CA1198952A - Method for producing a composite center electrode - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An improved method for producing a composite center electrode for a spark plug is disclosed. The method comprises the steps of forming from a corrosion-resistant metal a cup having a closed end, walls extending upwardly from the closed end to an open end and a cavity extending concentrically therein, and then forming a composite billet having closed and filled ends by inserting into the open end of the cup a billet of a metal having a high thermal conductivity and fitting tightly within the cup walls. The method also includes extruding the composite billet into an electrode blank having an upper headed portion and a lower portion of reduced diameter extending longitudinally therefrom. The improvement comprises the steps wherein the positions and the relative sizes of the billet and of the cup are controlled so that the former fits tightly within the cup walls adjacent the closed cup end, but terminating short of the open cup end so that the cup walls extend thereabove at the open cup end, and the cup walls adjacent the open cup end are rolled radially inwardly to form the composite billet. The method includes the additional improvement wherein the closed end of the composite billet is first inserted into a die having a stepped bore including an extrusion orifice of reduced diameter equal to that of a desired electrode head, and is then forced through the extrusion orifice to form an elongated composite billet. The elongated billet is inserted into a second die having a stepped bore including an extrusion orifice of reduced diameter, wherein all except an upper headed portion is forced through the extrusion orifice to form the composite center electrode.

Description

The instant invention is based on the discovery of an improved method for producing a composi-te center eLectrode for a spark plug.
~ ccording to -the in~elltion there is provided a method :For producing a composite center electrode :Eor a sp~r]i pl.ug, said method comprising forming from a corrosion-resistant meta:l a cup havincJ a closed end, a wall extending upwardly from tihe closed end to an open end and a cavity therein extending a distance Z from the closed end to the open end, forming a composite billet having closed and filled ends by inserting into the open end of the cup a close-fitting slug of a metal having a high thermal conductivity, rolling the cup wall adjacent the~pen cup end radially inwardly to form an improved composite billet in whi.ch the slug is at least partially enclosed by the inwardly rolled cup wall, said improved composite billet having first and second ends corresponding, respectively, with the open and closed ends of the cup, and extrùding the improved composite billet, second end first, into an electrode blank having an upper headed portion having a diameter of X and a lower portion having a diameter of Y extending longitudinally therefrom, where Y is less than X, said distance Z being greater than the length of said slug by an amount sufficient to permit the cup wall to be rolled inwardly over the slug without forcing the slug away from the closed cup and to permit confinement of -the slug by the inwardly rolled cup wall during extrusion by forcing the slug into in-timate contact with the closed cup end.
The invention also provides an electrode for spark plugs or the like, comprising a core -formed of one metal, such as copper or the like, and an outer surface of an outer metal completely encapsulating said core, said electrode being Eormed by seating the core metal wi-thin a cup-shaped body o.E said outer metal to form a composite, extrudillg cup end :Eirst the composite~ pal^tly throucjh an extrusioll die while maintclining substantially compl.ete contact between said cup eud and the core metal, said extrusion al.so shaping the unextruded open end of the cup to encapsulate the core and to form a protruding weld lug o:E said outer metal opposite the extruded cup end, located centrally in said extrusion die.
Preferably, the open cup encl, with the sluy positioned in the cavity thereof, is first inserted into a die having a cavity extending longitudinally therein to a lower concave surface and into whieh the cup Eits tightly, and then forced against the concave sur:Eace to roll the cup walls adjacent the open cup end radially inwardly to form the composite billet.
Preferably also, the closed end of the composite billet is first inserted into a die having a stepped bore including an upper bore in which the billet fits closely and an extrusion orifice of reduced diameter equal to that of a desired electrode head, and is then forced through the extrusion orifice to

- 2 -form an elongated composite billet having closed and filled ends, whereupon the closed end of the elongated composite billet is inserted into a second die having a stepped bore including an upper bore in which the billet fits closely and an extrusion arifice of reduced diameter, and all e~cept an upper headed portion adjacent to the filled end of the elongatsd hillet is forced through the extrusion orifice to form the composi-te center electrode. Therefore, the upper headed portion of the composite center electrode does not need shaping because the composite billet was first extruded to the desired diameter.
In the accompanying drawings:
Figure 1 is a partially schematic, vertical sectional view showing a corrosion-resistant metal cup and a right circular cylindrical billet of metal of hi~h thermal conductivity prior to being inserted into the cup in accordance with a previously ~nown method Figure 2 is a sectional view showing a composite billet formed from the cup and billet of Figure 1.
Figure 3 is a partially schematic, vertical sectional view showing the composite billet of Figure 2 inserted into a bore of a die having within the bore an extrusion orifice.
Figure 4 is a sectional view showing an electrode blank formed from the composite billet of Figure 3 after all except a terminal portion thereof is forced through the extrusion orifice.
Figure 5 is a partially schematic, vertical sectional view showing a right circular cylindrical billet of corrosion-resistant metal inserted into a cavity of a die in accordance with the present invention.
Figure 6 is a sectional view showing a cup formed by back-extruding the billet of Figure 5.
Figure 7 is a partially schematic, vertical sectional view showing a 5~

right circular cylindrical billet of metal of high thermal conductivity prior to being inserted into the cup of Figure 6.
Figure S is a sectional view showillg the billet of Figure 7 inserted into the cup in Figure 7.
Figure 9 is a partially schematic, vertical sectional view showing the billet and the cup of Figure 8 inserted into a cavity of a die.
Figure 10 is a partially schematic, vertical sectional view showing a composite billet formed from the cup and the billet within the cavity of the die of Figure 9, and inserted into a bore of a die having within the bore an extrusion orifice.
Figure 11 is a sectional view showing an electrode blank formed from the composite billet of Figure 1~ after all except an upper headed portion there-of is orced through the extrusion orifice.
Figure 12 is a partially schelllatic, vertical sectional view showing the electrode blank of Figure 11 positioned in a die havillg a stepped bore including an upper bore, a shearing shoulder~ a second shoulder and a lower bore.
Figure 13 is a partially schematic, vertical sectional view showing a composite center electrode formed by shearing the upper headed portion of ~he electrode blank of Figure 12.
Figure 14 is a partially schematic~ vertical sectional view showing a col~osite billet formed from the cup and the billet within the cavity of ~he die of Figure 9, and inserted into a bore of a die having within the bore an extrtl-sion orifice equal in diameter to that of a desired electrode head.
Figure 15 is a sectional view showing an elongated composite billet formed by forcing the composite billet of Figure 14 through the extrusion orifice and, thereabove, a second composite billet in a partially deformed condition.

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Figure 16 is a partially schematic, vertical sectional view showing the elongated composite billet of Figure 15 inserted into a bore of a die having within the bore an extrusion oriEice.
Figul^e l7 is a sectional view SllOWillg cl composite center electrode formed from -tlle elongatecl billet of l`igure 16 aEter all except an upper he.lded portion thereof is forced through the extrusion orifice.
Referring to Figure 1, one method for producing composite center electrodes involves first forming a cup 10 from a corrosion-resistant me-tal, such as nickel. The cup 10 has a closed end 11, walls 12 extending upwardly from the closed end 11 to an open end 13 and a cavity 14 extendin~ concentrically therein to a lower surface 15. ~ composite billet is then formed by poSitioning interiorly oE -the cup 10 a close-Eitting right circular cylindrical billet 16 of a metal having a high thermal conductivity, such as copper. The billet 16 fits tightly within the cup walls 12 to form a composite billet indicated generally at 17 in Figure 2, having closed and filled ends 18 and l~.The method further involves in-serting the closed end 18 of the composite bille-t 17 into a die in-dicated at 20 in Figure 3, having a stepped bore 21 including an upper bore 22 in which the billet 17 fits closely and an extrusion orifice 23 of reduced diameter relative to the upper bore 22.
Pressure is then applied to a plunger 24 to force all except a terminal portion 25 (Fiyure 4) oi the billet 17 -through the ex-trusion orifice 23. An electrode blank 26 thus formed has the unextruded terminal portion 25 as an upper headed portion, a lower portion 27 of reduced diameter extending longitudinally therefrom, and a copper core 28 extending therein. After the electrode blank 26 is removed from the die 20, it i$ suitable for use as a composite center elec-trode for a spark plug. If desired, however, the upper headed portion 25 can be shaped by cold-working or further extrusion into a more desirable electrode head configur-ation. An electrode assembly is formed by weldin~ ~ metal rod (not i]lustrated) to the upper headed portion 25 of the electrode blank 26. The primary disadvantage of the method just described is the difficulty involved in welding the rne-tal rod to the head 25 because the amount of nickel remaining after the copper core 28 has been extruded therein is insufficient.
The present invention relates to an improved method for producing a composite center electrode for a spark plug as de-scribed in detail hereinafter.
Referring to Figure 5, a back-extruder indicated generally at 29 comprises a die 30 positioned on a platen 31 and having a right circular bore 32 extending therethrough. The back-extruder 29 also comprises a piston 33 extending through the platen 31 in structural relationship with a 10ating ejector 34 which closes a lower opening of the bore 32, and a plunger 35 having a diameter less than that of the bore 32 and insertable therein, and having a lower surface 36. A cavity indicated generally at 37 is formed by walls of the bore 32 and an upper surface 38 of the floating ejec-tor 34.
The first step of the method involves forming a cup from a right circular cylindrical billet of a corrosion-resistant metal, cuch as nickel or nickel alloy. The cup can be formed by drilling or back-extrusion, the latter of which is preferred and comprises the following sub-steps. A right circular cylindrical - 5a -i2 billet 33 of nickel alloy having an upper end 40 is sized to fit tightly against -the walls of the bore 32 when inserted therein.
~fter the billet 39 is inserted into -the cavity 37 oE the bore 32 and superposed on the upper surface 38 of the floatinc3 ejector 34, the plunger 35 is inserted thereln agclinst the upper. end 40 of the billet 39. I'ressure is then applied to the plun~er 35 which plerces the billet 39 and causes back-extrusion there of to form a cup 41 as illustrated in Figure 6. The cup 41 has a closed end 42, walls 43 extending upwardly from the closed end 42 to an open end 44 and a cavity indicated generally at 45 extend-~i - 5b -ing concentrically therein to a lower surface 46 which corresponds to the shape of the lower surface 36 of the plunger 35. After the plunger 35 is extracted from the cavity 45 of the cup 41, pressure is applied to the piston 33 which causes the float.ing ejector 34 to force the cup 41 out of the cavity 37 of the die 30.
The next step of the met}lod involves forming a composite billet.
Referring to Figure 7, a close-fitting right circular cylindrical billet 47 of a metal having a high thermal conductivity, e. g., copper, is inserted, as indi-cated by an arrow, into the open end 44 of the cup 41 and fits closely within the cup ~alls ¢3. The copper billet 47 is compressed within the cavity 45 of the cup 41 into close-fitting relationship with the lower surface 46 thereof, as shown in Figure 8. The copper bille~ 47 fits tightly within the cup walls 43 adjacent the closed end 42, but terminates short of the open cup end 44 so that the cup ~alls 43 extend thereabove at the open end 44. Referring to Figure 9, a die indicated at 48 has a cavity 49 extending longitudinally therein to a lower con-cave surface 50. After the open cup end 44 is inserted into the cavity 49 of the die 48, a plunger 51 is inserted therein against the closed end 42. Force is then applied to the plunger 51 to roll the cup ~Yalls 43 adjacent the open cup end 44 radially inwardly to substantially enclose the billet 47 and to form a ~0 composite billet 52 having closed and inwardly turned ends 53 and 54 as illus-trated in Figure 10.
The next step of the method involves forming an electrode blank from the composite billet 52. Referring to Figure 10, a orward-extruder indicated generally at 55 comprises a die 56 having a stepped bore 57 including an upper bore 58 in which the billet 52 fits closely and an extrusion orifice 59 of re-duced diameter relative to the upper bore 58. The for~ard-extruder 55 also com-prises a plunger 60 having a diameter equal to that of the upper bore 58 and 5;~

insertable therein) and a lower surface 61. After the closed end 53 of the bil-let 52 is inserted into the Ipper bore 58 of the die 56, the plungcr 60 is in-serted therein against the im~ardly turned end 54 of thc billet 52. Referring to Figure ll~ pressure is then applied to the pl~ulger 60 wllich forces all ex-cept a terminal portion of the billet 52 througll the extrusioll orifice 59 of the die 56 to form an electrode blank indicated generally at 62. The electrode blank 62 has the unextruded terminal portion of the billet 52 as an upper headed portion 63 and a lower portion 64 of reduced diameter extending longitudinally therefrom, and a copper core 65 extending therein. After the electrode blank 62 is removed from the die 56, it is suitable for use as a composite center electrode for a spark plug. If desired, however, the upper headed portion 63 can be shaped by cold-working, further extruding, or shearing into a more de-sirable electrode head configuration. The latter of these is preerred.
The final step of the method involves shearing and shaping the upper headed portion 63 of the electrode blank 6~. Reerring to Eigure 12, a shearing and forming apparatus indicated generally at 66 comprises a die 67 having a stepped bore 68 including a right circular upper bore 69 extending to a shearing shoulder 70 of reduced diameter, a central bore below the shearing shoulder 70 and extending to a second shoulder 71, and a lower bore 72 extending from the second shoulder 71 through the die 67. The first step of the improved method in-volves inserting the electrode blank 62 within the stepped bore 68. ~hen the electrode blank 62 is so inserted, the upper headed portion 63 seats on the shear-ing shoulder 70 and fits closely within the upper bore 69, while the lower por-tion 64 fits closely within the lower bore 72. The shearing and forming appar-atus 66 also comprises a plunger 73 having a diameter substantially equal to that of the shearing shoulder 70 and insertable therethrough, and a lower sur-face 74.

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The plunger 73 is inserted concentrically within the upper bore 69 against the upper headed portion 63 of the 01ectrode blank 62. Pressure is then applied to the plunger 73 to force the upper headcd portion 63 of the electrode blank 62 past the shearing shoulder 70 leav;ng a ri~ng 75 ~Pigure 13) of excess material and against the second shoulder 71 (Figure 12) to form a desired com-posite center electrode indicated generally at 76 (Figure 13). The composite electrode 76 inclucles a head 77 and the rod 64 of the electrode blank 62 (Figures 11 and 12). The electrode head 77 (Figure 13) has an upper and under surface 78 and 79 conforming to the shape of the lo~er surface 74 (Figure 12) of the plunger 73 and the second shoulder 71 of the die 67 respectively. Although the lower surface 74 of the plunger 73 is illustrated as being concave it can be of any shape necessary to form the upper surface 78 (Figure 13) desired for the electrode head 77. The electrode head 77 also has a cylindrical side 80 llaving a diameter equal to that of the shearing shoulder 70 (Figure 12) of the die 67. The com-posite center electrode 76 (Figure 13) is then removed from the die (Figurs 12) through the upper bore 69 and is suitable for the desireduse without further cold-working or extruding steps.
The method includes the additional improvement wherein the composite billet 52 ~Figure 10) formed by the cup 41 and the billet 47 within the cavity 49 of the die 48 of Figure 9 is first extruded to the desired electrode head dia-meter. The first step of the method involves forming an elongated composite bil-let from the billet 52. Referring to Figure 14 a forward-extruder indicated generally at 81 comprises a die 82 having a stepped bore 83 including an upper bore 84 in which the billet 52 fits closely and an extrusion orifice 85 of re-duced di~neter relative to the upper bore 84and equal to that of the desired el- -trode head. The forward-extruder 81 also comprises a plunger 86 having a dia-meter equal to that of the upper bore 84 and insertable therein and a lower surface 87.

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After the closed end 53 of the billet 52 is inserted into the upper bore 84 of the die 82, the plunger 86 is inserted therein against the inwardly turned end 54 of the billet 52. Pressure is then applied to the plunger 86 which forces all except a terminal portion of the billet 52 through the extrusion orifice 85 of the die 82. The plunger 86 is withdrawn from the die 82, and a second billet (not shown), similar to the first billet 52, is inserted therein and superposed on the ins~ardly turned end 54 of the first billet 52. The plunger 86 is then re-inserted into the upper bore 84 of the die 82 against the second billet. Refer-ring to Figure 15, pressure is applied to the plunger 86 which compresses the second billet to an intermediate shape 88 and forces the re~;ning terminal portion of the first billet 52 through the extrusion orifice to form an elongated composite billet indicated generally at 89 and having closed and filled ends 90 and 91.
The final step of the method involves forming a composite center electrode from the elongated billet S9. Referring to Figure 16, a second forward-extruder indicated generally at 92 comprises a die 93 having a stepped bore 94 including an upper bore 95 extending to a shoulder 96, and an extrusion orifice 97 of reduced.diameter adjacent and below the shoulder 96. The forward-extruder 92 also comprises a plunger 98 having a diameter equal to that of the upper bore95 and insertable therein, and a lower surface 99. A~ter the closed end 90 of the elongated billet 89 is inserted into the upper bore 95 of the die 93, the plunger 98 is inserted therein, against the filled end 91 of the elongated billet 89. Referring to Figure 17, pressure is then applied to the plunger 98 which forces all except a terminal portion of the elongated billet 89 through the ex-trusion orifice 97 of the die 93 to form a composite center electrode indicated generally at 100. The composite ccnter electrode 100 ~.~s the ~l~xtruded ~erminal portion of the elongated billet 8g a~ ~ head 101, a~d a rod 102 eYtendI~g lo~gi-~ ,:
_9_ tudinally therefrom. The electrode llead 101 has an upper surface 103 conforming to the shape of the lower surface 99 of the plunger 98, a cylindrical side 104 having a diameter equal to that of the upper bore 95 of the clie 93, and an uncler surface 105 conforming to the shape of the sho-llder 96. Altho-lgll thc lower sur-face 99 of the plunger 98 is illustrated as beillg concave, it c~n be of any shape necessary to form the upper surface 103 desired for the electrode head 101.
The composite center electrode 100 is then removed from the die 93 through the upper bore 95 and is suitable for the desired use without further cold-working or extruding steps.

Claims (15)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINFD AS FOLLOWS:

1. A method for producing a composite center electrode for a spark plug, said method comprising forming from a corrosion-resistant metal a cup having a closed end, a wall extending upwardly from the closed end to an open end and a cavity therein extending a distance Z from the closed end to the open end, forming a composite billet having closed and filled ends by inserting into the open end of the cup a close-fitting slug of a metal having a high thermal conductivity, rolling the cup wall adjacent the open cup end radially inwardly to form an improved composite billet in which the slug is at least partially enclosed by the inwardly rolled cup wall, said improved composite billet having first and second ends corresponding, respectively, with the open and closed ends of the cup, and extruding the improved composite billet, second end first, into an electrode blank having an upper headed portion having a diameter of X and lower portion having a diameter of Y extending longitudinally therefrom, where Y is less than X, said distance Z being greater than the length of said slug by an amount sufficient to permit the cup wall to be rolled in-wardly over the slug without forcing the slug away from the closed cup and to permit confinement of the slug by the inwardly rolled cup wall during extrusion by forcing the slug into intimate contact with the closed cup end.

2. A method as claimed in claim 1, wherein said slug of a metal having a high thermal conductivity is a right circular cylindrical billet, and wherein the relative sizes of the right circular cylindrical billet and of the cup are controlled so that the former fits tightly within the cup wall adjacent the closed cup end.

3. A method as claimed in claim 1 wherein the slug is de-formed within the cup, prior to extrusion, to force the former to fit tightly within the latter.

4. A method as claimed in claim 1 wherein the electrode blank is inserted into a die comprising a central bore and an annular shearing shoulder having a diameter greater than Y but less than X and the headed portion of the electrode blank is forced through the shearing shoulder to shear a ring of excess material therefrom.

5. A method as claimed in claim 1, 2 or 4 wherein the ex-trusion step causes the corrosion-resistant metal to cover the metal having a high thermal conductivity completely.

6. A method as claimed in claim 3 wherein the extrusion step causes the corrosion-resistant metal to cover the metal having a high thermal conductivity completely.

7. A method as claimed in claim 1, 2 or 4 wherein, during extrusion, an axially projecting weld lug is formed on the upper portion of the electrode blank.

8. A method as claimed in claim 3 wherein said slug of a metal having a high thermal conductivity is a right circular cylindrical billet, and wherein the right circular cylindrical billet is deformed within the cup, prior to extrusion, to force the former to fit tightly within the latter.

9. A method as claimed in claim 1 wherein the extrusion of the improved composite billet is effected by a force applied thereto through a tool, said force, in addition to causing said extrusion, also fully closing said first end to encapsulate said core, said force being initially applied along an annular zone to cause a weld lug to be formed centrally of said zone.

10. A method as claimed in claim 9 wherein the end of the tool is so shaped that it applies the force which causes the weld lug to be formed.

11. A method as claimed in claim 9 wherein said core and cup, prior to extrusion thereof, but after the former has been positioned in the latter, are forced into close fitting engagement.

12. A method as claimed in claim 1, wherein the improved com-posite billet is one having a diameter greater than X which is extruded, closed end first, through a die to reduce its diameter to X, and is then partially extruded, closed end first, through a second die to reduce a shank adjacent the closed end to a diameter of Y while leaving an unextruded upper headed portion having a diameter of X to form the electrode blank.

13. A method as claimed in claim 12 wherein the extrusion steps cause the corrosion-resistant metal to cover the metal having a high thermal conductivity completely.

14. An electrode for spark plugs or the like, comprising a core formed of one metal, such as copper or the like, and an outer surface of an outer metal completely encapsulating said core, said electrode being formed by seating the core metal within a cup-shaped body of said outer metal to form a composite, extruding cup end first the composite partly through an extrusion die while main-taining substantially complete contact between said cup end and the core metal, said extrusion also shaping the unextruded open end of the cup to encapsulate the core and to form a protruding weld lug of said outer metal opposite the extruded cup end, located centrally in said extrusion die.

15. An electrode for spark plugs or the like, comprising a core formed of a first metal, such as copper or the like, and an outer surface of a second metal completely encapsulating said core, said electrode being formed by seating the core metal within a cup shaped body of said outer metal to form a composite having a first end composed of the outer second metal and a second end composed of the core first metal and the outer second metal, partially extruding the composite, first end first, through an extrusion die while maintaining substantially complete contact between said first and second metals, said extrusion also simultaneously shaping the unextruded open end of the cup to encapsulate the core and to form a protruding weld lug of said second metal on the second end of the composite, located centrally in said extrusion die.