Additive manufacturing
Additive manufacturing, also known as 3D printing, rapid prototyping or freeform fabrication, is ‘the
process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to
subtractive manufacturing methodologies’ such as machining. The use of Additive Manufacturing (AM)
with metal powders is a new and growing industry sector with many of its leading companies based in
Europe. It became a suitable process to produce complex metal net shape parts, and not only
prototypes, as before. Additive manufacturing now enables both a design and industrial revolution, in
various industrial sectors such as aerospace, energy, automotive, medical, tooling and consumer goods.
1.1 Vocabulary According to the ASTM standard F2792-10, additive manufacturing is the « process of
joining materials to make objects from 3D model data, usually layer upon layer, as opposed to
subtractive manufacturing methodologies, such as traditional machining.” Additive manufacturing
technologies for metals are numerous, hence the development of a wide variety of terms and acronyms,
as can be seen in the graph below. But today additive manufacturing is the most common term in
industry markets while 3D printing is more used in the consumer market. Fine metal part designed by
Bathsheba Grossman (Courtesy of Höganäs AB - Digital Metal®) The vocabulary of Additive
Manufacturing. In red, most common of standardised vocabulary Gas turbine demonstrator (diameter
250 mm and length 600 mm), by assembling parts made by Selective Laser Melting with Al-, Ti- and Ni-
base powders for integration of functions, reduced number of parts
The benefits of AM technology
Metal additive manufacturing technologies offer many key benefits. Increased design freedom versus
conventional casting and machining Light weight structures, made possible either by the use of lattice
design or by designing parts where material is only where it needs to be, without other constraints New
functions such as complex internal channels or several parts built in one Net shape process meaning less
raw material consumption, up to 25 times less versus machining , important in the case of expensive or
difficult to machine alloys. The net shape capability helps creating complex parts in one step only thus
reducing the number of assembly operations such as welding, brazing. No tools needed, unlike other
conventional metallurgy processes which require molds and metal forming or removal tools Short
production cycle time: complex parts can be produced layer by layer in a few hours in additive machines.
The total cycle time including post processing usually amounts to a few days or weeks and it is usually
much shorter than conventional metallurgy processes which often require production cycles of several
months. The process is recommended for the production of parts in small series.
The limits of AM technology
To take full advantage of AM technologies, it is important to be aware of some limitations: Part size: In
the case of powder bed technology, the part size is limited to powder bed size, such as 250x250x250
mm for standard powder bed systems. However, part sizes can be greater with direct energy deposition
(or laser metal deposition) processes. But, due to the low thickness of powder layers, it can be very slow
and costly building high parts or massive parts. Production series: the AM processes are generally
suitable for unitary or small series and is not relevant for mass production. But progresses are made to
increase machine productivity and thus the production of larger series. For small sized parts, series up to
25000 parts/year are already possible. Part design: in the case of powder bed technology, removable
support structures are needed when the overhang angle is below 45°. Other design considerations to be
taken into account can be seen in chapter 4 about design guidelines. Material choice: though many
alloys are available, non weldable metals cannot be processed by additive manufacturing and difficult-
to-weld alloys require specific approaches. Material properties: parts made by additive manufacturing
tend to show anisotropy in the Z axis (construction direction). Besides, though densities of 99.9% can be
reached, there can be some residual internal porosities. Mechanical properties are usually superior to
cast parts but in general inferior to wrought parts.
Market perspectives
The use of additive manufacturing technology is developing in many industries:
Aerospace
Energy
Medical, in particular in surgical implants and dental applications
Tooling in particular for plastics processing
automotive and transportation
Consumer goods etc.
Additive manufacturing technologies
Selective laser sintering
Selective laser sintering (SLS) is an additive manufacturing (AM) technique that uses a laser as the
power source to sinter powdered material (typically nylon/polyamide), aiming the laser automatically at
points in space defined by a 3D model, binding the material together to create a solid structure. It is
similar to direct metal laser sintering (DMLS); the two are instantiations of the same concept but differ
in technical details. Selective laser melting (SLM) uses a comparable concept, but in SLM the material is
fully melted rather than sintered, allowing different properties (crystal structure, porosity, and so on).
SLS (as well as the other mentioned AM techniques) is a relatively new technology that so far has mainly
been used for rapid prototyping and for low-volume production of component parts. Production roles
are expanding as the commercialization of AM technology improves.
Advantages
A distinct advantage of the SLS process is that because it is fully self-supporting, it allows for parts
to be built within other parts in a process called nesting – with highly complex geometry that simply
could not be constructed any other way.
Parts possess high strength and stiffness
Good chemical resistance
Various finishing possibilities (e.g., metallization, stove enameling, vibratory grinding, tub coloring,
bonding, powder, coating, flocking)
Bio compatible according to EN ISO 10993-1 and USP/level VI/121 °C
Complex parts with interior components, channels, can be built without trapping the material inside
and altering the surface from support removal.
Fastest additive manufacturing process for printing functional, durable, prototypes or end user parts.
Vast variety of materials and characteristics of Strength, durability, and functionality, SLS offers
Nylon based materials as a solution depending on the application.
Due to the excellent mechanical properties the material is often used to substitute typical injection
molding plastics.
Disadvantages
SLS printed parts have a porous surface. This can be sealed by applying a coating such as
cyanoacrylate.
