Features

Fused Filament Deposition Technology

Fused filament deposition (FFD) uses a continuous filament of a thermoplastic material fed from a spool through a moving, heated, printer extruder head. Molten material is forced out of the printhead’s nozzle, and is deposited on the growing workpiece to form a 3D object.

PLA is a biodegradable thermoplastic polyester. It is a commonly manufactured from renewable resources such as cornstarch, tapioca roots, and sugarcane. PLA is harder than ABS plastic, has a lower melting temperature (180-220 °C), and a glass transition temperature between 60 and 65 °C. It is dimensionally stable, and can be printed with or without a heated build plate. It adheres easily to borosilicate glass, Lexan, polycarbonate sheets, blue painters’ tape, polyimide (Kapton) tape, and so forth. PLA may be treated with a wide range of post-processing techniques (Figure 1). PLA prints may have slight dimensional variations compared to other materials. Color and brand have some small effects on printing.

ABS is a common thermoplastic. It is less brittle (tougher) than PLA. With a glass transition temperature approximately 105 °C, it requires a higher extruder temperature than PLA — 230 °C ±15 degrees. ABS creates mild fumes when being extruded, and printers should be operated in a well-ventilated area. ABS requires a heated build plate that is heated to approximately 110 °C due to its tendency to warp when printing larger prints. Figure 2 shows example polymer filaments.

The flexibility of the thermoplastic elastomer (TPE) filament makes it quite resilient and sturdy for producing objects with a Shore A hardness of approximately 75-85 A. This filament is easily printed in most printers capable of printing PLA or ABS plastics, although it has a slightly higher melting temperature (240 °C), and is ideal for multi-material applications requiring portions of the design to flex, such as shock absorption devices and hinges. Printing TPE benefits from a build plate that is heated to approximately 60 °C and direct drive extruders.

Stronger than PLA and more durable than ABS, nylon offers the benefit of a material robust enough for functional parts. Nylon’s high melting temperature and low friction coefficient present a versatile printing option that allows flexibility.

Figure 3. PEEK filament.

ULTEM offers high thermal resistance, high strength and stiffness, and broad chemical resistance. ULTEM is available in transparent and opaque custom colors as well as glass-filled grades. Plus, ULTEM copolymers are available for even higher heat, chemical, and elasticity needs. ULTEM 1000 (standard, unfilled PEI) has a high dielectric strength, inherent flame resistance, and extremely low smoke generation. These high mechanical properties perform in continuous use to 340 °F (170 °C), which makes it desirable for many engineering applications.

With its unique mechanical, chemical, and thermal properties, PEEK has many advantages over other polymers, and is able to replace industrial materials such as aluminum and steel. It allows its users to reduce total weight and processing cycles, and increase durability. Compared to metals, the PEEK polymer allows a greater freedom of design and improved performance. PEEK is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, high-performance liquid chromatography (HPLC) columns, compressor plate valves, and electrical cable insulation. It is one of the few plastics compatible with ultra-high vacuum applications. Figure 3 shows an example of a PEEK filament.

Stereolithography Technology

While FFD technology provides a means to rapidly prototype objects, stereolithography (SLA) is often better suited for detail and high-speed production. Parts are constructed in a layer-by-layer fashion using photo-polymerization, a process by which ultraviolet (UV) light causes chains of molecules to link and form polymers that then make up a 3D solid object. The production of these objects relies on materials that are currently available in many forms, including standard and engineering resins.

  • Standard Resins. The material selection for SLA is more limited than FFD, but general-purpose or standard resins have grown to include a variety of colors in varying opacities. Standard resins provide high resolution for applications like visual demonstrations and models.

  • Engineering Resins. Matching the detail provided with standard resins, engineering resins possess additional strength and functionality. The flexible resin variety simulates an 80A durometer rubber, which is often chosen for impact resistance and compression. The tough resin is similar to a finished product formed from ABS plastic. Applications that will undergo high stress and strain are frequently engineered with tough engineering resin, ensuring successful assembly, machining, snap-fits, and living hinge supports. The ceramic resin is UV-curable, with objects often glazed with commercially available coatings after firing.

Conclusion

Based on initial work in the PRIME2 program, a subset of materials was investigated for co-fabrication and realization of RF structures. Standard PLA, standard ABS, PEEK, and ULTEM were selected for further dielectric investigation.

The existence of a suitable solvent for the dielectric material can be helpful in preparing printed substrate surfaces for further additive manufacturing steps. In addition, the melt temperature of the material is important for post-processing steps that may be required when depositing certain conductive materials.

This article was written by Janice C. Booth, Army AMRDEC Weapons Development and Integration Directorate, Redstone Arsenal, AL; and Michael Whitley, Carl Rudd, and Michael Kranz of EngeniusMicro, Huntsville, AL. For more information, visit here.