Importance

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Abstract

The present invention relates to a composite spark plug center electrode having a sparking tip composed of a precious or semi-precious metal and a method for producing same is disclosed. A right circular cylindrical billet of a corrosion-resistant material is initially formed into a cylindrical cup having an opened end and a closed end. A small conical recess may be formed in the center of the exterior of the closed end during the formation. A hole is next formed in the closed end of the cup. A right circular cylindrical billet of a high thermal conductivity material is next inserted within the opened end of the cup and pressed to fit tightly against the sidewall and bottom of the cup cavity to form a composite billet. An insert formed of a precious or semi-precious metal is then inserted within the hole and pressed to fit tightly therein. The opened end of the cup is formed inwardly to partially encase the billet therein. The composite billet and precious metal insert are inserted within a close-fitting bore of a die having an extrusion orifice. A plunger is inserted within the bore of the die against the filled end of the composite billet to extrude all but a terminal portion of the composite billet, adjacent the filled end thereof, through the extrusion orifice to form a center electrode blank. The opposite end of the center electrode blank containing the precious metal insert is extruded a second time to form a reduced diameter portion. Lastly, the opposite end of the center electrode blank is ground to provide a flat end surface, while the terminal end thereof is ground to provide a precise longitudinal dimension of the center electrode blank.

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First Claim