Fastener Recess Geometry for Full-Surface Torque Contact
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Solution Overview
Problem
Existing fastener drive systems experience high surface contact stresses and premature failure due to point, line, or area contact patterns, leading to bit and recess damage as reaction torque increases, which can result in coating damage and premature fatigue.
Innovation Solution
A fastener design featuring a recess with a center post and lobes having drive surfaces formed of polygon involutes, each comprising a plurality of arcs with constant radii, providing full surface contact and minimizing stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional point or line contact drive systems are used, then the device complexity is reduced, but the contact stress increases and reliability decreases
Solution Approach 1:
The drive surfaces are formed with polygon involutes comprising multiple arcs with constant radii, creating curved contact surfaces that distribute stress across a broader area. The concave arcs relative to the center of the fastener enable full surface contact between the bit and recess, transforming point/line contact into area contact and reducing peak contact stresses.
Solution Approach 2:
The invention transitions from point contact (0D) or line contact (1D) to full surface area contact (2D) by designing the drive surfaces to engage across the entire interface between bit and recess. The polygon involute geometry with multiple arcs enables contact across the full surface area, maximizing the contact dimension and minimizing stress concentration.
2Stress or pressure
If area contact surface pattern is used, then contact stress is reduced, but bit-recess reaction torque causes elastic distortion and contact pattern shift
Solution Approach 1:
The polygon involute drive surfaces are designed with specific geometric parameters (multiple arcs with constant radii, concave relative to center) that maintain optimal contact characteristics under reaction torque. The geometric parameters are optimized so that as torque increases, the contact pattern remains stable across the full surface area rather than shifting toward the top of the recess.
Solution Approach 2:
The drive system employs a composite geometric structure combining multiple arc segments with different radii to form the polygon involute profiles. This composite geometry on both the bit and recess surfaces works together to maintain stable full-surface contact under varying torque conditions, preventing elastic distortion from causing contact pattern degradation.
3Area of stationary object
If polygon involutes with multiple arcs are used, then full surface contact is achieved, but manufacturing complexity increases
Solution Approach 1:
The complex polygon involute drive surfaces are segmented into multiple discrete arc segments, each with a constant radius. This segmentation allows each arc to be manufactured independently using standard machining operations, and the arcs are then combined to form the complete involute profile. The segmentation approach simplifies the manufacturing of what would otherwise be a complex continuous curve.
Data Source
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AI summary
A drive system with full surface drive contact. The drive system tends to maximize the surface contact pattern or area at typical bit-recess reaction (drive) torque values, thereby tending to minimize bit-recess surface contact stresses, coating damage, recess ream and premature bit fatigue failure. The drive system comprises a fastener and/or bit having drive surfaces formed of either polygon involutes or a single arc construction. A punch is also provided for forming a recess in either the fastener or the bit, wherein the punch has corresponding surfaces.