Large thermoplastic-printed parts, by contrast, can’t offer that strength throughout the part, even when they’re reinforced with carbon fiber. During the 3D printing process, the carbon fibers align in the direction of flow out of the extruder, providing high strength in the X and Y directions but little in the Z direction. There’s no chemical reaction that bonds the layers; the strength of this bond depends on how well each layer melts or fuses to the previous layer.
This alignment of the carbon fibers in the printed thermoplastic composite part also produces coefficient of thermal expansion (CTE) values that are significantly different between the X and Y directions and the Z direction. This is one reason why thermoplastics aren’t as well suited for high-temperature applications.
With thermoset AM, parts can be manufactured precisely and with less material. The nozzles used for thermoplastic 3D printing generally have opening diameters between ½-inch and 3 inches. That’s because the material has to be deposited as quickly as possible so that it won’t cool down too soon. “They have to come back to the previously deposited layer in a certain amount of time, because if they don’t the bottom has cooled too much and the top layer won’t stick to it,” says Mike Kastura, senior product manager at MVP.
With thermosets that’s not a concern because the bond is formed by a chemical reaction. Since there’s no need to make the beads large or to hurry the printing process to ensure the material retains heat, the nozzle size can be smaller.
“Most of the prints we are doing are with a 0.2-inch-diameter nozzle, so we are printing on a much finer resolution,” Kastura says. The part can be printed more precisely, so there’s less overprinting and less milling required to produce its final shape.
Sparse infill printing of thermoset AM parts also reduces material use. “We save time and money by essentially printing a honeycomb structure and not a solid print until we get near the surface that will likely be required to be milled,” explains Pauer.
The development team hopes the RAM equipment’s fine resolution capability will enable it to produce final parts rather than tooling to make a part. A 3D-printed replacement part could be ready in a few days rather than the weeks it takes to make a part from a 3D-printed tool.
Since the U.S. Department of Energy sponsors ORNL’s research, the energy efficiency of additive manufacturing is a big concern. Thermoset 3D printing has an energy advantage over thermoplastic AM.