3D Printer Technology Basics

CS 480: Robotics & 3D Printing Lecture, Dr. Lawlor

Picking a 3D Printer Technology

There are a number of good surveys of 3D printer technology, including commercial choices that are fridge-sized and cost from $15K-$1M.

Energy Added
Solid material
Liquid resin
Chemical crosslink
Inkjet powder printing
Paper lamination
SLA (bulk)
Polyjet (thin layer)
Beam Heating
DMLS/SLM/EBM
(from powder)

Conduction Heating
FDM/FFF
(from filament)

Stereolithography (SLA) uses an optically sensitive material, typically a vat of UV-curable photopolymer, to selectively cure 2D slices into a 3D object.  Speed and accuracy can be excellent depending on the optics used, in particular with newer digital light processing (DLP) projector chips, but the cost of the photopolymer is fairly high (at least $65/liter or Kg), and most photopolymers result in objects that are not very impact-resistant.  SLA was one of the first 3D printing technologies, and still dominates for small-size high-precision work. The standard file format "STL" (STereoLithography) derives its name from this technique.

PolyJet printers use a similar photopolymer to SLA, but use inkjet-type technology to spray the photopolymer onto the object before curing.  This allows them to use a wide variety of materials, including rubbery materials, and to grade materials into one another.

Direct Metal Laser Sintering (DMLS) or the higher temperature Selective Laser Melting (SLM) uses a laser to fuse a flat bed of powder or a gas-carried stream of powder into a solid, depositing material layer by layer.  With an inert atmosphere and high temperature chamber, this can be made to work with metals, including steel and aerospace metals like titanium or inconel.  This also provides automatic support structure, since the powder is deposited at the same time as the part.  Electron Beam Melting (EBM) uses an electron beam for the same purpose, but requires a vacuum chamber. 

Fluid Deposition Modeling (FDM) (or the generic term Fused Filament Fabrication / FFF) deposits a semi-solid material onto a build platform to assemble the shape, and is the dominant technology for home 3D printers. Unlike SLA, it is inherently a 1D fabrication process, since the material emerges in a single line.  Most models work by feeding a filament into a hotend, but this is only suitable for materials that have a viscous intermediate state--this includes most plastics, chocolate, and even glass when using a sufficiently hot hotend, but the low viscosity of most molten metals makes them unsuitable for FDM/FFF.  Another option is to extrude self-curing materials like epoxy or cement.  Advantages include inexpensive filament feedstock (as low as $20/Kg), and simple heating elements can be home fabricated, unlike lasers or optics.

Picking a 3D Printer Filament


Composition
Smell
Density
Tensile Strength
Elastic Modulus
Glass Temp Tg
Printing Range
PLA
Polylactic acid, plus plasticizers
pancakes
1.25 g/cc
55 MPa
3.5 GPa
57C
(very low!)
160-200C
ABS
Butadiene rubber plus acrylonitrile and styrene
headache
1.05 g/cc
40 MPa
1.4-3.1 GPa
80-125C
200-240C
HDPE
High-density polyethylene
candlewax
0.95 g/cc
15 MPa
0.8 GPa
(soft!)
-125C
220-230C?
Nylon Polyamide 66 ??
1.14 g/cc
70 MPa 2-4 GPa 50C 240+C
Lexan
Polycarbonate ?? 1.2 g/cc
50 MPa
2.6 GPa
150C
250-305C
PET
Polyethyelene terephthalate
??
1.38 g/cc
55 MPa
2.7 GPa
70-80C
250C?
Glass
Silicon dioxide with boron or sodium flux
none
2.5 g/cc
33 MPa
50-90 GPa
300C
1000C
Tin
w/ alloying copper, silver
toaster
7 g/cc
10-40 MPa
50 GPa
n/a
>230C
Aluminum
w/ alloying zinc, silicon
toaster
2.7 g/cc
110 MPa
69 GPa
n/a
>660C
Steel
w/ alloying carbon, chromium, nickel
fire
7.9 g/cc
400 MPa
200 GPa
n/a
>1370C

Several filaments are designed primarily as dissolvable support material, such as high impact polystyrene (HIPS), which dissolves in limonene, or polyvinyl acetate (PVA), which dissolves in hot water.  Their properties are compared here.

Many filaments are actually alloys of different substances--in particular, ABS, HDPE, and polycarbonate will intermix well.  And there are a variety of "improved" filament chemistry options.

Filament makers can also add small particles of various filler materials to the plastic matrix:

See also:

A key technology for designing toolpaths is calculating material flow rates: