“Weight is critical,” Mike Mowins said in a presentation on “Lightweight Fastener Design,” for aerospace and automotive fasteners, but also “strength is critical.”
“Light and robust,” the president of Phillips Screw Company described needed fasteners to a 2018 Fastener Fair USA conference.
For aerospace there are issues beyond weight and strength: Serviceability, mission critical for the military and aircraft downtime.
Controlling weight involves more than fasteners, but changes in aircraft construction to make planes lighter can require different fasteners, Mowins pointed out. For example, composite honeycomb panels have replaced traditional solid floor panels. The newer floors use blind-side installation and optimized screws.
In automotive CAFE standards and hybrid / electric range make weight more critical. But a continuing issue is strength which is critical for passenger safety. Other fastener issues include maintenance and collision repair as well as assembly speed with lower costs and fewer tool changes.
Automotive seat rigid joints are important for safety in automotive seat track joints, Mowins pointed out. Other issues include minimizing track height and weight, maintaining head strength while still meeting required torque for clamp load.
Automakers need improved tool life for assembly lines, less line stoppage and ease of torque monitoring down to the end of the line, Mowins said.
After a vehicle is manufactured and sold to a consumer, there is still servicing during the vehicle life and ultimately end of life disassembly, Mowins added.
Factors in weight reduction are minimizing fastener diameter through material strength and minimizing fastener head height for weight, Mowins noted. Extending endurance is a joint design issue.
A sample solution by fastener engineers: Lightweight low profile head fastener made of titanium mated with bonded CFRP nut plate.
Mowins cited external Mortorq high strength spiral drives for aircraft engines. The fasteners reduce weight with lower head height through an optimized drive system. The lower head replaces the traditional 12 pt/bi-hex head. The result is a fastener with 23% less volume, 31% lower height, 1.2x more drive contact and 2.2x more removal contact, Mowins demonstrated.
The Mortorq asymmetrical spiral drive increases contact, provides greater removal torque and the large recess is stronger than the driver. Beyond the spiral drive, the larger driver core provides balanced tool and recess strength for industrial and automotive assembly plus extends tool life. Web: Phillips-Screw.com
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