Investigation of elimination of powder spreading in manufacture of thin and wide preheating beads from Co–Cr alloy powders using a P-ebeam

A preheating step consisting of the heating of substrates and powder particles is necessary to prevent spreading phenomenon of powders in an electron beam melting (EBM) process. The preheating step, however, increases the overall manufacturing time as well as the energy consumption of the EBM process. In addition, the preheating causes thermal damages of surrounding parts in the vicinity of the powder bed. These drawbacks are particularly notable when both thin and wide parts are fabricated from the EBM process. The present paper newly investigates the manufacture of thin and wide preheated beads from a plasma electron beam (P-ebeam) and a Co–Cr alloy with a low temperature heating of the substrate. The effects of process parameters, including the working distance of P-ebeam, the probe current of the P-ebeam and the travel speed of the table, on the formation of preheated beads are examined to obtain feasible preheating conditions. The influence of the probe current and the travel speed on heat transfer characteristics in the vicinity of the irradiated region by P-ebeam are investigated via finite element analyses to analyze the cause of the powder spreading and defects. Finally, suitable preheating methods are proposed to fabricate thin and wide preheated beads through the elimination of the powder spreading.