Lo, J., "The Next Generation HI-LOK and HI-LITE System," SAE Technical Paper 2017-01-2086, 2017.
The fast growth of air traffic and the need for lighter and more fuel efficient aircraft is driving the ramp-up of important new aircraft programs. These increases in production rates are driving manufacturers to seek out robust and reliable installation systems. They must also adapt to the unique requirements of composite materials that now have an increasingly important place in the aerospace industry.Moreover, environmental constraints continue to evolve and drive new regulations, such as REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) in Europe. As an example, this regulation is leading to the adoption of non-chromate surface treatments and paints for most applications.The legacy generation of fasteners does not comply with all of these new requirements. Clearance fit installation and the lower coefficient of friction of composite structures increases the resultant installation torque on the pin recess, at levels the traditional hexagonal recess cannot safely withstand. A new range of technologies had to be developed while ensuring continuity in performance, tools and assembly methods.The solution was integrated within a proven and well-known structural aerospace fastener family, namely the HI-LOK and HI-LITE systems. The traditional hexagonal recess has been replaced by the ASTER recess, whose design is optimized for usage on the threaded end of fasteners. The ASTER recess helps achieve higher torque resistance for both installation and removal of the fasteners. This insures that the recess will not be damaged during installation and provides robust installation conditions. To address environmental and health concerns, the non-chromate HI-KOTE 1NC aluminum-pigmented coating replaces legacy coatings without compromising performance. These combined technologies form a complete, mature range of fasteners and tools that may be used as a direct drop-in replacement in any composite, metallic or hybrid structure, eliminating the need for joint redesign.