Review on powder-based electron beam additive manufacturing technology
Manufacturing Rev.
Review on powder-based electron beam additive manufacturing technology
Xibing Gong 1
Ted Anderson 0
Kevin Chou 1
0 Advanced Manufacturing Team, Marshall Space Flight Center , Huntsville, AL 35811 , USA
1 Mechanical Engineering Department, The University of Alabama , Tuscaloosa, AL 35487 , USA
- This paper presents a thorough literature review of the powder-based electron beam additive manufacturing (EBAM) technology. EBAM, a relatively new additive manufacturing (AM) process, can produce full-density metallic parts directly from the electronic data of the designed part geometry. EBAM has gained broad attentions from different industries such as aerospace and biomedical, with great potential in a variety of applications. The paper first introduces the general aspects of EBAM. The unique characteristics, advantages and challenges of EBAM are then presented. Moreover, the hub of this paper includes extensive discussions of microstructures, mechanical properties, geometric attributes, which impact the application ranges of EBAM parts, with focus on commonly used titanium alloys (in particular, Ti-6Al-4V). In the end, modeling efforts and process metrology of the EBAM process are discussed as well.
Electron beam additive manufacturing (EBAM); Geometric attributes; Mechanical properties; Microstructures; Metallic powder; Process modeling; Process metrology
Introduction
Additive manufacturing (AM), also known by various
terms, e.g., direct digital manufacturing, based on
‘‘layer-bylayer’’ fabrications is an emerging technology, by which
physical solid parts are made directly from electronic data, generally
files from computer-aided design (CAD) software. This group
of technologies offers many design and manufacturing
advantages such as short lead time, complex geometry capability, and
tooling free. Electron beam additive manufacturing (EBAM)
is a relatively new AM technology [
1
]. Similar to electron-beam
welding, EBAM utilizes a high-energy electron beam, as a
moving heat source, to melt and fuse, by rapid self-cooling,
metal powder and produce parts in a layer-building fashion.
Moreover, EBAM is one of a few AM technologies capable
of making full-density functional metallic parts, drastically
extending AM applications. In particular, the ability of direct
fabrications of metallic parts can significantly accelerate
product designs and developments in a wide variety of metallic-part
applications, especially for complex components, e.g., fine
network structures, internal cavities and channels, which are
difficult to make by conventional manufacturing means [
1, 2
].
EBAM machines were first commercialized, around 1997,
by Arcam AB Corporation in Sweden. Because EBAM has
many unique characteristics such as high energy efficiency,
high scan speed, and moderate operation cost, the technology
has attracted, in recent years, increased interests from different
industries. The use of an electron beam offers extensive features
such as higher build rates due to increased penetration depths
and rapid scanning speeds. Since then, many research groups
have been studying the EBAM technology from different
aspects and for various applications. Despite the potential
benefits over conventional manufacturing technologies, EBAM still
has a few process deficiencies, such as process stability, part
defects and quality variations [
3
], etc. As EBAM technology
is relatively new, there have not been detailed reviews. The
objective of this paper is to offer a survey of various
investigations into EBAM, especially for the study of the titanium (Ti)
alloy parts, along with the EBAM part microstructures and
associated mechanical properties. In addition, modeling and
simulation of the EBAM process, though rare, for process
understanding and advancements are also discussed.
EBAM details
Process principle
A conceptual schematic of an EBAM machine is shown in
Figure 1 [
2
]. The principle is very similar to that of a scanning
electron microscope. A heated tungsten filament, in the upper
column, emits electrons which are collimated and accelerated
to a kinetic energy of about 60 keV. The electron beam is
controlled by two magnetic coils, which are housed in the lower
column. The first one is a magnetic lens which focuses the
beam to the desired diameter, and the second one deflects the
focused beam to the desired point on a build platform. The
electron-beam gun itself is fixed, no moving mechanical parts
involved in beam deflections. The beam current is controlled
in the range 1–50 mA and the beam diameter can be focused
down to about 0.1 mm. In the chamber of the middle part of
the machine, fine metal powder, on the order of 10–100 lm,
is supplied from two hoppers and forms a thin layer by a raking
mechanism before each layer build. The typical layer thickness
is in the range 0.05–0.2 mm. The computer-controlled electron
beam scans over the powder layer in a predefined pattern and
consolidates the desired a (...truncated)