A couple of years back, Scott Blake was at a trade show in Baltimore when two researchers from the National Aeronautics and Space Administration Goddard Space Flight Center stopped at his company’s booth.
The NASA men were making composite components for a space-based observatory: the United States’ Wide-Field Infrared Survey Telescope. They wanted to check out Blake’s LaserGuide technology from his company Assembly Guidance (subsequently renamed Aligned Vision) for templating dry fabric layers (plies) directly from Siemens PLM’s Fibersim composite engineering software.
LaserGuide uses a diode-pumped, frequency-doubled, Nd:YAG laser to show a composite layup operator exactly where to apply epoxy resin prepreg plies of different sizes and shapes to assemble a part.
The templating technology is one innovative use of lasers in the aerospace industry to process advanced composites: Lasers are also used for machining, consolidating and additive manufacturing (AM) of the 21st-century materials.
Specifically, the NASA team was looking for a better way to make experimental design models of the telescope’s element wheel, a housing for all of its optics. This tapered octagonal component has a cross-section at its widest point of about 20 inches, and it’s about 7 inches tall. Its 3/16-inch thick walls consist of 16 to 24 plies of Cytec square-weave carbon/epoxy prepreg.
The NASA team had been eyeing a laser-templating system but weren’t sure they could justify the cost. Blake ended up working out a rental agreement for NASA Goddard and sent a LaserGuide to the facility with an application engineer who helped government workers master its use in one day.
“The concept that advanced manufacturing technology is too costly or risky to implement is incorrect,” Blake said. “The learning curve is not terribly steep or long with this kind of technology.”
The NASA element box is on the small end of the size range of parts made with LaserGuide. It’s also used to lay down the 800 plies for a 35-foot helicopter rotor blade and the hundreds of plies in the 7-foot-long conical radome of Lockheed Martin’s F-22 Raptor, among other parts.
Aligned Vision has in recent years added LaserVision inspection technology to its product line, which uses a digital camera and an algorithm to identify and point out potential problem areas as each ply in a composite is laid down. The company also added LaserVision to the Internet of Things so a Digital Twin of each project can be created.
More heat than light
While Aligned Vision’s technology depends on a laser’s visible light, Automated Dynamics employs an Ytterbium fiber laser that emits in the infrared wavelength. The heat it produces consolidates thermoplastic composite tape.
That heat is almost perfectly absorbed at >90 percent efficiency and ranges from 400-500°C (752-932°F) to melt .13mm-thick prepreg thermoplastic tape with unidirectional, continuous fiber. After the tape is heated in situ, it’s compacted with a chilled roller to help consolidate it with a previously laid down tape and to cool the work zone.
“It’s a dynamic process,” said David Hauber, engineering manager for Automated Dynamics, a unit of Trelleborg. “You’re using squeeze flow in the nip region (where the roller contacts the surface), which causes shear thinning and shear mixing to entangle polymer chains and create a strong bond between layers.”
Currently, about 90 percent of Automated Dynamics’ manufacturing involves producing thermoplastic components, such as cargo floor panels, tail booms, fixed wing fuselages and horizontal stabilizers, and many industrial applications, such as plain bearings, with its in situ process.
The firm’s engineers have also used the process to produce demonstration components, including a damage-resistant, highly survivable drive shaft for a rotary-wing helicopter using an IM7 carbon fiber/PEEK composite. In the most recent testing, the drive shaft demonstrated a 35 percent weight reduction and over 150 percent greater post-ballistic damage survivability over legacy aluminum designs. As a result, the company’s in situ process is currently at readiness level 6 (out of 9) in the U.S. Department of Defense’s procurement scale.
TRL 9 remains the ultimate goal and promises a payoff for Automated Dynamics, as well as the military.
“Achieving certification for a flight-critical component for manned flight with an in-situ-consolidated composite structure would be a first and would open the door for further applications,” Hauber said.
The company’s automatic fiber placement technology lays down carbon fiber PEEK tape at a rate of 300 mm/second—three times the deposition velocity and bonding achieved using legacy, super-heated nitrogen gas technology.
“I believe we can do better with optimized tapes, and we’re working with various vendors to do that,” Hauber said.
The ideal prepreg for the laser process has uniform fiber distribution with a microns-thick layer of resin on the surface, he said.
Compared with autoclave consolidation, the process produces slightly lower interlaminar properties but eliminates the energy-intensive, expensive and time-consuming use of autoclaves.
Hybrid composite capability
While Automated Dynamics’ technology is AM, 3D Systems makes materials and machines for what many people equate with AM: 3D printing.
3D Systems’ ProX SLS series of selective laser sintering printers use CO2 lasers to selectively melt and fuse very thin cross sections of glass fiber-reinforced nylon 12 powder, trade named DuraForm HST, to make non-structural components in aerospace. The components may include environmental control ductwork, electronics storage boxes and parts for unmanned aerial vehicles and combat UAVs.
“What you’ll find with HST is the glass fiber plays a significant role in contributing to tensile properties whereas the glass bead contributes significant properties to respond to compressive force,” said Patrick Dunne, vice president of advanced applications development at 3D Systems. “So, you get that hybrid composite capability where the resistance to compression and resistance to tension yield a very high strength, high stiffness material and, being glass and nylon, you have light weight.”
The 3D printing process is ideal for low-volume parts where it’s hard to justify the cost and effort associated with tooling to make them. It offers advantages in lightweighting, part-count reduction and complex design optimization opportunities.
For example, it allows the integration of internal baffles that not only reduce the need for assembly but also improve performance by diminishing tonal resonance. The last trick is accomplished by maintaining laminar flow.
Another 3D Systems material used widely in aerospace is Accura HPC, a ceramic-reinforced photopolymer epoxy that’s solidified with a UV laser in the company’s ProX 800 3D printer. Accura HPC is used to make cladding for scale models for aerodynamic wind tunnel testing, Dunne said.
“Using 3D printing to feed wind tunnels drives utilization and enables higher-fidelity data capture through the integration directly into the 3D printing process of dense networks of pressure tapings,” he said.
Like a knife through butter
Ceramic composites are one of many materials machined with Synova’s Laser MicroJet (LMJ) in the aerospace market, but in this case, ceramic is the matrix and not the reinforcement.
The LMJ process uses a stream of water to contain the beam from an Nd:YAG laser that maintains its cylindrical shape, like an optical fiber. The water offers the additional advantage of cooling the work area and flushing out debris as the laser does its job.
The cylindrical shape of the laser beam results in kerf walls that are nearly perfectly parallel, a feature that’s led to some surprise among customers who submit drawings with one dimension at the top of a cut and a second dimension at the bottom.
“I generally ask customers, ‘Which dimension do you want?’” said Jacques Coderre, U.S. business manager for Synova. “Because generally a laser or EDM (electrical discharge machining) cut is tapered, the industry has been living with an angled cut for a long time.
“The feature has led to a paradigm shift where top and bottom dimensions of a machined feature can now be the same.”
GE Power used the LMJ to machine ceramic matrix composites, a material designed to replace metal in gas turbines, at a rate 30X faster than grinding. The CMCs are used because they function at temperatures that will soften most metals, and they’re very tough.
“The microjet slices through CMCs like a knife through butter,” said Kurt Goodwin, who was GM of GE’s advanced manufacturing works until 2018 and is now managing member and chief engineer at the consulting firm Good Wind. “The material is already inside our new jet engines.”
LMJ is used to machine the shrouds for the LEAP engine produced by CFM International, a 50-50 joint venture of GE Aviation and Safran Aircraft Engines, and in GE’s 9X engine.
Synova’s technology is also used to machine carbon fiber-reinforced polymers (CFRPs) to make structural parts for aircraft. CFRPs can be machined with grinding, but the abrasive machining process creates heat-affected zones while LMJ doesn’t.
The future is thermoplastics
In the classic film “The Graduate,” Benjamin Braddock, played by Dustin Hoffman, absorbs some advice about the future from his father’s business partner—who asserts it is all about plastics.
Make that thermoplastics, reinforce them with fiber, and it’s about right for aerospace, said Lou Dorworth, direct services manager for Abaris Training, an advanced composite school.
The aerospace industry loves thermoplastics because they:
- are lighter than metals;
- can be molded rapidly;
- can be welded;
- are generally chemical resistant;
- have excellent damage resistance, and
- can be overmolded
Dorworth, who has worked in the production and training sectors of the composites industry for almost 40 years, said he’s noticed an uptick in technology development in thermoplastics since the early 2010s. One of the developments is Toray Advanced Composites’ Cetex RTL (previously branded as TenCate Cetex RTL before Toray’s acquisition of TenCate in 2018), a flat, structural 3.6 x 1.2-m (11.8 x 2.9-foot) multi-ply sheet.
“You’re able to fabricate structures with it in a similar way that you fabricate metals,” Dorworth said.
Cetex RTL, aka organo sheets, comes in a wide range of customizable fiber and resin combinations suitable for rapid thermoforming to make interior and exterior aerospace components. The material can be cut to shape, most commonly by sawing, milling or waterjetting, and thermally or inductively welded.
In addition to customizable specifications for embedded fiber, customers can specify ply count from 1-64, fiber and fabric orientation, embedded lightning strike protection, galvanic corrosion layers, color and surface effects.
PPS is a very common matrix for the Cetex sheets, which are consolidated in a heating, compression and cooling process that depends on sheet thickness and resin type, as well as desired resin crystallinity. Toray also produces Cetex sheets with LM PAEK, PEEK, PEKK, PA, PEI and other matrices.
“LM PAEK is becoming of high interest within the aerospace industry as it has similar attributes to PEEK and PEKK, but offers lower process temperatures, enhanced processing characteristics and is an enabler for next-generation, in situ fiber placement processes,” said Scott Unger, Toray’s chief technology officer. “In fact, Toray, the National Institute for Aviation Research and the FAA will soon finalize a publicly available, NCAMP database on LM PAEK with Toray’s T700G fiber.”
The National Center for Advanced Materials Performance database will be compliant with FAA and European Aviation Safety Agency requirements and allow designers to leverage a low-cost qualification path to use Toray’s thermoplastic material in aerospace and defense applications alike, Unger said.