Pulsed laser machining method and installation, in particular for welding, with variation of power within each pulse

摘要

The laser machining process comprises generating a laser beam using a laser source having an initial wavelength of 700-1200 nm and formed of many laser pulses, doubling the frequency of a part of the laser beam by a non linear crystal, and changing the power of each laser pulse emitted so that: the profile of power source on the period of the laser pulse is present in an initial sub-period (T1); and a peak of maximum power or a pulse part with a maximum power are present in intermediary sub- period (T2) of duration greater than the initial sub-period. The laser machining process comprises generating a laser beam using a laser source having an initial wavelength of 700-1200 nm and formed of many laser pulses, doubling the frequency of a part of the laser beam by a non linear crystal, and changing the power of each laser pulse emitted so that: the profile of power source on the period of the laser pulse is present in an initial sub-period (T1); a peak of maximum power or a pulse part with a maximum power are present in intermediary sub- period (T2) of duration greater than the initial sub-period; and a power is less than the maximum power on any intermediary sub period. The duration of the initial sub-period is less than 2 ms. The maximum power has a value of greater than 200 W, which is twice higher than the average power over the period of the laser pulse. A unit is arranged for focusing the laser beam, which is not fully compensated chromatically to obtain, at the focal point, a light spot for the light having double frequency that has a diameter of less than the light spot for the light of the initial wavelength. The process further comprises a step of high reflective metal welding. The light intensity having double frequency in combination with the initial light frequency in the power peak or the part of the pulse with the maximum power is greater the threshold of fusion, in initial sub-period, for the combination of light and for the welded material. The intensity of light having dual frequency is 0.1-10 MW/cm 2at focal point. The light intensity at the initial wavelength in the peak of power or the part of pulse with the maximum power is lower, in the initial sub- period, than the threshold of fusion for that light and for the weld metal. The laser pulses have a terminal sub-period in which the power decreases towards zero to optimize the cooling of the performed weld.