Hollow A286 Screw Forming for Lightweight Galling-Resistant Threads
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Solution Overview
Problem
Aircraft screws made from solid core materials are heavy, limiting aircraft fuel economy, and attempts to use lighter metals like aluminum or titanium result in thread damage due to galling during installation and removal.
Innovation Solution
A hollow metal screw design made from corrosion-resistant A286 steel with a wall thickness of 0.2 to 0.7 millimeters, annealed and hardened to achieve thread strength sufficient for aerospace applications while being approximately half the weight of a solid screw, featuring a rotational drive mechanism and captive washer for easy installation and removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a solid core screw made from corrosion-resistant steel is used, then thread strength and corrosion resistance are sufficient for aerospace applications, but the screw weight is too high, limiting aircraft fuel economy
Solution Approach 1:
The screw is segmented into a hollow tubular structure rather than a solid core, dividing the material distribution to reduce weight while maintaining structural integrity. The hollow shaft configuration removes unnecessary material from the interior while preserving the outer dimensional strength requirements for aerospace thread applications.
Solution Approach 2:
The invention uses a composite construction combining a hollow metal tubular shaft with a metal core insert that is cold-wrapped around the metal tube. This composite structure provides both the weight reduction benefits of the hollow design and the strength requirements through the metal-to-metal contact and interference fit between the shaft and insert.
2Weight of moving object
If lighter weight metals such as aluminum or titanium are used for the screw, then aircraft fuel economy improves, but thread galling occurs during repeated installation and removal
Solution Approach 1:
The invention changes the material parameters by using corrosion-resistant steel with specific hardness characteristics (Rockwell C 20-40) and controlling the wall thickness (0.2-0.7mm) to achieve optimal balance between weight reduction and thread durability. The metal-to-metal contact in the composite structure prevents galling while maintaining lightweight properties.
3Weight of moving object
If a hollow screw design is implemented, then screw weight is reduced by approximately 50% compared to solid screws, but manufacturing complexity increases due to multiple processing steps
Solution Approach 1:
The hollow tubular shaft is formed preliminarily through stamping and drawing operations before the final assembly. The metal core insert is prepared in advance with appropriate tolerances and surface characteristics. These preliminary actions enable the subsequent cold-wrapping and interference fit assembly to proceed efficiently, reducing overall manufacturing complexity despite the multi-step process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The hollow screw provides substantial thread strength, resists galling, and contributes to aircraft fuel economy by being significantly lighter than traditional solid screws while maintaining the necessary strength for aerospace applications.
Implementation Method 1
The screw shank is thereafter annealed to soften the screw shank for thread rolling
Implementation Method 2
after which the hollow metal screw is hardened sufficiently to meet aerospace thread strength requirements
Data Source
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AI summary
A method for making a hollow screw, comprising the steps of - forming a shallow cup having a radially outwardly extending rough cut flange at one end thereof from a generally flat metal material; - extruding an elongated and hollow body from the shallow cup; - clipping and flattening the generally radially outwardly extending rough cut flange to the desired size and shape of a screw head; - annealing to soften at least the elongated and hollow body; - rolling a plurality of threads to at least a portion of the exterior of the softened elongated and hollow body, thereby forming the elongated and hollow body into a substantially smooth shank portion and a threaded portion; - and hardening the hollow screw (Figure 1).