“We modeled everything, from machines and tools to people and shifts, to make sure that we had the right mix,” says Simon Peckham, manufacturing engineering and training leader for Dowty. Modeling manufacturing processes allowed researchers to analyze a wide range of data to identify bottlenecks in staffing, machinery placement and process type to identify more efficient alternatives. Among other options, DigiProp determined that expanding into thermoplastic materials offered the opportunity for improvement.
Dowty had previously manufactured blades with a blown thermoset foam core around which was added a dry fiber preform that consisted of hand layup carbon fabrics with biaxial fabric reinforcement. Through close collaboration with the National Composites Centre – one of three High Value Manufacturing Catapult centers that were critical collaborators on the program – DigiProp determined that thermoplastic part manufacturing could condense the cure process time to about five minutes. Compared to the four-hour process for a comparable thermoset epoxy resin component, this switch offered tremendous potential for high-volume cost savings.
“Triaxial thermoplastics are a good option when we are looking at very high-volume potential markets, in lower thrust areas of the propeller market,” says Trevarthen in reference to unmanned aerial vehicles (UAV).
Thermoplastics also allowed for removal of the foam core, improving fatigue life and reducing component weight. The recyclability of the material further hit the demand for more sustainable solutions.
DigiProp developed a new manufacturing process that uses a combination of bladder molding and triaxial braiding of CFRP composites. The bladder system uses a wax mold coated with a silicone product, which together creates a rigid mandrel for overbraiding the material. The mandrel is designed to be easily removed from the mold, leaving the inflatable silicone bladder behind. This allows for the application of pressure internally to the composite preform.
Dowty has made improvements to and automated many of its other manufacturing technologies as well, including blow molding capabilities for thermoset cores. The company has also worked with the Manufacturing Technology Centre, another catapult center, in the development of a process monitoring system for resin transfer molding to ensure the more complex geometries it is manufacturing will emerge from the press defect-free.
By virtue of the digital twin, Dowty designers can easily align structural design tool sets with complementary manufacturing techniques. “Aligning [materials] with the structural performance and linking the loads that you get from an aerodynamic shape back into structural design is critical for us,” Peckham says. “We can come up with some really wacky shapes that might give us a little of an edge performance-wise, but if we can’t then relate that into a manufacturable product, then it’s not feasible to produce.”