Water jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces

To characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average Rq derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet.