U.S. patent application number 10/004918 was filed with the patent office on 2003-06-05 for self-piercing element, method of attachment and die member.
Invention is credited to Ladouceur, Harold A..
Application Number | 20030101566 10/004918 |
Document ID | / |
Family ID | 21713174 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030101566 |
Kind Code |
A1 |
Ladouceur, Harold A. |
June 5, 2003 |
Self-piercing element, method of attachment and die member
Abstract
A self-piercing element including a shank, a radial flange and a
tubular barrel. The flange includes spaced concave surfaces and the
annular bearing surface has an area at least four times the concave
surfaces. The element is installed in a panel supported on a female
die including a central die post, wherein the outer side wall is a
frustoconical having an included angle between five and twelve
degrees. During installation, the tubular barrel pierces an opening
in the panel and the panel is drawn against the outer surface of
the tubular barrel and the barrel is deformed into a U-shape. The
flange is simultaneously received in the die cavity and the panel
is incrementally deformed radially into the concave surfaces
between the frustoconical side wall and the flange portion
providing improved torque resistance.
Inventors: |
Ladouceur, Harold A.;
(Livonia, MI) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS, P.C.
THE PINEHURST OFFICE CENTER, SUITE #101
39400 WOODWARD AVENUE
BLOOMFIELD HILLS
MI
48304-5151
US
|
Family ID: |
21713174 |
Appl. No.: |
10/004918 |
Filed: |
December 5, 2001 |
Current U.S.
Class: |
29/432.2 ;
29/798 |
Current CPC
Class: |
Y10T 29/49954 20150115;
Y10T 29/49837 20150115; Y10T 29/49915 20150115; Y10T 29/49835
20150115; Y10T 29/53996 20150115; Y10T 29/49947 20150115; Y10T
29/49908 20150115; Y10T 29/5343 20150115; F16B 37/062 20130101;
B23P 19/062 20130101 |
Class at
Publication: |
29/432.2 ;
29/798 |
International
Class: |
B23P 011/00; B23P
019/00 |
Claims
1. A method of attaching a self-piercing element in a panel
supported on a die member, said self-piercing element including a
tubular barrel portion having an open free end including a piercing
surface and an integral radial flange portion adjacent said tubular
barrel portion including an outer surface having a plurality of
spaced inwardly concaved surfaces, said die member including a
panel supporting end face, a central die post having an end surface
including a piercing surface spaced below the plane of said end
face and an annular die cavity surrounding said central die post,
said annular die cavity including a semicircular annular bottom
surface and a side wall extending from said semicircular annular
bottom surface to said end face, said method comprising the
following steps: supporting a panel on said end face of said die
member; driving said open free end of said self-piercing element
against said panel and said panel against said end surface of said
die post; continuing to drive said open free end of said barrel
portion against said panel, piercing a slug from said panel between
said piercing surfaces of said barrel portion and said end surface
of said central die post, forming an opening through said panel,
and simultaneously deforming a first portion of said panel adjacent
said opening into said annular die cavity against an outer surface
of said tubular barrel portion; driving said open free end of said
barrel portion against said semicircular annular bottom surface of
said annular die cavity, deforming said free open end of said
barrel portion radially outwardly and upwardly toward said end
face, forming a U-shaped end portion of said barrel portion, and
deforming a pierced edge of said panel portion into said U-shaped
end portion of said barrel portion; and continuously, incrementally
deforming a second panel portion in said annular die cavity between
said outer surface of said flange portion of said self-piercing
element and said side wall of said annular die cavity radially into
said inwardly concave surfaces.
2. The method as defined in claim 1, wherein said side wall is a
continuous frustoconical side wall extending tangentially from said
bottom surface having an included angle of between 5 degrees and 12
degrees, and said method includes deforming said free open end of
said barrel portion upwardly adjacent to but spaced from said side
wall.
3. The method as defined in claim 1, wherein a distance between
said continuous frustoconical side wall adjacent said end face and
said outer surface of said flange portion is less than the
thickness of said panel, said method including thinning said panel
at locations between said spaced inwardly concave surfaces.
4. The method as defined in claim 1, wherein said method includes
maintaining said first panel portion spaced from said outer wall of
said annular die cavity.
5. A method of attaching a self-piercing element in a panel
supported on a die member, said self-piercing element including a
tubular barrel portion having an open free end and an integral
radial flange portion adjacent said tubular barrel portion having a
generally cylindrical outer surface including a plurality of spaced
inwardly concave surfaces, said die member including an end face, a
central die post having an end surface spaced below the plane of
said end face and an annular die cavity surrounding said central
die post, said annular die cavity including an annular semicircular
bottom surface and a frustoconical side wall extending tangentially
from said semicircular bottom surface to said end face, said method
comprising: supporting a panel on said end face of said die member;
driving said open free end of said barrel portion of said
self-piercing element against said panel and said panel against
said end surface of said central die post; continuing to drive said
open free end of said barrel portion against said panel, thereby
piercing a slug from said panel between said open free end of said
barrel portion and said end surface of said central die post;
continuing to drive said open free end of said self-piercing
element against said panel, thereby piercing a slug from said panel
between said open free end of said barrel portion and said end
surface of said central die post, forming an opening through said
panel, and simultaneously deforming an end portion of said panel
adjacent said opening into said annular die cavity against an
external surface of said tubular barrel portion around an
intersection of said end face and said continuous smooth
frustoconical annular side wall of said die member; driving said
free open end of said barrel portion against said semicircular
annular bottom surface of said annular die cavity, thereby
deforming said free open end of said barrel portion radially
outwardly and upwardly toward said end face and around said end
portion of said panel, thereby forming a U-shaped end portion of
said barrel portion enclosing said end portion of said panel; and
continuously, incrementally deforming a second panel portion in
said annular die cavity adjacent said end face of said die member
between said cylindrical surface of said flange portion and said
side wall, thereby thinning said second panel portion and deforming
said second panel portion radially into said plurality of spaced
inwardly concave surfaces while the remainder of said panel is
spaced from side wall.
6. The method of claim 5, wherein said method includes deforming
said pierced edge of said first panel portion in said U-shaped end
portion into an enlarged bead having a thickness greater than the
thickness of said panel and having a height measured between said
flange portion and said U-shaped end portion of said barrel portion
greater than its width.
7. A die member for attaching a self-piercing element including a
tubular barrel portion and a radial flange portion in a panel, said
die member comprising: an end face, a central die post extending
generally perpendicular to said end face having an end surface, and
an annular die cavity surrounding said central die post, said
annular die cavity including an annular semicircular bottom surface
and a continuous smooth frustoconical side wall extending
tangentially from said semicircular bottom surface to said end
face.
8. The die member as defined in claim 7, wherein said continuous
smooth frustoconical side wall has an included angle of between 5
and 12 degrees.
9. The die member as defined in claim 7, wherein said continuous
frustoconical side wall joins said end face in a radiused surface
having a radius of less than 0.04 inches.
10. The die member as defined in claim 7, wherein said central die
post has an outer piercing edge defined by an outer annular planar
end surface and a frustoconical side wall extending tangentially
from said semicircular bottom surface to said outer annular planar
surface at an included angle of about 7 degrees.
11. A die member for attaching a self-piercing element having a
tubular barrel portion and a radial flange portion in a panel
supported on said die member, said die member comprising: a
generally planar panel-supporting end face, an annular concave die
cavity defined in said end face, and a central die post projecting
from said annular concave die cavity toward said end face including
an end surface spaced below the plane of said generally planar
panel-supporting end face and an outer piercing surface, said
annular concave die cavity including an annular semicircular bottom
surface and a continuous smooth frustoconical outer side wall
extending tangentially from said annular semicircular bottom
surface to said end face having an included angle of between 5 and
12 degrees.
12. The die member as defined in claim 11, wherein said
frustoconical outer side wall joins said end face in a radiused
surface having a radius of less than 0.04 inches.
13. The die member as defined in claim 11, wherein said outer
piercing surface of said central die post is defined by an outer
annular planar surface and a frustoconical inner surface extending
tangentially from said annular semicircular bottom surface to said
outer annular planar surface defining a sharp piercing edge.
14. A self-piercing male fastener element comprising a shank
portion, a radial flange portion integral with said shank portion
and a tubular barrel portion integral with said radial portion
including a free open end portion having a piercing surface for
piercing an opening in a panel, said flange portion including a
generally planar annular bearing surface surrounding said shank
portion having a diameter greater than said barrel portion and an
outer surface having a plurality of spaced concave surfaces,
wherein the area of said annular bearing surface is at least five
times the area of said concave surfaces measured in the plane of
said generally planar bearing surface.
15. The self-piercing male fastener element as defined in claim 14,
wherein said area of said bearing surface is at least six times
said area of said concave surfaces measured in the plan of said
bearing area.
16. The self-piercing male fastener element as defined in claim 14,
wherein said concave surfaces are spaced from said tubular barrel
portion a distance equal to or greater than the depth of said
concave surfaces.
17. The self-piercing male fastener element as defined in claim 14,
wherein the depth of said concave surfaces about 0.75 the width of
said bearing surface measured from said shank portion.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a self-piercing element, such as a
self-piercing stud having a tubular barrel portion, the method of
attachment, and a die member for attaching the self-piercing
element to a metal panel.
BACKGROUND OF THE INVENTION
[0002] Self-piercing and clinching female fasteners such as nuts
were developed by the predecessor in interest of the Applicant
(Multifastener Corporation) about 50 years ago as disclosed for
example in U.S. Pat. No. 2,707,322. Self-piercing and clinching
nuts are attached to a metal panel in a die press which may also be
used to simultaneously form the panel, wherein generally the upper
die platen includes an installation head and the lower die platen
includes a die member or die button. Such self-piercing and
clinching nuts include a projecting pilot portion which pierces an
opening in the panel and the panel metal adjacent the pierced panel
opening is then clinched to the fastener with each stroke of the
die press.
[0003] More recently, self-piercing and clinching male and female
fasteners were developed having a tubular barrel portion as
disclosed, for example, in U.S. Pat. No. 4,555,838 assigned to the
assignee of this Application. The self-piercing and clinching
fasteners disclosed in this patent include a tubular barrel portion
and a radial flange portion. Such self-attaching male fasteners are
installed in a die press, as described above, wherein the lower die
platen includes a die button having a panel supporting surface, a
central die post and an annular die cavity surrounding the die
post. The annular die cavity includes a semicircular annular bottom
surface, a radial lip portion at the upper extent of the
semicircular bottom surface and a generally frustoconical surface
extending from the radial lip portion to the end surface of the die
button. In the embodiment disclosed in this patent, the generally
frustoconical upper die surface includes a plurality of flats which
extend from the annular lip to the end or bearing face of the die
button which provide anti-rotation means by drawing and slightly
deforming the flange of the stud fastener. It is very important in
most applications of the self-piercing and riveting male fasteners
that the fastener be able to withstand significant torque loads
without twisting in the panel which may destroy the fastener and
panel assembly. It was found, however, that the anti-rotation means
disclosed in this patent was insufficient for many applications,
including automotive applications.
[0004] Various attempts have been made to improve the torque
resistance of self-piercing and riveting stud fasteners of the type
disclosed in U.S. Pat. No. 4,555,838. Initially, anti-rotation
protrusions or nubs were provided either on the barrel portion,
adjacent the body portion, or on the flange portion adjacent the
barrel portion as disclosed, for example, in U.S. Pat. No.
4,810,143, also assigned to the assignee of the present
Application. Presently, self-attaching stud fasteners of the type
disclosed herein include a plurality of spaced pockets in the outer
edge of the flange portion adjacent the barrel portion as disclosed
in U.S. Pat. No. 5,020,950, also assigned to the assignee of the
present Application. There remains, however, several problems
associated with the use of pockets in the flange portion as
disclosed in U.S. Pat. No. 5,020,950. First, the die surfaces which
form the pockets wear, such that the pockets are not always fully
formed in the flange portion resulting in insufficient torque
resistance. Second, the self-piercing stud fastener and panel
assembly is press sensitive. That is, if the panel metal is not
fully deformed into the pockets, the torque resistance will be
inadequate. Further, the pockets form stress risers in the panel
which can become a source of failure of the fastener and panel
assembly. Finally, the use of pockets in the flange portion may
provide insufficient torque resistance, particularly where extreme
torque resistance is required.
[0005] There are also other problems associated with self-piercing
and clinching fastener installations of the type disclosed herein
which are addressed by the improved fastener, method of
installation and die member of this invention. First, the flange
portion which surrounds the bolt or stud portion in a male fastener
for example is deformed both radially and axially relative to the
stud portion by the annular plunger of the installation head which
drives the self-piercing and clinching fastener into the panel and
the die button, particularly where the press setting is greater
than required for installation. This is because the flange portion
bottoms against the panel in the die button during installation. As
best described in the above-referenced U.S. Pat. No. 4,555,838, the
panel metal adjacent the pierced panel opening bottoms on the
radial lip of the die button and is then driven into the U-shaped
end portion formed in the free open end of the barrel portion.
Second, the installation of the self-piercing fastener in a panel
is press sensitive. That is, if the press does not provide
sufficient force for full installation, the fastener will be loose
in the panel providing insufficient pull-out strength and torque
resistance. Alternatively, in an "overhit" condition of the die
press, the flange portion will be deformed by cold working as
previously described. However, even where the fastener is properly
installed in the panel with the preferred die setting the torque
resistance may be insufficient, as described above, or the stud or
bolt may provide insufficient resistance to tilting in the panel
assembly. Finally, the die button is relatively complex and
therefore expensive to manufacture and has a relatively poor die
life, particularly where the die button is utilized to install
self-piercing fasteners of the type described herein in relatively
high strength metals, such as HSLA steel. It would therefore be
desirable to provide improved torque resistance, eliminate
deformation or cold working of the flange portion, reduce
sensitivity to die press settings and reduce the cost of the die
button, while improving die life.
[0006] As described below, the preferred embodiment of the
self-piercing and attaching fastener utilized in the method of
installation preferably includes a plurality of spaced arcuate
radially inwardly concave surfaces or arcuate scallops in the outer
side surface of the flange portion. U.S. Pat. No. 6,122,816,
assigned to the assignee of the present application, discloses a
self-riveting stud fastener including a tubular barrel portion and
a radial flange portion having a plurality of spaced arcuate
radially inwardly concave surfaces on the outer surface of the
flange portion which provide torque resistance and the barrel
portion has a conical outer surface developed for installation in
thicker panels having a preformed panel opening. Thus, the method
of installation disclosed in this patent preferably includes
preforming a panel opening and driving of the barrel portion
through the panel opening into a semicircular annular die cavity
which deforms the free end of the barrel portion into generally a
U- or C-shape as disclosed. Continued driving of the flange portion
with an annular plunger or punch then drives the flange portion
into the panel, cutting and deforming the panel into the shape of
the concave and convex surfaces, providing improved torque
resistance.
[0007] However, the method of installation disclosed in U.S. Pat.
No. 6,122,816 has many of the same problems described above in
regard to the present method of installing a self-piercing
fastener, including press sensitivity and deformation or cold
working of the flange portion, particularly in an "overhit" setting
of the press. It is possible to actually shear the flange portion
from the barrel or body portion in an overhit condition. As the
flange portion is driven into the panel by the method disclosed in
this patent, the scalloped flange cuts into the panel forming
stress risers particularly at the convex edges between the arcuate
concave surfaces or flutes, reducing the integrity of the joint.
Further, the panel metal under the flange is compressed, causing
deformation of the bearing surface at the top of the flange.
SUMMARY OF THE INVENTION
[0008] The method of attaching a self-piercing element in a panel,
self-piercing and clinching male fastener and die member of this
invention reduces or eliminates the problems associated with the
prior methods of installation and the die member is relatively
simple in construction, reducing costs and increasing die life. As
described further below, the self-piercing element utilized in the
method of this invention includes a tubular barrel portion having
an open free end and a radial flange portion adjacent the tubular
barrel portion including an outer surface having a plurality of
spaced inwardly concave surfaces or "scallops." In the preferred
embodiment, the open free end of the tubular barrel includes an
inner chamfer, such that the slug pierced from the panel has an
external diameter slightly greater than the internal diameter of
the tubular barrel portion. The panel slug is then received in the
tubular barrel portion during installation, and the hole formed in
the panel has an internal diameter less than the external diameter
of the barrel portion, such that the panel portion adjacent the
pierced panel opening will be driven into the die member as
disclosed for example in the above-referenced U.S. Pat. No.
4,555,838.
[0009] The female die member or die "button" of this invention
includes a generally planar panel-supporting end face, an annular
concave die cavity defined in the end face and a central die post
projecting from the annular concave die cavity toward the end face
including an end surface spaced below the plane of the end face
having an outer piercing surface preferably defined by a relatively
sharp circular edge. The concave die cavity includes an annular
semicircular bottom surface and preferably includes a continuous
smooth frustoconical side wall which extends tangentially from the
annular semicircular bottom surface to the end face, thereby
eliminating the annular lip between the annular semicircular bottom
surface and the generally frustoconical outer side wall as
disclosed in the above-referenced U.S. Pat. No. 4,555,838. The
smooth continuous frustoconical side wall preferably has an
included angle of between 5 and 12 degrees, most preferably between
about 6 and 10 degrees, which is substantially steeper than the
generally frustoconical upper die surface disclosed in the
above-referenced U.S. Pat. No. 4,555,838 and the more recent U.S.
Pat. No. 5,140,735, also assigned to the assignee of the present
Application.
[0010] As described further below, the preferred included angle of
the smooth continuous frustoconical side wall of the die member
will depend upon the diameter of the tubular barrel portion which
is determined by the diameter of the stud portion of a male
fastener and the thickness of the panel to which the self-piercing
element is installed. Further, because in the method of attaching a
self-piercing element in a panel of this invention, the panel
surrounding the pierced panel opening is deformed into the annular
concave die cavity around the intersection of the end face and the
continuous frustoconical outer side wall, this intersection is
preferably radiused with a radius of less than 0.04 inches, which
is less than the preferred radius used in the present die button.
In the preferred embodiment of the die member or die button, the
outer surface of the die post or inner surface of the concave die
cavity is defined by a frustoconical surface extending tangentially
from the semicircular bottom surface to the end surface of the die
post, preferably at an angle of about 7 degrees. Further, the
piercing surface at the outer edge of the central die post is
preferably relatively sharp and may include staking cavities as
disclosed in the above-referenced U.S. Pat. No. 5,140,735 to
permanently stake the pierced panel slug in the tubular barrel
portion.
[0011] The preferred embodiment of the self-piercing and clinching
fastener of this invention is a male fastener having a shank or
stud portion, which may be threaded or unthreaded depending upon
the application. For example, the stud portion could be the shank
of a ball joint. The fastener further includes a radial flange
portion integral with the shank portion and a tubular cylindrical
barrel portion integral with the flange portion coaxially aligned
with the stud portion having an open free piercing end. The outer
surface of the flange portion includes a plurality of spaced
concave surfaces which receive the panel during installation as
described below. The annular bearing surface of the flange portion
surrounding the stud portion is preferably flat and preferably has
a surface area of at least five times the adjacent area of the
concave surfaces measured in the plane of the bearing surface, more
preferably at least six times or greater. Preferably, the width of
the concave surfaces measured perpendicular to the shank portion is
about 0.75 the width of the flange portion measured to the barrel
portion.
[0012] The outer surface of the flange portion between the concave
surfaces is preferably cylindrical and the concave surfaces are
preferably spaced from the tubular barrel by a distance equal to or
greater than the width of the concave surfaces measured from the
outer cylindrical surface. Thus, the preferred embodiments of the
self-piercing and clinching stud fastener of this invention has a
substantially greater bearing area surrounding the stud portion
reducing the likelihood of deformation or cold-forming of the
flange portion during installation as described below. In the most
preferred embodiment, the concave surfaces on the outer surface of
the flange are cylindrical.
[0013] The method of attaching a self-piercing element in a panel
of this invention then includes supporting a panel on the end face
of the die button and driving the open free end of the tubular
barrel portion of the self-piercing element against the panel and
thereby the panel against the end surface of the central die post.
Continued driving of the barrel portion of the self-piercing
element against the panel pierces a slug from the panel between the
open free end of the barrel portion and the central die post,
forming an opening through the panel and simultaneously deforming a
first panel portion adjacent the pierced panel opening into the
annular die cavity around the intersection of the end face and the
continuous frustoconical side wall of the die member. As the
tubular barrel portion is driven through the pierced panel opening,
the panel is drawn into a tube-shape against the cylindrical
external surface of the barrel. The method of this invention then
includes driving the inside surface of the tubular barrel portion
against the semicircular bottom surface of the die cavity
surrounding the die post, deforming the free end of the barrel
portion into a U-shaped end portion. The panel is simultaneously
drawn against the outer surface of the tubular barrel portion and
into the developing U-shaped end of the tubular barrel portion.
However, because the die member does not include an annular lip
between the concave semicircular bottom surface and the
frustoconical outer wall as disclosed in the above-referenced U.S.
Pat. No. 4,555,838, the panel remains unsupported in the die cavity
and the flange portion does not bottom in the die cavity against
the panel as described above in regard to the prior method of
installation.
[0014] Finally, the method of this invention includes incrementally
deforming a second panel portion in the annular die cavity adjacent
the end face against the continuous frustoconical side wall and
into the spaced inwardly concave surfaces in the outer side surface
of the flange portion substantially, but preferably not completely
filling the concave surfaces. That is, the frustoconical outer side
wall of the die cavity, which is inclined inwardly from the end
surface, serves as a wedge, incrementally deforming the surrounding
panel radially inwardly into the concave surfaces. This method
should be differentiated from the method disclosed in the
above-referenced U.S. Pat. No. 6,122,816, wherein the scalloped
flange portion is driven into the panel, thereby cutting the panel
as described above.
[0015] Because the panel is unsupported in the annular die cavity
until the installation is complete and the flange is not driven
into the panel bottomed in the die cavity, as described above, the
method of this invention substantially eliminates deformation or
cold working of the flange portion by the annular punch or plunger
which drives the self-piercing element into the die cavity.
Further, because of the relative simplicity of the die member, the
cost is reduced and die life is improved. Further, because the
panel metal is incrementally deformed or "squeezed" into the spaced
inwardly concave surfaces on the outer surface of the flange
portion, the torque resistance of the self-piercing fastener in the
panel is significantly improved, particularly over the method
disclosed in the above-referenced U.S. Pat. No. 4,555,838. In fact,
testing indicates that the stud portion will fail normally in
torque before rotation of the fastener element in the panel in stud
fasteners having a shaft diameter of 6 mm or less. Further, because
the entire side surface of the flange is fully supported in the
panel, loose connections are substantially eliminated. Finally, the
installation method of this invention is less sensitive to the die
press setting. That is, an overhit condition will not result in
deformation of the flange and the installation is less sensitive to
"underhit" conditions.
[0016] The method of attaching a self-piercing element in a panel
and die member of this invention therefore reduces or eliminates
the problems associated with the prior methods of attaching a
self-piercing element to a panel and results in a better
installation. Other advantages and meritorious features of this
invention will be more fully understood from the following
description of the preferred embodiments, the claims and the
appended drawings, a brief description of which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an end perspective view of a preferred embodiment
of the self-piercing and clinching male fastener of this
invention;
[0018] FIG. 2 is an end view of the self-piercing and clinching
fastener shown in FIG. 1;
[0019] FIG. 3 is a partial side cross-sectional view of the
fastener illustrated in FIGS. 1 and 2;
[0020] FIG. 4 is an exploded side view partially cross-sectioned of
the fastener illustrated in FIGS. 1 to 3 aligned for installation
to a panel with a die member and driving member;
[0021] FIG. 5 is a side cross-sectional view during the initial
installation of the fastener illustrated in FIGS. 1 to 4 in a
preferred embodiment of the die member of this invention; and
[0022] FIGS. 6 to 14 are side cross-sectional views of the fastener
and die member of this invention illustrating the installation
sequence and the method of installation of this invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0023] As set forth above, this invention relates to an improved
self-piercing and clinching male fastener having significantly
improved torque resistance, the method of attaching a self-piercing
fastener to a panel and an improved female die member. As will be
understood by those skilled in this art, the drawings illustrate
preferred embodiments of this invention, but are not limiting
except as set forth in the appended claims.
[0024] FIGS. 1 to 3 illustrate one preferred embodiment of the
self-piercing and clinching fastener 20 of this invention in the
form of a male fastener having a threaded shank portion 22. As will
be understood, the stud or shank portion 22 may be threaded or
unthreaded and may take various forms. As used herein, the term
"fastener" is primarily used to refer to the function of the
fastener element, which is to attach a component to the panel or
plate to which the self-piercing fastener 20 is attached. The term
"self-piercing" refers to the function of the fastening element to
pierce its own hole in the panel during the fastener installation
as described below.
[0025] The self-piercing fastener 20 further includes a radial
flange portion 24 integral with the shank portion 22 and a tubular
barrel portion 26 integral with the radial flange portion 24 and
coaxially aligned with the shank portion 22. The preferred
embodiment of the tubular barrel portion 26 includes a cylindrical
external surface 28 and a cylindrical internal surface 30 as best
shown in FIG. 3. The tubular barrel portion includes a free open
piercing end 32 having an arcuate annular outer bearing surface 34
and a chamfered internal piercing surface 36. As described more
fully in the above-referenced U.S. Pat. No. 4,555,838, the
chamfered piercing surface 36 centers the fastener on the panel
during installation and pierces an opening in the panel having a
diameter less than the external diameter of the cylindrical
external surface 28.
[0026] The radial flange portion 24 includes an annular planar
bearing surface 38 surrounding the shank portion 22 and an outer
surface 40 includes spaced concave surfaces 42 and outer
cylindrical surfaces 44 located between the concave surfaces 42 as
best shown in FIG. 2. The outer surfaces 44 may also be flat. The
relation between the diameter of the shank portion 22, the annular
bearing face 38 and the concave surfaces 42 are important to the
function and improvements provided by the self-piercing fastener 20
and method of this invention is described further below.
[0027] The self-piercing fastener 20 of this invention is
particularly adapted for mass production applications, such as used
by the automotive industry to install self-piercing and clinching
fasteners in sheet metal parts including brackets, body panels and
the like. Such sheet metal parts are typically formed in a die
press. The self-piercing fastener of this invention may be
installed in the sheet metal panel or plate with each stroke of the
die press, wherein the upper platen typically includes an
installation head having a reciprocating plunger 52 and the lower
die platen includes a female die member or die button 54 as shown
in FIG. 4 and described more fully in the above-referenced U.S.
Pat. No. 4,555,838. The annular plunger 52 includes a cylindrical
bore 56 which receives the shank or stud portion 22 of the fastener
and the driving end portion 58 of the plunger is configured to be
received against the planer annular bearing face 38 of the radial
flange portion 24 as shown in FIGS. 4 et. seq. The female die
member or die button 54, best shown in FIG. 5, includes a planer
end bearing face 60 which supports the panel 50 and the panel 50
may be clamped to the bearing face 60 (not shown). The female die
member 54 includes an annular female die cavity 62 defined in the
bearing face 60 surrounding a central die post 64. The annular die
cavity 62 includes an annular semicircular bottom surface or wall
66 and a frustoconical outer side wall 68 which extends
tangentially from the semicircular bottom wall 66 to the bearing
face 60 and joins the bearing face 60 in a radius 70. The smooth
continuous frustoconical outer side wall 68 extends tangentially
from the annular semicircular bottom wall 66 at an included angle
"a" show in FIG. 5 of between 5 and 12 degrees, most preferably
between about 6 and 10 degrees and the radius joining the
frustoconical outer side wall 68 and the bearing face 60 is
preferably less than 0.04 inches. The end surface 76 of the central
die post 64 may also include staking cavities to retain the slug
pierced from the panel 50 as disclosed in the above-referenced U.S.
Pat. No. 5,056,207. The advantages of the unique die button 54 and
self-piercing fastener 20 of this invention will be understood from
the following description of the method of installation of this
invention described below.
[0028] As shown schematically in FIG. 4, the self-piercing male
fastener 20, plunger 52 and the die button 54 are aligned by the
installation apparatus or "head" (not shown) along the longitudinal
axis "b" prior to installation. As disclosed more fully in the
above-referenced U.S. Pat. No. 5,092,724, the self-piercing male
fastener element 20 is received in the installation head is
generally located in the upper die platen and the shank portion 22
is initially received in the axial bore 56 of the plunger prior to
installation. As set forth above, the panel 50 may be clamped to
the bearing face 60 of the die button in the lower die platen (not
shown). FIG. 5 illustrates the initial step in the installation
sequence of the self-piercing fastener 20 in the panel 50. The
driving end 58 of the plunger 52 is driven against the annular
bearing face 38 of the radial flange portion 24, which drives the
free open end 32 of the barrel portion 26 against the panel 50,
which deforms the panel 50 against the end face 76 of the die post
64 as shown in FIG. 5. The panel 50 is deformed into the die cavity
62 against the end face 76 of the die post 64 around the arcuate
surface 70 as shown.
[0029] FIGS. 6 to 14 illustrate the sequence of installation of the
fastener 20 in the panel 50, wherein the plunger 52 is replaced by
an arrow 52a for clarity. As shown in FIG. 6, the chamfered
piercing surface 36 cuts the panel against the circular outer sharp
piercing edge 74 of the die post 64 as shown in FIGS. 6 and 7 until
a slug 50a is cut from the panel as shown in FIG. 8. The edge
portion of the panel 50b adjacent the pierced slug 50a is then
received against the cylindrical external surface 28 of the tubular
barrel 26 as shown in FIGS. 8 and 9, wherein the external surface
28 of the tubular barrel 26 draws the panel portion 50b into the
annular die cavity 26. The internal surface 30 Of the tubular
barrel portion 26 is then received first against the frustoconical
surface 72 of the die post 64 as shown in FIG. 9 and then against
the annular semicircular bottom wall 66 as best shown in FIG. 10,
wherein the free open end 32 of the tubular barrel portion 26 is
deformed sequentially against the annular semicircular bottom wall
66 into a U-shape as shown in FIGS. 10 to 12. It should be noted
that during the sequence of installation illustrated in FIGS. 10 to
12, the panel portion 50b remains unsupported in the die cavity 26
and against the outer surface 28 of the tubular barrel. Further, it
is important to note that the flange portion 24 is not driven into
the panel portion 50b as shown in FIGS. 10 to 12 and the panel
portion 50b remains spaced from the outer wall 68 of the annular
die cavity, contrary to the teaching of the present method of
installation as disclosed in the above-referenced U.S. Patents. The
panel portion 50b adjacent the pierced panel edge is eventually
enclosed within the U-shaped end portion 32a as shown in FIGS. 12
and 13. However, upon forming of the free end 32a in the annular
semicircular bottom wall 66, the U-shaped free end 32a is spaced
from the frustoconical side wall 68 as shown in FIG. 13.
[0030] Finally, as shown in sequence drawings of FIGS. 13 and 14,
the panel portion 56c in the die cavity 26 adjacent the upper
radius 70 is then incrementally squeezed between the side wall 68
adjacent the radius 70 and the cylindrical surfaces 44 radially
into the spaced concave surfaces 42 until the panel metal
substantially fills the concave surfaces 42 as shown in FIG. 14. As
shown in FIG. 14, the flange portion 24 preferably is driven into
the die cavity 62 such that the annular bearing surface 38 is
slightly spaced below the plane of the panel 50. This is because
the fastener portion, which is the shank portion 22 in the
disclosed embodiment, is used to attach a component (not shown) to
the panel 50 wherein the component preferably lies flush on the
panel. As will be understood, if the installation was designed to
have the bearing surface 38 flush with the panel, normal tolerance
build up would result in some of the installations having a flange
portion above the panel 50. As will also be understood from the
above description of the method of this invention and the sequence
of installation shown in FIGS. 6 to 14, the panel 50 and the free
end 32a of the barrel portion does not contact the frustoconical
outer side wall 68 except adjacent the planar bearing face 60.
Thus, the frustoconical side wall 68 is not necessary except
adjacent the opening a depth equal to the width of the flange
portion plus the distance the flange portion is recessed below the
plane of the panel 50. Further, in the preferred embodiment, the
panel portion 56c is squeezed or deformed into the spaced concave
surfaces 42 to substantially, but not completely fill the concave
surfaces 42 to avoid deformation of the flange portion 24. The
frustoconical outer side wall 68 adjacent the bearing face 60 thus
serves as a wedge as the flange portion 24 is driven into the die
cavity 62, incrementally deforming the panel portion 56c into the
concave surfaces 42.
[0031] The panel slug 50a is simultaneously driven toward the
bottom surface 46 of the radial flange portion and may be retained
against the bottom portion as disclosed in the above-referenced
U.S. Pat. No. 5,067,207. As set forth above, the flange portion 24
is not driven into the panel as disclosed in the above-referenced
U.S. Patents, but is incrementally squeezed radially into the
spaced concave surfaces 42 by the cylindrical surfaces 44 between
the concave surfaces, thereby providing superior torque resistance
particularly in thin panels having a thickness of 0.030 to 0.040
inches while avoiding the problems associated with the prior
methods of installation as discussed further below. As set forth
above, the shank portion 22 failed during torque testing without
any rotational movement of the fastener in the panel assembly.
[0032] As set forth above, the relationship between the area of the
annular bearing face 38 and the spaced concave surfaces 42 is
important in the self-piercing fastener 20 and method of
installation of this invention. First, the bearing face 38 must be
sufficient to prevent axial deformation or cold working of the
flange portion which occurs with the prior methods of installation
particularly in an "overhit" condition of the die press although
the method of installing the self-piercing fastener 20 in a panel
is significantly less press sensitive than the prior methods
described in the above-referenced U.S. Patents. This is because the
radial flange portion 24 is not driven into the panel 50 and the
panel portion 56c remains unsupported radially in the die cavity
62. The panel metal does not fill the die cavity 62 even when the
installation is complete as shown in FIG. 14. Further, although in
the preferred embodiment, the concave surfaces 42 are cylindrical,
other concave surfaces may be employed providing superior torque
resistance.
[0033] The preferred dimensional relationship between the annular
bearing surface 38, the concave surfaces 42 and the tubular barrel
26 of the self-piercing fastener 20 of this invention with the
shank portion 22a integral with the radial portion 24 can best be
explained with reference to FIG. 2, wherein the shank portion 22a
is shown in phantom. The area of the annular bearing face 38
surrounding the shank portion 22a is at least five times the
surface area of the spaced concave surfaces or fillets 42 measured
in the plane of the bearing surface 38, more preferably at least
six times. More specifically, the surface area ratio in a 6 mm stud
is 6.3, the ratio for an 8 mm stud is 7.2 and the ratio for a 10 mm
stud is 8.5 Stated another way, the dimension "c" in FIG. 2
measured from the shank portion 22a to the spaced concave surfaces
42 is at least 70 percent of the dimension "d" measured from the
shank portion 22a to the cylindrical outer surfaces 44 between the
spaced concave surfaces. The concave surfaces 42 are also
preferably spaced from the cylindrical external surface 28 of the
tubular barrel portion 26 a distance equal to about 0.75 than the
distance between the cylindrical outer surface 28 of the tubular
barrel portion and the cylindrical external surfaces 44.
[0034] As will now be understood, the self-piercing fastener,
method of installation and die member of this invention provide
superior torque resistance while avoiding the problems associated
with the prior installation methods. As set forth above, the
bearing surface 38 of the flange portion 24 is not deformed
radially or axially relative to the stud portion 22 by the annular
plunger 52 during installation even where the die force is greater
than required for installation. Further, the installation is not as
press sensitive as the prior methods and because the flange portion
is not driven into the panel, stress risers are not created at the
concave surfaces or fillets.
* * * * *