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Electronic theses and dissertations repository


Tesi etd-02032015-190012

Thesis type
Tesi di dottorato di ricerca
Laser Based Processes in Modern Production System
Settore scientifico disciplinare
Corso di studi
relatore Dott. Romoli, Luca
tutor Prof. Dini, Gino
Parole chiave
  • Ultrashort pulsed laser
  • Micro-drilling
  • Laser Welding
  • Spray Holes
Data inizio appello
Riassunto analitico
The main objective of this research is to establish ultrashort pulsed laser in micro-drilling of fuel injector nozzles. The design of the internal nozzle flow is fundamental for the spray development and therefore in the air–fuel mixing and combustion processes due to the increasing concern for environment protection.

Currently, micro-EDM is used to drill micro-holes for fuel injector nozzles. Anyhow this consolidated process is recently facing new challenges which mainly concern the flexibility in changing the hole geometry and the decrease in process time. Laser based techniques are now in attention as alternative to micro-EDM. The aim is to see whether a particular drilling technique other than EDM is able to fulfill the requirement of flow stability and atomization of the spray. This implies evaluating how the surface texture is varying as a function of process parameters and compare the conventional drilling technique with other available alternatives from the point of view of surface quality, edge sharpness and the surface microstructure. Concerning holes characterization, the Scanning Electron Microscopy (SEM) technique allows a rapid survey of large sample areas, but it does not reveal the depth of defects and the three dimensional (3D) surface textures of machined specimens. Therefore, it is needed to find out a reliable and robust measuring technique to acquire 3D topography of the drilled surfaces yielding a better understanding of the size, shape and distribution of peaks and valleys along with their dependence on the adopted process parameters.

Based on the correlation between surface texture and process parameters obtained by experimental study, a drilling strategy is proposed with the aim to reduce coking deposition to avoid the risk of nozzle clogging.

Finally, as a part of fabrication of efficient fuel injector, the dissimilar welding of stainless steel is studied and analyzed to develop weld bead without surface defects.