[0001] The present invention relates to a die used in a self-piercing rivet fastening device
for fastening a plurality of fastened members using a self-piercing rivet having a
large-diameter head and hollow cylindrical legs extending down from the head. More
specifically, the present invention relates to a die used to fasten fastened members
made of poorly malleable material such as a die cast material.
[0002] A self-piercing rivet is able to be readily joined to a joined member simply by driving
in the rivet, even when a hole has not been machined in advance in a fastened member
for inserting a bolt or the like. Fig. 1 is an enlarged view of the self-piercing
rivet fastening process using a self-piercing rivet fastening device of the prior
art. The self-piercing rivet fastening device 1 uses a die 20 and a nose 3 to clamp
together two fastened members 41, 42 with strong force (see the arrows). The self-piercing
rivet 10 has a large-diameter head 11 and hollow cylindrical legs 12 extending downward
from the head 11.
[0003] The die 20 has a cavity 21 in the upper surface, and the bottom surface 22 of the
cavity is substantially flat. The self-piercing rivet 10 is driven by a punch 4 into
the fastened members 41, 42 arranged on top of the die 20. The tips 13 of the legs
in the self-piercing rivet 10 pierce the fastened member 41 adjacent to the punch
4, but remain inside without piercing the fastened member 42 on the receiving side
adjacent to the die 20. The tips of the legs 12 of the self-piercing rivet 10 are
deformed outward in the radial direction from the die 20. The fastened members 41,
42 are connected by the head 11 and the legs 12 opened inside the fastened member
42. In Fig. 1, the bottom surface 22 of the cavity is formed so as to be substantially
flat. A protrusion with a different shape is provided in the center of the cavity
21 and protrudes towards the punch.
[0004] A self-piercing rivet is suitable for aluminum body panels unfit for riveting. As
vehicle bodies have become lighter and aluminum bodies more widely used, the demand
for self-piercing rivets has increased. Because self-piercing rivets pierce the fastened
member on the punch side but remain inside and do not pierce the fastened member 42
on the receiving side adjacent to the die 20, a rivet piercing hole is not formed
in the surface of the fastened member 42 on the receiving side. As a result, the sealing
properties of the fastened member 42 on the receiving side are not compromised, and
the fastened member retains its external appearance.
[0005] When fastened members 41, 42 with poor malleability such as die cast materials are
fastened with a self-piercing fastening device using a conventional die 20, the tips
of the legs 12 of a self-piercing rivet 10 driven by the punch pierce and push into
the fastened members 41, 42, which are deformed by the cavity 21 of the die 20. When
this occurs, the fastened members 41, 42 cannot resist plastic deformation and sometimes
rupture. The fastened member 42 on the receiving side is more likely to rupture.
[0006] In Patent Document 1, joined members with low ductility are joined using a self-piercing
rivet. In Patent Document 1, the joined members are heated where the self-piercing
rivet is driven into the members. This can prevent cracking when a rivet is driven
into joined members with low ductility. However, a heating device is needed to heat
the joined members in the joining method of Patent Document 1. This increases the
amount of time needed to perform the joining process.
[0007] Patent Document 2 discloses a method for fastening thin-plate materials using a self-piercing
rivet. In the method of Patent Document 2, a through-hole is formed in at least one
of the joined members or the member is partially thinned to facilitate fastening with
a rivet. Because a through-hole or countersink has to be formed in the joined portion
of a fastened member in the fastening method of Patent Document 2, the machining of
the fastened members is more complicated. Because a hole has to be formed in a fastened
member in Patent Document 2, the advantages of using a self-piercing rivet are undermined.
[0008] Joined members can be easily joined using a self-piercing rivet when a hole is formed
in the fastened members. However, the fastened member on the die side sometimes ruptures
when fastened using a self-piercing rivet if the fastened member is a fastened member
with poor malleability formed using a die cast or the like. The joining methods in
Patent Documents 1-2 using self-piercing rivets can be made less likely to rupture
a fastened member, but they require addition operations during the fastening process,
and this complicates an otherwise simple fastening operation. Therefore, a self-piercing
rivet fastening device and fastening method are desired which can prevent the rupture
of fastened members when poorly malleable fastened members are fastened using a self-piercing
rivet.
[0010] The object of the present invention is to provide a die for a self-piercing rivet
fastening device which is able to use a self-piercing rivet to fasten fastened members
with poor malleability so that the members do not readily rupture.
[0011] In order to achieve this object, the present authors discovered that the deformation
of fastened members could be minimized and the rupturing of fastened members made
less likely by reducing the depth of the die cavity, forming a concave spherical surface
with a single radius R in the cavity, or forming a cavity with a bottom surface and
a surrounding inclined surface in which the angle between the inclined surface and
the bottom surface is from 165 to 175°.
[0012] One aspect of the present invention is a die for a self-piercing rivet fastening
device having a die and a punch for driving a self-piercing rivet having a large-diameter
head and hollow cylindrical legs extending down from the head, and configured so the
punch drives the self-piercing rivet into fastened members arranged on top of the
die, wherein a cavity is formed in the upper surface of the die for receiving portions
of the fastened members thrust out by the self-piercing rivet driven by the punch,
and wherein the cavity is formed as a concave spherical surface having a single radius
R centered on the central axis of the cavity.
[0013] When the cavity is formed with a spherical surface having a single radius and the
bottom surface of the cavity is smoothly continuous from the central portion to the
periphery, the fastened members are not bent at an acute angle when received by the
cavity, and deformation of the fastened members can be minimized. As a result, the
fastened members are less likely to rupture.
[0014] Another aspect of the present invention is a die for a self-piercing rivet fastening
device having a die and a punch for driving a self-piercing rivet having a large-diameter
head and hollow cylindrical legs extending down from the head, and configured so the
punch drives the self-piercing rivet into fastened members arranged on top of the
die, wherein a cavity is formed in the upper surface of the die for receiving portions
of the fastened members thrust out by the self-piercing rivet driven by the punch,
wherein the cavity is formed having a round bottom surface in the central portion
of the cavity, and an inclined surface on the outer periphery between the bottom surface
and the upper surface of the die, and wherein the inclination of the inclined surface
from the upper surface of the die is from 7 to 15°.
[0015] When the cavity is formed with a round bottom surface surrounded by an inclined surface
with a gentle incline, and the bottom surface and the inclined surface are continuous
at a gentle obtuse angle, the fastened members are not bent at an acute angle when
received by the cavity, and deformation of the fastened members can be minimized.
As a result, the fastened members are less likely to rupture.
[0016] Preferably, when the self-piercing rivet is driven into the fastened members, the
legs pierce the fastened member on the punch side, the tips of the legs push downward
through the fastened member on the receiving side adjacent to the die, the die receives
the fastened member on the receiving side deforming the tips of the legs so as to
expand outward radially and remain inside the die without piercing the fastened member
on the receiving side adjacent to the die, and the plurality of fastened members are
fastened to each other by the head and the expanded legs of the self-piercing rivet.
[0017] Preferably, the upper surface of the die and the upper portion of the cavity are
continuous at an obtuse angle. This can reduce deformation of the fastened members
where they come into contact with the boundary region between the upper surface of
the die and the upper end portion of the cavity.
[0018] The depth from the upper surface of the die to the central portion of the cavity
is preferably from 0.5 to 1.5 mm, and more preferably from 0.5 to 0.9 mm. When the
cavity is shallower than 0.5 mm, the self-piercing rivet is not driven sufficiently
into the fastened members. When the cavity is deeper than 1.5 mm, the deformation
of the fastened members is insufficient.
[0019] The diameter of the cavity in the upper surface of the die is preferably from 10
to 18 mm, and more preferably from 11 to 15 mm. When the diameter of the cavity is
less than 10 mm, it is difficult to expand the legs of the self-piercing rivet inside
the cavity. When the diameter of the cavity is greater than 18 mm, the legs of the
self-piercing rivet cannot hold the portion of the fastened members surrounding the
pierced portion, and the fastened members are difficult to fasten using a self-piercing
rivet.
[0020] The present invention is able to reduce deformation of fastened members and make
the rupturing of poorly malleable fastened members less likely compared to a situation
in which a self-piercing rivet is fastened using a conventional die. As a result,
a die for a self-piercing rivet fastening device can be provided that is able to use
a self-piercing rivet to readily fasten fastened members with poor malleability.
[0021] It will be understood that the features of the invention mentioned above and those
yet to be explained below can be used not only in the respective combination indicated,
but also in other combinations or in isolation, without leaving the scope of the present
invention. Exemplary embodiments of the invention are explained in more detail in
the following description and are represented in the drawings, in which:
- Fig. 1
- shows an enlarged view of the self-piercing rivet fastening process using a self-piercing
rivet fastening device of the prior art.
- Fig. 2
- shows a cross-sectional view of the die in the first embodiment of the present invention.
- Fig. 3
- shows an enlarged cross-sectional view of the dotted line portion A in Fig. 2.
- Fig. 4A
- shows an enlarged cross-sectional view of fastened members before being fastened by
a self-piercing rivet using a die of the prior art.
- Fig. 4B
- shows an enlarged cross-sectional view of fastened members after being fastened by
a self-piercing rivet using a die of the prior art.
- Fig. 5A
- shows an enlarged cross-sectional view of fastened members before being fastened by
a self-piercing rivet using the die in the first embodiment of the present invention.
- Fig. 5B
- shows an enlarged cross-sectional view of fastened members after being fastened by
a self-piercing rivet using the die in the first embodiment of the present invention.
- Fig. 6
- shows a graph plotting the relationship between cavity diameter ϕ, depth D, and spherical
surface radius R in a die according to the first embodiment of the present invention.
- Fig. 7
- shows an enlarged cross-sectional view of the dotted line portion A in Fig. 2 of a
die according to the second embodiment of the present invention.
- Fig. 8
- shows a diagram of a device used to measure load and displacement (a), and a graph
showing the relationship between load and displacement (b).
- Fig. 9
- shows a cross-sectional view of the cavity portion of a conventional die used in testing
(a), and a cross-sectional view of the cavity portion of a die according to a first
embodiment of the present invention (b).
[0022] The following is an explanation with reference to Fig. 2 and Fig. 3 of the die for
a self-piercing rivet in the first embodiment of the present invention. The self-piercing
rivet fastening device uses the die 30 in the first embodiment of the present invention
instead of a conventional die 20. The self-piercing rivet 10 is driven by the punch
4 into fastened members 41, 42 arranged on top of the die 30. In every other respect,
the self-piercing rivet fastening device is identical to the device of the prior art
shown in Fig. 1.
[0023] Fig. 2 is a cross-sectional view of the die 30 in the first embodiment of the present
invention being used in a self-piercing rivet fastening device 1. The die 30 is symmetrical
around the central axis, and has a column-shaped base 33 and a column-shaped machined
portion 34 with an outer diameter greater than that of the base 33. The upper portion
of the machined portion 34 is made of a hard material such as high-speed tool steel
to deform the legs 12 of the rivet 10. A cavity 31 is formed in the upper surface
of the machined portion 34 to deform the legs 12 of the self-piercing rivet 10. The
self-piercing rivet 10 is made of a bendable material such as a boron-copper alloy
or a chromium-molybdenum-copper alloy, and the outer diameter of the legs 12 is from
3 to 5.5 mm.
[0024] Fig. 3 is an enlarged cross-sectional view of the dotted line portion A of the die
30 in Fig. 2. The cavity 31 is symmetrical with respect to the central axis I, and
is formed with a concave spherical surface with a single radius R centered on the
central axis I. The diameter ϕ of the cavity 31 in the upper surface of the machined
portion 34 is from 10 to 18 mm, and the depth D from the upper surface of the machined
portion 34 to the lowest point in the bottom surface of the cavity 31 is from 0.5
to 1.5 mm. When the cavity 31 is relatively shallow, deformation of the fastened members
41, 42 can be minimized. As a result, rupture of the fastened members is less likely
to occur.
[0025] The diameter of the cavity 31 in the die 30 should be at least 7 mm greater than
the outer diameter of the legs 12 of the self-piercing rivet. When the outer diameter
of the legs 12 of the self-piercing rivet 10 is 3 mm and the diameter of the cavity
31 is less than 10 mm, it is difficult to expand the legs 12 of the self-piercing
rivet 10 inside the cavity. When the diameter of the cavity is greater than 18 mm,
the self-piercing rivet 10 cannot hold the portion of the fastened members 41, 42
surrounding the pierced portion, and the fastened members are difficult to fasten.
[0026] The following is an explanation with reference to Fig. 4A and Fig. 4B of the situation
when fastened members 41, 42 are fastened with a self-piercing rivet 10 using a die
20 of the prior art having a cavity 21 with a flat bottom surface 22. This is followed
by a comparative explanation with reference to Fig. 5A and Fig. 5B of the situation
when fastened members 41, 42 are fastened with a self-piercing rivet 10 using the
die 30 in the first embodiment of the present invention which includes a cavity 31
having a spherical surface with a single radius R. Fig. 4A is an enlarged cross-sectional
view of fastened members 41, 42 before being fastened by a self-piercing rivet 10
using a die 20 of the prior art. The die 20 has a cavity 21 in the upper surface.
The bottom surface 22 of the cavity 21 is substantially flat, and the side surface
23 is substantially cylindrical. The self-piercing rivet 10 has a large-diameter head
11 and hollow cylindrical legs 12 extending downward from the head 11. The fastened
members 41, 42 are stacked on the upper surface of the die 20, the area surrounding
the fastened portion is pushed down by a nose (not shown), and the leg tips 13 of
the self-piercing rivet 10 make contact with the fastened portion.
[0027] Fig. 4B is an enlarged cross-sectional view of the fastened members 41, 42 after
being fastened by the self-piercing rivet 10 using the die 20 of the prior art. When
the self-piercing rivet 10 has been driven by the punch 4, the punch 4 causes the
legs 12 to pierce the fastened member 41 on the punch side and to plastically deform
the fastened member 42 on the receiving side. The legs 12 cause the fastened member
42 to be thrust downward, and the portion of the fastened member 42 thrust downward
is received inside the cavity 21, and a portion of the lower surface of the fastened
member 42 makes contact with the bottom surface 22 of the cavity 21. Because the fastened
member 42 can no longer move vertically, the legs 12 of the self-piercing rivet 10
push outward in the radial direction in the fastened member 42, and are deformed so
as to extend outward in the radial direction. The tips 13 of the legs do not pierce
the fastened member 42 adjacent to the die 20 and remain inside. The fastened members
41, 42 are connected to each other by the head 11 and the expanded legs 12 inside
the fastened member 42.
[0028] Because the curvature in the boundary region between the bottom surface 22 and side
surface 23 of the die 20 can change greatly, the amount of deformation in the portion
of the fastened member 42 denoted by 42a is great, and a rupture is more likely to
occur. Also, because the boundary region between the upper surface of the die 20 and
the side surface 23 of the cavity 21 is at nearly a right angle, a rupture is more
likely to occur in the portion of the fastened member 42 denoted by 42b when it makes
contact with this angle.
[0029] Next, the situation when fastened members 41, 42 are fastened by a self-piercing
rivet 10 using the die 30 in the first embodiment of the present invention will be
explained with reference to Fig. 5A and Fig. 5B. Fig. 5A is an enlarged cross-sectional
view of fastened members 41, 42 before being fastened by a self-piercing rivet 10
using the die 30 in the first embodiment of the present invention. The die 30 has
a cavity 31 formed with a concave spherical surface having a single radius R. The
fastened members 41, 42 are set on top of the die 30, the outer periphery of the fastened
portion is pressed by the nose (not shown), and the leg tips 13 of the self-piercing
rivet 10 make contact with the surface of the fastened member 41.
[0030] Fig. 5B is an enlarged cross-sectional view of fastened members 41, 42 after being
fastened by the self-piercing rivet 10 using the die 30. When the self-piercing rivet
10 has been driven by the punch 4, the punch 4 causes the legs 12 to pierce the fastened
member 41 on the punch side and to plastically deform the fastened member 42 on the
receiving side. The legs 12 cause the fastened member 42 to be thrust downward, and
the portion of the fastened member 42 thrust downward is received inside the cavity
31 of the die 30, and a portion of the lower surface of the fastened member 42 makes
contact with the bottom surface 32 of the cavity 31. Because the fastened member 42
can no longer move vertically, the legs 12 of the self-piercing rivet 10 push outward
in the radial direction in the fastened member 42, and are deformed so as to extend
outward in the radial direction. The tips 13 of the legs do not pierce the fastened
member 42 adjacent to the die 30 and remain inside. The fastened members 41, 42 are
connected to each other by the head 11 and the expanded legs 12 inside the fastened
member 42.
[0031] In the die 30 of the first embodiment of the present invention, the bottom surface
32 of the cavity 31 is a spherical surface with a single radius R. There is no boundary
region between the bottom surface 32 of the cavity 31 and the side surface. Instead,
it is smooth and continuous. Also, the cavity 31 is shallower in the portion where
the legs 12 of the rivet 10 bite into the fastened member 42. As a result, there is
no sharp curve in the portion of the fastened member 42 denoted by 42a', and there
is little displacement. Also, the boundary region between the upper surface of the
die 30 and the cavity 31 has an obtuse angle. As a result, the portion of the fastened
member 42 denoted by 42b' is less likely to rupture when it comes into contact with
the boundary region between the upper surface of the die 30 and the cavity 31.
[0032] In order to provide the cavity 31 of the die 30 in the first embodiment of the present
invention with an optimum shape, variations in the diameter ϕ of the cavity 31, the
depth D of the cavity, and the radius R of the spherical surface were studied with
respect to a single-radius R cavity 31 for the die 30. The radius R of the spherical
surface of the cavity 31 was calculated when the diameter ϕ of the cavity 31 was changed
at 1 mm intervals in the 10 to 18 mm range, and the depth D of the cavity was changed
at 0.1 mm intervals in the 0.5 to 1.5 mm range. Fig. 6 is a graph plotting the calculation
results for the radius R when the diameter ϕ was changed between 10 and 18 mm, and
the depth D was changed between 0.5 and 1.5 mm. The radius R became larger as the
diameter ϕ became larger, and the radius R became larger as the depth D became greater.
[0033] The following is an explanation of the die 35 in the second embodiment of the present
invention. Fig. 7 shows the die 35 in the second embodiment, and is an enlarged cross-sectional
view of the dotted line portion A of the machined portion 34' of the die 35 in Fig.
2. The cavity 36 is axially symmetrical with respect to the central axis I', has a
round bottom surface 37 centered on the central axis I' and parallel to the upper
surface of the die 35, and has an inclined surface 38 surrounding the bottom surface
37. The inclined surface 38 has a truncated conical shape. The outer diameter ϕ of
the inclined surface 38 of the cavity 36 at the upper surface of the die 35 is from
11 to 15 mm, and the depth D from the upper surface of the die 35 to the bottom surface
37 of the cavity 31 is from 0.5 to 0.9 mm. The angle of inclination θ of the inclined
surface 38 from the upper surface of the die 35 is from 7 to 15° (the angle of the
bottom surface 37 and the inclined surface 38 is from 165 to 175°, preferably from
165° to 173°).
[0034] In the die 35 in the second embodiment, the bottom surface 37 of the cavity 36 is
round and flat, and is connected to the surrounding inclined surface 38 at an obtuse
angle. As a result, the portion of the fastened member 42 making contact near the
boundary between the bottom surface 37 and the inclined surface 38 is not bent sharply
and is not deformed very much. As a result, a rupture is less likely to occur. The
boundary between the upper surface of the die 35 and the inclined surface 38 is also
an obtuse angle. As a result, a rupture is also less likely to occur in the portion
of the fastened member 42 making contact with the boundary between the upper surface
of the die 35 and the inclined surface 38.
[0035] (Measuring Amount of Displacement When Rupturing of Fastened member Occurs)
A test was conducted to determine the amount of displacement when the fastened member
42 on the receiving side ruptures at the diameter ϕ of the die 30 in the first embodiment
of the present invention. The rivet 10 used in the test was made of a boron-copper
alloy, and the diameter of the legs 12 was 3.35 mm. The fastened member 41 on the
punch side was a mild steel plate (SCGA270-45) with a thickness of 0.65 mm, and the
fastened member 42 on the receiving side was a heat-treated aluminum die casting material
with a thickness of 2.4 mm. Fig. 8 (a) is a schematic diagram showing the measurement
method for the load and amount of displacement. As shown in Fig. 8 (a), the fastened
members 41, 42 were stacked on top of the die 20, and the rivet 10 was placed in a
position above the cavity 21 of a conventional die 20. The punch 4 was placed on top
of the rivet 10. In this test, a conventional die 20 with a flat bottom surface was
used, and the depth of the die was sufficiently greater than the rupture depth of
the fastened member 42 so that the amount of displacement could be measured when ruptured
by the die. The punch 4 was lowered at a rate of 1 mm/min, and the load applied by
the punch 4 and the displacement of the punch 4 is measured at this time.
[0036] Fig. 8 (b) is a graph showing the relationship between load and displacement. When
the load had been reduced as indicated by point B, the occurrence of a rupture in
the fastened member 42 was estimated, and the driving of the punch was stopped. At
this time, the displacement of the fastened member 42 on the receiving side was measured
using a micrometer.
[0037] Five dies 30 were prepared with different diameters ϕ for the cavity 31, and the
test was conducted in which the number of test samples was n = 5. The amount of displacement
in the fastened member 42 at the time of rupture was measured. The results are shown
in Table 1. The amount of displacement in the fastened member 42 is the average value
of the five test samples. Because deformation of the fastened members 41, 42 can be
suppressed by using a die 30 with cavity 31 having a shallower depth D, the depth
was set at 0.6 mm. This is the same depth as a conventional die.
[0038]
Table 1
Diameter ϕ (mm) of Cavity 31 |
Displacement of Fastened Member 42 (mm) |
Average Displacement (mm) |
7.0 |
0.67 |
0.65 |
7.3 |
0.70 |
7.5 |
0.63 |
7.8 |
0.64 |
8.0 |
0.62 |
[0039] From the results of the test, it is clear that the fastened member 42 experiences
hardly any displacement leading to rupture when the diameter ϕ of the cavity 31 in
the die 30 is in the range from 7.0 to 8.0 mm.
[0040] (Rupture Test When Fastened Using a Conventional Die and the Die in the First Embodiment
of the Present Invention)
In this test, fastened members were fastened by a self-piercing rivet 10 using a conventional
die 20 with a cavity 21 having a cylindrical side surface 23 and a flat bottom surface
22, and the die 30 in the first embodiment of the present invention with a cavity
31 whose bottom surface 32 is formed with a single radius R. This test was conducted
to determine whether or not a rupture would occur in the fastened members 41, 42.
[0041] Fig. 9 (a) is a cross-sectional view of the cavity 21 portion of the conventional
die 20 used in the test, and Fig. 9 (b) is a cross-sectional view of the cavity 31
portion of the die 30 in the first embodiment of the present invention used in the
test. The depth of both cavity 21 and cavity 31 was 0.60 mm. The fastened member 41
on the punch side was a mild steel plate (SCGA270-45) (thickness: 0.65 mm), and the
fastened member 42 on the receiving side was a heat-treated aluminum die casting material
(thickness: 2.4 mm). These were fastened together using a self-piercing rivet 10.
The self-piercing rivet 10 was the same rivet used in the test shown in Table 1 above.
[0042] When fastened using the conventional die 20 with a flat bottom surface 22 shown in
Fig. 9 (a), the fastened member 42 on the receiving side did not rupture in the portion
where it made contact with the bottom surface 22 of the die 20, but it did rupture
in the portion near the boundary region between the bottom surface 22 of the die 20
and the side surface 23. Because the boundary portion between the bottom surface 22
of the die 20 and the side surface 23 has significant curvature, the amount of displacement
on the fastened member 42 was great in this portion. Because the boundary portion
between the upper surface of the die 20 and the side surface 23 of the cavity 21 was
nearly at a right angle, a rupture is believed to be more likely to occur when the
fastened member 42 makes contact with this portion.
[0043] When fastened using the die 30 in the first embodiment of the present invention shown
in Fig. 9 (b) which has a bottom surface 32 with a single radius R, the fastening
member 42 on the receiving side did not rupture. Because the bottom surface 32 of
the cavity 31 is a spherical surface with a single radius R, there is no boundary
region between the bottom surface and the side surface of the cavity 31. Also, the
cavity 31 is shallow on the periphery. As a result, very little displacement occurs
in the fastened member 42 and a rupture is less likely to occur. Also, the boundary
region between the upper surface of the die 30 and the cavity 31 is an obtuse angle.
As a result, a rupture is less likely to occur in the portion making contact with
the boundary region between the upper surface of the die 30 and the cavity 31.
[0044] When aluminum die cast fastened members with poor malleability are fastened by a
self-piercing rivet using a die in an embodiment of the present invention, very little
deformation occurs in the fastened members, and a rupture in the fastened members
is unlikely to occur.
[Key to text in Figures]
[0045]
1: Self-Piercing Rivet Fastening Device
3: Nose
4: Punch
10: Self-Piercing Rivet
11: Head
12: Leg
13: Leg Tip
20: Conventional Die
21: Cavity
22: Bottom Surface
23: Side Surface
30: Die in First Embodiment of the Present Invention
31: Cavity
32: Cavity Bottom Surface
33: Base
34: Machined Portion
35: Die in Second Embodiment of the Present Invention
36: Cavity
37: Bottom Surface
38: Inclined Surface
41: Fastened Member (Punch Side)
42: Fastened Member (Receiving Side)
1. A die (35) for a self-piercing rivet fastening device (1) having a die (35) and a
punch (4) for driving a self-piercing rivet (10) having a large-diameter head (11)
and hollow cylindrical legs (12) extending down from the head (11), and configured
so that the punch (4) drives the self-piercing rivet (10) into fastened members (41,
42) arranged on top of the die (35),
wherein a cavity (36) is formed in the upper surface of the die (35) for receiving
portions of the fastened members (41, 42) thrust out by the self-piercing rivet (10)
driven by the punch (4), wherein the cavity (36) is formed having a round bottom surface
(37) in the central portion of the cavity (36), and an inclined surface (38) on the
outer periphery between the bottom surface (37) and the upper surface of the die (35),
and wherein the inclination (θ) of the inclined surface (38) from the upper surface
of the die (35) is from 7 to 15°.
2. A die (30) for a self-piercing rivet fastening device (1) having a die (30) and a
punch (4) for driving a self-piercing rivet (10) having a large-diameter head (11)
and hollow cylindrical legs (12) extending down from the head (11), and configured
so that the punch (4) drives the self-piercing rivet (10) into fastened members (41,
42) arranged on top of the die (30),
wherein a cavity (31) is formed in the upper surface of the die (30) for receiving
portions of the fastened members (41, 42) thrust out by the self-piercing rivet (10)
driven by the punch (4), and wherein the cavity (31) is formed as a concave spherical
surface having a single radius (R) centered on the central axis (I) of the cavity
(31).
3. A die according to claim 1 or claim 2, wherein, when the self-piercing rivet (10)
is driven into the fastened members (41, 42), the legs (12) pierce the fastened member
(41) on the punch side, the tips (13) of the legs (12) push downward through the fastened
member (42) on the receiving side adjacent to the die (30; 35), the die (30; 35) receives
the fastened member (42) on the receiving side deforming the tips (13) of the legs
(12) so as to expand outward radially and remain inside the die (30; 35) without piercing
the fastened member (42) on the receiving side adjacent to the die (30; 35), and the
plurality of fastened members (41, 42) are fastened to each other by the head (11)
and the expanded legs (12) of the self-piercing rivet (10).
4. A die according to any one of claims 1 through 3, wherein the upper surface of the
die (30; 35) and the upper portion of the cavity (31; 36) are continuous at an obtuse
angle.
5. A die according to any one of claims 1 through 4, wherein the depth (D) from the upper
surface of the die (30; 35) to the central portion of the cavity (31; 36) is from
0.5 to 1.5 mm, particularly from 0.5 to 1.4 mm, preferably from 0.5 to 0.9 mm.
6. A die according to any one of claims 1 through 5, wherein the diameter (φ) of the
cavity (31; 36) in the upper surface of the die (30; 35) is from 10 to 18 mm, particularly
from 11 to 15 mm or from 13 to 18 mm.
7. A die according to any one of claims 1 or 3 through 6, wherein the round bottom surface
is flat.
8. A die according to any one of claims 1 or 3 through 6, wherein the round bottom surface
is a concave spherical surface.
9. A die according to any one of claims 2 to 8, wherein the radius of the concave spherical
surface is in the range of 9 mm to 70 mm, particularly from 14 mm to 70 mm, and preferably
from 20 mm to 60 mm.