ELECTRON BEAM

Critical evaluation of electron beam and laser based additive layer manufacturing technologies

Critical Evaluation Of Electron Beam And Laser Based Additive Layer Manufacturing Technologies

Introduction

Due to the trend in direct manufacturing of high-quality metal goods, the importance of the corresponding additive layer manufacturing process is increasing. It is therefore essential, to reliably produce parts with defined requirements like density, stiffness or hardness. This especially includes parts, which are exposed to high strains or must fulfil high demands concerning lightweight construction.

Up to now, the additive layer manufacturing of metal parts was dominated by the use of laser beam systems. Despite to the advantages of the additive layer manufacturing technologies. Restrictions exist for the laser based systems regarding the use of different metal materials, the achievable building speed and the porosity of the parts. For example, especially the mirror galvanometers are limiting the process. First, the restricted thermal capacitance of the mirrors is restraining the applicable beam power (Cao, 2008, 89).

Second, a high inertia of the mirrors within the scanning system prevents that the track accuracy is adhered adequately also by a high scanning speed. As a result, the economic use of high-alloyed metals (e.g. tool or stainless steel) is limited. This prohibits a more extensive use of additive layer manufacturing technologies for example in the aerospace industry or the medical technology. It is necessary to solve the described difficulties to establish the additive layer manufacturing technologies for an industrial use. The electron beam as an energy source for the selective melting of powder materials is therefore a promising approach.

State of the art

The electron beam technology has been established in nearly all metal processing and in a number of other areas. Electron beam generators can possess a power reaching from several Watts up to some hundreds of Kilowatts.

They are used for electron-microscopy (low power), for vaporization systems (high power) and for non-thermal processes. Commonly manufacturing technologies, applying an electron beam are assigned to the group joining (e.g. eb-welding), machining (e.g. eb-drilling), coating (e.g. eb-coating) and the change of material properties (e.g. eb-hardening).

Furthermore, the improved beam guide enables, together with the increasing computer technology, the control of the beam deflection up to 50 MHz. It is therefore possible to realize complex beam deflection figures. In the area of the additive layer manufacturing the idea of using the electron beam as an energy source was pursued. In particular, it had the objective to increase the building speed and to use alternative materials. The disadvantages of the laser based technologies should be compensated by that approach.

The basic procedure of Electron Beam Sintering (EBS) is similar to the laser based technologies. First papers with a description of the electron beam as an energy source for direct manufacturing were published in 1992. In 1997, patents led to the foundation of the Swedish company ARCAM. ARCAM as an equipment manufacturer distributes the two systems EBM S12 and A2. Tamminger et al. and Dave uggested the use of wire feed systems to ...