fastened member 50 is not limited to a particular material, and is made of a metal that can be fastened with the rivet 1a (for example, aluminum, an aluminum alloy, magnesium, a magnesium alloy, copper, a copper alloy, titanium, a titanium alloy, or the like). The first to-be-fastened member 40 may be, for example, a casted member. In this case, it is desirable that the prepared hole 41 is also formed in a formation step of the first to-be-fastened member 40 by casting. The second to-be-fastened member 50 may be, for example, a plate member made of a metal or a resin. Note that the casted member is a material assumed to be obtained by putting a metal heated and melted to a liquid form referred to as molten metal into a die and cooling and solidifying the molten metal. Moreover, in this case, the casted member is preferably (a casted member made of) an Al—Si—Cu-based alloy, more preferably JISH5302 ADC12.

Regarding Riveting Method

A riveting method using the rivet 1a or 1b according to the embodiment of the present invention is explained in detail with reference to the drawings. A riveting apparatus 10 shown in FIG. 7 is an apparatus that drives the rivet 1a (or rivet 1b (same applies hereinafter)) at high speed into the two members (to-be-fastened members 30) that are to be fastened to each other and that are laid one on top of the other, and fastens the to-be-fastened members 30 together.

As shown in FIG. 7, the riveting apparatus 10 includes an air compressor 11, a first needle valve 12, a pressure booster 13, a second needle valve 14, a solenoid valve 15, a rivet ejector 16, and hoses 17 connecting these configurations to one another.

The air compressor 11 is a device that compresses and sends out air. The first needle valve 12 is a valve for the pressure booster 13. The pressure booster 13 is a device that increases the pressure of the air sent out from the air compressor 11. The second needle valve 14 and the solenoid valve 15 are adjustment valves for sending the compressed air to the rivet ejector 16.

The riveting method of the present embodiment includes a preparation step of laying the back surface 50a of the second to-be-fastened member 50 on the front surface 40a of the first to-be-fastened member 40 having the prepared hole 41 (setting the second to-be-fastened member 50 and the first to-be-fastened member 40 to the state of FIG. 6) and a riveting step of moving the metal rivet 1a set at a position away from a front surface 50b (FIG. 6) of the second to-be-fastened member 50 toward a position of the prepared hole 41 by using the riveting apparatus 10 and driving the rivet la into the second to-be-fastened member 50 and the first to-be-fastened member 40 in this order to cause the rivet 1a to reach the inside of the prepared hole 41.

Specifically, the rivet ejector 16 has a long cylindrical shape in this example, and ejects a bullet 20 housed inside the rivet ejector 16 toward the to-be-fastened members 30 by using the pressure of the compressed air (air pressure). The bullet 20 only needs to be configured to include the rivet 1a, and may be only the rivet 1a. In this example, as shown in FIG. 8, an object in which an auxiliary member 21 is attached to the rivet 1a is used as the bullet 20. The auxiliary member 21 is a member for driving the rivet 1a into the to-be-fastened members 30 in a stable state. Moreover, the auxiliary member 21 is a member that increases motion energy of the rivet 1a ejected together with the auxiliary member 21. For example, in the case where the rivet 1a is light weight, the auxiliary member 21 is used for weight adjustment.

The material, shape, and mass of the auxiliary member 21 may be any material, shape, and mass as long as the rivet 1a is driven into the to-be-fastened members 30 in the stable state, and can be set as appropriate. As shown in FIG. 8, the auxiliary member 21 in this example has a cylindrical shape in which an inner peripheral surface 21b with a substantially circular column shape is formed, and the second shaft portion 4 is inserted into the inner peripheral surface 21b from one opening portion 21a to fix the rivet 1a to the auxiliary member 21. Specifically, the inner peripheral surface 21b holds the second shaft portion 4 as a holding portion. The compressed air is taken in from the other opening portion 21c, and the bullet 20 is ejected from the rivet ejector 16 at high speed by using the pressure of the taken-in air. Note that the bullet 20 in the rivet ejector 16 is arranged such that the center axis of the first shaft portion 3 of the rivet 1a attached to the bullet 20 is aligned in advance with the center axis of the prepared hole 41 of the to-be-fastened members 30 located below the first shaft portion 3. Moreover, the rivet 1a may be fixed to the auxiliary member 21 in a form in which the rivet 1a is provided with no second shaft portion 4.

The bullet 20 ejected from the rivet ejector 16 moves in air at high speed in a non-rotating state, and reaches the to-be-fastened members 30. The rivet 1a having reached the to-be-fastened members 30 is driven into the to-be-fastened members 30 while being rotated and screwed-in by the helical groove 3b carved in the first shaft portion 3 (see FIG. 1). Then, the entire first shaft portion 3 is inserted into the to-be-fastened members 30, the head portion 2 (see FIG. 1) comes into contact with the to-be-fastened members 30, and the riveting is thereby completed. The to-be-fastened members 30 including the two members are thereby fastened together. As a result, the to-be-fastened members 30 are fastened to each other with the rivet 1a, and become a fastened product 60 as shown in the cross-sectional diagram of FIG. 9.

Regarding Numerical Ranges

Next, explanation is given of numerical ranges of the portions preferable for the riveting method according to the present embodiment.

First, the height (depth) H (FIG. 6) of the opening portion 42 normally has a relationship of “0.25×T<H<0.75×T” with respect to the thickness T (FIG. 6) of the second to-be-fastened member 50 at the driving position of the rivet 1a or 1b. The relationship between the height H of the opening portion 42 and the thickness T of the second to-be-fastened member 50 is preferably a relationship of 0.3×T<H, more preferably 0.35×T<H, even more preferably 0.4×T<H, particularly preferably 0.45×T<H. Moreover, the relationship between the height H of the opening portion 42 and the thickness T of the second to-be-fastened member 50 is preferably a relationship of H<0.7×T, more preferably H<0.65×T, even more preferably H<0.6×T, particularly preferably H<0.55×T. Operations and effects provided by the relationship in which the height H of the opening portion 42 is larger than the above-mentioned lower limit with respect to the thickness T of the second to-be-fastened member 50 and operations and effects provided by the relationship in which the height H of the opening portion 42 is smaller than the above-mentioned upper limit with respect to the thickness T of the second to-be-fastened member 50 are described later.

Moreover, the taper θ2 (FIG. 6) of the opening portion 42 in the prepared hole 41 is preferably 70 to 110°, more preferably 75 to 105°, even more preferably 80 to 100°, particularly preferably 85 to 95°. Operations and effects provided by setting the taper angle θ2 of the opening portion 42 equal to or more than the lower limit value described above and operations and effects provided by setting the taper angle θ2 of the opening portion 42 equal to or less than the upper limit value described above are described later.

Moreover, a relationship between the opening diameter φ1 (FIG. 6) that is the diameter of an entrance portion of the hole portion 43 in the prepared hole 41 and the diameter φ2 (FIG. 2) of the base end portion 3a2 of the main body portion 3a is preferably 1.0×φ2<φ1≤1.1×φ2, more preferably 1.01×φ2<φ1≤1.09×φ2, even more preferably 1.02×φ2<φ1≤1.08×φ2.

Furthermore, the taper angle φ3 (FIG. 6) that is a tilt of the inner wall surface of the hole portion 43 in the prepared hole 41 is preferably 2 to 10°, more preferably 3 to 9°, even more preferably 4 to 8°.

Moreover, the thickness of the peripheral edge portion 2b of the head portion 2 in the rivet 1a or the rivet 1b (see FIGS. 4 and 5. A portion with the largest thickness for the rivet 1b) is preferably 0.2 to 2.0 mm, more preferably 0.3 to 1.8 mm, even more preferably 0.5 to 1.5 mm.

Furthermore, as shown in FIG. 4, a tilt angel θ1 of the head portion 2 in the rivet 1a is angle between an imaginary plane perpendicular to the axis center of the rivet 1a and a lower surface of the peripheral edge portion 2b. Moreover, as shown in FIG. 5, the tilt angle θ1 of the head portion 2 in the rivet 1b is an angle between an imaginary plane perpendicular to the axis center of the rivet 1b and a lower surface of the peripheral edge portion 2b. In the case where the tilt angles of an upper surface and the lower surface of the peripheral edge portion 2b vary from each other as in the rivet 1b, the tilt angle of the lower surface is adopted. This is because the lower surface side is assumed to contribute to the leak resistance. The tilt angle θ1 is preferably 5 to 30°, more preferably 10 to 25°, even more preferably 15 to 20°.

Moreover, the helical angle β (see FIG. 3. As described above) is preferably 60° or more, more preferably 120° or more, even more preferably 180° or more, particularly preferably 240° or more. Furthermore, the helical angle β is preferably 360° or less, more preferably 330° or less, even more preferably 300° or less. In the case where the helical angle β is equal to or larger than the lower limit value described above, tensile strength exhibited by entering of the first to-be-fastened member 40 and the second to-be-fastened member 50 into the helical groove 3b of the rivet 1a, 1b and meshing of the first to-be-fastened member 40 and the second to-be-fastened member 50 with the helical groove 3b tends to be improved. Moreover, in the case where the helical angle β is equal to or less than the upper limit value described above, the rivet 1a or 1b tends to be driven into the first to-be-fastened member 40 and the second to-be-fastened member 50 while being smoothly rotated by being affected by the helical groove 3b in the driving of the rivet 1a or 1b.

Regarding Operations and Effects

Operations and effects of the embodiment and the examples explained above are explained.

A method of fastening two plate members by using a rivet in which a helical groove is carved has been conventionally known (Patent Literature 1 described above). In this background art, the rivet is screwed while being rotated, and this causes the two metal plates to enter and mesh with the helical groove of the rivet. Accordingly, the fastening force is increased. To be more specific, to-be-fastened members including an upper plate and a lower plate into which the rivet is driven are deformed such that a protrusion with a shape of a volcanic crater protruding in a direction of driving is formed, and the to-be-fastened members cut by the helical groove is wound around a shaft portion along the helical groove.

As described above, in the background art, the case of fastening the plate members is assumed, and the case where the lower to-be-fastened member is a block-shaped block member or the like is not assumed. Accordingly, in the case where the plate member or the like and the block member or the like are attempted to be fastened to each other by using the rivet in which the groove is carved, leak from the fastened product after the fastening sometimes occurs. This is due to the following reason. In the case where the rivet is driven into the to-be-fastened members that are in the state where the plate member or the like is laid on the block member or the like, the upper to-be-fastened member (plate member or the like) is deformed in a driving direction. Moreover, the block member or the like on the lower side is cut by the groove, and deformation occurs in the block member or the like around the rivet. Specifically, there is no space where parts formed by the deformation of both to-be-fastened members can escape between the upper to-be-fastened member and the block or the like that is the lower to-be-fastened member. Accordingly, the upper to-be-fastened member is deformed as if to be raised upward with the driving of the rivet, and a space is formed between both to-be-fastened members, thereby causing leak.

In the present embodiment, the rivet 1a or 1b is moved to the position of the prepared hole 41 in the state where the back surface 50a of the second to-be-fastened member 50 is laid on the front surface 40a of the first to-be-fastened member 40 having the prepared hole 41, and is driven into the second to-be-fastened member 50 and the first to-be-fastened member 40 in this order. Furthermore, the prepared hole 41 includes the hole portion 43 having the inner wall surface with the substantially cone shape or the substantially truncated cone shape that is the tapered shape and the opening portion 42 that expands and opens in the tapered shape from the hole portion 43. The height (depth) H of the opening portion 42 is in the relationship of “0.25×T<H<0.75×T” with respect to the thickness T of the second to-be-fastened member 50 at the driving position of the rivet 1a or 1b.

Thus, according to the present embodiment, driving the rivet 1a or 1b into the second to-be-fastened member 50) causes the second to-be-fastened member 50 into which the rivet 1a or 1b is driven to be deformed such that the protrusion with the volcanic crater shape protruding toward the first to-be-fastened member 40 is formed. Moreover, driving of the rivet 1a or 1b into the first to-be-fastened member 40 causes the groove to cut a part of the inner wall surface of the prepared hole 41 in the first to-be-fastened member 40 into which the rivet 1a or 1b is driven, and the cut part of the inner wall surface of the prepared hole 41 is partially taken into the groove. Furthermore, since the opening portion 42 is provided on the front surface 40a of the first to-be-fastened member 40 in the state where the back surface 50a of the second to-be-fastened member 50 is laid on the front surface 40a of the first to-be-fastened member 40, a space in the opening portion 42 surrounded by the opening portion 42 of the first to-be-fastened member 40 and the back surface 50a of the second to-be-fastened member 50 is filled with the cut part of the first to-be-fastened member 40 and the part of the second to-be-fastened member 50 deformed in the protruding shape that is the volcanic crater shape. In this case, setting the height H and the thickness T to satisfy the relationship of “0.25×T<H” allows securing of a sufficient space for housing the parts formed by the deformation of the to-be-fastened members 30 in the space in the opening portion 42. Accordingly, it is possible to prevent the case where the second to-be-fastened member 50 is raised by contact with the parts formed by the deformation of the to-be-fastened members 30 and the space between the first to-be-fastened member 40 and the second to-be-fastened member 50 is expanded, and the leak resistance can be improved. Moreover, setting the height H and the thickness T to satisfy the relationship of “H<0.75×T” causes the to-be-fastened members 30 to be fastened to each other in a state where the space in the opening portion 42 is filled with the parts formed by the deformation of the to-be-fastened members 30. This can improve the leak resistance. Moreover, setting the height H and the thickness T to satisfy the relationship of “H<0.75×T” can prevent the case where: an excessive gap is left in the opening portion 42 between the first to-be-fastened member 40 and the second to-be-fastened member 50 in filling of the space in the opening portion 42 with the parts formed by the deformation of the to-be-fastened members 30; the second to-be-fastened member 50 becomes more likely to be deformed in application of load to the to-be-fastened members 30 after the fastening thereof: and the joint strength is thereby reduced. In other words, setting the height H and the thickness T to satisfy the relationship of “H<0.75×T” allows the first to-be-fastened member 40 to support the second to-be-fastened member 50 laid on the first to-be-fastened member 40 via the parts that fill the inside of the opening portion 42 and that are formed by the deformation of the to-be-fastened members 30. Accordingly, the deformation of the second to-be-fastened member 50 in the case where load is applied after the fastening is suppressed, and the joint strength can be improved.

As described above, according to the present embodiment, filling the insides of the opening portion 42 and the helical groove 3b with the parts formed by the contact of the first to-be-fastened member 40 and the second to-be-fastened member 50 with the rivet 1a or 1b in the driving of the rivet 1a or 1b allows the rivet 1a or 1b to come into tight contact with the first to-be-fastened member 40 and the second to-be-fastened member 50, and can provide the manufacturing method of the fastened product and the fastened product 60 that are improved in leak resistance and that have sufficient joint strength.

Moreover, providing the groove in the first shaft portion 3 can cause the groove to cut the material of the first to-be-fastened member 40 in the driving of the rivet 1a or 1b. In a case of a screw; provision of a thread increases the circumferential length of the screw depending on the height of the thread. In the present embodiment, the circumferential length of the first shaft portion 3 does not change even in the case where the groove is provided on the outer peripheral surface of the first shaft portion 3. Accordingly, deformation of the first to-be-fastened member 40 to a periphery that occurs in the driving of the rivet 1a or 1b can be suppressed. Moreover, part of the material cut by the driving of the rivet 1a or 1b is taken into the groove, and this can reduce stress generated with the deformation of the first to-be-fastened member 40. Accordingly, it is possible to insert the rivet 1a or 1b into the prepared hole 41 and fasten the to-be-fastened members 30 to each other while suppressing occurrence of cracking in the first to-be-fastened member 40. Moreover, accuracy as high as that for the case of the self-tapping fastening using the self-tapping screw is not required for the shape of the prepared hole 41 provided in the aluminum alloy casted object, and the case where the die for the to-be-fastened members 30 has a short life can be suppressed.

Moreover, the taper angle θ2 of the opening portion 42 is 70 to 110°. This can improve the leak resistance. Setting the taper angle θ2 of the opening portion 42 equal to or more than the lower limit value enables securing of a space sufficient for housing the parts formed by the deformation of the to-be-fastened members 30 in the space of the opening portion 42. Accordingly, the leak resistance can be improved. Moreover, setting the taper angle θ2 of the opening portion 42 equal to or less than the upper limit value causes the to-be-fastened members 30 to be fastened in the state where the space of the opening portion 42 is filled with the parts formed by the deformation of the to-be-fastened members 30, and allows the second to-be-fastened member 50 laid on the first to-be-fastened member 40 to be supported. Accordingly, it is possible to improve the leak resistance and improve the joint strength.

The opening diameter φ1of the hole portion 43 of the prepared hole 41 is larger than the diameter φ2 of the base end portion 3a2 of the first shaft portion 3. This suppresses an increase of load between the opening portion 42 of the prepared hole 41 and the first shaft portion 3 of the rivet 1a or 1b in the driving of the rivet 1a or 1b, and the first shaft portion 3 can be smoothly inserted into the prepared hole 41.

Moreover, the relationship between the opening diameter φ1 of the hole portion 43 and the diameter φ2 of the base end portion 3a2 of the first shaft portion 3 is preferably 1.0×φ2<φ1≤1.1×φ2. This suppresses an increase of load between the opening portion 42 of the prepared hole 41 and the first shaft portion 3 of the rivet 1a or 1b in the driving of the rivet 1a or 1b, and allows the first shaft portion 3 to be smoothly inserted into the prepared hole 41.

Furthermore, the taper angle θ3 of the hole portion 43 is preferably 2 to 10°. The inner wall surface of the hole portion 43 formed in the tapered shape and the tip end portion 3a1 whose diameter decreases toward the tip end side thereby come into contact with each other. This causes the to-be-fastened members 30 to be deformed, and enables fastening with the rivet 1a or 1b.

Moreover, the rivet 1a or 1b further includes the head portion 2 including the center portion 2a and the peripheral edge portion 2b, and the diameter of the peripheral edge portion 2b of the head portion 2 is larger than the diameter of the first shaft portion 3. The head portion 2 thereby elastically deforms and comes into tight contact with the surface of the to-be-fastened members 30, and this can further improve the leak resistance of the fastened product 60. Specifically, the head portion 2 is a portion where the rivet 1a or 1b strongly comes into tight contact with the surface of the to-be-fastened members 30 in the case where the rivet 1a or 1b is driven into the to-be-fastened members 30. The head portion 2 elastically deforms by receiving energy (motion energy) generated by the driving of the rivet 1a or 1b, and is held by strongly coming into tight contact with the surface of the to-be-fastened members 30, and this supports airtightness. Moreover, since the rivet 1a or 1b is fastened to the to-be-fastened members 30, the head portion 2 is held while being elastically deformed. Moreover, the peripheral edge portion 2b of the head portion 2 also functions as a stopper in the driving of the rivet 1a or 1b, and can absorb motion energy.

Furthermore, since the head portion 2 has the umbrella shape in which the peripheral edge portion 2b spreads while being tilted toward the first shaft portion 3 side, the leak resistance of the fastened product 60 can be further improved.

Moreover, since the thickness of the peripheral edge portion 2b of the head portion 2 is in the numerical range of 0.1 to 2.0 mm, the leak resistance of the fastened product 60 can be further improved.

Furthermore, since the tilt angle θ1 of the head portion 2 is in the numerical range of 5 to 30°, the leak resistance of the fastened product 60 can be further improved.

Moreover, the groove carved in the first shaft portion 3 is the helical groove 3b formed in the helical shape on the outer surface of the first shaft portion 3, and in the riveting step, the rivet 1a or 1b set at the position away from the front surface 50b of the second to-be-fastened member 50 is moved toward the position of the prepared hole 41 a non-rotating state, and is made to reach the inside of the prepared hole 41 by being rotated and screwed into the second to-be-fastened member 50 and the first to-be-fastened member 40 in this order. Accordingly, the helical groove 3b can be made to cut the surface material of the to-be-fastened members 30 and fill the prepared hole 41 by the rotation of the rivet 1a or 1b. Moreover, the helical groove 3b can hold therein the material of the first to-be-fastened member 40 and the second to-be-fastened member 50 cut by the helical groove 3b, and suppress entrance of extra material into a space between the rivet 1a or 1b and the prepared hole 41. Accordingly, deformation due to bulging of the first to-be-fastened member 40 that occurs depending on the volume of the rivet 1a or 1b interfering with the first to-be-fastened member 40 and the second to-be-fastened member 50 with the driving of the rivet 1a or 1b is suppressed, and cracking in the first to-be-fastened member 40 is more likely to be suppressed. In the case where the first to-be-fastened member 40 is an aluminum alloy casted object with a low stretch property, suppression of cracking by the helical groove 3b is further effective.

Moreover, in the riveting step, the auxiliary member 21 including the holding portion (inner peripheral surface 21b) configured to hold the second shaft portion 4 is used, and the rivet 1a or 1b is moved toward the position of the prepared hole 41 together with the auxiliary member 21 in the state where the second shaft portion 4 is held by the auxiliary member 21. Accordingly, increasing the weight of the rivet 1a or 1b with the auxiliary member 21 can increase motion energy in the driving of the rivet 1a or 1b. Thus, the rivet 1a or 1b can be more efficiently driven by using the auxiliary member 21.

Moreover, in the case where the first to-be-fastened member 40 is a casted member, the prepared hole 41 can be formed in advance in the casting stage. Accordingly, it is possible to omit the step of forming the prepared hole 41 in the first to-be-fastened member 40 by drilling and improve productivity.

Others

Although the embodiment of the present invention has been described above, appropriate design changes can be made within a scope not contradicting with the spirit of the present invention.

Although the rivet 1a or 1b is ejected toward the to-be-fastened members 30 by using air pressure in the present embodiment, the rivet 1a or 1b may be driven into the to-be-fastened members 30 by using other methods. For example, pressure may be applied to the rivet 1a or 1b by using a substance other than air, or the rivet 1a or 1b may be driven into the to-be-fastened members 30 by a mechanical action (for example, reciprocating motion of a piston).

EXAMPLES

Next, examples of the present invention are explained. In the present example, tests of experiment data 1 and experiment data 2 were preformed to grasp the characteristics of the rivet 1a and the rivet 1b according to the present invention.

In the experiment data 1 and the experiment data 2, for each of multiple examples and multiple comparative examples corresponding to the examples, the rivet 1a or the rivet 1b was driven into the to-be-fastened members 30 under various conditions by using the riveting apparatus 10 described above to create the fastened product 60 (FIG. 9) in which the to-be-fastened members 30 were fastened together by the rivet 1a or the rivet 1b, and various evaluations were performed for the fastened product 60 (FIGS. 11 to 12).

Evaluation
Presence or Absence of Cracking

Presence or Absence of cracking in the fastened product 60 was visually checked. A case where cracking occurred in the fastened product 60 was evaluated as “x” to indicate “not good”, and a case where no cracking occurred was evaluated as “○” to indicate “good”.

Leak Test

A resin jig was arranged on the front surface 50b side of the second to-be-fastened member 50 in the fastened product 60 to cover the entire head portion 2 and the second shaft portion 4. After the arrangement of the resin jig, pressure was applied to the resin jig toward the second to-be-fastened member 50 to set the resin jig and the fastened product 60 to a state where no air leaks from a gap between the resin jig and the second to-be-fastened member 50, and a test sample was thus prepared. Air was blown into the resin jig from the front surface 50b side at a pressure of 0.3 MPa with the test sample submerged in water to perform pressurization. Generation of air bubbles from a joining surface of the first to-be-fastened member 40 and the second to-be-fastened member 50 was checked to evaluate presence or absence of leak. A case where no air bubbles were generated for one minute was evaluated as “good”, a case where the numbers of air bubbles generated in one minute was five or less was evaluated as “acceptable”, and a case where the number of air bubbles generated in one minute was six or more was evaluated as “not acceptable”. The leak test was performed for three to-be-fastened products, and a case where all three to-be-fastened products were good was evaluated as “○” to indicate “good”, a case where at least one of the three to-be-fastened products was good but the others were acceptable or not acceptable was evaluated as “Δ” to indicate “conditional”, and a case where all three to-be-fastened products were acceptable or not acceptable was evaluated as “x” to indicate “not good”.

Tensile Strength

As shown in FIGS. 10A and 10B, the first to-be-fastened member 40 in the fastened product 60 was arranged on the lower side while the second to-be-fastened member 50 was arranged on the upper side, and the lower end side of the second to-be-fastened member 50 was fixed with a predetermined jig (illustration omitted). In this state, force pulling the first to-be-fastened member 40 upward was applied to both ends of the first to-be-fastened member 40 by using a tensile tester (manufactured by Shimadzu Corporation, Autograph, AG-50KNX) to perform a pull-out test. Cross head speed of the tensile tester was set to 3 mm/min. In the pull-out test, load up to a point where the rivet 1a, 1b and the second to-be-fastened member 50 were pulled out from the first to-be-fastened member 40 was measured, and a numerical value indicating the maximum load was used as tensile strength of the fastened product 60. As a result, a case where the tensile strength of the fastened product 60 exceeded 2,500 N was evaluated as “○” to indicate “good”, a case where the tensile strength was 2,000 to 2,500 N was evaluated as “Δ” to indicate “conditional”, and a case where the tensile strength was less than 2,000 N was evaluated as “x” to indicate “not good”.

Experiment Data 1

In the experiment data 1, as explained with reference to FIG. 6, the back surface 50a of the plate-shaped second to-be-fastened member 50 was laid on the front surface 40a of the quadrilateral-prism-shaped first to-be-fastened member 40 having the prepared hole 41. In this state, as explained with reference to FIGS. 7 and 8, the rivet 1a, 1b attached to the auxiliary member 21 was driven into the second to-be-fastened member 50 and the first to-be-fastened member 40 in this order by using the riveting apparatus 10, and was made to reach the inside of the prepared hole 41. The fastened product 60 in which the first to-be-fastened member 40 and the second to-be-fastened member 50 are fastened to each other with the rivet 1a was thereby obtained.

In each of the examples and the comparative examples in the experiment data 1, the rivet 1a or the rivet 1b explained with reference to FIGS. 1 to 5 was used. In the rivet 1a, 1b, the length of the tip end portion 3a1 of the main body portion 3a was 9 mm, and the diameter φ2 of the base portion of the tip end portion 3a1 was 4 mm. Moreover, the curvature radius R1 of the arc forming the tip end portion 3a1 and the bulging portion 5 of the first shaft portion 3 in the side cross-sectional view was 22.5 (mm). Furthermore, the length of the base end portion 3a2 of the main body portion 3a was 3 mm, the diameter φ2 of the base end portion 3a2 was 4 mm, and the radius R2 of the base end portion 3a2 was 2 mm. Moreover, the helical angle β of the helical groove 3b was 180°. Furthermore, the length of the neck portion 3c was 2 mm, and the diameter of the neck portion 3c was 3 mm. Moreover, the length of the second shaft portion 4 was 10 mm, and the diameter of the second shaft portion 4 was 3 mm. In the rivet 1a, the length (height) of the head portion 2 in the axial direction was 3 mm, the tilt angle φ1 of the head portion 2 was 20°, and the thickness of the peripheral edge portion 2b was 1 mm. In the rivet 1b, the length (height) of the head portion 2 in the axial direction was 2.4 mm, the tilt angle φ1 of the head portion 2 was 10°, the thickness of the peripheral edge portion 2b around the center portion was 1 mm, and the thickness of the peripheral edge portion was 0.2 mm.

The first to-be-fastened member 40 was a quadrilateral-prism-shaped block member that had a square cross section with a vertical length of 12 mm and a horizontal length of 12 mm and that had a height of 35 mm. The taper angle φ3 (FIG. 6) of the hole portion 43 was 5°. ADC12 was used as the material of the first to-be-fastened member 40.

The second to-be-fastened member 50 was a plate member with a vertical length of 80 mm, a horizontal length of 30 mm, and a thickness of 2.0 mm. A5052-H34 was used as the material of the second to-be-fastened member 50.

In the riveting apparatus 10, the air pressure generated by the air compressor 11 was set to 0.75 MPa. Moreover, the driving speed by the riveting apparatus 10 was set to 70 m/sec.

The weight of the auxiliary member 21 was about 14.4 g.