Method of projection welding hardware to steel sheet for hot stamping

1. A method of projection welding hardware to a plated steel sheet for hot stamping, the method comprising:

pressing hardware and a plated steel sheet in a state in which a welding projection on the hardware is in contact with the plated steel sheet;

supplying a primary current to the hardware and the plated steel sheet in a state in which the hardware and the plated steel sheet are pressed; and

supplying a secondary current to the hardware and the plated steel sheet,

wherein the primary current has a value of 100% to 150% of the secondary current so that a plated layer of the plated steel sheet is melted and removed, and

wherein the secondary current has a value of a welding temperature.

2. The method of claim 1 , further including cooling the plated steel sheet and the hardware that are heated in the supplying of the primary current, between the supplying of the primary current and the supplying of the secondary current.

3. The method of claim 1 , wherein the primary current is applied for a time period until the welding projection is collapsed by heating so that the plated layer is extruded and removed.

4. The method of claim 3 , wherein the primary current is applied for the time period of 5 cycles or less.

5. The method of claim 1 , wherein the plated steel sheet is an Al—Si-plated steel sheet.

6. The method of claim 2 , wherein, in the cooling the plated steel sheet and the hardware, the plated steel sheet and the hardware are cooled after the supplying of the primary current is stopped.

7. The method of claim 2 , wherein the cooling of the plated steel sheet and the hardware is performed until the plated steel sheet and the hardware are thermally balanced.