Spark plug electrode and spark plug manufacturing method

1. A method of making a spark plug electrode, comprising the steps of:

a. providing an inner core of a ruthenium (Ru) based alloy or an iridium (Ir) based alloy;

b. providing an outer skin over at least a portion of said inner core to produce a core and skin assembly, said outer skin having platinum (Pt), gold (Au), silver (Ag), or nickel (Ni), or having an alloy of Pt, an alloy of Au, an alloy of Ag, or an alloy of Ni;

c. after said outer skin has been provided over said at least a portion of said inner core, increasing the temperature of said core and skin assembly to a temperature greater than 1,000° C.; and

d. hot forming said core and skin assembly at the increased temperature into an elongated wire, wherein both of said inner core and said outer skin are elongated during the hot forming process.

2. The method set forth in claim 1 , wherein, after hot forming said core and skin assembly, said outer skin has a thickness ranging between approximately 1 μm to 200 μm, inclusive.

3. The method set forth in claim 1 , wherein step (c) includes increasing the temperature of said core and skin assembly to a temperature greater than 1,000° C. but less than approximately 1,500° C.

4. The method set forth in claim 3 , wherein step (c) includes increasing the temperature of said core and skin assembly to a temperature greater than 1,000° C. but less than approximately 1,300° C.

5. The method set forth in claim 1 , wherein step (d) includes hot forming said core and skin assembly at the increased temperature into said elongated wire having a generally circular cross-section.

6. The method set forth in claim 5 , wherein step (d) includes hot forming said core and skin assembly at the increased temperature into said elongated wire having an overall diameter (D) ranging between approximately 0.2 mm to 2.0 mm, inclusive.

7. The method set forth in claim 6 , wherein step (d) includes hot forming said core and skin assembly at the increased temperature into said elongated wire having an overall diameter (D) of approximately 0.7 mm.

8. The method set forth in claim 1 , wherein step (d) includes hot forming said core and skin assembly at the increased temperature into said elongated wire via a co-extrusion process at the increased temperature.

9. The method set forth in claim 1 , further comprising the step of cutting said elongated wire into a plurality of spark plug electrodes.

10. The method set forth in claim 1 , wherein said inner core is a Ru based alloy comprising rhodium (Rh), rhenium (Re), and tungsten (W).

11. The method set forth in claim 10 , wherein said outer skin is an alloy of Pt comprising Ni.

12. The method set forth in claim 1 , wherein step (a) includes providing said inner core via a powder metallurgical process.

13. The method set forth in claim 12 , further comprising the step of providing said outer skin via an extrusion process to produce a hollow piece, and wherein step (b) includes providing said outer skin over said at least portion of said inner core via inserting said inner core into said hollow piece to produce said core and skin assembly.

14. The method set forth in claim 1 , wherein, during the performance of step (d), an alloying layer is produced adjacent an interface between said inner core and said outer skin via diffusion, and, after the performance of step (d), a metallurgical bond exists between said inner core and said outer skin.

15. A spark plug comprising at least one spark plug electrode made by the method of claim 1 .

16. A method of making a spark plug, comprising the steps of:

a. providing a center electrode, an insulator at least partly surrounding said center electrode, a shell at least partly surrounding said insulator, and a ground electrode attached to said shell;

b. providing an inner core via a powder metallurgical process to produce a solid piece, said inner core being of a ruthenium (Ru) based alloy or an iridium (Ir) based alloy;

c. providing an outer skin via an extrusion process to produce a hollow piece, said outer skin having platinum (Pt), gold (Au), silver (Ag), or nickel (Ni), or having an alloy of Pt, an alloy of Au, an alloy of Ag, or an alloy of Ni, wherein said solid piece of said inner core is formed separately from said hollow piece of said outer skin;

d. inserting said solid piece of said inner core into said hollow piece of said outer skin to produce a core and skin assembly;

e. increasing the temperature of said core and skin assembly;

f. hot forming said core and skin assembly at the increased temperature into an elongated wire, wherein both of said inner core and said outer skin are elongated during the hot forming process;

g. cutting said elongated wire into at least one spark plug electrode; and

h. attaching said spark plug electrode to said center electrode or to said ground electrode, or attaching a first spark plug electrode to said center electrode and a second spark plug electrode to said ground electrode.

17. The method set forth in claim 16 , wherein step (e) includes increasing the temperature of said core and skin assembly to a temperature greater than approximately 1,000° C. but less than approximately 1,500° C.

18. The method set forth in claim 17 , wherein step (f) includes hot forming said core and skin assembly at the increased temperature into an elongated wire having an overall diameter (D) ranging between approximately 0.2 mm to 2.0 mm, inclusive.

19. The method set forth in claim 18 , wherein step (f) is performed without said inner core of said core and skin assembly substantially experiencing oxidation and breakage and fracture.

20. The method set forth in claim 19 , wherein, during the performance of step (f), an alloying layer is produced adjacent an interface between said inner core and said outer skin via diffusion, and, after the performance of step (f), a metallurgical bond exists between said inner core and said outer skin.