When it comes to manufacturing aircraft components and assembling aerospace equipment, precision and reliability are of utmost importance. Even the smallest defect or variation can have catastrophic consequences miles above the Earth at speeds surpassing the sound barrier.
While features like wing contours, advanced composites, and aerodynamic designs rightly get much of the spotlight, one of the humble workhorses helping keep aircraft airborne and operating safely is the common yet critical threaded fastener.
From wing spar fittings secured by dense clusters of bolts to hot engine sections held together by studs to hydraulic lines coupled with fittings – threads are the hidden superpower enabling reliable joining and disassembly in aircraft construction. Let’s take a look at the vital role threading plays in keeping our airplanes flying high.
The aerospace threads
While many equate “aircraft grade” with ultra-high strengths, that’s not necessarily the key factor when it comes to threads. Rather, the greatest emphasis is placed on consistency, repeatability, and mitigating failure due to fatigue, vibration, temperature extremes, and galvanic corrosion.
Threads used must meet stringent manufacturing tolerances, generally much tighter than those used in commercial or industrial settings. Beyond just being sized accurately, the thread form itself must be flawless with a fine lead, smooth finish, and no defects, nicks, or imperfections whatsoever.
That’s because any slight deformation or irregularity in a thread’s geometry can initiate a crack. With the intense, persistent cycle of stressing thread root areas experience, even a microscopic crack can quickly propagate to total failure given enough time.
This is why specialized aerospace thread forms like the NAS0786 Unified Thread and primer anaerobic pre-applied lock helix inserts are commonly specified to boost fatigue life and reliability.
Creating the “Perfected Thread”
Given the above mission-critical requirements, achieving the “perfected thread” mandates adherence to the industry’s utmost best practices, optimal cutting tools, and proven quality processes during both manufacturing and assembly, this includes:
- Cutting tools: Only the finest thread-cutting taps, dies, and machining equipment make the cut. Quality makers like Jarvis produce aircraft-grade tooling from premium alloys like titanium with tight geometric specs and special coatings for long tool life.
- No regrinding: As precision taps and dies wear, their form degrades. Attempts to extend tool life via regrinding are prohibited, and all worn tools are discarded.
- SPC & thread checking: Statistical process control, go/no-go gaging, and other strict inspection procedures validate every threaded feature’s conformity.
- Installation techniques: Specialty lubrication, controlled preloads, stretch fit practices, and other essential steps are followed carefully during assembly.
- Materials engineering: Advanced metallurgics reduce phenomena like galling, seizing, hydrogen embrittlement, and corrosion by specifying compatible alloy combinations.
- Process documentation: Every aspect of manufacturing, tooling maintenance, assembly, and inspection is exhaustively documented per AS9100 requirements.
This multifaceted ecosystem of tools, training and systems may seem like overkill, but remains critical given the cost and catastrophic risk of failures.
Common aerospace thread applications
With threads playing an integral role across airframe manufacturing and component assemblies, some typical examples include:
- Airframe joining: Threaded fasteners are used to secure wing sections, bulkheads, fuselage skins and virtually all aircraft structural assemblies.
- Landing gear systems: The chassis, axles, struts, and other members rely on studs, bolts, and other threads to stay robustly attached.
- Hydraulic systems: Both rigid tubing and flex hoses connect to pumps, valves and actuators via threaded fittings and couplings.
- Environmental controls: Compressor studs, cabin air nozzle threads, and more on HVAC/pressurization systems.
- Electrical bonding: Conductive gaskets and EMI/RFI grounding use self-tapping threads frequently.
- Oil & fuel systems: Pipe threaded fittings, adapters, and other connections join tubing runs.
- Powerplant builds: From turbine discs to combustors to thrust fans – propulsion systems rely extensively on studs, jackscrews, and other fastener assemblies.
Summary
Robust, geometrically flawless threads cut with precision and installed following meticulous protocols remain mission-critical components ensuring passenger safety in the ultra-demanding field of aerospace manufacturing.
While threaded fasteners may seem mundane, they are life-critical connection points helping keep our airplanes securely stitched together while in flight. From initial component machining to final assembly, the pursuit of the “perfected thread” necessitates industry-leading cutting tools, flawless installation techniques, and rigorous quality control.
Continually advancing aerospace threading capabilities via premium tooling, exhaustive documentation, and persistent improvement in training and processes may seem like a painstaking task. But given the stakes at hand when working at Mach speeds and extreme altitudes, it’s the only approach ensuring all air travel maintains an uncompromisingly safe journey.
