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The prospect of micro/nano technology requires the development of advanced production processes which joins them into complex systems to interact with the macro world. This has led to the evolution of micro welding. During the micro welding process, the flow of heat needs to be checked so that the essential mechanical and electrical properties of the material are not lost. Also, the amount of melting and excess evaporation has to be controlled. These can be attained by welding using localized heat sources. In the present work, electron beam micro welding process is studied and heat transfer analysis has been carried out numerically, to obtain the temperature distribution in the material. For a specified depth of melting, the effect of Peclet number on the welding process is investigated. The study shows that the high Peclet number electron beam micro welding process provides two important advantages — Control of the maximum temperature on the surface which prevents excess material loss, and limited heat transfer under the beam.

A three-dimensional finite element model of micro electron beam welding is developed where the Kanaya-Okayama heat source formulated in Part I of this work is used to represent the electron beam. The large number of process variables is grouped into two non-dimensional parameters, namely, Peclet number and relative beam penetration, and their effect is analysed numerically to arrive at the optimum conditions of microwelding. Based on the minimum heat input of the process, the optimum Peclet number is found to be 100, and the beam penetration is twice that of the weld depth. The optimum parameters obtained using the Kanaya-Okayama heat source model are similar to the previous findings using the exponential decay heat source model; however, the predictions of the temperature field in the solid as a result of microwelding are relatively lower in case of the Kanaya-Okayama heat source model because of the differences in distribution of heat into the condensed matter. The lower weld surface temperatures in microwelding using the electron beam suggest significantly less ablation than in laser beams.

A three-dimensional distributed heat source model is developed to represent an electron beam as a heat source, which is novel to micro electron beam welding. The power distribution across the cross-section of the beam is represented by a Gaussian function. Along the penetration depth in the solid, the energy decay of the electrons is modelled according to the electron penetration theory proposed by Kanaya and Okayama. Further, this study presents for the first time a theoretical approach to calculate the heating efficiency of an electron beam as a function of the atomic number of the target material only.