µm (1,600 DPI). X–Y resolution is comparable to
that of laser printers. The particles (3D dots) are around 50 to 100 µm
(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 file for a given model input file. Specifying
higher resolution results in larger files 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 flexible
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 sufficient 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 effect on part surfaces which are curved or tilted in
respect to the building platform. The effects strongly depend on the
orientation of a part surface inside the building process.
Some
printable polymers such as ABS, allow the surface finish 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
off the metal substrate after deposition. A new process for the GMAW 3D
printing allows for substrate surface modifications to remove aluminum
or steel.
Processes and printers
A large number of additive processes
are available. The main differences 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 offer a choice of powder and polymer for the material used to
build the object. Others sometimes use standard, off-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 defines
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 filament 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 filament of thermoplastic, metal wire, or other material is
fed into an extrusion nozzle head (3D printer extruder), which heats the
material and turns the flow on and off. 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) filled with a liquid
photo-polymerizing resin; the solidified resin d) is progressively
dragged up by a lifting platform e)
Other methods cure liquid materials
using different 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 µm) 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 solidified 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 flow 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 efforts to develop affordable 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. \ref{705291}\ref{705291}). 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 three-dimensional objects. A
large variety of foods are appropriate candidates, such as chocolate and
candy, and flat 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-fit shoes for athletes. 3D
printing has come to the point where companies are printing consumer
grade eyewear with on-demand custom fit 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 significant value for fashion
companies down the road, especially if it transforms into a
print-it-yourself 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. \ref{215610}), Additive
Manufacturing is beginning to transform both (1) unibody and