Process for producing the center electrode of spark plug

A process for producing a center electrode for a spark plug comprising the following steps:

• providing a cylindrical electrode body of a less noble metal which is predominantly made of a nickel alloy or a composite thereof with a copper core, said electrode body having a larger diameter portion and a concentric, smaller-diameter projection from the tip of the larger diameter portion of said body;
• placing on the tip of said electrode body a disk which has a center hole into which said projection fits and which is made of a noble metal such as platinum or an alloy thereof;
• electrically welding said noble metal disk to the tip of said electrode body;
• and
• drawing and extruding the assembly to reduce its outside diameter to a diameter less than the original diameter of said larger diameter portion so that the layer of said noble metal or alloy thereof covers at least the side wall of the part close to the tip of said electrode body while leaving exposed a center portion of the end face of said electrode body.