Additive manufacturing (AM) or additive layer manufacturing (ALM) is the industrial

production name for 3D printing, a computer controlled process that creates three dimensional
objects by depositing materials, usually in layers

How Does Additive Manufacturing Work?

Using computer aided design (CAD) or 3D object scanners, additive manufacturing allows for the
creation of objects with precise geometric shapes. These are built layer by layer, as with a 3D
printing process, which is in contrast to traditional manufacturing that often requires machining or
other techniques to remove surplus material.
 1. 3D Model creation step -
First, the designer creates a 3D model of the object to be printed using computer-aided design (CAD)
software or a 3D object scanner. Since the part is a replica of the 3D model, every detail needs to be
correct and fully defined its external geometry.

Although AM can print complex parts and gives the product designer more design flexibility than
conventional manufacturing processes, there are still limitations and rules to adhere to when
designing to achieve the best results.

Figure 1. CAD model

The design guides vary according to the additive manufacturing technology type and material
selection. Equipment manufacturers and AM technology service providers have extensive design
guides on designing parts. Refer to the types of AM technology and their manufacturers to find out
more.

2. STL file creation step

Once the designer is happy with the design, the user converts the CAD file to a standard AM file
format called standard tessellation language (STL), which 3D Systems developed in the late 80s for
use in its Stereolithography (SLA) machines. You can read how the STL file is created and used for 3D
Printing here.

STL file
Most CAD software such as SolidWorks, Inventor and Catia can save any model as an STL file.
However, all printer manufacturers have software to take any CAD formats and convert the files into
an STL file.

As the name suggests, this will tessellate the 3D shape and slice the part into digital layers. The layer
thickness dictates the final quality and depends on the machine and process.

3. STL file transfer step -

STL file is then transferred to the printer, often using the custom machine software, where the
model will be manipulated to orientate for Printing. Machine software might create its file with extra
information at this stage, such as support structure and temperature.

Machine setup – with support

4. Machine set up -
Each additive manufacturing technology and its variants have its own steps and requirements to set
up a new printing job. Set up includes material selection, orientation, printer temperature, support
structure and build platform levelling. It also involves loading print material, binders, and other
consumables into the machine.

Machine software then converts the STL file information into G-code. G-code instructions are
information for the actuators, such as motors, telling them where to move, how quickly to move,
and what path to take.
 FDM part
(source:materialise.com)

Multiple parts can be set up to reduce the printing cost, and waste can also be minimised by
choosing the correct orientation.

5. Part building -
Once the build starts, it gradually builds the design one layer at a time. A typical layer is around
0.1mm in thickness, but depending on the technology and the material used, it can go down to 20
microns.

Depending on the build size, the printing machine, AM technology, material, and printing resolution,
this build process could take hours or even days to complete.

6. Part removal -
After building the part or multiple parts, in some cases, it may need a cooling-off period before
removing the parts from the machine. Again depending on the machine and technology, removal
could vary from simply peeling off the build platform in case of FDM to wire eroding from the build
plate in DMLS.
 3D-built part with supports

7. Post-processing step -
Almost all the additive manufacturing techniques will require some form of post-processing.
Depending on the AM technology used and the part’s end-use, it varies from simple cleaning and
polishing to machining and heating treating the part.

Finally, post-processing, such as cleaning, polishing, and painting, might be required

Additive Manufacturing Processes -

There are number of distinct AM processes with their own standards, which include:

1. Binder Jetting

This technique uses a 3d printing style head moving on x, y and z axes to deposit alternating layers of
powdered material and a liquid binder as an adhesive.

2. Directed Energy Deposition

Direct energy deposition additive manufacturing can be used with a wide variety of materials
including ceramics, metals and polymers. A laser, electric arc or an electron beam gun mounted on
an arm moves horizontally melting wire, filament feedstock or powder to build up material as a bed
moves vertically.

3. Material Extrusion

This common AM process uses spooled polymers which are either extruded or drawn through a
heated nozzle which is mounted on a movable arm. This builds melted material layer by layer as the
nozzle moves horizontally and the bed moves vertically. The layers adhere through temperature
control or chemical bonding agents.

4. Powder Bed Fusion

Powder bed fusion encompasses a variety of AM techniques including direct metal laser melting
(DMLM), direct metal laser sintering (DMLS), electron beam melting (EBM), selective laser sintering
(SLS) and selective heat sintering (SHS). Electron beams, lasers or thermal print heads are used to
melt or partially melt fine layers of material after which excess powder is blasted away.

5. Sheet Lamination

Sheet lamination can be split into two technologies; laminated object manufacturing (LOM) and
ultrasonic additive manufacturing (UAM). Laminated object manufacturing is suited to creating items
with visual or aesthetic appeal and uses alternate layers of paper and adhesive. UAM uses ultrasonic
welding to join thin metal sheets; a low energy, low temperature process, UAM can be used with
various metals such as aluminium, stainless steel and titanium.

6. Vat Polymerisation

This process uses a vat of liquid resin photopolymer to create an object layer by layer. Mirrors are
used to direct ultraviolet light which cures the successive layers of resin through
photopolymerisation.

7. Wire Arc Additive Manufacturing (Now known as Directed Energy Deposition-Arc (DED-arc))

Wire arc additive manufacturing uses arc welding power sources and manipulators to build 3D
shapes through arc deposition. This process commonly uses wire as a material source and follows a
predetermined path to create the desired shape. This method of additive manufacture is usually
performed using robotic welding equipment.

Additive Manufacturing Technologies

AM technologies can be broadly divided into three types.

The first of which is sintering whereby the material is heated without being liquified to create
complex high resolution objects. Direct metal laser sintering uses metal powder whereas selective
laser sintering uses a laser on thermoplastic powders so that the particles stick together.

The second AM technology fully melts the materials, this includes direct laser metal sintering which
uses a laser to melt layers of metal powder and electron beam melting, which uses electron beams
to melt the powders.
The third broad type of technology is stereolithography, which uses a process called
photopolymerisation, whereby an ultraviolet laser is fired into a vat of photopolymer resin to create
torque-resistant ceramic parts able to endure extreme temperatures.

Advantages and disadvantages of additive

manufacturing -
Advantages of additive manufacturing

 AM can print complex 3D geometries with internal features without any tooling

 Reduced waste compared to machining

 Part can be printed directly from the 3D model without the need for a drawing

 Prototypes can be made quicker, allowing designers to check different iterations resulting in
a quicker design cycle phase

 No or less tooling for smaller batches compared to traditional machining

 Production tooling can be printed

 Different materials can be mixed during the printing process to create a unique alloy

 Different sections of the part can be different variants of the same alloy

Disadvantages of additive manufacturing

 Because the technology is still in its infancy, the build process is slow and costly

 High production costs because of the equipment cost

 Various post-processing required depending on the type of additive manufacturing used

 Small build volume compared to other manufacturing part size such as sand casting

 Poor mechanical properties hence need post-processing

 Poor surface finish and texture compared manufacturing processes like CNC and investment
casting.

 The strength of the parts is comparably weaker compared to manufacturing processes such
as Die casting, Investment casting and CNC machining.