Patent ID: 8128446

Claim:
A method for manufacturing an insulator for a spark plug, the method comprising: a preparing step of preparing a press pin and a forming die having a cavity extending in an axial direction, the forming die defining a rear end side in the axial direction and an opposite, tip side in the axial direction and further having an opening of the cavity in the rear end side; a press pin arranging step of arranging the press pin within the cavity by advancing the press pin toward the tip side of the forming die in the axial direction from the opening; a powder filling step of filling powder into the cavity from the opening; a cavity blocking step of blocking the opening with a blocking member; a compression molding step of pressing the powder and the press pin within the cavity to form a compact, said compact integrating with the press pin; a die releasing step of releasing the integrated compact and press pin from the cavity; a press pin removing step of removing the press pin from the integrated compact after the die releasing step to obtain the compact having a hole extending in the axial direction, wherein the press pin has a first shaft portion at the tip thereof and having a predetermined length in the axial direction, a second shaft portion at the rear end side of the first shaft portion and having a larger diameter than the first shaft portion and a stepped portion located between the first shaft portion and the second shaft portion, wherein, in the press pin arranging step, the press pin is stopped at a position distanced from a final position by a stroke that is shorter than the axial length of the first shaft portion, and wherein, in the cavity blocking step, the press pin is moved by the stroke to reach the final position so that the blocking member concurrently or subsequently blocks the opening.