The production of large-scale, 3D-printed thermoplastic composite parts has proved that additive manufacturing (AM) can reduce the time, material and labor required to make tooling and other products. But these thermoplastic-printed parts have limitations; for example, they don’t hold up well in high-heat applications.
Thermoset composite materials could be used to overcome some of the problems in such applications, but until recently there’s been no large-scale additive manufacturing process for thermosets. Now there is. Over the last few years, Oak Ridge National Laboratory (ORNL) and Magnum Venus Products (MVP) co-developed the world’s first commercial, thermoset Reactive Additive Manufacturing (RAM) machine and partnered with Polynt Composites USA to develop a novel print material. The system can print parts as large as 8 x 16 x 3.5 feet.
Each of the partners brought experience and expertise to the RAM creation process. ORNL helped develop the Big Area Additive Manufacturing system (BAAM) for printing 3D thermoplastic parts. MVP has decades of experience in pumping solutions for composite manufacturing and in large-scale, automated production systems. Polymer chemistry supplier Polynt has developed coatings for 3D thermoplastic parts.
While their knowledge of 3D thermoplastic printing was helpful, the team had to develop a very different printing process for RAM. In thermoplastic 3D printing, heat is the key. The equipment melts a polymer material (continuous filament or pellets) so that it can flow through a nozzle that deposits it, layer by layer, on a heated printer table.
RAM, however, is an ambient temperature system that uses pumpable liquids to manufacture thermoset parts. Its raw materials include a formulated polymer with reinforcing fibers (the A side) and a peroxide initiator (the B side). The two sides are brought together in a mixer, beginning an exothermic reaction that continues as the mixture, which has the consistency of toothpaste, is deposited through a nozzle onto the printer table. A gantry moves the nozzle around the printer table, which lowers to accommodate the part’s growing height as the layers are added.
Polynt formulated PRD 1520 specifically for the RAM process, says Rick Pauer, applications specialist, Polynt Composites USA. The polymer/initiator mixture had to be void free, curable and able to set up rapidly so it didn’t slump or liquefy during the printing process. It had to maintain its viscous properties during the exothermic reaction and deliver all the mechanical properties that potential customers would want.
The team has printed several test parts on the RAM machine with the PRD 1520 formulation over the last year. ORNL and MVP have also been developing another thermoset printing process for RAM. It combines liquids from an epoxy resin line and a hardener line, but doesn’t include fiber, so it isn’t a composite material. Unlike most products produced using PRD 1520, these epoxy-printed parts require post-printing curing in an oven.