Thermoset polyurethanes, which are distinct from TPUs, are materials with a combination of flexibility, durability, and elasticity that are unmatched by acrylic-based rubbers and silicones. As a class, thermosets are the product of a chemical reaction of two liquids. The resulting product is a chemically cross-linked network. This network resists the creep, thermal degradation, and mechanical wear that can weaken thermoplastics. Printing polyurethanes requires liquid deposition techniques, but also requires modification of the reactive chemistry of the liquids. As the reactive liquid is deposited, chemical bonds are formed between layers. The final result is a printed part with excellent interlayer strength, durability, and flexibility. Liquid deposition of reactive polyurethanes also opens possibilities for parts with varied properties and for multi-material printing. In many respects, printing thermosets requires a re-thinking of the printing rules that have been developed for printing with filaments: temperature, printing speed, and part size affect part quality and resolution in very different way. We will discuss print head designs for polyurethane printing, and illustrate the versatility of the chemistry to achieve large formats, multi-material parts, and high definition. Today, available printers for liquid deposition include the Hyrel and German RepRap LAM printers.
- Identify applications and parts which would benefit from the flexibility and durability of polyurethane materials
- Define basic elements of printhead design for adapting a printer to use reactive polyurethanes