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In recent years, there has been an almost exponential increase in the number of companies using RM
across a broad range of industrial sectors. Examples of RM applications include aerospace and
automotive components (See Figure 4), packaging, medical implants (See Figure 5), hearing aid
shells and surgical guides, and consumer products as diverse as light shades, furniture and even
football boots.
Figure 5 – Replacement mandible for
maxiofacial reconstructive surgery.
Manufactured in Cobalt Chrome on an MCP
Realizer 100
How did we get to where we are today?
The technologies behind RM have been in existence since the mid to late 1980’s, when processes
with names like Stereolithography (SLA), Fused Deposition Modelled (FDM) and Selective Laser
Sintering (SLS) were introduced as solutions to manufacture prototype parts directly from 3D CAD
data (See Figure 6). Hence, the term Rapid Prototyping or RP was coined. However, in these early
days, the processes produced exclusively polymeric or paper parts. 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 (See Figure 7), sand casting or vacuum casting of
low melting alloys into silicon tools. Hence, Rapid Casting or RC was born.
Direct Rapid Manufacturing of Metallic Parts – A UK Industry overview 2008
Figure 7 – Rapid Casting pattern 3D Printed in
investment casting wax using a 3D Systems
Thermojet modelling system
Figure 6 – Traditional polymeric rapid
prototyping model manufactured using
Selective Laser Sintering of Nylon
During the mid 1990’s, developments in both ALM
systems and materials allowed us to manufacture ‘quasimetallic’
parts, directly from 3D-CAD data without the
need for intermediate Rapid Casting. There processes
produced ‘green-state’ parts made of metallic powders
held together with either binders (See Figure 8) or
polymers mixed with the metal powder. These ‘greenstate’
parts were then fired and infiltrated to achieve there
ultimate strength. The main limitation with this ‘in-direct’
approach, was that the final part, although resembling a
production part had none of the mechanical or
metallurgical characteristics of the desired component.
Hence, these parts 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
Figure 8 – Pro-Metal RX1 in-direct metal 3D
Printing machine using powder and binder
In the late 1990’s advances in both laser power and
electron beam control technology, allowed companies to
develop ALM systems capable of manufacturing 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. (See Figure 9)
The polymeric to metallic RM divide?
Although RM has now become a relatively main steam
(albeit little exploited) production process for polymeric
parts, the process remains in its infancy for metallic parts.
This is largely due to a lack of understanding of the
technologies available but also the relative immaturity of the technologies on offer. Moreover, most
metallic parts are subject to greater stresses, loading and environmental exposure than polymeric
parts. Hence, process and materials validation of metallic RM is a far greater consideration to end
users than for polymeric parts. Again, this has in many cases slowed the technology implementation.
However, there is no doubt that true metallic RM will happen. For example, aerospace companies
Figure 9 – Direct Medical implant
manufactured using ARCAM Electron Beam
Melting
Copyright - Econolyst 2008 www.econolyst.co.uk
3
Direct Rapid Manufacturing of Metallic Parts – A UK Industry overview 2008
such as Airbus, Boeing, Rolls Royce, GE, and BAE Systems have all investing 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?
Direct Metallic ALM processes fall into three camps, powder bed systems, powder feed systems and
sheet consolidation systems. However, processes must also be considered as both net shaped and
near net shaped. Net shaped parts are within the manufacturing tolerance to the original CAD
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