What Is Additive Manufacturing

What Is Additive
Manufacturing?
Additive manufacturing is the formalized term for what used to be called
rapid prototyping and what is popularly called 3D Printing.
The term rapid prototyping (RP) is used in a variety of industries to describe a

process for rapidly creating a system or part representation before final
release or commercialization. In other words, the emphasis is on creating
something quickly and that the output is a prototype or basis model from
which further models and eventually the final product will be derived.
Users of RP technology have come to realize that this term is
inadequate and in particular does not effectively describe more recent
applications of the technology. Improvements in the quality of the
output from these machines have meant that there is often a much
closer link to the final product. Many parts are in fact now directly
manufactured in these machines, so it is not possible for us to label
them as “prototypes.” The term rapid prototyping also overlooks the
basic principle of these technologies in that they all fabricate parts
using an additive approach.
Referred to in short as AM, the basic principle of this technology is that a model,
initially generated using a three-dimensional Computer-Aided Design (3D CAD) system,
can be fabricated directly without the need for process planning. Although this is not in
reality as simple as it first sounds, AM technology certainly significantly simplifies the
process of producing complex 3D objects directly from CAD data. Other manufacturing
processes require a careful and detailed analysis of the part geometry to determine
things like the order in which different features can be fabricated, what tools and
processes must be used, and what additional fixtures may be required to complete the
part. In contrast, AM needs only some basic dimensional details and a small amount of
understanding as to how the AM machine works and the materials that are used to
build the part.
The key to how AM works is that parts are made by adding material in layers; each layer
is a thin cross-section of the part derived from the original CAD data. Obviously in the
physical world, each layer must have a finite thickness to it and so the resulting part will
be an approximation of the original data, as illustrated by Fig. The thinner each layer is,
the closer the final part will be to the original. All commercialized AM machines to date
use a layer-based approach, and the major ways that they differ are in the materials
that can be used, how the layers are created, and how the layers are bonded to each
other. Such differences will determine factors like the accuracy of the final part plus its
material properties and mechanical properties. They will also determine factors like
how quickly the part can be made, how much post-processing is required, the size of
the AM machine used, and the overall cost of the machine and process.
CAD image of a teacup with further images showing the effects of building using
different layer thicknesses
What Are AM Parts Used for?
Initially, AM was used specifically to create visualization models for

products as they were being developed. It is widely known that models
can be much more helpful than drawings or renderings in fully
understanding the intent of the designer when presenting the conceptual
design. While drawings are quicker and easier to create, models are
nearly always required in the end to fully validate the design.
Following this initial purpose of simple model making, AM technology has developed
over time as materials, accuracy, and the overall quality of the output improved. Models
were quickly employed to supply information about what is known as the “3 Fs” of Form,
Fit, and Function. The initial models were used to help fully appreciate the shape and
general purpose of a design (Form). Improved accuracy in the process meant that
components were capable of being built to the tolerances required for assembly
purposes (Fit). Improved material properties meant that parts could be properly handled
so that they could be assessed according to how they would eventually work (Function).
To say that AM technology is only useful for making models, though, would be
inaccurate and undervaluing the technology. AM, when used in conjunction with other
technologies to form process chains, can be used to significantly shorten product
development times and costs. More recently, some of these technologies have been
developed to the extent that the output is suitable for end use. This explains why the
terminology has essentially evolved from rapid prototyping to additive manufacturing.
Furthermore, use of high-power laser technology has meant that parts can now also be
directly made in a variety of metals, thus extending the application range even further.
The Generic AM Process
AM involves a number of steps that move from the virtual CAD description to the physical
resultant part. Different products will involve AM in different ways and to different degrees.
Small, relatively simple products may only make use of AM for visualization models, while
larger, more complex products with greater engineering content may involve AM during
numerous stages and iterations throughout the development process. Furthermore, early
stages of the product development process may only require rough parts, with AM being
used because of the speed at which they can be fabricated. At later stages of the process,
parts may require careful cleaning and post-processing (including sanding, surface
preparation, and painting) before they are used, with AM being useful here because of the
complexity of form that can be created without having to consider tooling.
Generic process of CAD to part, showing all eight stages
Step 1: CAD
All AM parts must start from a software model that fully describes the
external geometry. This can involve the use of almost any professional
CAD solid modeling software, but the output must be a 3D solid or
surface representation. Reverse engineering equipment (e.g., laser and
optical scanning) can also be used to create this representation.
Step 2: Conversion to STL
Nearly every AM machine accepts the STL file format, which has
become a de facto standard, and nowadays nearly every CAD system
can output such a file format. This file describes the external closed
surfaces of the original CAD model and forms the basis for calculation
of the slices.
Step 3: Transfer to AM Machine and STL
File Manipulation
The STL file describing the part must be transferred to the AM machine.
Here, there may be some general manipulation of the file so that it is
the correct size, position, and orientation for building.
Step 4: Machine Setup
The AM machine must be properly set up prior to the build process.

Such settings would relate to the build parameters like the material
constraints, energy source, layer thickness, timings, etc.
Step 5: Build
Building the part is mainly an automated process and the machine can
largely carry on without supervision. Only superficial monitoring of the
machine needs to take place at this time to ensure no errors have taken
place like running out of material, power or software glitches, etc.
Step 6: Removal
Once the AM machine has completed the build, the parts must be
removed. This may require interaction with the machine, which may
have safety interlocks to ensure for example that the operating
temperatures are sufficiently low or that there are no actively moving
parts.
Step 7: Post-processing
Once removed from the machine, parts may require an amount of

additional cleaning up before they are ready for use. Parts may be weak
at this stage or they may have supporting features that must be
removed. This therefore often requires time and careful, experienced
manual manipulation.
Step 8: Application
Parts may now be ready to be used. However, they may also require
additional treatment before they are acceptable for use. For example,
they may require priming and painting to give an acceptable surface
texture and finish. Treatments may be laborious and lengthy if the
finishing requirements are very demanding. They may also be required to
be assembled together with other mechanical or electronic components
to form a final model or product.
AM machines require careful maintenance
Many AM machines use fragile laser or printer technology that must be carefully monitored
and that should preferably not be used in a dirty or noisy environment. While machines are
generally designed to operate unattended, it is important to include regular checks in the
maintenance schedule, and that different technologies require different levels of
maintenance. It is also important to note that AM processes fall outside of most materials
and process standards; explaining the recent interest in the ASTM F42 Technical Committee
on Additive Manufacturing Technologies, which is working to address and overcome this
problem . However, many machine vendors recommend and provide test patterns that can
be used periodically to confirm that the machines are operating within acceptable limits.
In addition to the machinery, materials may also require careful handling.
The raw materials used in some AM processes have limited shelf-life and
may also be required to be kept in conditions that prevent them from
unwanted chemical reactions. Exposure to moisture, excess light, and
other contaminants should also be avoided. Most processes use materials
that can be reused for more than one build. However, it may be that reuse
could degrade the properties if performed many times over, and therefore
a procedure for maintaining consistent material quality through recycling
should also be observed.

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What Is Additive Manufacturing

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What Is Additive

The term rapid prototyping (RP) is used in a variety of industries to describe a

Initially, AM was used specifically to create visualization models for

The AM machine must be properly set up prior to the build process.

Once removed from the machine, parts may require an amount of

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