Patent ID: 8183499

Claim:
A laser piercing method in which a laser beam is irradiated onto a processing portion of a workpiece, and at the same time as the laser irradiation, an assist gas is injected toward the processing portion from a nozzle arranged concentric to the laser beam so that the processing portion is covered with the assist gas, thereby processing a piercing hole on the processing portion, wherein a piercing hole processing is performed while moving the nozzle within a range of 5 mm from a processing start point after the laser irradiation is started, an oxygen content C and an injection pressure P of the assist gas are determined on the basis of the thickness of the processing portion, the oxygen content C is determined by the following formulas: for a plate thickness t in the range of 0<t<12.0 mm, the oxygen content C is in the range of 0<C<10; for a plate thickness t in the range of 12.0≦t<13.3 mm, the oxygen content C is in the range of 0<C≦−0.255t 2 +14.5t−127.2; and for a plate thickness t in the range of 13.3≦t≦26.33 mm, the oxygen content C is in the range of −0.255t 2 +14.5t−147.2≦C≦−0.255 t 2 +14.5t−127.2; and wherein the injection pressure P of the assist gas is determined by the following formulas: for a plate thickness t in the range of 0<t<13.0 mm, the injection pressure P is in the range of 0.015≦P≦0.05; and for a plate thickness t in the range of 13.0≦t≦26.33 mm, the injection pressure P is in the range of 0.002t−0.011≦P≦0.002t+0.024, wherein P denotes an injection pressure (MPa) of the assist gas, C denotes the oxygen content (volume %), and t denotes the thickness (mm) of the workpiece.