Method of installing self-attaching fastener and apparatus

An improved die member and method of attaching a self-piercing and riveting fastener to a panel wherein a slug pierced from the panel by the riveting fastener is securely staked in the barrel portion of the fastener during the installation of the fastener. The staking method includes driving a plurality of staking projections into said slug, thereby pinching said slug between the projections and a barrel side wall. This pinching action causes the slug to deform outwardly and lodge between the side walls of said fastener. The staking projections are preferably arranged around the perimeter of the die post, and in a most preferred embodiment, the projections have a canted side wall proximal the wall, forcing a portion of said slug toward the barrel side wall, when said slug is pinched between said canted side wall and a bottom wall of said fastener.

BACKGROUND OF THE INVENTION 
Self-piercing and riveting fasteners of the type disclosed in U.S. Pat. No. 
4,555,838, assigned to the assignee of the present application, are now 
used in mass production applications, including automotive applications. 
In such mass production applications, the fasteners are normally installed 
in a die press capable of generating several tons of die force. The die 
press may be utilized to simultaneously form the panel into a configured 
shape, such as an automotive body component or structural support member, 
and install several riveting fasteners. 
One or a plurality of installation heads are installed in one of the die 
platens of the die press, and the opposite die platen includes aligned 
riveting die members, commonly referred to as die buttons. The riveting 
fasteners are fed into the installation heads, generally through plastic 
tubes or chutes. The installation heads include a feed mechanism, which 
feeds a fastener to a plunger or punch, reciprocal in the installation 
head, to install a fastener in a panel located in the die press, with each 
stroke of the die press. 
The self-piercing and riveting fasteners of the type described herein 
generally include a body portion and an integral tubular or annular barrel 
portion. In a stud-type fastener of the type disclosed, for example, in 
the above-referenced U.S. Pat. No. 4,555,838, the body portion of the 
fastener includes a radial flange integrally joined to the annular barrel 
portion opposite the free end and a stud portion integrally joined to the 
flange portion extending in coaxial alignment with the barrel portion. The 
free end of the tubular barrel portion is comprised of barrel side walls 
which define an opening into said barrel and a piercing surface adjacent 
said barrel opening. The opposite end of the barrel portion is closed at 
the radial flange portion, forming a socket. The die button includes an 
annular concave die cavity surrounding a central die post. As disclosed, 
for example, in the above-referenced U.S. Pat. No. 4,555,838 (hereinafter 
'838), the central die post includes a free end having a peripheral 
piercing surface and an outer surface which slopes radially outwardly into 
the annular concave die cavity. 
A panel, such as a sheet steel panel or plate used for body panels and 
structural members by the automotive industry, is secured over the die 
member, preferably in a die press, as described above. The barrel opening 
portion is then driven into the panel in coaxial alignment with the 
central die post of the die button. The die post is configured to be 
received within the opening of the barrel portion. As the barrel portion 
is driven into the panel, the piercing surface adjacent the barrel opening 
pierces a slug from the panel, which is received on the free end of the 
die post of the die button. The barrel side wall portion is then driven 
through the opening formed in the panel into the annular die cavity, 
radially deforming the barrel side walls adjacent said barrel opening, 
thereby riveting the barrel portion to the panel as described, for 
example, in the above-referenced U.S. Pat. No. 4,555,838. 
When the self-piercing and riveting fastener of the type disclosed in the 
above-referenced patent was first introduced, several problems were 
experienced in producing a consistent, high-quality installation. A 
primary object of this fastening system is to provide a stud or nut-type 
fastener permanently installed in relatively thin metal panels, such as 
utilized by the automotive industry, which may have a thickness of 0.030 
inches or less. In the most preferred embodiment of the self-piercing and 
riveting fastener, the tubular barrel portion is deformed radially 
outwardly in the annular concave die cavity into a U-shaped channel 
opening toward the body portion of the fastener, and the panel portion 
surrounding the pierced opening is simultaneously driven into the center 
of the U-shaped channel and deformed to substantially fill the channel 
center, forming a very secure mechanical interlock between the fastener 
and the panel. As the slug is pierced from the panel, the slug is received 
in the tubular barrel portion and finally driven to the bottom of the 
tubular barrel portion by the central post of the die button. 
It was initially believed that the location of the slug in the tubular 
barrel portion was essential to prevent inward collapse of the barrel 
portion whenever the barrel portion underwent outward radial deformation 
into the preferred U-shaped channel because of resultant inwardly directed 
forces on the barrel portion as described, for example, in the '838 
patent. Although the slug does support the barrel portion during outward 
radial deformation, it has been found that it is possible to form a secure 
installation without locating the slug in the barrel portion based upon 
improvements in the installation, as described below. Nevertheless, the 
preferred embodiment of the stud-type fastener and panel assembly includes 
the slug in the barrel portion, particularly in mass production 
installations, such as automotive applications. This is the case because 
it is far more convenient to retain the slug in the assembly than to 
remove and discard the slug through the die button. Further, it may not be 
possible to remove the slug in certain existing applications because of 
lack or difficulty of access. In a typical automotive application, studs 
are attached to automotive structural components or panels in a die press, 
as described. Further, several studs may be installed simultaneously, and 
the die press is preferably run continuously during a given production 
run. Therefore, a substantial volume of panel slugs would have to be 
removed from the die press area unless the slugs are retained in the 
assembly. 
The initial problem with forming the preferred embodiment of the 
self-piercing and riveting fastener and panel assembly resulted from 
tolerance control and friction between the concave annular die cavity 
surface and the tubular barrel portion during the outward radial 
deformation of the tubular barrel portion, as described in U.S. Pat. No. 
4,825,525, assigned to the assignee of the present application. As 
described in this patent, the required installation force in a typical 
application is between about 10 and 20 tons. Particularly in mass 
production applications, orientation of the fasteners and the die member 
and very close tolerances are critical to achieving a good installation 
integrity. The installation force, which is composed of the forces 
required for piercing, forming of the barrel, and setting of the panel, 
results in very significant friction between the barrel portion of the 
fastener and the die cavity. The pressure between the barrel walls and the 
die cavity may exceed 50 tons per square inch. The frictional forces 
generated by this pressure sometimes resulted in collapse of the barrel 
portion or stud, poor or incomplete installations and stress risers or 
faults, all of which significantly reduced the integrity of the joint 
assembly. These problems were, however, overcome by coating at least the 
internal surface of the barrel portion with a friction-resistant coating, 
preferably a fluorocarbon coating, such as an air-drying 
polytetrafluoroethylene lubricant, suspended in a fast-drying 
thermoplastic resin as disclosed in U.S. Pat. No. 4,825,525. 
Substantial improvements in manufacturing tolerances and the use of a 
friction-resistant coating has resulted in more consistent installations, 
including an excellent mechanical interlock between the fastener barrel 
portion and the panel. In fact, in many applications, the pull-out 
strength of a typical stud fastener as disclosed in the above-referenced 
U.S. patents may be greater than the tensile strength of the stud. These 
improvements have, however, brought about another problem, namely, the 
inability to retain the panel slug in the barrel portion. When utilizing 
the above-mentioned improvements, the panel slug may drop out of the 
barrel portion as the die press is opened or while assembling a structural 
element to the panel on which the stud fastener is attached. In cases 
where the slug is released during installation of the stud-type fastener, 
the slug may remain on the center post of the female die member. When a 
subsequent stud is then installed in a new panel, a slug is pierced from 
the panel and received over the die button center post, over the first 
slug. This results in damage to the installation head or die button, and 
deformation of the flange portion of the second stud, which may actually 
be sheared from the fastener by the installation plunger. Thus, it is very 
important to securely retain the panel slug in the barrel portion of the 
stud-type fastener during installation. The problem of retaining the slug 
in the barrel portion is particularly difficult where the panel is 
relatively thin, such as automotive applications where the panel metal may 
be less than 0.040 inches or less. 
The problem of slug retention has been solved by the method of attaching a 
self-piercing and riveting fastener of this invention and the improved die 
button by securely staking the panel slug in the barrel portion. As will 
be understood, the slug must be retained in the barrel Portion during 
installation, avoiding the necessity of a separate step. The method of 
this invention and the improved die button stakes the slug in the barrel 
portion during installation of the fastener in the panel, thus eliminating 
a separate step. 
SUMMARY OF THE INVENTION 
The method of attaching a self-piercing and riveting fastener of this 
invention includes staking the panel slug in the barrel portion during the 
installation step. As described, the fastener includes an annular barrel 
portion having barrel side walls which define an opening into said barrel 
and a piercing surface adjacent said opening. The method includes driving 
the fastener barrel piercing surface against the panel, piercing a slug 
from the panel, and forming a panel opening. The barrel side walls are 
then driven through the panel opening and are preferably deformed radially 
outwardly, riveting the barrel portion to the panel. The panel slug is 
simultaneously driven into the barrel portion through the opening, and in 
the most preferred embodiment staking the slug against the barrel side 
walls, thereby lodging said slug within said barrel. The most preferred 
method of this invention includes driving a plurality of circumferentially 
spaced staking projections into said slug, thereby forcing said slug up 
against a bottom wall of said barrel, thereby causing a portion of said 
slug to deform outwardly and wedge against said barrel side walls. 
The improved die member or die button of this invention includes a 
plurality of spaced staking projections on the die post. As described in 
the above-referenced U.S. patent, the preferred die button includes an 
annular concave die cavity surrounding a projecting central die post. The 
central die post has a free end which receives the panel slug and an outer 
piercing surface configured to be received in the barrel opening. The 
outer surface of the central die post traverses radially outwardly into 
the die cavity to receive the inner surface of the barrel portion. The die 
cavity promotes the radial outward deformation of said barrel side walls, 
which is completed in the annular concave die cavity. 
In the most preferred embodiment of the die button, the free end of the die 
post includes a plurality of staking projections which are 
circumferentially spaced about the free end of the central die post. Each 
staking projection preferably includes a first and second canted side wall 
and a top wall. The first canted side wall is preferably proximal to the 
barrel side wall and sloped such that it drives a portion of the slug 
against the barrel side wall when the die post is driven into the barrel 
opening. The second canted side wall of the staking projections is 
preferably proximal the center of the die post free end. 
The most preferred method of this invention includes outwardly deforming 
the slug periphery by pinching it between the staking projections and the 
bottom wall of the barrel. When the slug is outwardly deformed, it lodges 
against the barrel walls, thereby staking the slug between the barrel 
walls, forming a very secure interlock between the barrel portion and the 
panel slug, preventing inadvertent removal of the panel slug. 
The method and improved die button of this invention therefore eliminate 
the problem of inadvertent removal of the panel slug, including 
installations in relatively thin panels. The panel slug is automatically 
staked in the barrel portion during installation, eliminating the 
requirement for a separate step. The staking of the panel slug in the 
barrel portion is performed by the die button, without any substantial 
increase in cost and without materially affecting the strength of the die 
button or the integrity of the fastener and panel assembly. Other 
advantages and meritorious features of the present invention will be more 
fully understood from the description of the preferred embodiments, the 
appended claims and the drawings, a brief description of which follows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
As described above, the disclosed self-piercing and riveting fastener and 
the improved die member of this invention is particularly adapted for mass 
production applications, including automotive applications. The 
self-piercing and riveting fastener 20 illustrated in the drawings is a 
stud fastener of the type disclosed in U.S. Pat. No. 4,555,838; however, 
the improved method of attaching a self-piercing and riveting fastener and 
improved female die member of this invention is not limited to the 
configuration of the fastener. Further, the use of the term "fastener" is 
not intended to be limited to a fastening element which is adapted for 
attaching the panel to a structural element by a female fastener or the 
like. 
The self-piercing and riveting fastener utilized in the method of this 
invention is intended for permanent attachment to a plate or panel, 
particularly a metal sheet or the like, such as utilized by the automotive 
industry for body panels and component parts. As described in the 
above-referenced patents, the self-piercing and riveting fastener 
disclosed herein is particularly suitable for installation in a 
conventional die press, such as utilized by the automotive industry to 
form sheet metal parts, including body panels and structural components. 
In such applications, the press installs one or more fastening elements 
with each stroke of the press, wherein the fastener element becomes a 
permanent part of the panel. As used herein, "panel" refers to any plate, 
panel or metal sheet having a thickness thin enough to permit piercing of 
the panel with the fastening element as described herein. The 
self-piercing and riveting fastener may also be utilized in any 
application where rivets are presently used, such as securing panels 
together and closures. The method and improved die member or button of 
this invention is particularly adapted for retaining the panel slug 
pierced from the panel by the self-piercing and riveting fastener in the 
barrel portion of the fastener, as now described. 
Now referring to FIG. 1, the disclosed embodiment of the self-piercing and 
riveting fastener 20 includes a barrel portion 22 and a body portion 
including a radial flange portion 24 and a stud portion 26. In the 
disclosed embodiment, the stud portion 26 is externally threaded; however, 
the stud portion may be smooth or any other configuration, including the 
stud portion of a ball joint or an internally threaded cavity functioning 
as a nut. 
The barrel portion 22 includes barrel walls 27 which define opening 28. 
Barrel walls 27 adjacent opening 28 have a chamfered piercing surface 30 
and an arcuate annular outer surface 32. As described in the 
above-referenced U.S. Pat. No. 4,555,838, the frusto-conical piercing 
surface 30 in combination with the arcuate annular surface 32 provides 
important advantages in a self-piercing and riveting fastener of the type 
disclosed herein. However, the method and improved die member of this 
invention are not limited to the configuration of the free end of the 
barrel portion. In the disclosed embodiment, the flange portion 24 bridges 
the barrel portion providing a bottom wall 34 which may be flat (as shown) 
or concave (not shown). The combination of bottom wall 34 and barrel walls 
27 form an open-ended socket within barrel 22. Further, the flange portion 
24 includes a radial annular surface 38 adjacent the barrel portion 22, 
sometimes referred to as the pressing surface, and a radial annular 
surface 40 adjacent the stud portion 26, sometimes referred to as the 
driven surface. 
Where the self-piercing and riveting fasteners 20 are installed by a die 
press, as described above, the fasteners are normally fed to an 
installation head (not shown) which is attached to one platen of the die 
press. The installation head includes a plunger 42 which in the disclosed 
embodiment includes an axial bore 44 which receives the stud portion 26 of 
the fastener. The plunger includes an annular driving surface 46 which is 
driven against the annular driven surface 40 of the flange portion 24 of 
the fastener. A die member or die button 50 is normally attached in the 
opposite die platen in coaxial alignment with the plunger 42. U.S. Pat. 
No. 4,555,838 includes further disclosures of suitable embodiments of 
installation heads adapted for installing self-piercing and riveting 
fasteners of the type described herein. For the purposes of this 
disclosure, however, it is sufficient to state that the plunger 42 is 
driven toward die member 50 with sufficient force to install the fastener 
20 in panel 76 supported on die member 50, as described below. 
Details of the improved die member or die button 50 are best shown in FIGS. 
2 to 5. As shown, the die member includes a die cavity 52, including an 
annular concave die surface 56 surrounding a center die post 58. The die 
post 58 includes a free end 60 having a piercing surface 62 at its outer 
peripheral edge. As shown, the piercing surface 62 is relatively sharp to 
cooperate with the frusto-conical piercing surface 30 of the barrel 
portion 22 to pierce a panel. Other configurations of piercing surface 
may, however, be used. In the disclosed embodiment, the piercing surface 
64 of the center post 58 tapers conically and radially outwardly at an 
angle of about 7 degrees 66 until it blends into the arcuate concave 
surface 56 of the annular die cavity. As will be understood by those 
skilled in the art, the surface of the annular arcuate concave die cavity 
56 is preferably smooth and polished to control the radial outward 
deformation of the barrel portion as described below. The die button 50 
further includes an annular bearing surface 67 which surrounds the die 
cavity 52, and the die cavity 52 includes an inwardly tapered die surface 
68 which receives and supports the panel 76 during deformation of the 
panel as described below. The panel 76 is supported on the annular bearing 
surface 68 during installation of the self-piercing and riveting fastener 
20. In actual operation, the panel should be securely clamped to prevent 
relative movement of the panel 76 and the die member 50. 
The preferred embodiment of the die member of this invention includes a 
plurality of staking projections 80 which preferably extend above the free 
end 60 of the center post 58. Each staking projection includes a top 
surface 82 which intersects a first canted surface 84 and a second canted 
surface 86. In a preferred embodiment, first canted surface 84 is sloped 
so that (during use) it partially faces fastener barrel walls 27 and 
partially faces fastener bottom wall 34. The purpose for the preferred 
slope of the first canted surface 84 will be discussed in detail in 
conjunction with FIGS. 6-9. Staking projections 80 preferably have a third 
side 88 and a fourth side 90. The third side 88 and fourth side 90 
preferably are tapered inwardly 92 to accommodate easy separation from the 
slug (not shown). 
In the preferred embodiment, the plurality of staking projections 80 are 
symmetrically distributed on the die post free end 60 Proximate its 
circumference. This distribution preferably includes arranging the 
plurality of staking projections 80 in a circle, as depicted in FIG. 5. It 
is important to note that although the staking projections 80 are shown as 
discrete entities, it is within the scope of this invention to comprise 
staking projections 80 from a single continuous ringed surface rising up 
from die post free end 60. A cross-section of this ringed surface would be 
identical to the cross-section of the plurality of staking projections as 
shown in FIG. 3. Die member 50 preferably has a central bore 53 which 
provides an air release passage for any air which may be trapped within 
die cavity 52 during the course of the fastening process. 
FIGS. 6-8 illustrate the preferred sequence of installation of a 
self-piercing and riveting fastener and the method of staking the panel 
slug in the barrel portion of this invention. As shown in FIG. 6, barrel 
side walls 27 are driven into panel 76, and panel 76 is thus driven 
against staking projections 80 of die post 58. Central bore 53 channels 
air away from die cavity 52 which would otherwise be entrapped during the 
fastening procedure. 
Now referring to FIG. 7, barrel walls 27 are further driven into panel 76, 
and die piercing surfaces 62 and barrel piercing portion 30, respectively, 
pierce slug 94 from panel 76. Slug 94 will generally assume a concave 
position because of the shearing forces it experiences along its 
peripheral edges. The portions of slug 94 which lay adjacent first canted 
surface 84 of staking projections 80 undergo an outward deformation as 
they are compressed between first canted surface 84 and barrel wall 
surface 96. A slug 94 is thus pierced from the panel in substantially one 
step, resulting in a generally circular slug 94. It will be understood, 
however, that the configuration of the slug will be dependent upon the 
shape of the tubular barrel portion 22 which need not be circular. For 
example, the tubular barrel portion 22 could be polygonal, wherein the die 
post 58 and die cavity 52 would be polygonal and configured to receive the 
barrel portion. 
As barrel walls 27 are driven into die cavity 52, portion 102 of the panel 
76 adjacent the pierced panel opening is simultaneously driven into the 
die cavity 52, and the panel slug 94, which is received on staking 
projections 80 and die post free end 60, is driven into the barrel portion 
22. As will be understood by those skilled in the art, the diameter of the 
panel slug 94 is substantially equal to or slightly greater than the 
internal diameter of the barrel portion 22. However, because staking 
projections 80 cause a slight deformation in slug 94 (during the period 
slug 94 is sheared from panel 76), the edges of slug 94 which are 
proximate first canted surface 84 are deformed against the internal 
surface of barrel walls 27. 
Now referring to FIG. 8 of the drawings, as the fastener barrel walls 27 
are driven into die cavity 52, they are received against concave annular 
die surface 56 of die cavity 52 and are deformed radially outwardly. 
Simultaneous with this radially deforming action, staking projections 80 
drive slug 94 against barrel bottom wall 34. Once slug 94 is seated 
against barrel bottom wall 34, staking projections 80 begin to pinch slug 
peripheral portions 98 against barrel bottom wall at point 99, thereby 
causing periphery portions 98 to deform against wall 27 at surface 96. 
First canted surface 84 aids in directing slug peripheral portions 98 
toward barrel wall surface 96 by virtue of its angular orientation. As 
staking projections 80 are driven into slug 94, first canted surface 84 is 
sloped to direct slug peripheral portions 98 toward barrel wall surface 
96, thereby frictionally lodging slug 94 within barrel 22 and against 
bottom wall 34. 
Now referring to the drawing of FIG. 9, the radial deformation of barrel 
side walls 27 forms a U-shaped channel 100. This channel 100 grips panel 
portion 102, thereby forming a secure mechanical interlock between barrel 
portion 22 and panel portion 102. 
Thus, it is seen that panel slug 94 is staked within barrel 22 
simultaneously with fastening barrel side walls 27 to panel portion 102. 
Having described the preferred method of attaching a self-piercing and 
riveting fastener and the improved die button of this invention, it will 
be understood that various modifications may be made within the purview of 
the appended claims. The dimensions of the self-piercing and riveting 
fasteners will depend upon the particular application and panel thickness. 
As described above, however, the method and improved die button of this 
invention is particularly suitable for permanent attachment of 
self-piercing and riveting fasteners to relatively thin panels, such as 
utilized for body and structural components in the automotive and 
appliance industries. As will be understood, the self-piercing and 
riveting fastener disclosed herein is preferably formed of a deformable 
metal, preferably steel, which may be heat-treated for surface hardness, 
ductility, etc. A suitable material for the self-piercing and riveting 
fasteners disclosed herein is typically medium carbon steels, including 
SAE 1022, 1023 and 1030 steels. Reference may also be made to the 
above-referenced U.S. patents for further information regarding suitable 
installation apparatus, self-piercing and riveting fasteners and methods 
of installation.