Additive Manufacturing UNIT-1
Additive Manufacturing UNIT-1
Additive Manufacturing UNIT-1
UNIT-1
Additive manufacturing (AM) process most commonly used to describe a variety of processes,
which are aimed at quickly creating three-dimensional physical parts from virtual 3D computer
models using automated machines. Additive manufacturing is different from traditional
fabrication in that it is only possible through the use of computers, both to generate the 3D CAD
model data, as well as to control the mechanical systems of the machines that build the parts. The
parts are “built” directly from the 3D CAD model and can match that model very closely.
This additive manufacturing process provides designers and engineers the capability to literally
print out their ideas in three dimensions. The AM processes provide a fast and inexpensive
alternative for producing prototypes and functional models as compared to the conventional
routes for part production.
The advantage of building a part in layers is that it allows you to build complex shapes that
would be virtually impossible to machine, in addition to the more simple designs. AM can build
intricate internal structures, parts inside of parts, and very thin-wall features just as easily as
building a simple cube.
AM process belong to the generative (or additive) production processes unlike subtractive or
forming processes such as lathing, milling, grinding or coining etc. in which form is shaped by
material removal or plastic deformation. In all commercial AM processes, the part is fabricated
by deposition of layers contoured in a (x-y) plane two dimensionally. The third dimension (z)
results from single layers being stacked up on top of each other, but not as a continuous z-
coordinate. Therefore, the prototypes are very exact on the x-y plane but have stair-stepping
effect in z-direction. If model is deposited with very fine layers, i.e., smaller z-stepping, model
looks like original. AM can be classified into two fundamental process steps namely generation
of mathematical layer information and generation of physical layer model. Typical process chain
of various AM systems is shown in figure 1.
Figure 1: RP process chain showing fundamental process steps
It can be seen from figure 1 that process starts with 3D modeling of the product and then STL
file is exported by tessellating the geometric 3D model. In tessellation various surfaces of a CAD
model are piecewise approximated by a series of triangles and co-ordinate of vertices of triangles
and their surface normals are listed.
These STL files are checked for defects like flip triangles, missing facets, overlapping facets,
dangling edges or faces etc. and are repaired if found faulty. Defect free STL files are used as an
input to various slicing software. At this stage choice of part deposition orientation is the most
important factor as part building time, surface quality, amount of support structures, cost etc. are
influenced. Once part deposition orientation is decided and slice thickness is selected, tessellated
model is sliced and the generated data in standard data formats like SLC (stereolithography
contour) or CLI (common layer interface) is stored. This information is used to move to step 2,
i.e., generation of physical model.
The software that operates AM systems generates laser-scanning paths (in processes like
stereolithography, Selective Laser Sintering etc.) or material deposition paths (in processes like
Fused Deposition Modeling). This step is different for different processes and depends on the
basic deposition principle used in RP machine. Information computed here is used to deposit the
part layer-by-layer on RP system platform.
The final step in the process chain is the post-processing task. At this stage, generally some
manual operations are necessary therefore skilled operator is required. In cleaning, excess
elements adhered with the part or support structures are removed. Sometimes the surface of the
model is finished by sanding, polishing or painting for better surface finish or aesthetic
appearance. Prototype is then tested or verified and suggested engineering changes are once
again incorporated during the solid modeling stage.
The automated processes are three types, they are subtractive, additive and formative processes.
In the subtractive process, one starts with a single block of solid material larger than the final
size of the desired object and material is removed until the desired shape is reached.
Ex: Subtractive fabrication processes include most forms of machining processes — CNC or
otherwise. These include milling,turning, drilling,planning, sawing, grinding, EDM, laser
cutting, water-jet cutting and the likes.
In contrast, an additive process is the exact reverse in that the end product is much larger than the
material when it started. A material is manipulated so that successive portions of it combine to
form the desired object.
Ex: Most forms of rapid prototyping processes such as Stereolithography and Selective Laser
Sintering fall into the additive fabrication processes category
Lastly, the formative process is one where mechanical forces or restricting forms are applied on a
material so as to form it into the desired shape.
Ex: of formative fabrication processes are: Bending, forging, electromagnetic forming and
plastic injection molding. These include both bending of sheet materials and molding of molten
or curable liquids.
DISADVANTAGES
Applications of AM process
MEDICINE
So much So much more is known about the human body than in the past, but the ability to create
tissue and organs has always been elusive. This ability to artificially regenerate is something
which is highly prized by medical scientists, having the potential to cure or at least overcome the
ravages of, disease, illness and injury
INDUSTRIAL USES
There’s a vast number of industries which have made use of the technology such as aerospace,
defense, industry and automotive, and each of these has found certain key elements particularly
beneficial. Tooling is used in all of these industries and has a broad number of applications, and
this is one area which can be significantly improved with the use of additive manufacturing.
Additive Manufacturing (AM) is an appropriate name to describe the technologies that build 3D
objects by adding layer-upon-layer of material, whether the material is plastic, metal, concrete or
one day a human tissue.
Fundamentally, the development of RP can be seen in four primary areas. The Rapid Prototyping
Wheel depicts these four key aspects of Rapid Prototyping. They are: Input, Method, Material
and Applications.
1. Input
Input refers to the electronic information required to describe the physical object with 3D data.
There are two possible starting points a computer model or a physical model. The computer
model created by a CAD system can be either a surface model or a solid model. On the other
hand, 3D data from the physical model is not at all straightforward. It requires data acquisition
through a method known as reverse engineering. In reverse engineering, a wide range of
equipment can be used, such as CMM (coordinate measuring machine) or a laser digitizer, to
capture data points of the physical model and “reconstruct” it in a CAD system.
2. Method
Photo-curing, cutting and glueing/joining, melting and solidifying/fusing and joining/binding.
Photo-curing can be further divided into categories of single laser beam, double laser beams and
masked lamp.
3. Material
The initial state of material can come in either solid, liquid or powder state. In solid state, it can
come in various forms such as pellets, wire or laminates. The current range materials include
paper, nylon, wax, resins, metals and ceramics.
4. Applications
Most of the RP parts are finished or touched up before they are used for their intended
applications. Applications can be grouped into:
1. Design
2. Engineering, Analysis, and Planning and
3. Tooling and Manufacturing.
A wide range of industries can benefit from RP and these include, but are not limited to,
aerospace, automotive, biomedical, consumer, electrical and electronics products.
The Better way is to classify Additive Manufacturing systems broadly by the initial form of its
material, all AM Systems can be easily categorised into:
Most liquid-based rapid prototyping systems build parts in a vat of photo-curable liquid resin, an
organic resin that cures or solidifies under the effect of exposure to laser radiation, usually in the
UV range.The laser cures the resin near the surface, forming a hardened layer. When a layer of
the part is formed, it is lowered by an elevation control system to allow the next layer of resin to
be similarly formed over it. This continues until the entire part is completed.
What are the three phases of prototyping? Contrasting these with those of geometric
modeling, what similarities can be drawn.
The 3 phases of prototyping are :
1. First Phase: Manual Prototyping,
2. Second Phase: Soft or Virtual Prototyping,
3. Third Phase: Rapid Prototyping.