Dale, Indiana-based Thermwood Corporation – a manufacturer of computer numeric control (CNC) routers and large-scale additive machines (LSAM) claims to have produced the largest autoclave capable tool made through additive manufacturing (AM), commonly referred to as 3D printing. The tool – one half of an 18-foot helicopter blade mold – was built up in just over three hours as part of a joint venture program between Thermwood and Bell Helicopter of Fort Worth, Texas.
Bell, seeking to reduce the expense and long lead time of tooling for aircraft development, entered into a partnership with Thermwood centered around the LSAM producer’s new 60-millimeter melt core technology recently installed on Thermwood’s LSAM system at its development lab in southern Indiana. The larger capacity melt core offers a higher maximum throughput during operation.
Using the 60 millimeter melt core technology, Thermwood was able to reproduce a model of one of Bell’s closed cavity blade molds measuring 20 feet long, 14 inches wide, and 17 inches high in one continuous run with a 25 percent carbon fiber reinforced polyethersulfone (PESU) developed specifically for LSAM manufacturing by Techmer PM, LLC.
According to Thermwood technicians, the PESU material is as easy to use as common acrylonitrile butadiene styrene (ABS) thermoplastic polymer.
(Image courtesy: Thermwood Corporation)
The PESU print medium has a glass transition temperature of over 400° Fahrenheit and can easily survive common aerospace component cure cycles of up to 360° Fahrenheit at 90 pounds per square inch of pressure. The combined use of the new medium and technology resulted in a print time of three hours and eight minutes with an “as printed” weight of 542 pounds that easily met Bell’s requirements:
- Must to be printed in one continuous run for vacuum integrity
- Surface finish must be 32 RMS
- Tooling must be able to withstand 90 psi at 360° Fahrenheit
- Tight tolerances and features required to ensure proper mating of the two blade mold halves
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The new 60 millimeter melt core has a measured maximum output of 480 to 570 pounds per hour depending on the polymer being printed and can print over 100 feet of typical print bead per minute. This high print rate, even when processing high temperature material, allows the print bead to be oriented along the length of the tool. This is desirable for Bell, who manufactures large composite parts, because thermal expansion is significantly lower in that direction, minimizing expansion and contraction of the tool with temperature changes.
Bell is continuing to investigate integrated technologies that support multiple manufacturing processes and tools. The LSAM is capable of supporting printing processes as well as trim and drill processes to meet aerospace specifications. Once printed, the team began to machine the bond tool half by utilizing the other aspect of the LSAM system. The total machining time of the lower blade mold half was 40 hours and completed bond tool was able to maintain Bell’s vacuum standards required for autoclave processing right from the machine, without the need for a seal coating.
(Image courtesy: Thermwood Corporation)
“Thermwood’s aggressive approach to pushing the boundaries and limitation of traditional #D printing and machining is exactly what we were looking for,” says Glenn Isbell, vice president of Rapid Prototyping and Manufacturing Innovation at Bell Helicopter.
LSAM technology is intended for full-fledged industrial AM of large-scale components. It is not a lab, evaluation, or demonstration machine, but much of the technology used in Thermwood's LSAM machines and print process is completely new. Thermwood has already received numerous patents on these developments and many more are in the works.
The Thermwood team will print the second half of the blade mold, with the intention of having Bell cure a full molded blade within the final additively-manufactured bond tool, another first. Further testing will be completed by both Thermwood and Bell teams on PESU printed molds, to continue innovating in this space.
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William Kucinski is content editor at SAE International, Aerospace Products Group in Warrendale, Pa. Previously, he worked as a writer at the NASA Safety Center in Cleveland, Ohio and was responsible for writing the agency’s System Failure Case Studies. His interests include literally anything that has to do with space, past and present military aircraft, and propulsion technology.
Contact him regarding any article or collaboration ideas by e-mail at firstname.lastname@example.org.