3D Printing in Schools

Materials
The most popular polymers for FDM 3D printers are ABS and PLA.

Acrylonitrile Butadiene Styrene (ABS)
Combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness of polybutadiene rubber. The 3D printers with enclosed build spaces heat the chamber to around 100ºC, just below the liquid state to ensure new layers fully bond with the previous layer.

Properties
• ABS has good impact resistance and toughness.
• ABS is amorphous with no specific melting point but the temperature when it changes to a liquid state (glass transition temperature) is 105ºC.
• Density – 0.350 – 3.50 g/cc
• Hardness – 90.0 – 119 (Rockwell)
• Tensile strength (ultimate) – 24.1 – 73.1 MPa
• Tensile modulus – 0.778 – 6.10 GPa

Polylactic Acid (PLA)
Plastics are produced from corn or dextrose including tapioca roots and sugarcane. PLA is bio-degradable and used for medical mplants and food containers although opinion seems divided on how green PLA actually is.

Properties
• PLA has good impact resistance and toughness.
• The glass transition temperature of PLA is 60 – 65ºC.
• Density – 1.00 – 1.62 g/cc
• Hardness – 59.0 – 77.0 (Shore D)
• Tensile strength (ultimate) – 16.0 – 114 MPa
• Tensile modulus – 2.7-16 GPa

The low melting point of PLA means it can be encased in plaster-like moulding materials then burned out with the space filled with molten metal, a variation on lost wax casting.

Advantages
• Low cost materials
• Low cost versions of printers available
• High strength models
• Relatively short build times

Disadvantages
• Additional material/structures are needed to support overhanging geometry.
• Support material must be removed by breaking away or dissolving.
• Support material is waste
• Parts cannot easily be nested inside one another or vertically.
• Single colour parts

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