Patent ID: 7690236

Claim:
A hole punching method, comprising: press-expanding a hole punching scheduled portion of a raw material disposed in a molding cavity of a closed die which molds the hole punching scheduled portion of the raw material into a scheduled shape by pressing the hole punching scheduled portion from opposite sides thereof across the hole punching scheduled portion with a pair of large diameter punch and small diameter punch different in diameter and arranged so as to face each other so that unfilled portions remain in the molding cavity; penetrating the small diameter punch into the hole punching scheduled portion of the raw material after the press-expanding so as not to punch and remove a material of the hole punching scheduled portion with the small diameter punch while releasing or after releasing pressurization by the large diameter punch to the hole punching scheduled portion; and penetrating the large diameter punch into the hole punching scheduled portion of the raw material after the penetrating of the small diameter punch so as not to punch and remove the material of the hole punching scheduled portion with the large diameter punch while pulling out or after pulling out the small diameter punch penetrated in the hole punching scheduled portion of the raw material from the hole punching scheduled portion of the raw material, wherein the penetrating of the small diameter punch and the penetrating of the large diameter punch are executed to fully fill the molding cavity with the material of the hole punching scheduled portion of the raw material.