Polylactic acid (PLA), Acrylonitrile butadiene styrene (ABS) and Thermoplastic polyurethane (TPU) are among the most commonly used materials for 3D printing filaments. Each have characteristics useful in creating 3D printed products. PLA is inexpensive and can be printed at low temperatures—ideal for hobbyists. ABS is known for its durability and glass transition temperature for good heat resistance (think plastic building bricks). TPU is elastic and useful for impact resistance, such on cases for mobile phones.
ABS and TPU resins and filaments are typically made with a single-screw extruder for mixing and transport. PLA, a biopolymer, typically requires a twin-screw extruder because it is sensitive to heat and shear and is prone to hydrolytic degradation if moisture is present.
As 3D printing has gained popularity for desktop and commercial production, new materials have come into use for reasons of cost, function and appearance, including nylon, polypropylene, polyvinyl alcohol, and polycarbonate. Additionally, new filler materials are available for carbon fiber-filled, metal-filled and wood-filled filaments.
A critical characteristic for 3D printing filaments is the dimensional accuracy (diameter) of the filament. Most filaments are sold with a nominal diameter specification, showing the minimum/maximum size in fractions of a millimeter. In order to assure good printing, this number must be consistent throughout the run of the filament spool.
Simple 3D filaments can be made from a base polymer on a single-screw extruder where high pressure build-up and constant output assure a constant filament diameter. The limitation of using single-screw extruders is that they are inefficient at mixing or compounding multiple-component formulations for creating the 3D filament. For this, a twin-screw extruder is necessary. The twin-screw extruder enables filament production in a single run, saving production time and reducing the thermal stress on the compounded filament by minimizing heat-cool cycles.
However, the twin-screw extrusion process results in a slight pulsating output that makes maintaining a constant filament diameter much more difficult. This can be remedied by adding a melt pump to the end of the extrusion process.
Application scientists at Thermo Fisher Scientific compared the output of three extruder configurations: single-screw, twin-screw, and twin-screw with melt pump. What they found is that using a melt pump enabled twin-screw compounding of 3D filaments with tolerances comparable to output from a single-screw extruder.
Review the data by reading Use of melt pump to produce filaments for additive manufacturing (3D printing).
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