Transient Physical Effects in Electron Beam Sintering

The extensive use of the electron beam in manufacturing processes like welding or perforating revealed the high potentials for also using it for solid freeform fabrication. First approaches like feeding wire into a melt pool have successfully shown the technical feasibility. Among other features, the electron beam exhibits high scanning speed, high power output, and beam density. While in laser-based machines the fabrication is working in a stable way, transient physical effects in the electron beam process can be observed, which still restrict process stability. For instance, a high power input of the electron beam can result in sudden scattering of the metal powder. The authors have developed an electron beam freeform fabrication system and examined the above mentioned effects. Thus, the paper provides methods in order to identify, isolate and avoid these effects, and to finally realize a reproducible process. Introduction Since the introduction of the first metal processing additive layer manufacturing machines in 1994, their development is proceeding with an enormous speed. Meanwhile, eight different companies are competing on the world market [1]. For all machines, the process implied is almost similar: A laser beam is used to solidify metal powder which is formed in layers. Most obvious distinctive features are the means of positioning the laser spot on the building plate, the composition of the powder material and the mechanical realization of forming a powder layer. At least one equipment manufacturer, the Swedish company ARCAM AB, has started the usage of an electron beam as an energy source for the solidification of the powder. The enormous potentials of this energy source [2] have been implied partially with a machine receivable on the market. Up to now, only a few independent scientific papers deal with the material related quality of the parts built on such a machine.