Note: Descriptions are shown in the official language in which they were submitted.
This invention relates *o a method for producing a composite spark
plug electrode. Methods of producing composite center electrodes are taught
by the prior art. United States Patent No. 3,14~,576 granted A~lgust 11,
1964 to Eugen Hagmaier discloses a method for producing a composite center
electrode by superposing a right circular cylindrical plate of a metal of a
good thermal conductivity, such as copper, on a right circular cylindrical
plate of corrosion-resistant metal, such as nickel, within a die and extrud-
ing the plates therethrough to form a rod having a core of good thermal con-
ductivity within a corrosion-resistant shell. The primary disadvantage of
this method is that the length of the rod is limited because the core is
formed with a taper which causes a correspondingly reduced thickness in
walls of the shell as the metal plates are being extruded. This makes it
impossible to assure uniform heat conductivity.
United States Patent No. 3,548,472 granted December 22, 1970 to
~isashi Urushiwara discloses a method for producing a composite center elec-
trode by subjecting a right circular cylindrical billet of corrosion-resis-
tant metal to successive extrusions and drawings to form an elongated cup
having a cavity extending therein, extruding a right circular cylindrical
billet of a metal of a relatively higher thermal conductivity to form a core
having a headed portion with a diameter equal to that of the elongated cup
and a protrudin~ portion of reduced diameter slightly less than that of the
cavity, inserting the protruding portion of the core into the cavity and
pressing the core therein to form an i.ntegral rod which is then subjected to
heat diffusion. A composite center electrode is then formed by cold working
the rod to form a head thereon. Both the elongated cup and the core are
worked separately to dimensions substantially the same as their final dimen-
sions before heat diffusion. Although this method produces a rod having a
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core of uniform diameter within a shell having walls of uniform thickness,
the use of successive extrusions and drawings to form the elongated cup is
uneconomical for mass production.
United States Patent No. 3,857,147 granted December 31, 1~74 to
Terumoto Yamaguchi teaches a method for producing a composite center elec-
trode by subjecting a right circular cylindrical billet of corrosion-resis-
tant metal to only one extrusion step to form a cup having a cavity extend-
ing therein, extruding a right circular cylindrical billet of a metal of a
good thermal conductivity to form a cap having a headed portion with a dia-
meter equal to that of the cup and a protruding portion of reduced diameter
slightly less than that of the cavity, inserting the protruding portion of
the cap into the cavity of the cup, superposing the cap on the cup within a
die and extruding both therethrough to form a rod having a core of uniform
diameter within a shell having walls of uniform thickness. A composite
center electrode is then formed by cold working the rod to form a head there-
on. Although the cup and the cap are worked separately, they are not worked
to their final dimensions until both are extruded together. Hence, the
total number of cold working steps is reduced to make mass production more
fea~ible.
It is an object of the invention to provide a method for producing
a composite spark plug electrode by a reduced number of cold working steps
to make mass production thereof more economically feasible.
It is a further object of the invention to provide a method for
producing a composite spark plug electrode in which only one step is requir-
ed to form a composite billet into an electrode blank having both an upper
headed portion and a lower portion of reduced diameter extending longitudi-
nally therefrom, that is suitable for use as a composite spark plug electrode.
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l'he invention provides a method of forming a bimetal
electrode having a shank of substantiall~ constant diameter Y
extending from a first end to an opposed, radially enlarged head
having a diameter of X, where Y is less than X, said method com-
prising forming a slug of a first metal into a cup having a
diameter of at least X, a closed end, an open end and a tubular
portion with a central cavity therein extending a distanca of Z
from said open end to said closed end, forming a cylindrical core
having a volume substantially equal to but not sreater than that
of the central cavi~y from a different metal, inserting the
cylindrical core into said central opening to form a composite
billet having first and second ends corresponding, respectively,
with the closed and open ends of the cup wherein said core does
not project beyond said open end, extruding a portion of said
: composite billet, first end firstt through an extrusion:orifice of
a die, said orifice having a diameter of Y, and terminating said
extrusion while a portion of said cup remains unextruded having a
diameter of at least X. The electrode blank is suitable for use
as a composite spark plug electrode, but the upper headed portion
thereof can be shaped into a more desirable electrode head con-
figuration.
To assure that the rod of the composite center electrode
has a core of uniform diameter within a shell having walls of
uniform thickness, the Urushiwara and Yamaguchi patents expanded
the Hagmaier patent to include the separate working of the billet
of corrosion-resistant metal and the billet of metal of good
thermal conductivity. The latter step of separately working or
,
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extruding the billet of metal of good thermal conductivit~ to form
a core, in the case of the Urushiwara patent, and a cap, in the
case of the
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Yamaguchi patent, each having a headed and protruding portion, has been
elimina~ed by the instant invention. The right circular cylindrical billet
is not worked separately at all, but simply inserted into the open end of
the cup to form a composite billet which is then extruded. To form the com-
posite center electrode, the ~rushiwara and Yamaguchi patents each include
the step of cold working the rod to form the head thereon. The instant in
vention eliminates this step by extruding all but the terminal portion of the
composite billet to form the upper headed portion of the electrode blank.
Even though the electrode blank is suitable for use as a composite spark plug
electrode, additional cold working can be used to shape the headed portion
thereof into a more desirable electrode head configura~ion.
In the accompanying drawings:-
; Figure 1 is a partially schematic, vertical sectional view show-
ing a right circular cylindrical billet of corrosion-resistant metal after
being sized and then inserted into a cavity of a die wherein the cavity has
closed and open ends.
Figure 2 is a sectional view showing the billet of Figure 1 after
being pierced and back-extruded to form a cup having closed and open ends
and a cavi~y extending concentrically therein.
; 20 ~igure 3 is a sectional view showing the billet of Figure 1 after
being inserted into a cavity of a die wherein the cavity has closed and open
ends and a chamferred surface adjacent to the closed end thereof.
Figure 4 is a sectional view showing the billet of Figure 3 after
being pierced and back extruded to form a cup having closed and open ends, a
chamferred edge adjacent to the closed end thereof~ and a cavity extending
concentrically therein.
Figure 5 is a partially schematic, vertical sectional view showing
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the cup of Figure ~ and a right circular cylindrical billet of metal of high
thermal conductivity prior to being inserted into the cavity of the cup.
Figure 6 is a sectional view showing the billet of Figure 5 after
being inserted into the cavity of the cup and compressed therein to form a
composite billet having filled and closed ends and a chamferred edge adjacent
to the closed end thereof.
Figure 7 is a partially schematic, vertical sectional view showing
the composite billet of Figure 6 after the closed end thereof is inserted
within a close-fitting bore of a die having within the bore an extrusion
orifice.
Figure 8 is a sectional view showing the composite billet of Figure
7 after a plunger is inserted into the bore of the dic against the filled end
of the composite billet and after pressure is applied to the plunger to force
all the composite billet except a terminal portion adjacent to the filled and
thereof through the extrusion orifice to form an electrode blank having the
unextruded terminal portion as an upper headed portion.
Figure 9 is a partially schematic, vertically sectional view show-
ing the electrode blank of Figure 8.
Figure 10 is a sectional view showing the electrode blank of Figure
9 after the upper headed portion is reduced in diameter.
~igure 11 is a sectional view showing the electrode blank of Figure
10 after the upper héaded portion of reduced diameter is subjected to addi-
tional heading.
Referring now in more detail to the drawings, and, in particular
to Figure 1, a back-extruder indicated generally at 10 comprises a die 1]
positioned on a platen 12 and having a right circular bore 13 extending there-
through, a piston 1~ extending through the platen 12 in structural relation-
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ship with a floating ejector 15 which closes a lower opening of the bore 13,
and a plunger 16 of smaller diameter than and insertable into an upper open-
ing of the bore 13. A cavity indicated generally at 17 is formed by walls
of the bore ].3 and an upper surface 18 of the floating ejector 15.
The first step of the method involves the formation o a right
circular cylindrical billet of a corrosion-Iesistant metal into a cup. The
billet can be nickel or nickel alloy which can be formed by drilling or back-
extrusion. In the preferred embodiment, a right circular cylindrical billet
19 of nickel alloy is formed into a cup by a back-extrusion step which com-
prises the following sub-steps. m e billet 19 having an upper concave end
20 is sized to fit tightly against the walls of the kore 13 cmd a convex face
21 of the plunger 16 and is superposed on the upper surface 18 of the float-
ing ejector 15. 'rhe plunger 16 is then inserted into the cavity 17 against
the upper concave end 20 of the billet 19. Referring to Pigure 2, pressure
is applied to the plunger 16 which pierces the billèt l9 ~See Figure 1) and
causes back-extrusion thereof to form a cup 22 having closed and open ends
23 and 24 and a cavity indicated generally at 25 with walls 26 extending con-
centrically therein to a lower concave surface 27. After the plunger 16 is
extracted from the cavity 25 of the cup 22~ pressure is applied to the piston
14 which causes the floating ejector 15 to Eorce the cup 22 out of the cavity
17 of the die ll.
Referring to Figure 3, another back-extruder indicated generally
at 28 is similar to the back-extruder lO in Figure 1 and comprises a compo-
site die 29 positioned on the platen 12 and having a right circular upper
bore 30 extending therein *o a chamferred shoulder 31 reducing in diameter to
a lower bore 32 extending therethrough, the piston 14 extending through the
platen 12 in structural relationship with a floating ejector 33 which fills
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the lower bore 32, and the plunger 16 of smaller diameter than and insertable
into the upper bore 30. A cavity indicated generally at 34 is ormed by walls
of the upper bore 30, an upper surface 35 of the floating ejector 33, and
walls of the chamferred shoulder 31 extending therebetween. In ~he preferred
embodiment, the back-extrusion step discussed hereinabove is accomplished in
this back-extruder 28 rather than the other. The billet 19 is sized to fit
tightly against the walls of the upper bore 30 and is seated on the chamferr-
ed shoulder 31 therein. After the plunger 16 is inserted into the cavity
34, and referring to Figure 4, the plunger 16 pierces ~he billet 19 ~See
Figure 3) to form a cup 36 having closed and open ends 37 and 38, a chamferr-
ed edge 39 adjacent to the closed end 37 thereofl and a cavi~y lndicated
generally at 40 having walls 41 extending concentrically therein to a lower
concave surface 42.
The next step of the method involves the formation of a com-
posite billet. Referring to Figure 5, a close-fitting right circular cylin-
drical billet 43 of a metal having a high thermal conductivity is inserted,
as indicated by an arrow, into the open end 37 of the cup 36 to fit
tightly against the walls 41 o the cavity 40 thereof to form a composite
billet. In the preferred embodiment, the billet 43 is copper and is
,
compressed within the cavity 40 of the cup 36 to force a lower end 44 and
the cylindrical walls thereof into close-fitting relationship with the
lower concave surface 42 and the walls 41 of the cavity 40 of the cup 36.
This step forms a composit0 billet indicated generally at 45 in Figure 6
having closed and filled ends 46 and 47 and a chamferred edge 48 adjacent
to the closed end 46 thereof. The purpose of forming an edge adjacent to
the closed end 46 of the composite billet 45 is to guide a composite billet
45 as it is forced through a forward-extruder. Hence, the chamferred
edge 48 can be of any other configuration sufficient to accomplish that pur-
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pose.
The final step of the method involves the formation of an electrode
blank from the composite billet 45. Referring to Pigure 7, a forward-extrud-
er indicated generally at 49 comprises a die 50 having a right circular upper
bore 51 extending therein to a concave shoulder 52 reducing in diameter to
form an extrusion orifice 53 which then enlarges in diameter to a lower bore
54 extending therethrough. The upper bore 51 has a diameter sufficiently
large to receive the composite billet 45 in a close-fitting relationship.
The forward-extruder 49 also comprises a plunger 55 having a diameter equal
to that of the upper bore 51 and insertable therein~ and a stud 56 extending
concentrically from a lower end thereo~. The stud 56 has a diameter equal
to that of the copper billet 43 ~see Figure 5) and a depth no greater than
one hal the diameter thereof.
In the preferred embodiment, the closed end 46 of the composite
billet 45 is inserted into the upper bore 51 of the die 50. The plunger 55
is then inserted into the upper bore 51 of the die 50 against the filled
end 47 of the composite billet 45. Referring to Figure 8~ pressure is appli-
ed to the plunger 55 which forces all of the composite billet 45 except a
terminal portion adjacent to the filled end 47 thereof through the extrusion
orifice 53 of the die 50 to form an electrode blank indicated generally at
57 having the unextruded terminal por~ion as an upper headed portion 58 and
a rod 59 of reduced diameter extending longitudinally therefrom as a lower
portion of a diameter equal to that of the extrusion orifice 53 and a length
greater than that of the composite billet 45 (See Figure 7). The electrode
blank 57 is then removed from the die 50 through the upper bore 51 thereof.
The rod 59 of the electrode blank 57 has a core 60 of sufficient-
ly uniform diameter within a shell 61 having walls of sufficiently uniform
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thickness to assure uniform heat conductivity. Even though the electrode
blank 57 is suitable for use as a composite spark plug electrode, a specific
application sometimes necessitates the additional step of shaping the upper
headed portion 58 of the electrode blank 57 into a more desirable electrode
head configuration. For example, the upper headed portion 58 of the electrode
blank 57 in Figure 9 comprises an under head 62 formed by the concave surface
of the shoulder 52 of the die 50, a side head 63 formed by walls of the upper
bore 51 of the die 50, and a recessed upper core surface 64 of copper concen-
tric within a stepped lip 65 of nickel and formed by the stud 56 extending
from the lower surface of the plunger 55 (see Figures 7 and 8).
In the preferred embodiment, the side head 63 of the upper headed
portion 58 of the electrode blank 57 is reduced in diameter by cold working
to form an upper headed portion 58' of an electrode blank 57' having a cham-
ferred under head 62' of reduced diameter, a side head 63' of reduced dia-
meter and increased height, and a recessed upper core surface 64' of reduced
diameter concentric with a rounded lip 55' of reduced diameter as illustrat-
ed in Figure 10. The under head 62' and the rounded lip 65' of the upper
headed portion 5&' are then flattened to form an upper headed por~ion 58"
of a composite spark plug electrode 57" having a chamferred under head 62"
of a reduced angle, a side head 63" of reduced height, and a recessed upper
core surface 64" of reduced diameter concentric with a round lip ~5" flatten-
ed to substantially cover the upper core surface 64" as illustrated in Figure
ll. The composite spark plug electrode 57" is now suitable for the specific
application referred to above.
