Patent ID: 7896720

Claim:
A method of producing a spark plug comprising a center electrode which includes a core portion, and a cover portion covering said core portion, wherein said method comprises: a first step of applying a plastic working process on a blank member which is configured by joining a material that will be used as said core portion, to a material that will be used as said cover portion, thereby forming a first intermediate member which is columnar, and in which said cover portion covers said core portion; a second step of applying a plastic working process on said first intermediate member to form a second intermediate member having: a tip end portion; a bulging flange portion which is disposed on a rear end side with respect to said tip end portion, and which has a larger diameter than said tip end portion; and a columnar intermediate portion which is disposed between said tip end portion and said flange portion; and a third step of cutting or polishing a surface of said cover portion of said intermediate portion of said second intermediate member to form said center electrode having a middle trunk portion which is configured by reducing a diameter of said intermediate portion.