• conduction welding
• temperature
• energy density
• stainless steel
• welding
• laser
• analytical modelling
• fuel injectors
• keyhole welding

The purpose of this study is to develop a mathematical model for the analysis of laser welding on stainless steel small-sized components in a regime between pure conduction and keyhole welding. The aim of the model is to predict the temperature field, therefore the shape of molten pool and so weld bead geometry.
This project has a direct application in the manufacturing technology, i.e., laser welding of small parts of Continental fuel injectors . As a matter of fact, in this case, too deep penetration is not required and plasma formation should be minimized but welding speed is not so high as to create a pure conduction regime. This “central” regime appears when the energy density (ED) value is approximately between 15 and 45 J/mm2.
The analytical approach has been chosen in order to create a simple and efficient model suitable for all the situations – similar to this one – in which there is no keyhole formation and ED is included in the aforestated interval. The numerical analysis has been avoided, firstly because of its instability and inefficiency in case of small-sized problems, then because several studies of this kind are already available in literature.
A double moving point source model has been created, whose parameters are functions of energy density. The model has been tuned up using the experimental data collected by Khan et al. [19] and subsequently a further experimental investigation has been carried out in order to validate the results.
Tests show that the model is able to predict the shape of weld bead from the process parameters and the material properties. The model is effective in the penetration depth prediction and in the resistance width estimate but introduces a small error in case of prediction of weld width. The experimental investigation also showed that feed rate variation affects the shape of the molten pool less than the power variation. Furthermore, the energy density can be only considered as a rough index of the heat exchange regime. Using the model it is possible to evaluate the melted region and to predict the temperature field around it. The contour plots of the temperature field show an heavy gradient in the direction perpendicular to velocity vector, both at the surface and under it, and underline an extremely strong gradient in front of the laser beam.
This model may be used – as future development – in order to predict the temperature trend during the time in the melted region and in the heat-affected zone as a function of input power, welding speed and material properties. In this way it may be possible to perform a metallurgical analysis and predict the material properties after welding.