process development
RM can eliminate
many secondary
manufacturing steps such
as internal machining
operations or secondary
fabrication
Examples of RM
applications include
aerospace and automotive
components
improved, parts were then used as patterns for down
stream casting processes, such as investment, sand or
vacuum casting of low melting alloys into silicon tools.
Hence, Rapid Casting or RC was born. As the accuracy
and repeatability of these early systems improved, parts
were then used as patterns for down stream casting
processes, such as investment (lost wax) casting, sand
casting or vacuum casting of low melting alloys into
silicon tools. Hence, Rapid Casting or RC was born.
In the mid 90’s, developments in ALM systems and
materials allowed manufacture of ‘quasi-metallic’ parts,
directly from 3D-CAD data without the need for
intermediate RC. There processes produced ‘green-state’
parts, metallic powders held together with either
binders or polymers mixed with the metal powder.
These were then fired and infiltrated to achieve their
ultimate strength. The main limitation was that the
final parts, although resembling a production part had
none of the desired mechanical or metallurgical
characteristics, so were very seldom used as end use
production items. However, some technologies were
used to manufacture Rapid Tool (RT) cavities for
injection moulding and die casting.
In the late 90’s advances in laser power and electron
beam control technology allowed development of ALM
systems which could make parts in ‘real’ engineering
metals. With the advent of higher powered solid state
lasers, such as yttrium fiber lasers in the early years of
this millennium, ‘direct’ additive manufacturing in
engineering grade metals has now become a reality.
The polymeric to metallic RM divide? Although
RM is now a relatively mainstream (albeit littleexploited)
production process for polymeric parts, the
process is in its infancy for metallics. This is due to a
lack of understanding of the technologies available, and
their relative immaturity. Moreover, most metallic parts
are subject to greater stresses, loading and
environmental exposure than polymeric parts; so
process and materials validation of metallic RM is a far
greater consideration to end users - which has often
slowed the technology implementation. However, there
is no doubt that true metallic RM will happen.
64 MWP march 2008
Aerospace companies such as Airbus, Boeing, Rolls
Royce, GE, and BAE Systems have all invested in either
direct metal technology platforms or research
collaborations to implement direct metallic RM into
mainstream production.
So what are the processes available for ‘direct’
metallic RM? They fall into three camps: powder bed
systems, powder feed systems and sheet consolidation
systems. However, process must also be considered as
both net shaped and near net shaped. Net shaped parts
are within the manufacturing tolerance to the original
CAD representation, whereas near net parts will require
some form of post process finishing or machining to
achieve their ultimate geometric tolerance.
Where are the current applications for direct
metallic ALM technologies? It would be misleading to
suggest that all direct ALM technologies are being used
for direct part manufacture, as most of the parts
produced are still being used as pre-production form,
fit and function prototypes. This is very much the case
in aerospace where the materials and production
process have yet to be fully validated. However, direct
metallic RM has already been validated in the medial
industry for the manufacture of Orthopaedic Implants,
maxiofacial reconstructive implants and surgical
cutting guides. Direct metallic RM has also been used
in automotive and motorsport applicationsand in the
manufacture of complex tooling cavities and inserts.
Economics and reality Direct metallic ALM is
expensive. Machine tools range from £200K to almost
£1-million, added to material costs of £80/kg for 316L
stainless steel up to £475/kg for titanium 6-4. Given the
relatively slow deposition rate of some technologies, the
resulting parts can seem disproportionately expensive
when compared to cast or even machined parts.
However for many users, the geometric complexity that
is possible with RM, coupled with the economics and
freedom of tool-less manufacture are compelling.
It should be stressed however, that it is not possible to
manufacture all geometries using these systems. Most
notably machines are limited in size. Moreover, certain
geometries can cause problems such with residual stress
during the build cycle, which can result in either
delaminating or more likely fouling with the powder
re-coating system. In truth, operator experience is the
only current way of predicting whether a geometry
will make a successful build.
Dr Phil Reeves (PhD Engineering, BEng Hons
Manufacturing) is the managing director of Econolyst
Ltd, and an experienced business strategist, researcher
and writer on the future of manufacturing industry. He
has spent the last 10-years in a number of roles advising
companies, organisations and governmental bodies on
the emergence of new technologies and how these will
impact on business and society. www.econolyst.co.uk
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