Abstract：The workpiece formed by electron beam melting powder do not need heat treatment ，only surface treatment
was used. However，the diameter of the raw powder used in electron beam melting powder is larger than that
in other melting powder forming methods，it is more difficult to eliminate pores inside the workpiece. This article
describes the fusion mechanism of electron beam melting powder and the process of pore disappearance based on
powder fusion theory and testing. In the research，the electron beam melting and forming process is divided into
three stages and the electron beam input energy is limited by the internal porosity and the shrinkage rate of the particle
fusion line. The results show that at the initial stage of fusion，the small-sized powder particles almost completely
melted into the large particles after the discrete powder was preheated，and the particles were connected to
be a polymerization neck. In the mid-stage of fusion，large-volume voids formed in the powder present columnar
structures because of the surface tension of molten pool and they are connected with each other. At the end of fusion，
due to material mass transfer by diffusion and surface tension，pores are gradually eliminated，and the density
is close to the theoretical density. The result shows that it is feasible to limit the input energy of electron beam by
controlling fusion line shrinkage and porosity. At the same time，the fusion control mechanism and practical test
are put forward for directing different powder melting forming technology.
2020, Vol. 30 
