Powder Bed Fusion
This main category includes common techniques such as,
Direct Metal Laser Sintering (DMLS)
Electron Beam Melting (EBM)
Selective Laser Melting (SLM)
Selective Heat Sintering (SHS)
Selective Laser Sintering (SLS)
Even though these have different names all these methods use either a laser or electron
beam to melt and fuse the material powder together.
In this method, firstly a layer of powder is spread over the build platform with the help of a
roller. Then a laser or electron beam is pointed on to the required area of the powder bed
with the help of a movable mirror. The laser increases the temperature of the powder material
to its melting point and the melted powder binds together and forms the first layer. Then
another layer of powder is added and the above process is repeated. The unfused powder
acts as a scaffold to succeeding layers.
Sheet Laminating
In this process, layers of adhesive-coated paper, plastic or metal laminates are successively
glued together and cut to shape with a knife or a laser cutter.
This process includes Ultrasonic Additive Manufacturing (UAM) and Laminated Object
Manufacturing (LOM). UAM uses sheets or ribbons of metal which are bound together using
ultrasonic welding. LOM uses a similar layer by layer approach but uses paper as a material
and the adhesive. LOM uses a cross-hatching method during the printing process which allows
easy removal of post build.
These methods often used for aesthetic and visual models, but not suitable for structural use.
Types of Defects
Unlike the other manufacturing methods, products made using 3D printing need not be
machined or do not have heavy finishing processes to get a quality final product. Even though,
still the products may have some defects due to different reasons.
There may be some shifted layers because of the lack of bonding between the layers. Prints
could be leaned. There may be gaps in the bottom surface because the first layer does not
stick well to the platform. Also, warping, ringing, stringing, hairy prints, ugly overhangs etc.
can be considered as defects in 3D printing.
Leaning
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Warping and Cracks
between layers
Shifted Layer
University of Peradeniya GAUGE Magazine
Over Heating
Stringing