Thermoplastic Processing
The Smart Susceptor technology is built on many years of development work in induction heating as well as stamping, molding, welding, and assembly techniques from the automotive industry. The technology was originally intended for the manufacturing of Boeing’s next-gen 757 commercial jet. However, after 15 years of process development efforts, the aircraft was canceled in 2020. Temper then received a license to make, use, and sell the Smart Susceptor, technology that it helped to develop for The Boeing Company. In addition, Temper has 18 other issued patents surrounding the base technology. The Smart Susceptor tooling architecture was first demonstrated by Temper in 2006 and further developed in a DOE program led by The Boeing Company.
The program, which was completed in 2012, produced a number of tools that were designed, built, and tested by Temper. The thermoplastic process development work cell, tool, and resulting aerospace-style seatback are shown in Figures 1, 2 and 3.
Figure 1: Photo of Smart Susceptor thermoplastic development work cell.
Figure 2: Photo of a Smart Susceptor tool designed and built during the DOE program.
Figure 3: Photo of the PPS seatback component made from the tool, 16 in x 26 in.
One of the tools, produces an aerospace style seatback made with a PPS resin and carbon fiber. The process temperature was 580°F and demonstrated the capability to go from room temperature to heated material to be molded, molded, quenched, held during recrystallization for 180 seconds, and finally cooled to the ejection temperature of 100°F in 540 seconds. Parts were run with processing times as short as 210 seconds. Additional tools made during this program include an automotive-style seat bottom and a large flat-panel tool for wind-energy applications.
A follow-on program, also funded by the DOE program and led by Boeing, shifted focus to the scalability and the use of an aluminum air bladder matching the part quality of autoclave processing methods. The air bladder’s purpose was to compensate for prepreg placement variations and cut size as well as to ensure even forming pressure over the entirety in concert with the use of Smart Susceptor processing techniques. This was accomplished using a modularly constructed low-cost cast ceramic tooling, shown in Figure 5. The nature of the cast ceramic tooling does not yield the same rapid cycle time as the previous laminated tooling; however, the program successfully produced a 40% section of a notional commercial aircraft wing skin design made from PEEK carbon fiber. The part is roughly 5 ft x 15 ft with varying prepreg thicknesses (1/4 – to 1/2-in thickness) in roughly 1.5 hours. (NOTE: processing speed was not a priority for this demonstration). The part is shown in Figure 6. In addition, thermal uniformity was maintained with a target temperature of 740±15°F.
Figure 5: Photo of wing skin tool in the modularly designed restraint.
Figure 6: Photo of completed PEKK CF part. Part consisted of 60% carbon fiber tow and, when inspected by Boeing BRT, contained <5% voids.
Thermoplastic Welding
The Problem: Thermoplastic composite materials are becoming ever more prevalent across all industry, however, joining these composites has its problems. Adhesives are not as robust as parent materials with incorrect cure can lead to weakened joints and the bond quality depends on a number of outside factors. In addition, ribs, spars, multi-thickness areas make heat activated/cured adhesives difficult, if not impossible. Surface preparation steps are added operations to the process.
Mechanical fastening increase weight, cost, and part count and may require regular maintenance (loosening, corrosion, etc.). In addition, mechanical fastening can create failure points due to fatigue and stress concentrations.
The Solution:
The solution is to accomplish the bonding at the joint interface using Smart Susceptor technology that directly welds the two parts to be joined.
A Smart Susceptor heats rapidly and efficiently to a target temperature, ±5 °F, and automatically shuts off. No overshoot on temperature regardless of power input and ramp rate.
The Smart Susceptor wire is embedded in part resin and placed between two thermoplastic parts to be joined. Then with light pressure the area to be bonded is subjected to a induction heating field that quickly heats the smart susceptor wire and bonds the two parts together at the bond line interface. That’s it.
Because the weld happens so quickly, heat from the weld wires at the interface does not have time to “heat through”, the parts being welded act as their own weld jigs and therefore the process does not need large expensive tool holding fixtures
Figure 1: Thermoplastic welding of two components together using Smart Susceptor wires