A new strategy of beam motion for the mass production of fuel injector nozzles by fs-laser drilling

A novel strategy of beam motion is proposed with the objective of introducing ultrashort pulsed laser micro-drilling of martensitic stainless steels for the production of fuel injector nozzles. In order to solve the common trade-off between drilling time and precision of the microhole shape the drilling operation was subdivided into three phases: a drilling through phase was preliminary performed to evacuate metal vapors and debris followed by an enlargement phase which generates a remarkable taper on the internal surface. A final finishing phase, performed inclining the laser beam, allows for cylindrical shapes even for aspect ratios (thickness/diameter) of about 2. SEM inspection of the internal surface revealed the presence of laser induced periodic surface structures (LIPSS) whose inclination respect to the hole axis can be predicted taking into account the hole taper at the beginning of the finishing phase. A straightforward model based on Fresnel laws is proposed in order to link LIPSS inclination to the direction of the electromagnetic field on the internal surface which is in turn related to light polarization