To provide a focal position setting method in a fiber laser machining apparatus capable of highly precisely and stably setting a focal position of laser light to be projected to a workpiece without use of an independent large-scale apparatus.
A fiber laser machining apparatus (51) includes a photo-detector (2c) that detects return light. A fiber laser machining method includes: a return light generation period acquisition step (Step 2) at which predetermined machining is performed as preliminary machining plural times at different focal positions prior to actual machining of predetermined machining, and a return light generation period (T) during which return light is detected by the photo-detector (2c) is obtained at each of the plural times; a set focal position calculation step (Step 4) at which a focal position at which a minimum value (Tm) of the return light generation period (T) is obtained is calculated as a set focal position (Fpm) through curve fitting on the basis of the relationship between the different focal positions and the return light generation periods associated with the different focal positions and obtained at the return light generation period acquisition step (Step 2); and a focal position setting step (Step 5) at which the calculated set focal position (Fpm) is set as a focal position for the actual machining.
Iwa Saki Kokuni
Shunichi Takahashi
Masakazu Ito
Toshio Takamatsu
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