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.
Saving Energy
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.
There are several energy-consuming steps in thermoplastic 3D printing. One is the conversion of the commonly used material, acrylonitrile butadiene styrene (ABS), into a polymer. Another is the re-melting of the ABS in a compounder to include additives like carbon fiber. The ABS, now in pellet or chopped form, is melted a third time for deposition during the print process. In addition, the printing table is typically heated during the thermoplastic printing process to prevent the parts from cooling too fast.
Thermosets, by contrast, require heat to make the original polymer, but beyond that the only added energy is what’s required to pump and mix the PRD 1520 as it’s processed through the RAM equipment.
The Electric Power Research Institute (EPRI) found that the thermoset additive manufacturing process is about 500% more energy efficient than the thermoplastic process, Hershey says.
Intriguing Possibilities
The ability to control the exothermic reaction in the RAM process provides opportunities to vary the characteristics of a part.
“With thermoplastics, once you lay the bead down that’s the hottest it’s going to be. It starts to cool so you can’t print through it,” says Kastura. “That’s not true with thermosets. You can literally cross through that previously laid bead on the same plane, so you can have different geometries, different print patterns.”
In addition, the RAM machine can be equipped with a robotic claw that can insert objects into a part as its being printed. “The claw could grab pipes for heating or cooling channels and drop them precisely into your print because it’s all part of the machine code,” says Kastura.
The claw could also precisely install different types of sensors inside a tool as it’s being manufactured. Those sensors could relay data to help predict the part’s end of life or to validate a tool’s effectiveness during the process by providing metrics at certain times. Embedded sensors could be used to monitor temperature within a tool to ensure that it’s at the proper temperature while it’s being used.
One other unique feature of RAM is its patent-pending removable printing table, which will enable a shop to index the table rather than the part, then easily move the printed part to its next location, such as milling or routing. Then, by inserting another table, the shop can continue to make the best use of its high-demand AM equipment.
Testing It Out
Thermoset additive manufacturing is attracting attention from government and commercial customers, including the military, automotive/transportation, wind/aerospace, tub and shower manufacturers and job shops. “Many of them have looked at thermoplastics 3D printing, and they know some of the limitations. There’s a strong case that can be made that thermosets can solve a lot of those issues,” says Kastura.
The RAM team continues to do more printing and testing to help ensure the new technology’s widespread acceptance. One part, printed for Design Concepts/Marine Concepts (DCMC), is a direct mold that would be used to create lightweight carbon fiber mold insets for a 60-plus foot deck liner.
“The part, measuring 10 x 4 x 2 feet and weighing 1,000 pounds, was large enough that it pushed the envelope for them as far as size, and it also aligned with one of our internal R&D projects, which was to develop an alternative to heavyweight standard mold insets,” says Ross Kennedy, director of business development at DCMC.
Company representatives watched the part being printed on the RAM equipment and shipped it back to their facility to mill. “It was a learning experience for everybody,” says Kennedy. “We got to understand better ways to index these oversized, near-net shape prints and provided feedback.” DCMC also tested the vacuum stability and surface finish on the printed molds.
Milling the printed thermoset composite was similar to milling a very high-density urethane tooling board. “The benefit that I see with the 3D print is that you can have a sparse interior, which uses a lot less material than a giant block of tooling board,” says Kennedy. In addition to lower material use and weight, the near-net printing discipline directly translates to less material having to be milled away.
Research on RAM has been slowed by coronavirus-related shutdowns, but when work can resume the RAM team will print another part for DCMC to see if the changes that they’ve made to the machine and the process have improved the printed product.
In the long term, Kennedy says there are three criteria that RAM-printed parts will have to meet for the equipment to gain a place in large tooling shops. One is the surface quality – the density and hardness – of the printed part. It will also have to meet glass transition temperature requirements and offer the right coefficient of thermal expansion properties. He expects that thermoset 3D printers like RAM will be able to meet those criteria very soon.
“We certainly feel that at some point this will become an everyday item in the larger tooling shops around the world,” he adds.
Ongoing Improvements
The RAM team will resume its research once work schedules at ORNL permit. ORNL and MVP have recently signed a second creative research and development agreement (CRADA), and Polynt is waiting on approval of its second CRADA with ORNL.
One problem the team plans to address is process speed, which is currently much slower than thermoplastic AM. To increase the rate of printing, the team will have to find a way to ensure a steady stream of the materials, which are currently available only in relatively small barrels that empty quickly. In addition, the hoses, which are about 30 feet long to reach all sides of the printing table, must have a diameter large enough to handle heavier flows of the viscous material used in the process.
The team may also explore the feasibility of adding another stream to the material being deposited during the RAM printing process, such as a second resin formulation that could add a functional coating to the surface of a printed part. In addition, it will continue to refine the thermoset printing process, work toward getting better resolution for near-net shapes and build case studies with industry partners to prove out the technology.
“There will no doubt be new challenges we have to overcome, just like we did in thermoplastics, but you don’t have the limitations in thermosets that you have in thermoplastics,” says Kastura. “We will be experiencing some of the excitement that we felt when we first started thinking that 3D printing could take over the world.”
