Press forming method for metal sheet and frame part for automotive body manufactured thereby

A method of press forming a metal sheet with a blank holder, a punch and an upper die comprising:

• supplying fluid with a kinematic viscosity of 500 mm2/s or lower (40° C.), as a lubricant, to a space between the metal sheet and the blank holder, a space between the metal sheet and the punch, and a space between the metal sheet and the upper die;
• starting forming of the metal sheet by contacting the metal sheet with the punch while the metal sheet is held by the blank holder and the upper die;
• before the punch reaches a stroke end and forming is completed, detaching the blank holder from the metal sheet;
• and
• resuming forming of the metal sheet using the punch, the upper die, and the blank holder,
• wherein dies, a surface roughness of which is an arithmetical mean roughness Ra of 7.5 μm or smaller, are used as the punch, the upper die, and the blank holder.

A method of press forming a metal sheet with a blank holder, a punch and an upper die comprising:

• supplying fluid with a kinematic viscosity of 500 mm2/s or lower (40° C.), as a lubricant, to a space between the metal sheet and the blank holder, a space between the metal sheet and the punch, and a space between the metal sheet and the upper die;
• starting forming of the metal sheet by contacting the metal sheet with the punch while the metal sheet is held by the blank holder and the upper die;
• before the punch reaches a stroke end and forming is completed, detaching the punch from the metal sheet;
• and
• resuming forming of the metal sheet using the punch, the upper die, and the blank holder,
• wherein dies, a surface roughness of which is an arithmetical mean roughness Ra of 7.5 μm or smaller, are used as the punch, the upper die, and the blank holder.

A method of press forming a metal sheet with a blank holder, a punch and an upper die comprising:

• starting forming of the metal sheet by contacting the metal sheet with the punch while the metal sheet is held by the blank holder and the upper die;
• before the punch reaches a stroke end and the forming is completed, detaching the upper die from the metal sheet;
• and
• resuming forming of the metal sheet using the punch, the upper die, and the blank holder.

A method of press forming a metal sheet with a blank holder, a punch and an upper die comprising:

• starting forming of the metal sheet by contacting the metal sheet with the punch while the metal sheet is held by the blank holder and the upper die;
• before the punch reaches a stroke end and the forming is completed, detaching the blank holder from the metal sheet;
• detaching the metal sheet from the upper die using a tool;
• and
• resuming forming of the metal sheet using the punch, the upper die, and the blank holder.