mm (1,600 DPI). X{Y resolution is comparable to that of laser printers. The particles (3D dots) are around
50 to 100 mm (510 to 250 DPI) in diameter. For that printer resolution, specifying a mesh resolution of
0.01{0.03 mm and a chord length ? 0.016 mm generate an optimal STL output le for a given model input
le. Specifying higher resolution results in larger les without increase in print quality.
Construction of a model with contemporary methods can take anywhere from several hours to several days,
depending on the method used and the size and complexity of the model. Additive systems can typically
reduce this time to a few hours, although it varies widely depending on the type of machine used and the
size and number of models being produced simultaneously.
Traditional techniques like injection moulding can be less expensive for manufacturing polymer products in
high quantities, but additive manufacturing can be faster, more
exible and less expensive when producing
relatively small quantities of parts. 3D printers give designers and concept development teams the ability to
produce parts and concept models using a desktop size printer.
Seemingly paradoxic, more complex objects can be cheaper for 3D printing production than less complex
objects.
Finishing
Though the printer-produced resolution is sucient for many applications, printing a slightly oversized
version of the desired object in standard resolution and then removing material with a higher-resolution
subtractive process can achieve greater precision.
The layered structure of all Additive Manufacturing processes leads inevitably to a strain-stepping eect on
part surfaces which are curved or tilted in respect to the building platform. The eects strongly depend on
the orientation of a part surface inside the building process.
Some printable polymers such as ABS, allow the surface nish to be smoothed and improved using chemical
vapor processes based on acetone or similar solvents.
Some additive manufacturing techniques are capable of using multiple materials in the course of constructing
parts. These techniques are able to print in multiple colors and color combinations simultaneously, and would not necessarily require painting.
Some printing techniques require internal supports to be built for overhanging features during construction.
These supports must be mechanically removed or dissolved upon completion of the print.
All of the commercialized metal 3D printers involve cutting the metal component o the metal substrate
after deposition. A new process for the GMAW 3D printing allows for substrate surface modications to
remove aluminum or steel.
Processes and printers
A large number of additive processes are available. The main dierences between processes are in the way
layers are deposited to create parts and in the materials that are used. Each method has its own advantages
and drawbacks, which is why some companies oer a choice of powder and polymer for the material used
to build the object. Others sometimes use standard, o-the-shelf business paper as the build material to
produce a durable prototype. The main considerations in choosing a machine are generally speed, costs of
the 3D printer, of the printed prototype, choice and cost of the materials, and color capabilities. Printers
that work directly with metals are generally expensive. However less expensive printers can be used to make
a mold, which is then used to make metal parts.
ISO/ASTM52900-15 denes seven categories of Additive Manufacturing (AM) processes within its meaning:
binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet
lamination, and vat photopolymerization.
Some methods melt or soften the material to produce the layers. In Fused lament fabrication, also known
as Fused deposition modeling (FDM), the model or part is produced by extruding small beads or streams of
material which harden immediately to form layers. A lament of thermoplastic, metal wire, or other material
is fed into an extrusion nozzle head (3D printer extruder), which heats the material and turns the
ow on
and o. FDM is somewhat restricted in the variation of shapes that may be fabricated. Another technique
fuses parts of the layer and then moves upward in the working area, adding another layer of granules and
repeating the process until the piece has built up. This process uses the unfused media to support overhangs
and thin walls in the part being produced, which reduces the need for temporary auxiliary supports for the
piece.
Laser sintering techniques include selective laser sintering, with both metals and polymers, and direct metal
laser sintering. Selective laser melting does not use sintering for the fusion of powder granules but will completely
melt the powder using a high-energy laser to create fully dense materials in a layer-wise method that
has mechanical properties similar to those of conventional manufactured metals. Electron beam melting is a
similar type of additive manufacturing technology for metal parts (e.g. titanium alloys). EBM manufactures
parts by melting metal powder layer by layer with an electron beam in a high vacuum. Another method
consists of an inkjet 3D printing system, which creates the model one layer at a time by spreading a layer of
powder (plaster, or resins) and printing a binder in the cross-section of the part using an inkjet-like process.
With laminated object manufacturing, thin layers are cut to shape and joined together.
Schematic representation of Stereolithography; a light-emitting device a) (laser or DLP) selectively illuminate
the transparent bottom c) of a tank b) lled with a liquid photo-polymerizing resin; the solidied resin d) is
progressively dragged up by a lifting platform e)
Other methods cure liquid materials using dierent sophisticated technologies, such as stereolithography.
Photopolymerization is primarily used in stereolithography to produce a solid part from a liquid. Inkjet
printer systems like the Objet PolyJet system spray photopolymer materials onto a build tray in ultra-thin
layers (between 16 and 30 mm) until the part is completed. Each photopolymer layer is cured with UV
light after it is jetted, producing fully cured models that can be handled and used immediately, without post-curing. Ultra-small features can be made with the 3D micro-fabrication technique used in multiphoton
photopolymerisation. Due to the nonlinear nature of photo excitation, the gel is cured to a solid only in the places where the laser was focused while the remaining gel is then washed away. Feature sizes of under
100 nm are easily produced, as well as complex structures with moving and interlocked parts. Yet another
approach uses a synthetic resin that is solidied using LEDs.
In Mask-image-projection-based stereolithography, a 3D digital model is sliced by a set of horizontal planes.
Each slice is converted into a two-dimensional mask image. The mask image is then projected onto a
photocurable liquid resin surface and light is projected onto the resin to cure it in the shape of the layer.
Continuous liquid interface production begins with a pool of liquid photopolymer resin. Part of the pool
bottom is transparent to ultraviolet light (the \window"), which causes the resin to solidify. The object
rises slowly enough to allow resin to
ow under and maintain contact with the bottom of the object. In
powder-fed directed-energy deposition, a high-power laser is used to melt metal powder supplied to the focus
of the laser beam. The powder fed directed energy process is similar to Selective Laser Sintering, but the
metal powder is applied only where material is being added to the part at that moment.
As of December 2017, additive manufacturing systems were on the market that ranged from $99 to $500,000
in price and were employed in industries including aerospace, architecture, automotive, defense, and medical
replacements, among many others. For example, General Electric uses the high-end model to build parts
for turbines. Many of these systems are used for rapid prototyping, before mass production methods are
employed. Higher education has proven to be a major buyer of desktop and professional 3D printers which
industry experts generally view as a positive indicator. Libraries around the world have also become locations
to house smaller 3D printers for educational and community access. Several projects and companies are
making eorts to develop aordable 3D printers for home desktop use. Much of this work has been driven
by and targeted at DIY/Maker/enthusiast/early adopter communities, with additional ties to the academic
and hacker communities.
Applications
In the current scenario, 3D printing or Additive Manufacturing has been used in manufacturing, medical, industry
and sociocultural sectors which facilitate 3D printing or Additive Manufacturing to become successful
commercial technology (Fig.5 ). The earliest application of additive manufacturing was on the toolroom end
of the manufacturing spectrum. For example, rapid prototyping was one of the earliest additive variants,
and its mission was to reduce the lead time and cost of developing prototypes of new parts and devices,
which was earlier only done with subtractive toolroom methods such as CNC milling, turning, and precision
grinding. In the 2010s, additive manufacturing entered production to a much greater extent.
Additive manufacturing of food is being developed by squeezing out food, layer by layer, into threedimensional
objects. A large variety of foods are appropriate candidates, such as chocolate and candy,
and
at foods such as crackers, pasta, and pizza.
3D printing has entered the world of clothing, with fashion designers experimenting with 3D-printed bikinis,
shoes, and dresses. In commercial production Nike is using 3D printing to prototype and manufacture the
2012 Vapor Laser Talon football shoe for players of American football, and New Balance is 3D manufacturing
custom-t shoes for athletes. 3D printing has come to the point where companies are printing consumer
grade eyewear with on-demand custom t and styling (although they cannot print the lenses). On-demand
customization of glasses is possible with rapid prototyping.
Vanessa Friedman, fashion director and chief fashion critic at The New York Times, says 3D printing will
have a signicant value for fashion companies down the road, especially if it transforms into a print-ityourself
tool for shoppers. \There's real sense that this is not going to happen anytime soon," she says, \but
it will happen, and it will create dramatic change in how we think both about intellectual property and how things are in the supply chain." She adds: \Certainly some of the fabrications that brands can use will be
dramatically changed by technology."
In cars, trucks, and aircraft (Fig. 6), Additive Manufacturing is beginning to transform both (1) unibody